Auto-connected electronic transformer (ACET) based multi-pulse rectifiers for utility interface of power electronic systems

In this paper, an auto-connected electronic transformer (ACET) for 12 and 24-pulse rectifier systems is proposed. Considerable reduction in size and weight is achieved by operating the transformer core at a higher frequency. The rating of the auto-transformer is a fraction of the output power. Utility line currents are multi-pulse in nature with the cancellation of several lower order harmonic currents. Further, the magnetic components on the rectifier DC-side are also exposed to high-frequency and are of small size and weight. With an operating frequency of 990 Hz and utilizing conventional 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 materials, would increase the performance advantage even further. Another unique feature of the proposed concept is that the switching frequency components are neutralized at the input side of the rectifier system. A low cost open-delta ACET implementation is also shown. The proposed concept is suitable for higher power rectifier systems, which demand clean input power characteristics. This paper presents analysis, simulations, design example and experimental results from a 208 V, 10 kVA prototype system.