Control and Measuring Method for Three Phase Induction Motor with Improved Efficiency

This thesis deals with improving and measuring the efficiency of variable speed induction motor drives. Optimized efficiency is achieved by adapting the magnetizing level in the motor according to the load percentage. The thesis investigates on the efficiency improvement of squirrel cage induction motors fed by SVM-VSI, by using the loss model method. A new expression for the optimal air gap flux is calculated from a detailed loss model. This loss model comprises the copper loss, iron loss, friction, windage, stray, and harmonic loss. The calculated optimal air gap flux is a function of these losses and also considers the non-linearity of the magnetizing inductance and the effect of the temperature on the motor parameters (stator and rotor resistances). The proposed loss model improves the efficiency of a speed sensorless indirect field oriented control (IFOC) induction motor. The (IFOC) of an induction motor is sensitive to motor parameter variation. Rotor and stator resistances vary with the motor temperature, and the proposed loss model controller depends on the motor parameters. So an on-line estimation of motor parameters using parameter adaptive observer is used. An on-line search control method shows the accuracy of the optimal flux values, which are calculated by using the proposed loss model. By using the calculated optimal air gap flux for speed sensorless indirect vector controlled induction motor, an improvement in motor efficiency and power factor are achieved especially at light load. If there is an increase in the load while the motor is operating with the optimal flux value, the flux will be right away increased to the rated value, and later, the suitable optimal flux value according to the new load torque is calculated. Measuring the efficiency of the induction motor according to IEEE-112B standard requires highly accurate measuring devices, where the inaccuracy of the power meter and torque meter should not exceed (0.1%), and (1 RPM) for speed sensor. But such devices are expensive. An accurate system using a FPGA was designed to calculate the motor efficiency without requiring a power meter. By adapting the motor voltages and currents signals, load torque meter signal, and position sensor signal the average electrical and mechanical motor powers are calculated in a FPGA. The accuracy of the calculated electrical power is verified by using advanced power meter (with accuracy equals 0.1%), in order to satisfy the recommendation of the standard IEEE-112B. Fuzzy Logic Controller improves the motor speed performance when compare to PI speed controller. The improvement in the efficiency, the power factor and the motor stability under fast load variations by using the proposed optimal flux control method is compared with the rated flux control method experimentally. Also, the experimental results show the accuracy of the designed efficiency measuring system