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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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Schematic diagram of the developed PV inverter
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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Simulated load current and predictive output voltage
Tested load current and grid voltage
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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)
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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:
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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[ ]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
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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.
8/9/2019 Development of a 10kw Single Phase Igbt Inverter for Grid Connected Pv Applications
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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