A PWM Control Method for Reducing dv/dt in Cascaded Power Converters

Abstract

Today’s semiconductor devices are accompanied by high switching frequencies (>kilo-hertz) and small transition times (<micro-seconds). Such fast transition times are accompanied by undesirable effects such as voltage overshoots at the load terminals, ground leakage currents, wide-band electromagnetic noise, etc. With the advent of wide band-gap devices, several applications are moving towards higher switching frequency operation with at-least an order of magnitude reduction in transition times. While these characteristics are considered necessary to break the next-generation barriers in power density, efficiency and applicability, the undesirable effects due to faster transitions are expected to present obstacles. This work proposes a PWM approach to modify the shape of the switching voltages to overcome the disadvantages of the fast transition times without an increase in switching losses. In fact, several of the transitions feature ZVS operation resulting in reduced switching losses. The paper discusses the analytical details of the approach using a simple dc-dc boost-buck converter and extends it to dc to three-phase AC converter using the principles of space vector modulation. The paper also presents the comparative results in terms of voltage over-shoots over long cables, loss calculations and electromagnetic noise.