IGBT Based Single-Phase Quasi Z-Source Inverter for PV.pptx
1. IGBT BASED SINGLE-PHASE QUASI Z-SOURCE
INVERTER FOR PV
CYCLE 1 – EXPERIMENT NO.2
DR. D.UMARANI AND DR.ALAGU DHEERAJ
2. WHAT IS AN INVERTER?
A static device that converts DC power into AC power at desired
output voltage and frequency is called an Inverter.
Few Applications:
Adjustable speed AC drives
Induction Heating
Aircraft power supplies
UPS etc….
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3. CLASSIFICATION OF INVERTERS
Inverters can be broadly classified into two types. They are
Voltage Source Inverter(VSI) - When the DC voltage remains
constant, then it is called Voltage Source Inverter(VSI) or Voltage
Fed Inverter (VFI).
Current Source Inverter(CSI) - When input current is maintained
constant, then it is called Current Source Inverter (CSI) or Current
Fed Inverter (CFI).
Some times, the DC input voltage to the inverter is controlled to
adjust the output. Such inverters are called Variable DC Link Inverters.
The inverters can have single-phase or three-phase output.
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4. NEED FOR PV INVERTERS
Grid-connected PV systems turned out to be the promising renewable energy
generation system in recent days.
To transfer energy from PV array to utility grid, the power conditioning unit
(Inverter) has to fulfill the following requirements:
1) To convert the DC voltage into AC voltage;
2) To boost the voltage, if the PV array voltage is lower than the grid voltage;
3) To ensure maximum power delivery of the PV modules.
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5. DRAWBACKS IN A CONVENTIONAL INVERTER
The ac output voltage of the VSI is limited below the input voltage, i.e., the VSI is a buck type inverter
which cannot serve the need of distributed generation and ac drives alone.
It requires an additional dc–dc boost converter to obtain a desired ac output, which increases system
cost and lowers efficiency.
In addition, the switching devices are vulnerable to electromagnetic interference as misgating-on causes
short-circuit across the inverter bridge and destroys the switching devices.
The dead time introduced in such cases causes waveform distortion at the output.
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6. DRAWBACKS IN A CONVENTIONAL INVERTER
On the other hand, in the case of the CSI, the output voltage cannot be less than the
input voltage.
For applications where a wide voltage range is desirable, an additional dc–dc buck
converter is needed.
In addition, the upper and lower switches of the inverter have to be gated on and
maintained on at any time.
Otherwise, an open circuit of the dc inductor would occur and destroy the devices.
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7. IMPEDANCE SOURCE INVERTERS
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IMPEDANCE networks provide an efficient means of power
conversion between source and load in a wide range of
electric power conversion applications.
The impedance-source network was originally invented to
overcome the limitations of the voltage-source inverter
(VSI) and current-source inverter (CSI) topologies which
are commonly used in electric power conversion.
11. QUASI Z-SOURCE INVERTER
Quasi Z-Source Inverter (qZSI) is a sub topology derived from the traditional impedance source inverter
called ZSI.
It inherits all the advantages of the ZSI, realize buck/boost operation, power conversion and power
conditioning with improved reliability in a single stage.
It also has the advantages such as lower component ratings and draws continuous current from the
PV/DC source.
All the boost control methods that are applied to ZSI are also applicable to qZSI.
The qZSI features a wide range of voltage gain that makes it suitable topology for applications in
photovoltaic (PV) systems, because of the fact that the PV array output power varies with variation in
temperature and solar irradiation.
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12. ADVANTAGES OF QUASI Z-SOURCE INVERTER
It can operate as buck or boost inverter.
There is no need of dead time between switching of the devices.
It can operate in shoot-through state by converting some of the zero states of the conventional PWM.
During this period, the input voltage is boosted by the impedance network.
It draws continuous input current from the PV source that is required for PV applications.
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17. SIMPLE BOOST TECHNIQUE
In this technique,
The PWM pulses are generated when the amplitude of sine wave (reference wave) is greater than triangle
carrier.
The Shoot-Through (ST) pulses are generated when the carrier wave is greater or lesser than the two
constant DC lines.
The PWM pulses and shoot-through pulses are logically ORed to get the final pulses.
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19. SHOOT-THROUGH DUTY RATIO
Each switching cycle will have a shoot through period (Ts) and a non-shoot through period (To).
With T as the time period, we have T= Ts+To
Ds=Ts /T
Do=To/T (i.e) Ds+Do=1
Ds is the shoot through duty ratio and Do is the non-shoot through duty ratio.
The maximum shoot-through duty ratio of the simple boost control is limited to
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25. PERFORMANCE PARAMETERS
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Modulation Index, Ma 0.6 0.7 0.8 0.9
Voltage gain, G
Boost Factor, B
Shoot through duty ratio,
Do
Voltage Stress (V)
Inverter Output Voltage
(V)
Output Voltage with
Filter (V)
THD %
26. PLOTS BETWEEN PERFORMANCE PARAMETERS
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Boost Factor
Vs
Duty Ratio
Modulation Index
Vs
Voltage Gain
27. EXPERIMENT-PROCEDURAL STEPS
Connect the circuit elements as per the circuit diagram.
Apply the input voltage from the PV panel.
Apply the pulses (Simple Boost PWM) to the IGBT’s of the Quasi Z-Source Inverter.
Using CRO/DSO, obtain the output voltage waveform.
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28. GATING CIRCUIT
The gating circuit is essentially important for providing the gate pulses to the IGBT‟s used in the inverter
in order to isolate the low power pulse circuit and high power inverter circuit.
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32. EXPERIMENT OUTCOME
To Understand the operation of Impedance Source Inverters and Quasi Impedance source Inverters
To understand the operating states of Quasi Impedance source Inverters
To generate pulses using simple boost technique and evaluate the performance parameters of the Quasi
Impedance source Inverters.
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