Abstract：Three-level(TL) DC/DC converters apply especially to high-voltage input occasions for the reason that the voltage stress across the power switches is only half of the input voltage. The four switches half-bridge TL converter studied in this paper can achieve wide range soft switching of the primary switches. Besides, it removes the clamped diodes and flying capacitor to ensure high reliability. However, the asymmetry of the main circuit and control circuit result in voltage unbalance among the input capacitors and blocking capacitor, which can result in high voltage stress of the power switches and the rectifier diodes. A novel capacitor voltage control strategy is proposed to realize voltage control and improve the reliability of the converter by regulating duty cycle and phase shift of the positive and negative half-cycles. Finally, an input 800V output 28V/2kW prototype was built and tested in the lab. The experimental results validate the theoretical analysis of voltage unbalance and capacitor voltage control strategy.
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2015, Vol. 30 
