FORM-2
THE PATENT ACT
(39 of 1970) &
THE PATENTS RULES, 2003 COMPLETE SPECIFICATION
(see section 10 and rule 13)
ROTOR STRUCTURES FOR PERMANENT MAGNET SYNCHRONOUS MOTOR
COLLEGE OF ENGINEERING, PUNE
an Indian Organization
of Wellesly Road, Shivaji Nagar,
Pune - 411005, Maharashtra, India
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE
MANNER IN WHICH IT IS TO BE PERFORMED.

FIELD OF DISCLOSURE
The present disclosure relates to rotor structure of permanent magnet motors. In particular, it relates to the placement of the magnets into the rotor in order to obtain maximum advantages and better performance from such magnet arrangement.
BACKGROUND OF THE DISCLOSURE
Line-start permanent magnet synchronous motor (LSPMSM) are described in the prior art for on-line applications. Such a motor is a hybrid motor having its stator structure substantially the same as that of an induction motor. However, its rotor structure is a combination of squirrel cage and permanent magnet structure in the rotor. When the stator of the LSPMSM is connected to the power source, a rotating magnetic field is generated by the stator and an induction current is induced in the rotor cage bars. Consequently, the LSPMSM is started by a starting torque generated by this induction current until the rotating speed of the rotor reaches a synchronous speed and then the rotor cage bar current vanishes. At this moment, the torque is produced by the interaction of the magnetic field generated by the permanent magnet.
TECHNICAL PROBLEM
In recent times, the LSPMSM can attain a very 'high operational efficiency' with the constant development of improved materials of the permanent magnet and 'magnetic energy product'. During the start-up period (i.e. the acceleration from zero speed to the synchronous speed), the motor also develops a braking torque because of the interaction of the magnetic field generated by the magnets on the rotor and stator winding, which behaves as a short circuit cage winding.

The presence of this speed dependent braking torque having maximum braking at 10 to 15% of the synchronous speed makes the rotor design very complicated. Therefore, the designer has to always make a suitable compromise between the starting performance and the steady state performance for this type of motor. For such machines, various types of magnet arrangements have been explored in the prior art. Several magnet arrangements have been proposed earlier both in the reviewed literature and several published patents. The common arrangements preferred for this type of machine are - circumferentially magnetized rotor or radially magnetized rotor. Some prior disclosures have also proposed a combination of these two types.
PRIOR ARTS
The most widely used circumferentially magnetized or spoke type rotor employs the flux squeezing principle. In such rotors, it is always possible to attain air gap flux density values higher than those present within the magnet.
The most rugged rotor structure is the embedded type radially magnetized rotor, which is widely preferred following the spoke type rotor mentioned above. This offers highest reliability, however needs single piece lamination. The fabrication of this type of rotor is quite difficult and thus costly too, because special stampings need to be punched for this rotor configuration.
Other rotor structures are proposed in the literature to combine the advantages of these two basic geometries. Some focus on combining the advantages, making larger room for magnets inside the rotor, while some others focus on the suitability for a 2- pole machine. Few attempted to shape the rotor such that more sinusoidal air gap flux density is obtained, while few others focus on reducing the flux leakage.

Some of the examples of the prior art documents are briefly discussed below:
US 7902713 B2 discloses a self-starting type permanent magnet synchronized induction motor, which comprises a stator, a rotor having a rotor core with a plurality of slots provided in an outer periphery thereof and a cage winding comprising conductive bars embedded in these slots and conductive end rings that short-circuit the conductive bars on both end faces of the bars in an axial direction thereof.
The rotor core comprises at least one magnet insertion hole arranged on an inner peripheral side from the slots, and at least one permanent magnet embedded in at least one magnet insertion hole. When a pole center axis is denoted as d-axis and an axis deviating from the pole center axis by an angle 90° is denoted as q-axis, the amount of flux generated by the cage winding during start-up period becomes maximal in the vicinity of and at one of the d- and q-axis.
US 2010/0133941 Al discloses Permanent-Magnet (PM) Rotors and Systems, which includes a line-start permanent-magnet (LSPM) rotors, rotor components, and machines using these LSPM rotors, wherein the PM rotors have PM bulks in W-like shapes, vent openings between PM bulks, and/or air gaps at the ends of PM bulks in W-like shapes.
US 2008/0272667 Al discloses an interior permanent magnet motor and rotor, wherein an electric machine includes a stator and a rotor core positioned adjacent to the stator and which is rotatable about a longitudinal axis. The rotor core includes a plurality of bar apertures, a plurality of elongated flux barriers separate from the bar apertures and positioned radially inward of the bar apertures, and a plurality of magnet slots separate from the bar slots and positioned radially inward of a portion of the bar apertures. The electric machine also includes a plurality of magnets, each positioned in one of the magnet slots. A plurality of conductive bars

are each positioned in one of the bar apertures and includes a first end and a second end. A first end ring is coupled to the first end of each of the bars and a second end ring is coupled to the second end of each of the bars.
US 7372183 B2 discloses a permanent magnet type synchronized motor, which includes a stator, a rotor and permanent magnets. The rotor includes a rotor iron core that is rotatable relative to the stator, and conductor bars are accommodated within corresponding slots in the rotor iron core. The conductor bars have their opposite ends short-circuited by the respective short circuit rings to form a starter cage conductor. The rotor also has a plurality of magnet retaining holes defined therein, in which permanent magnets are embedded. The conductor bar holes are positioned in an axial direction and inwardly from the magnet retaining holes. The conductor bars within the holes protrude outwardly from an axial end of the rotor iron core to form projections for securing an end plate to the end of the rotor iron core, the end plate is made of a non-magnetizable material.
US 7247965 B2 discloses a rotor for an electric motor. It relates to a rotor for an electric motor, especially an electric line-start motor, comprising spaces 4 to 7 which receive permanent magnets 10 to 13 and extend in an axial direction, and spaces 20 to 25 that accommodate conductor rods and extend in an axial direction. In order for the rotor to run as regularly as possible, the spaces 20 to 25 accommodating the conductor rods are provided with a substantially elongate cross-section in at least one sector of the rotor while being embodied in a curved manner along the longitudinal axis thereof in said sector, when viewed from a cross-sectional perspective.
US 2007/0138894 Al discloses rotor assembly for use in line-start permanent magnet synchronous motor, which includes a rotor core having a central portion and a circumferential portion, wherein a shaft hole is formed at the central portion,

and a plurality of conductors are arranged along the circumferential portion; a multiplicity of permanent magnets are provided at a portion of the rotor core around the shaft hole; and at least one first ripple-reduction conductor is formed at a polar switchover region of the rotor core, the polar switchover region being positioned between two opposite poles of two adjacent permanent magnets, so that a polar switchover of an induction voltage induced in the rotor core, is alleviated to reduce a torque ripple phenomenon.
US 2005/0023923 Al discloses a line-start permanent magnet (LSPM) synchronous motor including a shaft, four fan-shaped magnetic poles each having a first eccentric circular arcs of the surface of the magnetic poles which has a center 01 that is offset from the center O of the rotor with an offset length OS1 and which makes the maximum thickness of the air gap roughly two to five times as much as the minimum thickness of the air gap, four permanent magnets disposed in the inner loop of each of the fan-shaped magnetic poles, a plurality of pear-shaped conductor slots disposed in equal spaces in the outer loop of the rotor in each of the fan-shaped magnetic poles and oriented in a radial direction having 01 as the center for forming a squirrel cage winding and having four recesses at the midpoint of the first eccentric circular arcs of the surface of the magnetic poles in each of the fan-shaped magnetic poles.
US 5952757 A discloses a line-start permanent magnet motor, which is an electric motor including a stator having a stator core, a start winding and first and second main windings. The first main winding and the start winding are configured to form a lower number of poles than the second main windings. The stator core forms a stator bore. The motor also includes a rotor having a rotor shaft concentrically arranged axially of the stator core and a rotor core positioned concentrically with the rotor shaft. Secondary conductors are arranged axially with respect to the rotor shaft and extend through the rotor core. A plurality of

permanent magnets are located on the outer periphery of the rotor core and magnetized to form a number of poles equal to the number of poles formed by the second main winding.
US 5097166 A discloses a high-speed rotor for an AC permanent magnet synchronous motor including a stack of magnetically permeable rotor laminations. Each rotor lamination comprises a plurality of conductive bar slots for holding a stator winding and having openings facing outside for minimizing the flux leakage from the rotational magnetic field produced by primary windings on the stator, and having magnet slots for holding permanent magnets in order to produce an even number of magnetic poles on the periphery of the rotor. The lamination further includes a plurality of flux barrier slots connected to the magnet slots for minimizing the flux leakage from the permanent magnets and for forming bridges in a ring configuration between the conductive bar slots and the barrier slots, so that the integrality of the lamination is very much enhanced, while minimizing the power loss.
US 4922152 A discloses a rotor lamination for a permanent magnet synchronous machine. This rotor lamination can be used for a two, four or eight pole synchronous machine. The orientation of the permanent magnets determines the number of poles of the machine. The lamination can also include openings adapted to contain conductors used to bring a synchronous motor up to synchronous speed as an induction motor.
US 4748359 A discloses a permanent magnet rotor, wherein the rotary shaft has an orthogonal cross-sectional shape orthogonal in a longitudinal direction of the rotary shaft, a plurality of circular-arc portions which are disposed around the axis of rotation of the rotary shaft, and rectilinear portions which connect the adjacent circular-arc portions with straight lines and having no curved portion. Respective

permanent magnets, equal in number to the circular-arc portions, are fixed to be extending over the circular-arc portions and the rectilinear portions. The surface of each permanent magnet, disposed remote from the rotary shaft, has a cross-sectional contour orthogonal to the longitudinal direction of the rotary shaft, thus forming a circular arc which protrudes outward.
US 4139790 A discloses a permanent magnet rotor for a permanent magnet synchronously driven induction-state motor. This rotor has rare-earth magnets disposed in apertures in unitary laminations and disposed parallel to a tangent to the shaft. The magnets are magnetized outwardly, so that the direct flux of the magnets is additive to the direct axis flux of the stator at no load condition. The rotor has a squirrel cage winding and the ends of each magnet aperture are in communication through a flux barrier space to the inner end of an adjacent conductor bar aperture of the squirrel cage winding. The unitary laminations each have an even number of plurality of radially directed reinforcing ribs disposed along the magnetic neutral axes. The flux barriers are wide relative to the circumferential width of the reinforcing ribs for a minimum of circumferential leakage flux. The leakage flux from one magnet radially through a rib is in opposition to the leakage flux through a rib from the adjacent magnet for obtaining substantially zero net leakage flux therein.
Taiwanese patent TW 371126 discloses an improved structure for the roller of the synchronous machine of everlasting magnetic induction.
Taiwanese patent TW 363843 also discloses an improved structure for rotor of permanent magnet type induction synchronization machine.
US 2002/0084710 Al discloses a structure including a stator with a rotor journalled within the stator for rotation about an axis. The rotor includes a body of

ferromagnetic material having a nominally cylindrical peripheral surface concentric with respect to the axis. Permanent magnets are located on this peripheral surface in order to define equally angularly spaced magnetic poles, with one of the alternating poles being of opposite polarity. A thin, hollow cylinder formed of a good electrically conducting material is disposed on the body to sandwich the magnets against the peripheral surface of the body and provides a site for generating the localized induced electrical current, which generates magnetic fields that react with rotating magnetic fields in the stator in order to start the motor from a dead stop without the need for position sensors or control electronics.
US 4403161 discloses a permanent magnet rotor used in a synchronous motor or the like, comprising a shaft, an iron core and permanent magnets. Each of the permanent magnets mounted on the hollow rotor core has an arc shape, and the radial center of the arc shape is positioned on the axis of the shaft or at a point slightly deviated from this shaft axis.
DISCLOSURE
None of the prior art documents discussed above are suitable for a rotor structure of a line-start permanent magnet synchronous motor, which can increase the steady state performance of the motor without compromising on the desired starting performance of the same.
The disclosure proposes a combination of the circumferentially magnetized and radially magnetized rotor structures for an electrical machine, with the concept of induced poles, thereby reducing the number of magnets and indirectly magnet volume required. The present disclosure also proposes a combination of rectangular and arc types of magnets.

The present disclosure is suitable for an electrical machine which has self-starting capability and which is a combination of an induction motor and a synchronous motor. This type of motor starts as an induction motor directly on-line, because of the starting capability of the machine by the presence of a cage winding on the rotor. This motor reaches close to synchronous speed and because of the electromagnetic interaction between the stator and rotor; the rotor gets locked into the synchronous speed and runs as a synchronous motor during the steady state. The cage winding comes into picture during transients or dynamic conditions.
The present disclosure is also suitable for an electrical machine which is supplied via suitable power electronics converter in order to suit a particular system or application. The present disclosure is suitable both for the laminated and solid type of rotors.
The rotor structure in accordance with the present disclosure can be used for any type of permanent magnet machine, i.e. both inverter driven or self-start (line-start) types of machines. It can also be used for any power rating, for any duty of operation and for any type of back emf waveform (e.g. square, trapezoidal or sinusoidal or any combination of these waveforms).
Such a rotor can further be used for any type of power source (e.g. variable frequency drive, DC, battery, solar, or any combination of these power sources). The rotor of this type can also have any number of phases (e.g. it can be for a single, double or poly-phase motor). It can have any number of rotor poles and can be made of any type of permanent magnet material (e.g. ferrite, rare-earth, alnico or any combination of these).
The disclosure is also suitable for any type of magnetic material used for stator and rotor cores, for any number and shape of rotor slots and for any combination

of rotor and stator slots. It is further useful for normal cage, deep cage bar, double cage or any type of cage winding of the induction motors of the prior arts.
In accordance with the present disclosure, the air gap flux density is improved by adjusting the arc magnet length to be slightly more at the arc center. By this provision, the radial component of air gap flux density at the midway of the pole region is increased. This further increases the induced emf under no-load condition.
The present disclosure provides magnet arrangements, both for the directly driven on-line permanent magnet synchronous motor and for the electronically driven permanent magnet synchronous motor [either BLDC or PMSM as referred to in the available literature]. Both these arrangements are shown in Figures 3 and 4 of the accompanying drawings.
The present disclosure provides the same rotor lamination for 'N' and 62N' pole machines merely by changing the direction of magnetization of the magnets placed in the rotor, as shown in Figure 5. Further, a 4- pole permanent magnet rotor for single or poly-phase machine is shown in Figure 3. By changing the direction of magnetization for magnets S2, S3 and Al, or replacing SI, S2, S3, S4 with non magnetic material and reversing magnetization of Al. The same rotor can be used as a two- pole rotor for a 2- pole single or poly-phase machine.
The present disclosure can also be used for retrofitting of the conventional induction machine to a synchronous machine, using the same stator as well as the same rotor laminations and the same components in the same frame size.

OBJECTS OF THE DISCLOSURE
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to provide a rotor structure of a permanent magnet synchronous motor that aims to increase the steady state performance without any compromise in its starting performance.
A further object of the present disclosure is to combine the advantages of the aforesaid highly preferred circumferentially magnetized or spoke type rotor and the embedded type or radially magnetized rotor.
Another object of the present disclosure is to reduce the number of magnets and to eliminate the need of a non-magnetic shaft or non-magnetic sleeve.
Yet another object of the present disclosure is to increase the open circuit air gap flux density for a given magnet volume and to shape air gap flux density in a sinusoidal fashion.
Still further object of the present disclosure is to place the magnets in the rotor (near to the rotor surface) in such a manner that maximum advantages and better performance are obtained.
Yet another object of the present disclosure is to achieve an improved efficiency, power factor, torque to weight ratio, torque to volume ratio.
Yet further object of the present disclosure is to obtain a reduced line current and an increased pull-out torque of the motor.

A yet further object of the present disclosure is to achieve a good stability and obtain a low load angle of the motor.
SUMMARY
In accordance with the present disclosure, a magnet arrangement for a rotor of a permanent magnet motor, the rotor comprising two pairs of radially aligned extended rotor slots subtending an angle at the center of a shaft of the motor; said arrangement is characterized by:
* two pairs of circumferentially magnetized magnets having a proximal end and a
distal end from the shaft of the motor, each of said magnets being placed in the
extended rotor slot at a pre-determined distance from the periphery of the rotor;
and
• a connecting magnet placed in close proximity to each of said pairs and spaced
apart from the shaft of the motor; each of said connecting magnets being
adapted to extend between the proximal ends of said magnets of each of said
pairs.
Typically, the circumferentially magnetized magnets completely cover the rotor slot.
Typically, the circumferentially magnetized magnets partially cover the rotor slot.
Typically, the circumferentially magnetized magnets are rectangular.
Typically, the circumferentially magnetized magnets are stepped magnets.
Typically, each of said connecting magnets is an arcuate magnet.

Typically, each of said connecting magnets has varying thickness.
Typically, the circumferentially magnetized magnets are made of permanent magnetic material.
Typically, each of said circumferentially magnetized magnets is made of at least one magnetic material selected from the group consisting of ferrite, rare earth and alnico or a combination thereof.
Typically, the circumferentially magnetized magnets are made of at least one of bonded and sintered material.
Typically, at least one of the subtended angles is not equal to 90 degrees.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present disclosure will now be described with reference to the non-limiting, accompanying drawings, in which:
Figure 1 - illustrates a circumferentially magnetized or spoke type rotor,
Figures 2a, 2b -illustrate an embedded type of radially magnetized rotor,
Figure 3 - illustrates a magnet arrangement on a rotor in accordance with the
present disclosure, using four magnets which are circumferentially magnetized and respectively placed in four extended rotor slots, and this rotor is deployed for direct on line type permanent magnet synchronous motor,

Figure 4 - illustrates another magnet arrangement on a rotor in accordance
with the present disclosure, deployed for electronically driven permanent magnet synchronous motor,
Figure 5 - illustrates that by changing the direction of magnetization of
magnets placed in the rotor, the same rotor lamination can be used for 'N' pole and '2N' pole machine,
Figure 6 - illustrates two arc magnets have a varying thickness as against the
constant thickness shown in Figure 3,
Figure 7 - illustrates two arc magnets in a layered configuration,
Figure 8 - illustrates a combination of magnetic materials used for making
the hybrid permanent magnet rotor, and
Figure 9 - illustrates different types of rotor cage bars used in different parts
of the same rotor.
DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present disclosure will now be described with reference to the accompanying drawings which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples

used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
The description herein after, of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Figure 1 shows a conventional circumferentially magnetized or spoke type rotor which is most widely and employs the flux squeezing principle. In such rotors, it is always possible to attain air gap flux density values higher than those present within the magnet. This machine has inverse saliency like inset magnet type rotor, because of the different reluctance observed in'd' and 'q' axes. However, this rotor needs a non-magnetic shaft to reduce rotor leakage flux. This requirement of non-magnetic shaft is dispensed with, if a non-magnetic sleeve is fixed over the magnetic shaft. But, it has become a common practice to use a non-magnetic shaft for this type of rotor.
Figures 2a, 2b show the conventional embedded type of radially magnetized rotor having the most rugged structure and which is widely preferred next to the spoke

type rotor shown in Figure 2. This embedded type of rotor offers highest reliability, but needs a single piece lamination. The fabrication of this type of rotor is difficult and costly, because special stampings need to be punched for this type of rotor. In this configuration, two magnets come in series to magnetize one single iron pole. This increase in thickness reduces the effect of the armature reaction of 'd' axis. This type of rotor has highest saliency, thus the contribution of reluctance torque component is the highest. The maximum torque for this machine is higher for this type of machine for same magnetic loading. However, the air gap flux density value for this type of arrangement is low even when compared with the conventional induction motor or synchronous motor.
Figure 3 shows a magnet arrangement in accordance with the present disclosure, for direct on line type permanent magnet motor having four pole permanent magnet rotor for single or poly-phase machine. This magnet arrangement uses four circumferentially magnetized magnets. These magnets are placed in a respective extended slot on the rotor. These magnets may be placed at an angle 0A, which is variable. These magnets shown in Figure 3 are rectangular in shape, however, can also be configured in other shapes for improving the air gap flux density profiles specific to different applications. The rectangular magnets used here have the main dimensions LI and Wl and they can be suitably placed in respective four slots of the rotor, either fully or partially covering the rotor slots. These magnets are disposed at any distance Dl from the periphery of the rotor.
At the bottom or near their inner ends, two arc magnets Al and A2 are disposed in a particular direction of magnetization for strengthening the air gap magnetic field. The arc magnets Al and A2 may be disposed at any length D2 from the shaft. They may or may not be placed touching the circumferentially magnetized magnets. The angle 0B may or may not be equal to 0A. Therefore, by virtue of

these arc magnets, the requirement of non-magnetic shaft or non-magnetic sleeve is dispensed with.
These arc magnets may have a constant thickness from point PI to P2, as shown in Figure 3 or may have a varying thickness, as shown in Figure 6 described below. These arc magnets can also be replaced by rectangular magnets or even by stepped magnets. A suitable combination of magnet pieces in single or multiple layers can be used for these arc magnets Al and A2.
Figure 4 illustrates another magnet arrangement on a rotor in accordance with the present disclosure, however deployed for electronically driven permanent magnet synchronous motor.
Figure 5 shows that in accordance with the present disclosure, the same rotor lamination can be used for 'N' pole and '2N' pole machine merely by changing the direction of magnetization of magnets placed in the rotor. Therefore, by changing the direction of magnetization for magnets S2, S3 and Al, the same rotor can be used as a 2 pole rotor for a 2- pole single or poly-phase machine.
Figure 6 shows an enlarged view of the magnet arrangement on the rotor in accordance with the present disclosure, wherein the arc magnet Al has a varying thickness, which increases from the ends adjacent magnets S2 and S3 and is maximum at the middle portion thereof. This thickness profile may also be sinusoidal in shape to obtain desired air gap flux density, or it could be achieved economically by using multi-stepped/multilayered magnet arrangements, as shown in Figure 7 described below.
Figure 7 shows a magnet arrangement in accordance with the present disclosure, wherein a layered arrangement is used for arc magnets.

Figure 8 shows a magnet arrangement using a combination of magnetic materials, e.g. ferrite (F) for rectangular magnets and rare-earth (RE) for the arc magnets. This could also be reversed, i.e. the rectangular magnets could be made of rare-earth material and the arc magnets may be made of ferrite. However, all the magnets can also be made of the same material, i.e. ferrite, rare-earth or alnico and can be either bonded or sintered.
Figure 9 shows a rotor which employs different types of cage bars for different parts thereof. Regions 1 and 3 defined by the areas enclosed by the magnets, can have single cage arrangement having any conventional shape, while the regions 2 and 4 can have double cage arrangement because of more space being available there. This enhances the starting as well as dynamic performance of the machine. It also improves the synchronizing performance. Further, this configuration improves the stability of the machine because of the availability of more damping torque. However, a deep bar arrangement is also possible in these regions instead of the conventional double cage arrangement. Any prior art double cage arrangement can be used for these regions.
Accordingly, the examples shown herein should not be construed as limiting the scope of the embodiments of the present disclosure. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt these specific embodiments for various applications, without departing from the basic concept of the present disclosure. Therefore, such adaptations and modifications should be and are intended to be comprehended within the meaning and scope of the possible equivalents of the embodiments disclosed here. It is to be understood that the phraseology or terminology employed herein is used merely for the purpose of description of the present disclosure and cannot be construed to be a limitation thereof. Therefore, while the

embodiments herein have been described in terms of preferred embodiments, the person/s skilled in the art would be able to recognize that the embodiments disclosed herein can be practiced with modification within the spirit and scope of the present disclosure disclosed herein.

WE CLAIM:
1. A magnet arrangement for a rotor of a permanent magnet motor, the rotor
comprising two pairs of radially aligned extended rotor slots subtending an angle
at the center of a shaft of the motor; said arrangement is characterized by:
• two pairs of circumferentially magnetized magnets having a proximal end and a distal end from the shaft of the motor, each of said magnets being placed in the extended rotor slot at a pre-determined distance from the periphery of the rotor; and
• a connecting magnet placed in close proximity to each of said pairs and spaced apart from the shaft of the motor; each of said connecting magnets being adapted to extend between the proximal ends of said magnets of each of said pairs.

2. The magnet arrangement as claimed in claim 1, wherein said circumferentially magnetized magnets completely cover the rotor slot.
3. The magnet arrangement as claimed in claim 1, wherein said circumferentially magnetized magnets partially cover the rotor slot.
4. The magnet arrangement as claimed in claim 1, wherein said circumferentially magnetized magnets are rectangular.
5. The magnet arrangement as claimed in claim 1, wherein said circumferentially magnetized magnets are stepped magnets.

6. The magnet arrangement as claimed in claim 1, wherein each of said connecting magnets is an arcuate magnet.
7. The magnet arrangement as claimed in claim 1, wherein said circumferentially magnetized magnets are suitable for any pole motor with single or double or combined cage bars.
8. The magnet arrangement as claimed in claim 1, wherein each of said circumferentially magnetized magnets is made of at least one magnetic material selected from the group consisting of ferrite, rare earth and alnico or a combination having same or varying thickness thereof.
9. The magnet arrangement as claimed in claim I, wherein said circumferentially magnetized magnets are made of at least one of bonded and sintered material.
10. The magnet arrangement as claimed in claim 1, wherein at least one of the subtended angles is not equal to 90 degrees.