Comparison of different electrical machines for Belt Driven Alternator Starters

In this thesis focus is on the electromagnetic design of a synchronous machine suited for a belt driven alternator and starter (BAS) in a micro hybridisation of a mid size passenger car. The BAS needs to provide a high cranking torque to start the combustion engine, especially in a cool condition where the requirements is highest. Beside the high cranking torque is it desirable to have a high power performance over a wide speed range. The thesis compares four potential excitations of a synchronous machine: the permanently magnetized (PMSM), the electrically magnetized (EMSM), the EMSM with series magnetisation (SMSM) and the hybrid magnetized (HMSM). Those are treated both theoretically and with numerical analyses, where the numerical calculations uses finite element analyses (FEA). The fundamental boundary conditions, as current density set by thermal limitations are based on a deep analysis of an existing Lundell alternator. This is presented with computational fluid dynamic (CFD) and finite volume analysis (FVA) in order to give knowledge on the heat dissipation of the alternator. A complete loss separation of the alternator is discussed and presented, both by calculations and experimental work. The SMSM is a new configuration of an electrically excited synchronous machine with the field winding in series with the phase windings via a rectifier. This thesis shows the relation on both the magnetical and the electrical connection between the stator and the rotor. The power and torque characteristics are highlighted. The thesis presents an electromagnetic design and experimental evaluation of a compact HMSM. A relatively simple and compact slip ring less rotor with EM and PM excitation is proposed, analysed and tested. A series of 3D FE transient computations are made in order to estimate efficiency at different operation points and with different types of rotor cores: solid iron and powder composite core. A rotor with the solid iron core is built and tested including different aspects of torque and power loss production. iv Acknowledgements