High-voltage Bi-directional Half-bridge Three-level Series Resonant Converter with Frequency Modulation Control

This paper aims to develop a bi-directional half-bridge three-level series resonant converter for high-voltage DC micro-grid. The topology of three-level circuit can reduce the device voltage stresses and electromagnetic interference. The clamped diode and capacitor unit can provide an appropriate current path to achieve zero-voltage switching on power switches. By conventional frequency modulation control, the resonant tank can be operated in SRC region and achieve bi-directional power conversion. Since the proposed control method is developed in this paper, the circuit has a characteristic of transformer decoupling called LLC-SRC region. It achieves quasi-zero-current switching to reduce the switching loss. Synchronous rectifier is also implemented to reduce conduction loss on the secondary side. A laboratory prototype of bi-directional half-bridge three-level series resonant converter is designed and verified in high-voltage applications. The circuit specifications are 3-kW rated power, 1-kV input voltage, and 3 A output current. A digital signal processor (DSP) chip is used to realize the digital controller of this converter. The measured efficiency can be achieved 96% under different load conditions.