1. Selection of braking resistor resistance

The selection of braking resistor is limited by the maximum allowable current of the inverter-specific energy-consumption braking unit, and there is no clear correspondence with the braking unit. Its resistance is mainly selected according to the required braking torque. The power is determined according to the resistance value and usage rate of the resistor. There is an inviolable principle in the selection of the resistance of the braking resistor: it should be ensured that the current IC flowing through the braking resistor is less than the maximum allowable current output capacity of the braking unit, namely: R>800/Ic.

Among them: 800-the maximum DC voltage that may appear on the DC side of the inverter. Ic——The maximum allowable current of the braking unit. In order to make full use of the capacity of the selected inverter-specific braking unit, it is usually the most economical to select the braking resistance value close to the minimum value calculated by the above formula, and at the same time, the maximum braking torque can be obtained. However, this requires Larger braking resistor power. In some cases, a large braking torque is not required. At this time, it is more economical to choose a larger braking resistor resistance value, which can reduce the power of the braking resistor, thereby reducing the purchase of brakes. The cost of the resistance is that the capacity of the braking unit is not fully utilized.

Second, the calculation of the resistance power of the braking resistor

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 calculated as follows: P instant=7002/R, the braking resistor power value calculated according to the above formula is the power value that the braking resistor can dissipate for long-term uninterrupted work, but braking Resistor is not an uninterrupted work. There is a lot of waste in this selection. In this product, you can select the utilization rate of the braking resistor, which specifies the short-time work rate of the braking resistor. The actual power consumed by the braking resistor is calculated as follows: P amount=7002/R×rB[%]rB[%]: braking resistor utilization 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.

Three, the determination of the utilization rate of the braking resistor

The use rate of the braking resistor specifies the use efficiency of the braking resistor to avoid overheating and damage to the braking resistor, which will affect the braking effect of the braking unit. The lower the usage rate of the braking resistor is set, the smaller the heating degree of the resistor, the less energy is consumed on the resistor, and the worse the braking effect. At the same time, the capacity of the braking unit has not been fully utilized. Theoretically, when the braking resistor utilization rate is 100%, the capacity of the braking unit is fully utilized and the braking effect is the most obvious. However, this requires a larger braking resistor power, and the user should consider it comprehensively.

Under the premise that the resistance and power of the braking resistor have been determined, for a slower deceleration large inertia load, a lower resistance usage rate will achieve better results. For loads that need to be stopped quickly, a larger braking resistor utilization rate should be selected.