The power circuit handles incoming power from the generator and outgoing power to the grid. Managing high power, typical components are air circuit breakers and large contactors. Another key function is over-voltage protection (OVR, SPD).
Modern drivetrains normally include a converter and one the main solutions is called Full-power (with 3 variants: Low, Medium and High speed generator). In addition to the main circuit, the converter itself has several functions that need low voltage components.