Method for analysing the commutation in small universal motors

A method for analysing numerically the commutating characteristics in small universal motors is given. This analysis method can be applied to evaluate the commutating characteristics at the machine design stage and make it possible to perform relative comparisons of these characteristics before and after a modification of design specifications. The method consists of an iterative separate calculation of the circuit parameters by the finite element method on one hand and a solution of the commutation equation on the other hand until the value of the commutating coil current converges. This method is characterised by the various quantities related to commutation that can be easily calculated and examined. In a commutation equation, combined static and dynamic characteristics of brush contact voltage are adopted. The quality of commutation can be evaluated by the contact voltage at the trailing edge of the brush. An example of the commutation analysis is given for a motor of the type used in vacuum cleaners and the results obtained are in good correspondence with those found in experiments.