〖例 1〗某变频器有故障，无法运行并且LED显示“UV”（under voltage的缩写），说明书中该报警为直流母线欠压。因为该型号变频器的控制回路电源不是从直流母线取的，而是从交流输入端通过变压器单独整流出的控制电源。所以判断该报警应该是真实的。所以从电源入手检查，输入电源电压正确，滤波电容电压为0伏。由于充电电阻的短路接触器没动作，所以与整流桥无关。故障范围缩小到充电电阻，断电后用万用表检测发现是充电电阻断了。更换电阻马上就修好了。
〖例 2〗有一台三垦IF 11Kw的变频器用了3年多后，偶尔上电时显示“AL5”(alarm 5 的缩写)，说明书中说CPU被干扰。经过多次观察发现是在充电电阻短路接触器动作时出现的。怀疑是接触器造成的干扰，在控制脚加上阻容滤波后果然故障不再发生了。
〖例 3〗一台富士E9系列3.7千瓦变频器，在现场运行中突然出现OC3（恒速中过流）报警 停机，断电后重新上电运行出现OC1（加速中过流）报警停机。我先拆掉U、V、W到电机的导线，用万用表测量U、V、W之间电阻无穷大，空载运行，变频器没有报警，输出电压正常。可以初步断定变频器没有问题。原来是电机电缆的中部有个接头，用木版盖在地坑的分线槽中，绝缘胶布老化，工厂打扫卫生进水，造成输出短路。
〖例 1〗 三垦MF15千瓦变频器损坏，送回来修理，用户说不清具体情况。首先用万用表测量输入端R、S、T，除R、T之间有一定的阻值以外其他端子相互之间电阻无穷大，输入端子R,S,T分别对整流桥的正极或负极之间是二极管特性。为什么R、T之间与其他两组不一样哪？原来R、T断子内部有控制电源变压器，所以有一定的阻值。以上可以看出输入部分没问题。同样用万用表去检查U、V、W之间阻值，三相平衡。接下去检查输出各相对直流正负极的二极管特性时发现U对正极正反都不通，怀疑U相IGBT有问题，拆下来检查果然是IGBT坏了。驱动电路中上桥臂控制电路三组特性一致，下桥臂控制电路三组特性一致，采用对比方法检查发现Q1损坏。更换后,触发脚阻值各组一致，上电确认PWM波形正确。重新组装，上电测试修复。
〖例 3〗有一毛纺厂的梳毛机设备，选用西门子440变频器，两台5.5KW一台7.5KW实现同步运转。其中一台5.5KW的运行两年后经常出现F0011或A0511停机。这两个报警都表示电机过载，脱开电机皮带用手盘动电机及设备，没有异常沉重的现象，将两台5.5KW拖动的电机互换，发现还是原来的变频器报警，则确定是变频器出了问题。 类比法,不仅可以用在检查机器内部回路,也可以用于现场问题的判别。
〖例 2〗一台三垦IP 55KW变频器在保修期内损坏，上电无显示。打开机器盖子，仔细的观察各个部分，发现充电电阻烧坏，接触器线圈烧断而且外壳焦糊。经过追问，原来用户电源电压低，变频器常常因为欠压停机，就专门给变频器配了一个升压器。但是用户并没有注意到在夜间电压会恢复正常，结果首先烧坏接触器然后烧坏充电电阻。由于整流桥和电解电容耐压相对较高而幸免于难。更换损坏器件修复。
Inverter maintenance learning methods there are many, but the direction of the effort is not in vain, so grasp the direction is very important, in order to let you grasp the inverter maintenance knowledge faster, here to provide ten inverter maintenance learning methods to everyone.
1. Alarm parameter inspection method
There is something wrong with the inverter, it cannot operate and the LED shows "UV" (under voltage). The alarm in the instruction is dc bus undervoltage. Because the control circuit power supply of this type of inverter is not taken from the dc bus, but from the ac input end through a separate rectifier transformer control power supply. So it should be true. Therefore, starting from the power supply, check that the input power voltage is correct and the filter capacitor voltage is 0 v. Because the short circuit contactor of charging resistance has no action, so it has nothing to do with rectifying bridge. The fault range was narrowed down to charging resistance. After power failure, the multimeter was used to detect that the charging power was blocked. The replacement resistor was fixed immediately.
After using a sankenif 11Kw converter for more than three years, it occasionally displays "AL5" (an abbreviation of alarm 5) when it comes on, indicating that the CPU is being disturbed. After many observations found that the charging resistance short circuit contactor action occurred. It is suspected that the interference is caused by the contactor, and the fault no longer occurs after the control pin plus the blocking and capacitive filtering.
A Fuji E9 series 3.7-kw frequency converter suddenly appears OC3 (medium overcurrent at constant speed) to stop the machine during field operation, and OC1 (medium overcurrent at accelerated speed) to alarm and stop the machine when power is switched off. First, I removed the lead from U, V and W to the motor, and measured the infinite resistance between U, V and W with a multimeter. It ran on no load. The inverter did not alarm and the output voltage was normal. It can be preliminarily concluded that there is no problem with the inverter. It turned out that there was a joint in the middle of the electrical cable, which was covered by wood plate in the dividing channel of the pit. The insulation adhesive cloth aged, and the factory cleaned and had water, causing output short circuit.
Three Ken SVF303, show "5", "5" in the manual means dc overvoltage. Voltage value is sampled by the dc bus (about 530V dc) through the partial voltage and then isolated by the optocoupler. When the voltage exceeds a certain threshold, the optocoupler ACTS to give the processor a high level. Overvoltage alarm, we can see whether the resistance variable value, whether there is a short circuit in the photocoupler phenomenon.
From the above examples, it is not difficult to see how important the alarm reminder of the inverter to deal with the problem, prompt you to deal with the problem in the right direction.
2. Analogy test
This method can be the analogy of the same circuit itself, or the analogy between the fault plate and the known good plate. This can help the maintainer quickly narrow down the inspection area.
Sanken MF15 kw converter damaged, sent back to repair, the user can not tell the specific situation. Firstly, the multimeter is used to measure the input terminal R,S and T. Except that there is a certain resistance value between R and T, the resistance between other terminals is infinite. The input terminal R,S and T respectively have diode characteristics between the positive and negative poles of the rectifying bridge. Why are R and T different from the other two groups? The original R, T sub internal control power transformer, so there is a certain resistance value. So you can see that the input is fine. Also use the multimeter to check the resistance between U, V, W, three-phase balance. Then check the output of the relative dc positive and negative diode characteristics found that U is not positive and negative to the positive pole, suspected that there is a problem with U phase IGBT, down to check that IGBT is broken. In the driving circuit, three groups of upper bridge arm control circuit have the same characteristics, while three groups of lower bridge arm control circuit have the same characteristics. After replacement, the trigger foot resistance value of each group is consistent, power on to confirm the correct PWM waveform. Reassemble, power test and repair.
There is a frequency converter. It appears that the panel display is normal, the digital frequency setting and operation are normal, but the terminal control is out of order. Check terminal no 10V voltage with multimeter. Starting from the switch power supply, all the power supply is normal, it seems that the problem lies in the connection wire. However, it really takes some time to find 10V in 32 flat cables without drawing. There is just one intact 22KW one. Therefore, write down the voltage of 22KW connecting flat cables at each foot to the ground, and then compare the voltage of 37KW at each foot to the ground, and quickly find the difference. The original socket pin virtual welding, inverter with a period of time after the role of oxidation to make it completely blocked, rewelding and repair.
There is a carding machine equipment in a wool spinning mill, which adopts Siemens 440 frequency converter, and two machines with 5.5kw and one with 7.5kw can operate synchronously. F0011 or A0511 is often shut down after two years of operation of one of the 5.5kw machines. These two alarms both indicate that the motor is overloaded. If you take off the motor belt and move the motor and equipment by hand, there is no abnormal heavy phenomenon. If you switch the two 5.5kw dragging motors and find that the original frequency converter alarms you, it is sure that there is something wrong with the frequency converter. The analogy method can be used not only to check the internal circuit of the machine, but also to identify the field problems.
3. Inspection method of replacement of spare plate
Using the spare circuit board or circuit board of the same model to confirm the fault, narrow the scope of inspection is a very effective method. If there is a problem with the control board, there is often no other way but to replace it, because most users can hardly get the schematic diagram and layout diagram, which makes it difficult to do chip level maintenance. Circuit board other than power board and drive board can be repaired. Other chapters will be further introduced. The replacement of control board is mainly introduced here.
4, isolation inspection method
Some faults are often difficult to identify in that area, isolation can be taken to simplify the complex problem, quickly find out the cause of the fault.
Maintenance of an intime inverter, the phenomenon is after the electricity, there is no display, accompanied by the sound of di - di. It is empirically determined that the switching power supply is overloaded, and that the feedback protection functions to turn off the switching power output, and then turn it off again. First, remove the control panel and turn on the power to find that it is still the same. Then, disconnect the diodes of each power source one by one. Finally, it is found that there is something wrong with the 15V used by the fan. However, the fan does not have a working signal. It should not be the fan itself, but the front end of the fan. Finally, it was found that the characteristics of the filter capacitance of 15V were wrong, and the filter capacitance was removed to measure, so it was aging. Replace it with a new capacitor and it's fixed.
5, visual inspection method
Is to use the hands, eyes, ears, nose sensory organs to find the cause of the fault. This method is often used and used first. The maintenance principle of "first outside, then inside" requires that maintenance personnel should first adopt the methods of looking, smelling, asking and touching, and check one by one from outside to inside. Some faults can be quickly found by this intuitive method, otherwise it will waste a lot of time, or even unable to start. Vision can be used to determine whether the connection of line elements is loose, whether the broken wire contactor is ablated by electric shock, whether the pressure is frequent, whether the heating element is overheated and discolored, whether the electrolytic capacitor is expanded and deformed, and whether the pressure-resisting element has an obvious breakdown point. After the electricity smell whether there is burnt paste taste, touch the heating element is hot. It is very important to ask, ask the process that the user fails to produce, concent analyses the reason of the problem, facilitate direct hit crucial point.
A sanken IP 55KW frequency converter was damaged during the warranty period, and there was no display on the power supply. Open the cover of the machine and carefully observe each part. It is found that the charging resistance is burnt out, the contactor coil is burnt out and the shell is burnt out. After cross-examination, the original user power supply voltage, inverter often due to undervoltage shutdown, on the inverter with a booster. However, the user did not notice that the voltage would return to normal at night, which would first burn out the contactor and then the charging resistor. Because the rectifier bridge and electrolytic capacitor withstand relatively high voltage survived. Replace damaged parts and repair.
6, rising and cooling inspection
This method is very effective for some special faults. Artificially warm or cool some components with poor temperature characteristics to produce "symptoms" or eliminate "symptoms" to find the cause of the failure
There is a fault with a delixi frequency converter. The user reported that the inverter was often shut down after parameter initialization, and the fault reappeared in 20 to 30 minutes after parameter reset. First of all, I think the fault should be related to the temperature, because the temperature of the inverter will increase after running up to this time. I heated the thermistor with the hot air welding table. When the temperature of the fan was heated to the starting temperature, I observed that the LED of the control panel suddenly lost power, then turned on and then flickered. After taking away the hot air for 30 seconds, the LED of the control panel no longer flickered but displayed normally. Use isolation method to unplug all fan plugs, again heating experiment, fault elimination. Check all fans short circuit. It seems that after the temperature arrived, the control board gave the fan operation signal. As a result, the short-circuited fan caused the switch power overload and shut down the output. The control board lost power quickly and the parameter storage error resulted in parameter reset. Replace the fan. Problem solved.
7, break the inspection law
It is to take some measure to cancel the internal protection measures and simulate the failure conditions to destroy the problematic device. To highlight a faulty device or area. First of all, this method should be very sure to control the development of the situation, that is, the maintenance of the psychological to understand the most serious damage is what state, can accept the most serious further damage, and have control means to avoid more serious damage.
During the repair of the converter, we encountered a converter with a switching power failure. The action of its protective circuit 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 destructive method to find the static fault-free device. First, disconnect the feedback signal of the protection loop to make it lose the protection function. Then, switch on the dc power supply. The voltage regulator is required to slowly raise the dc voltage from 0v to observe relevant devices. If you find smoke coming out, turn off the power immediately. At the same time, use resistance to short-circuit dc filter capacitor to discharge quickly. Smoke is the fan power rectifier diode, the original fan has been short-circuit damage, and the fan control switch signal has been in the open state (device short-circuit caused by high level open state), as long as the switch power output normal voltage, the fan short-circuit fan power, resulting in switch power protection. In static measurement, the short circuit of the fan cannot be measured.
8. Tapping test
Inverter is composed of various circuit boards and modules with connectors, each circuit board are a lot of solder joints, any virtual welding and poor contact will occur fault. Striking suspicious areas with insulated rubber rods is likely to be the problem if the converter's malfunction disappears or reappears.
The inverter in a factory has been in normal operation for more than 3 years. Without any warning, it suddenly stops working, and there is no fault information. On closer inspection, nothing unusual was found, nor did the static measurements. After electrification, striking the shell of frequency converter, it is found that the operation signal will change with the striking. After inspection, it was found that the FR terminal screw of the external terminal was loose, and there was no pressing u-shaped terminal at the end of the running signal line, which was directly connected to the terminal. The wiring pressed the wire skin of the lead, resulting in virtual connection between the control wire wire and the end after the screw was loosened due to vibration. Press U - shaped terminal, re-tighten the screw troubleshooting.
9. Scrub test
Many special faults, sometimes no, looming, it is impossible to judge and deal with. The circuit board can be cleaned with water or alcohol, while using a soft brush to remove dust and rust on the circuit board, especially pay attention to the areas of dense solder joints, through holes and close to the 0 volt copper layer circuit should be cleaned, and then dry with hot air. It often achieves unexpected results. At least it's useful for observation.
The fault of a frequency converter is not shown. After preliminary testing, the rectified part and the inverter part are in good condition, so the power is switched on for inspection. The dc bus voltage is normal, but the starting voltage of the switch power control chip 3844 is only 2v. The resistance value of the partial voltage resistance online detection is much smaller, offline detection is normal. The problem was solved after washing. It turned out to be a capacitor positive pin pad close to the 0v layer, with residual flux leaving it in a semi-conducting state.
When the frequency converter was sent, there were several different alarm records. In the electrification test process there are also various false alarm. After carefully cleaning the solder joint between the control board and the driver board, the problem is solved.
10. Principle analysis and inspection
Principle analysis is the most fundamental method of troubleshooting, when other inspection methods are difficult to work, you can start from the basic principles of the circuit, step by step inspection, and finally find out the cause of the fault. Using this method, it is necessary to have a clear understanding of the principle of the circuit, master the logic level and characteristic parameters (such as voltage value and waveform) of each point at each time, then measure with a multimeter and oscilloscope, and compare with the normal situation, analyze and judge the cause of the fault, and narrow the fault range until the fault is found.
At the same time, one of the inverter under repair lost the signal of charging resistance short-circuit relay, fan operation and inverter status relay. Through comparative test, it is proved that the problem lies in the control board. After analysis, the problem may be in the latch, because these signals are controlled by the chip. It was repaired after replacement.
In general, the fault converter should be inspected from the outside to the inside, from the surface to the inside, from the static state to the dynamic state, and from the main circuit to the control circuit. The following three tests are generally mandatory.
Multimeter is used to detect the diode characteristics and three phase balance characteristics of the output terminals on the dc positive and negative poles respectively. This step can preliminarily determine the quality of the inverter module, so as to determine whether it can be output without load. If there is short circuit or unbalanced state between phases, no no-load output is allowed.
Open the cover to observe, if the above two steps did not find the problem, can open the chassis, remove dust, carefully observe the inverter internal whether there is any damage, whether there is a blackened parts, whether the capacitor leakage, and so on.
Above is the ten methods of inverter maintenance learning, through these methods to learn inverter maintenance is conducive to a better introduction, further grasp more abundant knowledge, for skilled learning inverter maintenance knowledge to do a good foundation.