Design Process of Spoke-Array Brushless Dual-Electrical-Port Dual-Mechanical-Port Machine

Brushless dual-electrical-port dual-mechanical-port (BLDD) machine worked on flux modulation principle has been proven to have high compactness, torque transmission capability and decoupled rotors, which becomes a good candidate for continuously variable transmission (CVT) device. However, there is little accurate analytical model for BLDD machine, due to double air-gap structure and complex magnetic field coupling. In this paper, an applicable analytical model named as air-gap mapping model is proposed to directly describe the characteristic of air-gap magnetic field. It should be pointed out that the slot effect of the inner air-gap is mapping into the outer air-gap in the proposed model, which simplify the double air-gap structure into a single air-gap model. A spoke-array BLDD (SABLDD) machine is chosen as an example to verify the validity of the analytical model. The analytical expression of the outer air-gap flux density, no-load back-EMF and torque are derived by combining air-gap mapping model with magnetomotive force (MMF)-permeance model. In order to guide the design and get reasonable initial values, the sizing equation is calculated and the effects of several main parameters in the sizing equation, such as slot/pole combination, electrical loading of regular and modulation windings, outer and inner air-gap radius, etc. on the electromagnetic performances are analyzed based on finite element analysis (FEA). Finally, the design flow of the SABLDD machine is summarized.