Do I use negative or positive grounding for 3 Phase inverters?

I am working on an install with SunPower solar panels and I want to use a Solectria PVI60 which is a 60 kW 3 phase inverter.  Can it be installed with positive grounding or is it only a negative grounded inverter?   If so, when installing the inverter how do  you switch the polarity of the grounding?