With the rapid development of modern technology, frequency converters have been widely used in various fields. The structure of VFD is complicated, it involves a wide range of knowledge, there are many types of faults, and it is difficult to maintain. If the maintenance personnel want to quickly improve the maintenance level, they must not only have a certain theoretical basis, but also master certain practical methods.

Using frequency conversion technology to adjust the speed of AC motors is not only far superior to traditional DC speed regulation in terms of performance indicators, but also superior to DC motor speed regulation in many aspects. Therefore, VFD has been widely used in various fields. However, in VFDs, as with everything in nature, there are issues of aging and longevity. During the long-term operation, the components in the VFD will inevitably fail due to various reasons.

Quick repair of VFD is not an easy task, it involves a wide range of knowledge and strong professionalism. If the maintenance personnel want to quickly improve the maintenance level, they must not only have a certain theoretical foundation, but also have a lot of practical experience. Combined with several specific maintenance cases, the author introduces several practical methods of VFD.

maintenance of vfd

1 stepwise reduction method

The so-called gradual reduction method is to gradually reduce the scope of the fault through the analysis of the fault phenomenon and the judgment of the measured parameters, and finally implement it on the specific circuit or component where the fault occurs. In essence, it is a judgment process of affirmation, negation, affirmation again, negation again, and finally affirmation (judgment).

For example, after a VFD is powered on, it is found that there is no display on the operation panel. First of all, it must be judged that there is no DC power supply (the DC power supply voltage can be measured with a multimeter). After further inspection, it was found that the high-voltage indicator light was on (the PN voltage was further measured and confirmed), negating the fault of the high-voltage circuit of the main circuit, and confirming that there was a problem with the power supply for the operation panel in the switching power supply. If the AC voltage of the power supply is normal, there is no DC output and short circuit, it can be concluded that the rectifier of the power supply circuit is damaged. This example uses the typical taper approach. Its whole process is to judge, affirm, and negate several rounds through analysis and parameter measurement, and finally determine that the rectifier is damaged.

2. Follow this path to the bottom

According to the working principle of VFD, the so-called following method is to follow the fault site, follow the signal path, go deep step by step, directly reach the fault location, and finally find the fault location.

For example, a VFD output voltage is unbalanced. This failure is apparently caused by two possibilities. One possibility is that at least one of the six units of the inverter bridge is damaged (open circuit), and the other possibility is that at least one of the six sets of drive signals is damaged. Assuming that an inverter unit has no drive signal, we can further determine the location of the fault in the drive circuit by tracing the source. Specifically, in this example, we 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 whether there is a signal at the input end of the optocoupler. If there is no signal, it means that the input from the CPU to the optocoupler is disconnected. If there is a signal, check the output of the optocoupler to see if there is a signal at the output of the optocoupler. If there is no signal, the optocoupler is damaged. If there is a signal, check the input and output of the amplifier circuit. If there is a signal at the input but no signal at the output, it means that the fault is caused by the amplifier circuit, or the amplifier tube or related components are damaged. Then further implementation will be easier.

With the rapid development of modern technology, frequency converters have been widely used in various fields. The structure of VFD is complicated, it involves a wide range of knowledge, there are many types of faults, and it is difficult to maintain. If the maintenance personnel want to quickly improve the maintenance level, they must not only have a certain theoretical basis, but also master certain practical methods.

Using frequency conversion technology to adjust the speed of AC motors is not only far superior to traditional DC speed regulation in terms of performance indicators, but also superior to DC motor speed regulation in many aspects. Therefore, VFD has been widely used in various fields. However, in VFDs, as with everything in nature, there are issues of aging and longevity. During the long-term operation, the components in the VFD will inevitably fail due to various reasons.

Quick repair of VFD is not an easy task, it involves a wide range of knowledge and strong professionalism. If the maintenance personnel want to quickly improve the maintenance level, they must not only have a certain theoretical foundation, but also have a lot of practical experience. Combined with several specific maintenance cases, the author introduces several practical methods of VFD.

maintenance of vfd

1 stepwise reduction method

The so-called gradual reduction method is to gradually reduce the scope of the fault through the analysis of the fault phenomenon and the judgment of the measured parameters, and finally implement it on the specific circuit or component where the fault occurs. In essence, it is a judgment process of affirmation, negation, affirmation again, negation again, and finally affirmation (judgment).

For example, after a VFD is powered on, it is found that there is no display on the operation panel. First of all, it must be judged that there is no DC power supply (the DC power supply voltage can be measured with a multimeter). After further inspection, it was found that the high-voltage indicator light was on (the PN voltage was further measured and confirmed), negating the fault of the high-voltage circuit of the main circuit, and confirming that there was a problem with the power supply for the operation panel in the switching power supply. If the AC voltage of the power supply is normal, there is no DC output and short circuit, it can be concluded that the rectifier of the power supply circuit is damaged. This example uses the typical taper approach. Its whole process is to judge, affirm, and negate several rounds through analysis and parameter measurement, and finally determine that the rectifier is damaged.

2. Follow this path to the bottom

According to the working principle of VFD, the so-called following method is to follow the fault site, follow the signal path, go deep step by step, directly reach the fault location, and finally find the fault location.

For example, a VFD output voltage is unbalanced. This failure is apparently caused by two possibilities. One possibility is that at least one of the six units of the inverter bridge is damaged (open circuit), and the other possibility is that at least one of the six sets of drive signals is damaged. Assuming that an inverter unit has no drive signal, we can further determine the location of the fault in the drive circuit by tracing the source. Specifically, in this example, we 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 whether there is a signal at the input end of the optocoupler. If there is no signal, it means that the input from the CPU to the optocoupler is disconnected. If there is a signal, check the output of the optocoupler to see if there is a signal at the output of the optocoupler. If there is no signal, the optocoupler is damaged. If there is a signal, check the input and output of the amplifier circuit. If there is a signal at the input but no signal at the output, it means that the fault is caused by the amplifier circuit, or the amplifier tube or related components are damaged. Then further implementation will be easier.

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