A voltage space approach to developing a soft-switched inverter topology with low device voltage stress

Scope and method of study. The purpose of this research was to develop a soft-switched inverter topology with substantially lower device voltage stress than resonant link topologies, which effectively comprise the entirety of soft-switched inverter technology. The premise of the study was that an inverter's topological structure imposes restrictions on the trajectories that its output voltage can traverse in voltage space and that these restrictions are directly related to key performance characteristics, such as device voltage stress and output waveform distortion. Techniques were devised to describe the output voltage trajectories of a generalized bridge-based inverter in terms of a finite set of primitive trajectory components. Analytical methods were developed for computing device voltage stress and certain output waveform quality metrics for a given inverter based on the subset of these primitive trajectory components allowed for the inverter's specific topological structure. These techniques and methods were used to synthesize a new soft-switched inverter with a predicted voltage stress level well below that of resonant link topologies. Modeling and simulation were used to evaluate the proposed inverter and to compare its performance characteristics to those of a leading resonant link inverter design.; Findings and conclusions. Analysis of resonant link topologies showed that a direct relationship exists between device voltage stress and the lower cutoff frequency of the output waveform distortion that exists when the inverter is synthesizing a static three-phase voltage. This was shown to result from the absence of specific primitive trajectory components that are available to conventional hard-switched inverters. The new inverter topology proposed in this work, which is capable of executing these trajectories, was shown to have the same low device stress level as a conventional hard-switched inverter. The addition of these primitive trajectories also increased the effective switching frequency by up to 50% over resonant link designs. Simulation results showed the proposed inverter to have 66.7% of the device voltage stress and 60% or less of the load current distortion seen for the leading resonant link design.