Fault Tolerant Backstepping Control for Double-Stage Grid-Connected Photovoltaic Systems Using Cascaded H-Bridge Multilevel Inverters

This letter introduces a complete DC-AC conversion system fed by photovoltaic (PV) energy. The system consists of N PV panels, N DC-DC boost converters, N cascaded H-bridge inverters, a DC-link composed of N capacitors and an LCL filter. This work aims at reaching threefold control objectives: i) Extracting the available maximum power by regulating the voltages across the PV panels, ii) Ensuring a unitary power factor, iii) Regulating the DC-link voltage to a desired reference. To achieve the mentioned objectives, a multi-loop regulator is designed. The PV panels are individually controlled to track the maximum power point in order to efficiently operate at either the same or different varying climatic conditions without failures. In addition to the maximum power point tracking (MPPT) controller, two cascaded loops guaranteeing a satisfactory power factor and DC-link voltage regulation are developed. The nonlinear backstepping approach combined with Lyapunov theory are used based on the averaged model for the synthesis of the multi-loop controller. The performance of the studied system is tested via MATLAB / SimPowerSystems environment. The obtained simulation results prove that the proposed controller meets its objectives and demonstrate the efficiency of the chosen control strategy under faulty conditions.