Back-EMF Decay Transient Based Identification Method of Rotor Time Constant of Inverter-Fed Induction Motors for Energy Conservation

Variable frequency speed regulation technology is widely used in energy-saving control systems for fan and pump loads. Replacing mechanical adjustment devices such as valves with variable frequency speed regulation can effectively reduce energy consumption. The energy-saving and speed regulation performance of induction motor variable frequency drive system based on the indirect rotor flux-oriented control (I-RFOC) heavily depends on the accuracy of rotor time constant. Traditional rotor time constant measurement methods often require the motor to be in a static state, which cannot reflect the different load conditions of the motor. In the process of stator back electromotive force decay of induction motor, the rotor side information is reflected in the change law of stator side voltage and current through flux linkage coupling. Aiming at the transient experimental phenomenon of stator winding back electromotive force decay after power is disconnected, this paper proposes a rotor time constant identification method based on curve fitting and differential evolution algorithm. The identification can be completed by measuring stator voltage and current. The influence of load, zero-sequence component and variable frequency supply conditions on the identification process is also analyzed. Finally, with a 55-kW induction motor, experimental validation is also performed to verify the proposed identification method.