Robust Repetitive Control Design for a Three-Phase Four Wire Shunt Active Power Filter

This paper presents a discrete repetitive control technique for three-phase four wire (3P4W) shunt active power filter (SAPF). Generally, the control design for power electronics devices involves two control loops: slow acting outer voltage loop and fast acting inner current control loop. The reference for inner current loop is periodic in nature and cannot be easily tracked by a proportional-integral regulator. The repetitive controllers (RCs) are well known for their tracking ability of periodic signals and offer high gain at all the frequencies. The high gain in higher frequency range may lead to instability. Therefore, in the proposed work, the regular RC is modified by squaring its sensitivity function. This approach results in low amplitude of sensitivity function while offering deep notches at low to mid frequencies range and smaller notches at higher frequencies. This control approach has been simulated and implemented on 3P4W SAPF.