Patent Application
20170335889
Embodiments of the present application generally relate to thrust or axial active magnetic bearings or actuators. More particularly, but not exclusively, embodiments of the present application relate to compensation windings for axial magnetic bearings that are adapted to at least attempt to minimize homopolar leakage of magnetic flux.
Magnetic bearing systems may utilize magnetism to at least levitate and/or support a rotable device or apparatus, such as, for example, a rotor, shaft, and/or disk of an electrical motor or generator, among other devices. Additionally, certain magnetic bearing systems can include active thrust or axial magnetic bearings or actuators that provide axial support for the rotatable device or component. Typically, active axial magnetic bearing pulling levitated apparatus to one direction utilize the flow of an electrical current in one, and only one, direction through electromagnetic coils or windings of the axial magnetic bearings to generate a magnetic field that, according to Ampere's circuital law, circles the electrical current. The associated generated thrust force often is associated with an axially induced magnetic field in an air-gap between the relatively stationary axial magnetic bearing and the levitated rotable device. Such a thrust force, which is often referred to as a reluctance force, is often generally directly proportional to the air-gap cross-sectional area and to the second power of the air-gap magnetic flux density.
When electrical current is flowing in only one direction through the electromagnetic coils or windings, the associated magnetic flux may also generally flow in only one direction, which can be referred to as a homopolar magnetic flux, along a main magnetic flux path. For example,
However, it is typically practically challenging, if not impossible, to keep all of the magnetic flux only in the main magnetic flux path. Moreover, typically, at least some of the magnetic flux, which may be referred to as leakage flux, flows outside of the main magnetic flux path. The degree of leakage flux present can depend, at least in part, on the magnetic saturation level of the main magnetic flux path, as well as the surrounding parts and materials near the axial magnetic bearing or actuator. Further, while such leakage flux typically is generally useless from a force generation standpoint, leakage flux can consume at least a portion of the total magneto-motive force that generates the magnetic field. Thus, leakage flux can reduce the load capacity of the axial magnetic bearing, while also increasing the total inductance of the axial magnetic bearing, which can reduce the dynamical capacity of the axial magnetic bearing.
Homopolar leakage flux can also cause electromagnetic interference for other electromagnetic components or devices of an apparatus or system. Moreover, axial magnetic bearings are typically positioned in relative close proximity to other components or devices of an apparatus or system, such as, for example, in relatively close proximity to other actuators and/or sensors. Accordingly, as depicted for example in
An aspect of an embodiment of the present application is an apparatus that includes an axial bearing core, at least a portion of the axial bearing core comprising a ferromagnetic material. The apparatus also includes a primary winding coupled to the axial bearing core, the primary winding having a plurality of first windings arranged to have a first number of turns. Additionally, the plurality of windings is further arranged for a flow of a current through the primary winding in a first direction. The apparatus also has a compensation winding that is coupled to the axial bearing core. The compensation winding can have a plurality of second windings that are arranged to have a second number of turns, the second number of turns being about one-half the number of turns as the first number of turns. Further, the compensation winding is arranged for a flow of a current through the compensation winding in a second direction, the second direction being opposite of the first direction.
Another aspect of an embodiment of the present application is an apparatus that includes a first axial magnetic bearing having a first stator core, a first primary winding, and at least one first compensation winding, the at least one first compensation winding having a number of turns that is at least equal to a number of turns of the first primary winding. The apparatus further includes a second axial magnetic bearing having a second stator core, a second primary winding, and at least one second compensation winding, the at least one second compensation winding having a number of turns that is at least equal to a number of turns of the second primary winding. The apparatus further includes a main rotor, the main rotor providing a flux return path for the flow of magnetic flux generated by at least the first and second primary windings. Additionally, the apparatus may not include a thrust plate.
A further aspect of an embodiment of the present application is a method that includes delivering a first electrical current to a first primary winding a first axial magnetic bearing. The delivered first electrical current can flow in a first direction through the primary winding. A second electrical current can be delivered to one or more first compensation windings of the first axial magnetic bearing. Further, the delivered second current can flow through the one or more first compensation windings in a second direction that is opposite of the first direction. Additionally, a third electrical current can be delivered to one or more second compensation windings of the second axial magnetic bearing. Further, the delivered third current can flow through the one or more second compensation windings in the second direction. The method can also include delivering a fourth electrical current to a second primary winding of a second axial magnetic bearing. The fourth electrical current can flow in the second direction. Further, the first and second axial magnetic bearings can be positioned on opposite sides of a rotable device, at least one of the first and fourth electrical currents including a biasing current. The method can also include compensating, through operation of the one or more first and second compensation windings, a magneto-motive force generated by the first and second primary windings to produce a net magneto-motive force of around zero ampere turns.
The description herein makes reference to the accompanying figures wherein like reference numerals refer to like parts throughout the several views.
The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentalities shown in the attached drawings.
Certain terminology is used in the foregoing description for convenience and is not intended to be limiting. Words such as “upper,” “lower,” “top,” “bottom,” “first,” and “second” designate directions in the drawings to which reference is made. This terminology includes the words specifically noted above, derivatives thereof, and words of similar import. Additionally, the words “a” and “one” are defined as including one or more of the referenced item unless specifically noted. The phrase “at least one of” followed by a list of two or more items, such as “A, B or C,” means any individual one of A, B or C, as well as any combination thereof.
The first and second axial magnetic bearings 202a, 202b each include an axial bearing core 214, which can be a stator core comprising at least a ferromagnetic material. The axial core bearing 214 can have an inner wall 216, an outer wall 218, and opposing first and second sides 220a, 220b. The inner wall 216 generally defines an aperture 222 that is sized to at least accommodate rotational displacement of an adjacent portion of the rotable device 204 that may extend through the aperture 222, while the outer wall 218 generally defines an outer periphery of the axial bearing core 214. Further, according to certain embodiments, the outer wall 218 can be configured to at least assist in relatively securely coupling the axial bearing core 214 to an adjacent structure, such as, for example, a motor, generator, or bearing housing, among other structures. Additionally, the inner and outer walls 216, 218 may each have a variety of similar or dissimilar shapes. For example, according to certain embodiments, both the inner and outer walls 216, 218 may be generally circular in cross-sectional shape such that the axial bearing cores 214 of the first and second axial magnetic bearings 202a, 202b are generally axisymmetric structures, such as, for example, ring shaped, among other shaped structures.
The first and second axial magnetic bearings 202a, 202b each further include a primary winding or electromagnetic coil 224a, 224b. The primary winding 224a, 224b may be configured to at least assist in the generation of a force that provides a magnetic bearing for the rotable device 204 in a thrust direction that is generally parallel to the axis of rotation. According to certain embodiments, the primary winding 224a, 224b comprises a plurality of number of turns wounded from an electrically conductive material, such as, for example, but not limited to, copper wire. Further, the plurality of windings for the primary winding 224a, 224b may generally be configured such that, when the rotable device 204 operably extends through the aperture 222 of the axial bearing core 214, the plurality of windings of the primary windings 224a, 224b are generally symmetrical about at least the axis of rotation 206 of the rotable device 204. The number of turns (NPW) of the plurality of windings of the primary windings 224a, 224b may depend on a variety of different factors, including, for example, the strength of the magneto-motive force that is to be generated by operation of the respective first or second axial magnetic bearing 202a, 202b. Moreover, the magneto-motive force (MMF) generated by the operation of the first or second axial magnetic bearing 202a, 202b can generally be the product of the number of turns (NPW) of the primary and the current (I) flowing inside of the primary winding 224a, 224b, which can be represented as:
MMF=(NPW)I (Eq. 1)
According to certain embodiments, the axial bearing core 214 of the first and second axial magnetic bearings 202a, 202b may each include a primary coil slot 226a, 226b that extends into the axial bearing core 214 from one of the first and second sides 220a, 220b of the axial bearing core 214. The primary coil slot 226a, 226b can be sized to house at least a portion of the primary winding 224a, 224b, as depicted in
The first and second axial magnetic bearings 202a, 202b each further include one or more compensation windings 228a, 228b. The compensation winding(s) 228a, 228b may be configured to, when operably subjected to an electrical current, at least assist in generating a magneto-motive force that reduces and/or minimizes homopolar magnetic flux leakage, as discussed below. Moreover, the compensation winding(s) 228a, 228b may be configured and/or operated such that the net MMF of the bearing system 200 is, or is around, zero. Moreover, the compensation winding(s) 228a, 228b may be configured and/or operated such that the net MMF generated by the flow of current through the first and/or second primary windings 224a, 224b is zero. As discussed below in more detail, depending on the circumstances and/or configuration of the bearing system 200, current may simultaneously flow through either or both of the first and second primary windings 224a, 224b. Further, as also discussed below, according to certain embodiments, the compensation winding(s) 228a, 228b may be configured such that each compensation winding 228a, 228b compensates for the MMF generated by the primary winding 224a, 224b of the bearing 202a, 202b associated with that compensation winding 228, 228b, respectively, or the compensation windings 228a, 228b operate together to both compensate for the net MMF generated by both the first and second primary windings 224a, 224b, such that the net MMF of the bearing system 200 is, or is about, zero.
Similar to the primary winding 224a, 224b, the compensation windings 228a, 228b comprises a plurality of number of turns wounded from an electrically conductive material, such as, for example, but not limited to, copper windings. Additionally, the windings for the compensation winding(s) 228a, 228b may generally be configured such that, when the rotable device 204 operably extends through the aperture 222 of the axial bearing core 214, the compensation winding(s) 228a, 228b are generally symmetrical about the axis of rotation 206 of the rotable device 204.
The number of turns (NCW) for the compensation winding(s) 228a, 228b may depend on a variety of different factors, including, for example, the strength of the magneto-motive force that is anticipated to be separately generated by each of the primary windings 224a, 224b. According to certain embodiments, the compensation winding(s) 228a for first magnetic bearing 202a has one-half the number of turns (NCW1) as the number of turns (NPW1) of the primary winding 224a of the first magnetic bearing 202a. Similarly, according to certain embodiments, the compensation winding(s) 228b for second axial magnetic bearing 202b has one-half of the number of turns (NCW2) as the number of turns as the number of turns (NPW2) as the primary winding 224b of the second axial magnetic bearing 202b. Accordingly, when the number of turns (NPW1) of the primary winding 224a of the first magnetic bearing 202a is the same as the number of turns (NPW2) of the primary winding 224b of the second axial magnetic bearing 202b, then:
N
PW1
=N
CW1
+N
CW2 (Eq. 2)
N
PW2
=N
CW1
+N
CW2 (Eq. 3)
Referencing
Additionally, the compensation windings 228a, 228b may, or may not, have a size, configuration, and/or position that is generally similar to that of the primary winding 224a, 224b. Further, the compensation windings 228a, 228b may be positioned at a variety of locations relative to the axial bearing core 214. For example, as shown in
Although
(NCWA+NCWB)=NPW/2 (Eq. 4)
During use, one of the first and second axial magnetic bearings 202a, 202b is positioned adjacent to the first side face 212a of the disk or plate 208, and the other of first and second axial magnetic bearings 202a, 202b is positioned adjacent to the second side face 212b of the disk or plate 208. Further, the first and second axial magnetic bearings 202a, 202b are positioned in relative close proximity to the adjacent first or second side faces 212a, 212b of the disk or plate 208. For example, according to the example illustrated in
When operated, electrical current can flow through the primary winding 224a, 224b of one of the first or second axial magnetic bearings 202a, 202b in a first direction, while electrical current flows through the one or more compensation windings 228a, 228b of both of the axial magnetic bearings 202a, 202b in a second direction, the second direction being opposite of the first direction. Moreover, according to the certain embodiments, current through the compensation windings 228a, 228b may generally flow in one, and only one, direction. Similarly, according to such embodiments, current through the primary windings 224a, 224b may generally flow in one, and only one, direction that is opposite to the direction that current is flowing through the compensation winding(s) 228a, 228b. For example, electrical current may flow through the primary winding 224a, 224b in one of a clockwise or counter-clockwise direction, while electrical current flows through the compensation winding(s) 228a, 228b in the other of the clockwise and counter-clockwise directions. Additionally, the current for the primary winding 224a, 224b and compensation winding(s) 228a, 228b may be provided from the same, or different, power sources. For example, according to certain embodiments, the primary winding 224a, 224b and the one or more compensation windings 228a, 228b can be all connected in series to a common current source, or can be supplied with power from separate current sources.
Thus, for a given primary winding 224a, 224b, such as, for example, the primary winding 224a of the first magnetic bearing 202a, the number of turns (NPW1) of the primary winding 224a is equal to the sum total number of turns of the compensation windings 228a, 228b of the first and second axial magnetic bearings 202a, 202b, as indicated by the application of above Equation 1. Accordingly, as current can be controlled to only flow in one of the first and second axial magnetic bearings 202a, 202b at a particular time, and flows in a direction that is opposite of the direction that current flows through the compensation windings 228a, 228b of both the first and second axial magnetic bearing 202a 202b, the net magneto-motive force (MMF) generated from the primary winding 224a and the compensation windings 228a, 228b is generally zero. For example, if current (I) is flowing through the primary winding 224a of the first magnetic bearing 202a to work against an opposing external thrust force, current may not be flowing through the primary winding 224b of the second axial magnetic bearing 202b. In such an example, the magneto-motive force (MMF2) provided by the primary winding 224b of the second axial magnetic bearing 202b can be zero. If, however, the first axial magnetic bearing has an winding having 100 turns (N=100), referencing above equation 1 (Eq. 1), the magneto-motive force (MMF1) provided by current flowing through the primary winding 224a of a first magnetic bearing 202a can be represented as MMF=100(I). In such an example, referencing above-equation 2, the compensation windings 228a of the first magnetic bearing 202a can have a sum total of 50 turns, and the compensation windings 228b of the second axial magnetic bearing 202b may also have a sum total of 50 turns. Further, as the current is flowing in the compensation windings 228a, 228b of the first and second axial magnetic bearings 202a, 202b in a direction that is opposite to the direction that current flows through the primary winding 224a of the first magnetic bearing 202a, the current flowing through the compensation windings 228a, 228b can be represented as a negative current (e.g., −I). Accordingly, in such an example, the magneto-motive force (MMF1) provided by current flowing through the compensation winding 228a of the first magnetic bearing 202a can be represented as −50(I), and the MMF provided by current flowing through the compensation winding 228b of the second axial magnetic bearing 202b can be represented as −50(I). In such an example, the sum of the MMF of the first axial magnetic bearing 202a (100(I)), the compensation winding 228a of the first axial magnetic bearing (−50(I)), and the compensation winding 228b of the second axial magnetic bearing (−50(I)) is generally zero.
Additionally, the inclusion of one or more compensation windings 228a, 228b to the axial magnetic bearings 202a, 202b may prevent and/or minimize the negative effects of the homopolar-leakage of magnetic flux that can otherwise be associated with axial magnetic bearings 202a, 202b in which current flows only in one direction. Further, by decreasing, if not generally eliminating, homopolar-leakage magnetic flux by the inclusion of one or more compensation windings 228a, 228b to each of the axial magnetic bearings 202a, 202b may at least assist in reducing, if not eliminating, the degree to which the operation of the axial magnetic bearings 202a, 202b generates electromagnetic interference for other relatively nearby electromagnetic components, such as, for example, other actuators, sensors, and/or an electric motor, among other components. Additionally, by maintaining a relatively high degree or density of main flux along the main flux path, the total inductance of the primary winding 224a, 224b may be reduced, which can improve the dynamical capability of the associated axial magnetic bearing 202a, 202b. Further, reducing, or eliminating the homopolar leakage of magnetic flux may reduce concerns relating to the materials of adjacent components extending the path of travel of the leakage flux. Accordingly, the reduction, or elimination, of homopolar leakage may enhance the degree of freedom in the selection of materials that can be used for adjacent parts or components, including, for example, the option of using ferromagnetic iron for a housing of an associated electrical motor, generator, and/or bearing. Further, enhancing the ability to retain a larger amount or density of magnetic flux along the main flux path may reduce the potential of other components or parts becoming inappropriately magnetized, and thereby reduce or eliminate potential adverse side effects of such magnetization, including, for example, the attraction and associated accumulation of debris, including dirt and metallic particles, that can be harmful to the operation of the associated system, device, or component.
While examples are discussed above in terms of a first current flowing through either the first or the second primary winding 224a, 224b, while little or no current flows through the other of the first and second primary windings 224a, 224b, embodiments of the present application can also be used in situations or configurations in which current flows through both the first and the second primary windings 224a, 224b. For example, according to certain embodiments, a first current can flow the first axial magnetic bearing 202a, a second current can flow through one or more first compensation windings 228a, 228a″, a third current can flow through a one or more second compensation windings 228b, 228b′, and a fourth current can flow through the second axial magnetic bearing 202b. Additionally, in certain situations, the first or the fourth current that flows through the first or second primary winding 224a, 224b, respectively, can be a biasing current. Further, which of the first and fourth currents is a biasing current can vary or alternate based on a number of circumstances. Such biasing current may be used to at least assist in linearizing the bearing force behavior capacity, as well as improve the speed of the associated bearing (s)202a, 202b.
For example, referencing the bearing system 200 shown in
Compensation for the first and second primary windings 224a, 224b such that the total MMF of the bearing system 200, which includes the compensation windings 228a, 228a′, 228b, 228b′, is zero ampere turns can be achieved in a variety of manners. For example, according to certain situations, the first compensation winding(s) 228a, 228a′ can have a total of 100 turns, and the second compensation winding(s) 228b, 228b′ can also have 100 turns. According to such a configuration, compensation for the MMF of the first and second primary windings 224a, 224b can be performed separately per side of the bearing system 200. For example, according to certain embodiments, the first compensation winding(s) 228a, 228a′ can receive a −4 amp current, and the second compensation winding(s) 228b, 228b′ can receive a +2 amp current. In such a situation, the first compensation winding 228a, 228a′ can compensate for the MMF of the first primary winding 224a such that the net MMF of the first primary winding 224a and the first compensation winding(s) 228a, 228a′ is, or is around, zero. Similarly, the second compensation winding 228b, 228b′ can separately compensate for the MMF of the second primary winding 224b, such that the net MMF of the second primary winding 224b and the second compensation winding(s) 228b, 228b′ is, or is about, zero.
According to another embodiment, rather than having the first and second compensation windings 228a, 228a′, 228b, 228b′ separately compensate for the MMF of their associated primary winding 224a, 224b, the first and second compensation windings 228a, 228a′, 228b, 228b′ can, together, both compensate for the total MMF of both the first and second primary windings 224a, 224b. For example, in the above example, the MMF of the first primary winding 224a is 400 ampere turns, while the MMF of the second primary winding 224b is −200 ampere turns. In such a situation, as discussed above, the first compensation winding(s) 228a, 228a′ and the second compensation winding 228b, 228b′ can each have a number of turns that is one-half the number of turns of the first primary winding 224a, and/or is one-half the number of turns of the second primary winding 224b. For example, following the previously discussed example in which the first and second primary windings 224a, 224b each had 100 turns, the first compensation winding(s) 228a, 228a′ may have a total of 50 turns, and the second compensation winding(s) 228b, 228b′ may also have a total of 50 turns. Accordingly, in such an example in which the total MMF of the first and second primary windings 224a, 224b is 200 amps (A), a 2 amp (A) current in an opposite direction, which in this example is a direction that is opposite of the flow of current through the first primary winding 224a, and can therefore be referred to as −2 A, can flow through each of the first and second compensation winding 228a, 228a′, 228b, 228b′. In such an example, a −2 A current to the 50 turn first compensation winding 228a, 228a′ will provide a −100 ampere turns, and similarly a −2 A current to the 50 turn second compensation winding 228b, 228b″ will also provide a −100 ampere turns for a total of −200 ampere turns. Thus, in this example, the total MMF or −200 ampere turns for the compensation windings and the total MMF of 200 ampere for the first and second primary windings 224a, 224b can result in a net MMF for the system 200 of, or around, 0 ampere turns.
Additionally, according to at least certain embodiments in which the first and second compensation windings 228a, 228a′, 228b, 228b′ both compensate together for the total MMF that is about equal to, but opposite of, the total MMF of both the first and second primary windings 224a, 224b, the first and second compensation windings 228a, 228a′, 228b, 228b′ may not be connected in series with the first and second primary windings 224a, 224b. Further, such an embodiment may be configured to include certain power electronics, such as, for example, an H-bridge configuration wherein the number of power amplifiers is increased compared to other situations that may utilize a half bridge connection, and wherein current may flow in only one direction.
Additionally, according to certain embodiments, the magnetic bearing system 200 may not include or utilize a thrust disk or plate, such as, for example, not include the disk or plate 208 that is depicted in
Additionally, according to certain embodiments, the ratio of electrical power delivered to the first and second axial magnetic bearings 202a, 202b can be based on at least attempting to axially displacing the rotor 203 in a particular direction. For example, according to certain embodiments, the system 200 can include one or more separate position sensors 116 that sense at least the axial position of the rotor 203. Further, the first and second axial magnetic bearings 202a, 202b can receive a supply of current, as determined for example by using a position and current control algorithm, that is to both levitate the rotor 203 as well as axially maintain the levitated rotor 203 at a central reference position. In the event that the rotor 203 is axially displaced away from the central reference position, such as in one of opposing first and second axial directions, the movement of the rotor 203 can be sensed by the one or more sensors 116. In such a situation, the position and current control algorithm can calculate a current, or ratio of current, that, when delivered to the first and second axial magnetic bearings 202a, 202b, can at least assist in returning the axially displaced rotor 203 back toward and/or to the central reference position.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.
