Overvoltage is a more prevalent issue. Once overvoltage occurs, the inverter’s overvoltage protection function activates to prevent damage to internal circuits, shutting down the inverter and disrupting normal equipment operation. Therefore, effective measures must be taken to eliminate overvoltage and avoid faults. Since inverters and motors are used in various applications, the causes of overvoltage differ, so corresponding preventive measures should be adopted based on specific conditions.

Overvoltage and Regenerative Braking

Overvoltage in an inverter refers to the operating voltage exceeding the rated value due to various factors, mainly reflected in the DC bus voltage. Under normal operation, the inverter’s DC voltage is the average value after three-phase full-wave rectification.

For a 380V supply, the average DC voltage Ud=1.35Uline=513V. When overvoltage occurs, the energy-storage capacitors on the DC bus are charged. When the voltage rises to approximately 700V (varies by model), the inverter’s overvoltage protection trips.

The main causes are power supply overvoltage and regenerative overvoltage.

Power supply overvoltage: Caused by excessively high input voltage. Most modern inverters accept a maximum input of 460V, so power supply overvoltage is extremely rare. This article focuses on regenerative overvoltage.

Causes of Regenerative Overvoltage

1.Excessively short deceleration time set for high GD2 (moment of inertia) loads during deceleration.

2.External forces acting on the motor (e.g., fans, winders) or lowering of potential loads (e.g.,elevators, cranes).

In these cases, the actual motor speed exceeds the inverter’s commanded speed (rotor speed > synchronous speed), making the slip negative. The rotor cuts the magnetic field in the opposite direction to motoring mode, generating a braking torque opposing rotation.

The motor thus operates as a generator, converting mechanical energy back into electrical energy. This regenerative energy charges the DC bus capacitors via the inverter’s rectifier diodes, raising the DC voltage — this is regenerative overvoltage.

Regenerative overvoltage coincides with regenerative braking, as the opposing torque acts as braking torque. Eliminating regenerative energy therefore enhances braking torque.

If the regenerative energy is small, the inverter and motor can dissipate about 20% internally. When energy exceeds this capacity, the DC capacitors overcharge, triggering overvoltage protection and shutdown. To prevent this, excess regenerative energy must be promptly dissipated, which also strengthens braking torque — this is the purpose of regenerative braking.