LAUSR

This paper presents a methodology to control a two-staged ac/dc converter, which is a cascade combination of a three-phase ac–dc boost power factor correction (PFC) rectifier and a phase-shifted full-bridge (PSFB) dc/dc converter. This paper explains the issues of instability and losing unity power factor operation, i.e., high reactive power transfer with conventional PI compensator due to the sensitive variation of output impedance of the PFC stage at different loads. In this paper, this instability issue is resolved by the proposed state-feedback control methodology, which shows that there exists a load-insensitive range of controller parameters, providing unity PFC. As an additional benefit of this control, total number of sensors are reduced by three (an input phase current, a dc/dc primary current, and an output dc voltage), in comparison to the conventional PI-based control. This reduction is achieved by introducing two augmented state variables followed by their reduced state observer design. A 6-kW laboratory prototype of the integrated three-phase PFC and PSFB dc/dc is developed and designed to validate the proposed control algorithm. The experimental results show a conversion efficiency of 95.4% at full load, input total harmonic distortion of 4.1%, power factor of 0.998, and output voltage ripple of ±1%.