The torque of asynchronous motor is proportional to the square of stator voltage. Changing the stator voltage can change the mechanical characteristics and torque of the motor. This method is not suitable for ordinary cage motor, because its rotor resistance is very small and the current will rise sharply at low speed.

It can be used in wound asynchronous motor, and its rotor circuit can be connected with resistor or variable frequency rheostat in series, which leads most of slip energy loss to external resistor or variable frequency rheostat to reduce motor heating.

2, change the rotor resistance speed regulation

This speed regulation method is only suitable for wound motor. When the load is constant, the greater the series resistance in the rotor circuit, the lower the motor speed and the smaller the motor speed. This method has simple equipment, convenient control and less initial investment, but the slip power is consumed on the resistor in the form of heating, which belongs to step speed regulation and has soft mechanical characteristics.

3, cascade speed regulation

The more advanced cascade speed regulation adopts the cascade speed regulation circuit controlled by thyristor inverter, which has the advantages of hard mechanical characteristics, small voltage drop of rectifier elements, small equipment occupation area, no rotating parts, low noise and simple maintenance. It is one of the most promising speed regulation methods of wound motor, but its disadvantage is that the rotor circuit is equipped with reactor for filtering, so the power factor is low.

Extended data:

From the point of view of energy consumption in the process of speed regulation, there are two kinds of speed regulation methods: efficient speed regulation means that the slip rate is constant, so there is no slip loss, such as multi-speed motor, variable frequency speed regulation and speed regulation that can recover the slip loss (such as cascade speed regulation).

The speed regulation method with slip loss is inefficient, such as the rotor series resistance speed regulation method, and the energy is lost in the rotor circuit; The speed regulation method of electromagnetic clutch, the energy loss is in the clutch coil; The hydraulic coupler adjusts the speed, and the energy is lost in the oil of the hydraulic coupler. Generally speaking, slip loss increases with the expansion of speed regulation range. If the speed range is not large, the energy loss is very small.