Iron loss models: A review of simplified models of magnetization losses in electrical machines

This paper gives a broad overview of methods to model core losses from the magnetization of soft magnetic iron cores in electrical machines. The review study starts with some commonly used models of loss separation for hysteresis losses and eddy current losses. The study links the models to physical models of magnetization, considering domain behaviour such as nucleation, formation and rotation, and also pinning and damping of domain wall motions. Both the non-linear behaviour of hysteresis and excess eddy currents is better understood by these underlying physical domain mechanisms. Classical eddy currents usually only consider the resistivity and the thickness of the lamination steel plates, but core losses are also related to several material properties, such as crystal grain size, type of alloy, texture and alignment of the crystal anisotropy. These dependencies could be considered by some adoptions of the loss models. The common approaches to core loss modelling neglects non-sinusoidal fields and three-dimensional fields and assumes a sine wave which only is directed along one direction. This paper also discusses non-sinusoidal losses, both for hysteresis and eddy current losses. It also covers three dimensional rotational losses, and how they could be handled by simplified models based on ellipse trajectories. The relation between iron losses and external physical factors is presented, such as dependence on the direction of an applied field, dependence on the temperature, dependence on cutting degradation and dependence on an applied stress.