Low stress switching for efficiency

Power modules that turn on or off "softly," at near zero voltage or current, promise marked gains in performance by cutting switching losses and allowing faster controls-to the likely benefit of power converters. Medium power inverters have undergone significant changes. One improvement stems from new power transistors such as insulated-gate bipolar transistors (IGBTs) with their increasing voltage- and current-carrying capabilities and increasing switching frequencies. Others derive from the use of digital signal processors and such modern control techniques as fuzzy logic and neural networks, as well as from advances in the applications of power converters that employ soft switching of the power devices. Soft-switching technologies promise marked gains in performance-lower losses and higher switching frequencies than those in the prevailing hard-switching technology. The idea is to switch a device only when the voltage across it, or the current through it, is zero. Representative soft switching converters include DC-to-DC converters rated at up to several hundred watts, as well as inductive chargers for electric vehicle batteries rated at up to 120 kW. Technologically speaking, advances in soft-switching inverters have arisen chiefly from enhancements to semiconductor power devices. Today, IGBTs lead the market for medium-power applications.