(1) When restarting, it will trip at a raise speed. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts stuck; inverter module damage; motor torque is too small and so on.
(2) Power-on jump, this phenomenon can not be reset generally, the main reasons are: bad module, bad drive circuit, bad current detection circuit.
(3) When restarting, it does not immediately trip, but when accelerating, the main reasons are: too short acceleration time setting, too low current limit setting, and high torque compensation (v/f) setting.
1. The inverter jumps “oc” as soon as it starts
Analysis and maintenance: Open the lid did not find any signs of burnt, online measurement igbt (7mbr25nf-0) basic judgment is no problem, in order to further determine the problem, after removing the igbt measured 7 units of high-power transistor opening and closing are well. When measuring the drive circuit of the upper half bridge, it was found that there was a clear difference between the two roads and the other two roads. After careful inspection, it was found that the output leg of the optocoupler a30 was short-circuited with the negative terminal of the power supply. After the replacement, the three circuits were basically the same. The module is powered on and everything is running fine.
Analysis and maintenance: First check the inverter module found no problems. Secondly, there is no abnormality in checking the drive circuit. It is estimated that the problem is not in this block. It may be in the part of the over-current signal processing. After removing the circuit sensor and powering it on, it shows that everything is normal. Therefore, it is considered that the sensor is broken, and a new one is needed. After loading the experiment, everything is normal.
2, over pressure
Overvoltage alarms usually occur at the time of shutdown. The main reason is that the deceleration time is too short or there is a problem with the braking resistor and the brake unit.
When the frequency converter decelerates, the motor rotor windings cut the rotating magnetic field faster, the rotor’s electromotive force and current increase, the motor is in the power generation state, and the feedback energy passes through the diode in parallel with the high-power switch tube in the inversion link to the DC link. Cause the DC bus voltage to rise, so we should focus on checking the brake circuit, measuring the discharge resistance is no problem, in the measurement of the brake pipe (et191) was found to have broken down, after the replacement of power running, and there is no problem with the fast stop .
3, under pressure
Underpressure is also a problem we often encounter in use. Mainly because the main circuit voltage is too low (220v series is lower than 200v, 380v series is lower than 400v), the main reason: a rectifier bridge or a SCR three-way work may lead to undervoltage fault The main circuit contactor appears damaged, causing the DC bus voltage loss to cause undervoltage on the charging resistor. There is a voltage detection circuit failure and undervoltage problems.
Inverter charging circuit does not use thyristor but by the contactor to complete the charging process, so that the fault may be in the contactor or the control circuit and the power supply part, remove the contactor alone plus 24V DC contactor work normal. Then check the 24v DC power supply, after careful inspection of the voltage is regulated by the lm7824 regulator after the output, measuring the regulator has been damaged, find a new replacement after the power is working properly.
Inverter also through the charging circuit, the contactor to complete the charging process, no abnormal phenomenon was found when the power is on, it is estimated that the voltage drop of the DC loop caused by the load, and the voltage of the DC loop is through the rectifier bridge full wave Rectification, and then provided by the capacitor after the flat wave, so should focus on checking the rectifier bridge, the measurement found that the rectifier bridge has a bridge arm open, replace the new problem after the solution.
4, overheated
Overheating is also a relatively common fault. The main causes are: high ambient temperature, blocked fans, poor temperature sensor performance, and motor overheating.
Inverter, output voltage difference of about 100v.
Analysis and maintenance: Open the machine for initial online inspection. The inverter module (6mbi50n-0) found no problem. No drive was found on the 6-way drive circuit. The module was removed and measurements were taken. It was found that the high-power transistors on the bridge cannot be turned on and off properly. , The module has been damaged, after the replacement of new products after confirming that the driver circuit has no fault, everything is normal.
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