Extreme efficiency power electronics

In this paper a generalized description and an overview of degrees of freedom and selected measures for efficiency improvement of power electronics converters is given. The background of all considerations is formed by single-phase PFC rectifier systems, but the concepts shown are fundamental and fully applicable for other converter systems. First, the influence of the main components of the losses of a converter on the efficiency characteristic over the output power is discussed. Subsequently, a detailed analysis of the possibilities, of minimizing the semiconductor losses, the losses of the passive components including the EMI filter, and the power requirements of auxiliary systems in the course of the design process are given. In this context also the technological boundaries that limit the maximum efficiency of a converter are clarified and the compromise that always has to be made between efficiency and power density is highlighted. Furthermore, a control procedure is discussed to maximize the efficiency in the partial load range and a resonant transition mode ZVS converter system is presented that allows to attain efficiencies significantly over 99% without the use of SiC semiconductors. In addition the accuracy of the input and output power measurements required for measuring highest efficiencies is clarified, whereby the advantage of a direct loss measurement by means of a calorimeter becomes immediately clear. Finally, results of measurements on a demonstrator of a CCM single-phase PFC rectifier system with 99.1% max. efficiency and η > 99% above half rated power, and on a resonant transition mode PFC rectifier system with η_max = 99.3% and η > 99% above 15% rated power are presented.