Comprehensive Optimization of Brushless Excitation of Synchronous Machine

Brushless excitation of wound rotor machines has an attractive property: the slip-rings can be omitted. Different methods are developed; this paper investigates the rotating transformer method, where the excitation machine is a wound rotor induction machine supplied by an excitation converter. The excitation circuit of the synchronous machine is connected to the three-phase rotor of the excitation machine through a diode bridge rectifier. One optimization is the proper selection of the power circuit for the excitation converter. The PWM AC chopper is proposed, providing almost sinusoidal supply for the excitation machine. In this case the operation of the system is essentially determined by the commutation of the rotating diode bridge. It has different working regions which should be considered. A model is developed to investigate the characteristics of the steady-state operation. Optimization related to the utilization of the excitation machine is introduced and generalized, providing a complex design method for the components and the control of the system. The overall efficiency of the excitation system is also investigated and found to be slip-dependent