I don't think there's an easy way for this.
If you look at the "Wound" configuration of the Asychronous Machine block, it exposes 6 physical connection ports -- 3 for the stator and 3 for the rotor.
You'd have to customize this block (using power_customize, for instance) and change the mathematical model such that the 6 voltages and currents correspond to the inside-delta connection points instead of the 3 stator and 3 rotor wye connections.
Alternatively, you could model the whole custom machine model using Simulink blocks. Either approach will require a modified mathematical model based on the existing Asynchronous Machine block.
- Sebastian
