Model of the commutation phenomena in a universal motor

An equivalent electrical circuit, characterised by the minimum coil sections number necessary to analyse the commutation in a universal motor, is found out. The model parameters were also determined: in particular, the self and mutual inductance coefficients and the EMF induced in the coil sections (taking into account the magnetic saturation), the brush-commutator voltage drop, the electric arc. By means of a numerical solution of the equivalent circuit, the current waveforms are analysed; the comparison between the computed and measured waveforms of the brush-commutator voltage drop allows verification of the model.