Braking of Frequency Inverter

2021-01-04

Ⅰ. Brake unit overview

The braking unit, called "frequency inverter energy braking unit", or "frequency inverter energy feedback unit", is mainly used to control heavy mechanical loads and very fast braking speed requirements, and the regenerative power generated by the motor is consumed through the Braking resistor to consume, or regenerative energy back to the power supply.

Ⅱ. The role of the brake unit

When the motor stops quickly, the motor will feedback energy to the frequency inverter, causing the direct current voltage to rise that even damage the IGBT, so the braking unit for inverter is needed to consume this energy to protect the inverter.

Ⅲ. The braking methods of frequency inverter

1. Power braking

It refers to the way of using the braking resistor set in the DC circuit to absorb the regenerative energy of the motor.

2. Feed-back braking

Mainly for the current type inverter or voltage type inverter with inverter in rectifier part, the regenerative energy of the motor is fed back to the AC grid.

3. Multi-inverter drive with a common DC busbar

The regenerative energy of motor A is fed back to the common DC bus, and then the regenerative energy is consumed by motor B. Multi-inverter drive with common DC bus can be divided into two ways: common DC equalization busbar and common DC circuit bus. The common DC equalization bus method uses a connection module to connect to the DC circuit busbar. The connection module includes inverter reactors, fuses, and contractors, which must be designed individually for each case. Each inverter is relatively independent and can be connected or disconnected from the DC busbar as required. The common DC busbar method is to connect only the inverter part to a common DC busbar.

4. DC braking

When the frequency inverter passes DC power to the stator of the motor, the asynchronous motor will be in the energy braking brake state. In this case, the output frequency of the inverter is zero, the stator field of the motor is no longer rotating, and the rotor is rotating to cut the static magnetic field and produce braking torque. The kinetic energy stored in the rotating system is converted into electrical energy and consumed in the rotor circuit of the motor.