Electric power from typically unstable multiple dc sources is converted to ac electric power of suitable quality for injection into an electric power grid. Conversion is accomplished by current regulation of the output from the dc sources to the input of each one of multiple inverters in a system, with each inverter outputting multiple phase currents that are out of phase with the multiple phase currents outputted from all other inverters in the system. The multiple phase currents from all of the inverters in a system are connected to the secondary windings of a phase transformation network that produces a three phase current output having a step-shaped waveform for injection into the electric power grid.