Motor braking is a common problem encountered in motor […]
Motor braking is a common problem encountered in motor control. Generally, motor braking can occur in two different situations. First, in order to achieve rapid stopping, the rotating direction of the rotating magnetic field and the direction of rotation of the rotor can be made in various ways. On the contrary, an electromagnetic braking torque is generated to cause the motor to stop and rotate rapidly; in another case, when the rotor speed exceeds the rotating magnetic field speed, the motor is also in a braking state. Motor braking methods are generally divided into three types: reverse braking, dynamic braking (DC braking) and regenerative braking. The following is a brief introduction to the principles and precautions of these braking methods.
First, reverse braking:
After the motor is disconnected from the power supply, in order to make the motor stop quickly, the control method is used to add a power supply that is opposite to the normal running power supply to the power supply of the motor. At this time, the rotation direction of the motor rotor is opposite to the rotation direction of the rotating magnetic field of the motor. At this time, the electromagnetic torque generated by the motor is the braking torque, which accelerates the deceleration of the motor. As shown in the figure below, the voltage across the armature is disconnected from the grid by the switch Q, and it is immediately connected to a braking resistor RL. At this time, the main magnetic field in the motor remains unchanged, and the armature continues to rotate due to inertia. At this point, the torque is the braking torque, so the motor speed is decreased until it stops.
One of the biggest drawbacks of reverse braking is that when the motor speed is 0, the motor will reverse if the reversed power supply is not removed in time. There are two ways to solve this problem: 1. In the control loop of the motor inverting power supply, add a time relay. When the reverse braking is performed for a period of time, the reversed power supply is turned off to avoid motor reversal. However, because the braking time of this method is difficult to estimate, the braking effect is not accurate. 2. Add a speed relay to the control loop of the motor inverting power supply. When the sensor detects that the motor speed is 0, cut off the inverter's inverting power supply in time. Because of this method, the speed relay monitors the motor speed in real time, so the braking effect is much better than the previous method. It is precisely because of the reverse brake has this feature, therefore, the machinery that does not allow reversal, such as some lathes, the brake method can not use the reverse brake, but only the energy brake or mechanical brake.