A Novel Capacitor Voltage-Balancing Method for Multiwinding Resonant Converters

Isolated dc/dc converters play a key role in electric vehicle applications, and novel multiwinding resonant converters have recently been proposed for on-board and off-board charging applications. Some of these topologies have two series capacitors at the dc bus with a mid-point connection to the windings. Parameter mismatch due to manufacturing differences will cause voltage unbalance on these capacitors, which can lead to safety and reliability concerns. However, the well-known capacitor balancing strategies proposed for other topologies are not applicable to these new resonant multiwinding topologies. Thus, this article proposes a novel capacitor voltage-balancing method for a resonant multiwinding converter. The method uses a simple table to decide on balancing switching states. Time-domain analysis is performed to quantify the control cycles required, and an adaptive control strategy is proposed. Experimental results with multiple bus capacitor sizes validate the effectiveness of the proposed method. Furthermore, use of the proposed method is found to slightly increase efficiency.