Grid-Current Control With Inverter-Current Feedback Active Damping for LCL Grid-Connected Inverter

The inverter-current proportional feedback (ICPF) active damping (AD) for an LCL grid-connected inverter (LCL-GCI) suffers from adverse gain reduction and loss of inductive ability in the low-frequency zone, making it unsuitable for active damping. To overcome the limitations of ICPF-AD, inverter-current bandpass filter feedback (ICBFF) AD is more conducive to suppressing the resonance of LCL-GCI. However, it is found that the system time delay constrains the damping capability of ICBFF-AD to resonance frequencies lower than those achievable with ICPF-AD. Therefore, this article proposes a second-order lead filter (SOLF) in cascade with the bandpass filter (BF) as an AD controller for inverter-current feedback AD. The analysis illustrates that cascading a SOLF with BF in the AD loop preserves the LCL filter's low-frequency gain and inductive nature resulting in improved dynamic response as compared to the ICPF-AD. Additionally, the cascaded filter AD allows the damping of higher resonance frequency with better noise immunity. The design approach for BF and SOLF is proposed and the effectiveness of the cascaded AD controller in the presence of different grid impedance is presented. The experimental results from a 10 kW laboratory setup corroborate the theoretical analysis.