Low voltage ride-through feature in single phase two stage grid tied PV inverter

The growth of single-phase solar photovoltaic systems and it’s integration with grid, necessitates Low Voltage Ride-Through (LVRT) capability for grid stability. Grid code mandates LVRT capabilities for all distributed generation (DG), including those connected to low voltage distribution grids. LVRT capability provides stable grid integration during transient conditions. This paper uses a variable power point tracking (VPPT) method along with the reactive power injection. Unlike the conventional PV inverter, the proposed techniques mitigate the issues of high DC link voltage and excessive grid current in low voltage grid faults. In this paper, two controllers are demonstrated for two different operations. DC link voltage controller is used for power control operation and proportional-integral (PI) with feed-forward controller is used for current control operation. Seamless LVRT capability is achieved through the peak value based fault detection and orthogonal signal generation (OSG) based voltage sag detection. Simulation in MATLAB/Simulink for 5kW single phase two stage system verifies the effectiveness of the algorithm in successful implementation of LVRT capabilities. During voltage sag, system seamlessly transitions from MPPT mode to VPPT mode hence maintaining the power balance and keeping the DC link voltage stable as well as avoiding over current tripping of the inverter. Additionally, the system demonstrated the capability of solar inverters to inject reactive power as required by grid codes.