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In this study, wide overview of the existing line start permanent magnet synchronous motors literature is presented. The treatment of the subject has been effectively subdivided in to five sections; (i) rotor topologies and design, (ii) steady state analysis, (iii) transient state analysis, (iv) parameter estimation and (v) high efficiency standards. Although, there are numerous papers published in each category, only those important papers which have made significant contributions in the developments and thus triggered research in this field are discussed here. 2 Rotor topologies and design The performance of the Merrill's PM excited synchronous motor [1] was found to be comparable with that of induction motor (IM). Fig. 1 shows the Merrill's rotor configuration. The four sets of flux loops (i.e. A, B, C and D) as shown in the figure, show the corresponding flux patterns under different operating conditions; and should not be taken as a complete flux distribution pattern for a single condition. The machine has negligible reluctance torque component. Alger's discussion on this paper is quite informative and he had postulated that LSPMSM will gain popularity if the future research produces a magnet of higher stored energy and coercive force. Douglas [2], then in 1959, derived the current loci of Merrill's motor by using Blondel's two-reactance theory and predicted that with improved magnet materials, the machine performance would be better. Subsequently, based on the guidelines by Merrill in his paper, a 2 pole, 0.5 hp machine was developed as shown in Fig. 2, and reported by Cahill and Adkins [3]. They found that the rated and the pull-out torque of this machine were less than those of IM of the same frame size because of the lower value of air gap flux density. Moreover, authors observed that this www.ietdl.org

This study presents a rotor structure, for a line start permanent magnet synchronous motors (LSPMSMs), which can be applied to other types of inverter driven motors, such as brushless dc and permanent magnet synchronous motors. In this development, the magnet configuration is a combination of both circumferentially (spoke) as well as radially magnetised (embedded) magnets which are so arranged that induced poles are generated in alternate positions in the heteropolar structure, thereby reducing the quantity of permanent magnets in the rotor. Both the transient as well as steady-state performances of the machine have been analysed by using time-stepping finite element method. For experimental demonstration a prototype which uses spoke magnets (P1), plus two prototypes (P2 and P3) of the proposed magnet arrangement have been built. The former (P1) is used for benchmarking the performance of the proposed configuration. Results have indicated that the rotor configuration reported here (P2) with reduced magnet volume gives better performance than the spoke magnet rotor LSPMSM. Also, the performances of prototype LSPMSMs are compared with that of the standard induction motor of the same frame size and physical dimensions.

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