2004 Volume 124 Issue 9 Pages 924-929
A hybrid converter system aims at a large capacity high voltage high efficiency converter system with being free from harmonics in the output. The system can consist of n GTO converters and a single NPC IGBT converter connected series by n+1 output transformers. It is proved that a triple converter system consists of two GTO converters and one IGBT converter is most feasible based on the performance evaluation. Thus, this paper treats a triple converter system in detail. The GTO converters operate in a square-wave switching mode, while the IGBT converter operates in a PWM switching mode. The former produces a base part of the total output voltage. The latter not only produces an additional part of the total output, but offsets the harmonic components generated by the GTO converters. The control strategy for the system is proposed, and the experiments on inverter, rectifier and STATCOM operation are demonstrated. The experimental results verified the validity of the proposed hybrid triple converter configuration and its control strategy.