Harmonic Analysis of Air-Gap Magnetic Field in Flux-Modulation Double-Stator Electrical-Excitation Synchronous Machine

This article presents a new field-modulation double-stator electrical-excitation synchronous machine (FM-DSEESM) and analyzes its harmonic components of double-layer air gap magnetic field. The key is that both the types and sources of various harmonic-components of air gap magnetic field are derived by taking into account the permeance components of both inner and outer stator teeth and modulation-ring rotor. The selection criteria of main working harmonic components of excitation field is clarified to achieve the armature-winding configuration. Then, the working harmonic components of air gap magnetic field, which have the same pole pairs, rotating direction, and rotating speed, respectively, can be figured out by comparing the mathematical derivation and finite-element analysis results from the excitation field and armature reaction magnetic field. By analyzing the contributions of the air gap flux density components to the electromagnetic torque, it is found that the electromagnetic torque of the proposed FM-DSEESM mainly consists of two parts, namely the reluctance torque components generated by the stationary working harmonic components and the armature reaction torque components provided by the rotating working harmonic components. A low-speed direct-drive FM-DSEESM prototype is fabricated to verify the validity of the proposed analysis approach.