Optimal operation of the rotating transformer brushless excitation of synchronous machine

The brushless excitation of synchronous machines is an attractive solution for wound rotor machines, since no slip rings are necessary. The paper investigates the rotating transformer method, where the excitation machine is a wound rotor induction machine supplied by an excitation converter. A diode bridge rectifier connected to the three-phase rotor of the excitation machine excites the synchronous machine. The possible power circuits for the excitation converter are presented and the PWM AC chopper is proposed, providing almost sinusoidal supply for the excitation machine. The operation of the system is essentially determined by the commutation of the rotating diode bridge. The different working regions of the diode bridge are considered. The characteristics of the steady-state operation considering the utilization of the excitation machine are introduced, providing a complex design method for the system. A simple and easy feasible method is given for the indirect sensing of the excitation current.