Strategy for online adaptation of the inverter switching frequency imposed by a predictive current controller

Pulse-width modulated power converters are currently the most widespread solution in industrial drive applications. The common trend in converter development is to operate all system components at, or - for short durations - even above their rated values. At system configurations where the inverter is operating at its thermal limit different points of operation of a connected machine require special measures to actively control the distribution of the overall inverter losses in an optimum way between conduction and switching losses. This control however implies the possibility of dynamically changing the switching frequency. In this paper a new control strategy for adjusting the switching frequency dependent on the point of operation is presented. It is based on a predictive fixed step current controller. Introducing a weighting factor for the switching decision, it is possible to influence potential switching transitions and thus also the resulting switching frequency. By applying the proposed method it is possible to operate the whole drive system with optimum performance with respect to both, the power devices losses as well as AC machine losses and control performance.