A novel control strategy for optimal inverter switching frequency associated with minimal current ripple using single step predictive current control

The common trend in converter development is to increase the drive system performance with simultaneous consideration of cost reduction by operating the whole drive at its thermal limit. For this purpose all system components are, for short durations, even stressed above their rated values. Because thermal losses have to be well balanced it is necessary to adjust inverter switching frequency to its optimum value depending on the point of operation. By varying the inverter switching frequency the distribution of overall inverter losses between conduction and switching losses can be influenced. This control however implies the possibility of adjusting the inverter switching frequency online dependent on the point of operation. In this paper a new control strategy for controlling the switching frequency near its optimum by using a predictive fixed step current controller is presented. By influencing the switching decision using a weighting factor, the resulting inverter switching frequency can be modified. Hence operating the whole drive system with optimum performance with respect to both, the power devices as well as the ac machine losses is possible. The performance of the proposed method is investigated by simulation. Measurements results verify the accuracy in adapting the switching frequency to the optimum value depending on the point of operation.