Analytical Field Calculation and Analysis of Surface Inset Permanent Magnet Machines With High Saliency Ratio

In this paper, an analytical field calculation model is built for surface inset permanent magnet (SIPM) machines with high saliency ratio. The high saliency ratio of SIPM machine is obtained using unequal d-q axis air-gap length based on the SIPM rotor structure. High saliency ratio can produce large reluctance torque and wide speed range. To get a fast and exact knowledge of flux distribution and operation parameters of the SIPM machine with high saliency ratio, the field solving domain is divided into five subdomains, i.e., stator slots, stator slot openings, air-gap, rotor air slots, and rotor magnets. The vector potential in each subdomain is governed by Maxwell's equation and can be solved using the variable separation method and boundary conditions between adjacent subdomains. In addition, the cogging torque, back electromotive force (EMF), inductance, output torque, and unbalanced magnetic force (UMF) are calculated based on the field model. All the field calculation results are compared with those of finite element analysis (FEA), and it is shown that analytical field calculation model is fast and accurate. Furthermore, the effects of q-axis air-gap length and pole arc ratio on machine parameters, such as cogging torque, back EMF, saliency ratio, output torque, and UMF, are also investigated using the analytical field calculation model.