The present invention relates to a multi-set switched DC brushless electric machine having its rotary part of electric machine being installed with an auxiliary excitation winding set, for being connected in series with a magnetic field winding set of electric machine of another electric machine through the auxiliary excitation winding set installed on the rotary part of electric machine, such that the excitation can be variable through altering the current of the magnetic field winding set of electric machine of the another electric machine thereby changing the operational characteristic of the electric machine.