Double resonant output filter to eliminating the tradeoff between bandwidth and switching ripple in shunt active power filters

Abstract

Since shunt active power filters (SAPFs) are designed to inject harmonic current, its bandwidth should be much wider compared to regular inverters. LCL filters are commonly employed in regular inverters. However, it cannot completely meet the requirements of SAPF due to its filtering performance and the impact on system stability. This study proposes a novel double resonant LCL (DR-LCL) filter for SAPFs. Derived from the conventional LCL filters, one RC damping circuit and two LC resonant circuits are employed in the proposed filter. Meanwhile, a resistor is connected in parallel with the grid-side inductor. The mutual impact among different components of the filter is discussed, and the stability of SAPF with DR-LCL filter is studied. This DR-LCL filter can not only inherit the advantages of LCL filters, but also eliminate the tradeoff between bandwidth and switching ripple in SAPFs. Finally, the design principle of the proposed output filter is presented and the parameters of the filter are applied to a 66 kW three-phase three-wire SAPF prototype. Simulation and experimental results verify the feasibility of DR-LCL filter.