PV inverter with decoupled active and reactive power control to mitigate grid faults

Abstract This paper proposes a grid-tied PV inverter installed at the low voltage side of a distribution grid. The architecture considers the operation of a grid-tied inverter and its robustness against the grid faults. Unlike previously proposed low-voltage-ride-through (LVRT) operation, the proposed control provides maximum-power-point-tracking (MPPT) in both normal and low-voltage fault conditions. The control strategy prevents the inverter shut-down by maintaining the DC-link. The inverter also supports the grid by reactive power injection during the voltage sags. The paper presents a prediction model of a two-stage voltage-source-inverter. The proposed predictive control can generate the appropriate references for both regular and LVRT modes based on the inverter's specification and the regulatory grid codes. The salient features of the proposed controller are: (1) decoupled power control in regular operation, (2) low-voltage-ride-through operation with reactive power support, (3) No DC-link fluctuation, and (4) MPPT in every mode. The inverter control is developed by formulating a cost function based on the prediction model of the inverter. A cost function minimization-based control eliminates the conventional cascaded-loop control, thus simplifying the controller implementation. The proposed model-predictive-control (MPC) algorithm is validated with mathematical analysis and simulations of the PV inverter in both standard and faulty grid conditions.