Three-Leg Active Bridge-Based Bidirectional Resonant Converter Using Hybrid Si/SiC Switches

This article proposes a bidirectional resonant converter that uses a three-leg active bridge and hybrid Si/SiC switches. The use of a three-leg active bridge on the secondary side of the transformer transfers twice as much power compared with the use of a single active bridge; one of the three legs is shared, which reduces the number of active power devices in the development process. The phase-shift modulation has been adopted for both power flow directions, which enables zero-voltage switching turn-on for all the switches. On the secondary side, the shared leg only requires the use of two SiC mosfets, because these particular switches undergo high conduction loss and high turn-off loss during both forward and backward operations. This trait reduces the implementation cost of the circuit further. The primary-side windings of the transformer are connected in series and each secondary-side winding has wound in the opposite direction. The resulting symmetric architecture of the dual transformer connected to a three-leg active bridge and the corresponding pulsewidth modulation (PWM) naturally balance the currents flowing through the middle leg and right leg on the secondary side. A 1-kW rated prototype that converts 150-200 V input to a 400 V output is designed and tested to validate the concept for cost-effective battery charging and discharging.