Variable Frequency Drive Main Circuit Faults: Maintenance and Solutions

Understanding the main circuit of a variable frequency drive (VFD) is crucial for identifying and addressing common issues. The main circuit comprises components such as three-phase or single-phase rectifier bridges, smoothing capacitors, filtering capacitors, IPM inverter bridges, limiting resistors, and contactors. Many common faults stem from electrolytic capacitors, whose lifespan is determined by the applied direct current voltage and internal temperature. With every 10°C temperature increase, the lifespan of the capacitor is halved. Therefore, careful consideration of ambient temperature during installation and measures to reduce ripple currents, such as employing improved power factor correction or DC reactors, can significantly extend the lifespan of electrolytic capacitors and the VFD itself.

When protecting capacitors, degradation can typically be determined by measuring the easily quantifiable static capacitance and insulation resistance. Capacitors with a static capacitance below 80% of the rated value and an insulation resistance below 5 MΩ should be considered for replacement.

Issue: VFD trips overcurrent during acceleration, deceleration, or normal operation.

Firstly, it’s essential to differentiate whether the fault is due to the load or the VFD itself. If it’s a VFD issue, checking historical records for the current during tripping can indicate whether it exceeded the VFD’s rated current or the setting of the electronic thermal relay. If the three-phase voltages and currents are balanced, considerations should be made for overloading or sudden changes, such as motor stalling. In cases of high load inertia, extending the acceleration time can protect the VFD without causing damage. Tripping within the VFD’s rated current or the range of the electronic thermal relay indicates issues with the IPM module or related components. Measuring the forward and reverse resistance between the main circuit output terminals U, V, W and the DC side terminals P, N can determine the integrity of the IPM module. If the module is intact, the fault lies within the drive circuit. Tripping due to overcurrent during deceleration is often associated with faults in the upper half-bridge module or its drive circuit, while overcurrent during acceleration is linked to issues in the lower half-bridge module or its drive circuit. These faults are often caused by external dust ingress or humid conditions within the VFD.

By understanding these common main circuit faults and their maintenance solutions, you can ensure the reliable and efficient operation of your variable frequency drive.

Web:www.cnshuyi.com;
Tel/Fax: 0086-577-62840011
WhatsApp: 008613355775769