An analytical model and parameter computation for universal motors

This paper presents an analytical model of universal motors with the brush shifting from its neutral position by a certain angle for the sake of improving the commutation. In universal motors, the air-gap field distribution of the armature reaction is generally far away from sinusoidal waveform. Therefore the analysis can not be based on the d- and q-axis parameters. For this reason, the paper also introduces a method for parameter computation based on the actual air-gap field distribution from the analytical field solutions by the conformal transformation. Results by the proposed analytical approach are compared with the finite element analysis (FEA) results.