Hybrid Method of AC Copper Loss Calculation with Magnetic Equivalent Circuit and Analytical Method Considering Iron Core Saturation

Accurate calculation of AC copper loss is critical for estimating the winding hotspot and temperature distribution in the slot of electrical machines. However, existing analytical methods are not able to consider the influence of iron core saturation on slot leakage flux. Finite element analysis (FEA) and hybrid methods which combine FEA with analytical methods are accurate but time consuming. The application of the existing hybrid method which combines magnetic equivalent circuit (MEC) with analytical method is limited to large-airgap high-speed electrical machine due to the ignorance about the influence of rotor flux and iron core saturation on AC copper loss. To overcome these disadvantages, this paper proposes a hybrid method which incorporates non-linear MEC for slot leakage flux and analytical method for AC copper loss. In the case studies of an E-shaped iron core wound with a coil and an electrically excited synchronous machine (EESM), the AC copper losses predicted by the proposed hybrid method and 2D FEA match very well at different frequency and magnitude of the input current, with a relative error less than 3%. Meanwhile, the time consumptions of the proposed hybrid method are less than 2% and 15% that of the FEA for the E-shaped iron core and EESM cases, respectively. Thus, the proposed hybrid method is accurate and timesaving for AC copper loss calculation.