Photovoltaic Power Converter

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Photovoltaic Power Converter
Advisors Dr. Woonki Na Dr. Brian Huggins
Students Thomas Carley Luke Ketcham Brendan
Zimmer
Bradley University Department Of Electrical
Engineering 5/1/12
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Presentation Outline

• Project Summary
• Project Motivation
• Overall System Block Diagram
• Boost Converter
• Inverter
• Future Work

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Project Summary

• Photovoltaic Array
• Supplies DC and AC Power
• Boost Converter to step up PV voltage
• Maximum Power Point Tracking
• DC-AC converter for 120Vrms 60Hz
• LC filter

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Project Motivation

• Power Electronics
• Alternative Energy Sources
• Useful Applications
• Household grid-tie inverter
• Electric drives

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System Block Diagram
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BP350J PV Panel

• Pmax 50W
• Voltage at Pmax 17.5V
• Current at Pmax 2.9A
• Nominal Voltage 12V
• Isc 3.2A
• Voc 21.8V

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DC Subsystem Requirements

• The boost converter shall accept a voltage from
  the photovoltaic cells.
• The input voltage shall be 48 Volts.
• The average output shall be 200 Volts /- 25
  Volts.
• The voltage ripple shall be less than 20 Volts
• The open-loop boost converter shall operate above
  65 efficiency.
• The boost converter shall perform maximum power
  point tracking.
• The PWM of the boost converter shall be regulated
  based on current and voltage from the PV array.
• The efficiency of the MPPT system shall be above
  80.

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Boost Converter
Test Boost Converter 20V to 66V D .3
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Boost Converter Design
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Hardware
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Key Components

• MOSFET (IRFP4768PbF)
• VDSS 250V Id 93A
• Ultrafast Diode (HFA50PA60C)
• VR 600V If 25A Trr 50ns
• Inductors (3mH)
• Capacitors (6000uF)

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Gate Driver

• IR2110

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Boost Converter Simulations
Output Voltage (V) 20V 66V
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Boost Converter Simulations
Boost Converter Current (A) 20V-66V
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Boost Converter Testing
10V to 16.5V 40 Duty Cycle
Output Voltage
Inductor Current
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Eliminating Voltage Spikes

• Parasitic capacitance and inductance
• Diode forward recovery time
• Circuit Layout
• Add Gate Resistor to increase turn-on and
  turn-off time
• Add RC snubber

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Increasing Turn off Time
Turn off time increased from 92 ns to 312 ns
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Determining RC snubber values
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Reducing Voltage Spikes
20V to 66V 70 duty
Without Gate Resistor And RC Snubber
With Gate Resistor And RC Snubber
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Boost Converter Current
Efficiency 60.7
Efficiency 58.1
With RC snubber and Gate Resistor
Without RC snubber and Gate Resistor
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Future Work For Boost Converter

• Optimize inductor value
• Printed Circuit Board Layout
• Optimize RC snubber values
• Test with multiple solar panels

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Maximum Power Point Tracking (MPPT)

• Every PV has a V-I and P-V curve for a given
  insolation and temperature
• The MPP is seen clearly from the P-V curve
• Anytime the system is not at the MPP, it is not
  at its most efficient point

I
V
MPP
P
V
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Perturb and Observe (PO)

• Slight voltage perturbation
• Observation of
• Change in PV power
• Change in boost converter duty cycle
• Make an increase or decrease in boost converter
  duty cycle based on observation

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PO
?P ?D D

- -
- -
- -
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MPPT Algorithm Comparison

• Perturb and Observe
• Pros
• Very popular
• Simple to implement
• Con
• Power loss from perturbation
• Incremental Conductance
• Pro
• Tracks a rapidly changing MPP
• Cons
• Increased complexity
• Increased susceptibility to noise

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Implementing MPPT

• Spectrum Digital eZdsp F2812
• Voltage Sensing
• Current Sensing
• Matlab Simulink Modeling with Code Composer Studio

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eZdsp F2812 features

• Texas Instruments TMS320F2812 chip
• 32-bit DSP Core 150 MIPS
• 18K 64K RAM
• 128K Flash
• 30 MHz clock
• 12 PWM outputs
• 16 ADC 12 bit inputs
• 60 ns conversion time

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Voltage Sensing

• Vpv is 0 to 24V
• VADC 0 to 3.3V

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Current Sensing

• Ipv 0 to 50A
• Vout 0 to 4V

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Simulink Model
PO

• ADC measurement
• Voltage and current every 100µs
• Mean value with running window of 1Hz

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Simulink Model
Soft Start
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MPPT and Soft Start Results

• Soft start duty cycle control
• 0 to 30
• 5 increase every 5 seconds
• Transition to MPPT after 40 seconds
• MPPT duty cycle control
• ADC measurements
• Voltage and current every 100µs
• Mean value with running window of 1Hz
• 1 increase/decrease every 1 second

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Power Supplies

• 120Vrms 60Hz input from wall
• 15V, 5V, and 3.3V output
• Consists of Transformer, Diode Rectifier, 470uF
  capacitor, and voltage regulators
• Needed for Gate Drivers, Op Amps, Sensing ICs,
  and other logic devices

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Power Supply

• Transformer (3FL20-125)
• Secondary Voltage of 10VAC
• Secondary Current of 0.25A RMS

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Power Supply
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AC Subsystem Overview
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AC Subsystem Goals

• DC power to AC power
• AC power quality

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AC Subsystem Requirements

• The AC side of the system shall invert the output
  of the boost converter.
• The output of the inverter shall be AC voltage.
• The output shall be 60Hz /- 0.1Hz.
• The inverter output shall be filtered by a LC
  filter.
• The filter shall remove high switching frequency
  harmonics.
• Total harmonic distortion of the output shall be
  less than 15.

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Topology - Inverter
Single-phase bridge inverter
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Switching Logic

• Desire to control
• Output frequency
• Output magnitude
• ? Sinusoidal PWM!

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Theory of Sinusoidal (Bipolar) PWM

• The magnitude of a triangle carrier signal is
  compared to a sinusoidal reference
• If Vreference gt VcarrierPWM high
• If Vreference lt VcarrierPWM low

A complementary signal drives opposite leg of
H-bridge
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Unipolar Sinusoidal PWM

• Two sinusoids compared to a triangle reference
• Each comparison drives one H-bridge leg
  respectively

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Unipolar PWM in Action

• Two comparisons
• Each leg of H-bridge driven independently
• 3-level output
• Less harmonic distortion than bipolar PWM

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Design Equations

• Fundamental Output Magnitude
• Output Frequency

• Modulation index, mi
• Frequency Modulation ratio, mf

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Implications

• mi can be used to control output magnitude
  (voltage)
• Typically 0 lt mi 1
• Overmodulation if mi gt 1 (non-linear operation)
• Useful for obtaining large output power, but
  harmonic distortion will be large

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Implications

• Output Frequency
• Can select mf to remove even harmonics from
  output spectrum
• For Bipolar PWM, mf odd integer
• For Unipolar PWM, mf even integer

Example (Unipolar) fcarrier 60 Hz ftriangle
2520 Hz mf 42
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Output

• Desire sinusoidal output
• Output isnt very sinusoidal
• Use a filter
• LC filter

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LC Filter

• Goal Smooth inverter output to smooth AC
• Second order LC filter transfer function G(s)
  1/(LCs21)
• fcarrier lt cutoff frequency lt fcarrier mf

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Simulation

• PSIM, Circuit Simulation Software
• Proof of concept simulations
• Bipolar PWM vs. Unipolar PWM
• Effectiveness of LC filter with both schemes

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PSIM Schematic (Bipolar PWM)
mi 0.8 mf 11 Vd 200 V
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PSIM Schematic (Unipolar PWM)
mi 0.8 mf 10 Vd 200 V
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Simulation Result Vout (unfiltered)
Bipolar PWM
Unipolar PWM
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Simulation Results (filtered)
Bipolar PWM
Unipolar PWM
fout 60 Hz (both cases)
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Bipolar PWM Frequency Domain
Unfiltered Output
Filtered Output
mi 0.8 mf 81
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Unipolar PWM Frequency Domain
Unfiltered Output
Filtered Output
mi 0.8 mf 80
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Implementation Major Hardware Components

• IGBT
• Gate Drive
• LC Filter
• Spectrum Digital eZdsp F2812
• Texas Instruments TMS320F2812
• Simulink, Code Composer Studio

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IGBT

• International Rectifier IRG4PC30UDPbF
• VCEmax 600 V
• fswitching max 40 kHz
• ICmax 12 A
• Cost 2-3 each

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Gate Drive

• International Rectifier IR2110
• Drives Two IGBTs/MOSFETs
• Cost 3 each

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LC Filter
L 1 mHC 100 µF fcutoff 500 Hz
Cost of components 6
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Sinusoidal PWM Simulink
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Experimental Results
Bipolar PWM Vd 10V (DC) Vout 13.6V
(AC) mi0.8 mf 83
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Future Work

• Closed-loop MPPT control with PV input
• Inverter voltage and current controller
• Tying the inverter to the grid
• Phase Locked Loop (PLL)

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• Special thanks to
• Dr. In Soo Ahn
• Mr. Steve Gutschlag

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References

• PV Module Simulink Models. ECEN2060. University
  of Colorado Boulder.
• Rozenblat, Lazar. "A Grid Tie Inverter for Solar
  Systems." Grid Tie Inverter Schematic and
  Principles of Operation. 6 Oct. 2011.
  lthttp//solar.smps.us/grid-tie-inverter-schematic.
  htmlgt.
• Tafticht, T., K. Agbossou, M. Doumbia, and A.
  Cheriti. "An Improved Maximum Power Point
  Tracking Method for Photovoltaic Systems."
  Renewable Energy 33.7 (2008) 1508-516.
• Tian, Yi. ANALYSIS, SIMULATION AND DSP BASED
  IMPLEMENTATION OF ASYMMETRIC THREE-LEVEL
  SINGLE-PHASE INVERTER IN SOLAR POWER SYSTEM.
  Thesis. Florida State University, 2007. 
• Zhou, Lining. EVALUATION AND DSP BASED
  IMPLEMENTATION OF PWM APPROACHES FOR SINGLE-PHASE
  DC-AC CONVERTERS. Thesis. Florida State
  University, 2005.

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Questions?