Overvoltage is more common. After the over-voltage, in order to avoid the internal circuit damage, its over-voltage protection function will run, so that the inverter will stop working, the equipment can not work normally. Therefore, it is necessary to take effective measures to eliminate over-voltage, to avoid failure. Because the application of frequency converter and motor is different, the cause of overvoltage is different, so corresponding preventive measures should be taken according to the specific situation.
The occurrence and regeneration of over-voltage, the over-voltage of frequency converter is that the working voltage of frequency converter is higher than the rated voltage because of many reasons. In normal operation, the DC working voltage of the converter is the average of the three-phase full-wave rectifier.
If measured at 380V, the mean DC voltage UD = 1.35 U line = 513V. When the over-voltage occurs, the energy storage capacitor in the DC bus will be charged. When the working voltage rises to about 700V, the over-voltage protection of the inverter works. There are two main reasons leading to overvoltage: switching power supply overvoltage and regeneration, power supply overvoltage.
Switching power supply over-voltage refers to the switching power supply voltage is too high and the DC bus voltage exceeds the rated voltage. Now most of the input voltage of the inverter ZUI can reach 460V, therefore, switching power supply caused by overvoltage JI its rare. This paper mainly discusses the regeneration overvoltage. The main reasons for the regeneration over-voltage are as follows: when the large GD2(wheel shaft torque) load deceleration, the speed reduction ratio is set too short; The motor is affected by external forces (centrifugal fan, yarn divider) or potential energy load (household elevator, lifting equipment) . For this reason, the specific speed ratio of the motor is higher than the command speed ratio of the inverter. In other words, the speed ratio of the motor rotor is higher than the synchronous speed. At this time, the slip ratio of the motor is negative, the rotor winding laser cutting electromagnetic oscillation of the direction and motor situation in turn, the electromagnetic torque occurs for blocking the direction of rotation of the brake torque. So the motor is actually generating electricity, and the power of the load is“Regenerated” into electrical energy.
The regenerative kinetic energy is charged by the inverter power supply rectifier diode to the converter DC energy storage technology capacitor, which makes the DC bus voltage rise, which is the regenerative overvoltage. Because of the regenerative overvoltage, the torque formed in the case of the original torque is opposite to the braking torque, so the regenerative overvoltage is actually the process of regenerative braking. In other words, the regenerative kinetic energy is eliminated, and the braking rotation distance is also increased. If the regenerative kinetic energy is not large, because the inverter and motor itself with 20% of the regenerative braking level, this part of the electrical energy will be inverter and motor consumption. If the kinetic energy of this part exceeds the consumption level of inverter and motor, the capacitor of DC control loop will be charged by overvoltage. To prevent this from happening, this part of the kinetic energy must be immediately eliminated, thereby increasing the brake rotation, which is the goal of regenerative braking.
