Efficiency maps of electrical machines

This paper investigates the calculation, modelling and interpretation of efficiency maps for electrical machines. The efficiency maps are calculated using a finite-element based mapping of losses, torque and flux-linkage as a function of the d- and q-axis currents and speed. For modelling efficiency maps, it is shown that a number of key loss types can be described in the form T^mωⁿ. The effect of each of these losses on the shape of the efficiency map is then explored. It is found that practical efficiency maps can be approximated using a series of such terms which leads to a better understanding of the losses in the machine. The above results are validated using the loss and efficiency maps of three example machines.