The motor is easy to use, reliable in operation, low in price and firm in structure, but its power factor is low and its speed regulation is difficult. Synchronous motors are commonly used for power machines with large capacity and low speed (see synchronous motors). The synchronous motor not only has high power factor, but also its speed is independent of the load size and only depends on the grid frequency. The work is relatively stable. DC motors are widely used in situations requiring wide range speed regulation. However, it has a commutator, which is complex in structure, expensive in price, difficult to maintain, and not suitable for harsh environment. After the 1970s, with the development of power electronics technology, the speed regulation technology of AC motor has become mature, and the equipment price has been decreasing, which has begun to be applied. The output mechanical power that the motor can bear under the specified working system (continuous type, short time operation system, intermittent cycle operation system) without causing overheating of the motor is called its rated power. Pay attention to the provisions on the nameplate when using. During the operation of the motor, attention should be paid to matching its load characteristics with the characteristics of the motor to avoid galloping or stalling. The power provided by the motor ranges from milliwatts to ten thousand kilowatts. The use and control of the motor is very convenient. It has the ability of self-starting, accelerating, braking, reversing and blocking. In general, the output power of the motor will change with the speed when the speed is adjusted.