The correct solution path starts with measuring and mitigating the harmonics generated by the drives
. (One useful tool for measuring harmonics and capacitance is the Fluke 43B Power Quality Analyzer.) Harmonic trap filters would generally be called for. These trap filters are installed locally on the line side of the drive. Their effect is very much like the traditional PF correction cap, in two senses: they reduce DPF as well as PF, and also they localize the circulation of the problem harmonics (generally the 5th). Harmonics mitigation and traditional DPF correction should be addressed as one systems issue. In other words, manage Total PF, not just DPF.