With the popularization of variable frequency power supplies, the starting problem of motors has become easy to solve. However, for ordinary power supplies, the starting of squirrel cage rotor asynchronous motors has always been a problem. From the analysis of the starting and operating performance of asynchronous motors, it can be seen that in order to increase the starting torque and reduce the current during starting, a higher rotor resistance is required; When the motor is running, in order to reduce the copper loss of the rotor and improve the efficiency of the motor, it is required to have a lower rotor resistance; This is clearly a contradiction. For wound rotor motors, the resistor can be connected in series during startup and then cut off during operation, thus meeting this requirement very well. However, the structure of wound asynchronous motors is complex, the cost is
