Passivity-Based Design of Repetitive Controller for LCL-Type Active Power Filters within a Complex Grid Condition

Repetitive controller (RC) is popular in the current control of active power filter (APF) due to its high tracking ability of periodic signals. RC is well designed using the discrete-time closed-loop transfer function based method, which is applicable for a single inverter connecting to a well-known inductive-impedance grid but may not be applicable for inverters operating in complex grid conditions, e.g., weak inductive-impedance grid, capacitive-impedance grid, etc. To address this issue, this paper presents a new passivity-based design method for RC for LCL-filtered APF. With the proposed design method, the output admittance of the APF is tuned to be passive in all frequencies, so that it can be connected to a grid regardless of grid impedance. Experimental results are provided to validate the effectiveness of the proposed design method.