Embodiments of the present invention relate to an a method, apparatus and computer program product for controlling the operation of a drive unit comprising a plurality of switching modules arranged to receive a DC electricity supply and generate an AC electricity supply for driving a load from the received DC electricity supply, the AC electricity supply being generated by the switching of the plurality of switching modules between a conducting state and a non-conducting state. The method comprises receiving one or more characteristics associated with each of the switching modules, comparing, for each switching module of the plurality of switching modules, a characteristic of the switching module with an equivalent characteristic associated with one or more other switching modules of the plurality of switching modules, and controlling a time period during which one or more of the plurality of switching modules are in the conducting state in accordance with a result of the comparison.