1 LINE-START PERMANENT MAGNET SYNCHRONOUS MOTORS. ANALYSIS AND DESIGN Dan STOIA 1 , Mihai CERNAT 1 , Kay HAMEYER 2 , Drago BAN 3 1 ”Transilvania” University of Brasov, Faculty of Electrical Engineering and Computer Sciences B-dul Eroilor 29, 500036 Brasov, Romania, stoiadan@ymail.com, m.cernat@unitbv.ro 2 RWTH Aachen University, Institute for Electrical Machines Schinkelstraße 4, 52062 Aachen, Germany, kay.hameyer@iem.rwth-aachen.de 3 University of Zagreb, Faculty of Electrical Engineering and Computing Unska 3, 10000 Zagreb, Croatia, drago.ban@fer.hr Abstract. The Line-Start Permanent Magnet Synchronous Motor (LSPMSM) attracted a considerable attention because of the higher value of the product between the power factor and the efficiency. The paper proposes an analytical design method for the permanent magnet, considering the operating point on the B-H characteristic alias the magnetic flux–magnetomotive characteristic, a design method for the LSPMSM considering the synchronous operation parameters and the asynchronous operation (starting) parameters. A design example for a motor having rated power 3.5 kW, rated phase voltage 200 V, rated frequency 50 Hz, rated speed 3000 rpm will be presented. Keywords. AC machines, design, electrical machines, permanent magnet motors, line-start syn- chronous motor. 1. INTRODUCTION In the last years, the LSPMSM has received more attention in the academic world and industries [1-38]. Worldwide new legislations demand higher efficiency motors. The use of LSPMM can help to achieve the new requirements. It became competitor to cage induction motor in the general purpose industrial applications due to its high efficiency, high power factor and its ability to self start from the regular fixed frequency supply [5-8]. The structure of LSPMSM is similar to this of the IM but with permanent magnets (PMs) inserted in the rotor [6, 9- 11]. The rotor can have many types of configurations since the inserted PMs may have different shapes, materials, sizes and positions [2, 4, 12, 13], which deeply influence the per- formances of the machine. The line-start property is obtained thanks to the design of the rotor with starting aluminium cage or with solid iron, or with a conducting ring on the surface [5, 14-16]. LSPMSM is in fact a synchronous machine at which the excitation field is produces by permanent magnets instead by a dc field winding. For starting and transients, the machine has the aluminium cage on the rotor. So, the functioning of the LSPMSM is characterized by two operation modes: the synchronous operation mode at steady state and the asynchronous operation mode at starting and transients [39]. The synchronizing process has been studied in [1-4, 28]. The steady-state characteristics are measured for different values of the output power [18-22]. In general, the LSPMSM has PMs buried below the squirrel-cage and these two constructive parts have different functions under different states. The PMs operate on alignment torque to drive synchronous speed in steady state and breaking torque in starting period, both dependent of the PM operating point and the non-load emf [9, 18, 19, 23, 35]. So, it is necessary to design PMs considering the alignment and breaking torque at once. In general, the optimal size of PMs provides the required magnetic flux so that the reactive power exchanged with the power supply is minimal, to get a highest power factor which corresponds to the minimum line current [15]. The rotor cage generates in transient operating modes (starting and load changes) an asynchronous torque. The breaking torque introduced by PMs in starting period lowers the total torque [11, 32, 34]. Because the PMs are buried below the squirrel cage, magnetic flux barriers in the rotor back iron are necessary. So, additionally to the PM breaking torque, these magnetic flux barriers introduce a breaking reluctance torque because of rotor saliency, which further lowers the total torque in starting period. In this way, the design of LSPMSM is somehow trouble- some because of various line starting performance degra- ding effects. For the aforementioned reasons, the LSPMSM designer has to find many compromises in the design process between an adequate starting characteristic in the asynchronous operating region and the torque capability and efficiency in the synchronous operating region. The paper proposes: an analytical design method for the PMs considering the operating point on the B-H characte- ristic taking into account of the iron saturation effect; followed by an analytical design method for the LSPMSM EDPE 2009, October 12-14, 2009, Dubrovnik, Croatia