Analysis of Induction Motor Drive Losses in the Field-Weakening Region

Operation of adjustable-frequency drives is accompanied by generation of losses in the converter and motor. These losses depend on the modulation frequency and on the drive output power. The change of modulation frequency modifies converter losses and also motor losses, because of the modified motor current waveform. Thus, it modifies total drive losses. Variation of the drive output power also modifies total drive losses and can be problematic when the drive operates in the field-weakening region. The paper presents a complete analysis of motor losses, converter losses and losses of the entire drive in the field-weakening region of an open loop controlled induction motor drive supplied by a voltage source inverter. Losses are presented in dependence of the voltage source inverter output frequency and the drive's output power. Presented results show that the modified voltage to frequency ratio causes an increase of the total drive losses in the region of high frequencies and high output powers. The paper also presents an analysis of the impact of modulation frequency on drive losses