Journal of Power Electronics

The Korean Institute of Power Electronics (전력전자학회)
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An Improved Active Damping Method with Capacitor Current Feedback

  • Geng, Yi-Wen (School of Electrical and Power Engineering, China University of Mining and Technology) ;
  • Qi, Ya-Wen (School of Electrical and Power Engineering, China University of Mining and Technology) ;
  • Liu, Hai-Wei (School of Electrical and Power Engineering, China University of Mining and Technology) ;
  • Guo, Fei (School of Electrical and Power Engineering, China University of Mining and Technology) ;
  • Zheng, Peng-Fei (School of Electrical and Power Engineering, China University of Mining and Technology) ;
  • Li, Yong-Gang (School of Electrical and Power Engineering, China University of Mining and Technology) ;
  • Dong, Wen-Ming (School of Electrical and Power Engineering, China University of Mining and Technology)
  • Received : 2017.03.29
  • Accepted : 2017.10.31
  • Published : 2018.03.20
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Abstract

Proportional capacitor current feedback active damping (CCFAD) has a limited valid damping region in the discrete time domain as (0, $f_s/6$. However, the resonance frequency ($f_r$) of an LCL-type filter is usually designed to be less than half the sampling frequency ($f_s$) with the symmetry regular sampling method. Therefore, ($f_s/6$, $f_s/2$) becomes an invalid damping region. This paper proposes an improved CCFAD method to extend the valid damping region from (0, $f_s/6$ to (0, $f_s/2$), which covers all of the possible resonance frequencies in the design procedure. The full-valid damping region is obtained and the stability margin of the system is analyzed in the discrete time domain with the Nyquist criterion. Results show that the system can operate stably with the proposed CCFAD method when the resonance frequency is in the region (0, $f_s/2$). The performances at the steady and dynamic state are enhanced by the selected feedback coefficient H and controller gain $K_p$. Finally, the feasibility and effectiveness of the proposed CCFAD method are verified by simulation and experimental results.

Keywords

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Fig. 1. System structure of an LCL-type three-phase grid-connectedinverter.

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Fig. 2. Diagram of the proportional CCFAD system in thecontinuous time domain.

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Fig. 3. Diagram of the proportional CCFAD system in thediscrete time domain.

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Fig. 4. Diagram of the improved CCFAD in the discrete timedomain.

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Fig. 5. Diagram of the improved CCFAD in the continuous time domain.

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Fig. 6. Curves of the equivalent resistance when λ= 1, 2, 4, 5.

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Fig. 7. Bode diagram of the improved CCFAD system when λ = 2.

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Fig. 8. Curves of the equivalent resistance and reactance with λ=1: (a) Equivalent resistance Req; (b) Equivalent reactance Xeq.

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Fig. 9. Bode diagram of the third condition of the improvedCCFAD system when λ = 1.

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Fig. 10. Structure of: (a) LCL filter without damping; (b) capacitor paralleled with a resistor; (c) capacitor paralleled with a reactor;(d) capacitor paralleled with both a resistor and a reactor.

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Fig. 11. Bode diagrams of the improved capacitive currentproportional feedback system.

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Fig. 12. Closed-loop zero-pole map of the improved CCFADsystem.

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Fig. 13. Simulation results with different resonance frequencies:(a) fr < fs/4, fr1 = 1.04 kHz; (b) fr > fs/4, fr2 = 1.42 kHz.

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Fig. 14. Waveforms of the phase-A voltage and current with andwithout the proposed CCFAD: (a) fr< fs/4; (b) fr > fs/4.

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Fig. 15. Waveforms of the phase-A voltage and current with fr

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Fig. 16. Waveforms of the phase-A voltage and current with fr >fs/4: (a) steady-state; (b) dynamic-state; (c) resonant-state.

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Fig. 17. Experimental results of the three-phase grid-side current:(a) fr< fs/4, fr1 = 1.04 kHz; (b) fr > fs/4, fr2 = 1.42 kHz.

TABLE I PARAMETERS OF THE IMPROVED CCFAD

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TABLE II MAIN PARAMETERS OF A BSM50GB120DLC IGBT

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