1.When the motor is decelerating, the rotation speed of the motor rotor is opposite to that before deceleration. At this time, the motor is equivalent to a generator, that is, it is in a power generation state, which will continue to generate renewable electric energy. The generated three-phase AC electromotive force is rectified by the internal rectifier device of the frequency converter. In the frequency converter without energy feedback system, the DC bus voltage in the frequency converter continues to rise due to the continuously generated regenerative electric energy.
2. When the voltage on the DC bus rises to the preset opening voltage of the braking unit, the power switch of the braking unit is turned on, and current flows through the braking resistor to discharge the braking resistor.
3. The conductive braking resistor starts to work, and the regenerative energy is converted into heat energy and released. The regenerative energy on the line decreases rapidly, the motor speed decreases, and the voltage on the DC bus of the inverter decreases.
4. When the DC bus voltage drops to the preset turn-off voltage of the braking unit, the power line of the braking unit is turned off. At this time, the braking resistor stops working and naturally dissipates heat, and the temperature of the braking resistor decreases.
5. When the voltage on the DC bus rises to the preset opening voltage of the braking unit again, the braking unit will repeat the above process to control the bus voltage within a range, so that the system can operate normally and the control system and motor can be protected from damage.