FIELD OF THE INVENTION

[001] The present invention relates to a rotary electrical machine.

BACKGROUND OF THE INVENTION [002] A typical rotary electrical machine consists of a stator and a rotor. Due to relative motion between the rotor and magnetic field produced by the stator, a back-emf is generated. Owing to mechanical limitations and design considerations of the rotor and the stator, the back-emf does not perfectly match an ideal sinusoidal waveform and has several harmonics. Such harmonics cause additional heat in the machine. [003] Stator winding of rotary machines may either have a star connection or a delta connection. However, in case of delta connection, voltage waveform in the stator winding has a higher level of harmonics. The higher level of harmonics results into formation of a circulating current inside the delta connection of the winding. Such circulating current causes additional heat, thereby heating the machine beyond safe and operable levels Accordingly, in view of the heat generated due to the harmonics present in the back-emf, usage of delta connection for stator winding is restricted. Thus, to employ and take advantage of delta connection, it becomes necessary to minimize the harmonics in the back-emf to obtain a more sinusoidal waveform.

[004] Further, in conventional rotor designs of rotary machines, the torque characteristics have increased ripples. The increased ripples create a cogging torque. When the cogging torque is high, the rotary machine has higher levels of obstruction in forward and backward movement of the rotor. This also causes a poor waveform of the back-emf wherein the back-emf has greater harmonics in it and the waveform is not purely sinusoidal.

[005] The torque characteristics of the conventional rotor design having increased ripples, is also dependent on the combination of magnets in the rotor of the rotary machine. Especially, in a 6-pole and 36 slot variant of distributed winding combination in the rotary machine, the torque ripple is increased when the saliency of the machine is increased. Saliency is defined as a measure of the reluctance difference between the rotor and the stator around the circumference of the rotor. A higher saliency has a detrimental effect on torque ripple causing a poor waveform, and hence, limiting the rotary machine in terms of not being able to employ delta connection in stator winding.

[006] Another issue with the rotor design in the conventional rotary machines is that the permanent magnets utilised in the rotor are non-commonized, i.e. the permanent magnets required in different arrangements such as V-arrangement or a delta arrangement are different, hence, different permanent magnets need to be produced for different arrangements of the permanent magnets in the rotor, which increases the manufacturing cost and assembly cost.

[007] Furthermore, saturation of lamination core is another limitation prevalent in rotor designs in conventional rotary machines. [008] Thus, there is a need in the art for a rotary electrical machine which addresses at least the aforementioned problems. SUMMARY OF THE INVENTION

[009] The present invention is directed towards a rotary electrical machine having a stator with a plurality of slots for winding, and a rotor having an even number of magnetic poles. The rotor is rotatably engaged with the stator. Each of the magnetic poles of the rotor has at least three magnets wherein a first set of at least two magnets are arranged in a substantially V-shaped configuration and a second set of at least one magnet is arranged between the first set of magnets and an outer periphery of the rotor. Further, at least one flux barrier is positioned between the first set of magnets and the outer periphery of the rotor, and at least one flux barrier is positioned between the second set of magnets and the outer periphery of the rotor.

[010] In an embodiment of the invention, the rotor has a plurality of depressions on the outer periphery of the rotor.

[011] In another embodiment of the invention, each magnet in the first set of two magnets has a first end and a second end wherein the first end of each of the magnets in the first set are adjacent to each other.

[012] In a further embodiment of the invention, the first end of each magnet in the first set are adjacent to each other with a gap between them.

[013] In another embodiment of the invention, poles numbered n= {2k+1 , K>0} has the first set of two magnets arranged in a substantially V-shaped configuration symmetrically along a central axis A-A’ of the pole, the second set of one magnet is arranged between the first set and the outer periphery of the rotor, and two flux barriers. Herein, a first end of each of the flux barriers is positioned at a first angle (qi) from the second end of each magnet of the first set, and a second end of each of the flux barriers is positioned adjacent to the outer periphery of the rotor. Further, a first end of each of the flux barriers is positioned at a third angle (Q3) from each end of the second set of one magnet, and a second end of each of the flux barriers is positioned adjacent to the outer periphery of the rotor. [014] In another embodiment of the invention, poles numbered n= {2k, K>1} has the first set of two magnets arranged in a substantially V-shaped configuration symmetrically along a central axis B-B’ of the pole, the second set of one magnet is arranged between the first set and the outer periphery of the rotor, and two flux barriers. Herein, the first end of each of the flux barriers is positioned at a second angle (Q2) from the second end of each magnet of the first set, and a second end of each of the flux barriers is positioned adjacent to the outer periphery of the rotor. Further, the first end of each of the flux barriers is positioned at a fourth angle (Q4) from each end of the second set of one magnet, and a second end of each of the flux barriers is positioned adjacent to the outer periphery of the rotor. [015] In another embodiment of the invention, the first angle (qi) is greater than the second angle (Q2) and the third angle (Q3) is greater than the fourth angle (Q4).

[016] In another embodiment of the invention, each of the depressions is adjacent to the second end of each flux barrier.

[017] In another embodiment of the invention, the first set of two magnets are arranged in V-shaped configuration together with the second set of one magnet to form a delta shape. [018] In a further embodiment of the invention, the number of magnetic poles is six and the number of slots for winding is thirty-six. BRIEF DESCRIPTION OF THE DRAWINGS

[019] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 illustrates a rotor of a rotary electrical machine in accordance with an embodiment of the invention.

Figure 2 illustrates the rotary electrical machine with the stator in accordance with an embodiment of the invention.

Figure 3 illustrates adjacent poles of the rotor of the rotary electrical machine in accordance with an embodiment of the invention.

Figure 4 illustrates an exemplary odd numbered pole of the rotor of the rotary electrical machine in accordance with an embodiment of the invention Figure 5 illustrates an exemplary even numbered pole of the rotor of the rotary electrical machine in accordance with an embodiment of the invention.

Figure 6 and 7 illustrate a plurality of depressions of the rotor in accordance with an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[020] The present invention relates to a rotary electrical machine. In particular, the present invention relates to a rotary electrical machine with reduced harmonics and reduced torque ripple. [021] Figure 1 illustrates a rotor 120 of a rotary electrical machine 100. As illustrated in the Figure, the rotor 120 has an even number of magnetic poles 122. Each of the magnetic poles 122 have substantially similar outer geometry. In the embodiment illustrated in Figure 1 , the rotor has six poles 122A,122B,122C,122D,122E,122F. The rotor 120 of the rotary electric machine 100 is rotatably engaged with a stator 110 (as shown in Figure 2). The stator 110 of the rotary electric machine 100 has a plurality of slots 112 (as shown in Figure 2) for winding of a coil. In an embodiment of the invention, the slots 112 of the stator 110 accommodate three pairs of coil windings (not shown), each pair evenly offset by an angle to each other, and equally distributed along the stator 110 depending on the positioning of the slots 112. In an embodiment of the invention, the rotary electric machine 100 has thirty- six slots 112, wherein each slot 112 is offset by an angle of 10 degrees to each other.

[022] As illustrated in Figure 1 , each of the magnetic poles 122 comprise at least three magnets. Herein, a first set 124 of at least two magnets 124A,124B are arranged in a substantially V-shaped configuration and a second set 128 of at least one magnet 128A is arranged between the first set 124 of magnets and an outer periphery 132 of the rotor 120. As further illustrated in Figure 1 , at least one flux barrier 126 is positioned between the first set 124 of magnets and the outer periphery 132 of the rotor 120, and at least one flux barrier 130 is positioned between the second set 128 of magnets and the outer periphery 132 of the rotor 120. As can be seen in Figure 1 , in an embodiment of the invention, the first set 124 of two magnets 124A,124B (as shown in Fig.3) arranged in V-shaped configuration together with the second set 128 of one magnet 128A to form a delta shape- configuration. The voltage that is obtained in delta-shape configuration of the present invention is lower as compared to the voltage in star-shape configuration of the conventional rotor design. However, an increase in the voltage of the delta-shape configuration is obtained by increasing the number of turns in the winding on the slots 112 of the stator 110. An increase in the number of turns in the winding on the stator 110 is preferable over higher strands of flux in the star-shape configuration for obtaining a sinusoidal voltage waveform.

[023] Figure 3 illustrates a portion of the rotor 120 of the rotary electrical machine 100, depicting two adjacent poles 122A,122B in the rotor 120 in accordance with an embodiment of the invention. Each magnet in the first set 124 of two magnets 124A,124B has a first end 124A’,124B’ (shown in Figure 4 and 5) and a second end 124A”,124B” (shown in Figure 4 and 5). Herein, the first end 124A’,124B’ of each of the magnets in the first set 124 are adjacent to each other. In an embodiment of the invention, the first end 124A’,124B’ of each magnet in the first set 124 are adjacent to each other with a gap between them.

[024] Figure 4 illustrates an exemplary odd numbered (n= {2k+1 , K>0}) pole 122A of the rotor 120. As illustrated in Figure 4, and referenced in Figure 3, in poles numbered (n= {2k+1 , K>0}) 122A,122C,122E, i.e. poles numbered 1 , 3, 5 and so on, the first set 124 of two magnets 124A,124B are arranged in a substantially V-shaped configuration symmetrically along a central axis A-A’ of the odd numbered pole 122A, and the second set 128 of one magnet 128A is arranged between the first set 124 and the outer periphery 132 of the rotor 120. The odd numbered poles 122A,122C,122E (shown in Fig.1 ) and so on, further have two flux barriers 126, wherein a first end 126A’,126B’ of each of the flux barriers 126A,126B is positioned at a first angle qi from the second end 124A”,124B” of each magnet of the first set 124, and a second end 126A”,126B” of each of the flux barriers 126A,126B is positioned adjacent to the outer periphery 132 of the rotor 120. In an embodiment, the first end 126A’,126B’ of the flux barriers 126A,126B is curved so as to align with the magnets 124A,124B of the first set 124, that they are attached to.

[025] The odd numbered poles 122A, 122C, 122E and so on, further have two flux barriers 130A,130B, wherein a first end 130A’,130B’ of each of the flux barriers 130A,130B is positioned at a third angle 03 from each end 128A’,128A” of the second set 128 of one magnet 128A, and a second end 130A”,130B” of each of the flux barriers 130A,130B is positioned adjacent to the outer periphery 132 of the rotor 120.

[026] Figure 5 illustrates an exemplary even numbered (n= {2K, K>1}) pole 122B of the rotor 120. As illustrated in Figures 3 and 5, in poles numbered n= {2K, K>1}

122B,122D,122F, i.e. poles numbered 2, 4, 6 and so on, the first set 124 of two magnets 124A,124B are arranged in a substantially V-shaped configuration symmetrically along a central axis B-B’ of the even numbered pole 122B, and the second set 128 of one magnet 128A is arranged between the first set 124 and the outer periphery 132 of the rotor 120. The even numbered poles 122B,122D,122F and so on, further have two flux barriers 126A,126B, wherein the first end 126A’,126B’ of each of the flux barriers 126A,126B is positioned at a second angle 02 from the second end 124A”,124B” of each magnet 124A,124B of the first set 124, and the second end 126A”,126B” of each of the flux barriers 126A,126B is positioned adjacent to the outer periphery 132 of the rotor 120. The first end 126A’,126B’ of the flux barriers 126A,126B is curved so as to align with the magnets

124A,124B of the first set 124, that they are attached to.

[027] The even numbered poles 122B,122D,122F and so on, further have two flux barriers 130A,130B, wherein the first end 130A’,130B’ of each of the flux barriers 130A,130B is positioned at a fourth angle 04 from each end 128A’,128A” of the second set 128 of one magnet 128A, and a second end 130A”,130B” of each of the flux barriers 130A,130B is positioned adjacent to the outer periphery 132 of the rotor 120.

[028] In an embodiment of the invention as referenced in Figure 3, 4 and 5, the first angle 01 is greater than the second angle 02, i.e. the angle formed between the first end

126A’,126B’ of each of the flux barriers 126A,126B from the second end 124A”,124B” of each magnet 124A,124B of the first set 124 in odd numbered poles 122A,122B,122E is greater than the angle formed between the first end 126A’,126B’ of each of the flux barriers 126A,126B from the second end 124A”,124B” of each magnet 124A,124B of the first set 124 in even numbered poles 122B,122D,122F. Further, the third angle 03 is greater than the fourth angle 04, i.e. the angle formed between the first end 130A’,130B’ of each of the flux barriers 130A,130B from each end 128A’,128A” of the second set 128 of one magnet 128A in odd numbered poles 122A,122C,122E is greater than the angle formed between the first end 130A’,130B’ of each of the flux barriers 130A,130B from each end 128A’,128A” of the second set 128 of one magnet 128A in even numbered poles

122B,122D,122F.

[029] Such an alternating arrangement of magnets 124,128 and flux barriers 126,130 in adjacent odd and even numbered poles 122 of the rotor 120 improves the reluctance difference between the rotor 120 and the stator 110 around the outer periphery 132 of the rotor 120, reducing the saliency and hence improving the usage of the magnets over a long period of time in operation. Further, the alternating arrangement of magnets 124,128 and flux barriers 126,130 in the adjacent poles 122 of the rotor 120 reduces the distortion in the back EMF waveform, resultantly reducing the harmonics in the waveform and giving rise to a more sinusoidal voltage waveform and reducing torque ripple.

[030] Further, the arrangement of magnets 124,128 and flux barriers 126,130 in the poles 122 of the rotor 120 are, in a manner that the flux barriers 126,130 have curved profile at their respective first ends 126A’,126B’,130A’,130B’ and the first ends 126A’,126B’,130A’,130B’ and second ends 126A”,126B”,130A”’,130B” of all the flux barriers 126,130 have curved edges, instead of the conventional sharp edges, reducing the chances of flux concentration at the sharp edges and hence reduce the possibility of core saturation. [031] As further illustrated in Figure 3, similar magnets have been used in the first set 124 of two magnets 124A,124B and the second set 128 of one magnet 128A across the odd numbered and even numbered poles 122, hence eliminating the need of separate manufacturing of magnets for the first set 124 and the second set 128.

[032] As illustrated in Figures 6 and 7, the rotor 120 has a plurality of depressions 134 on the outer periphery 132 of the rotor 120 creating a non-uniform outer periphery 132 of the rotor 120. The non-uniform outer periphery 132 of the rotor 120 creates a non-uniform air- gap between the rotor 120 and the stator 110. The non-uniform air-gap makes the air-gap MMF distribution closely sinusoidal and hence further making the back EMF waveform more sinusoidal. In an embodiment of the invention, each of the depressions 134 is adjacent to the second end 126A”,126B”,130A”’,130B” of each flux barrier 126A,126B,130A,130B. In an embodiment of the invention, each pole 122 has four depressions corresponding to the second ends 126A”,126B” of two flux barriers 126A,126B in connection with the first set 124 of two magnets 124A,124B, and the second ends 130A”’,130B” of two flux barriers 130A,130B in connection with the second end 128A” of one magnet 128A.

[033] Advantageously, the configuration of the magnets and the flux barriers in the poles of the rotor give rise to a closely sinusoidal back-emf curve, reducing the harmonics and the resultant heat generation, hence allowing for a delta connection to be used in the winding on the stator. A merit of using the delta connection in winding is higher reliability. If one of the three primary windings fails, the secondary will still produce full voltage on all three phases. The only requirement is that the remaining two phases must be able to carry the load. [034] Further, the cogging torque in the present invention is reduced along with the reduction in saliency, thereby reducing the torque ripple, which contributes towards a more sinusoidal back-emf waveform.

[035] Further, due to similar magnets being used in the first set and the second set in the poles, the requirement of manufacturing separate permanent magnets is eliminated, hence reducing the manufacturing and assembly cost. Also, the use of similar magnets in the rotor leads to lamination sheets of the rotor having rotational symmetry, which eases the rotor stacking process as in cases of asymmetric lamination sheet geometry the lamination sheets can be stacked in only one way.

[036] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.