Thank you for posting the image, this was helpful. It is not possible to directly interface physical signals in PLECS to physical SimScape signals. The information needs to be relayed via control signals. You will need to measure electrical quantities with meters in Simscape and pass those (control) signals into the inputs of the PLECS Circuit block. Further, you will need to use PLECS "Signal Inport" and "Signal Outport" blocks inside of the PLECS block, rather than "Electrical Port" blocks. Exiting the PLECS Circuit block, you will need to then measure the inverter three-phase outputs with Voltmeters and via the Signal Outport blocks, drive controlled sources (i.e., voltage) and connect these to the rest of the electrical system in Simscape.
By the way, you can model the complete system shown in your image inside of PLECS- have you considered doing this? It's more efficient than to combine PLECS and Simscape physical system blocks.