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Modelling and Analysis of Single-Phase Induction Motor with External Rotor Uma. R Edited By Sarath S Nair www.technologyfuturae.com www.technologyfuturae.com 1 Presentation Outline Introduction Why an external rotor? Equivalent circuit of rotor Lumped parameter equivalent circuit Mathematical model Role of conducting shell Steady state and dynamic analysis Summary References www.technologyfuturae.com 2 Introduction Many domestic appliances require low-power motors operating at constant speed that must start under load(compressors, pumps etc) Because of the reliability in operation the singlephase induction motor is one of the most widely used types of AC machines SPIM with external rotor is more advantageous for low power application Constant speed at different load can be easily achieved by increasing the motor inertia, by using an external rotor www.technologyfuturae.com 3 Why an external rotor? Allows a higher stability in operation at different loads due to higher inertia The fan blades can be attached directly to the outside of the rotor, making the motor more compact Heat generated within the rotor, is on the outside and can be dissipated easily The start-up and operating characteristics of singlephase induction motors with external rotor can be improved by covering the rotor with a conducting shell joining the two end rings www.technologyfuturae.com 4 External rotor of an Induction motor Fig1. axial half cross-section Fig2. Fluxes in longitudinal section L – laminations Φσbx - leakage fluxes of bar B - rotor cage bars Φδx - R - end rings Φex - leakage S - conducting shell airgap flux flux of shell www.technologyfuturae.com 5 Magnetic fluxes and Induced voltages Φσbx= Lσb Ibx Σ Irk= kr Ibx Φσrx= kr Lσr Ibx Φσrx= Lσr Irk kr =1/(2sin2(Πp/Z)) The induced voltage by these fluxes equals the resistive voltage drops on the path г b jω(Φδx + 2 Φσbx + 2Σ Φσrx )= 2Rb Ibx +2Rr Σ Irk On the path г e- (a closed path, consisting from two "external bars“) -jω(Φex + 2Σ Φσrx )= 2Re Iexwww.technologyfuturae.com +2Rr Σ Irk 6 Equivalent circuit of the Rotor • U1, U2 etc -the bar e.m.f.s Each bar is represented by its complex impedance Each ring by its ring-segment complex impedance www.technologyfuturae.com 7 Contd… External shell Due to the symmetry of the bar and ring segment currents, a star equivalent of impedance & for the ring segments can be established equivalent impedance of a bar circuit is: without external conducting shell with external conducting shell www.technologyfuturae.com 8 Lumped parameter Equivalent Circuit Assumptions 1. Only the fundamental space-harmonic component of the air-gap flux distribution is considered. 2. A nonlinear resistor that is associated with the total stator flux linkage models core loss in d and q axis. 3. Stray losses, temperature effects and rotational losses are neglected www.technologyfuturae.com 9 Mathematical Model Mathematical model is described by the following state-variable matrix equations: www.technologyfuturae.com 10 Contd… Where the inductance terms are calculated using the notations: The induced voltages in the magnetising branch are readily determined with: www.technologyfuturae.com 11 Contd… Where Torque equation is: www.technologyfuturae.com 12 Role of conducting shell The ring impedance is especially high in small external rotor motors, because of the increased ring mean diameter The external conducting shell ensures a parallel way for the ring currents diminishes the equivalent ring impedance decreases the rotor resistance and the leakage reactance increases the cooling surface area www.technologyfuturae.com 13 Steady state and Dynamic analysis A split phase induction motor with following parameters are considered for analysis o o o o o o o Rated output power: 60 W Rated frequency: 50 Hz Rated speed: 2850 rpm Rated voltage: 220 V Stator main winding resistance:37.57 ohm Stator auxiliary winding resistance: 56.83 ohm Rotor resistance: 76.23 ohm www.technologyfuturae.com 14 Contd… 1) steady-state torque versus speed for starting period 2) steady-state torque versus speed for rated operating period www.technologyfuturae.com 15 Contd… Fig(1) Fig(2) 1) instantaneous torque versus speed for motor with extemal rotor and without conducting shell 2) instantaneous torque versus speed for motor with extemal rotor with conducting shell www.technologyfuturae.com 16 Contd… Fig(1) Fig(2) 1)Start-up speed response for motor with external rotor and without conducting shell 2)Start-up speed response for motor with external rotor with conducting shell www.technologyfuturae.com 17 Summary This paper focused on a new construction of SPIM with external rotor and conducting shell An equivalent circuit for analysis and modelling of the single-phase induction motor with external rotor is derived. The torque and speed characteristics of the motor with and without the conducting shell is compared A SPIM with external rotor and conducting shell finds its application in compressors, pumps, air conditioners etc www.technologyfuturae.com 18 References [l] M. Popescu, “Analysis and Modelling of Single-Phase Induction Motor with External Rotor for Domestic Applications”, IEEE Trans. Ind. Appl.,2000,pp463-470 [2]P.C. Krause, 0. Waszynchuk, S.D. Sudhoff: Analysis of Electrical Machinery, IEEE Press, New York, 1995 [3] S . D. Umans, “Steady-state, lumped-parameter model for capacitor-run, single-phase induction motors”, IEEE Trans. Ind. Appl., Vo1.32, no. 1, Jan/Feb 1996, pp.169-179 [4] E. Levi: “A unified approach to main flux saturation modelling in D-Q axis models of induction machines”, IEEE Trans. Energy Conv., Vol. 10, no.3, Sept. 1995,pp 455-461 www.technologyfuturae.com 19 Technical Presentations, Research Reviews, New designs & Developments Log On to www.technologyfuturae.com THANK YOU www.technologyfuturae.com 21