Autoconnected-electronic-transformer-based multipulse rectifiers for utility interface of power electronic systems

In this paper, an autoconnected electronic transformer (ACET) for 12- and 2 4-pulse rectifier systems is proposed. Considerable reduction in size and w eight is achieved by operating the transformer core at a higher frequency. The rating of the autotransformer is a fraction of the output power. Utilit y line currents are multipulse in nature with the cancellation of several l ower order harmonic currents. Furthermore, the magnetic components on the r ectifier de side are also exposed to higher frequency and can be reduced in size and weight. With an operating frequency of 990 Hz and utilizing conve ntional grain-oriented steel, a size reduction of 1/3 is achieved compared to a conventional 60-Hz design. Finer grades of steel or alternatives, such as amorphous material, would increase the performance advantage even furth er. Another unique feature of the proposed concept is that the switching fr equency components are neutralized at the input side of the rectifier syste m. A second configuration using an open delta ACET is also presented. The p roposed concept is suitable for higher power rectifier systems, which deman d clean input power characteristics. This paper presents analysis, simulati ons, design example, and experimental results for a 208-V 10-kVA prototype system.