Determining the number of interpole turns needed for the perfect commutation of a DC machine

The authors describe a method of determining the number of interpole windings needed for the perfect commutation of a DC machine. The primitive slip-ring model of the machine is used to extract an equation that can ultimately be used to derive an expression describing the current in the conductors undergoing commutation at the end of the commutation period. The coefficients of this expression that depend on some form of inductance are readily obtained by the application of finite-element analysis. One of the coefficients obtained in this way depends on the interpole strength of the machine. To ensure perfect commutation, it is shown that this particular coefficient must arise from the correct number of interpole turns employed in the finite-element analysis model