Inverters are widely used in various fields. Inverters are structurally complex, covering a broad range of knowledge, and experiencing a variety of故障, making repairs challenging. Repair technicians aiming to quickly enhance their repair skills need not only a solid theoretical foundation but also practical methods.
Utilizing variable-frequency technology to control the speed of AC motors not only significantly outperforms traditional DC speed control in terms of performance indicators, but also excels in many aspects over DC motor speed control. As a result, variable-frequency drives are widely used in various fields. However, like all things in nature, variable-frequency drives face aging and a limited lifespan. During long-term operation, components within the drives inevitably encounter various types of failures due to numerous reasons.
Repairing inverters quickly is not an easy task, as it involves a broad range of knowledge and requires a high level of professionalism. To rapidly improve repair skills, technicians not only need a solid theoretical foundation but also ample practical experience. This author, combining several specific repair cases, introduces several practical methods for inverter maintenance.
1. Incremental Contraction Method
The so-called step-by-step reduction method involves analyzing the fault phenomenon and making judgments on measurement parameters to gradually narrow down the scope of the fault, eventually pinpointing the specific circuit or component where the fault occurs. Essentially, it is a process of affirming, negating, affirming again, and negating again, leading to a definitive (determined) judgment.
For instance, when a variable frequency inverter was powered on, no display was found on the operation panel. First, it was determined that there was no direct current (DC) power supply (this could be measured with a multimeter for the DC power voltage). Further inspection revealed that the high-voltage indicator light was on (which was further confirmed by measuring the PN voltage), ruling out a fault in the main circuit high-voltage circuit and confirming that there was an issue with the power supply to the operation panel from the switch power supply. The AC voltage of this power supply was measured as normal, with no DC output and no short-circuiting, leading to the conclusion that the rectifier tube in the power supply circuit was damaged. This example employed a typical method of gradual elimination. The entire process involved several rounds of analysis, parameter measurement, judgment, confirmation, and elimination, ultimately determining that the rectifier tube was the culprit.
Follow the Trail Method
The so-called "Follow the Thread" method is a technique that, based on the working principle of the variable frequency inverter, follows the fault scene and signal path, gradually delving deeper, directly to the point of fault occurrence, and identifying the location where the fault originates.
For instance, a variable frequency inverter exhibits a three-phase unbalanced output voltage. This fault is clearly caused by one of two possibilities. One possibility is that at least one of the six units within the inverter bridge is damaged (open circuit). Another possibility is that at least one of the six drive signal groups is damaged. Assuming it has been confirmed that one inverter unit lacks a drive signal, further determining the location of the fault within the drive circuit can be achieved by tracing back. Specifically in this case, the investigation can be conducted from top to bottom, starting from the source of the drive signal, which is the output end of the CPU.
When the CPU output has a signal, check if there's a signal at the optocoupler input end. If there's no signal, there is a disconnected line from the CPU to the optocoupler input end. If there is a signal, inspect the optocoupler output end to see if there's a signal. If there's no signal, it indicates the optocoupler is damaged. If there is a signal, then check the input and output ends of the amplification circuit. If there's a signal at the input end but none at the output end, it suggests the fault is in the amplification circuit, or the amplification tube or related components are damaged. Then, it's straightforward to pinpoint the issue further.
