Inverter maintenance is not an easy thing, because it involves a wide range of knowledge and professional. If the maintenance personnel want to improve the maintenance level quickly, not only must have the certain theory foundation, but also must have the massive practice experience. Using frequency conversion technology to regulate the speed of AC motor is not only much better than traditional DC speed regulation, but also better than DC motor speed regulation in many aspects. Therefore, frequency converters (VFD) are widely used in various fields. However, VFD, like everything in nature, has problems with aging and longevity. In the long run, components in the VFD will inevitably fail in one way or another for various reasons. It has complex structure, wide knowledge, many fault types and difficult maintenance. In order to improve the maintenance level quickly, the maintenance personnel should not only have certain theoretical basis, but also master certain practical methods.

Step by step

The so-called step-down method, is through the analysis of fault phenomena and measurement parameters of the judgment, gradually narrow the scope of the fault, the final implementation of the fault caused by specific circuits or components. In essence, it is a judgment process of affirmation, negation, affirmation again, negation again, and finally affirmation (judgment) .

For example, after the power is turned on, the operation panel is not shown. First, it must be determined that there is no DC power supply (its DC power supply voltage can be measured with a multimeter) . After further inspection, found that the high-voltage indicator light on (further confirmed by measuring the PN voltage) , the main circuit high-voltage circuit fault was rejected. There must be a problem with the switching power supply that supplies power to the Operation Panel. If the measured AC voltage of the power supply is normal and there is no DC output or short circuit, the damage of the rectifier in the power supply circuit can be determined. This example takes a typical step-by-step approach. The whole process is through the analysis and parameter measurement to judge, determine and deny several rounds, and finally determine the rectifier tube damage.

Follow the trail to the melon

According to the principle of VFD, the so-called“Follow the vine to find the melon” method is along the fault site and signal path deeper and deeper, to the fault point, and finally find the fault location method.

For example, VFD output voltage three-phase imbalance. This failure is clearly caused by two possibilities. One possibility is that at least one of the six units of the inverter bridge is damaged (open circuit) , and another possibility is that at least one of the six groups of drive signals is damaged. Assuming that an inverter unit does not have a drive signal, you can further determine the fault location of the drive circuit, along the vine can be found. For this particular example, you can check from top to bottom, that is, from the source of the drive signal, which is the output of the CPU.

When the CPU outputs a signal, check if there is a signal at the OPTOCOUPLER input. If there is no signal, the CPU and optocoupler inputs are disconnected. If there is a signal, check the output of the optocoupler to see if there is a signal. If there is no signal, the optocoupler is damaged. If there is a signal, double-check the input and output of the Electronic Amplifier. If the input signal, no signal output, the fault is caused by the amplifier circuit or amplifier or related components damaged. Further implementation will be easier.

Source: internet (for study only, intrusion and deletion)