V-Iq based control scheme for mitigation of transient overvoltage in distribution feeders with high PV penetration

High penetration of rooftop photovoltaic (PV) systems in distribution feeders can give rise to overvoltage during peak generation hours. A well-known solution for this problem is Volt-VAR control method, in which PV inverters mitigate the overvoltage by reactive power absorption. The conventional Volt-VAR scheme calculates the reactive power reference based on a limited bandwidth V-Q droop controller. Although the conventional method is capable of steady-state voltage regulation, it is not effective against voltage overshoots caused by fast solar irradiance variations. In this paper, a new V-Iq based Volt-VAR control scheme is presented to suppress the transient voltage overshoots during cloud passing. In this method, the bandwidth of the Volt-VAR controller is increased to enhance its responsiveness to voltage variations. To prevent instability caused by unwanted interaction between the high bandwidth Volt-VAR controller and the voltage feedforward section of the inner control loop, a low pass filter is added to the feedforward path. Small signal analysis of the proposed method provides a guideline for designing the bandwidths of Volt-VAR controller and feedforward filter. The stability of the proposed method is assessed based on Lyapunov method. Hardware in the Loop (HIL) experimental results are presented to validate the proposed scheme.