A new nonlinear controller for Active Power Filters

Linear controllers have been widely used for controlling Active Power Filters (APFs). However, due to their limitations, a tradeoff between the bandwidth of the current control loop (CCL) and the voltage control loop (VCL) need to be made to remain stable in all conditions. This tradeoff leads to imperfect usage of the APF's capacity. Nonlinear controllers can eliminate such limitations and simultaneously remain stable in all conditions. In this paper, a new nonlinear controller for controlling the output current and the DC voltage (V_dc) of an APF is proposed. Feedback linearization method is applied on the CCL and the VCL is controlled via indirect method. In this method, an auxiliary reference voltage is produced by the controller and V_dc is supposed to follow this auxiliary reference. Also, the VCL forces the auxiliary reference to trace the nominal voltage of the DC link using a semi-Least Mean Square (LMS) method. A hypothetical system is developed to demonstrate the performance of the proposed method.