Accuracy of determining the commutating inductance value of an automotive alternator by using armature and field circuit measurements

Experimental studies on an automotive alternator to evaluate the accuracy of commutating inductance value by armature circuit and field circuit measurements are described. This issue arises due to the fact that an automotive alternator uses a bridge rectifier to generate a DC voltage at its output and hence the current commutation comes into picture. It is generally recognized that the accurate method of determining this parameter is by means of measuring the commutation interval indicated by short circuit conditions across certain stater phase or line windings. However, in general physical access to the stator winding (of an automotive alternator) can be difficult to have. The other possible way suggested in the literature is by means of measurements done from the field circuit via the field terminals which (in case of an automotive alternator) may be available at the voltage regulator system. This can be easier (in many instances) to access in terms of electrical connections. It is noticed that the method loses accuracy by substantial amounts depending on the operating conditions of the alternator