The torque of the single-phase motor is pulsating, and the noise is relatively large, but the required power supply is relatively simple, especially in the family. Therefore, small household motor and instrument motors are mostly single-phase motors.
AC motors are divided into two major categories: synchronous motor and asynchronous motor. The rotor speed of synchronous motor ns is the same as that of rotating magnetic field. It is called synchronous speed. There is a strict relationship between ns and the frequency of the AC current (f) and the magnetic pole logarithm (P) of the motor. Ns = f/P in china,The power supply frequency is 50 Hz, so the synchronous speed of the dipole motor is 3000 revolutions per minute, and the synchronous speed of the quadrupole motor is 1500 revolutions per minute. The rotor speed of an induction motor is always lower than or higher than the speed of its rotating magnetic field, and the asynchronous name comes from it. The difference between the rotor speed of a induction motor and the rotating speed of a rotating magnetic field (referred to as slip) is usually less than 10%. It can be seen that the speed of AC motor (synchronous or asynchronous) is controlled by the frequency of power supply. Therefore, AC motor speed is difficult, the best way is to change the frequency of power supply, and in the past to change the frequency of power supply is more complex. Therefore, before 70s, in the speed control occasions, the use of DC motors. With the development of power electronic technology, AC motor frequency conversion speed regulation technology has begun to be practical.
AC motor has become the most common motor because of the great development of AC power system.Compared to the AC motor and DC motor, because there is no commutator (see DC motor commutation), therefore has the advantages of simple structure, convenient manufacture, relatively strong, easy to make high speed motor, high voltage, high current, large capacity. The coverage of AC motor power greatly, from a few watts to several 101000 watts, even millions of kilowatts. In the early 1980s, the largest turbo generator reached 1 million 500 thousand kilowatts.AC motors are usually divided into AC generators, AC motors and synchronous regulators according to their functions. Due to the reversibility of the working state of the motor (see the motor), the same motor can be used as a generator and an electric motor. It is not very precise to divide the motor into generator and motor, but some motors are mainly used as generator, some motors are mainly motor operated.
