Several braking modes of three-phase asynchronous motor

Update:06-05-2019
Summary:

1. Mechanical braking   A braking method is adopte […]

1. Mechanical braking

 

A braking method is adopted to make the motor stop quickly after disconnecting the power supply by mechanical device. Such as electromagnetic brake, electromagnetic clutch and other electromagnet brakes.

 

2. Electric braking

 

When the motor cuts off the power supply, it gives the motor an electromagnetic moment (braking moment) opposite to the actual steering to make the motor stop quickly. The most commonly used methods are reverse braking and energy dissipation braking.

 

2.1. Reverse Braking
The method of changing the power supply phase sequence of the motor stator winding while cutting off the normal power supply of the motor, so that it has a reverse trend and produces a larger braking moment. The essence of reverse braking: make the motor want to reverse and brake, so when the speed of the motor is close to zero, the reverse braking power should be cut off immediately, otherwise the motor will reverse. In actual control, the speed relay is used to automatically cut off the brake power supply.

 

Reverse connection brake control circuit, its main circuit and the positive and negative circuit is the same.Since the relative rotation speed of rotor and rotating magnetic field is higher when braking is reversed, which is about twice as high as when starting, the current in stator and rotor will be very large, which is about 10 times of the rated value.Therefore, the reverse braking circuit increases the current limiting resistance R.KM1 is the operating contactor, KM2 is the reverse contact brake contactor, KVIs the speed relay, which is connected with the motor shaft. When the motor speed rises to the action value of about 100 RPM, KVNormally open contact closure prepares the brake.

 

2.2. Energy Consumption Braking
When the motor cuts off the AC power supply, it adds any two-phase of the sub-winding to the DC power supply to generate the static magnetic field, which is cut by the inertial rotation of the rotor to generate the braking moment.

 

Principle analysis

When the motor cuts off the power supply, the rotor still rotates inertially in the original direction. Fig. 5 is set in clockwise direction. At this time, a constant static magnetic field is generated when the given sub-winding is connected to the DC current. When the rotor cuts the magnetic field, the induced current is generated. The direction of the rotor is judged by the right-hand rule as shown in the figure. The induced current is also acted by the magnetic field to produce electromagnetic torque. According to the left-hand rule, the direction of the induced current is just opposite to the direction of the motor, and the motor is braked to stop quickly.