power

After selecting the resistance value of the braking resistor, the power value of the braking resistor should be determined. The selection of the braking resistor power is relatively cumbersome, and it is related to many factors. The instantaneous power consumed by the braking resistor is the value of the power that the braking resistor can dissipate in a long-term uninterrupted operation. However, the braking resistor is not an uninterrupted operation. There is a lot of waste in this selection. You can choose the braking resistor. Utilization rate, it specifies the short-time working rate of the braking resistor. Braking resistor usage rate. In actual use, you can select the braking resistor power according to the above formula, or you can calculate the use rate that the braking resistor can withstand according to the selected braking resistor resistance and power, so as to set it correctly and avoid overheating the braking resistor And damaged.

Size calculation

First estimate the braking torque

Braking torque = [(Moment of inertia of the motor + motor load measurement converted to the measured moment of inertia of the motor) (speed before braking-speed after braking)]/375*Deceleration time-load torque. Generally, 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 the brake device.

Then calculate the resistance of the braking resistor

The resistance of the braking resistor = the square of the operating voltage value of the braking element/(0.1047*(brake torque-20% motor rated torque) motor speed before braking) the voltage of the DC bus during the working process of the braking unit The rise and fall depends on the constant RC, where R is the resistance of the braking resistor, and C is the capacity of the electrolytic capacitor inside the inverter. Here, the operating voltage of the braking unit is generally 710V.

Then select the brake unit

When selecting the braking unit, the maximum working current of the braking unit is the only basis for selection, and its calculation formula is as follows: instantaneous value of braking current = braking unit DC bus voltage value / braking resistance value and finally calculating the braking resistance Since the braking resistor is a short-time working system, according to the characteristics and technical indicators of the resistor, we know that the nominal power of the resistor will be less than the power consumption when it is energized. Generally, the following formula can be used to obtain: Power = braking resistor derating coefficient, average power consumption during braking, braking utilization rate%.

Braking characteristics

Energy consumption braking (resistance braking) has the advantage of simple structure, but the disadvantage is that the operating efficiency is reduced, especially during frequent braking, a large amount of energy will be consumed, and the capacity of the braking resistor will increase.