Methods of improving efficiency in wide input range boost converters at low input voltages

摘要

Development of switching power supplies for the telecom industry has been constantly moving towards higher efficiency and more compact units, with watts per cubic inch as a key design parameter. In recent years there has also been a growing demand for a wide input voltage range - the rectifier should be designed to operate at input voltages ranging from 90 V to 280 V while maintaining a high efficiency. A typical single-phase rectifier is composed of a power factor correction (PFC) stage and an isolated DC/DC stage. The PFC stage usually contains a full wave rectifier followed by a boost type DC/DC converter. This configuration of the PFC stage has several advantages including continuous input current and the ease of implementing power factor correction. The boost topology also yields excellent efficiency over a limited input range, but has difficulties in maintaining high efficiency at the lower end of a wide input range. AThe problem is of course well known and a number of papers have been published suggesting a variety of techniques to deal with it. The purpose of this paper is to present a survey covering some of the most interesting approaches the authors have come across. All the techniques discussed make use of one of the following basic strategies, or a combination of them: · Reducing the number of semiconductor forward voltage drops in current paths. · Dual input range configuration of the converter. · Reduction of conduction losses through the use of IGBT switches. · Paralleling of components and circuits. · Reduction of switching losses through the implementation of soft switching techniques. A detailed analysis of the different loss mechanisms is carried out and verified against measurements on a 1.2 kW rectifier from Emerson Energy Systems. An advanced Mathcad spreadsheet, based on this analysis, is used to give a clear picture of the distribution of losses in a conventional boost converter. The results from the spreadsheet are used to evaluate the potential of the alternative techniques. Advantages and drawbacks of the presented techniques are further discussed from a practical as well as an economical point of view.