Feb 27, 2012 - Keywords : variable reluctance motor, yoke thickness, average torque, ripple torque, ... stator yoke thickness and shape of stator teeth (see Fig.
Author manuscript, published in "Symposium SPEEDAM, TAORMINA : Italy (1994)"
SPEEDAM, 8-10 June 1994, Taormina (Italy), pp.145-149
Influence of Stator Yoke Thickness and Stator Teeth Shape upon Ripple and Average Torque of Switched Reluctance Motors E. HOANG, B. MULTON, R. VIVES FOS, M. GEOFFROY L.E.SI.R- U.R.A. C.N.R.S D1375-E.N.S Cachan 61 av du Pdt Wilson 94235 Cachan cedex France Tel : 33.1.47.40.21.11 Fax : 33.1.47.40.21.99
hal-00674032, version 1 - 27 Feb 2012
ABSTRACT During the investigation of the Switched Reluctance Motor (SRM), we became interested in two apparently secondary parameters which are: - the thickness of the stator yoke; - the shape of stator teeth. In keeping the other geometrical parameters, like the outer and air gap diameters, constant, we could study the impacts from varying these two parameters with respect to: - the curve of instantaneous single-phase torque; - the poly-phase ripple torque at low speed with a current supply mode; - the power semi-conductor rating at maximum power; - and the size power ratio of the converter with a full-wave voltage supply mode. A prototype has been built and enables drawing a comparison between the theoretical and practical results. Keywords : variable reluctance motor, yoke thickness, average torque, ripple torque, converter rating
SPEEDAM, 8-10 June 1994, Taormina (Italy), pp.145-149
I.Introduction
hal-00674032, version 1 - 27 Feb 2012
To design a motor meeting specifications, both experience and the use of equations are necessary. These equations take geometrical parameters and some constraints like copper losses into account [2]. An initial geometrical result motivated us to define all parameters, such as outer diameter, pole shaping and air gap radius. However, in order to assess precisely the ratio of average torque per copper losses and to fill coil space in the most optimal way, we became interested in two particular geometrical parameters for the switched reluctance motor (SRM): stator yoke thickness and shape of stator teeth (see Fig. 1). The use of a 2-D. finite-element software is essential for taking equations which are not linear into account (for example, saturable magnetic material) and for calculating the characteristic variables of a motor, like magnetic flux or torque. With this software, we can plot : - In the flux-current set of curves, two extreme position curves (opposition and conjunction) define average torque in the case of an ideal current supply mode. - Curve network flux in terms of electrical angle for several currents, which helps to estimate the influence of the stator yoke thickness and the shape of stator teeth by means of a simulation software on power semi-conductor rating at maximum power use and on " size power ratio " of the converter. Switched reluctance motor mode with full-wave voltage is also studied. At higher speed, many authors have shown that this supply mode is very efficient. - Curve network torque in terms of electrical angle for several currents to calculate ripple torque at low running speed .
II.Presentation of motors under study A.Geometrical definition In order to optimize several constraints which will be indicated, we modified the stator yoke thickness and the stator tooth shape of a SRM with 6 and 8 teeth at the stator and rotor, respectively a rated speed of 3000 rpm and a rated torque of 9.5 Nm; thus a power of 2.95 kW. The results of a initial sizing provides the dimensions of the machine (Ec1as1) as follows: - Outer diameter : 143 mm - Air gap diameter : 82 mm - Iron active length 80 mm - βs = 0.32 ; βr = 0.48 - Stator yoke thickness (Ec1) 6.5 mm - The tooth of the stator and rotor are right-pole shaped.
SPEEDAM, 8-10 June 1994, Taormina (Italy), pp.145-149 Ec1
10°
Ec2
Ec1 = 6.5 mm Ec2 = 8 mm
hal-00674032, version 1 - 27 Feb 2012
Fig. 1 Stator size of studied machines B.Magnetic core modifications The second (Ec2as1) differs from the first in yoke thickness (Ec2 = 8 mm ). The third (Ec2as2) differs from the first in yoke thickness (Ec2 = 8 mm) and in stator pole shape (angle of teeth side = 10°). The prototype has been built with Ec2as2 geometrical parametric results. C.Number of spires, winding area The converter topology is an asymmetric half-bridge per phase and the DC voltage supply is 300 volts. These 300 V are fixed by the power network. To optimise the motor's performance we varied the turn coils. We computed the turns coils to obtain an average torque of 9.5 Nm at 3000 rpm with a DC. supply voltage of 300 V ( see section V high speed and voltage feeding ). To compute iron losses : pcu = q R I rms2 nL R=ρ Scu n = number of turns, L = average length of a turn ⎛ ⎛ w ⎞⎞ L = 2⎜ L a + k tb ⎜⎜ w s + s ⎟⎟ ⎟ ⎜ 2 ⎠ ⎟⎠ ⎝ ⎝
π ⎛ ⎞ k tb is a coefficient to take into account winding-heads form ⎜1
