Using Differential Power Processing Converters in Photovoltaic Systems to Improve Lifetime Energy Production

Transcription

1 Using Differential Power Processing Converters in Photovoltaic Systems to Improve Lifetime Energy Production Supported by: Katherine A. Kim Advised by Philip T. Krein Collaboration with Roy Bell, Jason Galtieri, Shibin Qin, Robert Pilawa-Podgurski, Alejandro Domínguez-García February 2014

2 PV Systems in Real-Life Environment 2

3 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 3

4 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 4

5 PV Panels Consist of Substrings [Image Source: GreenSourceGS.com] n = 20 to 24 cells 5

6 PV Operation in Series - Ideal 6

7 PV Operation in Series - Degradation 7

8 PV Operation in Series - Degradation Mismatch causes power loss in strings 8

9 Sources of Panel Mismatch External Variation Partial shading Dust accumulation Temperature differential Angle Differences Internal Variation Manufacturing Cell Degradation Temporary Difficult to predict Difficult to model over lifetime Permanent Can be modeled over lifetime 9

10 PV Variation from Manufacture Wde HiPerforma 240 W W Vd 275 W W Vd SuperPoly 285 W W [Image Source: am.suntech-power.com] 10

11 PV Cell Binning Vd Vd SuperPoly Wde HiPerforma Laborious Adds Cost New panels have some mismatch 11

12 PV Degradation Model Mean, μ Decreases over time 0.5-1% per year (Si) Standard Deviation, σ Increases over time Coefficient of Variation [1] Vazquez and Rey-Stolle,

13 PV Degradation Field Study [2] C. Chamberlin, et al., Degradation linked to current characteristics Coefficient of variation (CV) over lifetime: CV 0 = 0.023, CV 20 = 0.074, CV 25 =

14 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 14

15 Overcoming Mismatch DC Optimizer Panel-level Independent MPP control of each panel Processes 100% power Power rated for panel Maximum output is proportional to efficiency [3] Walker and Sernia, [4] Deline and MacAlpine, [5] Pilawa-Podgurski andperreault,

16 Overcoming Mismatch DPP Subpanel-level Independent MPP control of each string Processes fraction of power Power rating lower than subpanel string Higher output than dc optimizers [6] Shenoy, et al., [7] Stauth, et al., [8] Olalla, et al.,

17 DPP Architectures PV-to-Bus PV-to-PV 17

18 DPP Converter Topologies PV-to-Bus Flyback PV-to-PV Buck-Boost 18

19 Example: Mismatched PV Cells 50 W 42 W 52 W 50 W Total Power 194 W 19

20 Example: Series String Power Output: 183 W, 94.5% Power processed: 0 W 20

21 Example: PV-to-Bus DPP Converter Power Output: 194 W, 100% Power Processed: 10.0 W, 5.2% Power (Current) Rating: 16% 21

22 Example: PV-to-PV DPP Converter PV-to-PV (>10% Rating) Power Output: 194 W, 100% Power Processed: 8.0 W, 4.1% Power (Current) Rating: 10% 22

23 Example: PV-to-Bus DPP Converter 8% Rating Power Output: 194 W, 99.9% Power Processed: 14.7 W, 7.6% 23

24 Example: PV-to-PV DPP Converter 8% Rating Power Output: 194 W, 99.9% Power Processed: 8.0 W, 4.1% 24

25 Research Goals 1. Determine appropriate DPP converter power rating for 25 years of operation 2. Evaluate performance improvement of DPP over series-string and dc optimizer architectures 25

26 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 26

27 DPP Simulation Setup 15 PV substrings (5 PV panels) Monte Carlo Simulation Power variation: 1-20% 100 sets at each 0.5% DPP converters employ active bypass Assumptions Ideal converters MPP known 27

28 PV-to-Bus DPP Architecture Converter Ratings: 22% (75 percentile) 17% (50 percentile) 15% (25 percentile) 28

29 PV-to-PV DPP Architecture Converter Ratings: 33% (75 percentile) 23% (50 percentile) 18% (25 percentile) 29

30 Converter Ratings Scale with System 30

31 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 31

32 Performance Improvement Metric Improvement Figure of Merit (IFoM) Power increase over series-string IFoM = 1 : Same as series-string performance IFoM > 1 : Better than series-string DPP architecture power output Series-string power output 32

33 PV-to-Bus DPP Performance 33

34 PV-to-PV DPP Performance 34

35 Number of DPP Modules Operating at MPP PV-to-Bus PV-to-PV 35

36 Improvement Distribution at 25-Year Variation 36

37 PV variation Findings CV for new panels CV after 25 years of operation PV-to-bus converters rated at 15-17% PV-to-PV converters rated at 23-33% At 25 years, DPP converters provide 6% more power than series string Over 25 years, DPP converter harvest 2.8% more energy [9] Katherine A. Kim, Pradeep S. Shenoy, and Philip T. Krein. Converter rating analysis for photovoltaic differential power processing systems. Submitted to IEEE Trans. Power Electron.,

38 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 38

39 Power Electronics for Mobile PV Applications PV-Powered Electric/Hybrid Vehicles PV-Powered Wearable Electronics [Image Source: wired.com] [Image Source:

40 Challenges of Mobile PV Applications Uneven Illumination Mismatch among PV cells Angle differences Shading Temperature gradient Series-string does not handle mismatch well Illumination Transients Extreme changes Frequent Traditional maximum power point tracking methods are slow 40

41 Potential Solutions Uneven Illumination: Parallel PV DPP Converters Illumination Transients: Voltage-Offset Resistive Control 41

42 Outline I. Mismatch in Photovoltaic (PV) Systems II. Differential Power Processing (DPP) Converters III. DPP Converter Power Rating IV. Improvement with DPP Converters V. Future Research Directions VI. Conclusion and Contributions 42

43 Contributions 1. Identified realistic CV value for PV variation over a 25-year lifetime 2. Outlined procedure to identify DPP converter power ratings for any size PV system 3. Identified 15-17% PV-to-bus and 23-33% PVto-PV converters increase 25-year energy harvest by 2.8% 4. Proposed application of DPP converters and advanced control in mobile PV applications Questions? 43