The overvoltage of the inverter is manifested in the tributary voltage of the DC bus. Under normal conditions, the direct current of the inverter is the average value of the three-phase full-wave rectification. If calculated by 380V line voltage, the average DC voltage Ud=1.35U line=513V.When the overvoltage occurs, the energy storage capacitor of the DC bus will be charged, and when the voltage goes up to about 760V, the inverter overvoltage maintenance action. Therefore, the inverter has a normal operating voltage scale, when the voltage exceeds this scale, it is likely to damage the inverter, and there are two types of common overvoltages.
The input AC power supply is overvoltaged. This situation means that the input voltage exceeds the normal scale, which generally occurs during holidays when the load is light, the voltage rises or decreases and the line is faulty, and it is best to disconnect the power supply at this moment, check and deal with it.
Power generation type overvoltage. The probability of this situation is higher, first of all, the synchronous speed of the motor is higher than the actual speed, so that the motor is in the power generation situation, and the inverter is not installed with a braking unit, there are two situations that can cause this problem.
When the inverter drags a large inertia load, its deceleration time is set to be relatively small, in the deceleration process, the speed of the inverter output is relatively fast, and the load decelerates slowly by its own resistance, so that the speed of the load dragging motor is higher than the speed corresponding to the frequency output of the inverter, the motor is in the power generation situation, and the inverter does not have an energy feedback unit, so the voltage of the inverter tributary DC circuit increases, exceeds the maintenance value, and the paper machine often occurs in a little chaff? To deal with this problem, you can add a regenerative braking unit, or modify the inverter parameters to set the inverter deceleration time longer. The functions of adding regenerative braking unit include energy consumption type, parallel DC bus absorption type, and energy feedback type. The energy consumption type is connected with a braking resistor in parallel in the DC circuit of the inverter, and the DC bus voltage is detected to control the on/off of the power tube. The parallel DC bus absorption type is used in multi-motor drive systems, which often have one or several motors that often operate in power generation conditions to generate renewable energy. This energy is absorbed by the motor in the electric condition through the parallel bus, and the grid-side converter of the energy feedback type is reversible, and the reversible converter will feed the regenerative energy back to the grid when there is regenerative energy.
When multiple electric vehicles apply the same load, this problem may also be presented, mainly due to the lack of load distribution. Taking two motors dragging a load as an example, when the practical speed of one motor is greater than the synchronous speed of the other motor, the motor with high speed is equivalent to the prime mover, and the motor with low speed is in the power generation condition, causing problems. In the paper machine, it often takes place in the press section and the net section, and the load distribution control is required during processing. It is possible to adjust the characteristics of the inverter at the branch of the paper machine speed chain to be softer.
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