How to eliminate the soft fault of frequency conve

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How to eliminate the soft fault of frequency converter

belongs to small category 1.1 phenomenon

(1) when restarting, it trips as soon as the speed is increased. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts are stuck; Inverter module is damaged; The torque of the motor is too small

(2) it jumps when powered on. This phenomenon generally cannot be reset. The main reasons are: the module is bad, the driving circuit is bad, and the current detection circuit is bad

(3) when restarting, it does not trip immediately, but when accelerating, the main reasons are: the acceleration time setting is too short, the upper current limit setting is too small, and the torque compensation (v/f) setting is high

1.2 example

(1) an lg-is 3.7KW frequency converter jumps "OC" as soon as it is started

analysis and maintenance: no sign of burnout is found when opening the cover, and there is basically no problem when measuring IGBT (7mbr25nf-120). In order to further determine the problem, it is good to measure the opening and closing of high-power transistors of 7 units after removing IGBT. When measuring the drive circuit of the upper half axle, it was found that one circuit was significantly different from the other two circuits. After careful inspection, it was found that the output pin of an optocoupler a3120 was short circuited with the negative pole of the power supply, and the three circuits after replacement were basically the same. The module is installed, powered on and running well

(2) when a beltro-vert 2.2kW frequency converter is powered on, it jumps "OC" and cannot be reset

analysis and maintenance: first, check the inverter module and find no problems. Secondly, check that there is no abnormal phenomenon in the driving circuit. It is estimated that the problem is not in this part. It may be due to the overcurrent signal processing. Remove the circuit sensor and power on. It shows that everything is normal. Therefore, it is considered that the sensor is broken. Find a new one and replace it. The test with load is normal

2. Overvoltage

overvoltage alarm usually occurs when the machine is stopped. The main reason is that the deceleration time is too short or there is a problem with the braking resistance and braking unit

(1) example

a Taian N2 series 3.7KW frequency converter jumps "Ou" during shutdown

analysis and maintenance: before repairing this machine, we must first find out the reason for the "Ou" alarm. This is because when the frequency converter decelerates, the speed of cutting the rotating magnetic field of the motor rotor winding accelerates, and the electromotive force and current of the rotor increase, so that the motor is in the state of power generation. The feedback energy flows to the DC link through the diode in parallel with the high-power switch in the inverter link, causing the DC bus voltage to rise, Therefore, we should focus on the inspection of braking 1. Cleaning and cleaning: the experiment shows that some dust circuits will inevitably be generated in the process of completing an experiment. There is no problem in measuring the discharge resistance. When measuring the brake pipe (ET191), it is found that it has been broken down. After replacement, it is powered on for operation, and there is no problem in stopping quickly

3. Undervoltage

undervoltage is also a problem we often encounter in use. The main reason is that the voltage of the main circuit is too low (220V series is lower than 200V, 380V series is lower than 400V). The main reason is that one circuit of the rectifier bridge is damaged or there is abnormal operation in the three circuits of the thyristor, which may lead to the occurrence of undervoltage fault. Secondly, the contactor of the main circuit is damaged, resulting in the loss of DC bus voltage above the charging resistance, which may lead to undervoltage There is also the undervoltage problem caused by the failure of the voltage detection circuit

3.1 example

(1) a CT 18.5kw frequency converter trips "UU" when powered on

analysis and maintenance: after inspection, the charging resistance of the rectifier bridge of this frequency converter is good, but the contactor action is not heard after power on, because the charging circuit of this frequency converter does not use thyristor, but relies on the attraction of the contactor to complete the charging process, so it is considered that the fault may be in the contactor or control circuit and the power supply part. Remove the contactor and add 24V DC contactor separately to work normally. Then check the 24V DC power supply. After careful inspection, the voltage is output after being stabilized by the lm7824 regulator tube. It is measured that the regulator tube has been damaged. Find a new one and replace it. It works normally when powered on

(2) a Danfoss vlt5004 frequency converter, the power on display is normal, but after loading, it jumps "DC link undervolt" (DC circuit voltage is low)

analysis and maintenance: this frequency converter is special in terms of phenomenon, but if you carefully analyze the problem, it is not so complicated. The frequency converter also completes the charging process through the charging circuit and contactor. No abnormal phenomenon is found when it is powered on. It is estimated that it is caused by the voltage drop of the DC circuit when loading, and the voltage of the DC circuit is rectified by the full wave rectifier of the rectifier bridge, Then it is provided by the capacitor after smoothing, so we should focus on checking the rectifier bridge. After measurement, it is found that one of the bridge arms of the rectifier bridge is open circuit, and the problem is solved after replacing it with a new one

4. Overheating

overheating is also a common fault. The main reasons are: the ambient temperature is too high, the fan is locked, the performance of the temperature sensor is poor, and the motor is overheated

4.1 example

the customer of an ABB acs500 22KW frequency converter reported that it jumped "Oh" in about half an hour of operation

analysis and maintenance: because the fault occurs after a period of operation, it is unlikely that the temperature sensor will be damaged. Maybe the temperature of the frequency converter is really too high. After power on, it is found that the fan rotates slowly, and the protective cover is filled with a lot of cotton wool (because the frequency converter is used in the textile industry). After cleaning, the fan runs well, and the fault does not jump again after running for several hours

5. Output imbalance

output imbalance is generally manifested in motor jitter and unstable speed. The main reasons are: bad module, bad drive circuit, bad reactor, etc

5.1 example

a fulux g9s 11kw frequency converter, the output voltage difference is about 100V

analysis and maintenance: turn on the machine and preliminarily check the inverter module (6mbi50n-120). No problem is found, and no fault is found in the 6-way drive circuit. After removing the module and measuring, it is found that the high-power transistor of one way bridge cannot be turned on and off normally. The module has been damaged. After confirming that the drive circuit is free of fault, everything is normal after replacing it with a new one

6. Overload

overload is also one of the faults that the frequency converter jumps more frequently. When we see the overload phenomenon at ordinary times, we should first analyze whether it is the motor overload or the overload of the frequency converter itself. Generally speaking, the motor has strong overload capacity. As long as the motor parameters in the frequency converter parameter table are set properly, the motor overload is generally not likely to occur The frequency converter itself is prone to overload alarm due to its poor overload capacity We can detect the inverter output voltage, current detection circuit, and other fault prone points to eliminate faults one by one

6.1 example

a LG IH 55kW frequency converter often jumps "ol" during operation

analysis and maintenance: according to the customer, this machine was originally used on a 37KW motor, but now it is used on a 55kW motor. The parameters have not been reset, so the problem may lie in the parameters. After inspection, the frequency conversion current limit is set to the rated current of 37KW motor. After the parameters are reset, everything with load is normal

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