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 lowering a load with a crane or dealing with a fast-moving inertial load—the kinetic or potential energy is converted back into electrical energy and fed back 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 when the voltage exceeds a set threshold and activate the switch between the braking resistor and the DC bus, allowing the excess energy to be dissipated as heat through the resistor. At this point, the braking resistor will generate heat.

Normally, the braking resistor should not get hot during regular operation. If it does, it may indicate that the braking unit is faulty, or that the braking circuit is continuously connected to the DC bus, which could lead to excessive energy consumption. While the inverter might still operate without major issues, the efficiency will be significantly reduced due to the high energy loss.

During acceleration or constant speed operation, the braking resistor remains inactive. However, when the motor decelerates or stops abruptly, the DC bus voltage rises because the motor enters a regenerative braking mode. The braking resistor then activates to consume the extra energy by converting it into heat, preventing the voltage from reaching dangerous levels.

In an asynchronous motor, during regenerative braking, the motor acts as a generator, producing a feedback current. This current flows back into the DC loop via the return diodes (D1 to D6), charging the main capacitor and increasing the DC voltage. To prevent overvoltage damage, the inverter connects the braking resistor to the DC bus when the voltage exceeds a certain level. The transistor switch TR turns on, allowing the braking resistor to dissipate the excess energy as heat, ensuring safe and stable operation of the system.