Low-harmonic resonant CLL-type AC/DC converter

A new resonant AC/DC converter is presented. It has been shown that the series parallel CLL topology is particularly useful in resonant rectifier applications. The transformer may be designed to replace one or both the inductances used in the resonant network. The converter is operated only in the lagging power factor mode, dispensing with the need of an external device snubber. Such a converter is analysed and simulation results are obtained by using MATLAB. Two new control strategies are proposed. Both control schemes are implemented and compared. Scheme 1 requires reduced hardware and no current sensor, but scheme 2 uses a current sensor and an additional PI controller. Scheme 2 performs better than scheme 1 in terms of total harmonic distortion (THD) of the converter input current. A laboratory prototype has been fabricated and excellent performances have been confirmed.