Power Quality Improvement for Grid Connected Inverters under Distorted and Unbalanced Grids

Kim, Hyun-Sou;Kim, Jung-Su;Kim, Kyeong-Hwa

  • Received : 2015.12.02
  • Accepted : 2016.04.17
  • Published : 2016.07.20


A power quality improvement scheme for grid connected inverters, even in the presence of the disturbances in grid voltages due to harmonic distortions and three-phase imbalance, is presented for distributed generation (DG) power systems. The control objective is to force the inverter currents to follow their references with robustness even under external disturbances in grid voltages. The proposed scheme is realized by a disturbance observer (DOB) based current control scheme. Since the uncertainty in a system can be effectively canceled out using an estimated disturbance by the DOB, the resultant system behaves like a closed-loop system consisting of a disturbance-free nominal model. For experimental verification, a 2 kVA laboratory prototype of a grid connected inverter has been built using a digital signal processor (DSP) TMS320F28335. Through comparative simulations and experimental results under grid disturbances such as harmonic distortion and imbalance, the effectiveness of the proposed DOB based current control scheme is demonstrated.


Distorted and unbalanced grid;Distributed generation;Disturbance observer;Grid connected inverter;Power quality


  1. C. Lascu, L. Asiminoaei, I. Boldea, and F. Blaabjerg, “High performance current controller for selective harmonic compensation in active power filters,” IEEE Trans. Power Electron., Vol. 22, No. 5, pp. 1826-1835, Sep. 2007.
  2. Q. N. Trinh and H. H. Lee, “An advanced current control strategy for three-phase shunt active power filters,” IEEE Trans. Ind. Electron., Vol. 60, No. 12, pp. 5400-5410, Dec. 2013.
  3. A. Timbus, M. Liserre, R. Teodorescu, P. Rodriguez, and F. Blaabjerg, “Evaluation of current controllers for distributed power generation systems,” IEEE Trans. Power Electron., Vol. 24, No. 3, pp. 654-664, Mar. 2009.
  4. S. W. Kang and K. H. Kim, “Sliding mode harmonic compensation strategy for power quality improvement of a grid-connected inverter under distorted grid condition,” IET Power Electron. Vol. 8, No. 8, pp. 1461-1472, Aug. 2015.
  5. J. Hu and Y. He, “Modeling and control of grid-connected voltage-sourced converters under generalized unbalanced operation conditions,” IEEE Trans. Energy Convers., Vol. 23, No. 3, pp. 903-913, Sep. 2008.
  6. M. Liserre, R. Teodorescu, R., and F. Blaabjerg, “Multiple harmonics control for three-phase grid converter systems with the use of PI-RES current controller in a rotating frame,” IEEE Trans. Power Electron., Vol. 21, No. 3, pp. 836-841, May. 2006.
  7. R. Teodorescu, F. Blaabjerg, M. Liserre, and P. C. Loh, “Proportional-resonant controllers and filters for grid-connected voltage-source converters,” IEE Electr. Power Appl., Vol. 153, No. 5, pp. 750-762, Sept. 2006.
  8. J. Xu, T. Tang, and S. Xie, “Research on low-order current harmonics rejections for grid-connected LCL-filter inverters,” IET Power Electron., Vol. 7, No. 5, pp. 1227-1234, May. 2014.
  9. B. Li, W. Yao, L. Hang, and L. M. Tolbert, “Robust proportional resonant regulator for grid-connected voltage source inverter (VSI) using direct pole placement design method,” IET Power Electron., Vol. 5, No. 8, pp. 1367-1373, Sept. 2012.
  10. S. Chen, Y. M. Lai, S. C. Tan, and C. K. Tse, “Analysis and design of repetitive controller for harmonic elimination in PWM voltage source inverter systems,” IET Power Electron., Vol. 1, No. 4, pp. 497-506, Dec. 2008.
  11. J. R. Fischer, S. A. Gonzalez, I. Carugati, M. A. Herran, M. G. Judewicz, and D. O. Carrica, “Robust predictive control of grid-tied converters based on direct power control,” IEEE Trans. Power Electron., Vol. 29, No. 10, pp 5634-5643, Oct. 2014.
  12. D. Chen, J. Zhang, and Z. Qian, “Research on fast transient and 6n ± 1 harmonics suppressing repetitive control scheme for three-phase grid-connected inverters,” IET Power Electron., Vol. 6, No. 3, pp. 601-610, Mar. 2013.
  13. H. S. Heo, G. H. Choe, and H. S. Mok, "Robust predictive current control of a grid-connected inverter with harmonics compensation," in Proc. Applied Power Electronics Conference and Exposition, pp. 2212-2217, 2013.
  14. M. I. Martinez, A. Susperregui, G. Tapia, and L. Xu, “Sliding-mode control of a wind turbine-driven double-fed induction generator under non-ideal grid voltages,” IET Renewable Power Generation, Vol. 7, No. 4, pp. 370-379, Jul. 2013.
  15. W. H. Chen, “Disturbance observer based control for nonlinear systems,” IEEE/ASME Trans. Mechatronics, Vol. 9, No. 4, pp. 706-710, Dec. 2004.
  16. K. Lee, T. M. Jahns, T. A. Lipo, and V. Blasko, "New observer-based source voltage unbalance control methods in PWM voltage-source converters," in Proc. Power Electronics Specialists Conference, pp. 1509-1514, Rhodes, Jun. 2008.
  17. K. Lee, T. M. Jahns, T. A. Lipo, V. Blasko, and R. D. Lorenz, “Observer-based control methods for combined source-voltage harmonics and unbalance disturbances in PWM voltage-source converters,” IEEE Trans. Ind. Appl., Vol. 45, No. 6, pp. 2010-2021, Nov. 2009.
  18. K. H. Kim, “Model reference adaptive control-based adaptive current control scheme of a PM synchronous motor with an improved servo performance,” IET Electr. Power Appl., Vol. 3, No. 1, pp. 8-18, Jan. 2009.
  19. Y. A. R. I. Mohamed and E. F. El-Saadany, “A control scheme for PWM voltage-source distributed-generation inverters for fast load-voltage regulation and effective mitigation of unbalanced voltage disturbances,” IEEE Trans. Ind. Electron., Vol. 55, No. 5, pp. 2072-2084, May 2008.
  20. J. Back and H. Shim, “Adding robustness to nominal output-feedback controllers for uncertain nonlinear systems: A nonlinear version of disturbance observer,” Automatica, Vol. 44, No. 10, pp. 2528-2537, Oct. 2008.
  21. J. Back, and H. Shim, “An inner-loop controller guaranteeing robust transient performance for uncertain MIMO nonlinear systems,” IEEE Trans. Autom. Contr., Vol. 54, No. 7, pp. 1601-1607, Jul. 2009.
  22. H. Khalil, Nonlinear Systems, Prentice - Hall, 2002.
  23. “TMS320F28335 Digital Signal Controller (DSC) - Data Manual,” Texas Instrument, 2008.

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