Principle of Optimal Voltage Regulation and Energy-Saving for Induction Motor With Unknown Constant-Torque Working Condition

To achieve optimal voltage regulation and energy savings of an AC induction motor operating under constant-torque and variable-working-load conditions, and consider a motor's T-type and 0-type equivalent circuit, the copper and iron losses of the stator were regarded as invariable losses that were only related to the stator voltage, and the copper losses of the rotor were regarded as variable losses that varied with the load torque. The total electrical loss formula and the optimal voltage regulation formula for the motor were deduced. The formulas revealed that the total electrical loss of the motor was affected by the stator voltage and the rotor load torque, and the optimal voltage regulation changed exponentially with the load torque of the motor. The calculation results of an engineering example showed that when s D 0.01-0.03 and the motor operated stably, the motor load torque error was not more than 1.8 N m based on the exact and approximate solutions of the slip s. The total electrical loss showed almost no calculation error when the working voltage of the motor was higher than 230 V. The optimal voltage regulation and its error increased with the increase in the motor load torque, but within the working voltage range of the motor, the optimal voltage regulation error did not exceed 6 V. The total electrical loss with the optimal voltage regulation mode and a variable load torque was less than the total electrical loss of a 380- or 220-V constant driving mode. With the increase in the load rate, the total electrical loss increased. When the motor's load did not exceed the medium load and the motor operated with optimal voltage regulation, the energy-saving effect was significant. In particular, when the motor operated without a load, the total electrical loss was almost 0.