A high-order-harmonic compound-rotor based brushless doubly-fed machine for variable speed constant frequency wind power generation

Abstract

This article addresses the issue of relatively inferior torque performance in brushless doubly fed machines (BLDFMs) used for variable speed constant frequency (VSCF) operation in wind power generation systems. To mitigate this limitation, a novel brushless dual-electrical-port dual-mechanical-port DFM (BLDD-DFM) structure is proposed, which employs high-order harmonic modulation to reduce energy consumption in the control winding during VSCF applications. The compound outer rotor is designed specifically to enhance the third-harmonic component within the inner airgap’s magnetomotive force (MMF). By implementing high-order harmonic modulation, the slip ratio is reduced, resulting in a threefold decrease in energy consumption compared to conventional designs. Additionally, under rated conditions, the proposed design exhibits maximum torque improvements of 23.03% for the outer rotor torque and 144.08% for the inner rotor torque compared to the conventional design. Finite element analysis and comparative studies with existing counterparts validate the effectiveness of the proposed machine. Furthermore, a prototype is presented to demonstrate the feasibility and advantages of the proposed design.