Hi ShuklaS
From my first understanding, maybe you can use a part like ACPL-796J. This is a voltage/current sensor hiring optically isolated S-D Modulator. What you need is a resistor bridge from L+ to L- of each phase and respective shunt across input of 796J should not be bigger than 1kOhm, in order not to disturb input impedance of the part.
Actually what is also nice, this component has input for sampling clock. So synchronization between phases will be achieved by a master clock from your DSP/FPGA. So, with help of synch, you can see realize unbalancing tightly specified.
Datasheet:
Hope it helps.