Cogging force reduction for tubular permanent magnet linear motor by slots with different sizes

Reduction of cogging force is one of the main concerns of tubular permanent magnet linear motor (TPMLM). In this paper, an analytical calculation of air-gap magnetic density is derived. In addition, an analytical calculation of cogging force is deduced by the energy method. The impact of slots with different sizes on the Fourier coefficients of relative air-gap permanence function is demonstrated. When the nz/4p is the integer, it will produce the cogging force. Therefore, it is practical to reduce the cogging force by changing the Fourier coefficient smaller. The effectiveness of the theoretical analysis is validated by experimental results