Inverter maintenance technicians often encounter situations where certain inverter modules frequently burn out. Many times, after replacing the module with a new one, little attention is paid to the root cause. According to the Electrical Automation Technology Network, most of these failures are related to issues in the drive circuit rather than the module itself. During maintenance, it's crucial to pay extra attention to smaller components that are more prone to aging or damage, such as capacitors, resistors, optocouplers, voltage regulators, and insulating varnish. Below is a detailed explanation of each of these critical parts.
Optocoupler
The full name of an optocoupler is opto-isolator, also known as a photo-coupler. It provides excellent isolation between input and output signals, making it widely used in various circuits. It is one of the most versatile optoelectronic devices available. The drive circuit using an optocoupler typically includes a feedback loop that detects signals from the output three-phase (Eu, Ev, Ew) and the drive signal. When an abnormality is detected in the inverter output, the optocoupler sends a high-level signal to the main board, which immediately cuts off the drive signal and displays a "overcurrent" or "IGBT short circuit" fault. This protection mechanism is very fast, making inverters with this design less likely to burn out their modules. However, if the drive components become unstable or aged, it can still affect the performance of the system.
Zener Diode
A Zener diode is a type of crystal diode that operates in the breakdown region of a PN junction, providing a stable voltage characteristic. These diodes are commonly used in voltage regulation and other electronic circuits. They are often referred to as Zeners to distinguish them from regular diodes used for rectification or detection. Electricians may find it difficult to test Zener diodes directly, so it's often recommended to replace them when in doubt. During inverter repair, it's important to clean the circuit board thoroughly, remove dust, dry it, and then apply insulating paint. Additionally, ensure the radiator's aluminum foil is clean, replace any faulty cooling fans, check the filter capacitor capacity (replace if it has aged by more than 20%), and tighten all main circuit coupling screws.
Insulating Paint
Insulating varnish is a key insulating material made from high-molecular polymers. It cures into an insulating film or structure under specific conditions. It's a special type of lacquer used in electrical applications. When maintaining an inverter, make sure the radiator's aluminum foil is free from dust. If the cooling fan is damaged or making noise, it should be replaced. Also, check the filter capacitor’s capacitance and replace it if it has aged by more than 20% (typically not more than 8 years). All major circuit connection screws must be securely tightened. When disassembling integrated blocks, avoid using high-temperature soldering irons that could damage the components. Instead, place a small piece of paper or cloth over the block to help dissipate heat during the process, which significantly improves the outcome.
Resistors
Resistance is the property of a material that opposes the flow of electric current. Materials with low resistance are called conductors, while those with high resistance are called insulators. When measuring the resistance of a capacitor, the multimeter's pointer will swing depending on the capacitance value—the larger the capacitance, the greater the swing. Always discharge the capacitor before taking a second measurement by shorting its terminals.
By understanding and properly maintaining these smaller but vital components, inverter technicians can significantly improve system reliability and reduce unexpected failures. Regular inspections, proper cleaning, and timely replacements are essential steps in ensuring long-term performance and safety.
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