Why can single-phase AC motors be controlled by voltage?
The low voltage is not equivalent to reducing the torque well, the slip is not big, the speed is not low, I understand it
Simply put, after the voltage is lowered, if the rotor spins at its original speed, the stator gets a very small current. The electromagnetic torque decrease under the same load torque under the action of slip increase speed decreased, resulting in decreased speed reflected impedance decreases according to the size of the formation of a low impedance voltage and current speed speed balance, therefore maintained at a low speed.
The principle that single-phase AC motor can be controlled by voltage is:1, synchronous motor torque = motor power / (2 * pi * speed /60) N = M.2, alternating current frequency is 50Hz, synthesis magnetic field synchronous speed is 50r/s, namely 3000r/min, if the electric motor more than one pair of magnetic poles, further analysis can also get synchronous speed.3, 4 pole synchronous speed is 1500r/min, 6 pole synchronous speed is 1000r/min, 8 pole synchronous speed is 750r/min.4, asynchronous motor speed = (60* frequency / pole count) * slip.5, the synchronous motor stator voltage reduction, according to the first, the motor torque drop, the motor is asynchronous, accord with the fourth formula, the slip is less than 1, the motor speed decline.6, if the motor torque and external resistance torque balance, the slip rate is also stabilized, the speed stabilized, the motor speed down success.After 7 and fifth, sixth, the stator voltage of the motor is increased, and the process is reversed. So realize voltage speed regulation.
