Comparison of Different Electrical Machines for Belt-driven Alternator and Starter

Abstract: This thesis focuses 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 are highest. Besides the high cranking torque it is desirable to have high power performance over a wide speed range. This thesis compares four potential excitations of a synchronous machine: the permanently magnetised (PMSM), the electrically magnetised (EMSM), the EMSM with series magnetisation (SMSM), and the hybrid magnetised (HMSM). These are treated both theoretically and with numerical analyses, where the numerical calculations use 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 explain 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 relationship between the magnetical and the electrical connection to the stator and the rotor. The power and torque characteristics are highlighted. This thesis presents an electromagnetic design and experimental evaluation of a compact HMSM. A relatively simple and compact slip ringless rotor with EM and PM excitation is proposed, analysed and tested. A series of 3D FE dynamic computations are made in order to estimate efficiency at different operation points and with different types of rotor core materials: 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.