Reactive power compensation using three current transformers instead of 1

Hi,
We have reactive power compensation controller (for condenser batteries) connected to 300/5A single phase current transformer, which is connected to L1. The controller always displays cosF equal to 0.98-1.00, therefore the compensation does not work, because there is almost nothing to compensate. However, according to electricity supplier, we are generating reactive power and in avg. cosF is equal to ~0.74. Questions:
1. Could it be, that the reactive power is generated in L2 and L3 only and therefore the controller cannot detect the reactive power, as it is measuring the current only in L1?
2. Is it possible to install current transformers on phases L2 and L3, connect them in parallel with the L1 phase current transformer and then connect all three of the transformers to the controller? If so, what should be current values of secondary winding of current transformers?
3. Is there any other solution?
Please find the wiring schematics of reactive power compensation controller in the attachments.

Your CT is measuring the current in one phase, and your input voltage is measuring the voltage between the two phases not measured by your CT. I may be wrong, but I think this means that, in the properly-compensated condition, the measured current is 90 degrees out-of-phase with the measured voltage. Does your controller have a means of telling your controller that the desired condition is 90 degrees rather than 0 degrees?

Your controller has a single current input and a single voltage input. This suggests to me that your controller is intended for single-phase service. I expect you need a controller intended for three-phase service.

You should not parallel the outputs of three CT's, as that will give you the net sum of the three currents, which will be zero with a well-balanced three-phase load. You need a controller intended to handle three-phase circuits.