1. Using the frequency converter power change speed, speed range, good stability smoothness, mechanical properties harder. Plus rated load speed is decreased less. It belongs to the variable speed. For most three-phase squirrel cage induction motor.
2. The number of pole pairs speed changes, belonging to a level speed, smoothness of speed difference, is generally used for metal cutting machine tools.
3. Change the slip speed.
- The rotor resistance series circuit: for AC induction motor winding. Small speed range, the resistance to electric power consumption is low motor efficiency. Generally used for cranes.
- changing the power supply voltage control, a small speed range, the torque dropped significantly with the voltage drop, generally do not three-phase motor. Single-phase motor speed, such as a fan.
- cascade control, in essence, is to introduce an additional rotor electromotive force, speed change its size. Only for motor winding, but the efficiency is improved.
- electromagnetic speed. Only for the slip motor. By changing the current stepless smooth speed exciting coil, a simple mechanism, but smaller power control. Not long-term low-speed operation. Speed of the fluid coupling 4