1. Causes of overcurrent
There are many reasons for the occurrence of overcurrent, including soft and hard problems.
1. Causes of soft failures
When the acceleration or deceleration time in the inverter parameters is set too short, and the motor power is heavier, it means that in the acceleration, the working frequency of the inverter rises too fast, and the synchronous speed n0 of the motor rises rapidly, and the motor speed n cannot keep up due to the large load inertia, resulting in the speed of the rotor cutting the magnetic field lines too fast (equivalent to too large slip), resulting in excessive current, causing the inverter to overcurrent.
2. Cause of hard failure
(1) The transmission organization is stalled, the work is not sensitive, and the motor load is too heavy, which causes the current to be added to the motor.
(2) The output of the inverter is short-circuited or the three-phase voltage is unbalanced, resulting in the three-phase current unbalance, resulting in overcurrent.
(3) The inverter itself is damaged, such as the aging of the inverter equipment, the malfunction of the current transformer, etc.
When the cable lead between the inverter and the motor is too long (the output wire recommended by the general inverter manufacturer is less than 50m), the force will not be enough, and the current needs to be added to meet the load requirements; The output voltage of other inverters is in a high-frequency state, and the cable lead can be equivalent to a capacitor, at this moment the inter-line capacitance and ground capacitance are added due to the lengthening of the cable, if the output carrier frequency of the inverter is very high at the moment, the output attenuation is very large, in order to meet the requirements of the load, it is necessary to add current, which may lead to overcurrent.
Second, the solution of overcurrent
Different measures are taken to prevent the occurrence of overcurrent.
1. On the premise of satisfying the requirements of production equipment and process, the acceleration or deceleration time should be increased as much as possible, so as to prevent the occurrence of overcurrent in the process of acceleration or deceleration.
2. Check whether the matching of inverter, motor and production equipment is outstanding, whether the transmission part is sensitive, and whether the material is stuck.
3. Whether the inverter itself is defective. Whether the three-phase voltage balance meets the requirements, if not, check whether the driving waveform of the inverter is normal. In other inverters, such as Danfoss products, there is a problem in the current detection link, and overcurrent will also appear. However, some brands of inverters, even if there is a problem with the current detection link, do not show overcurrent, which should be paid attention to in use. If there is a problem with the inverter main circuit equipment of the inverter, it will also present an overcurrent phenomenon.
4. When the output cable of the inverter is lengthened, the high-frequency loss is added, so that the output of the inverter is not enough, and the following two methods should be selected to deal with this problem.
(1) Make some corrections to the inverter parameters. In the case of agreeable conditions, the output carrier frequency of the inverter can be corrected, the output frequency can be reduced, and the high-frequency loss can be reduced. In addition, the output torque can be increased to reduce the effect of high-frequency losses.
(2) An AC reactor can be added to the output of the inverter to suppress the sudden change of current and prevent overcurrent. For the selection of reactors, you can contact the inverter manufacturer to select the reactor with the power. Others can also be consulted for the relevant materials to design by themselves.
In short, there are many reasons for the overcurrent of the inverter, which should be analyzed and dealt with according to the specific situation. If the inverter often overcurrent occurs, and it is confirmed that it is caused by overload, a higher-level inverter can be selected to overcome the overcurrent caused by overload.
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