Capacitor Voltage Control Strategy for Half-Bridge Three-Level DC/DC Converter

Three-level (TL) dc-dc converters are widely used in high-voltage input applications for the reason that the voltage stress on the power switches is only half of the input voltage. For the half-bridge TL dc-dc converter, the asymmetry of the main circuit and drive circuit result in voltage unbalance among the input divided capacitors and blocking capacitor, which will cause higher voltage stress on the power switches and the rectifier diodes. This paper proposes a novel capacitor voltage control strategy to adjust duty cycle and phase shift of the positive and negative half-cycles so that the voltage of the input-divided capacitors and blocking capacitor are corrected and the reliability of the converter can be guaranteed. An 800-V input 28-V/2-kW output prototype has been built and tested in the lab. The experimental results are shown to verify the theoretical analysis and the proposed control strategy.