A three-phase current-source type PWM rectifier with feed-forward compensation of input displacement factor

Three-phase current-source type PWM rectifiers are often used as the front-end power converter unit in utility-interfaced systems. Due to the input filter (needed for current harmonic suppression), the input displacement factor is less than unity. It varies with the rectifier operating point and may result in unacceptable low values. In this paper, a new control method is proposed to achieve unity displacement factor independent of the load conditions. The proposed method controls the phase shift of the input currents in a feedforward fashion. The modulating signals are phase shifted according to the rectifier operating point to always result in near unity input displacement factor. The compensation scheme makes use of a DC current loop and the standard DC voltage regulation loop to produce the modulating signals with the required phase shift. As a result, the control circuitry does not require additional sensors. The PWM pattern is generated online, which results in fast response to transients. The rectifier is analyzed and design equations are derived. A design example is given and theoretical considerations are verified through simulation and by experimental results obtained on a 1 kVA laboratory prototype