Photovoltaic Power Converter

1
Photovoltaic Power Converter

• Students
• Thomas Carley
  
• Luke Ketcham
• Brendan Zimmer
• Greg Landgren

Advisors Dr. Woonki Na Dr. Brian Huggins Dr.
Yufeng Lu
Bradley University Department Of Electrical
Engineering 11/30/11
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Presentation Outline

• Summary and Overall System Block Diagram
• DC Subsystem
• Maximum Power Point Tracking
• Boost Converter Testing
• AC Subsystem
• Schedule
• Component List

3
Project Summary

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

4
System Block Diagram
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DC Subsystem

• Boost Converter
• Maximum Power Point Tracking (MPPT) System

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Simulation Results
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Boost Converter Full Bridge
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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 3 Volts
• 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
  85.

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DC Subsystem Key Components

• Inductor
• 1mH 25A
• 500uH 35A
• Gate Driver
• MOSFET or IGBT
• 2.5A 500V
• Solar Panel x 4
• 50W
• 12V

• MOSFET
• Vds 250V
• Id 110A
• Pdiss 694W
• Heatsink

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DC Subsystem Components

• Current Sensor
• 30A
• 63-69 mV/A
• Sensing Op amp
• Used with voltage divider
• DSP Board
• TMS320F2812

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MPPT

• Perturb and Observe method
• Change Boost Converter duty cycle based on change
  in PV power
• Changing duty cycle changes the current drawn
  from the PV
• Anytime the system is not at themaximum power
  point, it is notat its most efficient point

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MPPT Flowchart
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Boost Without MPPT
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Boost With MPPT
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MPPT Circuit
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Output Power Without MPPT
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Output Power With MPPT
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PV Models in Simulink

• Made models of PVs using resources from the
  University of Colorado at Boulder
• Insolation a measure of solar energy on an area
  over a given amount of time.
• Usually in units of W/m2

Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL Solar Insolation Peoria, IL
  Jan Feb March April May June July Aug Sep Oct Nov Dec
kWh/(m2 day) 3.271 4.109 4.642 4.921 5.239 5.740 5.880 5.727 5.639 4.562 2.957 2.721
W/m2 136.292 171.208 193.417 205.042 218.292 239.167 245.000 238.625 234.958 190.083 123.208 113.375
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I
P
V
V
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Insolation 200, 400, 600, 800, 1000 W/m2
P
I
V
V
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I
V
P
V
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Boost Converter Lab Testing

• Built boost converter from components Dr. Na
  provided.

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Boost Converter Lab Testing

• 0 to 3.3V signal from DSP board controlling the
  MOSFET
• At a switching frequency of 10kHz with a 50 duty
  cycle the 5V input voltage was boosted to about
  10V.
• Increasing duty cycle, increased Vout
• Decreasing duty cycle, decreased Vout
• After testing this setup we will be able to build
  our Boost converter circuit quickly.

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DSP Board Programming

• Spectrum Digital eZdsp F2812
• Texas Instruments Code Composer
• Matlab/Simulink

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Simulink A/D Interfacing
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Simulink PWM Generation
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Manual PWM Duty Ratio Control
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PWM GenerationExperimental Results
80 Duty Ratio
30 Duty Ratio
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AC Subsystem

• Inverter
• Output filter

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AC Subsystem - Inverter

• Inverter topology
• Inverter operation
• Simulations

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AC SubsystemInverter Topology
Inverter single phase H-bridge
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AC SubsystemInverter Operation - Bipolar

• A reference sinusoidal waveform is compared to a
  triangular carrier waveform
• When the reference voltage is equal to the
  carrier voltage a transition in the switching
  signal occurs

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AC SubsystemInverter Operation - Bipolar
Simulation schematic
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AC SubsystemInverter Operation - Bipolar
Reference (blue) and carrier (red) waveforms
Switching signal
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AC SubsystemInverter Operation - Bipolar
Inverter output. Switches from Vd to -Vd
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AC SubsystemInverter Operation - Bipolar

• Switching signal is inverted and fed to other
  pair of switches
• Switch pairs are switched simultaneously
• Only one reference signal needed, but performance
  is poor

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AC SubsystemInverter Operation - Unipolar

• Two reference sinusoids are compared to a
  triangular waveform
• Switch pairs not switched simultaneously

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AC SubsystemInverter Operation - Unipolar
Simulation schematic
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AC SubsystemInverter Operation - Unipolar
References and carrier waves Switching signal
1 Switching signal 2 Output
Image source Tian
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Inverter Operation - Comparison
Bipolar harmonic output
Unipolar harmonic output
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AC Subsystem - Output Filter

• Inverter output includes switching harmonics
• Filter smoothes output

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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 120 Volts
  RMS.
• 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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AC Subsystem Key Components

• Inverter switches
• Gate drives
• Power supplies

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Commercial Grid Tie Inverters
Company SMA Solar Technology Xantrex
Product Sunny Boy 700-US GT2.8
AC Power 460W, 120Vac 2700 W, 208Vac / 2800W, 240Vac
AC Voltage Output 106 - 132 Vac 183 - 229 Vac / 211 - 264 Vac
Output Frequency 59.3 - 60.5 Hz 59.3 - 60.5 Hz
Harmonics gt 3 gt 3
Max. efficiency 92.4 94.6
Power Factor Unity gt 0.95
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Schedule
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Component List
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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?