System and method for surge control of dynamic compressor

Abstract

The system includes a dynamic compressor, a variable frequency drive (VFD), and a controller. The dynamic compressor includes a motor having a drive shaft rotatably supported within the dynamic compressor and a compression mechanism connected to the drive shaft and operable to compress a working fluid upon rotation of the drive shaft. The VFD includes a sensor configured to sense a current provided to the motor. The controller is connected to the motor and includes a processor and a memory. The memory stores instructions that program the processor to operate the motor using the VFD to compress the working fluid, receive a signal representative of the current to the motor from the VFD, and determine when a surge event has occurred based at least in part on the received signal representative of the current to the motor from the VFD.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. patent application Ser. Nos. 17 / 247,724 and 17 / 247,725, filed December 21, 2020, the disclosures of which are incorporated by reference in their entireties herein.

[0002] The field of the disclosure relates generally to control systems, and more particularly to control systems for machines including dynamic compressors. [Background technology]

[0003] Dynamic compressors, including centrifugal compressors, are used in many applications such as HVAC. Centrifugal compressors have a drive shaft operatively connected to a motor between compression mechanisms or impeller stages supported by gas foil bearings. The drive shaft can be located between the impeller stages such that the impeller rotates at a rotational speed to compress the refrigerant to a selected pressure in the HVAC system. The compressor bearings typically include one or more features to reduce friction between the compressor bearing and the drive shaft. When the shaft rotates fast enough, the gas pushes the foils away from the shaft so that no contact occurs. The shaft and the gas foil bearing are separated by a high pressure of the gas, which is generated by the rotation that draws the gas into the bearing by viscous effects. A high speed of the shaft relative to the gas foil bearing is required to initiate the gas gap, and once this is achieved, no contact occurs. These bearings have several advantages over other bearings, such as lighter weight, stable operation at high speeds and temperatures, low power losses at high speeds, and long life with little maintenance.

[0004] Compressor surge events cause accelerated wear on the compressor and compressor components, including bearings. Surge is a characteristic operation of a dynamic compressor that can occur when the head generated by the compressor to overcome the system pressure at the compressor discharge is insufficient. When surge occurs, the compressor output pressure drops significantly, resulting in a reversal of flow within the compressor. When a dynamic compressor surges, there is an actual reversal of gas flow through the impeller. Surge usually begins in one stage of a multi-stage compressor and can occur very quickly. Compressors are particularly susceptible to surge events during start-up or shutdown due to their low operating speeds. The severity of a surge event and the damage it causes increases with compressor speed.

[0005] This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to better understand the various aspects of the present disclosure. As such, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0006] One aspect of the disclosure is a system including a dynamic compressor, a variable frequency drive (VFD), and a controller. The dynamic compressor includes a motor having a drive shaft rotatably supported within the dynamic compressor and a compression mechanism connected to the drive shaft and operable to compress a working fluid upon rotation of the drive shaft. The VFD includes a sensor configured to sense a current provided to the motor. The controller is connected to the motor and includes a processor and a memory. The memory stores instructions that program the processor to operate the motor to compress the working fluid using the VFD, receive a signal representative of the current to the motor from the VFD, and determine when a surge event has occurred based at least in part on the received signal representative of the current to the motor from the VFD.

[0007] Another aspect is a controller for a dynamic compressor including a motor and a compression mechanism coupled to the motor and operable to compress a working fluid upon operation of the motor, the controller including a processor and a memory, the memory storing instructions programming the processor to operate the motor to compress the working fluid, receive a signal representative of a current supplied to the motor to operate the motor, and determine when a surge event has occurred based at least in part on the received signal representative of the current supplied to the motor.

[0008] Another aspect is a method of detecting the occurrence of a surge event in a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid upon operation of the motor, the method including the steps of operating the motor to compress the working fluid, receiving a signal representative of a current supplied to the motor to operate the motor, and determining when a surge event has occurred based solely on the received signal representative of the current supplied to the motor and a surge threshold.

[0009] Another aspect is a system including a dynamic compressor and a controller. The dynamic compressor includes a motor having a drive shaft rotatably supported within the dynamic compressor and a compression mechanism connected to the drive shaft and operable to compress a working fluid upon rotation of the drive shaft. The controller is connected to the motor and includes a processor and a memory. The memory stores instructions that program the processor to operate the motor to compress the working fluid at a motor speed that is greater than a predicted minimum surge speed plus a control margin, determine when a surge event has occurred, store in the memory an indication of each surge event that the processor determines has occurred, and determine whether to perform a protective action when the processor determines that a surge event has occurred.

[0010] Another aspect is a controller for a dynamic compressor including a motor and a compression mechanism coupled to the motor and operable to compress a working fluid upon operation of the motor, the controller including a processor and a memory, the memory storing instructions programming the processor to operate the motor to compress the working fluid at a motor speed greater than a predicted minimum surge speed plus a control margin, determine when a surge event has occurred, store in the memory an indication of each surge event that the processor determines has occurred, and determine whether to take a protective action when the processor determines that a surge event has occurred.

[0011] Another aspect is a method of controlling a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid upon operation of the motor, the method including operating the motor to compress the working fluid at a motor speed greater than a predicted minimum surge speed plus a control margin, determining when a surge event has occurred, storing an indication of each surge event that the processor determines has occurred, and determining whether to take a protective action when the processor determines that a surge event has occurred.

[0012] There are various refinements to the features noted in relation to the above aspects. Further features may be incorporated into the above aspects. These refinements and further features may exist individually or in any combination. For example, the various features described below in relation to any of the illustrated embodiments may be incorporated into any of the above aspects, either alone or in any combination. [Brief description of the drawings]

[0013] The following figures illustrate various aspects of the present disclosure.

[0014] [Figure 1] FIG. 2 is a perspective view of the assembled compressor.

[0015] [Diagram 2]FIG. 2 is a cross-sectional view of the compressor of FIG. 1 taken along line 2-2 with the external conduit removed.

[0016] [Diagram 3] 3 is a cross-sectional view through the sleeve of the bearing housing shown in FIG. 2, showing a drive shaft supported in a foil bearing assembly maintained in the sleeve of the bearing housing using a pair of retaining clips.

[0017] [Figure 4] FIG. 2 is a cross-sectional view of another embodiment of a bearing housing suitable for use with the compressor of FIG. 1 , showing a drive shaft supported in a foil bearing assembly maintained within the bearing housing between a retaining lip formed in the bearing housing at one end and a retaining clip at the other end.

[0018] [Diagram 5] FIG. 2 is an exploded view of the elements of the foil bearing assembly disposed relative to the bearing housing and the drive shaft.

[0019] [Figure 6] FIG. 2 is a block diagram of a control system for the dynamic compressor.

[0020] [Figure 7] 1 is a graph showing surge current characteristics of a dynamic centrifugal compressor.

[0021] [Figure 8] 1 is a speed graph of a dynamic centrifugal compressor.

[0022] [Figure 9] 1 is a current graph of a dynamic centrifugal compressor.

[0023] [Figure 10] 1 is a graphical relationship between current swing rate and speed rate of a dynamic centrifugal compressor.

[0024] [Figure 11] 2 is an operation map of a dynamic centrifugal compressor.

[0025] [Figure 12] 1 is a flow chart of a method for determining when a surge event has occurred for a dynamic centrifugal compressor.

[0026] [Figure 13] 13 is a flow chart of an exemplary embodiment of the method of FIG. 12.

[0027] [Figure 14] 4 is a flowchart of a method for determining whether to take protective action when a surge event occurs in a dynamic centrifugal compressor.

[0028] [Figure 15] 15 is a flow chart of an exemplary embodiment of the method of FIG. 14.

[0029] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] For the sake of brevity, an example is described for a centrifugal compressor with gas foil bearings (GFB). However, the methods and systems described herein can be applied to any suitable dynamic compressor. In a surge control system for a centrifugal compressor, monitoring the occurrence of surge events, monitoring the number of surge events that have occurred, monitoring the severity of the surge events, determining a surge threshold, determining the relationship between the motor speed and the surge events, adjusting the control margin to provide a larger surge margin, and determining whether to take protective actions such as issuing alerts or stopping the operation of the machine when a surge event occurs can prevent damage and extend the life of the centrifugal compressor. These steps may further prevent catastrophic failure of the centrifugal compressor by allowing more accurate scheduling of preventive maintenance, increasing the sensitivity of the anti-surge control, improving reliability by limiting the severity of surges during start-up by holding the centrifugal compressor at a low speed until stable, allowing the system to continue providing cooling by increasing the run time of the centrifugal compressor before failing and shutting down, and improving reliability by limiting the severity of surges by activating the unloading device on surge detection rather than on a deduced map.

[0031] Referring to FIG. 1, a compressor in the form of a two-stage refrigerant compressor is generally designated 100. The compressor 100 generally includes a compressor housing 102 forming at least one sealed cavity within which each stage of refrigerant compression is accomplished. The compressor 100 includes a first refrigerant inlet 110 for introducing refrigerant vapor into a first compression stage (not labeled in FIG. 1), a first refrigerant outlet 114, a refrigerant transfer conduit 112 for transferring compressed refrigerant from the first compression stage to a second compression stage, a second refrigerant inlet 118 for introducing refrigerant vapor into the second compression stage (not labeled in FIG. 1), and a second refrigerant outlet 120. The refrigerant transfer conduit 112 is connected at either end to each of the first refrigerant outlet 114 and the second refrigerant inlet 118. The second refrigerant outlet 120 delivers compressed refrigerant from the second compression stage to a refrigeration system in which the compressor 100 is incorporated.

[0032] Referring to FIG. 2, the compressor housing 102 encloses a first compression stage 124 and a second compression stage 126 at opposite ends of the compressor 100. The first compression stage 124 includes a first compression mechanism 106 configured to add kinetic energy to the refrigerant entering through the first refrigerant inlet 110. In some embodiments, the first compression mechanism 106 is an impeller. The kinetic energy imparted to the refrigerant by the first compression mechanism 106 is converted to an increased refrigerant pressure as the refrigerant velocity is reduced upon transfer to a closed cavity (e.g., a diffuser) formed in a volute 132. Similarly, the second compression stage 126 includes a second compression mechanism 116 configured to add kinetic energy to the refrigerant entering through the second refrigerant inlet 118 from the first compression stage 124. In some embodiments, the second compression mechanism 116 is an impeller. The kinetic energy imparted to the refrigerant by the second compression mechanism 116 is converted to increased refrigerant pressure as the refrigerant velocity is reduced upon transfer to a sealed cavity (e.g., a diffuser) formed within the volute 132. The compressed refrigerant exits the second compression stage 126 via a second refrigerant outlet 120 (not shown in FIG. 2).

[0033] 2, the first compression mechanism 106 and the second compression mechanism 116 are connected to opposite ends of a drive shaft 104. The drive shaft 104 is operatively connected to a motor 108 located between the first compression mechanism 106 and the second compression mechanism 116 such that the first compression mechanism 106 and the second compression mechanism 116 rotate at a rotational speed selected to compress the refrigerant to a preselected mass flow rate that exits from a second refrigerant outlet 120 (not shown in FIG. 2). Any suitable motor may be incorporated into the compressor 100, including, but not limited to, an electric motor. The drive shaft 104 is supported by a gas foil bearing assembly 300 disposed within a sleeve 202 of each bearing housing 200 / 200a, as described in further detail below. Each bearing housing 200 / 200a includes a mounting structure (not shown) for connecting each bearing housing 200 / 200a to the compressor housing 102, as shown in FIG. 2.

[0034] 2, each bearing housing 200 / 200a supports a drive shaft 104 that protrudes through the bearing housing 200 / 200a opposite the sleeve 202, and a compression mechanism 106 is connected to the protruding end of the drive shaft 104. With reference to FIGS. 3 and 5, a gas foil bearing assembly 300 is disposed within a cylindrical bore 206 in the bearing housing 200. The drive shaft 104 is closely fitted within the gas foil bearing assembly 300, which includes an outer compliant foil or foil layer 302 disposed adjacent to an inner wall of the sleeve 202, an inner compliant foil or foil layer 306 (also referred to as a "top foil") disposed adjacent the drive shaft 104, and a bump foil or foil layer 310 disposed between the inner foil layer 306 and the outer foil layer 302. The foils or layers 302 / 306 / 310 of the gas foil bearing assembly form an essentially cylindrical tube sized to receive the drive shaft 104 with relatively little or no gap as dictated by existing foil bearing design methods. The components of the foil bearing assembly 300, such as the outer foil layer 302, the inner foil layer 306, and the bump foil layer 310, may be constructed of any suitable material that enables the foil bearing assembly 300 to function as described herein. Suitable materials include, for example, but are not limited to, metal alloys. In some embodiments, for example, the outer foil layer 302, the inner foil layer 306, and the bump foil layer 310 are each constructed of stainless steel (e.g., 17-4 stainless steel).

[0035] 3, the foil bearing assembly 300 of the illustrated embodiment further includes a pair of foil keepers 312a / 312b disposed adjacent opposite ends of the layers 302 / 306 / 310 to restrain sliding of the layers 302 / 306 / 310 in the axial direction within the cylindrical bore 206 of the sleeve 202. A pair of foil retaining clips 314a / 314b disposed adjacent the foil keepers 312a / 312b, respectively, secure the layers 302 / 306 / 310 in a locked axial position within the cylindrical bore 206. The foil retaining clips 314a / 314b may be removably connected to the bearing housing 200.

[0036] In another embodiment, as shown in FIG. 4, each bearing housing 200a includes a foil retaining lip 214 that is integrally formed (e.g., cast) with the bearing housing 200a and that projects radially inward from a radial inner surface 204 that defines the cylindrical bore 206. In the illustrated embodiment, the foil retaining lip 214 is located near the compression mechanism end 216 of the cylindrical bore 206 proximate the compression mechanism 116 (shown in FIG. 2). The foil retaining lip 214 is sized and dimensioned to project a radial distance from the radial inner surface 204 that overlaps at least a portion of the layers 302 / 306 / 310 of the foil bearing assembly 300. The foil retaining lip 214 may extend completely around the radial inner surface 204, or the foil retaining lip may include two or more segments that extend over a portion of the circumference of the radial inner surface 204 and are separated by spaces that are flush with adjacent radial inner surfaces 204. The bearing housing 200 (not shown in FIG. 4) is similarly formed.

[0037] 4 further includes a single foil retaining clip 314 disposed adjacent an end of the layer 302 / 306 / 310 opposite the foil retaining lip 214 to restrain axial movement of the layer 302 / 306 / 310 within the cylindrical bore 206 of the sleeve 202. In this embodiment, the foil retaining clip 314 snaps into a circumferential groove 212 formed in the radial inner surface 204 of the cylindrical bore 206 near the motor end 218 of the cylindrical bore 206.

[0038] The foil retaining lip 214 may be located in any area of ​​the cylindrical bore 206 near the compression mechanism end 216, including, but not limited to, directly adjacent the opening of the cylindrical bore 206 at the compression mechanism end 216. Alternatively, the foil retaining lip 214 may be located in any area of ​​the cylindrical bore 206 near the motor end 218, including, but not limited to, directly adjacent the opening of the cylindrical bore 206 at the motor end 218. In such an embodiment, the foil retaining clip 314 fits into a circumferential groove 212 formed in the radial inner surface 204 of the cylindrical bore 206 near the compression mechanism end 216 in an essentially opposite arrangement to that shown in FIG.

[0039] 4, the foil bearing assembly 300 is installed within the bearing housing 200 by inserting the foil bearing assembly 300 into the cylindrical bore 206 of the bearing housing 200 at the motor end 218. The foil bearing assembly 300 is then advanced axially into the cylindrical bore 206 toward the compression mechanism end 216 until the layers 302 / 306 / 310 contact the foil retaining lip 214. The foil retaining clip 314 is then engaged into the circumferential groove 212 near the motor end 218 of the cylindrical bore 206 to lock the foil bearing assembly 300 in place.

[0040] In other embodiments, any suitable method may be used to attach the foil bearing assembly 300 within the sleeve 202. Non-limiting examples of suitable methods include keepers and retaining clips, adhesives, locking screws, and any other suitable attachment method.

[0041] The bearing housing 200 / 200a may further serve as a mounting structure for various elements including, but not limited to, radial bearings, such as the foil bearing assembly 300 described above, thrust bearings, and sensing devices (not shown) used as feedback for passive or active control schemes, such as proximity probes, pressure transducers, thermocouples, key phasers, etc.

[0042] The foil bearing assembly 300 may be provided in any suitable form without limitation. For example, the foil bearing assembly 300 may include, without limitation, two layers, three layers, four layers, or additional layers. The bump foil 310 of the foil bearing assembly 300 may be formed from a radially elastic structure to provide a resilient surface for the drive shaft 104 rotating during operation of the compressor 100. The bump foil 310 may be formed from any suitable radially elastic structure, including, but not limited to, an array of deformable bumps or other features designed to deform and rebound under intermittent compressive radial loads, and any other elastically resilient material that can compress and rebound under intermittent compressive radial loads. The bump foil 310 may be connected to at least one adjacent layer, including, but not limited to, at least one of the outer layer 302 and the inner layer 306. In some embodiments, the bump foil 310 may be connected to both the outer layer 302 and the inner layer 306. In other embodiments, the bump foil 310 is free-floating and not connected to any layers of the foil bearing assembly 300 .

[0043] Referring to FIG. 6, an exemplary embodiment of a system 400 includes a dynamic compressor 404. In one embodiment, the dynamic compressor is a centrifugal compressor. In another embodiment, the dynamic compressor is an axial compressor. The system 400 includes a compressor 404 having a compressor housing 405, an unloading device 401, a user interface 415, and a controller 410. The compressor includes a motor 406, a compression mechanism 407, a gas foil bearing 409, and a speed sensor 417. The system 400 further includes a variable frequency drive (VFD) 416 having a current sensor 408, and a motor interface 413 in communication with the motor 406. In some embodiments, the VFD 416 operates under the control of the controller 410. In some embodiments, the VFD 416 is part of the controller 410. In an exemplary embodiment, the compression mechanism 407 is an impeller and the dynamic compressor 404 is a centrifugal compressor. In other embodiments, the compression mechanism 407 is a blade and the dynamic compressor 404 is an axial compressor. The compressor housing 405 and compressor 404, including the motor 406, the compression mechanism 407 and the gas foil bearings 409, may be configured similarly to the compressor 100 described in FIGS. 1-5 or may be configured differently. The compressor 404 is not limited to a particular configuration in the system 400. The compressor 404 includes a controller 410 for controlling the operation of the compressor 404 and determining when a surge event occurs and whether to take protective action when one or more surge events occur. The controller 410 includes a processor 411, a memory 412, and an unload interface 414. The memory 412 includes instructions that are executed by the processor to execute a method for controlling the compressor 404 and determining whether and when a surge event occurs and whether to take protective action in response to a surge event.

[0044] The unloading device 401 in the system 400 removes and / or reduces the load on the compressor during start-up and shutdown routines and detected surge events, limiting the severity of the surge event. In an exemplary embodiment, the unloading device 401 is a bypass valve. A bypass valve, such as a refrigerant bypass valve, provides an alternative path for gas, thereby stopping the pressure rise of the compressor 404 and limiting any potential surge, regardless of how slowly the compressor motor 406 accelerates during start-up or decelerates during shutdown. In other embodiments, the unloading device 401 is an expansion valve. In other embodiments, the unloading device 401 can be a variable orifice or diameter valve, such as a servo valve, and a fixed orifice or diameter valve, such as a solenoid valve or a pulse width modulated (PWM) valve configured to control opening and closing according to a duty cycle. In yet other embodiments, the unloading device 401 can be, but is not limited to, a variable diffuser or a variable inlet guide vane (VIGV). Although many types of unloading devices are described herein, the unloading device 401 may be any suitable device or combination of devices that reduces the load on the compressor 404 .

[0045] The unloading device 401 is operatively coupled to a controller 410, which is configured to control at least one operating parameter of the unloading device 401, such as opening a bypass valve. A current sensor 408 measures the current of the motor 406, and the controller 410 determines if and when a surge event of the compressor 404 occurs by detecting a spike in the measured current of the motor 406. The controller 410 further determines when the surge event is completed and normal operation resumes when the measured current of the motor 406 is substantially constant. Other embodiments may detect the onset and end of a surge event using other techniques, such as detecting a change in voltage, detecting a change in pressure, sensing vibrations caused by a surge, etc. The controller 410 further determines whether to take a protective action when a surge event occurs. Non-limiting examples of suitable sensors for use in one or more control schemes include temperature sensors, pressure sensors, flow rate sensors, current sensors, voltage sensors, rotational rate sensors, and any other suitable sensors.

[0046] The control system 400 includes a motor interface 413 for connection of a VFD 416 to the motor 406, an interface for connection of a controller 410 to the VFD 416, and an unload interface 414 for connection of the controller 410 to the unload device 401. The processor 411 may then execute instructions stored in the memory 412 to determine, based at least in part on the received signal representing the current from the VFD 416 to the motor 406, when a surge event has occurred and whether to take protective action when the processor 411 determines that a surge event has occurred.

[0047] The control system 400 includes a user interface 415 configured to output (e.g., display) and / or receive information (e.g., from a user) related to the system 400. In some embodiments, the user interface 415 is configured to receive activation and / or deactivation inputs from a user to enable activation and deactivation (i.e., turning on and off) or otherwise operation of the system 400. Additionally, in some embodiments, the user interface 415 is configured to output information related to one or more operational characteristics of the system 400, including, for example, but not limited to, warning indicators such as severity warnings, occurrence warnings, fault warnings, and motor speed warnings, as well as the status of the gas foil bearings 409, and other suitable information.

[0048] The user interface 415 may include any suitable input and output devices that enable the user interface 415 to function as described herein. For example, the user interface 415 may include input devices, including, but not limited to, a keyboard, a mouse, a touch screen, joystick(s), throttle(s), buttons, switches, and / or other input devices. Additionally, the user interface 415 may include output devices, including, but not limited to, a display (e.g., a liquid crystal display (LCD) or an organic light emitting diode (OLED) display), a speaker, indicator lights, gauges, and / or other output devices. Additionally, the user interface 415 may be part of a different component, such as a system controller (not shown). Other embodiments do not include a user interface 415.

[0049] In some embodiments, system 400 may be controlled by a remote control interface. For example, system 400 may include a communications interface (not shown) configured to connect to a wireless control interface that allows for remote control and activation of system 400. The wireless control interface may be embodied on a portable computing device, such as a tablet or smartphone.

[0050] The controller 410 is generally configured to control the operation of the compressor 404. The controller 410 controls the operation via programming and instructions from other devices or controllers, or is integrated with the control system 400 via a system controller. In some embodiments, for example, the controller 410 receives user input from a user interface 415 and controls one or more components of the system 400 in response to such user input. For example, the controller 410 may control the motor 406 based on the user input received from the user interface 415.

[0051] The controller 410 may generally include any suitable computer and / or other processing unit, including any suitable combination of computers, processing units, and / or the like, that may be communicatively coupled to each other and that may operate independently or in conjunction with each other (e.g., the controller 410 may form all or part of a controller network). The controller 410 may include one or more modules or devices, one or more of which may be enclosed within the system 400 or located remotely from the system 400. The controller 410 may be part of the compressor 404, or may be separate, and may be part of a system controller in an HVAC system. The controller 410 and / or components of the controller 410 may be integrated or incorporated within other components of the system 400. In some embodiments, for example, the controller 410 may be incorporated within the motor 406 or the unloading device 401. The controller 410 may include one or more processors 411 and associated memory device(s) 412 configured to perform various computer-implemented functions (e.g., performing the calculations, decisions, and functions disclosed herein). As used herein, the term "processor" refers not only to integrated circuits, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Additionally, the memory device(s) 412 of the controller 410 can generally be or include memory element(s) including, but not limited to, a computer-readable medium (e.g., random access memory (RAM)), a computer-readable non-volatile medium (e.g., flash memory), a floppy disk, a compact disk read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disk (DVD), and / or other suitable memory elements.Such memory device(s) 412 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 411, configure or cause the controller 410 to perform various functions described herein, including, but not limited to, controlling the system 400, controlling the operation of the motor 406, receiving input from the user interface 415, providing output to an operator via the user interface 415, controlling the unloading apparatus 401, and / or other suitable computer-implemented functions.

[0052] Referring to Figure 7, a start-up surge current characteristic graph 600 is shown including a speed curve 601 and a motor current curve 602. Figure 7 illustrates accelerating the motor speed to a first speed and operating the motor 406 at the first speed for a period of time 605. While the motor 406 is operating at the first speed for the period of time 605, an area of ​​possible surge 603 is identified by oscillations in the motor current curve 602. The compressor 404 is held at the first speed until the surge current oscillation pattern stops 604, indicating the compressor 404 has fully started.

[0053] 8 and 9 are traces of signals used by the system to detect the occurrence of a surge (e.g., during period 605 in FIG. 7). FIG. 8 is a speed graph 800, and FIG. 9 is a current graph 900. With respect to FIG. 8, the actual speed 801 of the compressor motor is shown along with a baseline speed line 803, which may be used as a reference point to determine if a surge is occurring. The baseline speed line 803 is also referred to as the speed set point or commanded speed. With respect to FIG. 9, the actual current 901 (sensed using the current sensor 408) and the average current 902 supplied to the motor are shown. The average current 902 may be the current sensed just before the surge event, the average of all current measurements before the surge event, the average of a predetermined or variable number of current measurements before the surge event, or any other suitable current average. When the compressor 404 enters a surge event, the mass flow rate through the compressor is significantly reduced, thereby reducing the load on the compressor 404 and causing the speed of the unloaded motor 406 to increase above the baseline speed line 803. The VFD 416, via a control algorithm, then reduces the actual current 901 in response to the increased speed to bring the actual speed 801 back to the baseline speed line 803. Once the surge ends, the compressor 404 (and motor 406) load returns, causing the speed 801 to be rapidly reduced. The VFD 416 increases the current to bring the motor's speed back to the baseline speed 803. The result is the characteristic overshoot of the actual current 901 and undershoot of the actual speed 801 seen at the end of the surge event in Figures 8 and 9 before the speed and current return to approximately the pre-surge levels. The drop in the actual current 901 from the average current 902 is used by the controller to detect the occurrence of a surge event. When the change in current from the average current 902 exceeds a threshold, the controller determines that a surge event has occurred. The speed graph 800 shows the speed surge severity 802 and the current graph 900 shows the current surge severity 904 during the surge event. The current surge severity is the difference between the average current 902 and the minimum current 903. The severity of each surge event may be recorded in memory 412.

[0054] Referring to FIG. 10, an exemplary graphical relationship 1100 between current swing rate and speed rate is shown to indicate a threshold current swing for detecting a surge event. A linear surge curve 1103 represents the threshold for detecting a surge. A current swing (e.g., surge severity 904 in FIG. 9) on or above the linear surge curve 1103 at the current speed of the compressor (expressed as a percentage of maximum speed) is determined to indicate the occurrence of a surge event. If the current swing is less than the linear surge curve 1103, then the surge event is not detected. Alternatively, only current swings above the linear surge curve 1103 may be considered surge events, and current swings below the linear surge curve are not considered surge events.

[0055] Referring to FIG. 11, an operating envelope or operating map 1000 of an exemplary dynamic centrifugal compressor 404 is shown. The operating map 1000 graphically estimates and illustrates the compressor's performance in terms of flow rate, head, and speed. The map illustrates head versus inlet mass flow rate as a percentage of their values ​​at the design point of the compressor 404. The inlet mass flow rate is a measure of the amount of working fluid, such as a refrigerant, flowing through the compression mechanism 407. The head is the total pressure ratio of the outlet pressure to the inlet pressure. The operating map 1000 illustrates a number of compressor speed lines 1007. In this example, there are five speed lines 1007 ranging from 110% design speed to 70% design speed, each line separated by 10%. Although these particular speed lines are illustrated in this example, any number of speed lines at any different percentage of the compressor's design speed can be illustrated for any type of compressor.

[0056] A surge limit line 1004 indicates the maximum load condition before a surge occurs in a surge region 1006 (i.e., to the left of the surge limit line 1004). A surge control line 1003 roughly indicates the maximum load condition at which the compressor 404 can safely operate without risk of going into surge. The surge control line 1003 is defined by a surge margin 1005 from the surge limit line 1004. By operating to the right of the surge control line 1003, the compressor should avoid surge. An operating point 1009 of the operating map 1000 of the compressor 404 is shown as the intersection of the speed line, the inlet mass flow rate, and the total pressure ratio. For example, the operating point 1009 shown in the operating map 1000 is 80% inlet mass flow rate, 108% head, and 100% speed. If a surge occurs when operating at operating point 1009, the surge margin 1005 may be increased by an amount 1008, for example, to shift the surge control line 1003 to a new surge control line 1002. A choke line 1001 is shown in the operating map 1000.

[0057] Referring to FIG. 12, a method 1200 for determining when a surge event has occurred is shown. The method 1200 begins with operating 1201 the motor 406 using the VFD 416 to compress a working fluid. In some embodiments, the working fluid is a refrigerant. With the motor operating 1201, the method 1200 continues with receiving 1202 a signal representative of a current to the motor 406 from the VFD 416. The method 1200 concludes by determining 1203 when a surge event has occurred based at least in part on the received signal representative of a current to the motor 406 from the VFD 416. The method 1200 is implemented in the control system 400 shown in FIG. 6. Specifically, the controller 410 implements the method 1200 via the processor 411 using instructions stored in the memory 412. A measurement of the current to the motor 406 is provided by a current sensor 408 included in the VFD 416. Other embodiments may use any other suitable detection or estimation of the current provided to the motor 406. Compression of the working fluid during operation 1201 of the motor 406 is performed by a compression mechanism 407.

[0058] Determining 1203 that a surge event has occurred includes determining a difference between a previous current and a current current based on a received signal representing the current from the VFD 416 to the motor 406. In some embodiments, the previous current is determined by averaging multiple signals representing the current from the VFD 416 to the motor 406 received by the processor 411 prior to receiving a signal from the VFD representing the current current from the VFD 416 to the motor 406. The surge event occurs when the difference between the previous current and the current current exceeds a surge threshold. For example, the surge threshold may be a variable threshold (e.g., as shown in FIG. 10 ) and may be preloaded into the controller 410 by a user and subsequently modified via the user interface 415. The variable surge threshold is determined based at least in part on a detected speed from the speed sensor 417 of the motor 406 when the signal representing the current current is received. In other embodiments, determining a difference between a previous current and a current current based on a received signal representing the current from the VFD 416 to the motor 406 includes determining a magnitude of the surge based on the difference between the previous current and the current current. The processor 411 stores in the memory 412 an indication of the occurrence of a surge event and the determined magnitude of the surge.

[0059] 13, a flowchart 1300 of an exemplary embodiment of the method 1200 from FIG. 12 for determining a surge event is shown. The flowchart 1300 begins when the compressor 404 is starting up. The flowchart 1300 illustrates both normal and start-up operation of the compressor 404 when determining if a surge event has occurred. The compressor 404 begins operation and the current sensor 408 detects the present current I present is continuously measured, and the speed sensor 417 measures the speed S actual When the compressor 404 is running, N previously measured currents I previous is a rolling dataset

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[0060] Referring to FIG. 14, a method 1400 is shown for determining whether to take protective action when the processor 411 determines that a surge event has occurred. The method 1400 occurs after the method 1200 shown in FIG. 12 has determined that a surge event has occurred. While the previous method 1200 may be used simultaneously to determine the occurrence of a surge event, the method 1400 may be used in any situation in which a surge event has been detected (by any detection means) in a dynamic compressor. The method 1400 begins with operating 1401 the motor 406 to compress the working fluid at a motor speed that is greater than a predicted minimum surge speed plus a control margin. The method continues with determining 1402 when a surge event has occurred. In some embodiments, this step may utilize the method 1200 to determine that a surge event has occurred. The method 1400 continues with storing 1403 in the memory 412 an indication of each surge event that the processor 411 has determined to have occurred. The method 1400 ends with determining 1404 whether to take a protective action when the processor 411 determines that a surge event has occurred. In some embodiments, the protective action includes generating an alarm. The alarm can be an alarm signal sent to a remotely located system controller, a visual or audio alarm located near the compressor, or any other suitable alarm. In some embodiments, the protective action includes stopping the motor 406. In some embodiments, the protective action includes adjusting a control margin. As with the previous method 1200, the method 1400 is implemented in the control system 400 shown in FIG. 6. Specifically, the controller 410 implements the method 1400 via the processor 411 using instructions stored in the memory 412. Compression of the working fluid in operation 1401 of the motor 406 is performed by the compression mechanism 407.

[0061] If the determination 1404 step of the method 1400 concludes that generating an alert is a protective action required after the processor 411 determines that a surge event has occurred, the following steps are further performed in various embodiments: Generating the alert may include generating an occurrence alert if the number of surge events having instructions stored in the memory 412 is equal to or greater than an occurrence alarm limit. Generating the alert may include generating a fault alert if the number of surge events having instructions stored in the memory 412 is equal to or greater than a fault limit that is greater than the occurrence alarm limit. When a fault alert is generated, a control margin, such as the control margin 1005 of the operating map 1000 shown in FIG. 11, is increased for the dynamic compressor 404 in some embodiments. In some embodiments, the indication of each surge event includes an indication of the magnitude of the surge event, and generating the alert includes generating a severity alert if the sum of the determined magnitudes of the surge events stored in the memory 412 is equal to or greater than a severity alarm limit. Generating the alert further includes generating a fault alert when the sum of the determined surge event magnitudes stored in memory 412 is equal to or greater than a severity fault limit, which is greater than a severity alarm limit in some embodiments. And, as described above, when a fault alert is generated, the control margin can be increased. In some embodiments, generating the alert occurs when the speed of motor 406 during a surge event exceeds the sum of a predicted minimum surge speed, a control margin, and a charge margin when the working fluid is a refrigerant. And, as described above, when a warning is generated, the control margin is increased.

[0062] If the determining 1404 step of method 1400 concludes that stopping the motor 406 is a necessary protective action after determining that a surge event has occurred, and the indication of each surge event includes a magnitude of the surge event, the method may include: In some embodiments, stopping the motor 406 occurs if the number of detected surge events is greater than or equal to an occurrence stop threshold. Alternatively, or additionally, the motor 406 may be stopped if the sum of the determined surge event magnitudes is greater than or equal to an accumulated stop threshold.

[0063] 15, a flowchart 1500 of an exemplary embodiment of the method 1400 from FIG. 14 for determining whether to take protective action in the event of a surge event in the dynamic compressor 404 is shown. i=1,2, …N When a surge event is detected, the surge count N is incremented N=N+1. At the same time, the surge count N is incremented N=N+1 and the surge severity accumulation is calculated. The surge severity accumulation is the sum of the magnitudes of all N detected surge events.

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[0064] In some embodiments, when a surge event is detected, an unloading device is activated as a protective action to unload the compressor to reduce the severity of the surge. In an exemplary embodiment, the unloading device is a load balancing valve that unloads the compressor 404 for a time T delay Reduce the load on the compressor 404 for a period of 1 minute.

[0065] Technical advantages of the methods and systems described herein are: (a) continuously monitoring the number of surge events and surge severity seen by a compressor in an HVAC system; (b) comparing the surge events and surge severity to the maximum number of surges that the compressor in the HVAC system can handle; and (c) comparing the compressor speed during a surge event to the predicted surge speed at the current pressure ratio.

[0066] When introducing elements of the present disclosure or embodiments thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the element. The terms "comprise," "include," and "have" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The use of terms indicating a specific orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require a particular orientation of the described items.

[0067] Since various changes may be made in the above structures and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings be interpreted in an illustrative and not a limiting sense.

Claims

1. 1. A dynamic compressor comprising: A motor having a drive shaft rotatably supported within the dynamic compressor; and a compression mechanism connected to the drive shaft and operable to compress a working fluid upon rotation of the drive shaft; A dynamic compressor; a variable frequency drive (VFD) including a sensor configured to sense a current supplied to the motor; A controller coupled to the motor, the controller having a processor and a memory, the memory comprising: operating the motor using the VFD to compress the working fluid; receiving a signal from the VFD representative of the current to the motor; determining when a surge event has occurred based at least in part on the received signal representative of the current from the VFD to the motor; storing instructions for programming said processor; A controller; system.

2. The memory further stores instructions that program the processor to determine that the surge event has occurred by determining a difference between a previous current and a present current based on the received signal representing the current from the VFD to the motor. The system of claim 1 .

3. the memory storing further instructions that program the processor to determine the previous current by averaging a plurality of signals representing the current from the VFD to the motor that were received by the processor prior to receiving a signal from the VFD representing the current current from the VFD to the motor. The system of claim 2.

4. the memory storing further instructions for programming the processor to determine that the surge event has occurred when the difference exceeds a surge threshold. The system of claim 2.

5. the surge threshold is a variable threshold; The system of claim 4.

6. a speed sensor configured to detect a speed of the motor, the memory storing further instructions to program the processor to determine the surge threshold based at least in part on the detected speed of the motor when the signal representative of the present current is received. The system of claim 5.

7. The memory storing further instructions for programming the processor to determine a magnitude of the surge event based on the difference between the previous current and the present current. The system of claim 2.

8. the memory storing further instructions programming the processor to store an indication of the occurrence of the surge event and the determined magnitude of the surge event in the memory. The system of claim 7.

9. The dynamic compressor is a centrifugal compressor, and the compression mechanism is an impeller. The system of claim 1 .

10. the system is an HVAC system and the working fluid is a refrigerant; The system of claim 9.

11. 1. A controller for a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid upon operation of the motor, the controller comprising: A processor; A memory, the memory comprising: operating the motor to compress the working fluid; receiving a signal representative of a current provided to the motor to operate the motor; determining when a surge event occurred based at least in part on the received signal representative of the current supplied to the motor; a memory storing instructions for programming the processor to having controller.

12. The memory storing further instructions for programming the processor to determine that the surge event has occurred by determining a difference between a previous current and a present current based on the received signal representative of the current supplied to the motor. The controller of claim 11.

13. the memory storing further instructions to program the processor by averaging a plurality of signals representative of the current supplied to the motor received by the processor prior to receiving a signal representative of the current supplied to the motor. The controller of claim 12.

14. the memory storing further instructions for programming the processor to determine that the surge event has occurred when the difference exceeds a surge threshold. The controller of claim 12.

15. the surge threshold is a variable threshold, and the memory stores further instructions that program the processor to determine the surge threshold based at least in part on a detected speed of the motor when the signal representative of the present current is received. The controller of claim 14.

16. The memory includes: determining a magnitude of the surge event based on the difference between the previous current and the present current; storing an indication of the occurrence of the surge event and the determined magnitude of the surge event in the memory; storing further instructions to program the processor to The controller of claim 12.

17. 1. A method for detecting the occurrence of a surge event in a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid upon operation of the motor, the method comprising: operating the motor to compress the working fluid; receiving a signal representative of a current provided to the motor to operate the motor; determining when a surge event has occurred based solely on the received signal representative of the current supplied to the motor and a surge threshold. method.

18. The step of determining when a surge event has occurred comprises: determining a difference between a previous current and a current current based on the received signal representative of the current supplied to the motor; determining that the surge event has occurred when the difference exceeds the surge threshold.

20. The method of claim 17.

19. determining the previous current includes averaging a plurality of the signals representative of the current supplied to the motor received prior to receiving a signal representative of the present current supplied to the motor; 20. The method of claim 18.

20. the surge threshold is a variable threshold, and determining when the surge event has occurred includes determining the surge threshold based at least in part on a detected speed of the motor when the signal representative of the present current is received.

20. The method of claim 18.

21. 1. A dynamic compressor comprising: A motor having a drive shaft rotatably supported within the dynamic compressor; and a compression mechanism connected to the drive shaft and operable to compress a working fluid upon rotation of the drive shaft; A dynamic compressor having A controller coupled to the motor, the controller including a processor and a memory, the memory comprising: operating the motor to compress the working fluid at a motor speed greater than a minimum anticipated surge speed plus a control margin; Determine when a surge event occurred; storing in said memory an indication of each surge event that said processor determines has occurred; determining whether to perform a protective action when the processor determines that the surge event has occurred; storing instructions to program the processor to A controller; system.

22. The protective action includes generating an alert.

22. The system of claim 21.

23. the memory storing further instructions for programming the processor to determine to generate an occurrence alert as the alert when a number of surge events having an indication stored in the memory is equal to or greater than an occurrence alert limit.

23. The system of claim 22.

24. the memory storing further instructions for programming the processor to determine to generate a fault alert as the alert when the number of the surge events having an indication stored in the memory is equal to or greater than a fault limit that is greater than the occurrence alarm limit.

24. The system of claim 23.

25. the memory storing further instructions for programming the processor to increase the control margin each time the processor determines to generate the fault warning.

25. The system of claim 24.

26. the indication of each surge event includes an indication of a magnitude of the surge event, and the memory stores further instructions to program the processor to generate a severity alert as the alert when a sum of the determined magnitudes of the surge events stored in the memory is equal to or greater than a severity alert limit.

23. The system of claim 22.

27. the memory storing further instructions for programming the processor to generate a fault alert as the alert when the sum of the magnitudes of the determined surge events stored in the memory is equal to or greater than a fault severity limit that is greater than the alarm severity limit.

27. The system of claim 26.

28. the memory storing further instructions for programming the processor to increase the control margin each time the processor determines to generate the fault warning.

28. The system of claim 27.

29. the system is an HVAC system, the working fluid is a refrigerant, and the memory comprises: determining to generate the warning when a speed of the motor at the time when the surge event is determined to occur exceeds a sum of the predicted minimum surge speed, the control margin, and a charge margin; increasing the control margin when the processor determines to generate the warning; storing further instructions to program the processor to 23. The system of claim 22.

30. the alert comprises an alert signal transmitted to a remotely located system controller; 23. The system of claim 22.

31. the protective action includes stopping the motor; The indication of each surge event includes an indication of a magnitude of the surge event, and the memory stores: when the number of surge events determined by the processor to have occurred is equal to or exceeds an occurrence termination threshold; or when the sum of the magnitudes of the determined surge events stored in the memory is greater than or equal to a cumulative shutdown threshold; storing further instructions for programming the processor to determine to stop the motor; 22. The system of claim 21.

32. the system further comprising an unloading device, and the protective action includes operating the unloading device to unload the dynamic compressor to reduce a severity of the determined surge event.

22. The system of claim 21.

33. 1. A controller for a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid upon operation of the motor, the controller comprising: A processor; a memory, said memory comprising: operating the motor to compress the working fluid at a motor speed greater than a minimum anticipated surge speed plus a control margin; Determine when a surge event occurred; storing in said memory an indication of each surge event that said processor determines has occurred; determining whether to take protective action when the processor determines that the surge event has occurred; storing instructions to program the processor to controller.

34. The memory includes: generating an occurrence alert when a number of surge events having an indication stored in the memory is equal to or greater than an occurrence alert limit; generating a fault alert when the number of the surge events having an indication stored in the memory is equal to or greater than a fault limit that is greater than a trigger alarm limit; increasing the control margin each time the processor determines to generate the fault warning; and stopping the motor when a number of surge events determined by the processor to have occurred is equal to or exceeds an occurrence stop threshold; storing instructions for programming the processor to determine whether to take protective action when the processor determines that the surge event has occurred, 34. The controller of claim 33.

35. The indication of each surge event includes an indication of a magnitude of the surge event, and the memory stores: generating a severity alert when the sum of the magnitudes of the determined surge events stored in the memory is equal to or greater than a severity alert limit; generating a fault alert when the sum of the magnitudes of the determined surge events stored in the memory is equal to or greater than a severity fault limit that is greater than the severity alarm limit; increasing the control margin each time the processor determines to generate the fault warning; and shutting down the motor when the sum of the magnitudes of the determined surge events stored in the memory is greater than or equal to a cumulative shut-down threshold; storing further instructions for programming the processor to determine whether to take protective action when the processor determines that the surge event has occurred, 34. The controller of claim 33.

36. the dynamic compressor is part of an HVAC system and the working fluid is a refrigerant, and the memory stores further instructions that program the processor to determine whether to take a protective action when the processor determines that a surge event has occurred by determining to generate a charge alert when a speed of the motor at the time that a surge event is determined to have occurred exceeds the sum of the predicted minimum surge speed, the control margin, and a charge margin.

34. The controller of claim 33.

37. 1. A method for controlling a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid upon operation of the motor, the method comprising: operating the motor to compress the working fluid at a motor speed greater than a predicted minimum surge speed plus a control margin; determining when a surge event occurs; storing an indication of each surge event that the processor determines has occurred; determining whether to take protective action when the processor determines that a surge event has occurred; method.

38. The step of determining whether to take protective action when the processor determines that a surge event has occurred includes: generating an occurrence alert when the number of surge events having an indication stored in the memory is equal to or greater than an occurrence alert limit; generating a fault alert when a number of surge events having an indication stored in said memory is equal to or exceeds a fault limit that is greater than said occurrence alarm limit; increasing the control margin each time the processor determines to generate the fault warning; and stopping the motor when the number of surge events determined by the processor to have occurred is equal to or exceeds an occurrence stop threshold.

38. The method of claim 37.

39. The step of determining whether to take protective action when the processor determines that a surge event has occurred includes: generating a severity alert when the sum of the magnitudes of the determined surge events stored in the memory is equal to or greater than a severity alert limit; generating a fault alert when the sum of the magnitudes of the determined surge events stored in the memory is equal to or greater than a severity fault limit that is greater than the severity alarm limit; increasing the control margin each time the processor determines to generate the fault warning; and stopping the motor when the sum of the magnitudes of the determined surge events stored in the memory is equal to or greater than a cumulative stop threshold.

38. The method of claim 37.

40. the dynamic compressor is part of an HVAC system, the working fluid is a refrigerant, and determining whether to take protective action when the processor determines that a surge event has occurred includes determining to generate a charge alert when a speed of the motor at the time when the surge event is determined to have occurred exceeds a sum of the predicted minimum surge speed, the control margin, and a charge margin.

38. The method of claim 37.

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