For details of the brake unit, please refer to the following link: http://FeedbackView.asp QQ Contact: Miss Duan The process of dynamic braking is as follows: For details of the brake unit, please refer to the following link: http://FeedbackView.asp QQ Contact: Miss Duan
The process of dynamic braking is as follows: A. When the motor decelerates and reverses under external force (including being dragged), the motor runs in the state of power generation, and the energy is fed back to the DC circuit to increase the bus voltage; B. When the DC voltage reaches the open state of the braking unit, the power tube of the braking unit is turned on, and the current flows through the braking resistor; C. The power consumed by the braking resistor is thermal energy, the rotation speed of the motor is reduced, and the bus voltage is also reduced; D, busbars The voltage drops to the value of the braking unit to be turned off, the power transistor of the braking unit is turned off, no current flows through the braking resistor; E. The voltage value of the bus is sampled, the ON/OFF process of the braking unit is repeated, the bus voltage is balanced, and the system is normal operation.
Braking unit and braking resistor selection
A. First estimate the braking torque
= ((motor inertia = motor load measured to motor rotational inertia measured) * (pre-braking speed - post-braking speed)) / 375 * deceleration time - load torque In general, during motor braking 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 braking device;
B, then calculate the resistance of the braking resistor
= The square of the operating voltage value of the braking element / (0.1047 * (braking torque - 20% of the rated torque of the motor) * motor speed before braking)
During the work of the braking unit, the voltage of the DC bus rises and falls depending on the constant RC, R is the resistance of the braking resistor, and C is the capacity of the internal electrolytic capacitor of the inverter. The braking unit operating voltage here is generally 710V.
C. Then the selection of the braking unit When selecting the braking unit, the maximum working current of the braking unit is the only basis for the selection, and its calculation formula is as follows:
Instantaneous value of braking current = DC bus voltage of brake unit / braking resistor value
D. Finally, the nominal power of the braking resistor is calculated. Because the braking resistor is a short-time working system, we know that the nominal power of the resistor will be less than the power consumption when the power is turned on. The following formula can be used. Results: Nominal braking resistor power = braking resistor derating factor X Average power consumption during braking X Brake utilization%
Braking Characteristics The advantage of dynamic braking (resistive braking) is its simple construction. The disadvantage is that the operating efficiency is reduced. In particular, a large amount of energy will be consumed during frequent braking and the capacity of the braking resistor will increase.