Contributions to the Development of Automobile Electrical Power System

Doctoral thesis, 1995

Development trends for the Automobile Electrical Power System (AEPS) are discussed. Two systems are compared with respect to cost, weight, number of components, reliability and noise. One system is based on a conventional starter and generator and the other system is based on an Integrated Starter/Generator (ISG) that replaces both the starter and generator. For a vehicle with considerable electrical loads, the results show that an ISG is competitive. A simulation method for starting a combustion engine with an ISG is presented. Models of the components involved (combustion engine, electrical machine, converter and battery) are described. A comparison of simulation results and laboratory measurements shows a good coincidence, i.e. the method is useful when designing a start system. A BAttery STate of charge sensor (BAST) for vehicles is developed. Models for charge and discharge efficiency, open circuit voltage and internal resistance are described. Battery history before disconnection and ageing is discussed. An evaluation of the BAST in a vehicle shows that the accuracy for a new battery is better than +/- 7.5%.