Optimal Pole Number And Winding Designs For Low Speed–high Torque Synchronous Reluctance Machines10/29/2019
THREE-PHASE SYNCHRONOUS MACHINES 11.1 Introduction. Each phase winding has a number of coils connected in series to form a definite number of magnetic poles. A four-pole machine, for example, has four groups. 11.2 Main types of alternator rotors: (a) low speed-salient pole, (b) high speed-cylindrical.
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There is described a synchronous reluctance machine having a plurality of poles and comprising a stator with a plurality of spaced slots and a rotor. The rotor has one direct axis and one quadrature axis for each pole and comprises a plurality of flux barriers, each extending to a circumference thereof at least one barrier point. Successive angular separations between barrier points around the circumference of the rotor increase or decrease when moving around half a pole pitch from an initial axis to an adjacent finishing axis, the initial axis being one of a direct axis or a quadrature axis and the finishing axis being the other of a direct axis and a quadrature axis. The increase or decrease in size may be governed by a systematic progressive series.
The present invention relates to the design of synchronous reluctance machines and synchronous reluctance machines with permanent magnet assistance, particularly the rotor for such machines.Synchronous reluctance machines have a multiphase stator winding arranged in a slotted stator, and a rotor having the same number of poles. The stator winding is usually three phase distributed winding with overlapping coils spanning more than 50% of the pole pitch, with the most common stator examples having 12, 18, 24, 36 or 48 slots. Stator windings with less than 50% of the pole pitch are also possible where short end windings are desired but typically they have lower performance due to the reduced mutual coupling between coils of different phases.The rotor of the synchronous reluctance motor can be axially laminated with alternating layers of permeable and non-permeable steel, giving a high ratio between direct and quadrature reluctances. These axially laminated structures are difficult to manufacture cost effectively and do not provide high strength for rotation at speed and therefore for ease of manufacturing a transverse laminated structure is preferred.A rotor with transverse laminations was presented by Honsinger in U.S.
The transverse laminated rotor has a pattern of slots stamped in each lamination. The slotting pattern creates regions of the air-gap surface of the rotor where the rotor has low permeability (also known as the direct axis or d-axis) and regions of the rotor where it is more difficult for magnetic flux produced by the stator to penetrate the surface of the rotor. These regions of high permeability are known as the quadrature axis or q-axis.The interaction between the slotting on the rotor and the stator teeth and slotting creates torque variations or torque ripple. Torque ripple is undesirable due to the creation of acoustic noise and vibration.Prior art methods exist for the reduction of the torque ripple by careful choice of the number of equivalent rotor slots just under the surface of the rotor. 5,818,140 and Patent Application WO 2010/131233 the number of equivalent rotor slots per pole pair is recommended to be 4 more or 4 less than the number of stator slots per pole pair, to achieve the optimum performance. 5,818,140 also advises that the number of equivalent rotor slots per pole pair should not be equal to or differ by two from the number of stator slots per pole pair, if significant torque ripple is to be avoided.U.S. 6,239,526 provides an alternative method by arranging that if one end of a rotor flux barrier is adjacent to a stator tooth, the other end should reach the surface of the rotor adjacent to a stator slot.Whilst the methods described in the prior art provide for reduction in torque ripple they do not necessarily produce motor designs with highest efficiency.
One reason for this is that by choosing to have 4 additional equivalent rotor slots compared to the number of stator slots can lead to a higher flux frequency in the rotor steel as the frequency of flux barriers passing the stator teeth is increased. The higher localised flux frequencies cause higher iron losses in the rotor, reducing the efficiency of the motor.In accordance with one aspect of the present invention there is described a synchronous reluctance machine having a plurality of poles and comprising a stator with a plurality of spaced slots and a rotor. The rotor has one direct axis and one quadrature axis for each pole and comprises a plurality of flux barriers, each extending to a circumference thereof at at least one barrier point.
Successive angular separations between barrier points around the circumference of the rotor increase or decrease when moving around half a pole pitch from an initial axis to an adjacent finishing axis, the initial axis being one of a direct axis or a quadrature axis and the finishing axis being the other of a direct axis and a quadrature axis. The increase or decrease in size may be governed by a systematic progressive series. The machine of claim 5, wherein the sum of angular separations as a proportion of one pole pitch where there are nb barriers per half pole, and the presence or absence of extra barriers at the initial axis or finishing axis of the barrier sequence is signified by the Boolean variables, Ei and Ef respectively, is given by Pole Pitch = 2 ∑ k = 0 n b ( a + kd ) - ( 1 - E i ) ( a ) - ( 1 - E f ) ( a + n b d ) = ( n b + 1 ) ( 2 a + n b d ) - ( 1 - E i ) ( a ) - ( 1 - E f ) ( a + n b d ).
The machine of claim 7, wherein the sum of angular separations as a proportion of one pole pitch where there are nb barriers per half pole and the presence or absence of extra barriers at the initial axis or finishing axis of the barrier sequence is signified by the Boolean variables, Ei and Ef respectively is given by: Pole Pitch = 2 ∑ k = 0 n b ( ar k ) - ( 1 - E i ) ( a ) - ( 1 - E f ) ( ar n b ) = ( 2 a 1 - r ( n b + 1 ) 1 - r ) - ( 1 - E i ) ( a ) - ( 1 - E f ) ( ar n b ). 1 184 956March 2002EP2 790 296October 2014EP1 337 785November 1973GB2 378 323February 2003GB2001-037127February 2001JP2009-077458April 2009JP3July 2010KRWO 2010/102671September 2010WOWO 2010/131233November 2010WOWO 2015/170352November 2015WOOther references. British Search and Examination Report dated Dec. 29, 2015 for corresponding British Application No. GB1409281.1.
British Examination Report dated Jul. 25, 2016 for corresponding British Application No. GB1409281.1. International Search Report and Written Opinion for corresponding International Application No. PCT/GB2015/051512 dated Jul. 21, 2015.
Seok-Hee Han et al; “Design Tradeoffs between Stator Core Loss and Torque Ripple in IPM Machines”, Industry Applications Society Annual Meeting, 2008, IEEE, Piscataway, NJ, USA; Oct. 1-8, XP031353761. Sanada M. Et al; “Torque ripple improvement for synchronous reluctance motor using asymmetric flux barrier arrangement”, Conference Record of the 2003 IEEE Industry Applications Conference; 38 th IAS Annual Meeting, Salt Lake City, UT, Oct. 12-16, 2003; vol. 250-255, XP010676030.
Intention to Grant for corresponding British Application No. GB1409281.1, dated Dec.
30, 2016. Examination Report for corresponding British Application No. GB1409281.1, dated Dec.
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