6. hardware prototype and experimental results

CHAPTER-6 HARDWARE PROTOTYPE AND EXPERIMENTAL RESULTS.

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6. HARDWARE PROTOTYPE AND

EXPERIMENTAL RESULTS

Laboratory based hardware prototype is developed for the z-source inverter based

conversion set up in line with control system designed, simulated and discussed in earlier

chapters. The setup is used for the experimental verification of the results obtained through

simulation. The experimental setup shown in Figure 6.1 is broadly divided into following

sections:

Diode Rectifier-IGBT inverter power module

Z- network consisting of inductors and capacitors

Controller section consisting of number of modules

Three phase AC filter circuit

Three phase Load

Measuring digital meters, Digital Storage Oscilloscope (DSO)

PICKit3 programming module (with MPLAB software)

Variac

Figure 6.1 Hardware Prototype of ZSI


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For the experimental purpose a single phase variac is used for initializing variable power

source that rectifies through a bridge uncontrolled rectifier to generate variable dc voltage.

This dc source is connected to an IGBT based three phase bridge inverter through a z-

network. Main development in this hardware prototype is its controller section which senses

the voltage across a capacitor in z-network and through digital signal processing develops

shoot-through pulses. The capacitor voltage range 0-1000V is normalized to 0 to +5V. This

includes realization of PID controller through PIC microcontroller. With this variable pulse

width shoot-through pulse third harmonic injected (THI) maximum constant boost control

(MCBC) technique is used for switching the IGBTs. AC filters are used to suppress the

higher order harmonics in the three phase output. Digital meters are used to measure the

input ac voltage, DC bus Voltage, DC bus current, load current etc. DSO is used to verify

the waveforms in different sections. The programs code developed for different PIC

microcontrollers under MPLAB software The algorithm of which is presented in

Appendix-B.MPLAB Integrated Development Environment (IDE) is an integrated toolset

for the development of embedded applications on Microchip's PIC microcontrollers.

MPLAB IDE v8.87 is used to write the program for PIC16F886 (Peripheral interface

controller) microcontroller. The program code was uploaded and burned via the PICKit 3

module provided with the PID modules described later. Detailed description of the

hardware prototypes, their circuit diagram, components used including their photographic

view are presented in this chapter. It also presents the waveforms at different test points and

the results obtained through experiments for simple ZSI and Quasi-ZSI topologies.

6.1. Rectifier - Inverter power module

It consists of the following sections as sketched in Figure 6.2

(a)Diode Rectifier

Four 16NSR120 diode are used with heat-sink as full wave single phase bridge rectifier

circuit to rectify the variable ac input voltage. Two capacitors of value 470 microfarad, 450

maximum working voltages are connected at the output of the rectifier to get the smooth dc

bus output. Figure 6.4 shows the view of the rectifier section which includes a time-delay

circuit consisting of mainly a relay and microcontroller chip PIC16F. Time delay is

introduced to provide the power circuit a soft start through green LED. The delay is

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adjustable through the microcontroller program. The DC bus output is passed through a fast

switching diode to the inverter via z-network

(b) Three phase Inverter:

Three phase six switches bridge inverter consists of six IGBTs of model

FGA25N120ANTD as in

Figure 6.5 to generate three phase output which is to be connected with three phase load.

IGBTs are attached with suitable heat sink.

(c) IGBT driver circuit:

There are six driver circuits separately for six IBTS shown in the IGBT module in

Figure 6.5. includes 6N138 is a low input current high gain Darlington optocoupler. A

single driver circuit shown in Figure 6.6 includes an optocoupler and transistors. When an

electrical signal is applied to the input of the optocoupler, its LED lights, its light sensor

then activates and a corresponding electrical signal is generated at the output. Unlike a

transformer, the opto isolator allows for dc coupling and generally provides significant

protection from serious overvoltage condition in one circuit affecting the other. Pulses

coming out from the signal conditioner circuit are fed to pin 2 of the optocoupler. Output

from pin 8 is processed through various resistors, transistors and two back to back zener

diodes to generate required pulse for the gate of IGBT.

Table 6.1 Major components in Rectifier-Inverter Power Module

Name Specification/Type Quantity

Capacitor 470µF,450 V 2

Diodes for Rectifier,16NSR120 16A, 1200 V stud diode 4

Relay KT954 1

Microcontroller to introduce delay PIC16F-628A 1X 3

Optocoupler 6N138 1 X 6

Transistor for Driver circuit NPN, BC547 1 X 6

Transistor for Driver circuit PNP, BD140 1 X 6

Transistor for Driver circuit NPN, BD139 1 X 6

IGBT FGA25N120ANTD,25A,1200V 6

Driver power Supply IN 4007 / 470µF,35 V 4 X 6, 2 X 6


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Figure 6.2 Rectifier-Inverter power module and IGBT driver circuit schematic

Figure 6.3 Hardware circuit of Rectifier - Inverter power module


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Figure 6.4 Hardware circuit for Single phase Bridge rectifier


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Figure 6.5 IGBT Module with driver circuit

Figure 6.6 IGBT Driver circuit


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6.2. Triangle Wave generator

The function generator IC chip XR2206 has been used to generate high quality, high

frequency triangular wave. The output waveforms can be both amplitude and frequency

modulated by an external voltage. Frequency of operation can be selected externally over a

range of 0.01Hz to more than 1MHz. As shown in Figure 6.7 of the schematic, the fixed

capacitor of value 0.01 microfarad connected between the pin no 5 and 6 and 24.7 k

variable resistance across pin no 7 produces the desired frequency triangular wave at output

pin 2. A variable resistance is connected between pins 15 and 16 to adjust the symmetry of

the output waveform. Figure 6.6 represents the block diagram of the function generator IC

and Figure 6.9 show the view of the hardware circuit of the generator. The signal is then

amplified with the help of TL082 operational amplifier and offset is adjusted by 5K pot

connected with non-inverting terminal. Finally it produces a 6 KHz and 5 volt peak

triangular wave as captured in DSO and shown as Figure 6.10

Figure 6.7 Schematic of Triangle wave generator


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Figure 6.8 Block diagram of IC XR2206

Figure 6.9 Hardware circuit of triangle wave generator


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Figure 6.10 High frequency triangular wave of 5volt peak.

Table 6.2 Major components for triangle wave generator

Name Specification Quantity

Function generator, XR2206 Max operating frequency = 1 MHz

Adjustable Duty Cycle, 1% to 99% 1

Operational amplifier, TL082

Wide Gain Bandwidth: 4 MHz

High Slew Rate: 13 V/μs

Internally Trimmed Offset Voltage: 15 mV

1

Trim Pot 20K, 10K, 5K 2,1,1


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6.3. Voltage Sense

IC Chip ACPL-782T is used as voltage sensor to sense the voltage across capacitor of the z-

network. Capacitor voltage is passed through a voltage divider circuit of 1M x 4 and 50

ohm resistances and voltage across 50 ohm is connected to the 8-pin ACPL-782T IC chip.

ACPL-782T is an isolation amplifier applied mainly for voltage and current sensing. The

output from pin 6 and 7 of this chip is processed through LM358 op-amp to convert this in a

suitable level. It is then connected to the PID controller PCB to generate the shoot through

pulses to compensate the input voltage fluctuation. The schematic of the circuit is shown in

Figure 6.11 which also includes a 5V dc power supply for providing power to the ICs.

Figure 6.12 is the view of the PCB developed for the purpose.

Figure 6.11 Voltage Sense circuit diagram


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Table 6.3 Major components in voltage sense PCB


Diode IN4007 2

voltage regulator, 7805 Three terminal positive 5 V 1

Voltage Sensor chip, ACPL-

782T

8 pin isolation

amplifier DIP

2% Gain Tolerance

100 kHz Bandwidth

1

Operational Amplifiers,

LM358

Dual Differential Input

Large DC Voltage

Gain: 100Db

Wide Power Supply

Range

1


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Figure 6.12 Hardware circuit for Voltage Sense

6.4. Third Harmonic Injected (THI) Sine-wave modulating signal generation

PIC16F886 microcontroller is used to generate three phase 50 Hz sinusoidal waveform

which is then added with the third harmonic 16% of amplitude of same sinusoidal

waveform to get the third harmonic injected sine waveform. This total operation is made

through microcontroller program details of which is presented as APPENDIX-C. is

Presented in the circuit sketch in

Figure 6.13, terminals A1-A8, B1-B8 and C1-C8 generate the 8-bit three phase outputs

each 120 degree out of phase representing the THI sinusoidal digital signals. These signals

become the eight bit inputs to the three digital to analog converters DAC0800. The separate

analog outputs of DACs are processed through corresponding op-amp (LM358) to generate

variable maximum ±5 volt peak to peak THISIN three phase modulating signals. The

amplitude of these signals can be varied through program to adjust modulation index. The


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hardware view of this section is presented in Figure 6.14. The DSO captured view of these

three phase signals is shown in Figure 6.15.

PIC16F886 is a 28 pin CMOS Microcontrollers with nanoWatt technology having 24

numbers I/O pins, 8192 flash word memory, 368 bytes SRAM and 256 bytes EEPROM

memory with maximum operating speed of 20 MHz. The block diagram of the

microcontroller is copied in Figure 6.16. Program is developed for the microcontroller

through the MPLAB IDE software and burning of program is done through PICkit3

programmer shown in Figure 6.17.The DAC0800 is a commonly used 8-bit high-speed

current-output digital-to-analog converters (DAC) featuring typical settling times of 100 ns.

Figure 6.13 Circuit Diagram of THI Sine wave Generation Schematic


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Figure 6.14 Hardware circuit for THI Sinewave Generation PCB

Figure 6.15 THI Sine wave waveform


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Figure 6.16 Block Diagram of PIC16F886


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Figure 6.17 PIC kit-3 programmable module

6.5. PID Controller section

The signal which is coming from the voltage sense PCB is connected as input for this

section which through a voltage follower and zener is connected to the microcontroller

PIC16F886. It is supported by a 20 MHz crystal oscillator connected between pin 9 and 10.

A program is developed with extensive logics for the PID operation of the whole system.

There is a provision of burning the program in this PCB through a 6-pin connector. PID set

points like KP, KI and KD are set through 4 push-switches K1, K2, K3 and K4. The four

numbers seven segment displays are used to display the set values (SV) and also present

value (PV) by adjusting the push-switches a number of times. Five LEDs connected

alongside indicate the mode of display i.e. whether it is PV, SV, KP, KI or KD. The four

switches are used for selecting the parameter, setting the parameters i.e. increase and

decrease the values and entering the final value respectively. The 8 bit output from

microcontroller section is then connected to the DAC0800 for digital to analog conversion

of the control output signal. Finally through LM358 opamps this is processed and limited


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within a range of 0 to 5 V control signal which is fed to the signal conditioner circuit. The

schematic diagram of this section is shown in Figure 6.18 and photographic view in Figure

6.19.

Figure 6.18 PID Controller section

Figure 6.19 Hardware circuit for PID Controller section


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Table 6.4 Major components in PID Controller Section


DAC0800 8-Bit Digital-to-Analog Converters 1

LED Seven segment Display board 4×7 Segment Display 4x1

LM324 Low power quad op amp 1

Microcontrollers PIC16F886 Details given in THI sinewave generator

section 1

LM358 Low power dual operational amplifier

Details given earlier 2

LED Board 5 red LEDs for SP, PV, KP, KI and KD 1 X 5

Push switch board Push to connect ground switches 1X4

Crystal Oscillator for PIC 20 MHz 1

Connector for Programmer 6- pin 1

6.6. Signal Conditioner

Three phase third harmonic injected (THI) sinusoidal modulating signals are compared

separately by LM358 opamp comparators with a high frequency triangular carrier signal

coming from triangular signal generator card. Across the non-inverting and inverting input

terminals modulating and carrier signals are fed respectively to obtain high frequency PWM

switching pulses. Across the output terminals 5.1V zener diode is connected to ensure the 5

volt peak switching pulses. This comparison and generation of pulse for a single phase are

captured in a DSO and presented as Figure 6.22. These pulses are then fed to Schmitt

Trigger inverter IC7414. The 7414 IC is composed of six independent Schmitt-Triggered

single-Input inverter gates. Schmitt Trigger logic gates have a greater immunity to noise in

the input lines. With noise suppression, the logic gates (in this case inverters) are more

likely to remain in their current state unless a true change to the input was intended.

Glitches and high speed random noise in the line is less likely to toggle the status of the


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output. Pin 14 of IC7414 is connected to +5volt supply and pin no 7 is grounded. Across

pin no 1,5,11 the PWM pulses are applied as shown in the circuit schematic Figure 6.20.

Pin 2 is the complemented output of pin 1. Pin 2 and 3 are shorted and hence the output at

pin 4 is similar to the input at pin1 (because of double inversion). So pulses at pin 2 and pin

4 are complement to each other. Similarly pulses at pin 10 and 12 as well as pin 6 and 8 are

complement to each other. The six PWM pulses are fed to two OR gate IC7432 at pin 1,

4,9,12 and 1, 4 respectively.

As shown in the sketch in Figure 6.20, there are three microcontrollers PIC16F628A

connected in between and the three inverted PWM signals from IC7414 are passed through

them. There are two three pins jumpers connected at the output of each set of pulses. This

circuitry is made to introduce the options of dead time during switching. Though dead time

is not necessary in case of shoot-through switching, a provision is kept to include it, in case

of operating the circuit as conventional PWM inverter. A programmable dead time is

inserted to the three PIC16F628A separately. Dead time can be bypassed in case of shoot-

through operation with the help of jumper arrangements as shown in the sketch.

Again, in the lower half of the sketch in Figure 6.20, control voltage from the PID controller

PCB is compared with the same carrier triangular signal to generate the shoot through

pulses. Negative shoot through pulses for the lower half switches is generated by comparing

with the negative PID control voltage. Two sets of shoot-through pulses are then passed

through scmitt-trigger buffers (IC7414) without any inversion and are then ORed with the

PWM switching pulses by OR gate IC7432. Six output signals after OR-ing are fed to 20

pin IC74244 octal 3-state buffer/line driver to generate desired switching pulses which are

fed to individual IGBT driver circuit. The photoview of the signal conditioner Board is

shown in Figure 6.21.


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Figure 6.20 Signal Conditioner


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Table 6.5 Major components in Signal Conditioner PCB

Name Specification/Schematic diagram

Quantity

Microcontrollers PIC16F628A

8-Bit CMOS, 18 pin Microchip Microcontroller

Flash word memory 2048, SRAM 224 EEPROM

128 I/O 16, 20 MHz operating max speed.

3

Operational Amplifiers LM358 Details given earlier

4

Schmitt Trigger Inverter, 7414

Six inverting buffers with Schmitt-triggerLow-

power dissipation.

2

OR Gate IC chip 7432

Quad 2-Input OR

Gate 2

Buffer/Line Driver IC chip,

74244

Octal non-inverting buffer/line driver with 3-state

outputs.

1


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Figure 6.21 Signal Conditioner

Figure 6.22 THI SINPWM and Triangular wave comparator to produce single IGBT pulse

Figure 6.22 presents the DSO captured view of the THI Sine wave, triangular signal and

resulting PWM pulses together through three channels.


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Figure 6.23 The Controller section

Figure 6.23 shows the overall view of the controller section developed for the system and

Figure 6.24 represents the PWM pulse, shoot through pulse and the resulting pulses going

to the driver circuit of the single IGBT.


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Figure 6.24 pulse across single IGBT(Top- PWM pulses, Middle-shoot through pulses,

Bottom-pulse for each IGBT)

The impedance network and ac filter parameters for the experiment are chosen as

𝐿1 = 𝐿2 = 1𝑚𝐻 𝐶1 = 𝐶2 = 500𝜇𝐹

𝐿𝑓 = 10𝑚𝐻 𝐶f = 10𝜇𝐹

Table 6.6 and 6.7 present the experimental results of the simple ZSI system selecting two

different values of shoot through duty ratios D. With increase of D the output voltage as

well as capacitor voltage is increasing. Table 6.8 presents a closed loop experimental results

where the input single phase ac voltage is varied in steps from the variac and corresponding

output voltage is recorded. Output remains almost steady with little variation and this

satisfies the perfect working of the prototype under closed loop condition. Experiments are

carried out both for simple ZSI and Quasi ZSI. Figure 6.25 and Figure 6.26 are the DSO

captured waveforms separately taken without ac filter and with ac filter respectively.


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Table 6.6 Experimental results of ZSI(M=0.8,Shoot through duty ratio D=0.32)

𝑽𝒅𝒄(𝐕𝐨𝐥𝐭) 𝑽𝒄𝟏(Volt) 𝑽_𝒂𝒄 (Volt)

260 470 275

280 500 290

340 620 350

360 655 380

380 680 400

Table 6.7 Experimental results of ZSI (M=0.7,D=0.37)

𝑽𝒅𝒄(𝐕𝐨𝐥𝐭) 𝑽𝒄𝟏(Volt) 𝑽_𝒂𝒄 (Volt)

260 635 360

280 680 380

340 825 470

360 880 500

380 920 520

Table 6.8 Performance of the regulator

ZSI

Single phase

ac

input(Vrms)

DC Bus voltage(V) Three phase output line

voltage(Vrms)

60 141 250.5

75 177 255

95 225 258

110 260 258.5

130 308 263

150 351 260

QZSI

60 140 221

75 175 223

95 225 224

110 260 225.5

130 310 227

150 350 227.5


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Figure 6.25 Output line voltage without filter

Figure 6.26 Output line voltage with filter

6. hardware prototype and experimental results

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