Common frequency inverter common fault analysis and maintenance

General inverter common fault analysis and maintenance Introduction With the rapid development of electronic technology, inverter technology has gradually matured and improved, has been successfully applied to various fields. However, if the inverter is used improperly, it may still cause various faults or poor operation conditions, shortening the service life of the equipment. The author made a general analysis of the problems encountered during maintenance.

Although there are a wide variety of inverters and circuits are constantly being updated, the faults that occur are overcurrent, overvoltage, undervoltage, overload, overheating, unbalanced outputs, and no display faults.

2 overcurrent

Overcurrent is the most frequent phenomenon of inverter alarm.

2.1 phenomenon

(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.

2.2 Examples

(1) An RNB30033.7kW inverter jumps "OC" as soon as it starts

Analysis and maintenance: Open the lid did not find any signs of burnt, online measurement of IGBT basic judgments no problem, to determine the problem further, the IGBT removed after measuring 7 units of high-power transistors opened and closed are very good. 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 pin of the optocoupler A3120 was short-circuited to the negative terminal of the power supply. After the replacement, the three paths were basically the same. The module is powered on and everything is running fine.

(2) An RNB30022.2kW inverter energizes to jump “OC” and cannot be reset.

Analysis and maintenance: First check the inverter module did not find the problem. Second, check the drive circuit is also no abnormal phenomenon, the estimated problem is not in this piece, may be in the over-current signal processing of this part, its circuit sensor removed after power-up, shows that everything is normal, so that the sensor is bad, find a new one After loading the experiment, everything is normal.

3 over pressure

Overvoltage alarms generally occur at the time of shutdown. The main reason is that the deceleration time is too short or the brake resistor and brake unit have problems.

(1) Examples

One RNB30033.7kW inverter jumps "OU" when it stops.

Analysis and maintenance: Before the repair of this machine, we must first understand the reason why the “OU” alarm occurs. This is due to the acceleration of the motor rotor windings cutting the rotating magnetic field and the increase of the electromotive force and current of the rotor when the frequency converter is decelerating. Make the motor in the power generation state, the energy returned by the diode in the inverter circuit in parallel with the high-power switch tube to the DC link, so that the DC bus voltage rise caused by, so we should focus on checking the brake circuit, measuring discharge resistance no problem, When the brake pipe was measured, it was found to have been broken down. After the replacement, it was powered on. There was no problem with the quick stop.

4 Undervoltage

Underpressure is also a problem we often encounter in use. Mainly due to the main circuit voltage is too low (380V series is less than 400V), mainly due to: damage to a rectifier bridge or SCR three-way operation may lead to undervoltage failure, followed by the main loop contact Device damage, resulting in DC bus voltage loss above the charging resistor may lead to undervoltage. There is a voltage detection circuit failure and undervoltage problems.

4.1 Examples

One RNB301818.5kW inverter jumps "LU2".

● Analysis and maintenance: After checking the charging resistance of the rectifier bridge of this inverter is good, but no contactor action is heard after power-on, because the charging circuit of this inverter is not using thyristor but by contactor. The pull-in process completes the charging process, so it is thought that the fault may be in the contactor or the control circuit and the power supply section, and the removal of the contactor alone plus the 24V DC contactor is working properly. And 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 tube is damaged, find a new replacement after power-up is working properly.

5 overheating

Overheating is also a relatively common fault. The main causes are: high ambient temperatures, blocked fans, poor temperature sensor performance, and motor overheating.

5.1 Examples

One RNB302222kW inverter customer reported to jump “OH” about half an hour in operation.

● Analysis and maintenance: Because it is only after running for a period of time, there is no possibility that the temperature converter is bad. The temperature of the inverter may be too high. After the power is turned on, the fan is found to be rotating slowly. The protective cover is filled with a lot of Cotton wool (because the frequency converter is used in the textile industry), the boot fan runs well after being cleaned, and does not jump this fault after several hours of operation.

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