STATCOM applying flat-packaged IGBTs connected in series

A STATCOM, which compensates 60 MVA of a negative-phase-sequence power of Japanese bullet trains, has to achieve a low cost, a small size, and a high reliability. In order to enlarge capacity, the authors have developed techniques of connecting flat-packaged IGBTs in series. This STATCOM consists of two banks of inverters, where 12 single-phase inverters are connected by multistage (four-stage) transformers. When IGBTs are connected in series, the problem is to achieve stable and dynamic voltage balance among IGBTs. In order to realize a practical way, RC snubbers, a gate timing adjustment, and pole clamps are used for dynamic balance and resistors are used for static balance. In addition, active clamping circuits are used to prevent IGBTs from over-voltage during the severe network accident (e.g., short circuit). Furthermore, the control diagram of this STATCOM is shown and a method to operate without resonance between STATCOM and outer filter is discussed. Finally, this STATCOM has been evaluated in the actual field. During experiments of using bullet trains, it was shown that the negative-phase-sequence current was well compensated [1]. The STATCOM has been used in Central Japan Railway Company since September 2003.