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This paper presents a novel doubly‐fed doubly‐salient machine (DF‐DSM) with DC‐saturation‐relieving effect for wind power generation application, which possesses the advantages of enhanced torque density, reduced torque ripple and improved power density. The key is that PMs are introduced into the stator slot openings to mitigate the saturation effect in stator core caused by DC field excitation, and relatively large excitation current can be fed into stator field windings, which contributes to improved power density of machine. In addition, with the armature winding artificially connected, the reluctance of all magnetic paths is kept the same, and the variation of self‐inductance is compensated, and the torque ripple is greatly suppressed. In this paper, the machine structure and DC‐saturation‐relieving working principle are introduced. The slot‐pole combinations are analysed, and dimension parameters are optimized. By using time‐stepping finite‐element analysis, the electromagnetic performance of optimal machine is evaluated which verifies the validity of the proposed design.
Vernier reluctance machine (VRM) with DC field coils in stator is a competitive rare-earth-free design for variable-speed industrial applications due to its robust structure and controllable excitation, while its torque density is relatively disadvantageous. To address this issue, this paper proposes a new armature winding design method for VRM with DC field coils across two stator teeth.The key is to break the traditional winding design principle based on the flux modulation effect of fundamental DC field harmonic, and instead, reconstruct a novel harmonic winding to enhance the utilization factor of the modulated high-order DC field harmonics arising from the unique magnetomotive force distribution of DC field coils across two stator teeth. By this means, the torque density can be improved by 75.6% compared to the existing counterpart. In this paper, the machine structure and operation principle are introduced, with emphasis on the high-order DC field harmonics distribution rule and its influence on the armature winding design. By finite element design and optimization, a comparative study is performed to evaluate the electromagnetic performance of VRMs using two different winding configurations with variable slot pole combinations. A prototype is fabricated and tested, and the results agree well with finite element analysis, which verifies the feasibility and advantages of the proposed winding design method.
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