Duty-ratio feedforward for digitally controlled boost PFC converters

When a ´classical´ current control scheme is applied, the input current of a boost power factor correction (PFC) converter leads the input voltage, resulting in a nonunity fundamental displacement factor and in important zero-crossing distortion in applications with a high grid frequency (e.g. 400 Hz power systems on commercial aircraft). To resolve this problem, a current-control scheme is proposed using duty-ratio feedforward. In this paper, the input impedance of the boost PFC converter for both the classical current-loop controller and the controller using duty-ratio feedforward are derived theoretically. A comparison reveals the advantages of the proposed control scheme: a low total-harmonic-distortion (THD) of the input current, a resistive input impedance, virtually no zero-crossing distortion and a fundamental displacement power factor close to unity. The theoretical results obtained are verified using an experimental setup of a digitally controlled boost PFC converter.