The speed regulation and control of electric motor is one of the basic technologies of various industrial and agricultural machinery, office and people's livelihood electrical equipment. With the amazing development of power electronics technology and microelectronics technology, adopting the ac speed regulation mode of "special frequency conversion induction motor + frequency converter" is guiding the reform of replacing traditional speed regulation mode in the speed regulation field with its excellent performance and economy. The good news bring to all industries lies in making the degree of mechanical automation and production efficiency greatly improved, saving energy, improving product qualification rate and product quality, corresponding improvement of power system capacity, miniaturization of equipment, increasing comfort, and replacing the traditional mechanical speed regulation and dc speed regulation scheme with rapid speed.

Due to the particularity of frequency conversion power supply and the system's demand for high-speed or low-speed operation and dynamic response of rotating speed, the demanding requirements for the motor as the power main body have been put forward, bringing new topics in electromagnetic, structure and insulation to the motor.