Application of a Series-Connected Hybrid Multi-Converter System to STATCOM

Abstract

This paper gives an analysis and design of a static synchronous compensator (STATCOM) using a series-connected hybrid multi-converter system. The hybrid multi-converter system consists of two GTO converters and an IGBT converter connected in series by transformers. The proposed STATCOM has advantages that the harmonic components of the output voltage/current would be less than a conventional configuration STATCOM composed of a 12-, 24-, or 48-pulse converter; the total switching losses would be less than a PWM STATCOM; and the response would be as rapid as a PWM STATCOM. One problem of the hybrid configuration STATCOM is that it tends to operate in an over-modulation range if a considerable compensating reference change occurs. To solve this problem, this paper also proposes a variable DC voltage control strategy, where the DC voltage is adaptively adjusted in accordance with the required reactive power. The validity of the proposed configuration STATCOM and control strategies are verified by simulation and experimental results.