What is the cause of the overvoltage of the inverter? How to prevent it?
Published time: 2019-08-22
Everyone often encounters the problem of inverter over-voltage protection when dealing with inverter faults. The over-voltage of the inverter means that the inverter voltage exceeds the rated voltage. The over-voltage protection of the inverter is caused by the over-voltage of the inverter.
First, the inverter overvoltage reason
There are two main reasons for the inverter overvoltage: the inverter power supply overvoltage and the inverter regenerative overvoltage. The overvoltage of the power supply means that the DC bus voltage exceeds the rated value because the power supply voltage is too high. Most of the inverters now have an input voltage of up to 460V, so the overvoltage caused by the power supply is extremely rare.
Second, the inverter overvoltage prevention measures
The protection measures for the overvoltage of the inverter vary according to the cause of the overvoltage of the inverter.
For the overvoltage phenomenon generated during the parking process, if there is no special requirement for the parking time or position, it can be solved by extending the deceleration time of the inverter or free parking. Free stop means that the inverter disconnects the main switching device and allows the motor to coast and stop.
If there is a requirement for parking time or parking position, DC braking can be used. That is, after decelerating the motor to a certain frequency, a direct current is applied to the stator winding of the motor to form a static magnetic field. The rotor winding of the motor cuts this magnetic field to generate a braking torque, so that the kinetic energy of the load is converted into electrical energy and is consumed in the form of heat in the rotor circuit of the motor. Therefore, this braking is also called energy braking. In the process of DC braking, two processes of regenerative braking and energy braking are actually included. This braking method is only 30-60% efficient for regenerative braking and has a low braking torque. Since the motor is overheated by consuming energy in the motor, the braking time should not be too long. Moreover, the DC braking start frequency, braking time and braking voltage are all manually set, and cannot be automatically adjusted according to the level of the regenerative voltage. Therefore, DC braking cannot be used for overvoltage generated during normal operation, and can only be used for Braking when parking.
For deceleration (from high speed to low speed, but not stopping), the overvoltage generated by the excessive GD2 (flywheel torque) of the load can be solved by appropriately extending the deceleration time. In fact, this method also utilizes the principle of regenerative braking. The extension of the deceleration time is only to control the charging speed of the regenerative voltage of the load to the inverter, so that the regenerative braking capability of the inverter itself can be utilized. As for the load that causes the motor to regenerate due to the external force, since it is normally in the braking state, the regenerative energy is too high to be consumed by the inverter itself, so it is impossible to use DC braking or extend the deceleration time.
Compared with DC braking, regenerative braking has higher braking torque, and the braking torque can be related to the braking torque required by the load (ie, the level of regenerative energy). Automatic control. Regenerative braking is therefore best suited to provide braking torque to the load during normal operation.
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