Maximum efficiency per torque direct flux vector control of induction motor drives

In this paper, a loss-minimizing strategy is proposed for induction motor drives to ensure maximum efficiency operation for a given torque demand. The proposed strategy directly regulates the machine stator flux according to the desired torque, using an optimal stator flux reference. Therefore, the proposed strategy is suitable for motor control schemes that are based on direct flux regulation, such as direct torque control or direct flux vector control. The maximum efficiency per torque (MEPT) stator flux map is computed offline using the traditional no-load and short-circuit tests' data. An iron loss model based on the stator flux and frequency is also proposed for the calibration of the machine loss model and also for on-line monitoring of the iron losses during motor operation. The proposed MEPT strategy has been validated on a 2.2 kW induction machine and the motor efficiency has been measured for different speed values and variable load conditions. The experimental results confirm the effectiveness of the proposed solution.