PF Correction of DC Motor (thyristor control)

We have a 90KW DC motor drive a plastic extruder. The power supply is limited to 150A (415V 3 Phase). This is a new machine and only once connected, did we realise how inefficient DC variable drives are!

On low viscosity resins at full speed (430 rpm) the PF=0.89 and current ~ 130 Amps, at 200 rpm the current is 100A at PF=0.5 and at 50 rpm currrent is 110A at PF=0.35.

In all cases there seem to be a linear relationship between AC and DC amps ie. 100amp DC = 100amps AC (per phase).

With high viscosity material at 50 rpm the current rises to 190A and the PF =0.2 - Due to supply current limitations we have only maintained this for 1-2 minutes. It is impossible to increase speed due to current limitations.

As a trial we connected 6 * 30 KVA capacitors in Delta (3 banks of 2 caps in series). This gave us an ~ 20amp reduction in AC current with low viscosity material (down to 110-115amps) and a 40Aps reduction in AC current with the high viscosity material (down from 190A to 150A).Current drawn by the caps varied between 72A-76A. This correction was insufficent we need to reduce the current from 190A to 90A (guess) to run high viscosity resin at a commercial rate.

Questions:
1. What amount of PF correction would be needed to improve the P.F. from 0.2 to ~ 0.9 (to enable the processing of high viscosity resin). Is this amount of correction possible?
2. We know harmonics are being generated and from the literate on this site - inductive choke are stated as essential. Any suggestions of what size chokes would be necessary?
3. Due to cost, our preferred out come would be to connect a fixed bank of capacitors and chokes at the motor. Is this practical or is it necessary to have controlled (microproccessor)PF unit to cope with the varing speeds under load?
4. Would a 90KW AC variable speed motor be a more efficient option in this application considering the low speed torque reqirements?

Any comments would be greatly appreciated.

Thanks