Abstract
The CLLC converter is a promising topology for bidirectional power conversion applications, such as vehicle-to-grid and battery energy storage systems. In these applications, wide output voltage range is needed. However, traditional pulse frequency modulation method is not suitable for wide output range because of wide switching frequency range. Inner phase shift (IPS) control is a good solution for this issue. In CLLC converters, to further increase the efficiency, synchronous rectification (SR) is required. In this paper, a simplified sensorless SR method is proposed for IPS control. A comprehensive operation mode analysis and an accurate operation mode model is established for IPS control in CLLC converters. With the operation mode model, waveform of secondary side current is simplified. As a result, only a standard quadratic-root formula needs to be calculated to generate SR drive signal, and no extra sensors are needed. The method is low cost and is suitable to implement in embedded systems. A prototype is built to verify the proposed simplified sensorless SR method. The proposed method achieves an obvious efficiency improvement (up to 1.88%) over uncontrolled rectification, and the effect of the proposed method is nearly the same as that of complete SR (maximum efficiency difference is 0.40%).
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