Since the working condition of the braking unit is a short-time operation, that is, the power-on time is very short each time. During the power-on time, its temperature rise is far from reaching a stable temperature rise; and the intermittent time after each power-on is longer. During the intermittent time, its temperature is enough to drop to the same as the ambient temperature, so the rated power of the braking resistor will be greatly reduced, and the price will also drop; in addition, since there is only one IGBT, the braking time is ms level, and the power tube is turned on and The requirements for the transient performance index of turn-off are low, and the turn-off time is even required to be as short as possible to reduce the turn-off pulse voltage and protect the power tube; the control mechanism is also relatively simple and easy to implement. Due to the above advantages, it is widely used in potential energy loads such as cranes and situations where rapid braking is required but short-time working conditions are required.

The braking resistor has the function of protecting the frequency converter and ensuring the power supply network. During the rapid stopping process of the motor, due to inertia, a large amount of regenerated electric energy will be generated. If this part of the regenerated electric energy is not consumed in time, it will directly act on the DC circuit part of the inverter. In the worst case, the inverter will report a fault. In severe cases, the inverter will report a fault. Otherwise, it will damage the frequency converter; the emergence of braking resistor solves this problem very well and protects the frequency converter from the harm of the regenerated electric energy of the motor.

The braking resistor directly converts the regenerated electric energy during the rapid braking process of the motor into heat energy, so that the regenerated electric energy will not be fed back into the power supply network and will not cause voltage fluctuations in the power grid, thus ensuring the smooth operation of the power supply network.

To calculate the braking resistor, the braking torque must first be estimated. Braking torque = ((motor inertia moment + motor load measurement converted to motor inertia measurement) * (speed before braking - speed after braking)) / 375 * deceleration time - load torque. Under normal circumstances, when braking the motor, there is a certain loss inside the motor, which is about 18%-22% of the rated torque. Therefore, if the calculated result is less than this range, there is no need to connect a braking device.

Then calculate the resistance of the braking resistor. The resistance of the braking resistor = the square of the braking element operating voltage value/(0.1047*(braking torque-20% motor rated torque)*motor speed before braking) During the operation of the braking unit, the DC bus The rise and fall of the voltage depends on the constant RC, R is the resistance of the braking resistor, and C is the capacity of the electrolytic capacitor inside the frequency converter. The braking unit operating voltage here is generally 710V.
The braking resistor directly converts the regenerated electric energy during the rapid braking process of the motor into heat energy, so that the regenerated electric energy will not be fed back into the power supply network and will not cause voltage fluctuations in the power grid, thereby ensuring the smooth operation of the power supply network
.