Synchronous motor, and induction motor (asynchronous motor), is a common AC motor. Synchronous motor is the heart of power system, it is a set of rotating and static, electromagnetic and mechanical changes in one motion, electric energy and mechanical energy conversion element, its dynamic performance is very complex, but also greatly affect the dynamic performance of the whole power system dynamic performance. The characteristics are: steady state operation, the rotor speed and the frequency of the grid has a constant relationship between n=ns=60f/p, where f is the grid frequency, P is the pole of the motor, NS is called synchronous speed. If the frequency of the grid is constant, the speed of the synchronous motor is constant at steady state, independent of the magnitude of the load. Synchronous motor is divided into synchronous generator and synchronous motor. The alternator in modern power plant is mainly synchronous generator.