Inverter maintenance training methods
1. Alarm parameters Inspection method
All frequency converters give fault indications in different ways, which is very important information for maintenance personnel. Normally, the inverter will give corresponding error information for voltage, current, temperature, communication and other faults, and most inverters using microprocessors or DSP processors will have special parameters. Save more than 3 alarm records.
〖Example 1〗A frequency converter is faulty and cannot operate and LED displays “UV” (abbreviation of under voltage), in the manual, this alarm is DC bus undervoltage. Because the control circuit power of this type of inverter is not taken from the DC bus, but the control power is separately rectified from the AC input end through a transformer. Therefore, it is judged that the alarm should be real. So start with the power supply to check. The input power voltage is correct and the filter capacitor voltage is 0 volts. Since the short-circuit contactor of the charging resistor does not operate, it has nothing to do with the rectifier bridge. The scope of the fault was reduced to the charging resistor. After the power was cut off, a multimeter was used to detect that the charging resistor was blocked. Replacing the resistor fixed it immediately.
〖Example 2〗There is a SankenIF 11Kw frequency converter used3More than a year later, “AL5” is occasionally displayed when powering on.(alarm 5 The abbreviation of ), the manual says that CPU is interfered with. After many observations, it was found that it occurred when the charging resistor short-circuited the contactor. It was suspected that the interference was caused by the contactor. After adding a resistance-capacitance filter to the control pin, the fault no longer occurred.
〖Example 3〗A FujiE9Series3.7kW inverter suddenly appeared during on-site operationOC3 (Overcurrent during constant speed) alarm and shutdown occurs. After powering off and then powering on again, OC1 (Overcurrent during acceleration) alarm and shutdown appears. First remove U, V, W For the wires to the motor, use a multimeter to measure U, V, W is infinite, no-load operation, the inverter does not alarm, and the output voltage is normal. It can be initially concluded that there is no problem with the frequency converter. It turns out that there is a joint in the middle of the motor cable, which was covered with a wooden board in the distribution trough of the pit. The insulating tape aged and water entered during factory cleaning, causing an output short circuit.
〖Example 4〗SankenSVF303, displays “5”, “5” in the manual means DC overvoltage. The voltage value is sampled from the DC bus(DC around 530V) and then divided by the optocoupler Isolation is performed. When the voltage exceeds a certain threshold, the optocoupler acts and gives a high level to the processor. Overvoltage alarm, we can check whether the resistor changes value, whether there is a short circuit in the optocoupler, etc.
It is not difficult to see from the above examples how important the alarm prompts of the frequency converter are in solving problems, and remind you the correct direction to solve the problem.
2. Analogy inspection method
This method can be an analogy of the same circuit, or an analogy between a faulty board and a known good board. This can help repairers quickly narrow down the inspection scope.
〖Example 1〗 SankenMF15 The kilowatt inverter was damaged and was sent back for repair. The user said no Clarify the specific situation. First use a multimeter to measure the input terminalR, S, T, except R , T have a certain resistance value, other terminals have infinite resistance to each other, input terminals R, S, T The characteristics of the diode are between the positive or negative poles of the rectifier bridge respectively. Why are R and T different from the other two groups? It turns out that R and T breakers have control power transformers inside, so they have a certain resistance. It can be seen from the above that there is no problem with the input part. Also use a multimeter to check U, V, W, three-phase balance. Next, when I checked the diode characteristics of the positive and negative poles of the output DC, I found that U was not connected to the positive and negative poles. I suspected U There was a problem with the phaseIGBT. I took it apart and checked and it turned out that the IGBT was broken. In the drive circuit, the three sets of upper-side arm control circuits have the same characteristics, and the three sets of lower-side arm control circuits have the same characteristics. Comparison method was used to check and it was found that Q1 was damaged. After replacement, the trigger pin resistance values of each group are consistent, and the PWM waveform is confirmed to be correct after power-on. Reassemble, power on and test repair.
〖Example 2〗There is an inverter. The panel display is normal, the digital setting frequency and operation are normal, but the terminal control fails. Use a multimeter to check that there is no10V voltage at the terminals. Starting from the switching power supply, all groups of power supplies are normal. It seems that the problem lies in the connecting wires. But it takes a while to find 10V among 32 flat cables without drawings, and there happens to be one The table is intact22KW is there, so first note down the voltage between each pin of the flat cable connected to 22KW and then compare it. 37KW The difference in voltage between each pin and ground was quickly found. It turns out that the pins of the slot were weakly welded. After the inverter was used for a period of time, the oxidation effect caused it to completely stop conducting. It was repaired by re-soldering.
〖Example 3〗There is a wool spinning factory with carding machine equipment, and Siemens 440 Frequency converters, two 5.5KW and one 7.5KW achieve synchronous operation. One of the 5.5KW often appearsF0011 or A0511 after two years of operation. Shut down. Both alarms indicate that the motor is overloaded. Take off the motor belt and rotate the motor and equipment by hand. There is no abnormal heavy phenomenon. The two 5.5KW driven motors After exchanging them, if it is found that the original inverter is still alarming, then it is determined that there is something wrong with the inverter. The analogy method can not only be used to check the internal circuit of the machine, it can also be used to identify on-site problems.
3. Spare board replacement inspection method
Using a spare circuit board or a circuit board of the same model to confirm the fault and narrow the inspection scope is a very effective method. If there is a problem with the control board, there is often no other option but to replace it, because most users rarely get schematics and layout drawings, making it difficult to perform chip-level repairs. Circuit boards other than control boards such as power boards and driver boards can be repaired, and will be further introduced in other chapters. Here we mainly introduce the replacement of the control board.
4. Isolation inspection method
Some faults are often difficult to determine in which area they occur.By adopting isolation method, complex problems can be simplified and the cause of the fault can be found out quickly.
〖Example 1〗Repairing an Yingtai inverter, the phenomenon is that after power on, there is no display, accompanied by a beeping sound. Based on experience, it can be concluded that the switching power supply is overloaded, the feedback protection works and shuts off the output of the switching power supply, and the beep-beep sound occurs when it starts to vibrate again and is turned off again. First remove the control panel, power on and find that the problem remains the same, then disconnect the diodes of each power supply group one by one, and finally find that there is a problem with the 15V used by the fan. However, there is no running signal from the fan. It should not be a problem with the fan itself. It seems to be a problem with the front end of the fan. Finally, I found that the characteristics of the 15V filter capacitor were wrong. I removed the filter capacitor and measured it. It turned out that it was aging. Replacing new capacitors fixed it.
5. Intuitive inspection method
It is to use the sensory organs of human hands, eyes, ears and nose to find out cause of issue. This method is commonly used and used first. The maintenance principle of “outside first, then inside” requires that when encountering a fault, maintenance personnel should first use the methods of looking, smelling, asking, and touching to check one by one from the outside to the inside. Some faults can be quickly found out by using this intuitive method, otherwise a lot of time will be wasted and even no way to start. Use vision to check whether the connections of line components are loose, whether the disconnected contactor is ablated due to electric shock, whether the pressure is constant, whether the heating element is overheated and discolored, whether the electrolytic capacitor is expanded and deformed, and whether the voltage-resistant component has an obvious breakdown point. After powering on, smell whether there is a burning smell, and touch the heating element to see if it is hot. It is very important to ask questions. Asking the user how the fault occurred will help analyze the cause of the problem. It is easier to directly hit the key point. Sometimes asking peers is also a shortcut.
〖Example 2〗A SankenIP 55KW inverter is under warranty Internal damage, no display when powered on. Open the cover of the machine and carefully observe each part. It is found that the charging resistor is burned out, the contactor coil is burned out and the outer casing is burnt. After further questioning, it turned out that the user’s power supply voltage was low and the inverter often shut down due to undervoltage, so a booster was specially equipped for the inverter. But the user did not notice that the voltage would return to normal at night, resulting in first burning out the contactor and then the charging resistor. The rectifier bridge and electrolytic capacitors survived due to their relatively high withstand voltage. Replace damaged components and repair.
6. Temperature rise and fall inspection method
This method is very effective for some special faults. Artificially give some temperature specialHeating or cooling components with poor performance can produce “symptoms” or eliminate “symptoms” to find out the cause of the fault
〖Example 3〗There is a German Lixi inverter failure. Users reported that the inverter often shuts down after parameter initialization, usually after resetting parameters 20 minutes to 30 Minutes the fault reappears. First of all, the fault should be related to temperature, because the temperature of the inverter will increase after running for this time. Use a hot air soldering station to heat the thermistor. When it reaches the temperature at which the fan starts, observe Go to the control panel’s LED and suddenly it loses power and then lights up again and then flashes on and off, take away the hot air 30After a second, the LED of the control panel no longer flashes, but displays normally. Use the isolation method to unplug all the fan plugs, and heat the experiment again. The fault was eliminated. It was found that all the fans were short-circuited. It seems that after the temperature reached, the control board gave a fan operation signal. As a result, the short-circuited fan caused the switching power supply to overload and shut down the output. The control board quickly lost power and the parameters were stored incorrectly, causing parameter reset. Replace Remove the fan and the problem is solved.
7. Destruction inspection method
Is to adopt some means to cancel internal protection measures and simulate fault conditions to destroy problematic devices . Make the faulty device or area stand out. First of all, it is stated that this method must be very sure to control the development of the situation, that is, the maintainer must understand the state of the most serious damage and whether he can accept the most serious further damage. , and there are control measures to avoid more serious damage.
〖Example 1〗While repairing the inverter, an inverter with a switching power supply failure was encountered. When the protection loop operates, it can be concluded that there is a short-circuit branch at the output end of the transformer, but the fault point cannot be measured statically. We use the destruction method to find statically fault-free devices. First, disconnect the feedback signal of the protection loop, causing it to lose its protection function, and then Turn on the DC power supply and use a voltage regulator to slowly increase the DC voltage from 0v and observe the relevant components. If smoke comes out, turn off the power immediately and use If the resistor is short-circuited, the DC filter capacitor will discharge quickly.The cause of the smoke was the rectifier diode of the fan power supply. It turned out that the fan had been damaged by a short circuit, and the control switch signal of the fan was always on (the device was short-circuited and caused a high-level on state). As long as the switching power supply outputs normal voltage, the fan will short-circuit the fan. power supply, resulting in switching power supply protection. During static measurement, the short circuit status of the fan cannot be measured.
8. Knock inspection method
The inverter is composed of various circuit boards and module connectors. Each circuit board has many solder joints. Any weak soldering and poor contact will cause failure. Use an insulated rubber rod to tap the suspected defective part. If the inverter fault disappears or reappears, the problem is likely to be there.
〖Example 1〗The inverter of a certain factory has been running normally for more than 3 without any It suddenly shut down without warning, and no fault information was displayed. After starting, it would start and stop. After careful observation, no abnormalities were found, and static measurements did not reveal any problems. After powering on, tap the casing of the frequency converter and find that the running signal will change with the tapping. After inspection, it was found that the screws of the external terminalFR terminal were loose, and the running signal wire end was not crimped to theU type terminal. , directly connected to the terminal, and the wiring connection pressed against the wire sheath of the wire, causing the screw to loosen due to vibration, and the control wire wire was virtually connected to the terminal. Crimp the U type terminal and re-tighten the screw to eliminate the fault.
9. Brushing inspection method
Many special faults come and go, looming, making it difficult to judge and deal with . At this time, you can clean the circuit board with water or alcohol, and use a soft brush to remove dust and rust on the circuit board. Pay special attention to areas with dense solder joints, via holes and 0 volt copper The circuits close to each other should also be cleaned and then dried with hot air. Unexpected results are often achieved. At least it helps with the application of observation.
〖Example 1〗The fault of a certain inverter is that there is no display. After preliminary inspection, the rectifier part and the inverter part are intact, so the power is turned on for inspection. The DC bus voltage is normal, but the starting voltage of the switching power supply control chip 3844 is only 2v. The resistance of the voltage dividing resistor is much smaller when tested online, but normal when tested offline. After using the scrubbing method, the problem was solved. It turns out to be a capacitor’s positive pin pad and0v layer is very close, and the residual flux makes it semi-conductive.
〖Example 2〗When the inverter was delivered, there were several different alarm records. Various false alarms also occurred during the power-on test. After carefully cleaning the solder joints of the flat cable socket connecting the control board and driver board, the problem was solved.
10. Principle analysis and inspection method
Principle analysis is the most fundamental method for troubleshooting. When other inspection methods fail to work, you can start from the basic principles of the circuit, conduct inspection step by step, and finally find out the cause of the fault. To use this method, you must have a clear understanding of the principles of the circuit, master the logic levels and characteristic parameters (such as voltage values, waveforms) at each point at each moment, and then use a multimeter or oscilloscope to measure and compare with normal conditions to analyze and determine the fault. The cause is narrowed down to the fault scope until the fault is found.
〖Example 1〗An inverter sent for repair lost the charging resistor short-circuit relay, fan operation, and inverter status relay signals at the same time. After comparative testing, it was confirmed that the problem lies in the control board. After analysis, the problem may lie in the latch, because these signals are controlled by this chip. It was indeed repaired after replacement.
In general, the inspection of faulty frequency converters should be from the outside to the inside, from the outside to the inside, from static to dynamic, and from the main loop to the control loop. The following three checks are generally required.
Use a multimeter to detect the diode characteristics and three-phase balance characteristics of the output terminals for the DC positive and negative poles respectively. This step can initially determine the quality of the inverter module, thereby determining whether it can output without load. If there is a phase-to-phase short circuit or unbalanced state, no-load output is not possible.
Open the cover and observe. If no problem is found in the above two steps, you can open the case, remove the dust, and carefully observe whether there is any damage inside the inverter, whether there are burnt parts, whether the capacitor is leaking, etc.
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