Advantages and disadvantages of 5 commonly used speed regulating motors
From the output characteristics, speed regulating motors can be divided into two categories: stepless speed regulation and stepped speed regulation. When it comes to specific speed control methods, there are many types.

1、 Electromagnetic speed regulating motor

Composed of a single speed or multi speed squirrel cage asynchronous motor and an electromagnetic slip clutch, also commonly known as a slip motor, it is a constant torque AC continuously variable transmission motor. It is widely used in printing machines and staplers, wireless binding, high-frequency drying linkage machines, and chain boiler grate control.

Advantages: Simple structure, small control device capacity, and low value. Reliable operation and easy maintenance. No harmonic interference.
Disadvantage: Large speed loss. Due to the large slip of the electromagnetic differential clutch itself, the maximum speed of the output shaft is only 80% to 90% of the synchronous transmission of the motor; During the speed regulation process, all the differential power is converted into thermal energy, resulting in low efficiency and serious heating problems.   

2、 Variable frequency speed regulating motor
Variable frequency speed regulating motor is a general term for motors driven by frequency converters. Variable frequency speed regulating motor, abbreviated as variable frequency motor, is a general term for motors driven by frequency converters. In fact, the motor designed for the frequency converter is a dedicated motor for frequency conversion. The motor can achieve different speeds and torques under the drive of the frequency converter to adapt to changes in load requirements.
Advantages: No additional slip loss, high efficiency, wide speed range; For situations where the low load operation time is longer or the start stop operation is more frequent, the purpose of energy saving and motor protection can be achieved.
Disadvantages: The technology is complex and the price is high.   

3、 Variable pole multi speed motor

In some special drag circuits, dual speed motors are required; Sometimes it is even necessary to use a three speed or four speed motor. The principles and control methods of these multi speed motors are basically the same. Mainly used for various transmission machinery such as machine tools, mining, metallurgy, textiles, printing and dyeing, chemical industry, etc. that require step-by-step speed regulation according to the nature of the load. The requirement of achieving multiple speeds on the same motor is solved by different connections of the same winding and multiple sets of windings on the same motor.

Advantages: No additional slip loss, high efficiency; The control circuit is simple, easy to maintain, and has a low price; Cooperating with the electromagnetic differential clutch can achieve smooth speed regulation with high efficiency.
Disadvantage: It has a step speed regulation and cannot achieve stepless smooth speed regulation. And due to the limitations of motor structure and manufacturing process, only 2-3 pole pairs of graded speed regulation can usually be achieved, and the speed regulation range is quite limited.    

5、 Permanent magnet synchronous motor and permanent magnet brushless motor
Both permanent magnet synchronous motors and permanent magnet brushless motors achieve stepless speed regulation through PWM variable frequency speed control devices, with theoretically no limit on the maximum speed, high efficiency, and controllable power factors around.
Advantages: Stepless speed regulation, theoretically unlimited speed range.
Disadvantages: Magnetic steel is expensive and there is a problem of demagnetization.