An improved space vector PWM control algorithm for multilevel inverters

The research on the multilevel inverter has been receiving wide attention mainly due to its capability of high voltage operation without switching devices connected in series. In this paper, a simple, detailed and general space vector algorithm is given. To facilitate the design and digital implementation of the space vector algorithm, all the space vectors are transformed from the commonly used Cartesian coordinate system to a 60/spl deg/ coordinate system. At the same time, two switching states selection algorithms are studied for multilevel inverters: large small alternation (LSA) method and all mean (AM) switching states method, in which the latter one can give better performance in terms of the harmonics content on the transformer primary side though it has a higher device switching frequency than that of LSA. AM switching states selection method makes the concept of space vector modulation (SVM) consistent in two-level voltage source inverters and multilevel inverter; both output equivalent mean switching sates in every sampling period. Both of these two methods also features easy implementation and generality and can be used in any high-level cascaded H-bridge inverters. They are verified through computer simulations and experiments.