What's the function of the brake unit in variable speed drive?

The brake unit is used to connect braking resistor, the braking resistor function is to consume the regenerated electricity energy during emergency stop to protect the variable speed drive.

In some applications, it is necessary to get rapid deceleration. According to the principle of asynchronous motor, if the slip differential is greater, the torque is bigger. Similarly, the braking torque will be increased with the increase of the deceleration rate, to make the system decelerate time decrease greatly, energy feedback increased rapid, the DC bus voltage goes up fast.

Therefore, the feedback energy must be consumed quickly to maintain the DC bus voltage below a safe range. The main function of the brake unit system is consuming the regenerated energy quickly (the energy is converted to heat by braking resistor). It is effective to make up the shortcomings of ordinary variable speed drive's slow braking time and low braking torque (less than 20% rated torque), ideal for rapid braking in low frequency occasions.

Generally, The variable speed drive's brake unit is used in position control of fast stop to prevent bus over voltage, but not fans, pumps.