For portable AC electric generator sets, it is desired to maintain a constant output voltage under load. With wound-field synchronous generators this is done using field current (excitation) control. This type of control is not possible with PM machines however theoretical analysis is used to show that acceptable output voltage regulation can be obtained by using an optimized interior PM machine. The analysis of an example 4 pole, 16 kW spoke-type machine is described and experimental results are provided demonstrating its low THD, high voltage regulation and high efficiency.

Abstract —This paper investigates the performance and controlof a low-cost 6-kW concept demonstrator of an “inverterless”automotive alternator. This is based on a switched-mode rectifier(SMR) combined with a high-flux interior permanent-magnet(PM) machine. Duty cycle control of the SMR is described and thetheoretical predictions are compared with open-loop experimentalresults. The efficiency of the concept demonstrator is examined asa function of speed and load. Control issues regarding automotiveoperation are discussed. Index Terms —Alternator, interior permanent-magnet (PM)machine, inverterless, switched-mode rectifier. I. I NTRODUCTION I NCREASING automotive electrical loads have created ademand for low-cost high-power alternators. An examplespecification for such an alternator is an output power require-ment of 4 kW at an engine speed of 600 r/min and 6 kW at6000 r/min [1]. This is illustrated in Fig. 1 assuming a 3:1belt ratio between the alternator and engine giving an alternatorspeed range of 1800–18000 r/min.The conventional wound-field Lundell alternator is relativelycheap, at about US $75, but is only capable of producing1–2 kW of output power.Inverter-driven alternators have been proposed to meet thehigh-power alternator requirements. These include induction,switched reluctance, surface permanent-magnet (PM), andinterior PM machines. Unfortunately, these solutions are expen-sive, costing in excess of US $500 with much of the cost due tothe power electronics and the control complexity [1].Previous studies by Perreault and Caliskan [2],Rivas