Reliable and Effective Ride-Through Controller Operation for Smart PV Systems Connected to LV Distribution Grid Under Abnormal Voltages

Abstract

Proliferation of distributed photovoltaic (PV) systems forced utilities to demand ancillary features, such as voltage support (VS), ride-through (RT) operation, and islanding detection, to handle grid contingencies. An integrated controller to respond independently on situations like low grid voltages during faults, overvoltages during low-loading, and islanding is not yet discussed. A smart low-voltage (LV) RT controller for PVs connected at high penetration to LV grid is presented in this paper. The nature of power and currents fed from PVs for effective VS, and the coordinated operation of maximum-power-point-tracking and RT controller during grid abnormalities of longer duration are detailed. In LV grids, the ratio of $X/R$ is low; therefore, control of active power is given higher priority compared to reactive power from distributed PVs. The controller distinguishes the island and voltage disturbance event for reliable operation. The controller includes: 1) reactive power support with active power curtailment controller for dynamic support; 2) decoupled-double-synchronous-reference-frame based synchronization and sequence extraction from unbalanced voltages; 3) reference current generator which eliminates active power oscillations and compensates voltage unbalances; 4) peak current limiter; and 5) proportional-resonant controllers for injection of unbalanced currents. The performance of the controller during various grid conditions is evaluated with simulation and experimental results.