Enhancement of LLC Converter Circuit With Voltage Balancing Control Considerations for Output Voltage Range Extension

This paper proposes an LLC converter circuit with capacitor voltage balancing control for wide output voltage range applications. This proposed topology consists of a three-level half-bridge LLC structure on the primary side, which helps reduce the voltage stress on power devices and is suitable for high input voltage supply. It is operated in a complementary 50% duty cycle of fixed switching frequency for DC-DC transformer (DCX) mode and boost mode and operated in PWM for buck mode. The secondary side employs an active-bridge rectifier with phase-shift control to boost the output voltage, thereby extending the voltage regulation range. This design enables a wide range of voltage regulation capabilities and ensures a smooth transition between modes. In addition, considering two capacitors connected in series at the input of the three-level circuit that may cause voltage imbalances due to component mismatch or asymmetrical switching times of power devices, the study also proposes a control strategy with the designated control circuit to maintain the voltage balance of capacitors. To validate the effectiveness of this method, a circuit with a 400 V input, an output ranging from 150 to 400 V, and a power range of 1 kW has been implemented to realise the feasibility of the proposed approach.