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A novel voltage sensorless control technique for a bidirectional AC/DC converter is presented. Only a single current sensor that measures the inductor current is needed in the whole system. The sensed inductor current is used for two functions. The first one is for shaping the current waveform at the AC side and the second one is for deriving the inductor voltage by determining the rate of change of the inductor current. The AC-side and DC-side voltages, which are used for AC current synchronization and DC voltage regulation, respectively, are obtained by extracting the envelopes of the derived inductor voltage. Apart from reducing the number of sensing elements, the proposed method has additional advantages of: (1) inherent electrical isolation and reducing noise coupling between the power circuit and the controller; (2) wide operating range. Design criteria for the differentiator and the envelope detector circuit has been described. The applicability of the proposed method is verified with the experimental results of a laboratory prototype.