Multilevel converter and a method for controlling multilevel converter including balancing cell voltages

摘要

A multilevel converter for controlling a multilevel converter is provided. The multilevel converter is a single phase converter with one phase leg, or a three phase converter with three phase legs, the phase legs of the three phase converter are interconnected in a star-configuration. The single phase converter with one phase leg, or each three phase converter with three phase legs, phase leg includes switching cells, and each switching cell includes semi-conductor switches arranged to selectively provide a connection to a corresponding energy storage element. The converter also includes a controller, which is provided to monitor the DC voltage of the energy storage elements, and the controller is provided to control the switching of each switching cell. The phase leg of the single phase converter, or each phase leg of the three phase converter, includes two parallel branches of switching cells, the branches being configured in a closed circuit.

主权项

1. A multilevel converter comprising:
a single phase converter with one phase leg connected to a power network, or a three phase converter with three phase legs each connected to the power network, the phase legs of the three phase converter being interconnected in a star-configuration, the single phase converter with one phase leg, or each three phase converter with three phase legs having switching cells, each switching cell having semi-conductor switches arranged to selectively provide a connection to a corresponding energy storage element, the converter also includes a controller, which is provided to monitor the DC voltage of the energy storage elements, the controller is provided to control the switching of each switching cell, wherein the phase leg of the single phase converter, or each phase leg of the three phase converter, comprises two parallel branches of switching cells, the branches being configured in a closed circuit; wherein the controller is adapted to monitor the voltage levels of each energy storage element and to monitor phase voltages and phase currents of the power network, the controller transferring energy between the energy storage elements by controlling the switching of the switching cells in dependence of the voltage levels of each energy storage element to compensate for voltage unbalances the switching of the switching cells in each of the two branches causing a circulating current in the two branches without contributing to the phase current of the phase leg.