Synchronous motor, like induction motor (i.e. asynchronous motor), is a common AC motor. Synchronous motor is the heart of power system. It is an element that integrates rotation and static, electromagnetic change and mechanical motion to realize the transformation of electric energy and mechanical energy. Its dynamic performance is very complex, and its dynamic performance has a great impact on the dynamic performance of the whole power system.The characteristics of synchronous motor are: during steady-state operation, there is a constant relationship between rotor speed and grid frequency, n = ns = 60F / P, where f is grid frequency, P is pole logarithm of motor, and NS is called synchronous speed. If the frequency of the power grid remains unchanged, the speed of the synchronous motor in the steady state is constant regardless of the size of the load.Asynchronous motor, also known as induction motor, is an AC motor that generates electromagnetic torque by the interaction between air gap rotating magnetic field and rotor winding induced current, so as to realize the conversion of electromechanical energy into mechanical energy. According to the rotor structure, asynchronous motors are divided into two forms: Squirrel Cage (squirrel cage asynchronous motor) and wound asynchronous motor.

1. Differences in design between synchronous motor and asynchronous motorThe biggest difference between synchronous motor and asynchronous motor is whether their rotor speed is consistent with the stator rotating magnetic field. The rotor speed of the motor is the same as the stator rotating magnetic field, which is called synchronous motor, on the contrary, it is called asynchronous motor.In addition, the stator windings of synchronous motor and asynchronous motor are the same, and the difference lies in the rotor structure of the motor. The rotor of asynchronous motor is a short-circuit winding, which generates current by electromagnetic induction. The rotor structure of synchronous motor is relatively complex, with DC excitation winding, so it needs external excitation power supply to introduce current through slip ring; Therefore, the structure of synchronous motor is relatively complex, and the cost and maintenance cost are also relatively high.

2. The difference of reactive power between synchronous motor and asynchronous motorCompared with asynchronous motor can only absorb reactive power, synchronous motor can emit reactive power and absorb reactive power!3. Differences between synchronous motor and asynchronous motor in function and purpose

The speed of the synchronous motor is synchronized with the electromagnetic speed, while the speed of the asynchronous motor is lower than the electromagnetic speed. The speed of the synchronous motor will not change as long as it does not lose step regardless of the load. The speed of the asynchronous motor always changes with the change of the load. Synchronous motor has high precision, but complex manufacturing, high cost and relatively difficult maintenance. Although asynchronous motor has slow response, it is easy to install and use and cheap. Therefore, synchronous motor is not as widely used as asynchronous motor. Synchronous motors are mostly used in large generators, while asynchronous motors are almost used in motor occasions.