Systems and methods for increasing levitation forces in single sided linear induction motors

Abstract

A linear induction motor system for levitating a vehicle is disclosed herein The linear induction motor system comprises a linear induction motor. The linear induction motor comprises a back iron and a reaction rail adjacent to the back iron. The linear induction motor further comprises a primary separated from the reaction rail by a gap. The linear induction motor system further comprises a rear appendix adjacent to the primary, wherein the rear appendix generates magnetic poles in the primary in response to a magnetic flux density in the reaction rail and back iron.

Description

SYSTEMS AND METHODS FOR INCREASING LEVITATION FORCES IN SINGLE SIDED LINEAR INDUCTION MOTORSBACKGROUND OF THE DISCLOSURE1. Field of the Invention

[0001] The present disclosure relates to a levitation system for variable speed vehicles.2. Description of Related Art

[0002] Magnetic levitation trains (maglev) offer several advantages compared to traditional wheel-on-rail systems including reaching higher achievable speeds, reduced maintenance cost, less noise and vibration reduction, higher achievable curve radius, absence of gears, couplings, and other transmission systems, as well as low vulnerability to weather conditions. Despite the above-mentioned advantages, only a few commercial applications are operating today, and high-speed wheel-on-rail trains are still the preferred option. One of the main reasons for this is maglev’s high initial cost. The initial cost is based on the construction of a dedicated guideway system, the electrification of the guideway to accommodate the propulsion, levitation, and guidance systems (PLG) and a complicated mechanism to switch between guideway lanes.

[0003] In traditional systems, the propulsion of a maglev train is generally performed by either single-sided linear induction motors (SLIMs) or linear synchronous motors (LSMs), depending on the type of application. Short-primary (SP) SLIMs are the cheapest solutions since the guideway is passive and relatively simple to manufacture, whereas long-primary (LP) LSMs are the most expensive as the guideway is active and the vehicle carries the DC- excited or permanent-magnets (PMs) secondary.

[0004] Most of the existing commercial applications use short primary SLIM as the propulsion system, due to their manufacturing simplicity and low cost. These applications are mainly intended for medium-speed urban transportation. A common issue that affects a SLIM- propelled maglev is the necessity to compensate for the normal force generated by the motor, which is attractive at low slip operation points and therefore opposes the levitation force provided by the electromagnetic suspension (EMS) system.SUMMARY

[0005] A linear induction motor system for levitating a vehicle is disclosed herein. The linear induction motor system can comprise a linear induction motor. The linear induction motor can comprise a back iron, a reaction rail adjacent to the back iron, and a primary separated from the reaction rail by a gap. The linear induction motor system can further comprisea rear appendix adjacent to the primary, wherein the rear appendix generates magnetic poles in the primary in response to a magnetic flux density in the reaction rail and back iron.

[0006] The magnetic flux density experienced by linear induction motor system can be associated with an eddy current induced in the reaction rail by the displacement magnetic flux density that is generated by the primary, multiphase winding and relative motion between the primary and the reaction rail.

[0007] The rear appendix can be comprised of ferromagnetic material. A thickness of the rear appendix can be less than the thickness of the primary. The thickness of the rear appendix along a y-axis can be smaller than the thickness of the primary. An overall force generated by the linear induction motor can be based at least in part on the electromagnetic interaction along a surface of the reaction rail over a length of the linear induction motor and a length of the rear appendix.

[0008] In some embodiments, a force normal to the direction of travel of the vehicle can be based at least in part on a combination of one or more forces generated by the linear induction motor and one or more forces generated by the rear appendix. In other embodiments, a force normal to the direction of travel of the vehicle can be based at least in part on the combination of the one or more forces generated by the linear induction motor and the rear appendix. Yet still in other embodiments, a force normal to the direction of travel of the vehicle can be equal to a first force normal to the direction travel of the vehicle for a first length of the rear appendix and the force normal to the direction of the vehicle can be equal to a second force normal to the direction travel of the vehicle for a second length of the rear appendix. The second force normal to the direction of travel of the vehicle can be greater than the first force normal to the direction of travel of the vehicle and the second length of the rear appendix is greater than the first length of the rear appendix.

[0009] A linear induction motor system for levitating a vehicle is disclosed, in which the linear induction motor system comprises a linear induction motor that can generate a linear induction motor force that causes the vehicle to levitate. The linear induction motor can comprise a back iron, a reaction rail, and a primary. The linear induction motor system can also include a rear appendix that can generate an additional force, wherein the additional force can be based at least in part on a length of the rear appendix, and a total resulting force is generated based at least in part on the linear induction motor force and the additional force.

[0010] In some embodiments, the additional force can further be based at least in part on the weight of the rear appendix. In other embodiments, the additional force can further be based at least in part on the length of the rear appendix being a fraction of a length of the linear induction motor. Yet still in other embodiments, the total resulting force can be fifty percent greater than the force when the length of the rear appendix is one third the length of the linear induction motor. In other embodiments, the total resulting force can be sixty percent greater than the force when the length of the rear appendix is two thirds the length of the linear induction motor. The length of the linear induction motor can be .5 meters and the length of the rear appendix can be 0.5 meters. The length of the linear induction motor can be 1.5 meters and the length of the rear appendix can be 1 meter.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] These and other features and advantages of the present invention will be more fully understood by reference to the following detailed description in conjunction with the attached drawings in which like reference numerals refer to like elements throughout the different views. The drawings illustrate principals of the invention and, although not to scale, show relative dimensions.

[0012] FIG. 1 schematically depicts an exemplary reference geometry and winding detail of a single sided linear induction motor in accordance with some embodiments disclosed herein.

[0013] FIG. 2 schematically depicts an exemplary reference geometry and winding detail of a single sided linear induction motor in accordance with some embodiments disclosed herein.

[0014] FIG. 3 is a plot of magnetic flux density distributions generated by the single sided linear induction motor with different lengths of appendices in accordance with some embodiments disclosed herein.

[0015] FIG. 4 is a plot of force distributions generated by the single sided linear induction motor with different lengths of appendices in a direction normal to a direction of travel of the single sided linear induction motor in accordance with some embodiments disclosed herein.

[0016] FIG. 5 is a plot of ratios of a force generated by the single sided linear induction motor with a rear appendix to a force generated by the single sided linear induction motor without a rear appendix in accordance with some embodiments disclosed herein.

[0017] FIG. 6 is a flowchart of process of determining forces generated by the rear appendix affixed to the single sided linear induction motor in accordance with some embodiments disclosed herein.Detailed Description

[0018] As noted above, due to the shortcomings of existing EMS systems that are incorporated into high-speed levitated vehicles, by redesigning the rear section of a SLIM, the forces that are normal to the direction of travel of the SLIM can be increased without effecting the ability to control or propel a vehicle incorporating the SLIM design discussed herein. The proposed SLIM design can be integrated into most of existing control strategies that are available, and can be used to integrate propulsion and levitation functionalities into a single short primary (SP) SLIM.

[0019] Within the context of EMS systems for high-speed levitated vehicles, through the embodiments described herein the normal force of a SLIM is increased via a specific design of the rear section of the motor. As explained below, this can be also used to integrate propulsion and levitation functionalities into a single SP-SLIM.

[0020] FIG. 1 schematically depicts an exemplary reference geometry and winding detail of a single sided linear induction motor in accordance with some embodiments disclosed herein. FIG. 1 depicts a SLIM system 100. The SLIM system 100 can include two main components with existing sub-components. A first component of the SLIM system 100 can be a moving component made from a laminated ferromagnetic like material which is normally referred to as a primary 113. The primary 113 can have a thickness of tapp141. The laminated ferromagnetic like material can be iron in some embodiments. A second component can be a passive rail installed along a track that the vehicle travels along. The passive rail can be a conductive reaction rail 117, or plate, with a thickness s 125 and electrical conductivity c made of any electrically conductive materials. In some embodiments, the material of the reaction rail 117 is preferably aluminum or copper. The reaction rail 117 can be adjacent to, and on top of a ferromagnetic plate of thickness T 127, which can be referred to as a back iron 119. The distance separating the first component and the second component can be referred to as an air gap 115 which can also be represented by the symbol 8 123. The primary 113 can move along the x axis 133 with a velocity vm111, and the winding conductors can be along the z 137 axis. Because the winding conductors are oriented in the plane of the z 137 axis, the magnetic vector potential is oriented in the direction of the z 137 axis. The primary 113 generates a magnetic field. The primary width along the z-axis is represented by hm121 and the width of reaction rail 117 is represented by hr129.

[0021] The distance between the primary 113 and the back iron 119 can be a 131. A vehicle that the SLIM system 100 is integrated into can produce forces that cause the vehicle tolevitate in a y 135 axis. The primary 113 can have a length of lmot 103 and a rear appendix 139 can have a length of hear appendix 101. In one embodiment rear appendix 139 and primary 113 are a single piece, although they can be made separately. The primary 113 can have Tp105 pole pitch.

[0022] The primary 113 generates two force components. One is along the direction of travel and one is perpendicular to that direction (referred to as “normal”). The two force components can be applied along the length of the motor. The two force components can be distributed along the length lmot 103 of the primary 113. However, because the primary 113 is finite in length, the one or more forces generated by the leftmost portion of the primary 113 also includes forces that are not normal to the primary 113 itself, but to the left of the primary 113. The forces that are generated to the left of the primary 113 are correlated with the leftmost portion of the primary 113. The leftmost portion of the primary 113 that is responsible for the forces that are generated to the left of the primary 113 can vary based on the motor geometry. For example, the number of poles and the number of windings, and winding configuration can cause a change in the forces generated to the left of the primary 113. These forces that are not normal to the primary 113 can be referred to as rear appendix forces because they are generated by the rear appendix end of the primary 113 as it moves from left to right at a velocity of vm111.

[0023] As noted above, because the primary 113 has a finite length, the magnetic flux density associated with the eddy current induced in the reaction rail 117 can propagate behind the primary 113, but vanishes into the air. This can be referred to as the “tail effect” and can be leveraged to increase the normal force developed by the primary 113 while keeping the lowest weight possible. The rear appendix 139 can conserve part of the magnetic flux density at the rear of the primary 113, and use it to generate additional levitation forces. The distribution of these additional levitation forces, also referred to a normal forces, are shown in FIG. 4 as a function of the length hear appendix 101 of the rear appendix 139.

[0024] FIG. 2 schematically depicts an exemplary reference geometry and winding detail of a single sided linear induction motor in accordance with some embodiments disclosed herein. The reaction rail 117 and back iron 119 may form what is called a secondary, and is comprised of a plurality of magnetic poles that generate a magnetic field that interacts with the magnetic poles on the primary 113 thereby giving lift to the vehicle.

[0025] FIG. 3 is a plot 200 of magnetic flux density distributions generated by the single sided linear induction motor with different lengths of appendices in accordance with some embodiments disclosed herein. As described above, the rear appendix 139 can generateadditional levitation forces, which also means that the rear appendix 139 also aides in generating an additional magnetic flux density. More specifically the length of the rear appendix 139 has a direct impact on the magnetic flux density generated by the rear portion of the primary 113. For example, in a scenario in which there is no rear appendix affixed to, or adjacent to, the primary 113 as represented by curve 207 the magnetic flux density 201 decreases as a function of distance from the rear end of primary 113 faster than the magnetic flux density 201 associated with curves 203 and 205 which both correspond to a SLIM system including a rear appendix. Curve 205 represents a magnetic flux density 201 that is greater than the magnetic flux density 201 of curve 207 because curve 205 is associated with a SLIM system that has a rear appendix of length 2ipwhich is equal to twice the pole pitch. The curve 203 is associated with a SLIM system that has a rear appendix of length 4ipwhich is equal to four times the pole pitch. As can be seen in curves 203 and 205 in FIG. 3, the rate at which the magnetic flux density 201 of a SLIM system with a longer rear appendix dissipates slower than a SLIM system with a shorter rear appendix. As a result the magnetic flux density 201 of a SLIM system with a rear appendix increases as a function of the length of the rear appendix.

[0026] FIG. 4 is a plot 300 of force distributions generated by the single sided linear induction motor with different lengths of appendices in a direction normal to a direction of travel of the single sided linear induction motor in accordance with some embodiments disclosed herein. As described above, the rear appendix 139 can generate additional levitation forces. More specifically the length of the rear appendix 139 has a direct impact on the levitation forces generated by the rear portion of the primary 113. For example, in a scenario in which there is no rear appendix affixed to, or adjacent to, the primary 113 as represented by curve 305, the force 307 decreases as a function of distance from the rear end of primary 113 faster than the force 307 associated with curves 301 and 303 which both correspond to a SLIM system including a rear appendix. Curve 301 is representative of a force 307 that is greater than the force 307 that is representative of curve 303 because curve 303 is associated with a SLIM system that has a rear appendix of length 2ipwhich is equal to twice the pole pitch. The curve 301 is associated with a SLIM system that has a rear appendix of length 4ipwhich is equal to four times the pole pitch. As can be seen in curves 303 and 301 in FIG. 4, the rate at which the force 307 of a SLIM system with a longer rear appendix dissipates slower than a SLIM system with a shorter rear appendix. As a result the force 307 of a SLIM system with a rear appendix increases as a function of the length of the rear appendix.

[0027] FIG. 5 is a plot 400 of ratios of a levitation force generated by the single sided linear induction motor with a rear appendix to a force generated by the single sided linear induction motor without a rear appendix in accordance with some embodiments disclosed herein. Plot 400 illustrates a ratioFytad403 between the normal forces or levitation forces Fy generated by the SLIM system with a rear appendix and the lift generated by the SLIM without the rear appendix for a set 401 of thirteen different rear appendix lengths as a function of the velocity vm111 of the vehicle. The ratioFytad403 increases as the velocity Fy vm111 increases across all of the rear appendix lengths in the set 401. However the rate of increase, or slope, of each line associated with the velocity vm111 for a given rear appendix length increases as the length of the rear appendix increases. This implies that as the velocity vm111 of the vehicle increases as the length of the rear appendix increases, the levitation force produced by the SLIM system with the rear appendix is greater than the levitation force produced by a SLIM without a rear appendix. As a result, the length of rear appendix necessarily increases the levitation forces experienced by the vehicle as it the velocity of that vehicle increases.

[0028] FIG. 6 is a flowchart of process 500 of determining forces generated by the rear appendix affixed to the single sided linear induction motor in accordance with some embodiments disclosed herein. At step 501 the process can determine one or more forces that are generated by a linear induction motor (e.g., primary 113). The one or more forces can be a combination of forces generated by the primary 113 that are normal to the vehicle, and help levitate the vehicle, and forces that are not exerted on the vehicle, but are dissipated in air behind the vehicle as it is moving. After the process determines the one or more forces, the process can determine the forces generated behind the primary 113 by a rear portion of the primary 113. Based on the determination of the forces generated by the primary 113 in step 501 and the forces generated behind the primary 113 in strep 503, the process can determine the forces attributable to the primary 113 itself and forces generated by a rear appendix affixed to the primary 113.

[0029] The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in themarketplace, or to enable others of ordinary skill in the art to understand the embodiments described herein. For instance although the appendix is described as being appended to the rear of the primary, one of ordinary skill the art will appreciate that in certain embodiments the appendix can be placed at varying locations relative to the primary which can produce differing results.

[0030] While the disclosure is provided in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments of the disclosure have been described, it is to be understood that the exemplary embodiment s) may include only some of the described exemplary aspects. Accordingly, the disclosure is not to be seen as limited by the foregoing description. The embodiments described above are intended only to illustrate and teach one or more ways of making and using the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by one or more issued patent claims and their equivalents.

Claims

What is Claimed is:

1. A linear induction motor system for levitating a vehicle, the linear induction motor system comprising: a linear induction motor comprising: a back iron, a reaction rail adjacent to the back iron, and a primary separated from the reaction rail by a gap; and a rear appendix adjacent to the primary, wherein the rear appendix generates magnetic poles in the primary in response to a magnetic flux density in the reaction rail and back iron.2 The linear induction motor system of claim 1, wherein the magnetic flux density is associated with an eddy current induced in the reaction rail by the displacement magnetic flux density that is generated by the primary, multiphase winding and relative motion between the primary and the reaction rail.

3. The linear induction motor system of claim 1, wherein the rear appendix is comprised of ferromagnetic material. rear appendix.

4. The linear induction motor system of claim 3, wherein the thickness of the rear appendix along a y-axis is smaller than the thickness of the primary.

5. The linear induction motor system of claim 1, wherein an overall force generated by the linear induction motor is based at least in part on the electromagnetic interaction along a surface of the reaction rail over a length of the linear induction motor and a length of the rear appendix.

6. The linear induction motor system of claim 1, wherein a force normal to the direction of travel of the vehicle is based at least in part on a combination of one or more forces generated by the linear induction motor and one or more forces generated by the rear appendix.

7. The linear induction motor system of claim 6 , wherein a force normal to the direction of travel of the vehicle is based at least in part on the combination of the one or more forces generated by the linear induction motor and the rear appendix.

8. The linear induction motor system of claim 1, wherein a force normal to the direction of travel of the vehicle is equal to a first force normal to the direction travel of the vehicle for a first length of the rear appendix and the force normal to the direction of the vehicleis equal to a second force normal to the direction travel of the vehicle for a second length of the rear appendix, and the second force normal to the direction of travel of the vehicle is greater than the first force normal to the direction of travel of the vehicle and the second length of the rear appendix is greater than the first length of the rear appendix.

9. A linear induction motor system for levitating a vehicle, the linear induction motor system comprising: a linear induction motor that generates a linear induction motor force that causes the vehicle to levitate, the linear induction motor comprising: a back iron; a reaction rail; a primary; and a rear appendix that generates an additional force, wherein the additional force is based at least in part on a length of the rear appendix, and a total resulting force is generated based at least in part on the linear induction motor force and the additional force.

10. The linear induction motor system of claim 9, wherein the additional force is further based at least in part on the weight of the rear appendix.

11. The linear induction motor system of claim 9, wherein the additional force is further based at least in part on the length of the rear appendix being a fraction of a length of the linear induction motor.

12. The linear induction motor system of claim 11, wherein the total resulting force is fifty percent greater than the force when the length of the rear appendix is one third the length of the linear induction motor.

13. The linear induction motor system of claim 11, wherein the total resulting force is sixty percent greater than the force when the length of the rear appendix is two thirds the length of the linear induction motor.

14. The linear induction motor system of claim 12, wherein the length of the linear induction motor is 1.5 meters and the length of the rear appendix is 0.5 meters.

15. The linear induction motor system of claim 12, wherein the length of the linear induction motor is 1.5 meters and the length of the rear appendix is 1 meter.

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