Electric machine is an electromagnetic device which can convert mechanical energy and electric energy by magnetic field. In order to establish the necessary air gap magnetic field for the mechanical and electrical energy conversion, two methods can be made. In the motor winding through the current generation is a requires both specialized winding and a corresponding device, and needs a continuous supply of energy to maintain the current flow, such as ordinary DC motor and synchronous motor; another is by permanent magnets to generate a magnetic field, which can simplify the structure of the motor and saving energy, which is a permanent magnetic motor.