Composite Disturbance Observer-Based Control and H ∞ Control Framework for Enhanced Performance of Three-Phase Shunt Active Power Filters

This paper presents the design of a current controller for a three-phase shunt active power filter aimed at mitigating selective current harmonics caused by nonlinear loads at the point of common coupling (PCC). The proposed controller is developed by combining a disturbance observer, a state-feedback controller, andH∞control theory. The disturbance observer and feedback controller are designed to estimate and compensate for the effects of selective harmonics, whileH∞control is employed to attenuate the effects of unknown disturbances with bounded norms. The observer gains are obtained by solving a linear matrix inequality (LMI) problem to ensure regional pole placement while effectively attenuating unknown disturbances. The key feature of the composite controller is that it can be implemented as a simple proportional integral controller plus a multi-resonant controller. The proposed controller has been experimentally validated, demonstrating satisfactory performance that meets IEEE standards for harmonic control, even under distorted and unbalanced grid voltage conditions.