Hello Idaho Farmer
I came to the same conclusion about 15 years ago. The CSV was designed to replace VFD's and do exactly what you are trying to accomplish. I am a fourth generation well driller and pump installer. I have literally thousands of applications similar to yours. We replace VFD's every day.
Don't spend another dime on a VFD or filter, and lets have a talk! Your point is exactly the point I have been making for 15 years now. Pump manufacturers don't want to hear it, VFD manufacturers do not want to hear it, engineers do not want to hear it. They are making a killing replacing VFD's for millions of people just like you.
As an old pump man, I know pumps like yours (and the controls) can and should last 20, 30, even 40 years without ANY maintenance. And that is exactly why I have a hard time selling valves, they make everything last longer. Lasting longer is what gives you real savings, not a VFD.
Using a CSV will not only make your system last much longer but, will eliminate the problem of the RF interference with the guidance for the corner units. The CSV will also eliminate other problems from VFD controls such as bearing currents, harmonics, resonance vibration, voltage spikes, etc., etc..
Thank You
Cary Austin