development of a 10kw single phase igbt inverter for grid connected pv applications

8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications

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DEVELOPMENT OF A 10KW SINGLE-PHASEIGBT INVERTER

FOR GRID-CONNECTED PV APPLICATIONS

32nd Annual Canadian Solar Energy Conference

2nd Solar Buildings Research Network Conference

Calgary, AB, June 10-13, 2007

Gene Z. Guo



Presentation Contents

Introduction

Improved Predictive Current Control Algorithm

Fuzzy Logic Based Maximum Power Point Tracking

Strategy

Protection Functions of PV Inverter

Display and Communication of PV inverter

Conclusion



Introduction

For environmental and commercial benefits,

R&D on photovoltaic (PV) systems havebeen significantly advanced in recent years

Grid-connected PV inverter is one ofimportant solar energy applications.



Highly integrated grid-connected PV inverter should

Complete DC-AC conversion with high output quality

- Current THD is one of key index

- Demands advanced PWM strategy and proper designof output filter;

Employ suitable system control algorithm

- such as maximum power point trackingHas comprehensive protection functions

- Various protection functions, including anti-islandingprotection

Display and communication functions- Friendly user interface

- Remote control and communication function



Basing on experience of nearly 2 decades’ R&D work on

inverters, a 10kW, solar power input, grid-connected IGBTinverter is developed.

Main Specifications:

Input voltage: 150V-600V (rated voltage: 400V)Rated power: 10.0kWPeak power: 12.5kW

Grid: Single-phase, 240V/60Hz

DSP is employed to realize the control and protection function;Assembly language is used to program the code.

Another microprocessor, PIC18F6722 is used to complete thedisplay and communication function, C language is used toprogram the code of this part.



Schematic diagram of the developed PV inverter



The developed 10 kW PV inverter features:

Advanced predictive current controller for space vectorpulse-width-modulation

Fuzzy logic based maximum power point tracking

Comprehensive protection functions includingaccelerated phase shift anti-islanding algorithm

Display/remote control/communication functions throughinternet



IMPROVED PREDICTIVE CURRENT CONTROL

ALGORITHM

Current THD is one of the most specification of a grid-connectedinverter. To reduce the THD, suitable current control algorithm

should be employed.

Various inverter current controller/algorithms can be used:- Hysteresis current controllers (HCC),

- Ramp comparison current controllers (RCCC)- Predictive current controllers (PCC).

Different algorithm has different advantages, but certain

disadvantages also exist.

An improved predictive current control algorithm (IPCC) was

presented and applied to the developed PV inverter.



grid Op

load V V dt

di L −=

Grid-connected inverter topology

Govern equation:

Control target: at instant n+1, the real current

equals to the reference current

]1[ +n I load

]1[ref +

n I



Timing scheme of standard PCC

Timing scheme of improved PCC (IPCC)

period

loadref

gridgridop_avT

][]1[]1[5.0][5.1][

n I n I LnV nV nV

−++−−=

Predicted average output voltage:

SVPWM is then employed to realize the current control



START

System Initialization

Main Loop Module

Interrupt Serving

Modules

System

protection

MPPT algorithm

Input & Output

Control

Improved predictivecurrent control

computaion

Signal Sampling

Communication andremote control

SVPWM

Realization

Zero-crossing

Detection

ADC ISR

Capture ISR

PWM

Underflow ISR

Anti-islanding

Algorithm

Timers

Synchronization

Start/Stop

Control

LCD Display

Contactor/Fans

Control



Simulated load current and predictive output voltage

Tested load current and grid voltage



Tested current THD and inverter acoustic noise level

670.912

640.910

631.28.5

591.37

561.75.5

532.44

Noise

[dB(A)]

Current THD

(%)

Output Power

(kW)



FUZZY LOGIC BASED MAXIMUM POWER POINTTRACKING STRATEGY

To pursue a short payback of the PV system investment,extracting as much power as possible from the solar poweris desired, therefore Maximum Power Point Tracking (MPPT)

method should be employed.

Two system parameter-independent methods,Hill-climbing searching (HCS)Fuzzy logic searching (FLS)can be employed to realize the MPPT.

An advanced MPPT method, which combines HCS and FLSwas presented and applied in the developed 10kW PVinverter.



V

IGBT1 IGBT3

IGBT2 IGBT4

Vdc

VdcIload

INVERTER BRIDGE

V VgridL

Vgrid

Iload

Idc

Idc

HCS FLC CCVdc Idm

PWM

MPPT

Schematic diagram of inverter MPPT method.

HCS module: to search the optimal operation points of PV arrays

FLC module: to force follow through adjusting

CC module: current controller (IPCC and SVPWM)

dcV *

dcV dm

I



PROTECTION FUNCTIONS OF PV INVERTER

High operation reliability and comprehensive protectionfunction are critical for the commercialization of PV inverter.Real time fault detection and fast protection is realized by atwo-tier protection mechanism in the developed PV inverter.

Input over voltage/current Grid over/under voltage

Grid frequency fault Islanding operation Output over current Inverter over temperature

Control power supply under voltage…

Main fault conditions of PV inverter:



Two-tier fault detection mechanism is employed:

Software fault detectionHardware fault detection

The threshold settings of the software detection areslightly smaller than that of the hardware detection

When a fault, either a hardware detected one or asoftware detected one, is detected, relays and contactorof the inverter will be triggered.

Employment of two-tier fault detection mechanismsignificantly improve the safety and reliability of the PVinverter



Accelerated phase shift anti-islanding algorithm

Islanding is not desired for the PV inverter used as DGsystem

Anti-islanding protection is integrated in the developed PVinverter.

A novel Accelerated Phase-Shift (APS) algorithm wasproposed and applied to the complete the anti-islandingprotection function.

The proposed APS algorithm creates a quick phase shift

when a grid fails while only generates very small phase shiftwhen grid is normal.



The procedure to investigate islanding of DG system using APS is

as following:

[ ] jALPSθ

[ ]

[ ]⎩

⎨⎧

<+−=Δ

>+−=Δ

0if 01

0if 01

average

average

p

f

ALPS

ALPS

jT T T

jT T T

θ

θ

When islanding occurs and persists, following conditions more likely exist:

The cause and effect (PCE) of above conditions during N cycles

(starting from kth cycle, j=k-1, k, …k+N-1 ) is evaluated, when

PCE is larger than 0.5 at the end of N cycles, then T average

, the

average period during previous N cycles, remain previous value,

and an additional increment phase shift is added to the basic

phase shift to form total phase shift :[ ]k 0θ

A L P S Bθ

[ ]k 0ALPSBALPS θ θ θ += [ ] [ ] ( )T k k Δ⋅Δ+−= sgn100 θ θ θ

( )

⎩

⎨⎧

Δ−

≥Δ+=Δ

0,1

0,1sgn

pT

T T

θ Δ : a small constant[ ]

[ ]⎟⎟

⎠

⎞⎜⎜

⎝

⎛

−

−−=

1

1][

ALPSB

k T

k T T k

averageπ θ [ ]

∑−=

= N

N k i

iT N

T 1

average



[ ]k 0ALPSBALPSθ θ θ += [ ] [ ] ( )T k k Δ⋅Δ+−= sgn100 θ θ θ

During the periods with , each average value of N/2 voltageperiods is monitored. If the difference between two consecutiveN/2 periods is less than a specified value, will be set to 0, andthe computation of is resumed. Otherwise, is enabledbut remains previous value.

[ ]k 0θ

[ ]k 0θ

averageT [ ]k

0θ

averageT

If an island persists, thecalculated willdiverge, through suitableapproach, this diverge can

be detected thus theprotection can be triggered.

ALPSθ

Simulated Results



Laboratory test setup

Tested on the lab-made islanding condition. The presentedAPS anti-islanding algorithm successfully detected theislanding fault. 12 cycles is taken to trip off since theoccurrence of the power island.

The APS algorithm can produce intense positive feedback inthe current phase when a power island occurs while maintainsa tiny random phase shift in grid connected (normal) operation.



DISPLAY AND COMMUNICATION FUNCTIONS

In the developed PV inverter, LEDs and LCD display moduleare employed to indicate the inverter’s information.

Displayed information:

Normal operation: grid voltage/current, output power,generated energy, etc.

Fault condition: fault detail

PIC18F6722 from Microchip Technology is used to build thedisplay module. Communication with DSP and with other

units in the DG system, as well as the remote control throughinternet are also integrated to the module and realizedthrough PIC18F6722.C language is used to program the module.



CONCLUSION

A 10kW grid-connected PV inverter is developed using thepresented innovative techniques. These innovative technicalsolutions include:

Test results of the developed inverter have well verified the

presented algorithms.

Improved predictive current controller for space vectorPWM;

Fuzzy logic based maximum power point tracking;

Comprehensive protection functions including voltage,current, and frequency protections and acceleratedphase shift anti-islanding protection;

Provisions for communications and remote controlthrough internet



Questions and Comments…

Thank You!

development of a 10kw single phase igbt inverter for grid connected pv applications

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