An Improved LLC Resonant Converter with Variable-Rectifier for Electric-Vehicle Charger Application

An improved LLC converter with variable-rectifier (VR) is studied and evaluated for electric-vehicle charger applications with wide output voltage range. The VR can be reconfigured as center-tapped rectifier (CTR) and full-bridge rectifier (FBR) by the secondary side auxiliary switches. The output voltage range is extended by changing the configuration of rectifier, which results in reduced switching frequency range, circulating current, and conduction losses. Meanwhile, zero voltage switching are achieved for all MOSFETs. A mode transition scheme is employed to achieve smooth and fast transition between CTR and FBR modes. The operation principles are analyzed in detail. A 500W prototype with 400V input voltage and 40-160V output voltage is built and tested to verify the feasibility of the converter.