TECHNICAL FIELD

[001] The present invention relates to the field of induction motors, and more particularly to an induction motor with three-phase stator and outer rotor structure for low-power applications such as a ceiling fan, whose speed is controlled by a variable frequency drive with vector control algorithm.

BACKGROUND OF INVENTION

[002] Induction motors (IM) are very much popular in the industry because of their robust and less maintenance required nature. The most commonly available induction motors which is visible in every household and business establishment is a single-phase induction motor which is commonly used in ceiling fans. Because of unavailability of three phase power at the residential areas, single phase permanent capacitor start induction motors were chosen for the ceiling fan application.

[003] The single-phase ceiling fan motor has outer rotor and inner stator structure, where a die casted rotor with aluminum bars and end rings is used to rotate the fan blades to deliver air to the consumer. The main and auxiliary winding in the stator is placed in the slots located in the outer and inner stator periphery respectively. The resulting air gap magnetomotive force (MMF) from the single-phase induction motors is pulsating because they produce two rotating fields due to their winding structure which are of same magnitude but in opposite direction, thus making the motor not self-starting unlike their 3-phase counterparts. That’ s why the capacitor is connected to the inner stator slot periphery to the auxiliary winding to provide the phase split between the main and the auxiliary winding magnetomotive force (MMF) produced in the air gap. Both main and auxiliary winding are connected to the input AC supply.

[004] The winding is done with a tooth coil concentrated winding pattern for both main and auxiliary winding because of their high number of poles. This winding stmcture allows the mass production of these single-phase induction motors because of their low cost and easy manufacturability. Also, this winding structure is easier to rewind in case of any winding damage which may occur due to insulation failure or short-circuit.

[005] Further, the speed of the fan is controlled with the help of the TRIAC (triode for alternating current) based AC voltage controller and resistive based divider. The resistive based divide reduces the efficiency of the whole system because of the additional losses happening in it. While the TRIAC based voltage, controller is smoother and more efficient than the resistive divider still both does not provide an efficient and smooth control for the induction motor throughout its speed range.

[006] However, the single -phase induction motors used for ceiling fans have relatively poor energy efficiency as most of the drawn input power is wasted in losses (copper, iron and harmonics due to the single-phase winding structure the 3 ^rd , 5 ^th and 7 ^th are the dominant harmonics). For instance, the most efficient single-phase induction motor takes above 50 W of input power drawn from the supply to meet its 18-22 W of output power to deliver air flow of 210 CMM or more. A large portion of the input power is wasted in various losses (iron, copper, stray) happening in the motor. Although there have been attempts to modify the structure of the ceiling fan to improve its energy efficiency by reducing the input power below 35 W so as to comply with the criterion set by Bureau of Energy Efficiency (BEE), Government of India (GOI), according to which, in order to deliver an air flow of 210 CMM or above the ceiling fan to be labelled as 5 -star, it should take less than 35 W of input power from the supply. However, most of the existing single-phase induction motors are unable to satisfy the energy limit set by BEE, GOI.

[007] Another type of motor that was designed with the aim to improve the energy efficiency of a ceiling fan was the BLDC motor which is a permanent magnet-based motor. But the complex manufacturing process and high cost of production rendered it unsuitable for low cost ceiling fan application. [008] There is therefore a need for an efficient motor design for low-power applications such as a ceiling fan that can reduce the input power consumption below 35W as set by the BEE, GOI and is also cost-effective.

[009] The information disclosed in this background of the disclosure section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

SUMMARY OF THE INVENTION

[0010] The present disclosure overcomes one or more shortcomings of the prior art and provides additional advantages discussed throughout the present disclosure. Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

[0011] In one non-limiting embodiment of the present disclosure, a three-phase induction motor for optimizing power consumption is disclosed. The three-phase induction motor comprises a stator enclosed in a stator housing. The stator comprises a plurality of stator slots comprising a plurality of outer stator slots located on an outer periphery of the stator and a plurality of inner stator slots located on an inner periphery of the stator. The plurality of outer stator slots have a structure different from the plurality of inner stator slots. The stator further comprises a plurality of inner stator teeth and a plurality of outer stator teeth, wherein each inner stator tooth of the plurality of inner stator teeth separates an adjacent pair of inner stator slots of the plurality of stator slots, and wherein each outer stator tooth of the plurality of outer stator teeth separates an adjacent pair of outer stator slots of the plurality of stator slots. The three-phase induction motor further comprises a rotor placed outside the stator housing. Each of the plurality of inner stator teeth and each of the plurality of outer stator teeth are wound around with a predefined number of turns of a three-phase multi-pole tooth-coil winding in such a manner that the plurality of outer stator teeth are wound in a first direction and the plurality of inner stator teeth are wound in a second direction opposite to the first direction with the three -phases of the three-phase multi-pole tooth-coil winding, and wherein each stator slot houses two-phases of the three-phase multi-pole tooth-coil winding at a given instant of time.

[0012] In one non-limiting embodiment of the present disclosure, a three-phase induction motor for optimizing power consumption is disclosed. The three-phase induction motor comprises a stator enclosed in a stator housing. The stator comprises a plurality of stator slots located on a stator periphery, and a plurality of stator teeth, wherein each stator tooth of the plurality of stator teeth separates an adjacent pair of stator slots of the plurality of stator slots. The three-phase induction motor further comprises a rotor placed outside the stator housing. Each of the plurality of stator teeth is wound around with a predefined number of turns of each phase of a three-phase multi-pole tooth-coil winding in such a manner that each stator slot is divided into at least a top part and a bottom part, and wherein the three-phase multi-pole tooth-coil winding is placed in the top part of a stator slot in a first direction and the three-phase multi-pole tooth-coil winding is placed in the bottom part of the stator slot in a second direction opposite to the first direction, and wherein a coil span of each phase of the three-phase multi-pole tooth coil winding is 120° electrical.

[0013] In one non-limiting embodiment of the present disclosure, a three-phase induction motor for optimizing power consumption is disclosed. The three-phase induction motor comprises a stator enclosed in a stator housing. The stator comprises a plurality of stator slots located on a stator periphery, and a plurality of stator teeth, wherein each stator tooth of the plurality of stator teeth separates an adjacent pair of stator slots of the plurality of stator slots. The three-phase induction motor further comprises a rotor placed outside the stator housing. Each of the plurality of stator teeth is wound around with a predefined number of turns of a three-phase multi-pole tooth-coil winding by dividing each stator slot into at least a top part, a middle part and a bottom part such that each part houses a distinct phase of the three-phase multi-pole tooth coil winding, and wherein one quarter of the plurality of stator teeth are wound around with each phase of the three-phase multi-pole tooth-coil winding in a first direction and another quarter of the plurality of stator teeth are wound around with each phase of the three-phase multi-pole tooth-coil winding in a second direction opposite to the first direction in a cyclic manner. [0014] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCITPION OF DRAWINGS

[0015] The embodiments of the disclosure itself, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings in which:

[0016] Figure 1 depicts a stator housing 100, in accordance with an embodiment of the present disclosure;

[0017] Figure 2 shows the positioning of stator slots in mechanical and electrical domains, in accordance with an embodiment of the present disclosure;

[0018] Figure 3 depicts a three-phase multi -pole tooth-coil winding structure 300 across the stator 102, in accordance with an embodiment of the present disclosure;

[0019] Figure 4 depicts a density plot 400 of 3-phase motor with the all stator slots located on outer periphery of the stator 102, in accordance with an embodiment of the present disclosure;

[0020] Figure 5 depicts the pattern of winding one of the phases of the three-phase winding 500, in accordance with an embodiment of the present disclosure;

[0021] Figure 6 shows a no-load air gap flux density waveform 600 associated with the three- phase 4 pole tooth-coil winding, in accordance with an embodiment of the present disclosure; [0022] Figure 7 shows a no-load per phase back-EMF 700 corresponding to the no-load air gap flux density, in accordance with an embodiment of the present disclosure;

[0023] Figure 8 depicts a modified stator structure 800, in accordance with an embodiment of the present disclosure;

[0024] Figure 9 depicts a three-phase 4-pole concentrated winding pattern 900 for the modified stator structure 800, in accordance with an embodiment of the present disclosure;

[0025] Figure 10 depicts a 120° displaced winding pattern 1000 for the modified stator structure 800, in accordance with an embodiment of the present disclosure; and

[0026] Figure 11 shows multi-stepped winding pattern 1100 for the modified stator structure 800, in accordance with an embodiment of the present disclosure.

[0027] The Figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure.

[0029] The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying Figures. It is to be expressly understood, however, that each of the Figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. [0030] Disclosed herein is an inductor motor with a three-phase stator and outer rotor design with a stator winding pattern that is easily manufacturable, cost-effective and energy efficient for use in low-power applications, especially in ceiling fans. However, it may be noted to a skilled person in art that disclosed inductor motor may be used different low power application also. Generally, the three-phase induction motors are famous because of their robust, self-starting and efficient nature because of the sinusoidally distributed windings used in their stator. However, the existent designs have been used for high power motors, but none have been carried out in low power applications due of the higher copper losses which happen in a concentrated winding motor as compared to the induction motors wound with distributed windings. Further, due to small length to diameter ratio of the motor, the distributed winding loses its benefits because of the difficulty in finding them as they have large overhang as compared to the active copper length present in the machine. Due to this the losses and the copper requirement becomes high. To accommodate this, a higher outer diameter of the stator may be selected which increases the overall outer diameter of the fan and increases the volume of the electrical steel used in the motor, thus making it a costly alternative to present single-phase permanent capacitor-based induction motors available in the market. A major drawback with the existing single -phase induction motor of ceiling fan is low winding factor and air gap flux density chosen for the design which reduces the breakdown torque value. The breakdown torque is directly proportional to the square of back-EMF developed in the motor which in turn depends on the air gap flux density. Increasing the breakdown or pull-out torque of the motor will reduce the operating slip for same load, thus reducing the copper losses in both stator and rotor.

[0031] The present disclosure overcomes this disadvantage in the three-phase induction motor design where the chosen air gap flux density is higher. To do so, an appropriate structure is designed with a 3-phase winding pattern, the details of which are disclosed in the upcoming paragraphs.

[0032] The three-phase induction motor of the present disclosure comprises a stator enclosed within a housing and a rotor placed outside the stator housing. The stator comprises a plurality of stator slots located on its periphery and a plurality of stator teeth such that each stator tooth separates an adjacent pair of stator slots. The rotor comprises a plurality of rotor slots located on its periphery and a plurality of rotor teeth such that each rotor teeth separates an adjacent pair of rotor slots. However, in order to design such a structure, that can accommodate three-phase winding and has high flux density in the air gap while increasing the winding factor, two important factors are taken into consideration which are appropriate tooth width and slot fill factor. Higher air gap flux density means higher tooth- width such that tooth flux density in the stator as well as in rotor remains below 1.6 T. This is to avoid any saturation in the electrical steel which may bring down the air-gap flux density and increase iron losses also in the motor. The tooth saturation also leads to increase in the air-gap space harmonics causing heating, noise and vibration in the machine which are unwanted. Slot fill factor should be below 45% including the slot insulation, wedges and copper conductor (with its overall diameter included containing enameled insulation layer around the bare copper diameter). For any wire gauge, the slot fill factor should not be beyond 45% maximum to ensure easy manufacturability by the automated winding machine which can be done over stator tooth. Taking the above factors in consideration, the arrangement of the plurality of stator slots is modified as depicted in Figure 1.

[0033] Figure 1 depicts a stator 102 within a stator housing 100 having a plurality of stator slots 104, 106 that are divided in a manner such that that a plurality of inner stator slots 106 are located on an inner periphery of the stator 102 and a plurality of outer stator slots 104 are located on the outer periphery of the stator 102. In one embodiment, the plurality of stator slots 104, 106 is twelve and the plurality of stator slots 104, 106 is divided in such a manner that the plurality of inner stator slots 106 is equal to the plurality of outer stator slots 104. Such a division overcomes the difficulty of a distributed winding and avoids any large overhangs.

[0034] Further, Figure 2 shows the position of the plurality of stator slots 104, 106 in mechanical (actual position in space) and in electrical (mechanical angular position multiplied by pole pairs) domains. In accordance with the embodiment depicted in Figure 2, an electrical angular displacement between each adjacent pair of inner stator slots 106 and between each adjacent pair of outer stator slots 104 is 120°. Further, a mechanical angular displacement between each adjacent pair of inner stator slots 106 and between each adjacent pair of outer stator slots 104 is 120° divided by a number of stator pole pairs, wherein a stator pole pair is half of total number of stator poles and an electrical angular displacement between each adjacent pair of inner stator slot 106 and outer stator slot 104 is 60°. Figure 2 also depicts the positioning of the plurality of rotor slots 108 on the periphery of the rotor 110 placed outside the stator housing.

[0035] Further, as shown in Figures 1 and 2, the shape of the plurality of outer stator slots 104 and the shape of the plurality of inner stator slots 106 placed on the outer and inner periphery of the stator respectively are different as to avoid any magnetic saturation by providing large tooth width (which may cause the height of the stator slots to increase thus reducing the inner periphery leading to narrow tooth for the plurality of inner stator slots 106 to be realized). Thus, the plurality of outer stator slots 104 are designed in a broad slot top and bottom with short slot height so that some extra distance is provided for the iron bridge connecting the plurality of inner stator slots 106 and the plurality of outer stator slots 104 so as to avoid the touching of wires between the plurality of inner stator slots 106 and the plurality of outer stator slots 104 while carrying out the winding and also to avoid any saturation in those areas. In accordance with the embodiment depicted in Figures 1 and 2, the plurality of inner stator slots 106 have been designed with greater slot depth and narrow slot bottom as compared to the plurality of outer stator slots 104 to provide sufficient tooth width to avoid any magnetic saturation in those areas. However, it may be noted by a skilled person that the structure of the plurality of inner stator slots 106 and the plurality of outer stator slots 104 may be designed in a different manner with the same objective of reducing magnetic saturation.

[0036] Figure 3 depicts a three-phase multi-pole tooth-coil winding structure 300 across the stator 102 in accordance with an embodiment of the present disclosure. In particular, the winding structure depicted in Figure 3 is a three-phase 4 pole tooth-coil winding to be used for low- power applications such as a ceiling fan. However, it may be noted that the number of poles can be higher or lower depending on the requirement. For instance, the number of poles may be 2, 8 and 12. Further, the operation frequency of the three-phase induction motor depends upon the number of poles. For instance, an operation frequency for the three-phase 2-pole tooth-coil winding is 7Hz, for the three-phase 4-pole tooth-coil winding is 14Hz; and for the three-phase 8-pole tooth-coil winding is 28Hz.

[0037] The embodiment depicted in Figure 3 shows that the coil-span of the winding is 120°. Usually 3-phase distributed windings have span of 150° electrical under one pole. This 150° span has advantages as it reduces the 5 ^th and 7 ^th space harmonics in the air gap. However, due to the space constraints in an inner stator type structure, a slot design to achieve span of 150° electrical and its placement around the stator periphery becomes difficult. So, instead of 150° of coil span the stator winding is done with 120° of coil span. The slots are placed in the stator such that a tooth-based winding can be done. The 120° span of the winding has better winding factor as compared to the concentrated winding which is wound around a tooth having a 60° of coil span. This leads to less copper as compared to a 3-phase concentrated wound induction motor structure and also reduces the air-gap space harmonics by some extent. The effects of these harmonics can be reduced by appropriate skewing of the rotor bars thus cancelling their effects on rotor.

[0038] Further, as seen in Figure 4 which depicts a density plot 400 of 3 -phase motor with all stator slots located on outer periphery, to implement the three-phase 12 pole tooth-coil winding with 120° span, one has to divide one slot into two parts, the top one for creating positive MMF and bottom one to be used for creating negative MMF. In that process, the subsequent slot’s top/bottom parts have to be solely occupied by the winding going to the next top/bottom slot hence, making that slot space useless. It also makes it difficult for the bottom part of the slot to accommodate the desired number of turns with ease as the top part of the slot space remains unutilized because of the winding going from one top part of a slot to the top part of another slot. To solve this problem, 6 stator slots are moved to the inner periphery of the stator of and rest of the 6 are kept on the outer periphery of the stator as shown in Figure 1. This structure helps in doing tooth-based winding, thus reducing overhang. With the movement of 6 slots to inner periphery of the stator, whole slot space becomes available to be utilized. The structure as shown in Figure 2 may now accommodate a winding pattern 300 shown in Figure 3 in a more efficient way. The given winding pattern may now be wound around the tooth of the stator having a winding span of 120 ° instead of 60 ° which would arise from conventional 12 slots (all placed like how they are in Figure 4) concentrated winding structure. This improvement in the winding factor reduces the copper requirement to generate the same back-EMF, improves the total harmonic distortion in the air gap and makes the manufacturability of the motor with the proposed winding easier. The savings in the copper also reduces the overall cost of the material to be used for making the motor thus reducing the overall motor cost.

[0039] Figure 5 depicts the method of winding one of the phases of the three-phase winding 500 in accordance with an embodiment of the present disclosure. In particular, the winding depicted in Figure 5 is a R-phase (Red-phase) winding. The other two phases Y-phase (Yellow-phase) and the B-phase (Blue-phase) are wound in a similar fashion. A plurality of inner stator teeth and each of the plurality of outer stator teeth corresponding to the plurality of inner stator slots 106 and the plurality of outer stator slots 104 respectively are wound around with a predefined number of turns of the three-phase 4 -pole tooth-coil winding. The three-phase 4-pole tooth coil winding is done in such a manner that the plurality of outer stator slots 104 are wound in a first direction and the plurality of inner stator slots 106 are wound in a second direction opposite to the first direction with the three-phases (R, Y and B) of the three-phase 4-pole tooth-coil winding. However, at a given instant of time, each stator slot houses two-phases of the three-phase multi-pole tooth-coil winding where half of the space of the stator slot is given to one phase and another half for the other phase. In accordance, with the embodiment depicted in Figures 3 and 5, the predefined number of turns is 100. However, it may be noted by a skilled person that the number of turns may be higher or lower.

[0040] In accordance with the embodiment depicted in Figure 5, to wind the plurality of outer stator teeth in the first direction and the plurality of inner stator teeth in the second direction opposite to the first direction with the R-phase of the three-phase 4-pole tooth-coil winding, following methodology is employed. The R-phase 4-pole tooth-coil winding is wound around an outer stator tooth by initiating the R-phase 4-pole tooth-coil winding at an outer stator slot (A) corresponding to the outer stator tooth and terminating the R-phase 4-pole tooth-coil winding at another outer stator slot (B) in the first direction, Further, the R-phase 4-pole tooth-coil winding is wound around an inner stator tooth by initiating the three- phase multi-pole tooth-coil winding at a first inner stator slot (G) corresponding to the inner stator tooth and terminating the R-phase 4-pole tooth-coil winding at a inner stator slot (H) in the second direction. Further, an electrical angular displacement between the first outer stator slot (A) and the first inner stator slot (G) is 180°. Furthermore, in accordance with the depicted embodiment, the first direction is anti-clockwise, and the second direction is clockwise. That is the plurality of outer stator slots 104 are wound in anti-clockwise direction while the plurality of inner stator slots 106 are wound in clockwise direction. However, it may be understood by a skilled person that the first and second directions are interchangeable, that is in another embodiment, the plurality of outer stator slots 104 may be wound in clockwise direction and the plurality of inner stator slots 106 may be wound in anti-clockwise direction.

[0041] Figure 6 shows a no-load air gap flux density waveform associated with the three-phase 4 pole tooth-coil winding described above. The flux density waveform in the air-gap is a quasi-square wave with the coil span of 120° electrical. The peak of the no-load flux density is 0.55 T which is much higher than the air gap flux density which is used for the single -phase ceiling fan motors. In accordance with the embodiment depicted in Figures 3 and 5, a winding wire gauge of 25 SWG is selected to reduce the stator copper loss, however, in other embodiments, SWG 24 may also be used for the winding structure as shown in Figure 3.

[0042] Further, Figure 7 shows a no-load per phase back-EMF corresponding to the no-load air gap flux density depicted in Figure 6. The notches on top of the back-EMF and the air-gap flux density waveform is due to the slot openings. The fundamental value of the back-EMF obtained through the FFT analysis meets the initial design calculation done for the selected peak flux density in the air-gap. The overall fan diameter of 180 mm is selected to avoid any saturation which may arise due to the selection of high flux density in the air gap.

[0043] The stator structure and the winding pattern of the three-phase motor depicted in Figures 1 , 3 and 5 have shown to take 30W in simulations as input for 18W of output power at the speed of 360 RPM. The slot fill factor with 25 SWG, 100 turns per tooth is 33 % for outer stator slots 104 and 28 % for inner stator slots 106. The copper required to carry out the winding pattern on the structure shown in Figure 1 is around 321 g. [0044] In accordance with another embodiment of the present disclosure, the stator 102 structure depicted in Figure 1 is modified in order to accommodate various other winding patterns. The modified stator structure is depicted in Figure 8. The stator 802 of Figure 8 contains a plurality of stator slots 804, all of which are located on an outer periphery of the stator 802. This reduces any complexity in design as it was present in case of 6 stator slots on outer periphery and 6 stator slots on inner periphery structure as shown in Figure 1. But with this stator structure, the winding structure described in Figures 3 and 5 is not feasible. The present disclosure hence describes various winding patterns that can be accommodated in the stator 802 of Figure 8.

[0045] Figure 9 depicts a three-phase 4-pole concentrated winding pattern 900 for the stator 802 where all the 12 slots are located on the outer periphery of the stator 802. Each stator slot of the plurality of stator slots 804 is divided into two parts and each stator slot houses two- phases of the three-phase winding pattern. The winding structure 900 is comparatively simple but uses a large amount of copper in comparison to the winding structure 300 depicted in Figure 3 because of its poor winding factor (=0.5) that arises due to a coil span of 60°. Further, the number of turns around a stator tooth is also large (=200). The air-gap flux density is rich in lower order harmonics with this winding structure like 3 ^rd ,5 ^th and 7 ^th due to the 60° winding coil span. Therefore, while implementing the winding structure 900, rotor bars need to be appropriately skewed to avoid any unwanted noise and heating caused by the induced harmonics voltages or currents in the rotor bars due to the space harmonics present in the air-gap with the winding structure 900.

[0046] Figure 10 depicts a 120° displaced winding pattern 1000 for the stator 802. To accommodate the winding pattern 1000, each stator slot of the plurality of stator slots 804 is divided into 4 parts which will house different phases of the positive winding group (the winding which are placed in the bottom part of the slot as shown in Figure 10) which are wound in one direction across the stator teeth while the top part of the slot houses the negative winding group (the winding which are placed in the top part of the slot as shown in Figure 10) which are wound in opposite direction across the stator teeth as compared to the positive group winding. [0047] Further, the MMF waveshape of the winding structure 900 as shown in Figure 9 is improved by dividing the number of turns wound on one tooth into two halves and placing them on the two consecutive slots as shown in the Figure 10. The 200 turns of R-phase which was wound on tooth 1 on Figure 9 is divided into two 100 turns each wound on tooth number 1 and 2 respectively as shown in Figure 10 for R-phase (similarly is done for the other 2 phases also). This distribution makes the MMF waveshape span of each phase as 120° compared to the MMF waveshape of a concentrated winding where it is 60°. Increasing the span of the square wave helps in reducing some of the dominant lower order harmonics magnitude which are present in the air gap with the proposed winding pattern 1000.

[0048] Figure 11 shows multi-stepped winding pattern 1100 where the distribution of the winding around one pole pair resembles close to a multi-stepped sinusoid distribution. Table 1 shows the number of turns to be wound around each tooth. The winding pattern repeats itself after tooth number 6 to form a 12 slot, 4 pole, 3-phase winding. The positive number of turns shown in the winding table represents the turn around a tooth in an anti-clockwise direction, whereas negative number of turns represents turns wound around a tooth in clockwise direction.

Table 1: Winding Pattern for Multi-Stepped Winding Pattern

[0049] The proposed winding structure 1100 shown in Figure 11, provides a smooth air-gap MMF thus reducing the harmonics in the air-gap as compared to the previously mentioned winding structures 300, 900, 1000 where the MMF waveshape resembles to square wave or a quasi-square waveshape. The winding is done around the stator by dividing the stator slot area into 3 parts as shown in Figure 11. The lower part of the slot is utilized for the R- phase winding alone, middle part for Y-phase and the top part of the slot for B-phase winding. The N shown in table 1 is 100, the 200 turns around one pole of a concentrated winding is divided into 3 turns of 50, 100 and 50 each placed around 3 subsequent stator tooth in one direction as shown in Figure 10 to form positive set of winding and then repeated in other direction compared to the first to form negative winding set for each phase. The cyclic distribution of 50, 100, 50 turns of R phase winding is done (the winding of other 2 phases are displaced by 2 slots). This way, the proposed winding structure 1100 reduces the harmonics in the air-gap and thereby reduce harmonic losses.

[0050] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.).

[0051] It will be further understood by those skilled in the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds tme for the use of definite articles used to introduce claim recitations. [0052] In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

[0053] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.