Active Resonance Damping for an Ultra Weak Grid-Connected Voltage Source Inverter with LCL Filter based on an Optimization and Sliding Mode Control

This paper proposes a novel and robust control strategy for mitigating the resonance of a grid-connected voltage source converter (VSC) with LCL filter. It is well-known that LCL filter provides better attenuation for the system distortions, yet causes high peak resonance at its resonance frequency. This condition is compounded under an ultra weak grid condition whose short circuit ratio is close to one, which may jeopardize the system stability. To counteract these issues, the active damping (AD) based on optimization and sliding mode control (OSMC) with an observer is proposed. The OSMC, synthesized with linear quadratic regulator (LQR), is able to improve the system performance and maintain system stability. Fast and robust dynamic responses have been demonstrated by the proposed method under various conditions. Theoretical studies related to stability analysis and robustness against parametric variations are carried out and then the performance of the proposed method is verified against some of the existing methods via hardware-in-the-loop (HIL) simulation.