A method of determining the maximum performance torque-speed characteristic for an induction motor drive over its entire speed range

This paper discusses a simple and efficient method of determining the maximum performance torque-speed characteristic for an induction motor drive. The proposed method considers the voltage and current constraints of the inverter supply for the drive. The mathematical description of the motor in DQ reference frames was adapted to build a model applicable for numeric calculation. It has been shown that the torque-speed characteristic has 3 operating speed regions. The optimal relationship between the magnetisation and q-axis currents is derived for the third speed region. The model performs tracking of the magnetisation current in order to keep the output voltage and current under the limits of the inverter. In addition, the proposed model provides a method of calculation for the output power, the apparent power, the power factor and the efficiency vs speed. The proposed method is applicable for the analysis of the induction motor drive operating over its entire speed range.