Double Modulation Applied to a High Power Factor Rectifier with High Frequency Transformer for Ups Application

Abstract

The bridgeless boost-full-bridge rectifier is used as preregulator for a high frequency isolated UPS and the asymmetric pulse width modulation (APWM) modulation is applied in order to obtain a high quality input current with high power factor. The rectifier operates with soft-switching and reduced conduction losses improving the efficiency. A simultaneous phase-shift modulation allows obtain a fast output voltage control and step-up/step-down static gain, becoming possible the operation in a wide voltage range. An auxiliary power feed-forward action allows improving the dynamic response of the output voltage and primary side DC-bus voltage for the load transient. The double modulation and the auxiliary control action reduce the DC-bus voltage overshoot and undershoot during the output load transients, reduce the converter filters capacitance and limit the maximum voltage across the switches. The theoretical analysis and design procedure are presented for the modulations proposed and the experimental results were obtained from a 2 kW prototype operating with switching frequency equal to 44 kHz. The experimental results are presented using four different combinations of control structures showing comparatively the dynamic improvements.

Keywords

• AC-DC Power Conversion
• Digital control
• Rectifiers