Claims:1. A permanent magnet assisted synchronous motor (100), comprising:
a stator (400) having a predetermined number of toothed stator magnetic pole portions wound by armature coils, and
a rotor (200) rotatably supported at an inner peripheral surface of said stator and having a plurality of flux barriers (104 and 106) defined therein towards an outer circumference of said rotor (200) at predetermined locations.
wherein,
said plurality of flux barriers (104 and 106) are at least rectangular flux barriers which are non-parallel and inclined at an angle to a d-axis and a q-axis.

2. A rotor (200) for a permanent magnet assisted synchronous motor (100), said rotor (200) formed by stacking a plurality of rotor laminations (300), said rotor lamination (300) comprising:
a plurality of flux barriers (104 and 106) defined therein towards an outer circumference of said rotor lamination (300) at predetermined locations, said plurality of flux barriers include:
at least one first flux barrier (104) having at least two rectangular slots (104r) which are disposed at an angle to each other and extend in a radial direction of said rotor lamination (300); and
at least one second flux barrier (106) having a plurality of rectangular slots(106r) defined in a partially curved shape (or convex shaped)toward a center rotation axis of said rotor lamination (300),
wherein,
said first flux barriers (104) and said second flux barriers (106) are mutually spaced out in a circumferential direction; and
said rectangular slots (104r and 106r) are adapted to receive rectangular permanent magnets (108).

3. The rotor (200) of the permanent magnet assisted synchronous motor as claimed in claim 2, wherein said first flux barrier (104) is defined such that said rectangular slots define a V-shape in said radial direction of said rotor (200).

4. The rotor (200) of the permanent magnet assisted synchronous motor as claimed in claim 2, wherein said each rectangular slot (106r) of said second flux barrier (106) is disposed at a predetermined angle to each other such that they form said partially curved shape (or convex shaped).

5. The rotor (200) of the permanent magnet assisted synchronous motor as claimed in claim 2, wherein said rectangular slots (104r) defined in said first flux barrier (104) and said second flux barrier (106) includes a rib(or a collar) (110)provided at both ends of each rectangular permanent magnet (108), said rib (110) is defined such that said rectangular magnet is held at a predetermined location.

6. The rotor (200) of the permanent magnet assisted synchronous motor as claimed in claim 3, wherein said ribs (110) are at least partition members which are provided to define a space between two consecutive rectangular permanent magnets (108).

7. The rotor (200) of the permanent magnet assisted synchronous motor as claimed in claim 3, wherein said each rectangular permanent magnet (108) is made up of at least one of a ferrite magnet and NdFeB magnet with zero rare earth content.

8. The permanent magnet assisted synchronous motor (100) as claimed in claim 1, wherein said motor (100) is at least a synchronous reluctance motor with or without said rectangular permanent magnets (108) being disposed in said first and second flux barriers (104 and 106).

9. The permanent magnet assisted synchronous motor (100) as claimed in claim 1, wherein said motor (100) may be configured to have a predetermined power by one of disposing said rectangular magnets (108) only in said rectangular slots (104r) of said first flux barrier (104), disposing said rectangular magnets (108) only in said rectangular slots (106r) of said second flux barrier (106), disposing said rectangular magnets (108) in said rectangular slots (104r and 106r) at predetermined locations of said first and second flux barriers (104 and 106), disposing said rectangular magnets (108) in all said rectangular slots (104r and 106r) of said first and second flux barriers (104 and 106), and excluding said rectangular magnets (108) in all said rectangular slots (104r and 106r) of said first and second flux barriers (104 and 106).

10. The permanent magnet assisted synchronous motor (100) as claimed in claim 1, wherein said rectangular slots (104r and 106r) includes a predetermined dimension and a number of said rectangular flux barriers disposed circumferentially on said outer circumference of said rotor (200) is selected based on number of poles of permanent magnets.
, Description:TECHNICAL FIELD
[001] The embodiments herein relate to a permanent magnet assisted synchronous motor and its rotor.

BACKGROUND
[002] In recent years, high efficiency electric motors have become desirable to meet the challenges of providing power without the usage of fossil fuel sources, for example in hybrid and electric vehicles. Interior permanent magnet (IPM) motors have become popular due to their high efficiency performance, as an IPM is an increasingly efficient synchronous motor due to advances in high-energy permanent magnet technology, smart inverters, and digital controllers.
[003] IPM electric machines have magnets built into the interior of the rotor, and each magnetic pole on the rotor is conventionally created by putting permanent magnet material into slots formed in the laminated stack of the rotor. Such slots are typically not completely filled with magnetic material, instead being designed to hold a magnet in the center with voids at two opposite ends of the slot. The rotor is rotatable within a stator which includes multiple windings to produce a rotating magnetic field in the frame of reference of the stator.
[004] Among known conventional synchronous electric motors are a permanent magnet synchronous electric motor (PMSM), which includes a permanent magnet in a rotor; a synchronous electric motor which includes field coils in a rotor (FCSM: Field Coil Synchronous Motor) and a reluctance motor (RM), which includes magnetic salient poles in a rotor.
[005] A synchronous motor has a stator and a rotor supported in the inner periphery of the stator and is capable of being locally exciting, being structurally the same as the stator of a common induction motor. Generally, the synchronous reluctance motor is well known as a motor which is simply structured so as to not need electric current channels and permanent magnets in the rotor.
[006] Presently, synchronous reluctance motors having a good power factor and efficiency by a structurally improved rotor are well known. A known art discloses a permanent-magnetic motor additionally generating a reluctance torque by using a synchronous reluctance motor to generate a rotational torque is proposed. In other words, the above permanent-magnetic motor can be regarded as the synchronous reluctance motor generating the rotational torque by mainly permanent magnets. This synchronous reluctance motor (the disclosed permanent-magnetic motor) has a rotor having some pairs of slots that are formed approximately parallel to each other in the circumferential direction of the rotor. The slots are extended adjacent to the outer peripheral surface of the rotor, and the permanent magnets are secured in the pairs of slots.
[007] The synchronous reluctance motor is designed with the aim of generating a larger torque and higher power by using reluctance torque. The reluctance torque is generated by a difference between the inductance Ld of the rotor in a d-axis direction (defined by connecting a center-point of the permanent magnet in circumferential direction of the rotor with a rotational center of the rotor), and an induction Lq of the rotor in a q-axis direction (defined as a direction rotated relative to the d-axis direction by 90 electrical degrees).
[008] As described above, this synchronous reluctance motor is aimed to use the reluctance torque. In the rotor of this synchronous reluctance motor, portions of the rotor defined between the permanent magnets neighboring each other in the circumferential direction (or distance S defined between the permanent magnets neighboring each other in the circumferential direction) are determined to be as small or narrow as possible. To the contrary, the permanent magnets are designed to be as large in size as possible so that the magnetic flux will not leak outside of the distance S, and for efficiently using the magnet torque.
[009] In this synchronous reluctance motor, the inductance Lq should be large, while the inductance Ld should be small for generating the reluctance torque. Only for determining the inductances Ld and Lq as above, the distance S should be determined to be large or wide. Because the inductance Lq is increased due to the increased gap S, the inductance Ld is not so increased that the magnetic circuit connecting magnetic pole portions of the stator is formed in the rotor. If the reluctance torque is increased relative to the total torque generated by the synchronous reluctance motor, a torque ripple may occur. To reduce the torque ripple, a plurality of permanent magnets needs to be disposed in the radial direction of the rotor, but then, for example, the manufacturing cost of the rotor will be increased.
[0010] Therefore, there exists a need for a permanent magnet assisted synchronous motor and its rotor, which obviates the aforementioned drawbacks.
OBJECTS
[0011] The principal object of embodiments herein is to provide a permanent magnet assisted synchronous motor and its rotor.
[0012] Another object of the present invention is to provide the permanent magnet assisted synchronous motor which is aimed at reducing a ripple torque while also improving a reluctance torque.
[0013] Yet another object of the present invention is to provide the permanent magnet assisted synchronous motor which includes a plurality of rectangular flux barriers which are adapted to receive rectangular magnets whereby enabling easy manufacturing of the synchronous motor.
[0014] Yet another object of the present invention is to provide the permanent magnet assisted synchronous motor which includes rectangular flux barriers that are non-parallel and inclined at an angle to a d-axis and a q-axis.
[0015] Another object of the present invention is to provide the permanent magnet assisted synchronous motor which facilitates in torque enhancement by utilizing NdFeB magnets or ferrite magnets with zero rare earth content where the torque demand is not very high.
[0016] These and other objects of embodiments herein will be better appreciated and understood when considered in conjunction with following description and accompanying drawings. It should be understood, however, that the following descriptions, while indicating embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.

BRIEF DESCRIPTION OF DRAWINGS
[0017] The embodiments are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0018] Fig. 1 depicts a schematic view of a lamination of a rotor of a permanent magnet assisted synchronous motor, according to embodiments as disclosed herein.
[0019] Figs. 2a-2d depicts different locations of magnet placed in flux barriers of the rotor of the permanent magnet assisted synchronous motor, according to embodiments as disclosed herein.
[0020] Fig.3. depicts a torque map as a function of d-axis and q-axis current, according to embodiments as disclosed herein;
[0021] Fig. 4 depicts a torque map as a function of d-axis and q-axis current, according to embodiments as disclosed herein; and
[0022] Fig. 5 depicts a sectional view of the permanent magnet assisted synchronous motor, according to embodiments as disclosed herein.

 
DETAILED DESCRIPTION
[0023] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed 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.
[0024] The embodiments herein achieve a permanent magnet assisted synchronous motor and its rotor. Further, the embodiments herein achieve the permanent magnet assisted synchronous motor which is aimed at reducing a ripple torque while also improving a reluctance torque. Furthermore, the embodiments herein achieve the permanent magnet assisted synchronous motor which includes a plurality of rectangular flux barriers which are adapted to receive rectangular magnets whereby enabling easy manufacturing of the synchronous motor. Additionally, the embodiments herein achieve the permanent magnet assisted synchronous motor which includes rectangular flux barriers that are non-parallel and inclined at an angle to the d-axis and q-axis. Moreover, the embodiments herein achieve the permanent magnet assisted synchronous motor which facilitates in torque enhancement by utilizing NdFeB magnets or ferrite magnets with zero rare earth content where the torque demand is not very high. Referring now to the drawings, particularly through Figs 1 to 5, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.
[0025] For the purpose of this description and ease of understanding, the rotor (200) is explained herein with below reference to permanent magnet assisted synchronous motor (100) (also referred to as synchronous reluctance motor or motor in this description). However, it is also within the scope of the invention to practice and/or use the rotor (200) in internal permanent magnet motor or any other similar motor, without otherwise deterring the intended function of the rotor (200) as can be deduced from the description and corresponding drawings.
[0026] The motor (100) has a stator (400) having stator magnetic pole portions (not shown), and the rotor (200) having plurality of flux barriers, as shown in FIG. 1. The stator (400) has a predetermined number of teeth (402) (as shown in Fig. 5) arranged towards an outer periphery of the rotor (200). Each tooth (402) is wound by armature coils (not shown) to be the stator magnetic pole portion. The stator (400) supports the rotor (200) on its inner peripheral side.
[0027] Fig. 1 depicts a schematic view of a lamination of a rotor (200) of a permanent magnet assisted synchronous motor, according to embodiments as disclosed herein. The permanent magnet assisted synchronous motor (100) includes the rotor (200) which is formed by stacking a plurality of rotor laminations (300). A lamination (300) of the rotor is depicted in Fig. 1. The rotor (200) of the motor (100) includes a plurality of flux barriers (102) defined therein towards an outer circumference of the rotor (200). The flux barriers (102) are defined at predetermined locations i.e. at regular intervals of the rotor (200) outer circumference. In an embodiment, the plurality of flux barriers (102) which are at least rectangular flux barriers are non-parallel and inclined at an angle to a d-axis and a q-axis. In an embodiment, the angle may be varied w.r.t the d-axis and the q-axis. For the purpose of this description and ease of understanding, the d-axis and the q-axis referred herein are conventional d-axis and q-axis of the permanent magnet synchronous motor i.e., the d-axis is defined as the axis from where the magnetic flux from magnets converges and enters/leaves an air-gap and the q-axis is defined as the axis that is devoid of magnetic flux.
[0028] Further, the plurality of flux barriers (102) includes at least one first flux barrier (104) and at least one second flux barrier (106). In an embodiment, the first flux barrier (104) defines at least two rectangular slots (104r) which are disposed at an angle to each other i.e., the first flux barrier (104) is defined such that said rectangular slots (104r) define a V-shape and extend in a radial direction of the rotor lamination (300). Furthermore, the second flux barrier (106) defines a plurality of rectangular slots (106r) which are defined in a partially curved shape (or convex shaped) toward a center rotation axis of the rotor lamination (300) i.e., each rectangular slot of the second flux barrier (106) is disposed at a predetermined angle to each other such that they form the partially curved shape (or convex shaped) combinedly. The first flux barrier (104) and the second flux barrier (106) are mutually spaced out in a circumferential direction of the rotor lamination (300). The rectangular slots (104r and 106r) are adapted to receive rectangular permanent magnets (108).
[0029] The rotor (200) of the motor (100) further includes a plurality of ribs (or a collar) (110) which are provided at both ends of each rectangular permanent magnet (108). The ribs (110) are defined such that the rectangular magnets (108) are held at a predetermined location in the rectangular slots. In an embodiment, the plurality of ribs (110) are at least partition members which are provided to define a space between two consecutive rectangular permanent magnets (108). The rectangular slots (108) include a predetermined dimension and a number of the rectangular flux barriers which are disposed circumferentially on the outer circumference of the rotor (200). The number of flux barriers in the rotor (200) is selected based on number of poles of permanent magnets.
[0030] The rectangular slots (104r and 106r) of the rotor (200) is adapted to receive the rectangular permanent magnet (108) which is at least one of ferrite magnet and NdFeB magnet with zero rare earth content thereby achieving a torque enhancement.
[0031] In an embodiment, the motor (100) is at least a synchronous reluctance motor which may be used with or without the rectangular permanent magnets (108) being disposed in the first and second flux barriers (104 and 106). Further, the motor (100) may be configured to have a predetermined power by one of disposing the rectangular magnets (108) only in the rectangular slots (104r) of the first flux barrier (104), disposing the rectangular magnets (108) only in the rectangular slots (106r) of the second flux barrier (106), disposing the rectangular magnets (108) in the rectangular slots (104r and 106r) at predetermined locations of the first and second flux barriers (104 and 106), disposing the rectangular magnets (108) in all rectangular slots (104r and 106r) of the first and second flux barriers (104 and 106), and excluding the rectangular magnets (108) in all the rectangular slots (104r and 106r) of the first and second flux barriers (104 and 106) as shown in Figs 2a-2d.
[0032] Fig.3. depicts a torque map as a function of d-axis and q-axis current, according to embodiments as disclosed herein. Fig. 4 depicts a torque map as a function of d-axis and q-axis current, according to embodiments as disclosed herein. Fig .3 shows the torque developed by the rotor if all the rectangular magnets (108) included in the rotor (200) are ferrite magnets. For example, as shown in fig 2a when all the rectangular slots rectangular slots (104r and 106r) are filled with the ferrite magnets, the torque developed by the motor (100) for the corresponding configuration is depicted in Fig. 3. Similarly, when the rotor (200) is filled by four NdFeB magnets as shown in Fig. 2b, the torque developed by the motor (100) for corresponding configuration is depicted in Fig. 4.
[0033] The technical advantages disclosed by the embodiments herein include reduced ripple torque and improved reluctance torque, improved average torque using permanent magnets containing zero rare earth elements, and enabling easy manufacture using rectangular magnets.
[0034] 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 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 embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications within the spirit and scope of the embodiments as described herein.