How to Select the Braking Resistor of the Frequency Converter?

What are the differences between inverter braking resistors, braking units and braking choppers? How to choose? (We take a 380V inverter as an example):

What are the differences between inverter braking resistors, braking units and braking choppers? How to choose? (We take a 380V inverter as an example):
​
01
The braking unit is also called a braking chopper. It works together with the braking resistor and is an option of the frequency converter.
​
The normal bus voltage of the inverter is 540V (AC 380V model). When the motor is in the power generation state, the bus voltage will exceed 540V, and the maximum allowed is 700-800V. If this maximum value is exceeded for a long time or frequently, the inverter will be damaged, so Use the braking unit and braking resistor to dissipate energy and prevent the bus voltage from being too high.
​
02
There are two situations when the motor will change from electric state to power generation state:
A. Rapid deceleration of large inertia load or too short deceleration time
B. It is always in the power generation state when the lifting load is going down.
​
03
It is relatively simple to select a braking unit. Generally, the braking unit has the same power as the frequency converter.
​
04
The current flowing through the resistor can be calculated using the following formula:
R=U/I
​
U is generally 710-750V (braking unit operating voltage). Each manufacturer's design is different, so it can be considered as 750V.
​
R is the resistance of the braking resistor. Generally, the braking unit has a specified minimum resistance. Please select according to the manual. If there is no such data, please calculate it according to U/I. I is the maximum allowable braking current, which should be selected according to 80% of the rated current of the inverter.
​
05
The power of the braking resistor is selected as follows:
P＝ED%*U^2/R
​
ED%: brake usage rate. According to general experience, the range of ED% is from 10% to 50%.
​
If the braking frequency is low (occasional action), select 10%. If it is a long-term or frequent action, just select 30%-50%. Generally, 30% can meet most application requirements.