Enhanced Fault Ride-Through of Grid-Connected PV Systems Using PIR-MPC-Controlled Supercapacitor Energy Storage

Abstract

Grid-connected solar photovoltaic (GSPV) systems experience prominent double-frequency oscillations in the DC-link voltage, real and reactive power during asymmetrical grid fault scenarios, which can severely affect low-voltage ride-through (LVRT) capability. This paper proposes a combined control strategy based on an optimized supercapacitor energy storage system (SCESS) and negative-sequence reactive current injection for improving the LVRT capability of GSPV systems under an extensive range of short circuit ratio (SCR) conditions. A multi-objective optimization method is formulated to simultaneously minimize DC-link voltage ripple, real and reactive power oscillations, and SCESS energy requirements. A proportionalintegral-resonant (PIR) controller is employed for DC-link voltage regulation, while finite control set based model predictive control (FCS-MPC) is implemented to achieve fast and accurate current tracking. The PIR and MPC gains, together with the negative-sequence reactive current contributing factor, are optimally determined within the proposed methodology. A dual second-order generalized integrator phase-locked loop (DSOGI-PLL) is incorporated for offering better synchronization under unbalanced and distorted grid conditions. Unlike conventional strategies based on braking choppers (BC) and positive-sequenceprioritized reactive current injection, the proposed approach coordinates SCESS power exchange with optimal negative-sequence current compensation, thereby improving the mitigation of double-frequency oscillations of the DC-link voltage, real and reactive power during severe asymmetrical fault scenarios. The effectiveness of the proposed strategy is evaluated under balanced and unbalanced faults and different SCR conditions. Simulation results and comparative analysis demonstrate significant reductions of the double frequency oscillations in the DC-link voltage, real and reactive power injections while maintaining the required LVRT response and limiting the SCESS energy requirement. The proposed multi-objective coordinated control strategy therefore provides an effective solution for robust grid integration of GSPV systems under adverse grid conditions.