A Three-Level Inverter Based Static Compensator (STATCOM)

In an electric utility network, the occurrence of voltage depression on transmission and distribution lines is due to the flow of reactive power. It is desirable to regulate the voltage within a narrow range of its nominal value (±5% range around their nominal values). Thus, reactive power control is necessary so as to control dynamic voltage swings under various system conditions and thereby improve the power system transmission and distribution performance. A fast acting Static Compensator (STATCOM) is required to produce or absorb reactive power so as to provide the necessary reactive power balance in transmission and distribution system. Modern reactive power compensation employs voltage source inverter (VSI). In this paper, a static compensator based on three-phase, three-level voltage source inverter (VSI) was investigated. The paper is intended to show how this STATCOM can be used to improve the ac system power factor and voltage regulation, and hence improve the performance of the transmission and distribution lines. Application of this STATCOM to a transmission system achieved unity power factor, thereby reducing the active power loss by 38.7% and consequently decreasing power costs, as well as increasing transmission system capacity. The presence of the STATCOM also reduced the reactive power flowing on the line from 2.79 MVAr to 1745VAr - resulting in optimum voltage regulation at the load bus. The reactive elements (L and C) are small in size.