A study on correcting the nonlinearity between stack length and back electromotive force in spoke type ferrite magnet motors

The accurate estimation of the performance change according to varies in stack length of motors is important in related industries. A permanent magnet (PM) motor usually represents a characteristic in which its back-emf constant is linearly proportional to stack length. It is an enormous advantage in designing and estimating the performance of PM motors. However, the linearity cannot be held in spoke type ferrite magnet synchronous motors (SFMSMs) due to the axial leakage flux that is irrelevant to the stack length. Thus, it is possible to accurately analyze the performance of SFMSM using a 3D-finite element analysis method but this method is very inefficient. In this study, a new correction factor that can consider the nonlinearity between stack length and back-emf constant in SFMSM is proposed. This equation can estimate the back-emf constant in a new stack length based on the results of 2D-FEA and 3D-FEA in a specific stack length. Finally, the validity of this equation is verified through analyzing its accuracy and testing it according to changes in motor parameters.