The cause of the inverter overcurrent fault

Overcurrent faults can be divided into short circuit, light load, heavy load, acceleration, deceleration and constant speed overcurrent. Overcurrent faults are usually caused by too short inverter acceleration and deceleration time, sudden load changes, uneven load distribution, and output short circuit. At this point, the line can usually be checked by extending the acceleration and deceleration time, reducing the sudden load change, adding energy-consuming brake components, and carrying out load-sharing design. If the inverter still has overcurrent fault when the load is disconnected, it means that the main circuit of the inverter or the detection and control circuit is faulty, and the fault should be judged and dealt with separately.

The frequency converter has an \"OVERCURRENT\" fault. To analyze its causes, two aspects should be considered: one is the external cause; the other is the cause of the frequency converter itself.

The object of overcurrent protection in the inverter mainly refers to the situation when the current peak value with a sudden change exceeds the allowable value of the inverter. Since the overload capacity of the switching device in the inverter is low, the overcurrent protection of the inverter is a crucial element. So far, the overcurrent protection of frequency converters has been very well developed.

The inverter may also cause overcurrent protection action for the following reasons.

① If the current and voltage detection channels of the main circuit interface board are damaged, overcurrent will occur. The reason for circuit board damage is as follows.nte: Due to the bad environment, solid particles are attached to the circuit board, causing static damage, or corrosive gas corrodes the circuit. The zero potential of the printed circuit board is connected to the housing. Since the case and cabinet are connected to the protective ground, the ground potential on the protective ground will affect the operation performance of the circuit on the circuit board. In severe cases, the potential of the zero potential point of the circuit board will increase, which will also damage the circuit board.

②The plug-in connection is not tight or firm. For example, if the current or voltage feedback signal line is in poor contact, there will occasionally be overcurrent faults.

③When the load is unstable, the DTC check mode should be used, because the DTC check speed is very fast, every 25 μs output a setof actual values ​​of torque and magnetic flux, then pass through the torque comparator, and the magnetic flux comparator come out after comparison, and the switching position of the inverter is determined by the optimized pulse selector, which can suppress overcurrent effectively. In addition, the speed loop self-tuning will automatically adjust the PID parameters, so that the output current from the frequency converter to the motor is stable.

The external causes of overcurrent are as follows.

①The motor load changes suddenly, causing large inrush current and overcurrent protection action. These failures are usually temporary and normal operation will resume after a reboot. If there are frequent load mutations, measures should be taken to limit the load mutations or replace a larger capacity inverter. It is recommended to user a direct torque control inverter, which has fast dynamic response and very fast control speed. The self-adaptive ability of the ring can make the inverter output current stable and avoid overcurrent.

②The insulation inside the motor and motor cable is damaged, causing a short circuit between turns or phases to ground, resulting in overcurrent.

③In the motor coil, there is a large parasitic between the motor cable and the ground, and there will be high-frequency leakage current flowing to the ground through the parasitic capacitance, resulting in an overcurrent.

④ If there is a power factor correction capacitor or a surge absorbing device on the output side of the inverter, its failure will also cause an overcurrent fault.

⑤ During the operation of the inverter, the control circuit is subject to electromagnetic interference, resulting int a control signal error, causing the inverter to operate incorrectly, and when the speed feedback signal is lost or abnormal, it also causes overcurrents.

⑥ Incorrect selection of the inverter capacity does not match the load characteristics, causing the inverter to malfunction, abnormal operation, overcurrent or even fault damage.

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