DIRECTLY DRIVEN RARE-EARTH PERMANENT-MAGNET ELECTRICAL- MACHINE PROTOTYPE FOR WIND ENERGY APPLICATIONS M.S.Widyan ) 1 ( and R.E.Hanitsch ) 2 ( (1) Electrical Engineering Department, The Hashemite University, Zarqa 13115, Jordan (2) Institute of Energy and Automation Technology, Berlin University of Technology, Einsteinufer 11, D-10587 Berlin, Germany ABSTRACT This paper presents finite element design and analysis of two radial-flux high-energy rare-earth permanent magnet electrical machines with new topology. It allows for short endwindings, which contributes to higher efficiency, higher power to weight ratio and low active material cost. Locating the windings in flat slots has further reduced the cost of active material. The permanent magnets are sintered NdFeB with flux concentration arrangement and magnetized tangentially on the rotor support structure. To produce any easy path for the flux penetration and therefore to increase the linkage flux, soft magnetic material is fixed on both poles of the magnets. One of the machines was manufactured and tested as a variable low-speed generator. The relatively high efficiency, the typical ‘rule of thumb’ value of the leakage flux coefficient and the good agreement between the theoretically predicted and experimentally obtained results, which were achieved, demonstrate the success of this topology in its original design. Keywords: Rare-earth permanent-magnets, finite element analysis, electrical machines. 1 INTRODUCTION Due to the absence of the field windings, permanent magnet electrical machines exhibit high efficiency and high power to weight ratio. In this proposed topology, the short endwindings have further improved the efficiency and reduced the weight of active material. The cost of active material has also been reduced by placing the windings in flat slots. The topology comes from a patent holder for a similar configuration [1]. Slotted machines have small effective air gap length in which thinner permanent magnets can be used. This largely reduces the cost of active material as it is dominated by that of the magnets. Based on the direction of the magnetic flux penetration, permanent magnet machines can be classified as: radial-flux [2], axial-flux [3] and transversal-flux machines [4]. This paper deals with the design of two machines. One of them is single phase and the other is three-phase. The single-phase machine was manufactured and tested as a variable low-speed generator. For the three-phase machines, theoretical finite element design was carried out. The machines are radial-flux and low speed. This paper is organized as follows. Section II presents the topology of the machines. The finite element designs are outlined in Section III. The technical data of the machines and permanent magnets are given in Section IV. The focus of Section V is on the laboratory test results along with some comparison with theoretical results. Conclusions are drawn in Section VI. 2 MACHINE TOPOLOGY The topology and arrangement of active material are shown in Fig. 1, 2 and 3. The first machine is 20-slot, 20-pole and single phase. The second machine is three- phase, two slots per phase and ten poles. The permanent magnets are high-energy rare-earth (NdFeB) with flux concentration arrangement and magnetized tangentially on the rotor support structure. Apparently, the slots are flat where toriodal windings (torus) with short ends are placed. Slotted configuration is chosen as it permits lower air-gap length, which in turn allows for thinner magnets. In order to increase the compactness of the windings similar slots were dug on the outer surface of the stator. The soft magnetic material attached to the poles of the magnets is to increase the linkage (useful) flux. Protuberance is left over the permanent magnets to prevent the effects of the centrifugal forces. Having the rotor support structure made from nonmagnetic material allows for fabricating it from light material like Aluminum, which in turn reduces the total weight of the machine and improves the dynamical performance, for example the starting time decreases. All sharp points of the stator are smoothed by curving because otherwise the high flux concentration of the magnets might saturate them. 3 FINITE ELEMENT DESIGN The no-load flux lines distribution of the two machines are shown in Fig. 5, 6 and 7. It can be noted that the UPEC 2007 - 786