Permanent Magnetic Generator

In a siemens generator excitation system there are two exciter one named pilot exciter is (permanent magnet generator)type and other is seperatley excited type, PMG Has 07 wires,05 wires for output i-e UH1 &UH2=80V AC, WH1 & WH2=80V AC, And WH1 & WH3=175V AC These 175v ac going to a rectifier bridge to convert in DC supply from here these DC VOLT are going to stator of same PM Generator by remaining 02 wires(Input wires) and 80v ac supply of this PMG is going to AVR, output of this AVR is going to excit separately excited generator, output of this separately excited generator is going ROTOR of main generator, this permanent Magnet Generator fuction getting back supply in STATOR is new for me which I want to know Why this supply is going back in stator of PMG