The objective of this paper is to describe the role that reluctance plays in interior permanent magnet (IPM) starter-generator (SG) analytically. 4-pole and 6-pole models of SG including the radial and tangential flux are analyzed. For increasing the value of $q$ -axis reactance, several possible factors are considered. The stationary torque versus control angle was predicted by finite element analysis (FEA). The permanent magnet and the reluctance components of the torque were analyzed and computed. The results show that the rotor shape, magnet length, magnet thickness and the amount of poles etc., will observably affect the component of the reluctance. One working prototype of the SG-1 was built and fully tested. The motoring torque within 1700 rpm and the generating power within 6000 rpm were measured. The motoring power can supply 8 kW at 1700 rpm and the torque can keep constantly with 45 Nm; Generating results have proven that the ISG is capable of meeting the specification for output power 4 kW up to 6000 rpm and the maximal speed can reach to 7927 rpm. In addition, the efficiency contour maps of motoring and generating are obtained by experiment. The results show that the prototype has wide high efficiency region. The FEA prediction and experiment results were proved well. The improved prototype SG-2 was simulated by FEA. SG-2 is a radial-flux structure machine, and its utilization of permanent magnet and the saliency ratio are both higher than SG-1. The results show that no matter constant torque ability or the constant power range, compared with SG-1, SG-2 both has an improvement to a large extent.
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