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

2. Presentation Outline Project Summary Project Motivation
Overall System Block Diagram
Boost Converter
Inverter
Future Work

3. 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

4. Project Motivation Power Electronics Alternative Energy Sources
Useful Applications
Household grid-tie inverter
Electric drives

5. System Block Diagram

6. BP350J PV Panel Pmax = 50W Voltage at Pmax = 17.5V
Current at Pmax = 2.9A
Nominal Voltage = 12V
Isc = 3.2A
Voc = 21.8V

7. 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%.

8. Boost Converter
Test Boost Converter
20V to 66V D = .3

9. Boost Converter Design

10. Hardware

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

12. Gate Driver
IR2110

13. Boost Converter Simulations
Output Voltage (V)
20V – 66V

14. Boost Converter Simulations
Boost Converter Current (A)
20V-66V

15. Boost Converter Testing
10V to 16.5V
40% Duty Cycle
Output Voltage
Inductor Current

16. 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

17. Increasing Turn off Time
Turn off time increased from 92 ns to 312 ns

18. Determining RC snubber values

19. Reducing Voltage Spikes
20V to 66V % duty
Without Gate Resistor And RC Snubber
With Gate Resistor And RC Snubber

20. Boost Converter Current
Efficiency = 60.7%
Efficiency = 58.1%
Without RC snubber and Gate Resistor
With RC snubber and Gate Resistor

21. Future Work For Boost Converter
Optimize inductor value
Printed Circuit Board Layout
Optimize RC snubber values
Test with multiple solar panels

22. 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 it’s most efficient point I V
MPP P V

23. Perturb and Observe (P&O)
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

24. P&O ΔP ΔD D+ + -

25. 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

26. Implementing MPPT Spectrum Digital eZdsp F2812 Voltage Sensing
Current Sensing
Matlab Simulink Modeling with Code Composer Studio

27. 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

28. Voltage Sensing
Vpv is 0 to 24V
VADC 0 to 3.3V

29. Current Sensing
Ipv: 0 to 50A
Vout: 0 to 4V

30. Simulink Model ADC measurement P&O Voltage and current every 100μs
Mean value with running window of 1Hz

31. Simulink Model
Soft Start

32. 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

33. 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

34. Power Supply Transformer (3FL20-125) Secondary Voltage of 10VAC
Secondary Current of 0.25A RMS

35. Power Supply

36. AC Subsystem Overview

37. AC Subsystem Goals
DC power to AC power
AC power quality

38. 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%.

39. Topology - Inverter
Single-phase bridge inverter

40. Switching Logic Desire to control Output frequency Output magnitude
 Sinusoidal PWM!

41. Theory of Sinusoidal (Bipolar) PWM
The magnitude of a triangle carrier signal is compared to a sinusoidal reference
If Vreference > Vcarrier PWM = high
If Vreference < Vcarrier PWM = low
A complementary signal drives opposite leg of H-bridge

42. Unipolar Sinusoidal PWM
Two sinusoids compared to a triangle reference
Each comparison drives one H-bridge leg respectively

43. Unipolar PWM in Action Two comparisons
Each leg of H-bridge driven independently
3-level output
Less harmonic distortion than bipolar PWM

44. Design Equations Modulation index, mi Frequency Modulation ratio, mf
Fundamental Output Magnitude
Output Frequency

45. Implications mi can be used to control output magnitude (voltage)
Typically 0 < mi ≤ 1
Overmodulation if mi > 1 (non-linear operation)
Useful for obtaining large output power, but harmonic distortion will be large

46. 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

47. Output Desire sinusoidal output Use a filter
Output isn’t very sinusoidal
Use a filter
LC filter

48. LC Filter Goal: Smooth inverter output to smooth AC
Second order LC filter transfer function: G(s) = 1/(L*C*s^2+1)
fcarrier < cutoff frequency < fcarrier ∙ mf

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

50. PSIM Schematic (Bipolar PWM)
mi = 0.8
mf = 11
Vd = 200 V

51. PSIM Schematic (Unipolar PWM)
mi = 0.8
mf = 10
Vd = 200 V

52. Simulation Result – Vout (unfiltered)
Bipolar PWM
Unipolar PWM

53. Simulation Results (filtered)
Bipolar PWM
Unipolar PWM
fout = 60 Hz (both cases)

54. Bipolar PWM – Frequency Domain
Unfiltered Output
Filtered Output
mi = 0.8
mf = 81

55. Unipolar PWM – Frequency Domain
Unfiltered Output
Filtered Output
mi = 0.8
mf = 80

56. Implementation Major Hardware Components
IGBT
Gate Drive
LC Filter
Spectrum Digital eZdsp F2812
Texas Instruments TMS320F2812
Simulink, Code Composer Studio

57. IGBT International Rectifier IRG4PC30UDPbF VCEmax = 600 V
fswitching max = 40 kHz
ICmax = 12 A
Cost = $2-3 each

58. Gate Drive International Rectifier IR2110 Drives Two IGBTs/MOSFETs
Cost $3 each

59. LC Filter
L = 1 mH C = 100 μF
fcutoff ≈ 500 Hz
Cost of components = $6

60. Sinusoidal PWM – Simulink

61. Experimental Results Bipolar PWM Vd = 10V (DC) Vout = 13.6V (AC)
mi=0.8
mf = 83

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

63. Special thanks to:
Dr. In Soo Ahn
Mr. Steve Gutschlag

64. 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 <
Tafticht, T., K. Agbossou, M. Doumbia, and A. Cheriti. "An Improved Maximum Power Point Tracking Method for Photovoltaic Systems." Renewable Energy 33.7 (2008):
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.

65. Questions?