Simplified analytical model for rapid evaluation of interior PM traction machines considering magnetic nonlinearity

The article presents an analytically rapid evaluation technique for interior permanent magnet (IPM) traction machines considering magnetic nonlinearity. First, a simplified model employing equivalent magnetic circuit together with winding function to determine no-load airgap flux density and dq-axis armature-reaction airgap flux densities for parameter determination is proposed. Then, a process loop is utilized for nonlinear magnetic analysis under full range on-load dq-axis currents. Using the obtained parameter information, losses/efficiency determination for tested machine could be achieved. It is shown that in the field-weakening (FW) operation region, the high-order synchronous flux density harmonics highly contributing to machine iron loss may also significantly contribute to magnetic saturation and therefore should be considered together with fundamental component for nonlinear magnetic analysis. In comparison to computationally expensive finite element analysis (FEA), sufficiently accurate parameters and efficiency for tested machine could be obtained within minutes. Thus, the proposed technique is very essential to rapidly evaluate a given design specification at the preliminary design stage where repeated adjustment on design specification is necessary for a multi-physics optimization achievement and with that, repeated re-construction and re-evaluation of FEA model may be undesirable. The proposed method is validated by FEA for a high-speed high-power (15krpm/120kW) IPM traction machine.