Causes and repairs of common inverter faults
1, Analysis and treatment of parameter setting fault causes
When using the inverter, whether it can meet the control requirements of the transmission system, the parameter settings of the inverter are very important, such as parameters If the setting is incorrect, the control effect will be poor, or the inverter will not operate normally. For a newly purchased inverter, the manufacturer generally sets a default value for each parameter when it leaves the factory. Under these parameter values, the inverter can operate normally in the panel operation mode, but only this and It cannot meet the requirements of most transmission systems. To obtain better control effects, the user must modify the parameters of the inverter according to the actual conditions of the transmission system and refer to its instruction manual.
Once a parameter setting fault occurs and the inverter cannot operate normally, it is best to restore all parameters to factory values and then reset the relevant parameters according to the parameter setting steps in the instruction manual. The parameter recovery methods for different types of inverters are also different. Improper parameter setting. This problem often occurs in constant torque loads. When encountering such problems, you should focus on checking the acceleration and deceleration time settings or increasing the torque setting value.
(1)Example1:A Fujifilmfrn280g11—4cxThe inverter jumps during operation and displays: Undervoltage “lu“.
Analysis and maintenance: When starting high-power equipment, (such as2#nitrogen Hydrogen compressor4000kwsynchronous motor), the other two Fujis on the same power supplyfrn5.5g11—4cxThe inverter did not jump during operation, only this inverter jumped during operation, and the display : Undervoltage “lu” alarm. After the power is turned off, open the casing and check that the internal primary and secondary circuit medium-voltage wiring of the inverter is not loose; check that there is no loose contact in the internal wiring of the motor junction box. After power on, check the setting parameters of the inverter, f14: The setting value is “1” (Momentary stop and restart does not work), modify the setting parameters of the inverterf14: The setting value is “3“(Instant stop and restart action ), after the inverter detects undervoltage, the protection function does not operate, stops output, and automatically restarts when the power is restored. Since the setting parameters of the inverter were modified, when starting high-power equipment, the secondary inverter did not skip undervoltage “lu” during operation.
(2)Instance2: One setfrn1.5g11 —4cx The inverter is newly put into use. The frequency setting is already very high, but the motor speed is obviously lower than other motors at the same frequency, and the motor speed is still not high. .
Analysis and maintenance: Check the setting parameters of the frequency converter. After checking the frequency gain f17, the setting range is 0.0～200%The factory setting value is 100%, and the user’s actual The setting value is 200%. Since the frequency setting signal gain is the ratio of the set analog frequency signal to the output frequency, that is, if the set frequency is 40hz, the actual output frequency is only 20hz. After changing the set frequency gain setting value to the factory setting value100%, the problem was solved.
2,Overvoltage(ou) type faults Cause Analysis and Treatment
The overvoltage of the frequency converter is concentrated on the tributary voltage of the DC bus. Under normal circumstances, the DC power of the frequency converter is three-phase full-wave rectification The average value after. If calculated based on 380v line voltage, the average DC voltage ud=1.35, uLine=513v. When overvoltage occurs, the energy storage capacitor of the DC bus will be charged, the voltage will increase, and the overvoltage detection value 800vdc, when the voltage rises to the overvoltage detection value, the inverter overvoltage protection operates. Therefore, for the inverter, there is a normal operating voltage range. When the voltage exceeds this range, it is likely to damage the inverter.
There are three common types of overvoltage in inverters:ou1Acceleration overvoltage, span>ou2Deceleration overvoltage, ou3Constant speed overvoltage. Overvoltage alarms generally appear during shutdown, and their main The reason is that the deceleration time is too short or the braking resistor and braking unit are not installed. When an overvoltage fault occurs in the inverter, it is usually caused by a thunderstorm. The lightning enters the power supply of the inverter, causing the voltage detector on the DC side of the inverter to operate. Trip, in this case, usually only need to disconnect the power supply of the frequency converter for about 1min and then turn the power on to reset; in another case, the frequency converter driver When the load is large inertia, the deceleration time is set to “shorter” because in this case, the deceleration stop of the inverter is regenerative braking. During the stop process, the output frequency of the inverter decreases linearly, and the frequency of the load motor is high. Depending on the output frequency of the frequency converter, the load motor is in the power generation state, and the mechanical energy is converted into electrical energy and absorbed by the smoothing capacitor on the DC side of the frequency converter. When this energy is large enough, the so-called “pumping phenomenon” will occur. The power on the DC side of theThe voltage will exceed the maximum voltage of the DC bus and trip. For this kind of fault, the first is to set the “deceleration time” parameter longer; the second is to install the braking unit and increase the braking resistor; the third is to set the stopping mode of the inverter for “free parking”. There is also a situation where the inverter works normally when the motor is unloaded, but cannot be started with load. This problem often occurs with constant torque loads. When encountering such problems, you should focus on checking the acceleration and deceleration time settings or the torque boost function. As a result, the DC circuit voltage of the inverter rises, exceeds its protection value, and malfunctions occur.
(1)Example1: One installationn2 series3.7kw inverter jumps “ou” when stopped.
Analysis and maintenance: Before repairing this machine, we must first understand the reason why the “ou” alarm , this is because when the frequency converter is decelerating, the motor rotor winding cuts the rotating magnetic field faster, the electromotive force and current of the rotor increase, making the motor in a power generation state, and the feedback energy passes through the diode in parallel with the high-power switching tube in the inverter link. It flows to the DC link, causing the DC bus voltage to increase, so we should focus on checking the brake circuit. There is no problem in measuring the discharge resistance. When measuring the brake tube(et191) It was found that it had broken down, and after replacement, it was powered on and ran, and it stopped quickly without any problems.
(2)Example2:A Fujifilmfrn110g9—4cxThe inverter jumps during operation and displays: constant speed overvoltage “ou3“.
Analysis and maintenance: First analyze what causes the inverter to jump during operation and display a constant speed overvoltage(ou3)alarm. What are the possible causes? reasons, and then find the root causes one by one based on possible causes.
3, Undervoltage (lu)Analysis and treatment of causes of similar faults
Under voltage is also a problem often encountered in use. Mainly because the main circuit voltage is too low (380v series is lower than 400v). The main reason is: one path of the rectifier bridge is damaged or the three thyristors are damaged. If something on the circuit is not working properly, it may lead to an undervoltage fault. Secondly, the main circuit contactor is damaged, resulting in DC bus voltage loss on the charging resistor, which may lead to undervoltage. There is also an undervoltage problem caused by a failure of the voltage detection circuit. The lower limit of the bus voltage of most frequency converters is 400v, that is, when the DC bus voltage drops below 400vdc, The inverter reports a DC bus low voltage fault. When two-phase input is used, the DC bus voltage is 3801.2＝452v>400v . When the frequency converter is not running, due to the effect of the smoothing capacitor, the DC voltage can also reach the normal value. New frequency converters adopt pwm control technology to regulate voltage and frequency. The work is completed in the inverter bridge, so it can still work normally if the input phase is missing in the low frequency band. However, because the input voltage is low and the output voltage is low, the asynchronous motor torque is low and the frequency cannot increase.
(1)Example1:A Fujifilmfrn18.5g11—4cxThe inverter jumps “lu” when it is powered on.
Analysis and maintenance: After checking, the charging resistance of the rectifier bridge of this inverter is good, but no contactor action is heard after powering on, because this inverter The charging circuit does not use a thyristor, but relies on the pull-in of the contactor to complete the process of limiting the charging current. Therefore, it is believed that the fault may lie in the contactor or control circuit and power supply part. Remove the contactor and charge it separately The 24vDC contactor is working fine. Then check the 24v DC power supply. After careful inspection, the voltage is passed through lm7824The voltage regulator tube outputs the voltage after stabilization. It is measured that the voltage regulator tube is damaged. Replace it with a new one and it will work normally after powering on.
(2)Example2:A Danfossvlt5004, 2.2kw inverter, the power-on display is normal, but after adding load, it jumps “dclinkundervolt“(DC link voltage is low).
Analysis and maintenance: This inverter looks special in appearance, but if you analyze it carefully, the problem is not that complicated. The inverter also passes the charging circuit. , the contactor is used to complete the process of limiting the charging current. No abnormality was found when powering on. It is estimated that it is caused by the voltage drop of the DC circuit when the load is added, and the voltage of the DC circuit is full-wave rectified through the rectifier bridge , Then it is provided by the capacitor after smoothing, so the rectifier bridge should be checked carefully. After measurement, it was found that one of the bridge arms of the rectifier bridge was open. The problem was solved after replacing it with a new one. It means there is a problem with the power input circuit, which may be caused by severe overloading of the line or poor line contact. The letters “ are displayed on the LCD panel of Siemens6se70 series inverters. e“, when this happens, the inverter cannot work. Pressing the p key and re-stopping the power supply are ineffective. Check the operation manual again. There is no relevant introduction. When checking the external dc24v power supply, it was found that the voltage was low. After solving the problem, the inverter worked normally.
4, Overcurrent (oc)Cause analysis and treatment of similar faults
Overcurrent fault
Overcurrent is the most frequent alarm phenomenon of the inverter. When this kind of fault display occurs,, first check whether the motor connection terminals u, v, w circuits are interphase Short circuit or short circuit to ground; secondly check whether the load is too heavy and reduce the load; finally check whether the acceleration and deceleration time parameters are too short and whether the torque boost parameters are too large and reduce the amount of torque boost. If there are no such phenomena, you can disconnect the current transformer on the output side and the Hall current detection point on the DC side, run after reset, and see if overcurrent occurs. If so, it is likely to be1pm The module fails because 1pmThe module contains protection functions such as overvoltage and overcurrent, undervoltage, overload, overheating, phase loss, and short circuit. These fault signals are transmitted to the microcontroller through the output fn pin of the module control pin. After receiving the fault information, the microcontroller blocks the pulses. output, on the other hand, the fault information is displayed on the panel, and the 1pm module is generally replaced. Overcurrent during acceleration or deceleration, which is often caused by excessive acceleration or deceleration. You can increase the acceleration time or preset the acceleration time correctly. (Reduce)Speed self-processing(Anti-stall) function and solved.
Three common types of overcurrent faults in frequency converters
(1) When restarting, it trips as soon as the speed increases
This is a very serious overcurrent phenomenon. The main reasons are: load short circuit, mechanical parts are stuck; inverter module is damaged; motor torque is too small, etc.
(2)It jumps when power is turned on
This phenomenon generally cannot be reset. The reasons are: the module is bad, the drive circuit is bad, and the current detection circuit is bad.
(3)It does not trip immediately when restarting;Trip during acceleration
The main reasons are: acceleration time setting is too short, current upper limit setting is too small, torque compensation(v/f) is set higher.
Case analysis
(1)One setlg-is3-43.7kw span>The inverter jumps as soon as it is started and displays “oc“.
Analysis and maintenance: No signs of burnout were found after opening the cover, and online measurementigbt(7mbr25nf-120)The basic judgment is that there is no problem. To further determine the problem, remove the igbt and measure the opening and closing of the high-power transistors of 7 units. good. When measuring the drive circuit of the upper half-bridge, it was found that one circuit was obviously different from the other two circuits. After careful inspection, it was found that the output pin of an optocouplera3120 was short-circuited to the negative pole of the power supply. After replacement, the three channels are basically the same. After the module is installed and powered on, everything runs fine.
(2)One setbeltro-vert2.2kwThe frequency converter jumps when power is turned on and displays “oc”, and “oc” cannot be reset.
Analysis and maintenance: First check the inverter module and no problem is found. Secondly, check the drive circuit and there is no abnormality. It is estimated that the problem is not in this area. It may be in the over-current signal processing part. After removing the circuit sensor and powering it on, it shows that everything is normal, so I think the sensor is broken. Find a new one and replace it. Everything is normal in the load test after loading.
5, Overload fault( olu)Cause Analysis and Treatment
Overload is also one of the faults that cause frequent inverter jumps. When you see the overload phenomenon, first of all It should be analyzed whether the motor is overloaded or the frequency converter itself is overloaded. Generally speaking, because the motor has a strong overload capacity, as long as it changesIf the motor parameters in the frequency converter parameter table are properly set, motor overload is generally unlikely to occur. The frequency converter itself is prone to overload alarm due to its poor overload capability. We can detect the inverter output voltage. The possible reasons are that the acceleration time is too short, the grid voltage is too low, the load is too heavy, etc. Generally, you can extend the acceleration time, extend the braking time, check the grid voltage, etc.; the load is too heavy, reduce the load; the selected inverter cannot drag the load, replace or increase the inverter capacity; it may also be due to mechanical lubrication If something goes wrong, the production machinery must be inspected and repaired.
Example: A Fujifilmfrn11g11—4cxDrag a frequency convertery132s-6, 7.5kw motor, when put into operation, jumps and stops frequently, displaying (olu) .
Analysis and maintenance: On-site inspection of the machinery, the mechanical part turns easily and there is no stalling phenomenon; refer to its operating instructions to check the parameters of the inverter. After inspection, the bias frequency The original setting is 3hz. Before the inverter receives the operation command but does not give the frequency modulation signal, the motor will always receive the low-frequency operation of 3hz command and cannot be started. It has been measured that the locked-rotor current of the motor reaches 50a, which is about 3 times the rated current of the motor; the frequency converter The overload protection action is normal. Modify the parameters of the inverter, restore the “bias frequency” to the factory value, modify the bias frequency to 0hz, and the motor startup can return to normal.
6, External condition failure cause analysis and processing
External condition fault is also a relatively common fault. This fault has no alarm code display, and the fault is relatively hidden and difficult to find. For example, after the inverter is running, use the “potentiometer” external analog input voltage command value to adjust the frequency normally, and use “dc4~20ma” external analog input current command value, frequency cannot be adjusted. The possible reasons; one is “dc4～20ma” The external analog input current command signal is weak and cannot meet the working requirements; one is “dc4～20ma“External analog input current command signal”, –polarity” is reversed, connect Counter.
Example: an Emersontd1000-4t0037p, 3.7kw frequency converter , the craftsman reported that the “potentiometer” used to adjust the speed on site was normal, but the use of dcs“dc4~20ma” Automatic speed adjustment is not possible.
Analysis and maintenance: According to the situation reported by the craftsman, the frequency conversion described Check the inverter failure phenomenon and check that the setting parameters of the inverter have not changed. After removing it, replace it with an inverter of the same model. After the parameter setting is completed, the fault is the same as above after starting up. After the power is cut off, turn on the inverter. Use a digital multimeter to measure the “analog current” signals of the inverter control terminals cci and gnd. The digital multimeter displays: 10ma. The reason is that when the maintenance personnel replaced the inverter and restored the secondary line, they mistakenly connected the inverter control terminalscci, The two wires of gnd are connected in the wrong position. Connect the inverter control terminals cci, gndThe two wires were removed and replaced. After the processing was completed, the fault was eliminated after powering on and test running.
7, Overheating in the inverter(oh3)Cause of fault Analysis and processing
oh3 is also a comparisonCommon faults, the main reasons are: whether the load is too large; the frequency converter temperature is too high. If an overtemperature alarm occurs, if the temperature sensor is normal after checking, it may be caused by interference, and the fault can be shielded. In addition, the ventilation condition of the cooling fan and heat sink of the inverter should be checked, the locked-rotor cooling fan should be replaced, the slow fan should be turned for repair, the inverter should be cleaned, and the blockage of the heat sink should be eliminated; whether the ambient temperature is too high, reduce the ambient temperature. For other types of failures, it is best to contact the manufacturer for quick and feasible solutions.
Example: A abbacs50022kw inverter customer reported that it jumped after about half an hour of operation and displayed “oh“.
Analysis and maintenance: Because the fault occurred after a period of operation, the temperature sensor is unlikely to be broken. Maybe the temperature of the inverter is indeed too high, and the fan is found to be rotating after power is turned on. Slowly. After the power was cut off, it was checked that the protective cover of the frequency converter was filled with a lot of cotton wool. After cleaning, the fan ran well after starting up. This fault did not occur again after running for several hours.
8, The heat sink is overheated (oh1)Fault Cause Analysis and Treatment
oh1 is also a relatively common fault. The main reason is: inspection. Inverter control terminals(13, 12, 11) is short-circuited; check whether the temperature sensor detection circuit is normal; in addition, check whether the cooling fan of the inverter is running normally; whether the heat sink is ventilated and whether the heat sink is blocked; whether the ambient temperature is too high.
Example: a Fujifilmfrn15g11—4cx frequency converter, power-on display shows heat dissipation The tablet is overheated(oh1).
Analysis and maintenance: Because the inverter is newly installed and it malfunctions as soon as the power is supplied, the possibility of the inverter being broken is unlikely; the heat sink is not clogged; The cooling fan is operating normally. After the power is cut off, use a multimeter to test the analog input circuit and check the inverter control terminals(13, 12, 11) are short-circuited. The reason is that the analog input circuit The resistance value of the external frequency setting “potentiometer” is too small. Replace it with wxwxx0.25-1, 0.25w47 ～4.7k potentiometer, the inverter ran well after power on, and this fault did not occur again during operation.
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