Patent ID: 8829723

Claim:
A method of operating a multi-level converter comprising a plurality of series connected converter units that each include an electrical charge storage unit and a switch arrangement, the method comprising: detecting a charge state of the charge storage units of the converter units; providing a set of parameter sets dependent on a desired output voltage waveform, wherein at least one parameter set defines a fixed duty-cycle; assigning the parameter sets to the converter units based on the detected charge states, assigning comprising assigning the at least one parameter set to one converter unit for a duration of at least one half-cycle of an AC output voltage; generating control signals coupled to the switch arrangements of the plurality of series connected converter units, wherein the generating is based on the set of parameter sets; generating an output voltage for each of the plurality of series connected converter units based on the control signals, wherein the generating the output voltage comprises providing a voltage amplitude level of one of two different voltage amplitude levels in accordance with the fixed duty cycle; and providing the AC output voltage at output terminals of the multi-level converter based on generating the output voltage for each of the plurality of series connected converter units.