Bidirectional, unregulated series resonant DAB converters are widely used with the merits of simplicity and high efficiency. However, the efficiency of the converter is compromised due to switching frequency deviation from the desired resonant frequency. In this paper, a bidirectional resonant frequency tracking method using only a single current measurement is proposed for unregulated SR-DAB applications. The phase pattern of resonant current and the current variation in dead-time is leveraged to recognize the frequency deviation. Considering the cost requirements for unregulated converters, an equivalent high-frequency sampling method with low-speed ADC is proposed to ensure the accuracy of the current analysis.
