DOI QR코드

DOI QR Code

Optimized Hybrid Modulation Strategy for AC Bypass Transformerless Single-Phase Photovoltaic Inverters

  • Deng, Shuhao (Department of Information Science and Engineering, Central South University) ;
  • Sun, Yao (Department of Information Science and Engineering, Central South University) ;
  • Yang, Jian (Department of Information Science and Engineering, Central South University) ;
  • Zhu, Qi (Department of Information Science and Engineering, Central South University) ;
  • Su, Mei (Department of Information Science and Engineering, Central South University)
  • Received : 2016.01.07
  • Accepted : 2016.08.24
  • Published : 2016.11.20

Abstract

The full-bridge inverter, widely used for single-phase photovoltaic grid-connected applications, presents a leakage current issue. Therefore, an AC bypass branch is introduced to overcome this challenge. Nevertheless, existing modulation strategies entail drawbacks that should be addressed. One is the zero-crossing distortion (ZCD) of the AC current caused by neglecting the AC filter inductor voltage. Another is that the system cannot deliver reactive power because the AC bypass branch switches at the power frequency. To address these problems, this work proposes an optimized hybrid modulation strategy. To reduce ZCD, the phase angle of the inverter output voltage reference is shifted, thereby compensating for the neglected leading angle. To generate the reactive power, the interval of the negative power output is calculated using the power factor. In addition, the freewheeling switch is kept on when power is flowing into the grid and commutates at a high frequency when power is fed back to the DC side. In this manner, the dead-time insertion in the high-frequency switching area is minimized. Finally, the performances of the proposed modulation strategy and traditional strategies are compared on a universal prototype inverter. Experimental results validate the theoretical analysis.

Acknowledgement

Supported by : National Natural Science Foundation of China, Natural Science Foundation of Hunan Province of China, Central South University

References

  1. M. Islam, S. Mekhilef, and M. Hasan, "Single phase transformer less inverter topologies for grid-tied photovoltaic system: A review," Renewable and Sustainable Energy Reviews, Vol. 45, pp. 69-86, May 2015. https://doi.org/10.1016/j.rser.2015.01.009
  2. W. Li, Y. Gu, H. Luo, W. Cui, X. He, and C. Xia, "Topology review and derivation methodology of single-phase transformer less photovoltaic inverters for leakage current suppression," IEEE Trans. Ind. Electron., Vol. 62, No. 7, pp.4537-4551, Jul. 2015. https://doi.org/10.1109/TIE.2015.2399278
  3. W. J. Cha, K. T. Kim, Y. W. Cho, S. H. Lee, and B. H. Kwon, "Evaluation and analysis of transformerless photovoltaic inverter topology for efficiency improvement and reduction of leakage current," IET Power Electronics, Vol. 8, No. 2, pp. 255-267, Feb. 2015. https://doi.org/10.1049/iet-pel.2014.0401
  4. D. Meneses, F. Blaabjerg, O. Garcia, and J. A. Cobos, "Review and comparison of step-up transformerless topologies for photovoltaic AC-module application," IEEE Trans. Power Electron., Vol. 28, No. 6, pp. 2649-2663, Jun. 2013. https://doi.org/10.1109/TPEL.2012.2227820
  5. Z. Ozkan and A. M. Hava. "A survey and extension of high efficiency grid connected transformerless solar inverters with focus on leakage current characteristics," in IEEE Energy Conversion Congress and Exposition (ECCE), pp. 3453-3460, Sep. 2012.
  6. H. Xiao and S. Xie, "Leakage current analytical model and application in single-phase transformerless photovoltaic grid-connected inverter," IEEE Trans. Electromagn. Compat., Vol. 52, No. 4, pp. 902-913, Nov. 2010. https://doi.org/10.1109/TEMC.2010.2064169
  7. J. C. Hernandez, P. G. Vidal, and A. Medina, "Characterization of the insulation and leakage currents of PV generators: Relevance for human safety," Renewable Energy, Vol. 35, No. 3, pp. 593-601, Mar. 2010. https://doi.org/10.1016/j.renene.2009.08.006
  8. (2011)[Online].Available:http://www.vde-verlag.de/standards/0105029/vde-ar-n-4105-anwendungsregel-2011-08-html.
  9. R. Gonzalez, J. Lopez, P. Sanchis, and L. Marroyo, "Transformerless inverter for single-phase photovoltaic systems," IEEE Trans. Power Electron., Vol. 22, No. 2, pp. 693-697, Mar. 2007. https://doi.org/10.1109/TPEL.2007.892120
  10. M. Victor, F. Greizer, S. Bremicker, and U. Hubler, "Method of converting a direct current voltage from a source of direct current voltage, more specifically from a photovoltaic source of direct current voltage, into an alternating current voltage," U.S. Patent No. 7 411 802. B2, Aug. 2008.
  11. H. Xiao, S. Xie, Y. Chen, and R. Huang, "An optimized transformerless photovoltaic grid-connected inverter," IEEE Trans. Ind. Electron., Vol. 58, No. 5, pp. 1887-1895, May 2011. https://doi.org/10.1109/TIE.2010.2054056
  12. B. Yang, W. Li, Y. Gu, W. Cui, and X. He, "Improved transformerless inverter with common-mode leakage current elimination for a photovoltaic grid-connected power system," IEEE Trans. Power Electron., Vol. 27, No. 2, pp. 752-762, Feb. 2012. https://doi.org/10.1109/TPEL.2011.2160359
  13. T. Kerekes, R. Teodorescu, P. Rodriguez, G. Vazquez, and E. Aldabas, "A new high-efficiency single-phase transformerless PV inverter topology," IEEE Trans. Ind. Electron., Vol. 58, No.1, pp. 184-191, Jan. 2011. https://doi.org/10.1109/TIE.2009.2024092
  14. H. F. Xiao, K. Lan, and L. Zhang, "A quasi-unipolar SPWM full-bridge transformerless PV grid-connected inverter with constant common-mode voltage," IEEE Trans. Power Electron., Vol. 30, No. 6, pp. 3122-3132, Jun. 2015. https://doi.org/10.1109/TPEL.2014.2331367
  15. H. Schmidt, C. Siedle, and J. Ketterer, "Wechselrichter zum Unwandeln einer elektrischen Gleichspannung in einen Wechselstrom oder eine Wechselspannung," EP Patent 2086102A2, 2003.
  16. W. Yu, J. S. J. Lai, H. Qian, and C. Hutchens, "High-efficiency MOSFET inverter with H6-type configuration for photovoltaic nonisolated AC-module applications," IEEE Trans. Power Electron., Vol. 26, No. 4, pp. 1253-1260, Apr. 2011. https://doi.org/10.1109/TPEL.2010.2071402
  17. B. Ji, J. Wang, and J. Zhao, "High-efficiency single-phase transformerless PV H6 inverter with hybrid modulation method," IEEE Trans. Ind. Electron., Vol. 60, No.5, pp. 2104-2115, May 2013. https://doi.org/10.1109/TIE.2012.2225391
  18. M. Islam and S. Mekhilef, "H6-type transformerless single-phase inverter for grid-tied photovoltaic system," IET Power Electronics, Vol. 8, No. 4, pp. 636-644, Apr. 2015. https://doi.org/10.1049/iet-pel.2014.0251
  19. H. Xiao, X. Liu, and K. Lan. "Optimized full-bridge transformerless photovoltaic grid-connected inverter with low conduction loss and low leakage current," IET Power Electronics, Vol. 7, No. 4, pp. 1008-1015, Apr. 2014. https://doi.org/10.1049/iet-pel.2013.0404
  20. M. Islam and S. Mekhilef, "A new high efficient transformerless inverter for single phase grid-tied photovoltaic system with reactive power control," in IEEE Applied Power Electronics Conference and Exposition (APEC), Mar. 2015.
  21. Y. Yang, H. Wang, and F. Blaabjerg, "Reactive power injection strategies for single-phase photovoltaic systems considering grid requirements," IEEE Trans. Ind. Appl., Vol. 50, No. 6, pp. 4065-4076, Nov./Dec. 2014. https://doi.org/10.1109/TIA.2014.2346692
  22. F. Wu, B. Sun, K. Zhao, and L. Sun, "Analysis and solution of current zero-crossing distortion with unipolar hysteresis current control in grid-connected inverter," IEEE Trans. Ind. Electron., Vol. 60, No. 10, pp. 4450-4457, Oct. 2013. https://doi.org/10.1109/TIE.2012.2217720
  23. F. Wu, X. Li, and J. Duan, "Improved elimination scheme of current zero-crossing distortion in unipolar hysteresis current controlled grid-connected inverter," IEEE Trans. Ind. Informat., Vol. 11, No. 5, pp. 1111-1118, Oct. 2015. https://doi.org/10.1109/TII.2015.2470540
  24. T.-F. Wu, C.-L. Kuo, K.-H. Sun, and H.-C. Hsieh, "Combined unipolar and bipolar PWM for current distortion improvement during power compensation," IEEE Trans. Power Electron., Vol. 29, No. 4, pp. 1702-1709, Apr. 2014. https://doi.org/10.1109/TPEL.2013.2265399