Specification:

Variable Frequency Inverter, 5.5/7.5kw, 440V, 3-Phase

If your small rating variable frequency drive (VFD) getting damage then there may be a voltage spikes issue because according to the thumb rule if the transformer KVA rating is 10 times of KVA rating of VFD, say a 100 kVA transformer for 10 hp VFD, then it is subjected to voltage spikes that can damage it. Line reactors are the best way to compensate that but mostly users don't use the reactors for small rating VFDs.

If your VFD is large enough compared to your generator then there can be issues with the semi-conductors on the VFD firing correctly. This was an issue one of VFDs experts always checked when large VFDs needed to be run by a back-up generator.

You may always want to look at the power quality during start-up. Voltage spike will damage the semiconductors on the front end to the VFD. So if you were using the reactors then the problem may be different but if you don't then I suggest you use reactors.