Inverter maintenance learning methods are many, but the direction is not a waste of effort, so it is important to seize the direction, in order to allow everyone to quickly master the inverter maintenance knowledge, here to provide ten kinds of inverter maintenance learning methods for everyone.
1, alarm parameter inspection method
〖Example 1〗 The inverter has a fault and cannot be operated and the LED shows “UV†(abbreviation of under voltage). This alarm is the DC bus undervoltage in the manual. Because the control circuit power supply of this type of frequency converter is not taken from the DC bus, it is the control power that is separately rectified from the AC input terminal through the transformer. So judge that the alarm should be true. Therefore, starting from the power supply inspection, input power supply voltage is correct, filter capacitor voltage is 0 volts. Since the short-circuit contactor of the charging resistor does not operate, it is not related to the rectifying bridge. The fault range is reduced to the charging resistance. After the power is turned off, the multimeter detects that the charging resistor is broken. The replacement resistor is repaired immediately.
Example 2 There is a three-phase IF 11Kw inverter that has been used for more than 3 years and occasionally shows "AL5" (an abbreviation for alarm 5) when it is powered on. The instructions say that the CPU has been disturbed. After many observations, it was found that the charge resistor shorted the contactor action. Suspected of interference caused by the contactor, in the control of the filter plus resistance and capacitance, then the failure no longer occurs.
Example 3: A Fuji E9 series 3.7-kilowatt inverter suddenly caused an OC3 (overflow in constant speed) alarm during on-site operation. After power-off, the OC1 (acceleration overcurrent) alarm shutdown occurred. I first removed the U, V, W wires to the motor, and measured the resistance between U, V, and W with a multimeter to infinity, no-load operation, no alarm from the inverter, and normal output voltage. It can be initially concluded that there is no problem with the frequency converter. The original is a joint in the middle of the motor cable, covered with a wood block in the pit of the pit, the insulation tape aging, the factory cleaning sanitation water, resulting in output short circuit.
Example 4 Sanken SVF303, showing "5", "5" in the specification indicates DC overvoltage. The voltage value is sampled by the DC bus (about 530V DC) and then isolated by the optocoupler. When the voltage exceeds a certain threshold, the optocoupler operates to give the processor a high level. Overvoltage alarm, we can see whether the resistance value, whether the optocoupler short circuit phenomenon.
From the above examples, it is easy to see how important the alarm prompt of the inverter is to the processing problem, and it prompts you to correctly handle the problem.
2, analogy test
This method can be an analogy of its own circuit, or it can be an analogy of a fault board and a known good board. This can help repairers quickly narrow the inspection.
Example 1 The three-input MF15-kilowatt inverter was damaged and sent back for repair. The user could not tell the specific situation. First, use a multimeter to measure the input terminals R, S, and T. Except for a certain resistance between R and T, the resistance of the other terminals is infinite, and the input terminals R, S, and T are respectively between the positive and negative terminals of the rectifier bridge. Diode characteristics. Why are R and T different from the other two groups? The original R, T fault internal control power transformer, so there is a certain resistance. The above can be seen no problem with the input part. Also use a multimeter to check the resistance between U, V, W, three-phase balance. Next, check the diode characteristics of the output of the relative DC positive and negative poles and find that U is not connected to the positive and negative poles of the positive pole. It is suspected that the U-phase IGBT has a problem, and the IGBT is broken when the inspection is removed. In the driving circuit, the characteristics of the three groups of the upper arm control circuit are the same, and the characteristics of the three groups of the lower arm control circuit are the same. The inspection of the Q1 is found through the comparison method. After the replacement, the trigger resistance value is the same for each group, and the power waveform is correct after the power is turned on. Reassemble, power on test repair.
Example 2 There is a frequency converter. The phenomenon is that the panel display is normal, the digital setting frequency and operation are normal, but the terminal control fails. Use a multimeter to check the terminal for no 10V voltage. Starting from the switching power supply, the power of each group is normal, and it seems that the problem lies in the connection wire. However, if there is no drawing, it will take a while to find 10V in 32 flat cables, and there is exactly one 22KW in good condition. Therefore, first record the foot-to-ground voltage of the 22KW connection flat cable, and then compare 37KW. Each foot-to-ground voltage quickly finds differences. The original socket pins were soldered, and the inverter used a certain period of time to oxidize it to make it completely non-conductive, reweld and repaired.
[Example 3] There is a wool mill's carding machine equipment, Siemens 440 frequency converter is selected, two 5.5KW one 7.5KW to achieve synchronous operation. One of the 5.5KW's two years after the operation often appeared F0011 or A0511 downtime. These two alarms all indicate that the motor is overloaded. The motor belt and the device are disconnected from the motor belt. There is no abnormally heavy phenomenon. The two 5.5KW motors are swapped and the original inverter alarm is found. The inverter has a problem. The analogy method can be used not only to check the internal circuit of a machine but also to discriminate field problems.
3, spare board replacement inspection method
Using a backup circuit board or a circuit board of the same type to confirm the fault and narrow the inspection range is a very effective method. If the control board is out of order, it is often the only alternative, because most users will hardly get schematics and layout drawings, making it difficult to do maintenance at the chip level. Circuit boards other than control boards such as the power board and driver board can be repaired, and other chapters will be further introduced. The replacement of the control board is mainly introduced here.
4, isolation test
Some faults are often difficult to judge in that area. Using isolated methods can simplify complex problems and find out the cause of the problem faster.
[Example 1] Maintenance of an Indo-China inverter. The phenomenon is that there is no display after power-on, and there is a 嘀-嘀 sound. Based on experience, it can be concluded that the switching power supply is overloaded, and the feedback protection is used to turn off the switching power supply output, and the click-and-pop sound produced by the re-shutdown again starts. First, remove the control panel, and after power-on discovery, it is still the same, and then disconnect the diodes of each power supply one by one, and finally find that there is a problem with the 15V used by the fan. However, the fan does not have a running signal. It should not be the fan itself. It seems to be a problem at the front of the fan. Finally, the 15V filter capacitor was found to be incorrect. Removing the filter capacitor measurement was really aging. Replace it with a new one.
5, visual inspection
It is to use human hands, eyes, ears, and nose to find the cause of the malfunction. This method is commonly used and used first. The maintenance principle of “first outside and then inside†requires that maintenance personnel should first use the methods of sight, smell, question, and touch to conduct inspections from the outside to the inside. Some faults use this intuitive method to quickly find the cause, otherwise it will waste a lot of time, or even have no way to start. The use of vision can be connected to the circuit components are loose, whether the contact of the broken contactor is ablated, whether the pressure is frequent, whether the heating element is overheated and discolored, whether the electrolytic capacitor expands and deforms, and whether the pressure element has a significant breakdown point. After the electricity, you smell the scorched smell. If you touch the heating element by hand, it is hot. It is very important to ask, asking the user about the process of failures is helpful to analyze the causes of the problems, and it is easy to hit the point directly. Sometimes asking a colleague is a shortcut.
[Example 2] A Sanken IP 55KW inverter was damaged during the warranty period, and no power was displayed. Open the lid of the machine, carefully observe the various parts and find that the charging resistor is burned out, the coil of the contactor is blown and the case is scorched. After questioning, the original user's power supply voltage is low, often due to undervoltage shutdown, the frequency converter is specially equipped with a booster. However, the user does not notice that the voltage will return to normal at night, and as a result, the contactor is first burnt out and then the charging resistor is burned. As the rectifier bridge and electrolytic capacitor withstand relatively high pressure and survived. Replace damaged device repair.
6, heating and cooling inspection method
This method is very effective for some special faults. Artificially warming or cooling some components with poor temperature characteristics, producing "diseases" or eliminating "diseases to find the cause of the malfunction
Example 3 has a Delixi inverter fault. The user reports that the inverter frequently initiates the shutdown of the parameters, and the fault is reappeared after 20 minutes to 30 minutes after the parameters are reset. First of all, I think that the fault should be related to the temperature, because the inverter temperature will rise after this time. I used a hot air soldering station to heat the thermistor. When it was heated to the temperature at which the fan was started, the LED of the control panel was suddenly turned off and then turned on. Then the flickering was followed by the flickering of the hot air for 30 seconds. The LED is no longer flashing, but the normal display. Use the isolation method to unplug all fan plugs and reheat the experiment to eliminate the fault. Check that all fans are short-circuited. It seems that after the temperature is reached, the control board gives the fan operation signal. As a result, the short-circuited fan causes the switching power supply to overload and shut down the output. The control board quickly loses power and the parameters are stored incorrectly, causing the parameters to be reset. Replace the fan and solve the problem.
7, destruction inspection method
It is to take some measures to eliminate internal protection measures and simulate failure conditions to destroy problematic devices. Make the faulty device or area stand out. First of all, it is stated that this method requires a great deal of control to control the development of the situation. That is, the repairer must understand the state of the most serious damage, whether it can accept the most serious further damage, and have control measures to avoid more serious problems. damage.
Example 1 In repairing a frequency converter, when a converter with a switching power supply fault is encountered, his protection circuit operates, and a short-circuit branch at the output end of the transformer can be determined, but the failure point cannot be measured statically. We use the damage method to find static and fault-free devices. First, the feedback signal of the protection circuit is disconnected, so that it loses its protection function. Then, the DC power supply is turned on, and a voltage regulator is required to slowly increase the DC voltage from 0 V to observe the relevant devices. Smoke was found, and the power was turned off immediately. At the same time, a short-circuit DC filter capacitor was used to quickly discharge. Smoke is the rectifying diode of the fan power supply. The original fan has been short-circuited, and the control switch signal of the fan is always on (the device short-circuit causes a high-level on state). As long as the switching power supply outputs a normal voltage, the fan is short-circuited. Fan power supply, resulting in switching power supply protection. In the static measurement, the short-circuit condition of the fan is not detected.
8, percussion inspection
The inverter is composed of connectors for various circuit boards and modules. Each circuit board has a lot of solder joints, and any soldering or poor contact will fail. Use an insulating rubber rod to knock a suspected bad part. If the inverter's fault disappears or reappears, the problem is likely to be there.
Example 1 The frequency converter of a certain factory has been operating normally for more than three years. Suddenly, the inverter was stopped without any symptoms. There was no indication of faults. After the start, the inverter was stopped. Observed carefully, did not find any strange, static measurement did not find the problem. After power on, tap the casing of the inverter and find that the operation signal changes with tapping. After inspection, it was found that the screw of the external terminal FR terminal is loose, and the U-shaped terminal of the operating signal line is not crimped. It is directly connected to the terminal. The connection point is pressed against the wire sheath of the wire, resulting in loosening of the screw due to vibration, and the control line leads and terminals. Virtual connection. Crimp the U-shaped terminal and re-tighten the screw for troubleshooting.
9, brush inspection method
Many special faults, sometimes and sometimes, are looming and can't be judged and dealt with. At this time, the circuit board can be cleaned with clean water or alcohol, and at the same time, dust and rust on the circuit board can be brushed off with a soft bristle brush, paying particular attention to where solder joints are dense. The vias and the circuit close to the 0-volt copper layer are also to be cleaned. Clean and dry with hot air. Unexpected results are often achieved. At least to help the application of observation method.
Example 1 The fault of a frequency converter is no display. After a preliminary test, the rectifier and inverter parts are in good condition. 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 divider resistance is much smaller on-line and the off-line detection is normal. After using the scrubbing method, the problem is solved. It turns out that the positive electrode pad of a capacitor is in close proximity to the 0V layer, and the remaining flux makes it in a semiconducting state.
Example 2 There are several different alarm records when the frequency converter is sent. Various false alarms also appeared during the power-on test. Careful cleaning of the control board and drive board connected flat cable socket solder joints, the problem is solved.
10. Principle analysis and inspection
Principle analysis is the most fundamental method of troubleshooting. When other inspection methods are ineffective, you can proceed from the basic principles of the circuit and check the process step by step to determine the cause of the fault. The use of this method must have a clear understanding of the principle of the circuit, grasp the logic level and characteristic parameters (such as voltage value, waveform) at various points in time, and then use a multimeter, oscilloscope measurements, and compared with the normal situation, analyze and determine the fault The reason is to narrow down the fault until it finds a fault.
Example 1 An inverter that was repaired lost the charging resistor short-circuit relay, the fan operation, and the inverter status relay signal. After a comparative test, it was confirmed that the problem was in the control board. After analysis, the problem may be in the latch, because these signals are controlled by this chip. Replace the result and fix it.
In general, the faulty inverters are checked from the outside to the inside, from the table to the inside, from static to dynamic, and from the main loop to the control loop. The following three checks are generally necessary.
Use a multimeter to test the diode characteristics and three-phase balance characteristics of the output terminals for the DC positive and negative electrodes, respectively. This step can initially determine whether the inverter module is good or bad, so as to decide whether it can be no-load output. If there is a phase-to-phase short circuit or an unbalanced condition, the output cannot be idling.
Open the lid and observe that if no problems are found in the above two steps, you can open the case, remove the dust, and carefully observe whether the inverter is damaged inside, whether there are black parts, whether the capacitor leaks, and so on.
The above is the ten kinds of learning methods for frequency inverter maintenance. Learning the frequency converter through these methods helps to get a better start, further mastering richer knowledge, and provide a good basis for learning the knowledge of frequency converter maintenance.
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