What are the speed regulating methods of AC motors? Detailed point
(1) rotor circuit series resistance: used in AC winding asynchronous motors. The range of speed regulation is small, the resistance consumes power, and the motor efficiency is low. Used of cranes.(2) change the speed of power supply voltage, the speed range is small, the torque decreases greatly with the voltage drop, and the three-phase motor is usually not used. Used for single-phase motor speed regulation, such as fan.(3) cascade speed regulation, in essence, is the introduction of additional rotor electromotive force, change its size to speed. It is also only used in wound motors, but the efficiency is improved.(4) electromagnetic speed regulation. Used only for slip motors. By changing the exciting coil current, stepless smooth speed regulation, the mechanism is simple, but the control power is smaller. Not suitable for long term low speed operation.
1. use frequency changer to change power frequency speed regulation, speed range is wide, stability smoothness is better, mechanical characteristic is hard. That is, with the rated load, the speed drops much less. Stepless speed regulation. It is suitable for most three-phase squirrel cage asynchronous motors.2., change the magnetic pole logarithmic speed regulation, belong to level speed regulation, speed adjustment smoothness, generally used in metal cutting machine tools.3. change slip speed regulation.
