Design of 6-slot 2-pole High-Speed Permanent Magnet Synchronous Machines with Tooth-Coil Windings Nikita Uzhegov, Janne Nerg and Juha Pyrh¨ onen Abstract—This paper investigates the advantages and draw- backs of High-Speed Permanent Magnet Synchronous Machines (HSPMSM) having a special topology. The analysis is made by using 3.5 kW and 11 kW machines prototypes. The machines under consideration have 6 slots and 2 poles. The rotor is man- ufactured as a full cylindrical magnet inside a retaining sleeve. Non-overlapping Tooth-Coil (TC) windings were implemented to improve the manufacturing process. The similarities and differ- ences of the prototypes are discussed. Machines’ performances are verified by test measurements. I. I NTRODUCTION High-speed electrical machines are used in many industrial applications where high power density, small physical size as well as high efficiency are required. Such applications include, for example, gas compression applications, air blowers, and high-speed energy conversion units where high-speed machine is placed on the same shaft with turbine and compressor units [1]–[4]. In all the aforementioned applications one of the main benefits of using high-speed electrical machine technology is the high level of integration which, in turn, gives advantages in terms of total space saving. In high-speed machinery the number of pole pairs is usually minimized in order to avoid the costs due to the increase of the inverter switching frequency. If we consider a machine with the number of pole pairs p = 1, the axial length required normal integral-slot winding end-windings could easily be more than the axial length of the active stator stack. This problem is quite evident in low power machines having traditional integral slot wound stator. To minimize the space needed by the end- windings, tooth-coils can be utilized in the stator instead of traditional windings. In this paper a three-phase, high-speed permanent magnet synchronous machine topology having six stator slots and two poles is presented. The rotor structure consists of diametrically magnetized permanent magnet and metallic retaining sleeve. The stator winding consists of six tooth coils, and the winding scheme is equivalent of a traditional slot winding having a short pitching of 1/3. Two high-speed machines were designed and manufactured. The first machine was designed for a gas blower application. The power of the first machine is 3.5 kW and its nominal speed is 45 000 rpm. The machine utilizes active magnetic bearings (AMBs) [5], [6]. The second machine was designed as a generator in a micro Organic Rankine Cycle (ORC) power plant. Its nominal power and speed are 11 kW and 32 000 rpm, respectively. The second machine Nikita Uzhegov, Janne Nerg and Juha Pyrh¨ onen are with LUT- Energy, Lappeenranta University of Technology, P.O. Box 20, 53851 Lappeenranta, Finland (e-mail: nikita.uzhegov@lut.fi, janne.nerg@lut.fi, juha.pyrhonen@lut.fi). has a segmented stator structure to facilitate easy winding manufacturing. The paper is organized as follows. First the design and the main parameters of both the machines are presented. The calculation results obtained by Finite element analysis (FEA) are presented. The measurement results of the 11 kW machine are given and the calculation results obtained from FEA are compared with the measurements. II. DESIGN AND LOSS DISTRIBUTION The topologies of both 3.5 kW and 11 kW high-speed machines are similar. Each machine has 6 slots and 2 poles. The rotor consist of the diametrically magnetized full cylindri- cal magnets inside the retaining sleeves. The retaining sleeves transfer the torque to the shaft. Both machines have tooth- coil windings. Semi-magnetic wedges are installed between the tooth tips. However, 3.5 kW machine topology utilizes open stator slots because the coils are wound separately in a jig and then plugged into the stator. This reduces winding work costs. 11 kW machine topology uses semi-closed slots to decrease iron losses and reduce harmonic content. High-speed machine design raise the materials require- ments. The stator iron losses are highly frequency dependent. Thereby, to minimize the stator iron losses SURA NO10 steel with 0.1 mm thickness was selected as a stator lamination material for the 3.5 kW machine. This material has low per unit losses even at high frequencies. For the 11 kW machine the M-270-35A stator lamination material with 0.35 mm thickness was selected. This material has a higher value of specific losses, however the geometry optimization was performed to obtain minimum possible stator iron losses. In both cases the lamination sheets were laser cut. Table I compares the main parameters of the machines under consideration. The rated speed of the 3.5 kW machine is 45 krpm, which is 45 % more than the rated speed of the 11 kW TABLE I. DESIGNED MOTORS MAIN PARAMETERS Machine parameter 3.5 kW PMSM 11 kW PMSM Rated speed nn, min -1 45000 31200 Number of stator slots Qs 6 6 Number of poles p 2 2 Rated torque Tn, Nm 0.74 3.36 Rated phase back-EMF EPM, pu 0.91 0.87 Rotor outer diameter Do,m 0.039 0.046 Air-gap diameter Di ,m 0.043 0.052 External diameter De,m 0.140 0.242 Active length l,m 0.022 0.060 Permanent magnet length lPM,m 0.032 0.070 Permanent magnet remanence Br,T 1.10 1.12 978-1-4799-4775-1/14/$31.00 ©2014 IEEE 2525