Design of Critical Passive Damping Parameters for LCL-Type Grid-Connected Inverter

doi:10.12204/j.issn.1000-7229.2022.01.008

Abstract

Abstract:

LCL filter is widely used in grid-connected inverter system for its advanced filtering performance. However, the inherent resonance characteristic of LCL filter and digital control delay will seriously endanger system stability. To increase the system robustness, passive damping method is usually applied to suppress the filter resonance in engineering. Since the filter resonance problem is affected by many factors, the selection standard of damping resistor is unclear. In order to design the damping resistor accurately and efficiently, this paper introduces the index of“critical damping factor”and analyzes two typical passive damping methods: damping resistor in series with filter capacitor or in parallel with filter capacitor. When system damping factor is larger than the critical damping factor, the resonant peak of the amplitude frequency characteristic curve can be completely suppressed and the stability of grid-connected inverter system is fully guaranteed with the minimum cost of passive damping losses. Moreover, the simulation of three-phase grid-connected inverter is carried out in PLECS and the simulation results verify the effectiveness and correctness of the theoretical analysis.

Key words: LCL-type grid-connected inverter, passive damping, critical damping factor, control time delay

CLC Number:

TM76

CHEN Wei, ZHANG Yan, TU Yiming, LIU Jinjun, JIANG Xinsheng. Design of Critical Passive Damping Parameters for LCL-Type Grid-Connected Inverter[J]. ELECTRIC POWER CONSTRUCTION, 2022, 43(1): 70-77.

Figures/Tables 10

Fig.1 System structure of the LCL-type grid-connected inverter with single closed-loop control

Fig.2 Block diagram of grid current single closed-loop control of LCL-type grid-connected inverter

Fig.3 Bode diagram of open-loop gain

Fig.4 Six kinds of passive damping methods

Fig.5 Curves of num(ζ,α) against α

Fig.6 Open-loop gain Bode diagram of resistor in series with capacitor damping strategy when damping factor is 0.28

Fig.7 Curves of dN(ζ,α)/dα against α

Fig.8 Open-loop gain Bode diagram of resistor in parallel with capacitor damping strategy when damping factor is 0.26

Table 1 Simulation parameters of three-phase grid-connected inverter system

Fig.9 Simulation waveforms of grid-connected current and voltage when different damping resistors are connected in series with filter capacitors

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