An Interleaved PWM Method With Better Voltage-Balancing Ability for Half-Bridge Three-Level DC/DC Converter

Since the voltage stress on the power switches is only half of the input voltage, three-level (TL) converters have been widely used in high-voltage applications. To ensure normal operation of TL converters, the voltages on the input divided capacitors and the blocking capacitor must be essentially balanced. In practice, asymmetry of the main circuit and the drive circuit may result in unbalance of these voltages, leading to higher voltage stress on the power switches and other problems. This letter proposes a novel pulse-width modulation (PWM) method with better voltage-balancing ability, which is implemented by interleaving two traditional PWM methods. First, the mechanism of voltage unbalance is analyzed. The new PWM method decouples the blocking capacitor voltage from the voltages of the input divided capacitors, and ensures that the former voltage is always kept around its ideal value, which can greatly simplify the sampling circuit and the voltage-balancing control scheme. Then, a voltage-balancing strategy aiming to adjust the phase shift of the drive signals only is given. Finally, experimental results are presented to verify the effectiveness of the proposed method and voltage-balancing strategy.