Control of a PV-fed Cascaded Half-Bridge Multilevel Inverter with Shunt Active Power Filter Capabilities

Due to increasingly use of nonlinear loads in power grids, an Active Power Filter (APF) is unavoidable for guaranteeing the stable and efficient operation of power systems. APFs based on Cascaded Half-Bridge (CHB) inverters with low switching frequency can compensate high-order harmonics in medium and high voltage systems. Since grid-connected Photovoltaic (PV) systems interface to the grid with inverters, they can be multi-functionally used both as APFs and power feeders. In this paper, the control of a grid-connected 5-level CHB inverter acting as a shunt APF is addressed in presence of nonlinear loading conditions. The CHB converter is fed by PV arrays interfacing DC-DC boost converters whose main objective is to track maximum available power from the PV sources. The CHB is controlled to keep the grid current sinusoidal and in phase with the grid voltage hence achieving a unitary power factor as well as to regulate DC-link voltages. The active component of the inverter output current is determined by low pass filtering the sum of the PV sources powers. In addition, the compensating current signal is calculated based on synchronous reference frame (SRF) theory, and then it is added to the current control loop. To achieve a high-quality steady-state current, a proportional resonant controller is used for the current loop. PSIM© numerical simulations are performed to validate the CHB performances as a shunt APF under irradiance and load change conditions.