On-line optimal switching patterns for 2-level and 3-level inverters using the fish method

The proposed fish method calculates, from any switching pattern, a unique and useful signature. This graphical signature, called fish, is a representation of the integrated voltage vector in revolving coordinates. Online switching rules which limit the radial and tangential flux deviations for voltage-source power-converters are shown. In this way the relative torque- and current-ripple are reduced while any given minimum on-time constraint of the applied semiconductor switches and snubbers is strictly obeyed. This online switching strategy can deal with a varying DC-link voltage, thus tolerating smaller DC-link capacitors and a weaker grid (long cables e.g.). The method is applicable to both two-level and three-level inverters