Inverter braking resistor working principle - News - Global IC Trade Starts Here.

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When the inverter drives a motor into a braking state—such as when a crane lowers a heavy load or when an inertia load is moving quickly—the kinetic or potential energy is converted back into electrical energy and returned to the DC bus of the inverter. This causes the DC bus voltage to rise. If your inverter is equipped with a braking unit, it will detect this increase in voltage and activate the switch between the braking resistor and the DC bus, allowing the excess energy to be dissipated as heat through the resistor.

Under normal operation, the braking resistor should not generate heat. However, if it becomes hot during regular use, it may indicate that the braking unit is faulty or that the braking resistor is continuously connected to the DC bus. While this might not immediately affect the inverter’s performance, it could lead to significant energy loss and unnecessary power consumption.

The braking resistor typically only activates when the motor is decelerating or coming to an emergency stop. During acceleration or constant speed operation, the resistor remains inactive. However, during deceleration, the motor enters a regenerative braking mode, causing the DC bus voltage to increase. The braking resistor then engages to absorb this excess energy by converting it into heat.

In the case of an asynchronous motor, it can enter a regenerative power generation state, producing a feedback current. This current is directed back into the DC loop via the return diodes (D1 to D6), charging the main capacitor and increasing the DC voltage. To prevent the voltage from rising to dangerous levels and potentially damaging the inverter, the DC circuit is connected to the braking resistor R. When the voltage exceeds a set threshold, the transistor switch TR turns on, connecting the braking resistor to the DC bus. The excess energy is then safely dissipated as heat through the resistor.