Inverter maintenance method - hope sunland

1. Look

After taking over a faulty inverter, remove the inverter shell and clean it up, and carefully investigate the appearance, shape, and integrity of the relevant components on the circuit board with both eyes according to the type of inverter fault. This method is very important for the preliminary judgment of the quality of charging resistors, filter electrolytic capacitors, IGBT/rectifier bridge modules, and even PCB circuit boards. Figure 1 shows that the display screen display value of a certain brand of 75KW inverter is generated during the use of the time; The motherboard outputs DC10V power supply with intermittent problems. After dismantling, the author found the cause of the problem at a glance - the rectifier diode used by the switching power supply to the motherboard +15V power supply branch was caused by serious ablation of the PCB board due to soldering and ignition!

Inverter maintenance method - hope sunland

Inverter maintenance method - hope sunland

2. Listen

The method is mainly aimed at the three aspects of the inverter: the first is to judge whether the DC bus charging relay/contactor is normal, which is very important to eliminate the undervoltage fault reported during the operation of the inverter. In addition, it is very useful to listen carefully to whether the transformer used in the switching power supply has abnormal noise, which is also very useful for preliminarily determining whether there is an overload phenomenon in the switching power supply part. Finally, there is the monitoring of the operation status of the inverter cooling fan.

3. Touch

After the inverter presents a problem and loses power, quickly disassemble the machine and do a good job of protection, and quickly touch the relevant electronic components and IC integrated blocks on the internal circuit board of the inverter with your fingers. Once it is found that the temperature rise of some components is obvious compared to the same period last year, the problem must be on it or its surrounding lines! Figure 2 shows a brand of 35KW inverter, due to the deterioration of the resistance value of the DC bus voltage monitoring and the DC bus overvoltage maintenance, you can feel how high the heat emitted by the resistance at the time of the incident can be felt from the figure!

Fourth, pressure

When the inverter operation is good and bad, it may be caused by the welding problem of some components on the edge of the internal line. For some chip ICs with a lot of finely placed pins, it is not easy to find out if there is a problem simply by visual investigation. In this case, we have no problem pressing the suspect element appropriately and vigorously with the help of an insulated plastic rod/mallet (it is strictly forbidden to use conductive metal objects) in the energized state. This method is very useful for cleaning small chip components, especially chip ICs, but it must be done to prevent electric shock and short circuit during operation.

5. Knock

This method is a supplement to the fourth detection method, which can only be useful for small chip components, and the part of the line that may have a high voltage hazard for some high-power electronic components is not very convenient to operate. In this regard, we can change the pressure to knock, and use insulating tools to strike appropriately near the suspicious fault point, and in most cases we can quickly determine the problem object. Figure 3 shows the virtual solder joints of the components detected by this method that cause the intermittent overpressure problem of a small-capacity inverter!

Sixth, the quantity

This method mainly relies on multimeter detection, and at present, it is more carried out by using digital multimeters. For the maintenance of various faults of the inverter, about 65% of them are solved by using a multimeter. On how to use the multimeter to measure, I believe that the majority of electrician friends can be proficient in the use, here I only focus on one point: because of the inverter's internal high-voltage energy storage components, remember to discharge first and then go through the measurement operation after the power failure, otherwise the multimeter is difficult to protect! The appearance and color of the one shown in Figure 4 look no abnormal, and the 1/4W color ring resistance with a nominal resistance of 15KΩ has become infinity with a multimeter (because the resistor deteriorates, resulting in a certain brand of 22KW inverter reporting the problem of "output current unbalance")!

7. Measurement

After talking about using a multimeter to measure, let's talk about testing - it refers to using an oscilloscope that can visualize the waveform diagram to perform the test. Purely for the repair of the inverter, the use of oscilloscopes is generally mostly for the six-way inverter pulse signal of the inverter (the driving signal of the braking power tube/module is a switching quantity, and there is no need to choose an oscilloscope for detection). When using oscilloscope detection, it is necessary to focus on whether the waveform of the signal is normal and can meet the operation requirements; Information such as the amplitude of the driving signal and whether the frequency scale is satisfactory for propulsion. This repair method is indispensable for the maintenance of the inverter power tube/module after incineration!

8. Short

The method is talking about shorting. In the process of inverter repair, especially when the IGBT/IPM is removed due to damage, and the pulse drive line is repaired by powering on alone, if the driving optocoupler model is A316J and other chips containing the function of detecting IGBT/IPM faults, the optocoupler is often unable to register normally due to module damage or removal. At this time, it is required to use the wire to short-circuit the components (most of which are high backpressure diode anodes) for IGBT/IPM fault detection and the negative end of the DC bus of the inverter (some are marked N or GND), so as to deceive the main controller of the inverter, so that it thinks that the power module is intact and then reaches the intention that the driving pulse signal can be sent normally. Figure 5 shows the introduction of a brand of 55KW inverter, the pulse signal drive circuit for IGBT module detection.

9. Break

Off – off also. We all know that the internal circuit of the inverter contains a lot of maintenance functions for itself or the load, and when these maintenance functions present problems, we can use the method of circuit break/disconnection to determine and repair.

For example, all inverters contain an overcurrent monitoring and maintenance function at the output end. However, some products design this function very unscientifically - when there is a problem, it is impossible to clearly point out which phase presents the problem, which is a headache for the repairer. For the maintenance of this situation, we can take the practice of disconnecting the current transformer/current detection subunit used in each phase detection from the subsequent comparison circuit one by one, and the fault point can be seen at a glance when the input signal defect disappears at the disconnection (some models need to be manually reset to clear the fault appearance). Of course, this method is also suitable for the maintenance of temperature and other maintenance lines.

10. Put

Discharge – Discharge. The inverter contains electrolytic capacitors of various specifications and capacities, and the probability of inverter defects caused by the reduction of capacitance is very high. For the detection of these capacitors, the general repair personnel mostly choose to observe their shape and use the capacitance meter to measure the method for maintenance, but both methods have certain limitations. To this end, they use incandescent bulbs/small electric beads to carry out a discharge comparison test after charging the measured object, and the method can intuitively compare whether the capacity of the measured object meets the requirements, and the usefulness rate of the method is more than 80%. The electrolytic capacitor with the nominal 50V 220uF actual capacity on the side of Figure 6 is identified by the discharge detection method.

Inverter maintenance method - hope sunland

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