Inverter component damage, such as power module burst, short circuit or open circuit, capacitor discharge, drum top, IC circuit breakdown damage, open circuit resistance components, etc., not only with a multimeter from the resistance value of components or on-line voltage Values ​​can be easily detected and some of the damage is caused by visually observing the shape and deformation of its appearance, which can give a clear judgment. The deterioration of the performance of components is not the state of “significant damage†for short circuit or open circuit. Not only is there no obvious abnormality in the appearance of the device, but sometimes even multimeters and other measuring equipments are ineffective. . Such damage, such as the large lead electrolytic resistance of the electrolytic capacitor, the dielectric loss of the small-capacity capacitor increases, the high-frequency characteristics deteriorate, and the transistor amplification ability deteriorates, the rectification characteristics of the diode deteriorates, etc. We use multimeters and capacitors. Table tests are all good, but faulty components “do not perform well†in the actual work of the circuit. It seems that a person works hard with negative emotions. Therefore, the work is bound to be full of loopholes, and it is difficult to complete tasks successfully.
The deterioration of the performance of inverter components is not a qualitative change but a quantitative change. After many years of use of the machine, the electrolytic solution such as the capacitor dried up, the amplification ability of the triode reduced, and the oxidation of the component pins gradually changed with the passage of time. Therefore, to overhaul the "old machine", it is necessary to pay attention to this aspect. The problem.
The definition of damage to such components is more appropriate for aging, inefficiency, failure, and performance degradation, and breakdowns, disconnections, and the like are not appropriate. The deterioration of the performance of components and components, the degree of deterioration is often very different, the phenomenon of failure and detection difficulties are also ever-changing, not easy to grasp, but often manifested as difficult problems, or called "soft failure", people scratch their heads - Can not find the bad parts, but the circuit is obviously not normal! Overhaul such failures, need to repair the basic skills of the electronic circuit solid, many years of accumulated experience, and even the maintenance of psychological quality, but also a test.
Fortunately, such failures are after all a minority, and generally the components are "hard". If repairers are willing to accept this challenge, the maintenance of such soft faults will also be transformed into a pleasure. The process of repair can even become a process of enjoyment. (Ordinary faults will change parts, and those who have fun will have fun. What?) It makes people feel very fulfilled. In the long-term maintenance work, we will always encounter such failures, we can simply not repair such machines, we can also accept it, enjoy one, what is not good?
For some components, the manufacturer has given the useful life, such as cooling fan and electrolytic capacitor in the inverter. The replacement period given by the manufacturer is 8-10 years. Fan is a rotating part, rotating parts such as bearings, always wear long-term use; In order to increase the capacity, the electrolytic capacitor is filled with electrolyte, so there is a negative leakage current production, installation and use should pay attention to its polarity. At the same time, with the increase in the number of years of use, the electrolyte must gradually dry out, so that the capacity decreases. After reaching the useful life, even if the inverter is not broken, in principle, fans and electrolytic capacitors should also be replaced to prevent problems.
The fan is damaged and relatively intuitive. Let's talk about the damage of the DC circuit's energy storage capacitor by the fault example.
First, the phenomenon of failure of the large-capacity electrolytic capacitor aging and repair ideas:
[Fault Example 1] A Fujitsu 5000 G9 90kW inverter, running under voltage fault. The frequency converter has been working continuously for nearly 10 years. After taking over, it first uses a capacitance meter to measure the capacity of the DC circuit's energy storage capacitor. There are 6 energy storage capacitors, each with a capacity of 8200 uF, and a capacity of 8000-8300 uF. Feeling capacitance is no problem. From the regulator into the adjustable three-phase power supply, check the voltage detection circuit and monitor the panel display DC voltage value, indicating that there is no problem with the DC voltage detection circuit. DC loop voltage is measured. When the input voltage is 380V, the DC voltage is about 540V (light load), and the problem can not be checked.
The inverter is driven by a 37kW motor, full load operation, and no circuit undervoltage fault. Still feel uneasy, and later found a factory, using a frequency converter to drive 75kW motor, full-load operation, jumping under voltage fault shutdown, running detection DC circuit voltage, has dropped to 430V. There is a fault in the inverter!
Under load conditions, the DC link voltage is low, and there are only two components that can be suspected: One is a three-phase rectifier circuit. This unit consists of six 100A rectifier modules to form a three-phase rectifier circuit, and each two are used in parallel. With the diode file of the digital multimeter, measure the forward voltage drop of the rectifier bridge, around 430 (0.43V), use an analog multimeter to measure the forward and reverse resistance, and there is no problem. The inverter has a characteristic that the use of the rectifier module and the inverter module has a considerable margin in power, and the stability of the rectifier module is also superior to the electrolytic capacitor. So still can not rule out the suspect of the capacitor. If you want to replace the test, you don't have so many rectifier modules and capacitor spare parts on hand. Only by determining whether the bridge is a bridge or a capacitor, verify the fault after purchasing the part.
Obviously, the damage of the capacitor is not due to the decrease of capacity caused by the long service life. The test capacity of the capacitance meter is also satisfactory. However, the performance of the local fault does indeed appear to be a decrease in the capacity of the storage capacitor, which does not achieve the proper energy storage function, and the voltage of the DC loop is reduced, causing the voltage detection circuit to report an undervoltage fault.
The capacity of the capacitor is reduced. Lighter ones are characterized by poor load capacity. When the load increases, they often jump to the under-voltage fault of the DC circuit. Further damage to the capacitor may also cause the DC link voltage to fluctuate and form a fatal blow to the inverter module. Such failures are often more subtle, unlike component short-circuiting, which is easy to attract attention, and sometimes it is difficult to check them up, especially for capacitors in high-power inverters. After many years of operation, the lead-out electrodes withstand hundreds of Hertz for many years. High-current charge and discharge shock, there are different degrees of oxidation, measured with a capacitance meter, normal capacity; measured with a multimeter, there is a clear charge and discharge phenomenon, reverse leakage resistance is within the allowable range, but connected to the circuit In the case of an increase in the internal resistance of charge and discharge, it is equivalent to a resistance and a discharge circuit connected in series with a resistance of a certain resistance! The transient charge and discharge current values ​​of the capacitor are greatly reduced, and the capacity of the capacitor is substantially reduced. Equivalent to a serious reduction in capacity. Due to the decrease of the power storage capacity, the DC link voltage drops, the inverter cannot work normally, and the maintenance personnel may make a misjudgment! If the non-load state, at the same time, the voltage value of the DC loop is monitored, it is difficult under the light load condition of the maintenance department. The problem of energy storage capacitance is determined and analyzed.
The appearance of the capacitance electrode lead resistance cannot be measured by conventional measurement methods. In-depth analysis has led to this conclusion.
After the above analysis, 6 high-quality electrolytic capacitors of 8200uf400V were mail-ordered. After all the energy storage capacitors of the aircraft were replaced, the 75kW motor was re-driven and the motor was in the full-load running state. No voltage fault was detected and the DC loop voltage was measured. Below, it has reached more than 520V. Inverter repair.
Second, the failure phenomenon of the poor contact of the main contacts of the charging contactor and the maintenance method:
When the contact of the charging contactor is bad, the voltage (or DC link voltage is low) is also skipped. See the examples below.
[Fault Example 2] A 37kW Dongyuan 7300MA inverter was operated with a random jump "DC circuit low voltage" fault, sometimes several times a day failure, sometimes running for several days. When the fault is reproduced, the frequency converter can be normally operated for a period of time after the inverter is powered back on. The user's work site voltage supply voltage is stable, there is no problem, while the use of several other inverters, and the same type of inverter, there is no such problem.
After sending the maintenance department, after the inverter is powered on, it hears a sound of “jingle bell†and the charging contactor is closed. When the inverter is empty or lightly loaded, it can run continuously for three days and the DC link voltage is not tripped. The three-phase voltage regulator is used to adjust the input voltage, and the DC link voltage value displayed on the operation display panel is monitored and changed in proportion to the input voltage. In a large range, the inverter does not report a fault, indicating that the detection circuit has no problem. .
The focus has also checked the energy storage capacity of the DC circuit. Its capacity and nominal value have not been greatly affected. The useful life of the machine is not long. The storage capacitor is also a high-quality component. It should be no problem.
Repeatedly power on several times, can hear the charging contactor charging sound, indicating that the charge contactor control circuit is also good. What causes the low DC link voltage?
Further associating that: Although the charge contactor is closed, the main contact is closed, but it can only be observed after the contactor is disassembled. After dismantling the contactor, it was found that the three pairs of main contacts burned severely, and it was found that most of the three-phase inverter modules were renewed and the machine had been repaired. It may be that when the module is blown up, the main contacts of the charging contactor are damaged at the same time.
The contactor is an electromagnetic switch. The closing and releasing of the contactor is accomplished by the cooperation of electromagnetic action and mechanical components. When the main contactor of the contactor burns and deforms, or if the service life is too long, resulting in mechanical deformation or mechanical aging, mechanical action will be hindered, resulting in insufficient suction and failure of the main contact.
In this example, due to contact burn-in, contact resistance occurs, and ignition is caused during operation. Randomness of the contacts is degraded, and the DC link voltage has a random drop phenomenon, resulting in undervoltage alarm. After the power is turned off, the contact state of the contactor is improved and the inverter can run for a while. After the mechanical deformation of the contactor, there are also such phenomena, and even some electricians have obtained this kind of experience. When the voltage fails, or after the inverter is repeatedly powered on several times, or after several times of shaking the inverter, the frequency conversion The device is "nervous" and "good."
Replace with a good contactor, troubleshooting.
In this example, there is a maintenance feature that “the ear is imaginary and seeing is believingâ€. The sound contactor is closed, but the closed state of the main contact can only be better determined by seeing the eye.
Third, the failure phenomenon of the transistor aging failure and maintenance ideas:
Transistor device aging and failure failures are more subtle, and the fault phenomena that they exhibit are even more difficult to understand. It is more difficult to wait for a component than repairing capacitors, contactors, and other components. The following two examples of failures of the inspection switch power supply are used to illustrate the overhaul of transistor aging faults. In the case of these two faults, one example is that the output voltage is high, and one example is that the output voltage is low, but the faulty components are hidden and interesting.
[Fault Example 3] The machine is a Dongfang 7200PA 37kW inverter. The fault phenomenon is: Random shutdown occurs during operation. It may be stopped several times in a few days, or it may be shut down in a few hours; it is difficult to start and the capacitor is charged during the start-up process. The device jumps and the start fails, but the operation panel does not display the fault code. After some effort to start successfully, it can run for a while.
Remove the control board from the site and short-circuit the terminals of the thermal relay to prevent it from entering the thermal protection state; do not test the machine; short the contact detection terminals of the charging contactor to prevent the low voltage protection state from entering the test machine. It's okay to overhaul and check what's wrong.
In addition, the control board is returned to the machine and the power-on test machine is started. When the starter starts, the charging contactor will jump. Unplug the 12CN plug cooling fan connection to reduce the load for the switching power supply, the situation improved, the starting success rate increased. Carefully observe that the display brightness of the display panel is reduced during the start-up process, and it is determined that the fault is due to poor switching power supply capability.
Remove the power/driver board and send a 500V DC maintenance power supply from outside the unit. Check the switch power supply circuit separately.
The local switching power supply circuit is a single-ended forward-type isolated switching power supply. The circuit consists of discrete components with a low failure rate. The switch and the shunt control tube constitute the backbone of the oscillation and voltage regulator circuit, and the peripheral circuit is extremely simple.
Remove the power/driver board and send 500V DC repair power from the outside of the unit. Check the switch power circuit separately.
The secondary winding of the switching power supply and the subsequent rectifying and filtering circuit, when the power output of each channel is unloaded, the output voltage is a normal value. Connect the power output of each channel to a resistive load (eg, 50 ohms, 5W resistor). The voltage value is slightly reduced. After +24V is connected to the cooling fan and relay load, +5V is reduced to +4.7V. At this time, the screen display and other operations are Are normal. However, if the inverter is brought into the start-up state, the relay 哒哒 jumps, and the fault codes such as “low DC voltage†and “interruption of communication between CPU and operation panel†appear, and the operation fails. During the measurement, when the +5V drops below +4.5V, the inverter immediately changes from the start-up state to the standby state. Detailed inspection of each power load circuit, no exception.
Analysis: The judgment that the control power source has a poor load capacity is correct. Due to the severe requirements of the CPU on the power supply, when not less than 4.7V, it can still work hard; but when less than 4.5V, it is forced into the "standby state"; when 4.7V to 4.5V, it is detected The circuit works and the CPU issues a fault alarm.
Unexpected is that the repair of this fault is actually quite tricky, and the related components of the switching power supply are actually “no damageâ€! In desperation, try R1 (5101) which is one of the reference voltage divider resistors of U1 (KA431AZ). Parallel resistance test, its purpose is to change the partial pressure value and increase the output voltage. The measured output voltage rises slightly, but the carrying capacity is still poor. The switch tube Q2 of this machine is a bipolar transistor (NPN power tube) with high back pressure and high amplification. The model is QM5HLL-24; Q1 is a shunt control tube, and the circuit has stricter requirements on the parameters of these two tubes. It's harder to buy on the market. Combined with the analysis of the fault phenomenon, it may be a low efficiency of the switching transistor Q2. If the value of β decreases, the energy storage of the TC2 will decrease and the load capacity of the circuit will become worse. Also, the work offset of the Q1 may be used, and the current shunting capability of the Q2 base may be too strong. , Make the power load capacity worse. However, there is no original type switch tube on hand, and users are very urgent to repair. Try to adjust the circuit to reduce the operating point of the shunt regulator to reduce the shunting effect on the base current of Q2, thereby improving the turn-on capability of the switch Q2 and increasing the energy storage of the TC2.
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