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This paper proposes a novel brushless excitation topology for a three-phase synchronous machine based on a customary current-controlled voltage source inverter (VSI). The inverter employs a simple hysteresis-controller-based current control scheme that enables it to inject a three-phase armature current to the stator winding which contains a dc offset. This dc offset generates an additional air gap magneto-motive force (MMF). On the rotor side, an additional harmonic winding is mounted to harness the harmonic power from the air gap flux. Since a third harmonic flux is generated in this type of topology, the machine structure is also modified to accommodate the third harmonic rotor winding to have a voltage induced as the rotor rotates at synchronous speed. Specifically, four-pole armature and field winding patterns are used, whereas the harmonic winding is configured for a twelve-pole pattern. A diode rectifier is also mounted on the rotor between the harmonic and field windings. Therefore, the generated voltage on the harmonic winding feeds the current to the field winding for excitation. A 2D-finite element analysis (FEA) in JMAG-Designer was carried out for performance evaluation and verification of the topology. The simulation results are consistent with the proposed theory. The topology could reduce the cost and stator winding volume compared to a conventional brushless machine, with good potential for various applications. [ABSTRACT FROM AUTHOR]

This paper discusses the design and analysis of a high-harmonic injection-based field excitation scheme for the brushless operation of wound field synchronous machines (WFSMs) in order to achieve a higher efficiency. The proposed scheme involves two inverters. One of these inverters provides the three-phase fundamental-harmonic current to the armature winding, whereas the second inverter injects the single-phase high-harmonic i.e., 6th harmonic current in this case, to the neutral-point of the Y-connected armature winding. The injection of the high-harmonic current in the armature winding develops the high-harmonic magnetomotive force (MMF) in the air gap of the machine beside the fundamental. The high-harmonic MMF induces the harmonic current in the excitation winding of the rotor, whereas the fundamental MMF develops the main armature field. The harmonic current is rectified to inject the direct current (DC) into the main rotor field winding. The main armature and rotor fields, when interacting with each other, produce torque. Finite element analysis (FEA) is carried out in order to develop a 4-pole 24-slot machine and investigate it using a 6th harmonic current injection for the rotor field excitation to both attain a brushless operation and analyze its electromagnetic performance. Later on, the performance of the proposed topology is compared with the typical brushless WFSM topology employing the 3rd harmonic current injection-based field excitation scheme. [ABSTRACT FROM AUTHOR]