Zero Sequences Optimizing Different Criteria for Three-Phase Multilevel Inverters

In a world with growing concern for efficiency, power electronics associated to high level control techniques are more and more used in different fields of application. One of the most common applications are three-phase machines fed by three-phase inverters to tune precisely the power consumption. In recent years, multilevel inverters have become the best solution to address the problems of high voltage, high current or high efficiency. PWM modulation strategies play an important role in the design of such converters and one may choose adequate carriers and zero order signals in order to improve the design of an important component of the system. Some PWM methods found in the literature minimize some key elements of three-phase systems, however when multilevel converters are considered, little is found. The aim of the paper is to present a simple but powerful approach which allows us to determine optimal zero sequence signals (also called Common Mode Offset, CMO) corresponding to any desired objective for many different topologies. It will be shown that some widely accepted PWM methods as well as new optimal methods are found by this method. These PWM methods will be compared by means of simulation and some CMOs created using our approach are validated by experimental results.