Improving distribution system performance with integrated STATCOM and supercapacitor energy storage system

The STATCOM (Synchronous Static Compensator) based on Voltage Source Converter (VSC) is used for voltage regulation in transmission and distribution systems. However, strict requirements of STATCOM losses and total system loss penalty preclude the use of high frequency PWM (Pulse-Width Modulation) for VSC based STATCOM applications. This constraint of implementing VSC without PWM results in VSC DC voltage dip, over-currents and trips of the STATCOM during and after system disturbances and faults, when its VAR support functionality is most required. In this paper, the integration and control of energy storage systems (ESSs), such as Supercapacitor (Ultracapacitor - UCAP) into a D-STATCOM (Distribution system STATCOM) is developed to mitigate such problems, enhance power quality and improve distribution system reliability. This paper develops the control concepts to charge/discharge the UCAP by the D-STATCOM, and validate the performance of an integrated D-STATCOM/UCAP system for improving distribution system performance under all types of system related disturbances and system faults — such as single-line to ground fault (SLG), line-line fault and 3-phase system faults. Simulation results of a 125 kVA D-STATCOM validate that integrated the D-STATCOM with 600V, 1.0 Farad UCAP is suited for distribution system voltage regulation and voltage sag mitigation. In case of a system fault, UCAP based energy storage will aid to keep the D-STATCOM DC voltage constant and avoid over-current and trips of the VSC based D-STATCOM.