DC motor has fast response, large starting torque, and the performance of providing rated torque from zero speed to rated speed. However, the advantages of DC motor are its disadvantages. If DC motor wants to produce the performance of constant torque under rated load, the armature magnetic field and rotor magnetic field must be maintained at 90 ° constantly, which requires carbon brush and commutator. The carbon brush and commutator will produce sparks and carbon powder when the motor is rotating, which will not only cause damage to the components, but also limit the use occasions.
There is no carbon brush and commutator in AC motor, which is maintenance free, robust and widely used. However, to achieve the performance equivalent to that of DC motor, complex control technology must be used. AC motor can be divided into asynchronous motor and synchronous motor. According to the different number of stator phases, asynchronous motor can be divided into single-phase asynchronous motor, two-phase asynchronous motor and three-phase asynchronous motor. The three-phase asynchronous motor has the advantages of simple structure, reliable operation and low cost.