Abstract : This paper briefly introduces some characteristics of variable frequency speed control for asynchronous motors, analyzes the principle of variable frequency speed control for asynchronous motors and the main types of frequency converters, and elaborates on the main problems existing in the operation of variable frequency motors. Keywords : Frequency converter, Asynchronous motor, PWM 1 Introduction Asynchronous motors are the most widely used AC motors in national production and daily life, but their speed regulation performance is relatively poor. Therefore, DC motors are often used to drive some production machinery with high speed regulation requirements or those requiring large starting torque. However, DC motors have complex structures and are inconvenient to maintain. With the application of new power electronic devices and high-performance microprocessors and the development of control technology, the performance-price ratio of frequency converters is getting higher and higher. Therefore, they are widely used in the speed regulation of asynchronous motors, which continuously improves the speed regulation performance of asynchronous motors that are simple, robust, inexpensive, and easy to maintain. The application of variable frequency speed control is becoming more and more widespread, thus fundamentally solving the speed regulation problem of squirrel-cage asynchronous motors. 2. Variable Frequency Speed ​​Control of Asynchronous Motors The speed of an asynchronous motor is given by: n = 60f1/P (1-S), where S is the slip, f1 is the power supply frequency, and p is the number of pole pairs. When the slip rate does not change significantly, n is basically proportional to a certain value. Clearly, if there is a power supply device with a smoothly adjustable ratio, the speed of the asynchronous motor can be smoothly adjusted. During variable frequency speed control, it is desirable for the main magnetic flux m to remain constant. If the main magnetic flux is greater than that during normal operation, the magnetic circuit will become oversaturated, increasing the excitation current and decreasing the power factor; if the main magnetic flux is less than that during normal operation, the motor torque will decrease. Ignoring stator leakage impedance, we have: [b][align=center]For more details, please click: A Brief Discussion on Variable Frequency Speed ​​Control in Asynchronous Motors[/align][/b]