What is the starting and speed regulation method of asynchronous motor?

An asynchronous motor is an AC motor, also known as an induction motor. Its working principle is to generate an induced current based on the relative movement of the magnetic field, thereby generating torque. An asynchronous motor usually consists of a stator and a rotor. There are three windings on the stator, namely the main winding, the starting winding and the auxiliary winding, and the rotor consists of a conductor and a magnetic core. When working, a rotating magnetic field is generated by energizing the stator, thereby exciting the induced current in the rotor, thereby generating torque. Since the speed of the rotor and the rotating magnetic field are different, the motor is called an "asynchronous motor".

There are several ways to start an asynchronous motor:

1. Start-up: Connect the motor directly to the power supply and start the motor from a stationary state. This method is suitable for low-power motors, but for high-power motors, the starting current is too large, which can easily cause grid voltage fluctuations, so it is not suitable for starting large asynchronous motors.

2. Autotransformer starting: Use autotransformer to limit the motor starting current within a suitable range to reduce the impact on the power grid. At the same time, it can reduce the voltage fluctuation during starting. It is suitable for small and medium power motors.

3. Resistance start: insert a resistor in series in the motor rotor circuit to limit the starting current, gradually reduce the resistance after starting, and improve the motor's operating efficiency. Suitable for low-power motors.

4. Frequency start: The power supply voltage and frequency are adjusted by the frequency converter to achieve precise control of the motor speed. It is suitable for large and high-power motors, with smooth start-up, little impact on the power grid, and can achieve precise speed regulation.

Asynchronous motor speed regulation methods include:

1. Frequency speed regulation: The speed of the motor is regulated by changing the power supply frequency of the motor. The motor speed can be controlled by adjusting the inverter output frequency. Therefore, frequency conversion speed regulation is widely used in occasions where the speed needs to be adjusted frequently, such as elevators, fans, etc.

2. Sub-resistance speed regulation: The torque and speed of the motor can be changed by changing the size of the motor rotor resistance. By adding an adjustable resistor in the rotor circuit, the starting current and torque of the motor can be reduced, and the speed regulation within a certain range can be achieved.

3. Doubly-fed asynchronous motor speed regulation: Doubly-fed asynchronous motor is a special asynchronous motor that adds an additional winding on the rotor. The motor speed regulation is achieved through the interaction between the rotor circuit and the stator circuit. Doubly-fed asynchronous motor has the advantages of high efficiency, high torque, wide speed range, etc. It is widely used in high-power load occasions such as mining, metallurgy, and water pumps.

Asynchronous motors are widely used in industry, transportation, agriculture and other fields. They have simple structure, low manufacturing cost, high reliability and simple maintenance. They are one of the most commonly used motors.