Full-Range ZVS Modulation of Switched Capacitor Converter for Sensorless Voltage Balancing

This paper presents a new sensorless full-range zero-voltage switching (ZVS) modulation technique for a resonant switched-capacitor converter (RSCC) using a constant non-symmetrical duty cycle control and demonstrated as a DC-link voltage balancing circuit in split-phase inverter applications. A DC-link voltage balancer is required in a split-phase inverter to compensate for load imbalances between the two output phases, and it typically operates under slightly unbalanced or light-load conditions. While the existing phase-shift modulation of the RSCC can achieve high efficiency with ZVS operation, it has inherent non-ZVS regions and a notable efficiency decline at light loads. A decline in light load efficiency is also evident with the typical zero-current switching (ZCS) modulation of the RSCC. As a solution, in the proposed sensorless ZVS modulation, the minimum required ZVS current is maintained across the entire load range using a constant non-symmetrical duty cycle control, ensuring ZVS operation for all switching devices even during load transients. The proposed ZVS modulation is verified in simulation and experimental results from a 5-kW hardware prototype confirmed the full-range ZVS operation of the RSCC and efficiency improvement of the split-phase inverter for both balanced and unbalanced load conditions across the entire load range.