Abstract : This paper briefly introduces the operating principle of AC asynchronous motors, focusing on several methods and principles of electrical braking for asynchronous motors powered by frequency converters, and pointing out the advantages and disadvantages of various braking methods and their applicable occasions. Keywords : Frequency converter, asynchronous motor, operating principle, braking method 1 Introduction In a variable frequency speed control transmission system composed of a general-purpose frequency converter, an asynchronous motor, and a mechanical load, when the motor decelerates or drags a potential energy load, the actual speed of the motor will be higher than the rotational speed of the rotating magnetic field. In order to make the actual speed of the motor match the given speed, braking measures must be taken. The braking methods for asynchronous motors include regenerative braking, DC braking, and mechanical braking. Mechanical braking is intuitive and will not be introduced here; only the first two electrical braking methods will be introduced. To facilitate the introduction of the principle and method of electrical braking, let's first review the operating principle of asynchronous motors. 2 Operating Principle of Asynchronous Motors As is well known, the stator of an asynchronous motor is equipped with a set of three-phase windings AX, BY, and CZ that are symmetrically distributed in space, as shown in Figure 1. When alternating current is applied to these three-phase windings, a magnetic field is generated in the air gap between the stator and rotor. This magnetic field at any given instant is the sum of the magnetic fields of each of the three-phase windings. Using the right-hand rule to examine the relationship between the current and the magnetic field direction at different instants in Figure 1, we can see that the direction of the composite magnetic field FE is consistent with the axis of the winding with the maximum current. Therefore, as the maximum current changes sequentially from phase A to phase B to phase C to phase A, the direction of the composite magnetic field also points sequentially to the axis of each phase winding from phase A to phase B to phase C to phase A. This means that the composite magnetic field is a "rotating magnetic field." Its rotational speed n (synchronous speed) is directly proportional to the frequency of the AC power supply and inversely proportional to the number of magnetic field pole pairs. [b][align=center]For more details, please click: Electrical Braking Methods and Principles of Asynchronous Motors Powered by Frequency Converters[/align][/b]