Design Considerations for a Novel Single-Stage AC-DC PWM Full-Bridge Converter
Abstract— A new ac-dc single-stage PWM full-bridge converter is proposed in this paper. The
converter uses an auxiliary transformer winding to keep the voltage across the primary-side dc bus below 450V over a universal line and wide load range. In this paper, the fundamental operating principles of the proposed converter are discussed, and a mathematical analysis of the converter is then performed. The analysis is used to derive graphs of steady-state characteristic curves that can be used to form the basis of a design procedure. The procedure can be used to select the values of key converter components, and is demonstrated with an example showing the design of a 48 Vdc, 500W power supply. Experimental results obtained on a laboratory prototype are presented to confirm the concepts presented in this paper.
I. INTRODUCTION
Ac-dc full-bridge single-stage converters can generally be classified as being either current-fed or voltage-fed converters [1]-[11]. Voltage-fed converters have a large energy-storage capacitor at the input of the full-bridge converter, across the primary-side dc bus. This capacitor keeps voltage overshoots and ringing from appearing across the dc bus, and filters out a large 120 Hz ac component so that it does not appear at the output. The primary-side dc bus voltage in these converters, however, can become excessive. It can exceed 500-600Vdc when the converter is operating with a high input line voltage. This voltage is dependent on input line and output load conditions, and the component values of the converter, especially the input inductor Lin and the output inductor Lo.
It is possible to reduce this voltage through the selection of appropriate component values although overall converter performance suffers as a result. A new single-phase, single-stage, voltage-fed, ac-dc full-bridge converter that can operate with a lower dc bus voltage than other voltage-fed converters was, however, proposed in [12]. The lower dc bus voltage allows the selection of the converter components to be done under less stringent conditions. A greater emphasis on converter performance can therefore be placed when selecting converter components.
In [12], however, the steady-state characteristics of the converter were not examined, and only a few, very general design guidelines were given. In this paper, the fundamental operating principles of the proposed converter are discussed, and a steady-state analysis of the converter is performed. The analysis is then used to derive graphs of steady-state characteristic curves. These graphs show the effect of certain key components on the operation of the converter, and are used as the basis of a design procedure. The procedure can be used to select appropriate values for the key components and is demonstrated with an example in the paper. Results obtained from an experimental prototype that confirm the feasibility of the converter are also presented in the paper.
II. CONVERTER OPERATION
The proposed converter is shown in Fig. 1. It can be seen in Fig. 1 that the input
