A high power interior permanent magnet alternator for automotive applications.

Abstract

This thesis examines the operation of a 6 kW interior permanent magnet machine as a generator and its use in conjunction with a switched-mode rectifier as a controllable current source. The interior permanent magnet machine was designed for optimum field-weakening performance which allows it to achieve a wide constant-power speed range. This configuration has possible applications in power generation, e.g. as an alternator in automotive electrical systems and in renewable energy systems such as small-scale wind turbines. The thesis starts from a study of the behaviour of the interior PM machine while generating into a three-phase resistive load and also through a rectifier into a voltage source load. Steady-state and dynamic d-q models are developed which describe the machine generation characteristics. The concept of the VI locus is introduced which provides insights into the generating performance of interior PM machines. In particular, the phenomenon of hysteresis in the current versus speed characteristic of highly salient interior PM machines is explained using the VI locus and for the first time is experimentally demonstrated. The steady-state and transient response of the 6 kW interior PM machine while operating with a switched-mode rectifier is modeled and experimentally measured, forming the basis for the design of a closed-loop controller to regulate the output voltage. The experimental performance and stability of the closed-loop system is examined and evaluated. Further improvements to the output power of the system at low speed using a switched-mode rectifier modulation scheme are investigated and a 66% improvement in output power from 2.8 kW to 4.7 kW is experimentally demonstrated.