A Novel DC-Coil-Free Hybrid-Excited Machine with Consequent-Pole PM Rotor
This paper proposes a new DC coil free hybrid excited machine concept, which has no external field windings. The technical novelty is the integration of field windings and armature windings. DC bias current is injected into the excitation and the field windings in the traditional hybrid excited machine are eliminated. Compared with traditional hybrid-excited machines with additional field windings, the proposed machine can realize a higher slot utilization ratio, hence achieve a higher torque
... e a higher torque density and a wider flux adjusting range. Another advantage of the proposed machine is that the voltage drop associated with flux regulation is small due to the small DC resistance, and the torque generating capability at the flux regulating region can be improved accordingly. The rotor is specifically designed with magnet-iron sequences and a consequent-pole, in which the permanent magnet and iron pole are alternatively employed. A bi-directional flux modulating effect can be achieved, which can contribute to the magnetic coupling in the air-gap. Analytical derivation is used to describe the operating principle, and the proposed machine was optimally designed using the Tabu search algorithm. A prototype was made, and its performances investigated through experimental tests. Energies 2018, 11, 700 2 of 16 excitation on the stator can result in robust rotor structure, the magnet inevitably takes up some stator space and the space for electric loading is reduced, which reduces the torque density accordingly. Meanwhile, the magnets are located in the stator thermal field, which increases the demagnetization risk of the magnets. Therefore, from the point of achieving good distribution of electric loading and magnetic loading, and reducing the demagnetization risk of magnets, employing magnets on the rotor and field coils on the stator is a better choice for HEMs. Since the field coils of HEMs are only used during flux regulation, and reduce the effective slot area for armature coils, the torque density of HEMs is reduced by the field coils, especially during low-speed operation. The same goes for the flux regulating capability, which is limited by the slot area used for the field windings. A novel DC-coil-free HEM (DCF-HEM) is proposed in this paper. Compared with traditional HEMs with additional DC coils, the proposed DCF-HEM can achieve higher torque density and wider field adjusting range. The field windings and armature windings in the proposed design are integrated, and DC bias current is injected into the integrated stator winding to achieve flux regulation. The rotor consists of magnet poles and iron segments, namely a magnet-iron consequent-pole rotor, which has a flux modulating effect and can provide PM excitation. The operating principle and field adjusting theory of the proposed DCF-HEM are here analytically investigated. The Tabu search algorithm is used to conduct design optimization of the proposed DCF-HEM. The electromagnetic performances are studied through both the finite element method (FEM) and experimental tests.