Cause of overvoltage
(1) Overvoltage from the power input side
Under normal circumstances, the power supply voltage is 380V, and the allowable error is -5% to +10%. The peak value of the intermediate DC after three-phase bridge full-wave rectification is 591V. Generally, the power supply voltage will not cause the inverter to trip due to overvoltage. The overvoltage on the input side of the power supply mainly refers to the impulse overvoltage on the power supply side, such as the overvoltage caused by lightning, the overvoltage formed when the compensation capacitor is closed or disconnected, etc. The main features are the voltage change rate dv/dt and amplitude. are very large.
(2) The braking or deceleration time is too short or the braking resistor is damaged.
When the inverter drags a large inertia load, its deceleration time is set relatively small. During the deceleration process, the output frequency of the inverter decreases faster, but the load inertia is relatively large, and the deceleration is relatively slow due to its own resistance, so that the load drags The rotational speed of the moving motor is higher than the rotational speed corresponding to the frequency output by the inverter. The motor is in the power generation state, and the energy is fed back to the intermediate DC circuit of the inverter from the load side. The concentrated feedback of energy in a short time may cause the intermediate DC circuit and its The withstand capability of the energy processing unit causes an overvoltage fault. If the inverter has no energy processing unit or its function is limited, the voltage of the intermediate DC circuit of the inverter will rise and exceed the protection value, and an overvoltage trip fault will occur.
Countermeasures for Overvoltage
(1) Increase the absorption device on the input side of the power supply to reduce the overvoltage factor
In the case of surge overvoltage on the input side of the power supply, overvoltage caused by lightning, and overvoltage formed by the compensation capacitor during closing or disconnection, methods such as connecting a surge absorbing device or a series reactor in parallel on the input side can be used. be resolved. Regarding this point, the equipment of our factory has been designed with an incoming line reactor on the input side to enhance the ability of the inverter to resist voltage changes.
(2) The method of adding an inverter circuit on the input side
The best way to deal with the energy of the intermediate DC link of the inverter is to add an inverter circuit on the input side, which can feed back the excess energy to the grid. Regarding this point, our factory considers a feedback device when selecting equipment.
(3) Find solutions from the parameters that have been set by the inverter
Under the condition that the control requirements are met, appropriately increase or prolong the braking time or deceleration time (especially for the shutdown of the large inertia load).
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