System and method for magnetic bearing

Abstract

Compressor assemblies (120) are provided. Embodiments of the present disclosure relate generally to compressors for use in chiller air conditioning systems for indoor spaces. The disclosed compressors have magnetic bearings (290, 300, 320) that support rotating components. In one embodiment, the compressor includes a segmented thrust bearing (320) stator core (430). Additional systems, devices, and methods are also disclosed.

Description

TECHNICAL FIELD

[0001] This document relates to systems and methods for magnetic bearings. BACKGROUND

[0002] This section is intended to introduce the reader to various aspects of art that can be related to various aspects of the presently described embodiments and are not necessarily all drawn to prior art. Accordingly, this section is not intended to limit the scope of what can be claimed unless otherwise explicitly so limited.

[0003] Modern residential and commercial customers desire the ability to control the climate of an indoor space. Typically, a heating, ventilation, and air conditioning ("HVAC") system circulates the air of an indoor space over a source of low temperature (for cooling) or high temperature (for heating) to adjust the ambient air temperature of the indoor space. HVAC systems produce these sources of low and high temperature by techniques that utilize well-known physical principles that heat is released when a fluid changes from a gas to a liquid, and heat is absorbed when a fluid changes from a liquid to a gas.

[0004] In a typical residential system, a fluid refrigerant is circulated through a closed loop of piping that uses a compressor and other flow control devices to manipulate the flow and pressure of the refrigerant to circulate the refrigerant between a liquid phase and a gas phase. These phase changes typically occur in heat exchangers of the HVAC that are part of the closed loop and are designed to transfer heat between the circulating refrigerant and the flowing ambient air. This is the basis of the refrigeration cycle. The heat exchanger where the refrigerant changes from a gas to a liquid is called a "condenser" and the condensing fluid releases heat to the surrounding environment. The heat exchanger where the refrigerant changes from a liquid to a gas is called an "evaporator" and the evaporating refrigerant absorbs heat from the surrounding environment.

[0005] For commercial applications, centrifugal chillers are an economical way to control the indoor climate of large indoor spaces. In a typical chiller system, multiple fluid circuits cooperate to transfer heat from one location to another. At the heart of a typical chiller is a refrigerant circuit that circulates a fluid refrigerant that changes between a liquid phase and a gas phase to achieve the desired heat absorption or rejection. This is similar to a traditional residential system. However, rather than the refrigerant directly transferring heat to or from the surrounding or circulating air, a chiller typically employs a circulating water loop that transfers the heat. To cool a building, the evaporator of the refrigerant circuit can be designed to absorb heat from water circulating in a chilled water loop, which in turn absorbs heat from the indoor environment via a heat exchanger in an air handling unit. And the condenser of the refrigerant circuit can be designed to release heat from the circulating refrigerant to water circulating in a cooling water loop, which in turn releases heat to the outdoor environment via a heat exchanger in a cooling tower.

[0006] Refrigerant circulation within a refrigerant circuit can be partially motivated by a centrifugal compressor that receives low pressure refrigerant, primarily in a gaseous state at a low temperature, and compresses the refrigerant using a rotating impeller to increase the pressure and temperature of the refrigerant. The impeller is rotated by a motor. More specifically, a typical motor has a shaft that extends through a motor rotor and is coupled to the motor rotor, and the impeller is typically coupled to the shaft. Thus, rotation of the motor rotor causes the impeller to rotate.

[0007] Support bearings support the shaft, which in turn supports the motor rotor, allowing the motor rotor to rotate relative to a stationary motor stator that surrounds the motor rotor. Typically, the support bearings are ball bearing systems, where balls housed between an inner raceway and an outer raceway cause the two raceways to rotate relative to one another. This is a mechanical arrangement, and the power energy provided by the motor is often lost due to friction between the bearing raceways and the balls. Furthermore, the mechanical interaction between the raceways and the balls can cause unnecessary wear on the bearing assembly. These negative factors are amplified in large chiller compressors that can rotate at relatively high speeds for long periods of time. This often means that the mechanical components must be lubricated by an expensive and complex lubrication system.

[0008] Certain chillers use magnetic bearings instead of mechanical bearings to facilitate rotation of the shaft and the motor rotor. In other words, opposing magnetic fields are used to balance the shaft relative to the stator in both axial and radial directions. Magnetic bearings do not have the same frictional losses and mechanical wear as ball bearing systems. But they do have some energy losses. For example, magnetic bearings typically maintain balance by frequently changing the magnetic field that is used to counteract the forces acting on the shaft due to operation. These changes in the field induce eddy currents, which reduce the overall operating efficiency and performance of the compressor.

[0009] Eddy currents can be reduced by segmenting the bearing core or forming the bearing core from laminated sheets instead of forming the core from a single piece. However, segmenting the bearing into multiple pieces in order to reduce eddy currents also presents challenges. SUMMARY

[0010] Certain aspects of some implementations disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention can take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention can encompass a variety of aspects that can not be set forth below.

[0011] Embodiments of the present disclosure generally relate to magnetic thrust bearing assemblies having a partially segmented stator core. In some embodiments, a magnetic thrust bearing assembly includes an annular stator core configured to support an electrical winding. The stator core includes a plurality of grooves that partially and radially extend through the stator core. In other embodiments, a compressor includes a shaft and a magnetic thrust bearing configured to support rotation of the shaft. The magnetic thrust bearing further includes an annular stator core having a plurality of grooves that partially and radially extend through the stator core.

[0012] With respect to various aspects of the embodiments, various modifications of the features recited above can exist. Further features can also be incorporated into these various aspects. These modifications and additional features can exist alone or in any combination. For example, various features discussed below with respect to one or more of the illustrated embodiments can be incorporated into any of the above aspects of the present disclosure, alone or in any combination. Again, the above summary of the application is intended to be merely a summary of some aspects and context of some embodiments and does not limit the claimed subject matter. BRIEF DESCRIPTION OF DRAWINGS

[0013] These and other features, aspects, and advantages of certain embodiments will become better understood with reference to the following detailed description, appended claims, and accompanying drawings where like reference numbers are used to represent like elements throughout. The drawings are not intended to be to scale.

[0014] Figure 1

[0015] Figure 1 schematically illustrates a chiller system for a building according to one embodiment of the present disclosure;

[0016] Figure 2

[0017] Figure 2 schematically illustrates a cross-section of a compressor assembly according to one embodiment of the present disclosure;

[0018] Figure 3

[0019] Figure 3 schematically illustrates an isometric cross-section of a magnetic thrust bearing assembly around a shaft according to one embodiment of the present disclosure;

[0020] Figure 4

[0021] Figure 4 schematically illustrates an axial cross-section of a support ring mounted to a shaft according to one embodiment of the present disclosure; and

[0022] Figure 5

[0023] ​​​​​​​​​​Figure 5 A cross-section of a support ring according to one embodiment of the present disclosure is schematically and isometrically illustrated. DETAILED DESCRIPTION

[0024] One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation can not be described in the description. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which can vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0025] When introducing elements of various embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there can be additional elements other than the listed elements.

[0026] Turning now to the drawings, Figure 1 An overview of the chiller system 100 is illustrated. At the center of the system is the refrigerant circuit 110. The compressor 120 converts a relatively cold, low pressure refrigerant gas into a hot, high pressure gas. As shown, the compressor 120 is a two-stage compressor: the low pressure refrigerant is pressurized via a first stage impeller 130, and the refrigerant output from the first stage impeller is received by a second stage impeller 140 for further pressurization. It is contemplated that certain embodiments can employ a single stage compressor or multiple compressors with various stages. And it is contemplated that the refrigerant can be any number of refrigerants including R410A, R32, R454B, R452B, R125, R466A, R1233zd, R1233zd(E), R1234ze, R134a, R513A, R515A, R515B, and R1234yf, or any number of combinations and mixtures thereof in various percentages.

[0027] The hot, high pressure gas is then converted into a high pressure liquid refrigerant in the condenser 150. During this step, the heat rejected from the high pressure gas conversion is typically transferred through a heat exchanger in the condenser 150 to water circulating in the cooling water circuit 160. Ultimately, the heat transferred to the water in the cooling water circuit 160 is rejected to the outdoor environment via another heat exchanger in the cooling tower 170.

[0028] The now liquid refrigerant leaving the condenser 150 in the refrigerant circuit is converted to a low pressure liquid as it passes through the expansion valve 180. The pressure drop of the refrigerant also lowers its temperature, making it a low pressure, low temperature liquid. The cool, low pressure liquid then enters the evaporator 190 where heat is transferred back into the refrigerant, converting the refrigerant back to a low pressure gas to be compressed by the compressor. The heat transferred to the refrigerant in the evaporator 190 is typically provided by water circulating in a second chilled water circuit 200 through a heat exchanger in the evaporator 190. The chilled water circuit 200 delivers the now chilled water to an air handling unit (AHU) 210 which circulates the building's indoor air over the heat exchanger to cool the indoor space.

[0029] To coordinate the operation, the system 100 can include a controller providing a human-machine interface. The controller 220 can control the operation of the compressor, the magnetic bearings in the compressor, and various other flow control components in the chiller system, for example, can communicate wirelessly through any number of wireless protocols such as WiFi, short range RF signals such as the Bluetooth (registered trademark) signal protocol available from the Bluetooth SIG organization, or wired via the use of a wired protocol such as BacNET, CAN, or proprietary control logic such as P1 / P2 or S21, just to name a few. In addition, the controller can connect to the internet and provide cloud-based or web-based operation from a remote location.

[0030] Figure 2 Focusing on an exemplary compressor assembly for a chiller shown in a schematic cross-section. (For ease of discussion, only a portion of the compressor is shown), as discussed above, the compressor receives low pressure, low temperature refrigerant which is converted to a high pressure, high temperature state by the rotation of the impeller 230.

[0031] To effect rotation of the impeller, the compressor 120 includes a motor assembly 240, which can be any number of types of motors, such as hydraulic, pneumatic, or electric. As shown, the compressor assembly 230 employs an electric motor assembly 240 having a stationary annular stator 250 and a rotating rotor 260 disposed inside the annular stator. The stator and rotor of the motor cooperate to convert electrical current into rotational motion, as is well known in the art. Advantageously, the controller 220 can provide and receive signals from the compressor 120 to optimize its operation. For example, the controller can send control signals and coordinate with a power source to send electrical current to wires in the stator 250 (such as wound coils 270), which when properly energized, the stator 250 generates varying magnetic flux that causes the magnetic rotor 260 to rotate. And the controller 220 can be configured to coordinate with a power source that provides pulse width modulated current to the wound coils. The pulse width modulated current can be generated through the use of appropriate conditioning circuitry, such as that which converts alternating current to direct current, and helps to modulate the duration of the direct current to simulate alternating waveforms of various frequencies. The controller can also be part of a building management system that sends signals to and receives signals from the building, enabling the operation of the chiller system to be optimized.

[0032] A shaft 280 extends through and is coupled to the rotor 260, which rotates with the rotor 260. And rotation of the shaft is imparted to the impeller 230, which is mechanically coupled to the shaft. In some embodiments, a gear assembly can be interposed between the shaft and the impeller to coordinate or change the rotational speed of the shaft relative to the impeller. However, as shown, the shaft 280 is directly driven by the motor assembly, such that the rotational speeds of the shaft and the impeller are matched.

[0033] Shaft 280 and rotor 260 attached thereto are supported by bearings 290. In the illustrated embodiment, bearings 290 are annular magnetic bearings surrounding shaft 280 and include radial bearings 300 that support the shaft in the Y-Y direction 310 and thrust bearings 320 that support the shaft in the X-X direction 330. More specifically, bearings 300, 320 have windings that, when energized, create magnetic flux that supports the shaft without mechanical contact. For example, shaft 280 includes a magnetic portion 350 that magnetically interacts with the created flux to support in the Y-Y direction. This magnetic portion 350 can be integral with the shaft. Or it can be a separate annular component that is mounted to the shaft, as shown. Additionally, by way of example, the illustrated shaft 280 carries an annular thrust rotor 370 made of magnetic material, where thrust rotor 370 interacts with magnetic flux created by windings 340 in thrust stator 380 to control the position of the shaft (and components mounted on the shaft) in the X-X direction. In the illustrated embodiment, thrust rotor 370 and magnetic portion 350 surround the shaft and are positionally fixed to the shaft in the X-X direction by annular support ring 390. Thrust rotor 370 is disposed partially within an annular space 395 defined by the thrust stator core.

[0034] Advantageously, controller 220 can provide signals 400 to the windings 340 of the magnetic bearings and manage the current 400, thereby controlling the magnetic flux created by the windings, which in turn stabilizes the position of the shaft in the compressor assembly as the shaft rotates.

[0035] Figure 3 Focusing on the thrust bearing assembly 320, which is illustrated schematically, isometrically, and in cross-section. As shown, annular thrust bearing assembly 320 surrounds shaft 280 and supports shaft 280 in the X-X direction using created magnetic flux. Directly mounted to shaft 280 is thrust rotor 370, which is positionally fixed to the shaft in the X-X direction 330 by a shoulder 410 on one side and support ring 390 (see Figure 2 ) on the other. As discussed above, thrust rotor 370 rotates with the shaft.

[0036] During this rotation, axial forces (i.e., forces in the X-X direction) can attempt to move the shaft, which can cause operational problems. The role of the thrust bearings is to counteract these operational forces and keep the shaft in place. The role of the windings (not shown) disposed in coil housing 420, which is an annular space in the thrust stator (more specifically, in thrust stator core 430), is to provide counteracting magnetic forces to keep thrust rotor 370 in place. For example, X+ side windings (referenced Figure 3The X-side coils (e.g., the coils shown in the shaft) can provide flux in the X- direction to drive the thrust rotor. Conversely, the X+ side coils can provide flux in the X+ direction to drive the thrust rotor. By adjusting the flux in each of the wound coils, the position of the thrust rotor is stabilized in the X-X direction.

[0037] However, when the wound coils generate this flux, eddy currents can form in the thrust bearing (particularly in the thrust bearing core). These eddy currents can indirectly cause the operational efficiency of the compressor to decrease. For example, the eddy currents can cause the frequency response to decrease (i.e., the lag of the bearing inductance to rapid fluctuations in the control current to decrease). This, in turn, makes it more difficult for the compressor to operate at or near the surge margin, as the compressor is considered to operate most efficiently at the surge margin.

[0038] By completely segmenting the thrust stator core 430, the generation and density of eddy currents can be reduced. That is, the thrust stator core 430 can be composed of a plurality of pie-shaped and separate stator core segments (not shown) that are then mechanically assembled to form the annular thrust stator core 430. Unfortunately, when this is done, misalignments and other factors related to the assembly can occur. Also, it can be difficult to manufacture a completely segmented stator core.

[0039] According to one embodiment, it is believed that eddy currents are reduced without the need to segment or laminate (i.e., make from laminated sheets) the thrust stator core 430. In this embodiment, as Figure 3 As illustrated, the thrust stator core 430 includes a plurality of grooves 450 that extend radially and partially through the annular thrust stator core 430. The grooves 450 begin on a radially inward outer surface 460 of the thrust stator core 430 and extend axially across the radially inward outer surface 460, and also radially through the thrust stator core 430, but not to a radially outward outer surface 470 of the thrust stator core 430. In other embodiments (not shown), the grooves extend from the radially outermost outer surface 470 and radially through the stator core, but not to the radially innermost outer surface 460.

[0040] In either embodiment, the grooves create gaps between adjacent portions of the thrust stator core while retaining the thrust stator core 430 as a one-piece assembly or unitary body, it is believed that such a stator core is easily manufactured using conventional casting processes and off-the-shelf materials such as AISI 1008 low carbon steel. By having gaps but still setting the stator up as one piece, the illustrated thrust stator core 430 can be partially segmented.

[0041] The grooves are also believed to reduce the generation of eddy currents, and in turn, promote more efficient operation when applying rapidly fluctuating currents, such as during surge and trip operations. In fact, the grooves 450 are believed to improve the dynamic load capacity of the thrust bearing, making the compressor more suitable for harsh and demanding operating environments or performance requirements. Moreover, the grooves 450 increase the surface area of the bearing, and the increased surface area helps dissipate heat.

[0042] In one embodiment, the radial height RH of the grooves matches the expected location of eddy currents in the thrust stator core 430. For example, eddy currents are believed to tend to form on the inner surface of the stator core 430, and the highest density of eddy currents occurs near the outward corner 425 of the coil housing 420. Accordingly, the height RH of the grooves can correlate to the radial distance of the corner 425 from the innermost outer surface 460. In one example, the radial height of the corner 425 from the innermost outer surface 460 can be the same as, and proximate to, the height RH of the grooves.

[0043] In certain embodiments, various compressor components mounted to the shaft 280 can be fixed in position in the axial direction via one or more support rings 390 (see Figure 2 ). However, it can be desirable to remove components that have been mounted to the shaft 280, for example, during maintenance. In such cases, the support ring 390 is removed axially from the shaft so that the fixed components, such as the magnetic portion 350, the thrust rotor 390, can be separated from the shaft.

[0044] Because the support ring 390 rotates with the shaft 280 and fixes other rotating components, it is beneficial to have a tight friction fit or coupling between the shaft 280 and the support ring 390. But such a tight fit can become a deciding factor during, for example, maintenance operations, when it makes it more difficult to remove the support ring 390.

[0045] Advantageously, according to one embodiment, the support ring 390 includes features that reduce the frictional forces between the shaft 280 and the support ring 390 when the shaft 280 is not rotating, but increase these frictional forces when the shaft is rotating. Figure 4 and Figure 5 An example support ring 390 having such features is illustrated. The illustrated support ring includes grooves 480 located near the shaft bore 490 (i.e., toward the radially inward outer surface). These grooves 480, along with the support members 500, help define (in the radial direction) a relatively thin mounting portion 510 that contacts the shaft to establish a frictional fit between the shaft and the support ring 390.

[0046] In Figure 4In the middle, support ring 390 is illustrated in an operational state, with shaft 280 and installed support ring 390 rotating in direction R-R. During rotation, thin mounting portion 510 is asymmetrically deformed due to centrifugal forces. This causes the area of mounting portion 510 to move radially away (outward) from shaft 280, but the contact face 520, generally at the midpoint of mounting portion 510 between supports 500, moves radially toward (inward) shaft 280, generally improving the friction or interference fit between support ring 390 and shaft 280. But when shaft 280 is stationary, support ring 390 returns to its more undeformed, more circular configuration, with more of mounting portion 510 contacting the shaft but with the friction or interference fit reduced, making it easier to remove support ring 390 from shaft 280.

[0047] The disclosed chiller system can use a large amount of refrigerant. For example, system 100 can circulate a single refrigerant such as R32. Alternatively, the system can employ a mixture of multiple refrigerants. For example, the system can employ a refrigerant having the following composition (by weight):

[0048]

[0049] As another potential implementation, the system can employ a hydrofluoroolefin (HFO) refrigerant. The HFO refrigerant employed can be of a single type or a mixture. For example, the system can employ a HFO refrigerant having the following composition (by weight):

[0050]

[0051] While aspects of the disclosure can be susceptible to various modifications and alternative forms, specific implementations have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the application is not intended to be limited to the particular forms disclosed. Rather, the application is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the following appended claims. For example, it is contemplated that the implementations described herein can be applicable to magnetic bearing systems used outside of chiller compressors, including magnetic bearings in motors for other industrial purposes.

[0052] List of Reference Characters

[0053] 100: chiller system

[0054] 110: refrigerant circuit

[0055] 120: compressor

[0056] 160: cooling water circuit

[0057] 200: chilled water circuit

[0058] 280: shaft

[0059] 320: thrust bearing assembly

[0060] 370: thrust rotor

[0061] 380: thrust stator

[0062] 390: support ring

[0063] 395: annular space

[0064] 430: thrust stator core

[0065] 450: recess

[0066] 460: radially innermost outer surface

[0067] 470: radially outermost outer surface

[0068] 480: slot

[0069] 510: mounting portion

Claims

1. A compressor for increasing the pressure of a fluid refrigerant, the compressor comprising: A magnetic thrust bearing configured to support the rotation of a shaft, wherein the magnetic thrust bearing comprises: An annular thrust stator core having a plurality of grooves extending locally and radially through the annular thrust stator core; and An annular thrust rotor, which is at least partially disposed within an annular space defined by the annular thrust stator core. The shaft extends through the annular thrust rotor. In the radial direction of the annular thrust stator core, the plurality of grooves extend from the innermost radial surface of the annular thrust stator core toward the outermost radial surface of the annular thrust stator core and at least to the annular space within the annular thrust stator core where the wound coil is disposed, i.e., the annular coil housing.

2. The compressor according to claim 1, wherein, The compressor is in fluid communication with a refrigerant circuit that circulates the fluid refrigerant, and wherein the refrigerant circuit is configured to exchange heat energy with a water circulation circuit.

3. The compressor according to claim 2, wherein, The fluid refrigerant is R32, R134A, R452B, R454B, R513A, R515A, R515B, R466A, R1233zd, R1233zd(E) or a refrigerant mixture containing HFO-1234yf.

4. The compressor of claim 1, wherein the compressor includes a controller configured to control a simulated frequency of pulse-width modulated power from a power source.

5. The compressor according to claim 1, wherein, The radial height of at least one of the plurality of grooves is substantially the same as the radial height of the position with the highest eddy current density in the annular thrust stator core.

6. The compressor according to claim 1, wherein the compressor includes a support ring radially disposed outside the shaft, wherein, The support ring includes a plurality of grooves that partially define a mounting portion configured to press radially inward against the shaft during rotation of the shaft.

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