Optimized rotor design for ferrite-assisted synchronous reluctance motors

Abstract

The present disclosure provides an optimized rotor 200 Ferrite-assisted Synchronous Reluctance Motors (Fe-SynRMs) The rotor 200 includes flux barriers 101, ferrite magnets 103, flux carriers 105, and a shaft 107. In addition, the rotor 200 further includes midribs 203, pockets 205 and opening 201. The midribs 203 are positioned radially inward from the outer periphery of the rotor 200. The pockets 205 are positioned near the air gap in the rotor 200. An opening 201 is provided for each of the plurality of pockets 205. By shifting the midribs 203 radially inward away from the outer periphery of the rotor 200, rotor iron losses are significantly reduced, and the efficiency of the Fe-SynRM is enhanced, especially at high motor speeds.

Description

OPTIMIZED ROTOR DESIGN FOR FERRITE-ASSISTED SYNCHRONOUS RELUCTANCE MOTORSTECHNICAL FIELD

[0001] The subject matter of the present disclosure relates generally to Ferrite-assisted Synchronous Reluctance Motors (Fe-SynRMs). Particularly, the subject matter of the present disclosure is related to an optimized rotor that increases the efficiency of Fe-SynRMs by significantly reducing rotor iron losses, especially at high motor speeds.BACKGROUND

[0002] Synchronous reluctance motors (SynRMs) operate on the principle of magnetic reluctance. Unlike traditional motors that use permanent magnets or electromagnets to create a magnetic field, SynRMs utilize the reluctance principle to generate torque. The rotor is designed with specific geometric features that create varying magnetic reluctance, enabling it to align itself with the rotating magnetic field generated by the stator.

[0003] Ferrite-assisted Synchronous Reluctance Motors (Fe-SynRMs) introduce an improved approach to motor technology by integrating the advantages of synchronous reluctance with the magnetic properties of ferrite materials, aiming to enhance the overall performance of the underlying motor. However, despite their promising capabilities, Fe-SynRMs encounter several challenges that limit their widespread adoption, including elevated rotor losses, reduced efficiency at low load conditions, and increased complexity in the associated control systems.

[0004] One of the primary challenges associated with Fe-SynRMs is the rotor loss, which mainly arises from eddy current losses and hysteresis losses. These losses significantly impact the efficiency and performance of the Fe-SynRMs. Further, Fe-SynRMs exhibit diminished efficiency when operating under low load conditions, which can be a disadvantage in applications that do not consistently run at full capacity. Furthermore, high rotor losses associated with flux saturation near the rotor periphery also result in excessive heat production. The increased heat reduces the motor's efficiency, requires more complex cooling mechanisms, and limits the motor's operating life.

[0005] Excessive rotor losses and inefficient flux paths diminish overall efficiency and reduce power density, limiting the motor’s ability to deliver high output relative to its size. As a result, Fe-SynRMs become less competitive in applications that demand compact, high-power machines. Additionally, some existing reluctance motor designs feature rotor structures that are not fully optimized for mechanical strength. The arrangement of flux carriers and their interconnections can introduce localized stresses and mechanical vulnerabilities, compromising structural integrity and restricting performance under high-load conditions.

[0006] FIGURE-1A (prior art) illustrates a conventional rotor of a Ferrite-assisted Synchronous Reluctance motor (Fe-SynRM). The conventional rotor 100 contains regions of differing magnetic reluctance, a key characteristic that strongly influences the Fe-SynRM’s performance. The conventional rotor 100 includes flux barriers 101, ferrite magnets 103, flux carriers 105, a shaft 107, and peripheral tangential ribs 109. The rotor 100 includes a plurality of peripheral, tangential ribs 109.

[0007] The peripheral, tangential ribs 109 of the rotor 100 function as natural conduits for magnetic flux, directing it along the shortest possible path. Since the reluctance of the path through the peripheral, tangential ribs 109 is lower than that of other potential paths, the flux lines preferentially pass through these peripheral, tangential ribs 109.

[0008] Consequently, flux lines accumulate in these peripheral tangential ribs 109, resulting in a higher local flux density contributing to flux saturation near the air gap. This saturation, in turn, increases both eddy current and hysteresis losses, which together constitute the primary sources of rotor losses.

[0009] The eddy current loss (Pe) and Hysteresis Loss (Ph) can be calculated using equations (1) and (2) mentioned below:(a) Pe=Ke*Bm2*f2*t2*V Watts - (1)(b) Ph=K*f*Bmx*V Wattswhere,• Keis the Eddy current constant,• Bmis the maximum flux density (Weber per square meter (Wb / m2)),• f is the frequency of supply (Hertz (Hz)),• t is the thickness of lamination (meter (m)),• V is the volume of the material (cubic meter (m3)),• K is the Steinmetz hysteresis constant,• x is the Steinmetz constant, and

[0010] The equations (1) and (2) indicate that the rotor losses are directly influenced by the flux density, and that higher flux densities result in increased rotor losses. In the conventional rotor 100, rotor losses are substantially elevated due to the combined contributions of eddy current loss (Pe), hysteresis loss (Ph), and the inherent flux-density fluctuations arising from the stator.

[0011] In the conventional rotor 100, the flux carriers 105 are connected to each other by peripheral tangential ribs 109. Due to the vicinity of the stator windings and the stator teeth to the peripheral tangential ribs 109, regions with high magnetic flux density develop at the rotor’s periphery, resulting in higher iron losses. These excessive rotor losses typically lead to reduced efficiency, increased heat generation, and decreased power density, among other issues.

[0012] Hence, there exists a need for an optimized rotor for Fe-SynRMs that solves the drawbacks of the existing solutions mentioned above.OBJECTS

[0013] A few of the objects of the invention described as a part of the present disclosure are as follows.

[0014] The principal object of the present disclosure is to design an optimized rotor for reducing rotor losses by shifting the peripheral connections or ribs of the rotor towards the center of the rotor and optimizing their thickness and placement. This design modification minimizes variations in magnetic flux density and reduces losses caused by flux saturation, leading to a significant decrease in eddy currents and hysteresis losses.

[0015] Another object of the present disclosure is to provide optimization in the placement of flux carriers by introducing pockets near air gaps and incorporating a mid-rib configuration. This design modification reduces torque ripple and improves the overall efficiency of the motor.

[0016] Another object of the present disclosure is to improve upon the structural integrity of the rotor by introducing non-peripheral connections or ribs and incorporating a mid-rib. This modification improves the mechanical robustness of the rotor, ensuring that the generated stress remains within permissible limits, thereby allowing the motor to operate reliably under normal conditions.

[0017] Another object of the present disclosure is to provide a rotor design that optimizes the magnetic flux flow, ensuring that the flux travels from one end of a flux carrier to the other end in the most efficient manner, thereby reducing iron losses and enhancing the motor’s overall performance.

[0018] Another object of the present disclosure is to provide for a smooth operating experience of the rotor by reducing variations in the flux density and optimizing the peripheral gaps, and thereby minimizing torque ripples, and contributing to a softer and more efficient operation of the motor; and

[0019] Another object of the present disclosure is to reduce rotor losses and enhance rotor efficiency, which, in turn, results in improved power density and heat dissipation, making the motor more suitable for high- performance applications while maintaining high reliability.

[0020] These and other objects and advantages of the present disclosure will be apparent from the following detailed description perused in conjunction with the accompanying drawings.SUMMARY

[0021] According to an embodiment of the present subject matter, disclosed herein is a rotor for a ferrite- assisted synchronous reluctance motor (Fe-SynRm), comprising: a shaft disposed along an axis; a plurality of flux barriers extending radially and circumferentially within a rotor core; a plurality of ferrite magnets disposed within the plurality of flux barriers ; a plurality of flux carriers formed of ferromagnetic material and positionedbetween adjacent flux barriers; characterized in that a plurality of midribs positioned radially inward from an outer periphery of the rotor core; and a plurality of pockets positioned adjacent the outer periphery of the rotor core, wherein the flux carriers are disconnected peripherally from each other by an opening at the rotor periphery, and wherein the midribs are positioned and dimensioned to shift high-flux-density regions away from the rotor periphery, thereby reducing rotor iron losses.

[0022] According to an embodiment of the present subject matter, the midribs comprise elongated rib structures extending between adjacent flux barriers and are positioned inward from the air-gap-facing region.

[0023] According to an embodiment of the present subject matter, the midribs have a reduced thickness of up to approximately 10% relative to peripheral tangential ribs of a conventional rotor.

[0024] According to an embodiment of the present subject matter, the peripherally disconnected flux carriers are incorporated to minimize flux concentration at the air-gap boundary.

[0025] According to an embodiment of the present subject matter, flux density from the rotor periphery to the midribs is minimized to reduce eddy-current losses and hysteresis losses during operation.

[0026] According to an embodiment of the present subject matter, the rotor provides a reduction in rotor iron losses of at least about 54% relative to a rotor having peripherally connected flux carriers.

[0027] According to an embodiment of the present subject matter, the flux carriers are arranged to support a modular geometry permitting a selectable number of midribs, pockets and openings.

[0028] According to an embodiment of the present subject matter, the configuration of the peripherally disconnected flux carriers along with midribs, pockets and openings, reduces torque ripple.

[0029] According to an embodiment of the present subject matter, the reduced rotor losses result in lower thermal gradients and lower thermal stress during high-speed operation.

[0030] According to an embodiment of the present subj ect matter, the stress levels in the midribs remain within permissible limits under standard operating conditions.

[0031] According to an embodiment of the present subject matter, the peripherally disconnected flux carriers along with midribs, pockets and openings provide structural robustness to the rotor during high-speed rotation.

[0032] According to an embodiment of the present subject matter, the highest flux-density region is located in the midribs rather than near the air gap.

[0033] According to an embodiment of the present subject matter, two or more pockets are arranged circumferentially along the rotor periphery.

[0034] According to an embodiment of the present subject matter, three or more peripherally disconnected flux carriers are incorporated for applications requiring enhanced reluctance torque shaping.

[0035] According to an embodiment of the present subject matter, the pockets are filled with non-magnetic materials for high-speed motor applications.BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0036] The embodiments of the present disclosure are described with reference to the following figures, in which same reference letters and numerals are used to indicate like parts across various figures and various views unless otherwise specified. It will be appreciated that for the sake of simplicity and clarity of illustration, elements illustrated in figures have not necessarily been drawn to scale. The Figures include:

[0037] FIGURE-1A (prior art) illustrates the design of a conventional rotor of a Ferrite -assisted Synchronous Reluctance motor (Fe-SynRMs);

[0038] FIGURE-1B (prior art) illustrates the flux density distribution of a conventional rotor;

[0039] FIGURE-2A illustrates a rotor with an optimized design that has peripherally disconnected flux carriers along with midribs, pockets and openings which reduces the rotor iron losses, in accordance with an embodiment of the present disclosure;

[0040] FIGURE-2B illustrates the flux density distribution of the rotor with optimized design that has peripherally disconnected flux carriers along with midribs, pockets and openings, in accordance with another embodiment of the present disclosure;

[0041] FIGURES -3A-I illustrate various shapes utilized to design the optimized rotor that has peripherally disconnected flux carriers along with midribs, pockets and openings, in accordance with the present disclosure;

[0042] FIGURE-4 indicates the stress generated in the peripheral, tangential ribs of the conventional rotor; and

[0043] FIGURE-5 indicates the stress generated in the midribs of the optimized rotor that has peripherally disconnected flux carriers along with midribs, pockets and openings, in accordance with an embodiment of the present disclosure.DETAIEED DESCRIPTION

[0044] To forestall the drawbacks and disadvantages associated with the prior art and to provide additional advantages, an optimized rotor that has peripherally disconnected flux carriers for a Ferrite-based Synchronous Reluctance motor (Fe-SynRM) is illustrated and explained herein. This invention also applies to the general category of ferrite magnets irrespective of their composition.

[0045] The various embodiments of the invention are described in detail below with reference to Figures 2 through 5.

[0046] FIGURE -2A illustrates a rotor with an optimized design that has peripherally disconnected flux carriers reduces rotor iron losses. The rotor increases motor efficiency by significantly reducing rotor iron losses, especially at high motor speeds. In all embodiments, the rotor of the present invention is particularlysuitable for high-speed applications such as electric vehicle traction motors, compressors, and industrial spindles, where efficiency, reliability, and thermal performance are critical.

[0047] In one embodiment, the rotor 200 comprises a laminated rotor core rotatable about an axis, a shaft 107 disposed along the axis, a plurality of flux barriers 101, ferrite permanent magnets 103 inserted in at least some of the flux barriers 101, and a plurality of flux carriers 105 formed of ferromagnetic material between adjacent flux barriers. Unlike the conventional rotor, the present rotor 200 as disclosed herein, includes a plurality of midribs 203 positioned radially inward from the outer periphery of the rotor core, and a plurality of pockets 205 located adjacent the outer periphery. Each pocket 205 is provided with the opening 201 at the peripheral edge to achieve the design of peripherally disconnected flux carriers. The rotor core material is laminated electrical steel, including all variants of this steel, such as grain oriented, non-grain-oriented etcetera. The unique introduction of the opening 201, pockets 205 and midribs 203, together modify the magnetic flux paths to reduce rotor iron losses.

[0048] The pockets 205 and the opening 201 may be air-filled or filled with non-magnetic material and extends circumferentially and / or radially to prevent magnetic connection between adjacent flux carriers at the periphery. The midribs 203 are positioned at a radial distance of preferably 70% to 90% of the rotor radius from the axis. This positioning ensures that the peak magnetic flux density occurs predominantly in the midribs 203 (as shown in Figure 2B) rather than near the air gap, thereby reducing flux density variations and associated iron losses.

[0049] In a preferred embodiment, the thickness of each midrib 203 is reduced by 5% to 10% compared to the peripheral tangential ribs 109 of the conventional rotor 100. Despite the reduced thickness, mechanical stress in the midribs 203 remains lower and within permissible limits even at rotational speeds exceeding 12,000 rpm (see Figure 5).

[0050] In a conventional operational scenario, the magnetic flux originates from the stator windings and traverses the air gap to enter the rotor 200. By introducing an opening 201, pockets 205 and midribs 203, the path of magnetic flux is altered. By optimizing this arrangement, the flux flow from the stator to the rotor can be optimized to reduce saturation and hence reduce losses. The precise shape and thickness of the midribs 203 may vary across different motor sizes, with different rotor and stator dimensions.

[0051] Experimental results show that the rotor 200 of the present invention reduces combined eddy current and hysteresis losses by approximately 54% compared to the conventional rotor 100, leading to an overall motor efficiency improvement of 2-5% at high speeds. It breaks the flow of flux to reduce saturation, irrespective of lamination thickness.

[0052] The midribs 203 are positioned radially inward from the outer periphery of the rotor 200. The pockets 205 are positioned near the air gaps in the rotor 200. The number of midribs 203 and pockets 205 vary based on the number of ferrite magnets in the rotor 200. The opening 201 is provided for each of the plurality of pockets 205 and any number of pockets 205 can be provided for each of the plurality of flux barrier 101. Thepurpose of opening 201 is to eliminate the low-reluctance tangential flux path that exist at the rotor periphery in conventional designs. The precise gap size of each opening 201 is not fixed and must be obtained by optimization techniques to effectively disrupt tangential flux flow while maintaining manufacturability and avoiding excessive mechanical weakening. The opening 201 (along with midribs 203) can be air-filled or filled with non-magnetic material.

[0053] By shifting the midribs 203 (peripheral, tangential ribs 109 of the conventional rotor 100 (shown in FIGURE-1A) radially inward away from the outer periphery of the rotor 200, iron losses are reduced. The optimal location, size, and orientation of the midribs 203 is determined using derivative-free optimization techniques. Placing the midribs 203 radially inward from the outer periphery of the rotor 200 helps minimize flux density variation, thereby improving efficiency. Additionally, optimizing the peripheral gaps between the flux carriers 105 reduces torque ripples, resulting in a smoother operating experience.

[0054] Referring to FIGURE IB, it is observed that the flux density is at its peak in the tangential ribs 109 located near the air gaps in the conventional rotor 100. Conversely, in FIGURE-2B, the highest flux density is found in the midribs 203, which is positioned further away from the air gap. This positioning of the midribs 203 makes the rotor 200 less susceptible to variations in flux density, consequently lowering the rotor losses.

[0055] By reducing rotor losses, the optimized rotor 200 significantly enhances the Fe-SynRM’s efficiency. In accordance with the present disclosure, rotor losses in the optimized rotor that has peripherally disconnected flux carriers are reduced by nearly fifty-four (54%) percent with the introduction of midribs 203, pockets 205 and openings 201; vis-a-vis the conventional rotor 100. Reducing rotor losses typically enhances motor efficiency.

[0056] FIGURES-3A-I illustrate various shapes utilized for designing the optimized rotor 200. Referring to FIGURES-3A-3I, the rotor 200 includes flux barriers 101, ferrite magnets 103, flux carriers 105, a shaft 107. In addition, the rotor 200 further includes midribs 203 pockets 205 and openings 201. The mid ribs 203 are positioned radially inward from the outer periphery of the rotor 200. The pockets 205 are positioned near the air gap in the rotor 200. The number of midribs 203 and the pockets 205 may vary based on the number of ferrite magnets in the rotor 200. Figures 3A to 31 illustrate various embodiments of the invention. The rotor may include two flux carriers per pole (Figures 3A-3H) or three flux carriers per pole (Figure 31). The shape, number, and arrangement of openings 201 and midribs 203 may vary depending on the number of poles, ferrite magnets, and application requirements, while maintaining the core inventive feature of peripheral disconnection and inward flux shifting. The flexibility in the design of the rotor 200 allows for the addition of any number of pockets 205. This modular approach optimizes the rotor’s performance based on specific application requirements. It is to be noted that all other parts of the rotor 200 illustrated in FIGURES-3A-3I remain the same as the optimized rotor 200 in FIGURE 2A.

[0057] FIGURE-4 shows the stress generated in the peripheral, tangential ribs 109 of the conventional rotor 100, in accordance with an embodiment of the present disclosure. FIGURE-5 illustrates the stress generatedin the midribs 203 of the optimized rotor that has peripherally disconnected flux carriers 200, in accordance with an embodiment of the present disclosure.

[0058] In accordance with the present disclosure, FIGURE-5 illustrates that the midribs 203 are shifted radially inward away from the outer periphery of the rotor 200, and their thickness has been reduced by up to ten percent (10%), vis-a-vis the conventional rotor 100 shown in FIGURE-4.

[0059] In accordance with the present disclosure, FIGURE-5 also illustrates the peripherally disconnected flux carriers. In accordance with the present disclosure, the stress generated in the midribs 203 of the optimized rotor that has peripherally disconnected flux carriers 200 remains within permissible limits, whereas the stress generated in the peripheral tangential ribs 109 of the conventional rotor 100 is higher (as shown in FIGURE- 4) than the optimized rotor that has peripherally disconnected flux carriers 200.

[0060] The structural modification of the optimized rotor that has peripherally disconnected flux carriers 200 results in superior performance when compared to the traditional rotor 100, given the presence of peripherally connected flux carriers in the optimized rotor 200. The inclusion of the midribs 203 in the peripherally disconnected flux carriers in the optimized rotor 200 confers structural benefits over the conventional rotor 100.TECHNICAE ADVANTAGES

[0061] The optimized rotor that has peripherally disconnected flux carriers described hitherto provides a more efficient and structurally sound solution that demonstrates enhanced overall performance by minimizing rotor losses and improving the motor’s operational efficiency. The optimized rotor design that has peripherally disconnected flux carriers, envisaged by the present disclosure, not only reduces rotor losses and improves motor efficiency but also simplifies thermal management, minimizes thermal stresses, and ensures smooth operation at high speeds, making it a viable and reliable solution for high-performance applications. Optimized midribs provide sufficient mechanical bridging to withstand centrifugal forces, wherein 10000 rpm and above is considered high speed.

[0062] One of the key benefits of the optimized rotor design is the substantial reduction in rotor losses, which directly enhances the motor's overall efficiency. With lower rotor losses, the motor operates more efficiently, leading to reduced energy consumption and better performance. In addition, reduced rotor losses also simplify thermal management, as the motor generates less heat. Traditional high-speed rotors require complex and sophisticated cooling systems to maintain safe operating temperatures. However, with lower losses, the need for advanced cooling techniques is minimized, making the system easier to manage thermally.

[0063] With lower thermal losses, the rotor experiences smaller temperature gradients, reducing thermal stresses and deformation. This allows the rotor to operate safely at very high speeds, as it minimizes the risk of heat-induced damage and distortion, ensuring greater reliability and longevity of the motor. Furthermore, byapplying derivative-free optimization techniques to fine-tune the rotor's geometric parameters, the torque ripple is reduced well below acceptable thresholds. This results in smoother motor operation, reducing vibrations and noise, and enhancing the overall performance of the motor. Derivative-free optimization is a computer implemented smart frial-and-error method used to make the rotor as good as possible, without needing complicated math formulas.

Claims

CLAIMSWe claim:

1. A rotor (200) for a ferrite-assisted synchronous reluctance motor (Fe-SynRm), comprising: a shaft (107) disposed along an axis; a plurality of flux barriers (101) extending radially and circumferentially within a rotor core; a plurality of ferrite magnets (103) disposed within the plurality of flux barriers (101); a plurality of flux carriers (105) formed of ferromagnetic material and positioned between adjacent flux barriers; characterized in that a plurality of midribs (203) positioned radially inward from an outer periphery of the rotor core; and a plurality of pockets (205) positioned adjacent to the outer periphery of the rotor core; wherein each flux carrier (105) is separated from adjacent flux carriers at the rotor (200) periphery by a respective opening (201), and wherein the midribs (203) are positioned and dimensioned to shift high-flux-density regions away from the rotor periphery, thereby reducing rotor iron losses.

2. The rotor as claimed in claim 1, wherein the midribs (203) comprise elongated rib structures extending between adjacent flux carriers (105) and are positioned inward from the air-gap-facing region.

3. The rotor as claimed in claim 1, wherein the midribs (203) have a reduced thickness of up to approximately 10% relative to peripheral tangential ribs (109) of a conventional rotor.

4. The rotor as claimed in claim 1, wherein the peripherally disconnected flux carriers are incorporated to minimize flux concentration at the air-gap boundary.

5. The rotor as claimed in claim 1, wherein flux density from the rotor periphery to the midribs is minimized to reduce eddy-current losses and hysteresis losses during operation.

6. The rotor as claimed in claim 1, wherein the rotor provides a reduction in rotor iron losses of at least about 54% relative to a rotor having peripherally connected flux carriers.

7. The rotor as claimed in claim 1, wherein the midribs (203) and openings (201) are arranged to support a modular geometry permitting a selectable number of pockets (205).

8. The rotor as claimed in claim 1, wherein the configuration of the midribs (203) and pockets (205) reduces torque ripple.

9. The rotor as claimed in claim 1, wherein the reduced rotor losses result in lower thermal gradients and lower thermal stress during high-speed operation.

10. The rotor as claimed in claim 1 , wherein the stress levels in the midribs (203) remain within permissible limits under standard operating conditions.

11. The rotor as claimed in claim 1, wherein the midribs (203) provide structural robustness to the rotor during high-speed rotation.

12. The rotor as claimed in claim 1, wherein the highest flux-density region is located in the midribs (203) rather than near the air gap.

13. The rotor as claimed in claim 1, wherein two or more pockets (205) are arranged circumferentially along the rotor periphery.

14. The rotor as claimed in claim 1, wherein three or more peripherally disconnected flux carriers are incorporated for applications requiring enhanced reluctance torque shaping.

15. The rotor as claimed in claim 1, wherein the pockets are filled with non-magnetic materials for highspeed motor applications.

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