A comparison of radial force level of DC motors using an electromagnetic force analysis considering currents during commutation

DC motors are widely used in automobiles because of their low cost and controllability, and are required to reduce noise levels. Not only the torque ripple but also the radial electromagnetic force needs to be estimated for proper noise reduction. In this paper, we calculated the radial electromagnetic force of DC motors using an electromagnetic field analysis that takes account of the currents during commutation, The result is that when the number of rotor slots is even, the radial force is completely zero due to its symmetry. However, when the number of rotor slots is odd, the radial force of the lap-wound rotor rotates in a certain frequency and that of the wave-wound rotor is almost constant in a certain direction.