Study of the voltage response in hybrid compensators

Hybrid VAr compensation systems are typically used to improve the voltage profile at transmission and distribution levels. The most commonly used hybrid configuration is based on the combined use of Static Synchronous Compensator (STATCOM) and Thyristor-Switched Capacitors (TSCs); this device is able to represent a good compromise between fast transient response and reduced losses under steady-state conditions, also, they provide fast voltage regulation, for example in systems characterized by a large percentage of induction-type air-conditioning loads. Hybrid configurations are also expected to assist in limiting temporary over-voltages, mitigating voltage instabilities, and preventing voltage collapse or motor stalling in case of fault conditions. The response to a step function in the input signal of voltage reference is an established method to assess the dynamic behavior of power electronically controlled devices, such as the Static Var Compensator (SVC) and the Static Synchronous Compensator (STATCOM). Requirements such as maximum overshoot, settling time and rise time need to be met when assessing the voltage response. The aim of this paper is to study the dynamic behavior of a hybrid compensator under different system scenarios and investigate possible control strategies to mitigate the voltage overshoot caused by the TSC switching while applying a step. The proposed solution is to estimate the TSC transient currents and actively filter them by aims of the STATCOM. The obtained results show a proper performance of the system, given some restrictions preventing the full TSC current compensation.