A novel high input power factor soft-switching single-stage single-phase AC/DC/AC converter

This paper proposes novel soft-switching single-stage single-phase AC/DC/AC converter to give high input power factor and low current distortion on the rectifier side and provide clean and stable AC voltage on the inverter side. In the proposed converter, besides operating at constant frequency, all semiconductor devices operate at soft-switching without additional voltage stress and current stress. A significant reduction in the conduction losses is achieved, since the circulating current for the soft switching flows only through the auxiliary circuit and a minimum number of switching devices are involved in the circulating current path, and the rectifier in the proposed converter uses a single converter instead of the conventional configuration composed of a four-diode front-end rectifier followed by a boost converter. An average-current-mode control is employed in the rectifier side of proposed converter to detect the transition time and synthesize a suitable low harmonics sinusoidal waveform for the input current. The sinusoidal pulse-width modulation (SPWM) control strategy is employed in the inverter of proposed converter to achieve well dynamic regulation. A design example of 1000 W soft-switching single-stage single-phase AC/DC/AC converter is examined to assess the converter performance.

I. Introduction

Matrix converters have received considerable attention [1]–[3] due to their potentiality to provide direct AC/AC conversion without energy storage. However, they turned into wide application due to severe requirements: four-quadrant switches, critical timing, sensing of switch voltage and current, snubber circuits needed to absorb overvoltages coming from the inductive commutation. As a result, circuit efficiency and reliability are affected. More popular is the indirect ac/dc/ac conversion by means of PWM rectifier-inverter systems with dc link. As compared to matrix converters, these systems show improved reliability and allow a greater output voltage. The one of conventional single-phase ac/dc/ac converters is shown in Fig. 1(a). In this system, a big tank capacitor in the dc link provides decoupling between the rectifier and the inverter, so that the two converters can be driven independently according to usual PWM techniques [4]–[5], providing excellent input and output performances. In fact, this system is the combination of the boost rectifier and the buck inverter. The boost rectifier performs the functions of power factor correction and boost ac/dc conversion. The buck inverter performs the function of buck dc/ac conversion with output voltage of variable amplitude and frequency. Therefore, the ac/dc/ac system shown in fig. 1(a) have been widely used in industrial application such as uninterruptible power supplies, static frequency changes and variable speed drives. For minimization of size and weight of overall system, increasing switching frequency in them is required. However, increasing switching frequency will result in the more switching losses and electromagnetic interference (EMI). In order to improve this problem, they must use own the soft-switching techniques, respectively. This solution will result in high complexity of overall circuit, high weight, high cost and low efficiency. Fig. 1 (a) Traditional single-stage single-phase AC/DC/DC converter (b) Proposed soft-switching single-stage single-phase AC/DC/AC converter