Although not a motor control question directly; what effect does multiple generators and multiple Igbt drives have on a grid feed when added with standard inductive loads?

Question needs more details....size of generators, size of Igt drives, capacity of inductor loads and of course the size of the grid ! As such, Igt drives may produce (3n + 1) harmonics, generators may feed real or reactive power (depending on its excitation) , but total effect cannot be said with so little information.

The effect depends on the impedance of the grid feed and the approach of paralleling the generators to the grid. The grid feed rating should be significantly larger than the rating of all of the drive loads. The effect of harmonic currents is to distort grid feed voltage. If generators are feeding the grid and it is isolated from another source of supply it is possible for the source/grid/drive interaction to lead to instability, manifested by high circulating currents between generators and ac drives and eventual overcurrent of the generators. This occurs because the drives represent a negative resistance to the grid--i.e. voltage drops due to loading and current draw increases further. Resistive/Inductive loading of the grid can use up the allowable margin of transient response on the grid. Adding generators to the grid could actually help the stability if they are tuned to supply reactive current to the grid. This can be done by voltage drooping and adjustment of the no load setpoints.

It is helpful to simulate these types of systems in order to anticipate potential problems, but this can be a daunting task for some.