Output Voltage Model of the Automotive Alternator

The automotive alternator is a key component of the power supply system providing power to consumers of the on-board electric system and battery charge. The evaluation of the alternator technical condition is possible based on comparing the current output voltage with the voltage of an alternator in good order. To do this, one needs to know how the output voltage of an efficient alternator changes at the varied speed and load modes. The alternator EMF depends on the rotor rotation frequency and the magnitude of the magnetic flux, for which a polynomial model of the third degree is proposed. The load connection brings about the occurrence of the alternator voltage which is less than the EMF due to the voltage drop at the active (ohmic) and inductive resistances of the stator winding. The inductive resistance of the stator winding is obtained from the data of the idling and short circuit experiments and is approximated by a linear model. To verify the accuracy of the developed analytical expressions, a mixed load cycle is proposed, during which the rotor rotation frequency, the excitation winding current and the alternator current change simultaneously. The developed model of the output voltage of the automotive alternator has confirmed its operability with the account of the operational limitations of the input parameters.