Variable frequency drive units are widely used due to their powerful functions. In practice, what are the symptoms of variable frequency drive failures? Below, we will look at their common faults and repair methods. If you're interested, keep reading!
VFD Fault Diagnosis:
(1) The equipment itself is of poor quality.
(2) Excessive overcurrent, imbalance, motor winding short circuits, internal phase winding short circuits, mechanical load jamming, phase-to-phase breakdown, output line short circuits, etc.
(3) The capacitor is connected to the load, or due to incorrect wiring, the capacitance to ground is too large, causing the power tube to produce surge currents.
(4) Overvoltage damage caused by excessive grid voltage or transient overvoltage spikes.
(5) Capacitor filters, due to long-term aging, may experience a decrease in capacitance or an increase in internal inductance, which reduces the busbar's overvoltage absorption capability, leading to IGBT damage. When the inverter switch devices close their pulses, the energy storage in the busbar circuit changes, resulting in overvoltage on the busbar during normal operation.
Fault Diagnosis and Repair Methods for Variable Frequency Drives
(1) IGBTs, like insulated gate field-effect transistors, should be protected from static damage. The fundamental measure to prevent damage during assembly is to connect all equipment to be repaired, IGBT modules, soldering irons, operators, and workbench mats together, so that they operate at the same electric field potential and all common points are grounded. Particularly, the soldering iron tips must not have high-voltage city power, and the power supply to the oscilloscope should be isolated by a transformer with good insulation. The control terminal G and emitter E of the IGBT module should remain connected before use, and the anti-static protection measures between G and E should not be removed arbitrarily before shipment.
(2) A thermal conductive grease is applied between the power module and the radiator, ensuring a coating thickness of 0.1-0.25mm and a contact area exceeding 80%. The clamping torque is applied according to the size of the fastening screws (M4: 13kgcm, M5: 17kgcm, M6: 22kgcm) to ensure optimal component cooling.
(3) When disassembling the machine, label the removed parts, wire ends, and components. Do not simplify or omit any original assembly technical measures. For instance, the resistance of each electrode connection, insulation parts, absorbent plates, or absorbent capacitors should remain constant; clean the welding driver printed circuit board to prevent arcing, ensure reliable insulation, and of course, avoid installing incorrect parts.
In summary, that's how a variable frequency inverter fault diagnosis is conducted, and here's an overview of its repair methods. For more information, stay tuned for our future article updates.
