Effects of Current Distortion on DC Link Inductor and Capacitor Lifetime in Variable Frequency Drive Connected to Grid With Active Harmonic Filter

In this research article, new investigation and comprehensive analysis is done on the current distortion effects of dc link inductor and capacitor in variable frequency drive (VFD). Shunt active filter (SAF) is the most prominent solution for harmonic mitigation at the point of common coupling in the power distribution system. However, SAF connectivity reduces the grid impedance (Z(TH)) seen at the input of six pulse diode bridge rectifier in VFD. Commutation behavior of the diode rectifier is changed due to this grid impedance variation resulting in increased harmonic current distortion (THDi) at the input of the rectifier bridge. This effect increases the ripple current of dc capacitor, dc link inductor losses, and diode rectifier conduction losses. This study investigates the drive dc link inductor and capacitor lifetime reduction with and without SAF, under various grid operating conditions of 3% voltage unbalance and 8% predistortion. Moreover, the high frequency (2-9 kHz) impact on dc link inductor core and copper losses is detailed. A 250 kW VFD with SAF of 180 A capacity is used for test measurement under various operating conditions. Current distortion effects are analyzed, and test results are compared with MATLAB simulation. Grid impedance variation due to SAF and its effect on the reliability of the VFD front-end components were not covered in detail in any of the earlier research. Lifetime estimation of dc link inductor and capacitor due to grid impedance variation is one among the significant outcomes of this investigation.

Automated summary

This research article investigates the distortion effects of dc link inductor and capacitor in variable frequency drives (VFD), with a focus on the impact of shunt active filters (SAF) on grid impedance and harmonic distortion. The study also looks at the high frequency impact on dc link inductor losses. Test results from a 250 kW VFD with SAF are compared with MATLAB simulation. The investigation highlights the importance of considering grid impedance variation on the reliability and lifetime of VFD components.