Ripple Current Reduction by Optimizing Load Dependend Switching Losses Using Adaptive Current Control

In modern inverter fed drive applications the power semiconductors used are typically designed to operate at their maximum thermal operation conditions. Semiconductors worst case thermal considerations in general define the uppermost inverter switching frequency dependent on maximum load current. Fixing this frequency to a constant value, the drive will not be operated with best possible performance at partial load. With the help of the proposed modified predictive current controller it is possible to control both machine current as well as inverter switching frequency at once. Using a thermal model of the power semiconductors hence enables operation at their thermal limit as well as a reduction of current ripple. In a first step the modified predictive current controller as well as the thermal model of the power semiconductors is described. Finally measurement results on a 220kW high precision industrial load dynamometer are presented to compare the performance of a classical predictive current controller and the proposed modification with switching frequency adaptation.