A PM-Free Brushless Synchronous Machine With a Novel Compensated Wound-Field Excited by Modulated Rotating Magnetic Flux

The brushless wound-field synchronous machine (BWFSM), a low-maintenance and cost-effective option, targets various applications, especially electric vehicles (EVs), by eliminating permanent magnets. This paper proposes a novel BWFSM with a multi-phase winding capable of generating two independent rotating magnetomotive forces (MMFs), each with a different number of poles. The fundamental MMF is utilized for electromagnetic (EM) torque production, while the secondary (“modulated”) MMF transfers power to the rotor for exciting the field winding. The addition term to the excitation current with a different phase sequence creates the modulated MMF. There is a field winding on the rotor for interacting with the fundamental MMF and an auxiliary winding for receiving power from the modulated MMF. The number of poles for the auxiliary winding is identical to that of the modulated MMF and is connected to the field winding with a rectifier. By tuning the frequency of the modulated current, the field current can be controlled to achieve the desired EM torque, rather than resorting to injecting higher current into the windings. The performance of this topology is evaluated using finite element analysis (FEA). A prototype is constructed, and experimental results validate the feasibility of the proposed concept.