Method of controlling the switching of a multilevel converter, a controller for a multilevel converter, and a computer program for controlling a converter

Abstract

A method of controlling a multilevel converter, a computer program and a controller for a converter is provided. The method includes determining a transition voltage from a control period to a following control period, analyzing the switching cells of each phase leg, selecting capacitors to provide the transition voltage and synthesize the output voltage for the following control period, and connecting the selected capacitors during the following control period. The analyzing of each switching cell includes analyzing a first switching leg and a second switching leg of the switching cell. The method includes determining whether a change of state of the first switching leg would contribute to the direction of the transition voltage, and determining whether a change of state of the second switching leg would contribute to the direction of the transition voltage, and determining the internal conditions of each of the first and the second switching leg that are determined as contributing to the transition. Thus, the two legs of the H-bridge are analyzed separately. The selecting of capacitors is performed by selecting the capacitors of the switching legs of the phase leg for the transition voltage on the basis of the determined internal conditions of the switching legs, including comparing the internal conditions of all the switching legs of the phase leg. A controller is configured to control the multilevel converter by performing the method.