Analysis and design of a near unity power factor single phase trapezoidal AC power supply

Abstract

Single phase AC power supplies used for powering optical fiber/coax cable are required to generate trapezoidal-shaped waveform. The proposed converter topology has the following main features: (a) a small DC bus capacitor resulting in a DC bus having a very large 120 Hz component; (b) an on-line instantaneous voltage controlled feedforward PWM pattern generator, based on reset integral control technique, in which the PWM modulating function is synchronized with the DC bus ripple; the trapezoidal output voltage fits within the envelope of the ripple, leading to maximum voltage utilization; and (c) the input current flows during the complete period which yields low overall distortion and high power factor. A power circuit realization of the proposed power supply and control scheme based on the one-cycle reset integral PWM pattern generator, required to produce a trapezoidal output voltage is shown. The one-cycle reset integral control technique produced the best overall results in terms of power factor (PF), total harmonic distortion (THD) and efficiency (/spl eta/). This paper presents detailed analysis and design curves that are required to implement the proposed power supply. The analytical expression for the RMS value of the current through the capacitor and input AC line are derived. A design procedure to select and rate components of the power and control circuit is illustrated by means of a design example. Finally, the theoretical and simulated results presented are experimentally verified.