pontifical catholic university of paranÁ state …

PONTIFICAL CATHOLIC UNIVERSITY OF PARANÁ STATE

POLYTECHNIC SCHOOL

ELECTRONIC ENGINEERING COURSE

JOÃO PAULO DE MELO CARDOSO

MATHEUS EDUARDO GARBELINI

LOW COST TRANSFORMER MONITORING SYSTEM

WITH LORA/LTE CONNECTIVITY

CURITIBA

2018





Bachelor's Degree Final Project presented to the Electronic Engineering course at the Pontifical Catholic University of Paraná State, as a partial requirement to obtain the title of Engineer in Electronics. Advisor: Prof. Dr. Ivan Jorge Chueiri

CURITIBA

2018





Bachelor's Degree Final Project presented to the Electronic Engineering course at the Pontifical Catholic University of Paraná State, as a partial requirement to obtain the title of Engineer in Electronics.

EXAMINING COMMISSION

_____________________________________

Ivan Jorge Chueiri, M.Sc.

Pontifical Catholic University of Paraná

_____________________________________

Luiz Augusto de Paula Lima Jr., Ph.D.

Pontifical Catholic University of Paraná

Curitiba, Octuber 21, 2018.

ABSTRACT

The main purpose of this project consists of using new available wireless communication technologies applied to energy monitoring in low voltage local area transformers. The hardware measures the voltage and current of each phase of a 3-phase transformer, allowing to obtain energy quality parameters like active, reactive, and apparent energy on each phase and on the overall system. Concepts of signal processing and electrical power systems are applied in the embedded hardware in order to provide the necessary behavior, informing when something in the measured transformer is wrong. Lora/LTE communication is presented to be the main features to access the hardware remotely.

Key-words: Transformer Monitoring, Lora, LTE.

RESUMO

O principal objetivo deste projeto consiste no uso de novas tecnologias de comunicação sem fio disponíveis aplicadas ao monitoramento de energia em transformadores locais de baixa tensão. O hardware mede a tensão e a corrente de cada fase de um transformador trifásico, permitindo obter parâmetros de qualidade de energia como energia ativa, reativa e aparente em cada fase e no sistema geral. Conceitos de processamento de sinal e sistemas de energia elétrica são aplicados no hardware embarcado para fornecer o comportamento necessário, informando quando algo no transformador medido está errado. A comunicação LoRa/LTE é apresentada como os principais recursos para acessar o hardware remotamente.

Palavras-chaves: Monitor de transformado, LoRa, LTE.

LIST OF ILLUSTRATIONS

Figure 1 - General project diagram ............................................................................ 14

Figure 2 - Energy measuring system and processing system. .................................. 18

Figure 3 – Current Transformer ................................................................................. 19

Figure 4 - ATT7022EU .............................................................................................. 20

Figure 5 - Block diagram of the AC Sensors and the Energy Meter Hardware.......... 21

Figure 6 - ESP32-WROOM Module .......................................................................... 22

Figure 7 - Bootloader Flowchart ................................................................................ 23

Figure 8 - Development of applications for ESP32 .................................................... 24

Figure 9 - MCU Simplified Firmware Flowchart ......................................................... 25

Figure 10 – Classes and Threads diagram ............................................................... 27

Figure 11 - GPS Schematic ....................................................................................... 27

Figure 12 - Battery Charging Profile .......................................................................... 29

Figure 13 - LoRa SX1278 Module ............................................................................. 29

Figure 14 - ZTE MF823L 4G Modem ........................................................................ 30

Figure 15 - Orange Pi Zero........................................................................................ 31

Figure 16 - Orange Pi Zero connector ....................................................................... 31

Figure 17 - High Charts Javascript Graph Library example. ...................................... 33

Figure 18 - LoopBack Rest Framework ..................................................................... 34

Figure 19 - Configuration JSON File ......................................................................... 35

Figure 20 - Web Server architecture ......................................................................... 36

Figure 21 - Testing and validation flowchart .............................................................. 43

Figure 22 - Simplified Step-Down Regulator ............................................................. 45

Figure 23 - Simplified step-down regulator model response ..................................... 46

Figure 24 - Power supply circuit model ..................................................................... 47

Figure 25 - Input and output voltage simulation results ............................................. 48

Figure 26 - Connection diagram of the voltage sampling to the ATT7022EU ............ 49

Figure 27 - Connection diagram of the current sampling to the ATT7022EU ............ 50

Figure 28 - Connection diagram of the DC voltage of the analog board .................... 50

Figure 29 - Connection diagram of the DC voltage of the analog board .................... 51

Figure 30 - Analog. board PCB layout ....................................................................... 52

Figure 31 - Digital Board Layout ................................................................................ 53

Figure 32 - Digital Board 3D Mounting ...................................................................... 55

Figure 33 - LoRa Dongle 3D Project ......................................................................... 55

Figure 34 - General project diagram .......................................................................... 56

Figure 35 - GPS NMEA information on serial terminal screen .................................. 58

Figure 36 – Decoded GPS module information on serial terminal screen ................. 59

Figure 37 - Google maps location pointed by the GPS ............................................. 59

Figure 38 - LoRa dongle ............................................................................................ 60

Figure 39 - Orange PI terminal screen ...................................................................... 61

Figure 40 – OrangePi user Web interface ................................................................. 62

Figure 41 - IHM interface ........................................................................................... 63

Figure 42 - EMONCMS dashboard ........................................................................... 64

Figure 43 – RoHS component summary ................................................................... 66

Figure 44 - Complete mounted hardware .................................................................. 67

Figure 45 - Analog voltage signal .............................................................................. 68

Figure 46 - Analog simulated current signal .............................................................. 68

Figure 47 - Frequency measurements ...................................................................... 69

Figure 48 - Realtime dashboard 1 ............................................................................. 69

Figure 49 - Realtime dashboard 2 ............................................................................. 70

Figure 50 - LoRa remote measurements responses ................................................. 70

Figure 51 - Functional IHM ........................................................................................ 71

Figure 52 – 2-cell lithium battery ............................................................................... 72

LIST OF TABLES

Table 1 - Microcontroller Options .............................................................................. 21

Table 2 - Project Risks .............................................................................................. 37

Table 3 - Power supply circuit behavior ..................................................................... 47

ACRONYMS

AC - Alternate Current

MCU - Microcontroller Unity

LTE - Long Term Evolution

HMI - Human Machine Interface

IC – Integrated Circuit

PCB - Printed Circuit Board

TTL - Transistor-Transistor Logic

USB - Universal Serial Bus

ISA - Socio-environmental Impact (Impacto)

Copel - Paraná Energy Company

LACTEC - Institute of Technology for Development

AC - Analog current

IC – Integrated Circuit

USB – Universal Serial Bus

FIFO – First In First Out

MCU - Microcontroller

Scada - Supervisory Control and Data Acquisition

HMI – Human Machine Interface

RMS – Root Mean Square

SRAM – Static Random-Access Memory

MIPS - Million instruction per second

PPS – Pulse per second

GPS – Global Positioning System

NMEA - National Marine Electronics Association

UTC - Universal Time Coordinated

EMI – Eelectromagnetic Interference

SUMMARY

ACRONYMS ............................................................................................................... 8

1 INTRODUCTION .......................................................................................... 11

2 PROJECT PLANNING ................................................................................. 12

2.1 PROJECT APPLICATION ............................................................................ 12

2.2 PROJECT OVERVIEW ................................................................................. 14

2.2.1 AC Sensors .................................................................................................. 14

2.2.2 Energy Meter Hardware ................................................................................ 15

2.2.3 Analog Front-End.......................................................................................... 15

2.2.4 Processing Unity ........................................................................................... 15

2.2.5 Power Supply ............................................................................................... 16

2.2.6 Local Connectivity......................................................................................... 16

2.2.7 Remote Connectivity ..................................................................................... 16

2.2.8 Web Application ............................................................................................ 16

2.3 PROJECT DETAILED DESCRIPTION ......................................................... 17

2.3.1 AC Sensors and Energy Meter Hardware ..................................................... 18

2.3.2 Main micro-controller .................................................................................... 21

2.3.2.1 Bootloader support ....................................................................................... 23

2.3.2.2 Development Framework .............................................................................. 24

2.3.2.3 Main Application Logic .................................................................................. 25

2.3.2.4 GPS Time Synchronization ........................................................................... 27

2.3.3 System Power Supply ................................................................................... 28

2.3.4 External Communication Interfaces .............................................................. 29

2.3.4.1 LoRa Communication ................................................................................... 29

2.3.4.2 LTE Connectivity........................................................................................... 30

2.3.4.3 RS-485 ......................................................................................................... 31

2.3.4.4 USB .............................................................................................................. 32

2.3.4.5 HMI ............................................................................................................... 32

2.3.5 Web User Interface ....................................................................................... 32

2.3.5.1 Measurement Graphs ................................................................................... 33

2.3.6 Web Server ................................................................................................... 33

2.4 RISK ANALISYS ........................................................................................... 37

2.4.1 General Risks ............................................................................................... 37

2.4.2 Hardware Risks ............................................................................................ 38

2.4.3 Software Risks .............................................................................................. 40

2.5 PROJECT SCHEDULE ................................................................................ 42

2.6 TESTING METHODOLOGY ......................................................................... 43

2.7 HARDWARE PROJECT ............................................................................... 44

2.7.1 Simulation ..................................................................................................... 44

2.7.2 Analog board design ..................................................................................... 48

2.7.3 Digital Board design ...................................................................................... 52

3 PROJECT PROTOTYPE AND TESTING .................................................... 56

4 SUSTAINABILITY AND ENVIRONMENTAL IMPACT ................................ 65

5 RESULTS ..................................................................................................... 67

6 FINAL CONSIDERATIONS AND FUTURE WORK ..................................... 73

REFERENCES .......................................................................................................... 75

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1 INTRODUCTION

The main goal of this project is the producing of a robust hardware to be

able to measure voltage and current, anomaly detection and remote data sending

to a management center using Lora or LTE technologies. Our challenge and goal

are in the research for new and alternatives technologies that make our hardware

technological, efficient, robust and more cost-effective compared to other

technologies.

Connectivity, undoubtedly, is the word of our century until then (2018). To

share something, perform the remote control of some device or to do the

control/supervise something remotely is becoming easier, cheaper and widely

used today. Even when we do not realize that we are doing it, indirectly, we are

sending or receiving something to/from someone. The use of the Internet and

other resources allowed us to carry out the supervision of a process remotely to

allow activities that were previously not possible.

Connecting things is the future. Even if that future is not far from now, there

are many technologies to be developed. The use of smart meters that can

communicate with a management center is another important tool in these

innumerable connectivity platforms that we see in our daily lives and that can

positively impact all the people involved. The device of this project, thus, can be

a tool capable of increasing efficiency and cost reduction by the companies that

use it and impact the services used by the final consumer. It can be considered

as one of most important tools in the revolution called Internet of things (IoT).

The following chapters are presented as the following: A description of the

problem involved in the project; Technologies that are in our final physical project;

The test procedures used to test and validate the component parts of the project;

The risk analysis of the main problems that we may face during development;

The project schedule and finally a conclusion pointing the principal project

aspects.

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2 PROJECT PLANNING

2.1 PROJECT APPLICATION

Electrical power applications are changing rapidly. LED lighting is

replacing incandescent lamps, variable speed motor drives replace directly

coupled electric motors, electric vehicle is gradually replacing internal combustion

engine vehicle and photovoltaic installations and wind turbines are gradually been

added to the grid to generate additional electrical power. It shows the load on the

electric network is changing and the consumption of electricity is increasing. As

a result of it, we have the increase of the number of harmonics and the also a

highter risk of voltage and current unbalance, voltage sags and swells,

harmonics, transients. In a balanced three-phase system, the phase voltages

should be equal or very close to equal. Unbalance is a measurement of the

inequality of the phase voltages. Voltage unbalance is the measure of voltage

differences between the phases of a three-phase system. It degrades the

performance and shortens the life of three-phase devices – as motors, three-

phase loads and power transformers, for example. It can cause to these three-

phase a poor performance or a premature failure. Voltage and current unbalances

could also indicate maintenance issues such as loose connections and worn

contacts (Fluke, 2018).

Unbalance can occur at any point throughout the distribution system.

Loads should be equally divided across each phase of a panelboard. Should one

phase become too heavily loaded in comparison to others, voltage will be lower

on that phase. Transformers and three-phase motors exposed the above-

mentioned anomalies, may run hotter, be unusually noisy, vibrate excessively,

and even suffer premature failure, which generates high costs for fixing or

replacing the damaged equipment (Fluke, 2018).

These are some of our motivations in having developed our bachelor’s

degree Final Project in this subject, as well it is a technology that has a direct and

a good impact on people's lives and the today’s economy, beside it is a

technology that meets the future of smart and connected things (Fluke, 2018).

With the use of our system in real transmission/distribution systems, these

anomalies, that currently are detected mainly when a failure or damage occurs –

13

or even when the costumer detects a fault or a lack of electricity and warns the

power utility company, can be detected before a defect happens, which also

changes the way of the practice of maintenance, from corrective maintenance

into predictive maintenance, which reduce costs and also contributes to better

understand the system and it needs/requirements.

Ravaglio et. All (2004), realized and study intituled “Life Valuation of Copel

Distribution Transformers”, where Copel means Paraná Energy Company and it

is the company responsible for generating and distributing electricity in the state

Brazilian stat of Paraná This is a large study carried out jointly with the electric

company with the Institute of Technology for Development - LACTEC that has

quantitative and qualitative data related to power transformers, their useful life

and the main faults and problems related to it. In an extremely objective and

applied to the subject of this project, they show that in 2004, based on operational

data, Copel had around 370 thousand transformers and, according to records,

they present malfunctions in an average time of 9.0 years "of life", that means, 9

years after its construction and the real life of 93% of the fixed transformers is a

maximum of 20 years - only 1% of them has a life of more than 27 years. The

authors point out as some of the reasons of the damages in the transformers are:

lightning, inadequate adjustment of protection devices, short circuits in the

network and overloads due to unbalance of loads and voltages. Among other

motivations, it is explicit the need for a technology that helps in detecting

problems in transformers in order to prevent damage and repairs in an efficient

way, given the price of a transformer and accessible, considering the amount of

transformers that exist only in the state of Paraná - Brazil (2004 data) and the

already existing technology that still not beeing using by some factors (Some pre-

existing solutions still have an expensive price).

14

2.2 PROJECT OVERVIEW

The project’s general diagram is shown in the Figure 1. On it is shown the

connections between the functional blocks of the system.

Figure 1 - General project diagram

Source: The authors, 2018.

As discussed in the previous sections, the project goals are, besides

performing fundamental measurements of a three-phase power transformer, to

provide a simple and easy solution to read those measurements through local

or/and remote connectivity. This is accomplished by the following functional

blocks, which are described in the 2.2.1 to 2.2.8 subsections.

2.2.1 AC Sensors

To measure the voltage and current flowing through the three-phase power

transformer, external current and voltage transducer are used to ensure that next

functional block will receive the sampled measurements properly.

15

2.2.2 Energy Meter Hardware

The energy meter hardware is divided into two main blocks. The first one

is related to AC sensors connection and from which the analogical integrated

circuit is responsible for the signal processing, informing it’s results to the second

block - the processing unity.

2.2.3 Analog Front-End

This block is responsible to adequate the sampled measurements from AC

voltage and current transducers and make it compatible to the levels supported

by the analog integrate circuit that is responsible to process these signals into

other energy measurements. As this block is directly connected to the AC

electrical network, it must be isolated from all the other blocks to avoid possible

electrical surges from damaging them. Also, the hardware must be correctly

designed in order to avoid that high currents can interfere with its measurements.

2.2.4 Processing Unity

The processing unity uses a microcontroller to read a three-phase energy

metering IC information through an isolated interface and stores them in its main

flash memory. The stored values can be polled by optional interfaces like RS-

485, USB or sent remotely throught LoRa Radio or a 4G connection (indirectly

through another serial interface). The memory works like a FIFO memory in a

measurement can be stored for a certain amount of time before being overwritten

by a new value.

The MCU also includes a real-time clock for generating a timestamp of the

measurement so it can be further analyzed. A low power mode is also necessary

to maintain maximum battery life in situations where main power supply Is not

available. This allows the MCU to alert the situation of the power transformer for

a certain time before the energy meter shuts down entirely.

16

2.2.5 Power Supply

The power supply block is responsible to provide appropriate voltage and

current to the circuit. It supplies other blocks such as the Analog Front-End,

Processing Unity and remote connectivity. It also must isolate the Analog front

and supply from other blocks and contain necessary circuit protection to possible

high voltage surge. Optionally, a 2-Cell Lithium-Ion battery backup system can be

used when there is no AC Supply available.

2.2.6 Local Connectivity

The local connectivity with the proposed hardware is an extremely

important component of the system as it enables user interaction, whether it is for

configuration, manual data receiving, visualization of stored information or simply

to easy development. The RS-485 Communication enables the use of MODBUS

RTU communication protocol, so the data can be polled by a master that is

connected to a Scada system. The USB enables to only communication to a

nearby computer but also helps developing the system. Finally, the optional HMI

enables fast interaction with the system, informing its current configuration and

main measurements received from the electrical network (LI; ZHANG; QIU,

2007).

2.2.7 Remote Connectivity

Through an external connection, the processing unity sends energy

information to the communication processor that is responsible to forward them

using a LoRa radio or 4G LTE connectivity. Optionally, Ethernet cable can be

used to enable internet connection or MODBUS TCP communication (SWALES;

OTHERS, 1999).

2.2.8 Web Application

The Web application is composed of two parts, the application framework

and the Web server: The application framework is an intuitive graphic interface

that enables the user to interact with the hardware such as graphical visualization,

17

parameters and connectivity configuration. Finally, the web server allows remote

access to this framework and to receive remote information from the energy meter

system via 4G or Ethernet cable. To be able to receive LoRa radio information,

a dedicated LoRa gateway or a host computer with a LoRa USB stick attached to

it must be used.

Regarding the user interface, the following measurements information

related to the power transformer shall be presented in its graphical visualization

tool:

• RMS voltage of each phase;

• RMS current of each phase;

• Active power of each phase;

• Reactive power of each phase;

• Phase lag of each phase;

• Frequency;

• Total Harmonic distorcion (THD) of each phase voltage and current.

The EMONCMS Open source web-app project is used as a bridge to

receive, store the data and to easily create a visual interfaces that contain all the

necessary tools to depict all the energy measurement variables in real time. It can

also allow to download the energy (BALAMURUGAN; SARAVANAKAMALAM,

2017).

2.3 PROJECT DETAILED DESCRIPTION

The main hardware and its connections not including the communication

processor, is shown with more details in the Figure 2.

18

Figure 2 - Energy measuring system and processing system.


Most of the technologies chosen in the development of this project took

into the consideration of the principle of using electronic components, boards,

modules etc., that meets the technical needs, robustness, technology and price.

Since there are already some solutions available on the task of monitoring

transformers, we will seek alternatives, add new technologies and always look for

an optimized way to implement them - either by manufacturing new circuits or

purchasing existing modules.

2.3.1 AC Sensors and Energy Meter Hardware

To measure the voltage and current flowing through the three-phase power

transformer, external current and voltage transducer are used to ensure that next

functional block will receive the sampled measurements properly. The current

transducer chosen to be used in our project is the LEM LA 100-P shown in the

Figure 3 - once this transducer meets the technical requirements for our

application and we already had some units available to use.

19

Figure 3 – Current Transformer

Source: The authors

We found the price of this kind of transducers do not change significantly

when comparing different manufacturers. Others current transducer for other

brands could be used since it meets voltage or current requirements of our

system and is compatible with the currents that are measured.

For sampling the voltage, we choose to use a direct method for it, that

means, the use of two insulation piercing connectors to make a fused conductive

connection to the power line. Resistors and small transformers were used in order

to make the samples compatible with the with the other system components.

The 3-phase electronic energy metering chip we have chosen is the

ATT7022 as shown in the Figure 4. It is an integrated chip and it is suitable for

measuring a wide range of things that demonstrate the quality of the measured

energy - as active power, reactive power, apparent power and reactive energy for

each phase and 3 phases combined; voltage RMS, current RMS, power factor,

phase difference, and frequency etc.

The big advantage of this chip is the cost-benefit ratio. With the use of this,

we reduced the cost, when compared to the solutions of meters already available

in the market – most of them uses IC that costs five times more than ours, and at

the same time we have the measurements that we are interested. Other

peripheral parts, such as the sensors that will be used in the line of the voltage

network, the entrance protection part and the insulation circuit, among others,

20

were all designed and implemented in the analog board. Similar projects used

this IC to provide solutions in intelligent energy metering solutions as can be seen

in (QI; GAO; ZHANG, 2015; XUPENG; XIU, 2010).

Figure 4 - ATT7022EU

Source: http://lcsc.com, 2018

ADE7868 form the ADE78XX series is one alternatives to use instead the

ATT, however, it is about 5 times expensive than the Chinese IC (MHETRE;

KULKARNI; BHARADWAJ, 2015). The Figure 5 shows a block diagram of the

principal components between the power line and the ATT7022EU energy meter

IC. The AC Sensors block constitutes of sensors to measure the voltage and the

current from the power line. As mentioned in the previous sections, the filter and

protection block are the blocks responsible for protecting the subsequent circuits

in cases of outbreaks that may damage the other components of the circuit and

filtering noise or signals that are undesirable during the acquisition and

processing of the sampled signals respectively.

The Signal Adquancy block is responsible for adjusting the voltage

samples to signals in hundreds of millivolts in order to enable the ATT7022 to

correctly measure these signals.

21

Figure 5 - Block diagram of the AC Sensors and the Energy Meter Hardware


2.3.2 Main micro-controller

The main controller needs to be fast in order to receive signals and process

them in real time. A range of possible microcontrollers feasible for this project

based on their Speed, Flash and SRAM are depicted in Table 1.

Table 1 - Microcontroller Options

MCU Manufacturer Architecture Flash SRAM Speed Unity Price @

500

STM32F103C8T6 ST

Microelectronics ARM Cortex-M3

128 KB

20KB 72Mhz $ 3.90

STM32F722RET6 ST

Microelectronics ARM Cortex-M7

512 KB

256 KB

216Mhz $ 6.74

ESP32-WROOM Espressif Dual Xtensa

LX6 4 MB 512KB 260Mhz $ 4.20

ESP32-WROVER Espressif Dual Xtensa

LX6 4 MB 4.5KB 260Mhz $ 4.57

Source: The Authors, 2018.

22

The Microcontroller Architecture, It’s Speed, Flash and SRAM were

considered for the selection. Even tough MCU frequency is not the only

determinist to indicate how fast it performs, it allows an indication of the MCU

million instruction per second (MIPS) ranking (PESOVIC et al., 2012).

Due to the project requirements of being innovative, low cost and robust,

Espressif’s ESP32 shown in Figure 6 was used as the most viable option. It’s is

the cheapest when compared to other micro-controllers of the same category

(Cortex-M7 from STMicroelectronics) at around 5 dollars each unity at the current

year of this paper. Furthermore, it includes WiFi that can benefit in developments

due to the support for over the air update and flexible boot-loader schemes. It’s

also very successful in current IoT application as discussed in (MAIER; SHARP;

VAGAPOV, 2017).

Figure 6 - ESP32-WROOM Module

Source: Kolban, 2017

ESP32-WROVER module specifications are listed below:

• 240M HZ System frequency;

• 4MB of SRAM + 512KB of System RAM;

• Dual core Xtensa 32-bit LX6 microprocessor;

• Integrated RTC;

To allow correct behavior of the MCU during supply startup and guarantee

correct operation under rough circumstances and some indication during

development a bootstrap circui was used alongside an external watchdog that

prevents the internal MCU to fail due to some not planned internal software loops.

23

2.3.2.1 Bootloader support

To ease development, there is a need to use a bootloader. ESP32 MCU

supports this by default in its main serial, but some external circuit must be used

in order to reset and make the device enter in bootloader state automatically

without needing to reset the board. This functionality is shown in Figure 7.

When the MCU is initialized with it’s Boot pin in a lower voltage level, it will

initiate in the bootloader state, which will allow code to be uploaded to it’s main

flash memory through UART peripheral. When the code is uploaded without

erros, the MCU is then rebooted to RUN mode with the user new code. The reset

pin is the key fator to enable programing the board without turning the system off

and on.

The protocol of the bootloader communication is specific to Espressif chips

(ESP8266 and ESP32 family), but flashing software tools can be found freely in

the company’s repository1.

Figure 7 - Bootloader Flowchart

Source: The Authors, 2018

_______________ 1 Available in <https://github.com/espressif/arduino-esp32>

24

2.3.2.2 Development Framework

The Developement Framework used in this project is the Espressif IoT

Development Framework (ESP-IDF) is exclusivelly for the ESP32 MCU.

Furthermore, to start developing in C/C++ for this system, a toolchain must be

obtained so it can compile the Framework that allows out of box examples to be

tried in the system.

The official IDE support for the ESP-IDF is Eclipse, although, alternative

IDEs such as Visual Studio 2017 are preferable to be used due to it’s rich

features. Third Party extensions such as Visual Micro2 allows this alternative to

be used.

Normally to compile the toolchain in the Windows operatinal system, the

CygWin container software must be used in order to support the necessary linux

build system envernment (RACINE, 2000). This windows container is officialy

supported and can be downloaded in Espressif’s main site. The development

workflow is presented in Figure 8.

Figure 8 - Development of applications for ESP32

Source: https://esp-idf.readthedocs.io/

_______________ 2 Available in <https://www.visualmicro.com/>

25

2.3.2.3 Main Application Logic

The main MCU firmware needed to get the energy measurements and

send them remotely, to better explain this logic, the alghorithm is shown in Figure

9.

As the ESP32 MCU has two processing cores - one core (Core 1) is

responsible to initialize the system and then start the second core (Core 0), this

includes initializing the module system clocks and peripherals such as SPI and

UART before doing so. Following this, the first core starts a thread to read

ATT7022 energy measurements in a loop. In parallel of this, the second core also

starts a thread, but it waits to execute until the thread from core 0 finishes it’s job.

When the second core receives a signal, it can send remote messages

related to the measurements or alerts that are generated by some problem in the

ATT7022 reading. This alert indicates power failures or SPI communication

issues.

After all this procedure finishes, the second cores return to wait for a signal

and core 0 reads the measurements again.

Figure 9 - MCU Simplified Firmware Flowchart


With the simplified flowchart in mind, the firmware can be extended to be

more organized and expanded in 6 different classes which are handled by a

dedicated thread each. As the ESP32 has 2 cores and its SDK supports the

26

FreeRTOS operational system out of the box, it’s easy to implement these

features in the way presented in the Figure 10. Each Class/Thread is highlighted

in green and is responsible for specific tasks that handle peripherics configuration

and reading.

The advantage in using FreeRTOS operational system with

microcontrollers such as the ESP32 is not only related to its code being efficienty

executed and automatically distributed across available CPU cores, but to

achieve a huge flexibility to develop IHM handling code. It’s common for HMI

handling or communication protocols implementation to use timeouts for waiting

responses. In order to implement correct behavior for different states it’s common

to implement an extensive non-blocking machine state, thus, by using threads it’s

possible to simply implement blocking procedures which can be preempted by

tasks with higher priority. Implementing non-blocking code over asynchronous

one is generally easier, making the firmware development and testing faster

(POLIĆ, 2018).

Each thread is given a certain priority and execution time according to the

project design requirement. For instance, the “Measurement Manager” thread

which is responsible to read the energy metering IC (ATT7022EU) is assigned

the highest possible priority and a periodic execution of 50ms (this corresponds

to a little more than 3 cycles in a 60Hz power grid). All the other threads have a

lower priority and longer execution period which can be always preempted by the

Measurements Manager thread.

27

Figure 10 – Classes and Threads diagram


2.3.2.4 GPS Time Synchronization

To capture energy measurements with a precise time stamp, a GPS can

be used as can be seen in the schematic shown in the Figure 11. The PPS signals

allows the MCU to receive each second a precise interrupt while the GPS Serial

line sends NMEA messages so the MCU can know not only it’s position but also

it’s UTC Time (GIAMMARINI et al., 2015).

Figure 11 - GPS Schematic


28

The following steps are applied on the main microntroller firmware to

synchronize the timestamp for the energy masurements:

1. When NMEA messages are received, the MCU decodes it and

check if there is the UTC time is valid;

2. If the decoded UTC time is valid, update its internal time to the

received UTC time and enable interrupt synchronization for the next

second is enabled;

3. When the MCU receives a rising PPS signal from the GPS second,

it updated its internal time to the last decoded UTC time and adds

1 second to it.

When the system is powered on, the step 2 only occurs if step 1 succeds.

Also, these steps are repeated each 60 seconds to guarantee time

synchronization each minute. If the GPS signal is lost due to some environmental

issue, the MCU continues to use its internal reference. The time drift is around 20

parts per million (ppm) which is the external crystal specification.

2.3.3 System Power Supply

The supply circuit uses a switched regulator to power the system as it can

consume large current depending on what he communication processor is doing

or what remote communication is used, so efficiency must be considered here.

A basic protection circuit is used on it for the input voltage coming from the

supply connector, this envolves a resettable fuse and a voltage transient

suppressor that is capable to cut spikes above 13 V that can harm the system.

Additionally, there’s a circuit that allows a change in the supply logic when

the board is not powered by main supply connector, but instead, powered by a

battery in emergency situations.

If only a battery is used to power the system and it has maximum charged

voltage less than 6 V, a conditional supply circuit allows the battery to bypass the

switched regulator to avoid voltage dropout.

29

The hardware can also optionally be powered by an alternative 2 cell

Lithium-ion, or a super capacitor bank. Both technologies are included as factors

such as battery longevity and high temperature operation are important.

The charging curve that the IC follows are depicted in Figure 12. Note that

even tough the graph indicates charging end at 4.2V, this can be adjusted for any

voltage based on the feedback resistors.

Figure 12 - Battery Charging Profile


2.3.4 External Communication Interfaces

2.3.4.1 LoRa Communication

The popular module SX1278 is used in this project (Figure 13).

Figure 13 - LoRa SX1278 Module

Source: http://lcsc.com, 2018.

30

Besides the SX1278 low cost, a variety of selectable base frequency

modules from the supplier can be bought. Furthermore, It’s a well tested device

in IoT applications (DAUD et al., 2018).

2.3.4.2 LTE Connectivity

The connectivity with a 4G/3G network can then be made with a USB

modem such as the ZTE MF823L 4G Modem Figure 14. They are very cheap

and can be found in national market. It also supports external antennas to achieve

better reception and transition.

Figure 14 - ZTE MF823L 4G Modem

Source: http://www.ztebrasil.com.br.

The application of a communication processor for this project is

essential as it is independently isolate the communication tasks from the main

processor responsible for the energy readings. Due to this reason and 4G/LTE

support pricing options, the best solution we encountered so far is the use of

cheap embedded linux module called Orage Pi Zero depicted in Figure 15.

The Orange Pi Zero is a board that costs about 10 dollars with 512MB

of RAM, has a quad core ARM processor and wifi capabilities by default. Its

board size is very short and a single USB and Ethernet connector is present -

Just as this project needs according to the general diagram showed in the

beginning of this section.

http://www.ztebrasil.com.br/

31

Figure 15 - Orange Pi Zero

Source: http://www.orangepi.org

It’s integration in the schematic is showed in the schematic of Figure

16. The connector J5 is a 10-pin female header in which the OrangePi Zero is

connected.

Figure 16 - Orange Pi Zero connector


2.3.4.3 RS-485

The use of an isolated cost efective RS-485 IC is a must for a project

involving power transformers as a transient in the communication cable cannot

damage the board. The commercial used for this is the ADM2484 IC. Other

solutions such as the MAX14938GW were not considered due to their price.

32

2.3.4.4 USB

To allows easy hardware setup and programming, a USB is be included

on the board. As the onboard MCU doesn’t have an internal USB controller so

an external serial-USB controller IC is be used such as the CH340C instead of

the commonly used FT232 IC. A commom choice such as FTDI counterpart

costs almost 4 times more than the chosen solution and does the same for our

application.

USB protection is also included by using a bidirectional TVS and a

perfect diode circuit which allows almost all the USB voltage to power the

system and protect the USB against reverse current.

2.3.4.5 HMI

A TTL serial interface is used to communicate with hardware or to program

the display. The HMI interface is programmed using a specialized editor (Nextion

Editor) provided by Nextion free of charge. It allows to simulate the user interface

before deploying to the display itself via a SD card integrated in the display.

Nextion also provides a lot of libraries to allow integration with the project

hadware as easy and fast as possible.

2.3.5 Web User Interface

The web user interface needs to be a clean and easy to depict data coming

from the hardware. Thinking of that, Quasar Framework is an open source web

framework that help developers to create responsive websites that look native. It

means that the same web page can be showed in desktop or mobile devices

without the need to rewrite the code.

Quasar is built on top of technologies such as VueJS to allow HTML and

Javascript interaction to be as clean and complete as possible. For that reason,

this framework was chosen instead of similar alternatives like React, Ionic or

AngularJs.

33

2.3.5.1 Measurement Graphs

To present a clean and easy to understand measurement information to

the user through the web user interface, a JavaScript charting library such as

High Charts is used (Figure 17).

High Chart is very well known by the web community, it’s very reliable and

easy to use (KUAN, 2012). Other solution such as Taucharts, Vega, Chart.js and

Edraw Max Chart Maker were discarded due to their poor documentation and

software support when compared to High Charts.

Figure 17 - High Charts Javascript Graph Library example.

Source: https://www.highcharts.com/

As discussed in the Section 2.1,

2.3.6 Web Server

This project is using a virtual private server (VPS) that is located in New

York Through the RamNodes Service. This allows to easily test web ideas such

as the application data base.

There is alternatives that helps building the infrastructure of the webserver

application such as hapijs, expressjs, Restify, Strapy, Sailsjs, ActionHero but the

most applicable for our project in consequence of it’s flexibility, ease to use and

documentation support is the LoopBack rest framework (MARDAN, 2014).

Loopback allows to focus on writing reusable application logic instead of

spen- ding time building infrastructure. Also, it generates beautiful API’s

documentation as can be seen in Figure 18.

https://www.highcharts.com/

34

Figure 18 - LoopBack Rest Framework

Source: https://loopback.io/

The Web Server architecture is shown in Figure 20. The communication

processor (Orange Pi Zero) sends its local information through a private port that

can only be accessed through a VPN connection.

The LoopBack framework handles the logic between inserting new data

using generic access to a database such as MySQL. This API access can be

made through normal API calls in NodeJS (RAUCH, 2012).

The communication processor will also use LoopBack Framework for it’s

interaction with the database, allowing a more robust access to configure the

digital board and so on. A configuration JSON file is used to store OrangePi

configuration so it’s connectivity and general option can be configured. These

options are depicted in Figure 19 and are described as following:

▪ CommunicationMode: Allows to use one or more

communication modes to ssend measurement data.

Ethernet and Cellular networks can send information

directly to the server but for LoRa, a LoRa gateway needs

to be used.

▪ DeiveID: Used to identify the device as a ModbusSlave or

a LoRa node in a local network.

▪ DeviceUUI: Unique device ID. It’s used to register get the

device serial number for production control.

35

▪ EnableCaptivePortal: To enable the user to fastly

configure the device, a CaptivePortal Available through

the WiFi is enabled.

▪ EnableModbusSlave: This enables the device to respond

for Modbus Master requests based on its DeviceID

previsly configured.

▪ EnableModbusSlaveEthernet: Same as

EnableModbusSlave, but it mirrors the functionality for

ethernet connection.

▪ EnableOTA: Allows the integrated ESP32 to be

programmed remotely via its own WiFi connection. This is

used only for development porpoises.

▪ EnableSSH: Allows SSH connection to the embbeded

linux in order to manually configure its behavior. This is

only used for development purposes.

Figure 19 - Configuration JSON File


36

Figure 20 - Web Server architecture


37

2.4 RISK ANALISYS

To ensure that the project development occurs with the least number of surpri-

ses, a risk analysis must be done to all it’s possible scenarios and factors that could

make the development slower or not feasible. There are two main topics to cover in

this analysis: The first is related to general project factors regarding this final year

undergrate project; The second is related to specific details about the type and

complexity of an energy meter hardware proposed in this work.

A table containing a summary of all the listed risks and avoidance difficult is

depicted in Table 2.

Table 2 - Project Risks


2.4.1 General Risks

In the end of the analysis, some solutions must be proposed to avoid or create

an action plan to achieve the project goal. Below are presented some general risks

regarding the project subject:

• Components Supply: as this project involves the use of components that are

not available in the country of this project (Brazil), international components

supplier alternatives must be used. There are well knows companies such as

DigiKey, Mouser, Farnell, LCSC and RC Components. In order to avoid initial

hardware development time, a supplier must be chosen according to its arrival

time and price.

38

• Printed circuit board: Most of the problems can occur in an initial prototyping

stage of the hardware. The use of inadequate or low-quality printed circuit

boards can affect significantly the development time due to issues such as

electrical issues on the board, poor signal integrity, limited board options, etc.

To avoid those problems, professional printed circuit company must be used

such as JLPCB, AllPCB, PCBWAY. Combined with DHL courier as the shipping

option, the board can arrive in maximum of one week.

• Project Complexity: There are 3 main system blocks in the project: Low

voltage Energy measurement, Hardware processing unity and local/remote LTE

communication. In each one there are specific critical details that if not followed

would imply incorrect or faulty behavior of the hardware. The project complexity

is also product of how much tasks are necessary to conclude each project part

and how familiarized and skilled are the students with the concepts and

procedures involved contained in the project development.

• Project cost: There is a maximum amount of resources available that can be

spent in development. Each development phase must agree with a maximum

cost. This problem consists of expenses in electronic components, shipping,

software, PCB manufacturing, manufacturing materials, sensors, modules, etc.

Exceeding the maximum quota would imply in not being able to conclude the

project with integral hardware and functionalities. The cost must always be

aligned with each development step, choosing the only necessary resources

that will be used in order to achieve the goals.

2.4.2 Hardware Risks3

Besides the general risks listed above, there’s also hardware and software

specific risks that must be taken in account. Starting with the hardware risks, a list is

presented below:

• Low Voltage: The front end of the hardware must deal with voltages in the

range of 110-240 Vrms. Thus, must be developed solutions not only to support

_______________ 3 This section was made in March-April 2018, that explain some things that were to be validated.

39

the specified voltage limit, but also provide protection and suppression from

electrical network surges. Not being able to develop this solution would imply in

damaging the hardware in a possible transient scenario. In order to avoid this

problems, guides and components specifications must be followed.

• Electromagnetic Interference: As the hardware will be near a power

transformer, high currents may interfere with the energy monitoring circuit and

communication. EMI suppression techniques must be used such as RF shield

to suppress interferences. Also, modularizing the hardware to separate vital

parts can help eliminate the problem if such techniques are not enough.

• LTE Connectivity: Depending on the region in which the hardware is

installed, internet connectivity or bandwidth is not always guaranteed, even if

dedicated receiver antennas are used. In order to solve this issue, a third

communication option must be used to poll the energy metering data from the

hardware. For instance, RS-485 and LoRa radio communication could be

added.

• Energy fault: There’s a risk that an electrical network measured by the

hardware is turned off intentionally or by some accident. If the hardware doesn’t

detect this, faulty behavior would occur in the measuring system. To avoid this

issue, the main measuring integrated circuit must provide some mechanism.

This must be used as one of the main project criteria for the component’s

selection.

• Integrated Circuit malfunctioning: There is a possibility that a faulty

component is used. It’s difficult to identify this kind of problem as other similar

issues could present similar behavior. To also avoid this problem and also non-

intentional components shortage or maximum parameters exceeding,

redundant components must be bought.

• Schematic and Layout validation: Besides the need of a correct and clean

schematic and layout project according to the project criteria’s, if a further

validation step is not done in early hardware step, the possibility in hardware

faulty behavior that is difficult to find such as incorrect pin placement, incorrect

expected signals, incorrect supply voltage. To avoid those problems or to at

40

least help to identifying them, montecarlo simulation must be done whether is

possible and the schematic and layout must additionally be organized in isolated

blocks and include testing probes, jumpers and extra components. This helps

to better test the hardware when mounted and to promptly identify the origin of

an issue. Furthermore, with extra redundant components included in the

schematic, it gets easy to rework some circuit block for instance.

2.4.3 Software Risks4

With all those possible hardware risks mentioned, there is the software side of

the project that itself contains equally important development steps that could be prune

to some risks:

• Micro-controller peripherals support: There’s a common risk that even

tough using a micro-controller with initially all it’s available peripherals that the

project needs, in practice, an incomplete or faulty peripheral behavior is

supported on software. To avoid this issue in the micro-controller selection, the

errata of it must be read and official forums could be searched to detect if

anyone is having some problem or hardware conflict in a specific peripheral and

also if there’s a software workaround to use it normally use. This presents

initially as low risk as can be done early in the project, but if for some reason

this step is overlooked, the consequences are catastrophic in later hardware

validation. Official sample codes for the targeted micro-controller also must be

seen.

• Software feasibility and complexity: The software running on the

microcontroller must support a complete mathematic library and the

manufacturer must support a compiler with C++11 enabled. If using an ARM

Cortex-M architecture as target micro-controller, the ARM tool-chain must allow

Newlib nano (nano. Specs enabled). As nowadays micro-controllers supporting

these features are getting cheaper, the preferable micro-controller must depict

those capabilities in order to avoid future problems with libraries support such

_______________ 4 This section was made in March-April 2018, that explain some things that were to be validated.

41

as JSON parsing and remote communication. This allows major timing

reduction in project development and avoid libraries incapability and

implementation complexity. One could argue that C++ is too heavy for a micro-

controller, but with the correct compiler optimization and light-weight standard

library usage this is not true anymore.

• Integrated circuit support: By using a dedicated integrated circuit to

measure the energy, a communication to the micro-controller is needed. To

avoid development slow downs in IC communication testing and configuration,

sample codes from manufacturer must be used as reference implementation.

This also reduces the chance in generating bugs that causes undefined

behavior when reading or configuring the IC.

42

2.5 PROJECT SCHEDULE


43

2.6 TESTING METHODOLOGY

The basic flowchart of the testing and validation procedure is presented in Figure

21. The first steps involve the schematic and layout validation trough simulations

whether they are possible. Following this, the PCB Layout must be verified with the

desired PCB manufacturer service do guarantee correct fabrication.

When the board and the components arrive, the PCB is soldered, and each part

of the circuit is independently verified in order to validate all it’s components behavior.

If during initial tests (including fast software IC tests) something goes wrong, a

hardware analysis must be used in order to apply a workaround, getting back to the

component validation step.

An important step that must done in the initial test is the use of a three-phase

signal generator. It allowsto testthe energy measurement IC by generating the

necessary signals of voltage and current with a lag of 120 degrees of each other.

Figure 21 - Testing and validation flowchart


44

2.7 HARDWARE PROJECT

The following subsections will present the project development procedure,

including simulations and design considerations.

2.7.1 Simulation

Some parts of the project were realized in the PSPICE software. The software

presented as a fast model based electronic circuit simulator, in which allowed to

validate some electrical behavior specially in the power supply circuit. The following

paragraph will present the fundamentals steps during the circuit planning.

The first fundamental circuit to simulate is the power supply, for that we

considered a switched DC regulator as this would allow better efficiency and size

reduction for the project. In the PSPICE software unfortunately the switched regulator

doesn’t exist and is required to be manually designed. Fortuntelly, as the simulator is

model based we can use control blocks to simulate the fundamental voltage feedback

circuit present in buck step-down regulators (ZURITA-BUSTAMANTE et al., 2011).

These elements can be seen in Figure 22.

The simplified model of the the switched regulator contains an internal

reference, an error-based controller such as a PID controller, a triangular wave

oscillator tuned to 340Khz (specified for this project) and a voltage comparator followed

by a mosfet which is responsible to turn on and off the the load. The voltage is fed back

to the PID controller trough a diferential voltage sensor. As the Supply circuit uses 5.1V

for higher voltage drop tolerance, the internal regulator reference is also fixed to 5.1V.

45

Figure 22 - Simplified Step-Down Regulator


With all this taken into consideration, it’s possible to validate the model

functionality by checking if the response signals are behaving equally to a normal Buck

regulator. This can be verified in the response graph of Figure 23. The S.VWave

corresponds to the triangle wave that is compared to the input error signal S.VERR;

Fynally, the switched signal S1.VSW is then applied to the mosfet gate terminal,

allowing the series inductor to be charged with the objective to maintain a constant

voltage at the load, which in this case is the microcontroller, embbeded linux and

peripherals within the digital board of this project.

46

Figure 23 - Simplified step-down regulator model response


After this basic model is tested independently, thus ensuring that it supports an

extensive range of loads ranging from few miliampers to 2 ampers, a submodel of it is

created and placed in the main power supply circuit as depicted in Figure 24.

The switched regulator is an important component to support input voltages at

the maximum of 24V for this project. Allownig the digital board to be as independent

as possible to the actual analog board that is responsible to read power quality

masurements. To ensure this specification support for a beckup battery, not only the

regulator has to work properly, but an auxiliary circuit must be designed to permit low

voltages such as 5V to supply the entire board without voltage drop. The components

responsible for the auxiliary circuit are some voltage comparator ICs and mosfet

transistors that act such as logic gates.

Depending on the voltage applied to the main power supply input, the switched

regulator is used or not. And when the buck regulator is not used, a transistor circuit

turns it off and shorts the input with the output in a way that lower voltages such as 5V

can supply directly the circuit without a considerable voltage drop to occur (in the order

of few millivolts).

47

Figure 24 - Power supply circuit model


To better explain the auxiliary circuit behavior, the conditional behavior the

supply circuit is presented in Table 3.

Input Voltage /Battery Voltage

Buck regulator status

Bypass Transistor

>= 7.4V ON OFF

>= 5.9 & < 7.4V OFF OFF

< 5.9V OFF ON

Table 3 - Power supply circuit behavior

When the input supply voltage is over or equal 7.4V, the buck regulator is turned

on. However, when the input voltage drops to a level ranging from 5.9V to lower than

7.4V, the regulator is turned off. This is the desired behavior for a 2 Cells lithium-ion

battery as turning off the regulator and the bypass transistor prevents the battery to

discharge even more, thus avoiding damage to the battery. On the other hand, when

the complimentary circuit receives a voltage lower than 5.9V it assumes that the board

is being supplied intentionally with low voltage such as the association with 2 series

48

super-capacitors and enables the bypass transistor. This voltage level is not critical to

the digital board as its internal regulators are rated to support it.

The simulation yields the expected results which can be seen in Figure 25. Input

and output voltage are plotted in red and blue respectively. When Vin=5V there’s no

voltage drop at the output due to the bypass transistor being enabled.

Figure 25 - Input and output voltage simulation results


2.7.2 Analog board design

For the development of the schematic and PCB of the analog part of the project,

in addition of the knowledge and experiences got during the undergraduate classes

and projects, technical data, design suggestions and some wiring diagrams found in

the datasheets of the components - ATT7022EU, voltage regulators, protection

devices, etc. - were used. Briefly, this part consists of, once the sampling the voltage

and current is performance, the signals got from the transducers are reduced aiming

to make them compatibles with the levels that are compatible with the ATT7022EU

voltage input and sending the data sent from IC to the processing unit. In addition, the

49

developed analog part includes the generation of the DC voltages used and some

measurement points for the validation of the correct operation of the circuit. The

connection diagram of the voltage sampling is shown in Figure 26.

Figure 26 - Connection diagram of the voltage sampling to the ATT7022EU


Firstly, we have the interface between the analog board with the transmission

line – the “interface with the transducer” block. Once this part is about the voltage

sampling, a direct sampling in the low side of the transformer must be performance.

The next step consists in some protection components to avoid damages with

overvoltage and overcurrent and filters. The “signal adequacy and isolation circuit”

block consists on resistors and transformers to set the signal from the transducers

down to levels that are compatibles with de ATT IC.

For the current, the connection diagram of the current sampling is shown in

Figure 27.

50

Figure 27 - Connection diagram of the current sampling to the ATT7022EU


Once the current sampling is done indirectly – using a current transducer

“connection with the transducer” box, the connection between the transducer and the

analog board is done indirectlly. Once the cureent is sampled, it goes to the “signal

adquacy circuit” that has two main tasks. The first one is to reduce the current from the

transducer to values that are compatible with the ATT IC and isolation between the

external measurement and all the the rest of the systems’ circuit. The next step – the

“current to voltage transformation and filter” is responsible to transform a current signal

into a voltage and filter it, avoiding high frequency noises for then to conect to the ATT

IC.

Another system that is part of the analog boars is the part that is responsible of

the adquation of the DC voltage to levels that are used in this board - Figure 28.

Figure 28 - Connection diagram of the DC voltage of the analog board


51

In the Figure 29, the connection diagram of the DC voltage of the analog board

is shown. The first stage is about the supply voltage. For instance, this voltage will be

supplied by an external power supply. The second block – the “filter and circuit

protection” is about filtering the voltage that come from the power supply to avoid high

frequency noise that may come through from the main power supply, that can be a

linear or switched power supply type, and the protection from voltage transients

induced by lightning and other transient voltage events. In the next step dropped down

from 12 V to 5 V using a regular voltage regulator with the capacitors suggested in the

datasheet. Lastly, the voltage is reduced again from 5 V to 3.3 V and then used to

supply the respective components.

Figure 29 - Connection diagram of the DC voltage of the analog board


The layout of the analog board is shown in Figure 30. It’s a simple design

but some considerations needed to be made during the project such as circuit

protection and correct components placement according to the ATT7022 manufacturer

datasheet. There are analog tracks that need to be folloed by gounding to avoid

interference. Also, the right side of the board that contains the current transformers

must not contain ground as high voltages are involved during the energy reading.

52

Furthermore, circuit protection was added right after the terminal block connectors to

avoid circuit damage during a powervoltage period.

Figure 30 - Analog. board PCB layout


2.7.3 Digital Board design

The Layout of the digital board is depicted in the Figure 31. The layout involves

deferent ground plans to best avoid noise and to shield the board. This will be

explained in following paragraphs.

The division between each functional part of the digital board is done in a way

to best isolate the power supply circuit from the MCU and antennas. This can be seen

in Figure 31 as each functional part has its ground isolated but at the same time, they

are united at just one point, at the lower right side of the board, where the power supply

components are present. This technique is widely applied to mixed analog/digital

53

hardware such as studied electromagnetic interference mitigation theory (CHEN,

2005).

Figure 31 - Digital Board Layout


For each part of the board, a certain layout criterion were applied:

• Power supply & battery: The layout design of the power supply is done in a way

to centralize every ground from the other peripherals. This is important due to;

• Comms: The communication consists of two peripherals, the RS-485

transceiver and the CAN transceiver, although CAN is not used in this project,

it’s future support is beneficial for future applications using the same digital

board. The RS-485 transceiver is totally isolated; thus it has its own ground and

voltage regulation circuitry which need to be connected to an external power

supply tied from the bus master side. In a different way, the CAN transceiver is

not isolated but has a separated ground which then unifies at the power supply

segment of the board;

• MCU & Linux: This segment consists of a large grounding which is divided with

USB peripherals, watchdog supervisor, analog board and IHM connectors and

54

Orange Pi Zero female header. As all the peripherals are mostly communicating

with binary communication protocols such as USART and SPI, there’s no

worries about interference between tracks influencing each other in a negative

way, that is, digital crosstalk is not taken into account here as we are dealing

with low clock speeds for communication. It’s understood as high speed

communication when it comes to signals operating with 100Mhz or more

(JOHNSON; JOHNSON; GRAHAM, 2003). However, even at this point it’s

optional to use more complex techniques evolving track width calculation if the

total length of a net from a peripheral to other is short. This is exactly the case

where our project fits. In short, the project’s board doesn’t have high speed

signals nor long signal tracks between components.

• GPS and LoRa: The GPS and LoRa segment are generally equal in the sence

that both have an antenna connector near their respectives modules. For this

layout, the importance relays on the shielding near the antenna tracks. Several

vias was placed on the ground to equalize impedance and fast transient

response near the module, this is called via stitching. Another interference

refuction technique applied was the track shield in which consists in placing a

high amount of vias near the antenna track, thus allowing the antenna path to

be horizontally protected from EMI sources.

A 3D Overview of the board is also generated and is shown in Figure 32. The

main connectors are disposed in the edge of the board, so it allows easy board wiring.

Communication connectors for Cellular modem, ethernet and antennas are in the back

side of the board.

In order to receive LoRa messages, a USB dongle is designed so it can be

placed not only in the a commom gateway, but also in a simple computer, allowing

faster development and cost reduction. This dongle is shown in Figure 33.

55

Figure 32 - Digital Board 3D Mounting


Figure 33 - LoRa Dongle 3D Project


56

3 PROJECT PROTOTYPE AND TESTING

The general project diagram is shown in Figure 34. The numbers from 1 to 9

are the subststem that will be better described in the following subsections.

Figure 34 - General project diagram


1 – ENERGY METER HARDWARE

This part is responsible of getting the values of voltage and current sampled

from the low side of the transformer and process it in the ATT7022EU IC. For it, the

sampled signals must be in the range that the ATT7022EU operate. For it, some

circuits were designed aiming to make this interface.

• POWER SUPPLY: A 12V power supply is used to supply the circuit. Once 12 V

is a voltage that is too high for some IC – the ATT, for example, works with 3.3

V, it must be dropped down. By powering the analog board with +12 V DC, we

can validate the right functionality of the power supply system of the used ICs.

57

• VOLTAGE MEASUREMENT: By plugging the voltage connector a 127 V AC

and measuring the voltage on the measure pin after the current transformer, it

is possible to validate that the system that changes the voltage to values that

are compatibles with the ATT IC are working properly.

2 – POWER SUPPLY

In this part of the project, we are going to validate the right functionality of the

system that the manage the battery and the right functionality of the digital board when

supplied by the battery or by and external supply.

1. Testing the functionality of the digital board only powered with the battery - In

this test, we are going to validate the operation of the digital board even when

the external power supply is “out of working”, that mean, there is no external

power supply supplying the circuit. In this case, LED disposed in the digital

board will turn on indicating the operation of the board without any problems or

restrictions.

2. Testing the functionality of the circuit that manage the power supply system - In

this test, we are going to validate the operation of the circuit that manage the

power supply system, that means, we can see it operating when we plug in a

battery that is not completely charged and will be charged – during the charging

process, a LED that indicate the “charging battery” status will turn on. For it, the

board must be supplied for and external power supply and a battery not

completely charged needs to be plugged in. When the battery is completely

charged, the LED that indicate the “battery charged” status will turn on and the

LED that indicate the “charging battery” status will turn off.

58

3 – ESP32

In this test, we are going to validate the MCU by re-uploading the program in it.

Once it is very important for the right functionality of other blocks, it is hard to make a

test that shows only the ESP32 working by itself without user interaction.

4 – Realtime Clock (GPS)

The GPS module is used for the identification of the right location of the energy

meter. Using the NMEA information showed in Figure 35, we can get the coordinates

of the device and some information’s about the right functionality of some parts of the

GPS hardware. For example, using “$GPTXT” parameter we can get information’s

about the right functionality of the antenna and the “$GPFLL” the coordinates of the

current location of the device. The Figure 36 shows the decoded GPS module

information and the Figure 37 the position got from the GPS module.

Figure 35 - GPS NMEA information on serial terminal screen


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Figure 36 – Decoded GPS module information on serial terminal screen


Figure 37 - Google maps location pointed by the GPS


5 – RS-485 and USB

The RS-485 validation will be performance through some date send from a USB

connection from a PC using a serial monitor – Arduino serial monitor, for example and

it will arrive in the digital board as a RS-485 message. To validate that it is working

properly, the LoRa connection may be used to show that any request sent through the

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USB-RS-485 has arrived in the digital board, the answer got can be send through the

LoRa communication and show in a serial monitor.

6 – REMOTE CONECTIVITY

For the validation of the LoRa communication, we are going to test to scenarios.

The first one is called “transparent” and the second “protocol”. A LoRa dongle (Figure

38) was developed in parallel of this project in order to better debug such

communication modes.

Figure 38 - LoRa dongle


The following testing procedures were used to validade the remote LoRa

communication:

1. For the “transparent” validation, 2 PC are needed to have the communication

between the PC and the digital board working properly. One of them must have

the LoRa Dongo plugged in a USB input and a serial monitor configured with a

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baud rate of 115200 bps. The second one has the digital board plugged in a

USB port and has a serial monitor configured with a baud rate of 115200 bps.

Messages can be sent and received for both and the messages will be show in

the monitor serial of the receiver. In this test we can validate the right

functionality of the hardware, software and firmware developed.

2. For the “protocol” communication, we have the communication between the

digital board and the PC. In this scenario, unlike the previous, the digital board

is not connected with the PC and its decisions and answers are done by itself -

through programming. The digital board is configured to answer the received

questions in a determined interval of time.

For the 3G connectivity, a USB modem must be attached to the Orange PI board

to provide to it an internet connection. Once this is done, the system can send data

and communicate with other devices through internet connection. The Figure 39 shows

the Shell screen from the Orange PI subsystem and the Figure 40 shows the User

Web Interface.

Figure 39 - Orange PI terminal screen


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Figure 40 – OrangePi user Web interface


7 – IHM (Human Machine Interface):

The IHM will start since the startup of the system. It will show a “loading screen”

while the microcontroller is getting ready and makes the transition to another screen

where its possible to see the voltage, current and power from each of the 3-phase

measured and shows the status of the availability of the GPS system and the data

connectivity. It has, also, a button where it is possible to activate and de-activate the

LoRa communication and a place that shows if is the embedded Linux is available or

not. With it, we can validate the code done for the IHM and the communication with the

other subsystems.

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Figure 41 - IHM interface


8 – CLIENT

This part is the validation of the client side of the system. As shown in the other

validations step, a PC can almost every time interact with the systems and its data. A

simple terminal application can be used to check or configure the system usin JSON

syntax.

9 – WEB APPLICATION

In this stage, it is possible to test the integration with the MQTT connectivity. An

application called MQTT.fx is used to connect to the server and send some relevant

data (this can be done by using the broker link http://mote.ddns.net). Further it’s

possible to check that correct data was receiving by opening the EMONCMS web

dashboard. The Figure 42 shows measurements sent from the MQTT.fx. Later the

same procediment is done, but with the embedded linux connection to the MQTT

broker and sending real energy measurement data.

http://mote.ddns.net/

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Figure 42 - EMONCMS dashboard


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4 SUSTAINABILITY AND ENVIRONMENTAL IMPACT

According to according to the Manual of the technological R & D programs of

the Brazilian electric sector of 2001, the production, transportation and consumption of

electricity - and electronic devices affect various aspects of the environment such as

air quality, water quality and availability, populations and habitat of aquatic and

terrestrial fauna and flora, the use of hazardous material and waste the impact of

electromagnetic effects on health as general and the environment, etc. Doing a briefly

analisys on sustainability and environmental impact aspects of the developed project,

we selected some aspects to analyze and to discuss about. Whenever possible, we

tried to choose technologies that have the minimum environmental impacts.

Thinking about alternative ways of powering our systems, we can quote solar

systems as one alternative. However, it was not implemented in our system due the

need of our project - since our hardware will be coupled in the output of a transformer

and it has a low consumption, it was chosen powering it with the voltage of the network

itself, adjusting in the voltage to make it compatible with levels of the circuit, which is

more appropriate - it is already used by other available and functional solutions and

has a better cost-benefit ratio – implementing a solar system has an additional cost

besides the system.

During the process of choosing the components of our hardware, we took care

to choose components that have a seal that demonstrates that the product in question

complies with the RoHS directive in the manufacturing process and the product itself -

as can be seen in Figure 32, which shows that RoHS is a parameter of the product in

our supplier.

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Figure 43 – RoHS component summary


Aiming the quality and reliability of our solution, besides the hardware was

developed for this specific solution, the electronic components used were new. We cite

as ways of reducing the cost, in the hardware part, the purchase of components in big

quantities and the search for other national suppliers.

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5 RESULTS

The complete mounted board is present in Figure 44. The analog board is

assembled on top of the analog board which is connected to a digital power supply

regulated to 12 volts. The 3G dongle is attached on the available port on the embedded

Linux. The connectivity link is checked trough the local user interface.

Figure 44 - Complete mounted hardware


The hardware is connected to the available laboratory ac power and tied to a

voltage generator for current signal simulation. The analog board response for

acquired voltage and current signals are shown in Figure 45 and Figure 46

respectively.

The microcontroller is programmed to collect data for a period of 30 minutes.

After this period the data is collected on the web interface which can be seen in

Figure 45. The average values are always in the range of 59.9 – 60.1 HZ.

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Figure 45 - Analog voltage signal


Figure 46 - Analog simulated current signal


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Figure 47 - Frequency measurements


Moreover, the realtime data of most important energy information is observed

in the EMONCMS realtime dashboard containing measurements the ac frequency,

phase voltage, current, active power and power factor of each phase.

Figure 48 - Realtime dashboard 1


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Figure 49 - Realtime dashboard 2


The LoRa dongle is attached to a notebook close to the board and LoRa

communication is validated by receiving the aggregated energy measurements

information with its average, minimum and maximum values each 1,5 and 15 minutes

respectivelly. This can be seen in the serial terminal application of Figure 50.

Figure 50 - LoRa remote measurements responses


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Further the IHM is attached to the board in order to easily show the main

energy measurements. This is presented on Figure 51.

Figure 51 - Functional IHM


Finally, the 2-cell lithium battery was attached on the battery connector of the

digital board (Figure 52) and verified to work when the main 12V power was disabled,

allowing a continuous operation without causing the system restart.

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Figure 52 – 2-cell lithium battery


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6 FINAL CONSIDERATIONS AND FUTURE WORK

The development of this project was a very challenging task. We started with an

abstract idea and when we reach the end of the discipline of TFG 2 with a hardware

that can perform the assignments that we planned in the initial documents delivered in

the TFG 1 discipline. It was a very good experience that, in our opinion, brought us

closer to the day-to-day/activities of an engineer.

All aspects the technologies foreseen in the planning stage were maintained

and implemented in the final soluton. We are very satisfied with the results obtained in

the final implementation that will be presented in the final presentation of the discipline,

since we seek to develop the hardware used by ourselves and today we can see our

technical and practial evolution when we compare our knowledge at the beginning of

the discipline of TFG 1. For our solution to gain even more robustness and that can be

implemented in a real physical system, we are aware that there are still aspects that

need to be developed - encapsulation with isolation of electromagnetic interference,

for example, and field tests need to be performed. However, considering the time and

complexity of our solution, we are very satisfied with the results achieved.

Making a superficial comparison with the technologies that already exist and

that apply in the same area as our solution, we can say that the hardware we use are

according to the needs of the application and have, for the most part, a lower price.

For example, Babelbee (avalible in http://www.babelbee.org/#About) uses the ARM

core as the main CPU running at 700 MHz, with a price of approximately $ 20.00

(2018). In our solution, we used the ESP32-WROVER, with a price of approximately $

4.57 (2018), showing a difference of prices of $ 15.43 (2018), which represents

approximately 337.64% of difference between the values. It is worth mentioning that

one of the requirements for the choice of technologies embedded in our final solution

considered what was already in the market and its purchase price. In total, the

components used present a technical characteristic compatible with those used in pre-

existing solutions but with a lower value. Another rugged and portable solution we

found is Fluke's advanced Power Quality and energy analyzer. It is a complete and

versatile equipment but, according to values found on Fluke's website for sales in the

United States, it costs $ 7,599.00, which is equivalent to R$ 35,000.00 (Brazilian

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currency). in general, we can state that our solution has the technical potential and an

interesting financial aspect to be applied in environments where the Babelbee or Fluke

energy meter could be applied with a more cost-effective ratio and flexible

communication systems.

It can also be said that the project has extrapolated the barriers of technical

knowledge in electronics and covered aspects related to electrical engineering,

computer engineering, administration, marketing, etc. We didn't just go beyond

developing the hardware, we had to think about alternative ways of its implementation

aiming minimizing costs, which impacted in searching for suppliers with the lowest

price of the components and we found LCSC - a worldwide supplier of electronic

components located in China, and with that, we had to understand the process of

importing a product and also that it takes time (shipping) - for physical distance and

legal issues. We had to manage our time and the activities we needed to develop. As

the work developed in a group, we used Trello tool for the management part of the

activities and the deadline that we needed to fulfill. We also sought a tool for the

development of the schematics in a cooperative way and we found easyeda, which, in

addition to working in a cooperative way, we had a direct connection with LCSC

components and it allowed us to buy the necessary components directly from them

and at the same time generate the layout of the printed circuit board and order it - with

a great price.

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