Control and performance analysis for a capacitor-coordinated static synchronous compensator to enhance dynamic compensation capability

This article proposes a capacitor-coordinated static synchronous compensator, a combination of a relay-switched shunt capacitor and a voltage-sourced inverter based static synchronous compensator, for both steady-state and dynamic reactive power compensation purposes. The utilization of the shunt capacitor is to restore static synchronous compensator capacity such that the fast voltage control for successive transient disturbances is achievable. To attain tight regulation in AC- and DC-link voltages, a voltage-regulation-oriented current command generator derived from a synchronous reference frame is proposed. To facilitate the static synchronous compensator capacity restoration, the equivalent reactive current of the shunt capacitor is considered to modify the current command. A hysteresis current tracker is employed to take place of the conventional pulse width modulated voltage modulation, providing direct and fast current control. The validity of the proposed direct current controlled capacitor-coordinated static synchronous compensator has been verified by laboratory experiments on a 3-kVA digital signal processor based controlled prototype. The experimental results for the system subjected to successive load changes associated with the switching of the shunt capacitor are presented to demonstrate the effectiveness of the proposed system.