Investigation of alternative actuator configurations for aerospace applications

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Investigation of alternative actuator configurations  for aerospace applications


application/pdf Investigation of alternative actuator configurations for aerospace applications K. Anagnostopoulos, M. Beniakar, A. Sarigiannidis, A. Kladas
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Investigation of alternative actuator configurations  for aerospace applications


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Investigation of alternative actuator configurations for aerospace applications K. Anagnostopoulos (1), M. Beniakar (2), A. Sarigiannidis (3) and A. Kladas (4) Laboratory of Electrical Machines and Power Electronics, School of Electrical and Computer Engineering, National Technical University of Athens, 9 Iroon Polytechneiou street, 15780 Zografou Athens, Greece. e-mails: 1, 2 :, 3 :, 4 : Abstract This paper undertakes the design optimization and comparative study of different candidate motor topologies for aerospace actuation applications. In the particular case of PM machines, a Surface Mounted PM motor and a PM assisted flux Switching motor are in depth investigated and compared. For the first candidate machine type both single and double layer winding configurations are considered and for the second the impact of a slot separator is assessed. Initially, analytical machine equations and 2D Finite Element (FE) analysis are employed for the determination of the motors basic dimensional and operating characteristics. Both configurations considered are in a next step optimized regarding the mean torque, efficiency, fault tolerance capability, torque ripple, induced Electromotive Force (EMF) quality and motor weight. The proposed methodology involves appropriate handling of mean torque and induced EMF as constraints through the application of an extended sensitivity analysis. Introduction Current trends in aerospace engineering lead to the concept of more electric aircraft. Replacing hydraulic, pneumatic, mechanical systems and sub-systems with electric equivalents is becoming a dominant practise in the aviation industry. Advances in the areas of electric motors and power electronics are providing technological solutions for improving efficiency and safety of aircraft systems operation [1],[2],[5]. Alternative motor topologies Permanent Magnet Motors (PMMs) employing Fractional Slot Concentrated Winding (FSCW) configurations are considered to be an advantageous option for aerospace actuator applications, due to their superior characteristics. High efficiency, high torque density and excellent transient behavior are issues of crucial importance in aerospace applications [3], [4]. More specifically, PMMs establish an independent and strong excitation system, enabling substantial overloading of the motor, while providing higher torque density values. However, Permanent Magnet (PM) demagnetization issues, mainly due to the high armature field and temperature rise, taken place in overloading, should be taken into consideration in the design procedure. The fact that there is no copper in the rotor leads to lower rotor moment of inertia, boosting their transient behavior, while benefitting from simplified scheme and maintenance issues. Furthermore, the high torque density values, in conjunction with the advances in PM rare-earth materials technologies, result in high overall efficiency due to lower stator currents for the same torque levels compared with other motor types [5]. PM assisted flux switching machines comprise both windings and permanent magnets in the stator and a rotor structure similar to a switched reluctance machine. The machine rotor is a simple steel, salient pole structure while the stator incorporates salient poles with armature windings coiled around them and permanent magnets embedded inside the stator steel poles. Through this configuration PMFSM achieves merits that are present in permanent magnet motors and switched reluctance motors. Namely, through the use of PMs, PMFSM have high power density and high efficiency [6],[7]. The fact that the PMs are in the stator also gives the advantages of mechanical robustness in the rotor and easier cooling of the PMs resulting in high reliability [6]. In addition the PMFSM can achieve high speed and increased flux weakening capabilities. On the other hand it should be noted that PMFSM suffer from the magnetic coupling between phases, which limits their fault tolerance performance. However there are some new emerging PMFSM topologies that promise enhanced magnetic isolation of the phases without serious decrease of the power density [7]. Methodology In this paper, the design procedure as well as the qualitative and quantitative comparison of different PMM and flux switching motor configurations for a fault-tolerant Electromechanical Actuation (EMA) system for a helicopter swash plate is implemented. In a first step, conventional analytical design techniques are introduced, in order to calculate the basic dimensional characteristics of the motor. Such an analytical approach does not facilitate detailed design optimization, due to the approximate nature of the electromagnetic field representation, but it delivers a suboptimum set of design variables adequately close to the region of the global optimum. The initial design is focused on the satisfaction of the fundamental spatial limitations and operational specifications. In a second step, a 2-D FE model is employed, in order to validate the analytical preliminary design process and to evaluate precisely the initial motor’s topology performance, efficiency and power quality. In a next step, a particular extended sensitivity analysis, coupled with an external 2-D FE model, is developed, enabling the further tuning of the design variables. Results and discussion Two different PMMs with 10 poles, 12 slots with fractional slot concentrated winding were analyzed, comprising a single and a double layer winding respectively. Additionally, two PMFSMS with 6 stator and 4 rotor teeth, with and without a slot separator were investigated. Figures 1 and 2 illustrate the magnetic flux distribution for the studied motors while Figs. 2 and 4 depict the respective simulated torque waveforms. (a) sl (b) dl Fig. 1: Magnetic flux distribution for (a) SL winding, (b) DL winding. 0 10 20 30 40 50 60 70 5.1 5.15 5.2 5.25 5.3 5.35 5.4 5.45 5.5 Angular displacement (degrees) Instantaneous Torque (Nm) Double layer winding Single Layer winding Fig. 2: Torque waveforms for the two examined PMMs. (a) sl (b) dl Fig. 3: Magnetic flux distribution for (a) PMFSM with no slot separator, (b) PMFSM with slot separator. 0 10 20 30 40 50 60 70 80 90 3.8 4 4.2 4.4 4.6 4.8 5 Angular Displacement (degrees) Instantaneous Torque (Nm) PMFSM without slot separator PMFSM with slot separator Fig. 4: Torque waveforms for the two examined PMFSMs. Conclusions A particular methodology for the comparative design optimization and performance analysis of actuators for aerospace applications, involving different rotor and stator configurations has been introduced. The studied topologies have been compared in terms of efficiency, torque capacity, fault tolerance capability, EMF quality and power density. Acknowledgements The research leading to these results has received funding from the European Commission, in the frame of “Clean Sky” Programme, Topic Nbr: JTI-CS-2010- 3-SGO-02-020 under grant agreement 271850 HPEM. References 1 W. Cao et al, “Overview of Electric Motor Technologies Used for More Electric Aircraft (MEA),” IEEE Trans. Ind. Electron., Sep. 2012, vol. 59, no. 9, pp. 3523-31. 2 M. Villani et al, “Electromechanical actuator for helicopter rotor damper application,” in ICEM 2012, pp. 2552-8. 3 P.E. Kakosimos et al, “Induction Motors versus Permanent Magnet Actuators for Aerospace Applications,” IEEE Trans. Ind. Electron., Aug. 2014, vol. 61, no. 8, pp. 4315-25. 4 M.E. Beniakar et al, “Multi-objective Evolutionary Optimization of a Surface Mounted PM Actuator with Fractional Slot Winding for Aerospace Applications,” IEEE Trans. Magn., Feb. 2014, vol. 50, no. 2, pp. 665-8. 5 E.M. Tsampouris et al, “Geometry Optimization of PMSMs Comparing Full and Fractional Pitch Winding Configurations for Aerospace Actuation Applications,” IEEE Trans. Magn., Feb. 2012, vol. 48, no. 2, pp. 943-6. 6 Y. Amara et al, “Design and comparison of different flux-switch synchronous machines for an aircraft oil breather application,” European Transactions on Electrical Power, 2009, Vol. 15, Issue 6, pp. 497 – 511. 7 T. Raminosoa et al, “A comparative study of permanent magnet -synchronous and permanent magnet -flux switching machines for fault tolerant drive systems”, in ECCE 2010, pp. 2471-8.