Inverter supplied induction motor it is not my specialty [in our power station even BFPump of 10 MW starts D.O.L.!]
What I know about neutral shift it is what NEMA MG1 and IEC 60034-17 [up to 1000 V] recommend.
Since the voltage to ground reaches 1.86 times the rated, a motor up to 500 V rating will not be in danger. For higher than 500 -mainly for 4.16 kV -an isolation transformer is required. See-for instance-Toshiba Application Guide:
Thank you, I will take a look at it.Good point. Code only address nonlinear loads with Y-connected transformers. Delta xfmrs are not considered.
However, when sizing neutrals for continuous loading, or short-circuit current, you might be interested in the last paragraph of example D3(a) in Annex D.