A Novel PWM High Voltage Conversion Ratio Bidirectional Three-Phase DC/DC Converter With Y-Δ Connected Transformer

In order to solve the problem of high voltage conversion ratio between dc bus and energy storage unit, a novel bidirectional three-phase dc/dc converter applicable to high-power condition is proposed in this paper. With the new PWM strategy and inherent ability of increasing voltage conversion ratio of Y-Delta connected transformer, the voltage conversion ratio is doubled. With the new PWM strategy, the effective duty cycle range of three-phase dc/dc converter is expanded, which results in halved filter inductance. Three-phase full-bridge structure is connected to the dc bus, while current-tripler unit is connected to the battery. As three-phase interleaved structure is adopted, not only current stress of switches decreases but also the frequency of input and output current ripple increases to three times of switching frequency, which leads to smaller filters and extended lives cycle of batteries. The operating principle and characteristics of the converter are analyzed in detail. A prototype with the 360-V dc bus converted to 48 V/42 A batteries was built and the results are given based on the experiments.