Investigation of Brushless Doubly-Fed Dual-Stator Machines for Traction Applications

Two brushless doubly-fed dual-stator machines (BDFDSMs) with different inner-stator field windings, namely ac and dc field windings, are proposed and investigated. It is shown that the proposed machine with ac field windings exhibits the advantages of higher torque density and wider flux-regulation range compared with its dc field winding counterpart. Unlike conventional doubly-fed hybrid-excited machines, the proposed machine consists of ac field windings and hence resulting in more flexible field current control. Its armature and field windings are separately placed in two stators, which can alleviate the space competition between the field and armature slots, as well as significantly enhance space utilization. Consequently, both flux-regulation capability and torque density can be effectively improved. The topology, operating principle, and mathematical model of the proposed machines are introduced. Then, a sectored flux-weakening control method is proposed and elaborated. Based on the finite element method (FEM), the main electromagnetic performances of the proposed machines are comprehensively evaluated. The FEM results manifest that the proposed machine with ac field windings shows greatly improved flux-regulation range, higher torque, and output power under the proposed sectored flux-weakening method over the whole speed range. Finally, the prototype machine of the proposed machine is fabricated, and experimental verifications are performed to validate the feasibility of the proposed machines.