Surge control system and method for a dynamic compressor

Abstract

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 as the drive shaft rotates. 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 indicative of the current from the VFD to the motor, and determine when a surge event occurs based at least in part on the received signal indicative of the current from the VFD to the motor.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. non-provisional patent applications, serial numbers 17 / 247724 and 17 / 247725, both filed on December 21, 2020, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The field of this disclosure generally relates to control systems, and more specifically to control systems for machines including power compressors. Background Technology

[0004] Centrifugal compressors, including those used in centrifugal compressors, are used in many applications, such as HVAC. Centrifugal compressors have a drive shaft operatively connected to a motor supported by gas foil bearings between the compression mechanism or impeller stages. The drive shaft can be positioned between the impeller stages such that the impellers rotate at a certain speed to compress the refrigerant to a selected pressure in the HVAC system. Compressor bearings typically incorporate one or more features designed to reduce friction between the compressor bearings and the drive shaft. Once the shaft rotates fast enough, the gas pushes the foil away from the shaft, preventing contact. The shaft and gas foil bearings are separated by the high pressure of the gas, generated by the rotation that forces the gas into the bearings via a viscosity effect. A high speed relative to the gas foil bearing is required to initiate the gas gap, and once this is achieved, contact should not occur. These bearings offer several advantages over other bearings, including reduced weight, stable operation at higher speeds and temperatures, low power loss at high speeds, and a longer lifespan with less maintenance.

[0005] Compressor surge events lead to accelerated wear of the compressor and its components, including bearings. Surge is a characteristic behavior of dynamic compressors that can occur when the head generated by the compressor is insufficient to overcome the system pressure at the compressor discharge port. Once surge occurs, the compressor's output pressure decreases sharply, resulting in backflow within the compressor. When a dynamic compressor surges, there is actual gas backflow through the impeller. Surge typically begins in one stage of a multi-stage compressor and can occur very rapidly. Compressors are particularly vulnerable to surge events during startup and shutdown due to their lower operating speeds. The severity of surge events and the damage they cause increase with compressor speed.

[0006] This background section is intended to introduce the reader to various aspects of the technology that may relate to the aspects described and / or claimed below in this disclosure. This discussion is intended to help provide the reader with background information to better understand the various aspects of this disclosure. Therefore, it should be understood that these statements are to be understood from that perspective and not as an admission of prior art.

[0007] Public content

[0008] One aspect of this disclosure is a system comprising a powered compressor, a variable frequency drive (VFD), and a controller. The powered compressor includes: a motor having a drive shaft rotatably supported within the powered compressor; and a compression mechanism connected to the drive shaft and operable to compress a working fluid as the drive shaft rotates. The VFD includes a sensor configured to sense a current supplied to the motor. The controller is connected to the motor and includes a processor and a memory. The memory stores instructions for programming the processor to: operate the motor using the VFD to compress the working fluid; receive a signal representing a current from the VFD to the motor; and determine, at least in part, when a surge event occurs based on the received signal representing the current from the VFD to the motor.

[0009] On the other hand, there is a controller for a powered compressor, which includes a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operated. The controller includes a processor and a memory. The memory stores instructions for programming the processor to: operate the motor to compress the working fluid; receive a signal representing the current supplied to the motor to operate the motor; and determine, at least in part, when a surge event occurs based on the received signal representing the current supplied to the motor.

[0010] Another method is to detect surge events in a powered compressor, the powered compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operated. The method includes: operating the motor to compress the working fluid; receiving a signal representing a current supplied to the motor to operate the motor; and determining when a surge event occurs based solely on the received signal representing the current supplied to the motor and a surge threshold.

[0011] On the other hand, there is a system including a powered compressor and a controller. The powered compressor includes: a motor having a drive shaft rotatably supported within the powered compressor; and a compression mechanism connected to the drive shaft and operable to compress a working fluid when the drive shaft rotates. The controller is connected to the motor and includes a processor and a memory. The memory stores instructions for programming the processor to: operate the motor at a speed greater than the predicted minimum surge speed plus a control margin to compress the working fluid; determine when a surge event occurs; store indications of each surge event determined by the processor in the memory; and determine whether to take protective action when the processor determines that a surge event has occurred.

[0012] On the other hand, there is a controller for a powered compressor, which includes a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operated. The controller includes a processor and a memory. The memory stores instructions for programming the processor to: operate the motor at a speed greater than the predicted minimum surge speed plus a control margin to compress the working fluid; determine when a surge event occurs; store indications of each surge event determined by the processor in the memory; and determine whether to take protective action when the processor determines that a surge event has occurred.

[0013] On the other hand, there is a method for controlling a powered compressor, the powered compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operated. The method includes: operating the motor at a speed greater than the predicted minimum surge speed plus a control margin to compress the working fluid; determining when a surge event occurs; storing indications of each surge event determined by the processor; and determining whether to take protective action when the processor determines that a surge event has occurred.

[0014] Various improvements exist to the features proposed in the above aspects. Other features may also be incorporated into the above aspects. These improvements and additional features may exist individually or in any combination. For example, the features discussed below with respect to any embodiment of the illustrated embodiments may be incorporated individually or in any combination into any aspect of the above aspects. Attached Figure Description

[0015] The following figures illustrate various aspects of this disclosure.

[0016] Figure 1 This is a 3D view of an assembled compressor.

[0017] Figure 2 It is cut along line 2-2. Figure 1 A cross-sectional view of the compressor, in which the external conduit has been removed.

[0018] Figure 3 Is it through Figure 2 The diagram shows a cross-sectional view of the sleeve of the bearing housing, illustrating the drive shaft supported within a foil bearing assembly held within the sleeve of the bearing housing by a pair of retaining clips.

[0019] Figure 4 It is suitable for Figure 1 A cross-sectional view of another embodiment of the bearing housing used in the compressor, illustrating a drive shaft supported within a foil bearing assembly held within the bearing housing between a retaining lip formed at one end of the bearing housing and a retaining clip at the opposite end.

[0020] Figure 5 This is an exploded view of the foil bearing assembly, showing the components arranged relative to the bearing housing and drive shaft.

[0021] Figure 6 This is a block diagram of the control system used for a power compressor.

[0022] Figure 7 This is a surge current characteristic curve for a centrifugal compressor.

[0023] Figure 8 It is a speed curve diagram for a centrifugal compressor.

[0024] Figure 9 This is a current curve diagram for a centrifugal compressor.

[0025] Figure 10 It is a graphical relationship between the percentage of current swing and the percentage of speed in a centrifugal compressor.

[0026] Figure 11 This is an operation diagram for a power centrifugal compressor.

[0027] Figure 12 This is a flowchart of a method for determining when a surge event occurs in a powered centrifugal compressor.

[0028] Figure 13 yes Figure 12 A flowchart of an example implementation of the method.

[0029] Figure 14 This is a flowchart illustrating the method for determining whether to take protective actions in the event of a surge in a centrifugal compressor.

[0030] Figure 15 yes Figure 14 A flowchart of an example implementation of the method.

[0031] Throughout the accompanying figures, the corresponding reference numerals indicate the corresponding parts. Detailed Implementation

[0032] For the sake of brevity, an example of a centrifugal compressor with a gas foil bearing (GFB) will be described. However, the methods and systems described herein can be applied to any suitable power compressor. In the surge control system of a centrifugal compressor, the following can prevent damage and increase the life of the centrifugal compressor: monitor the occurrence of surge events; monitor the number of surge events that have occurred; monitor the severity of surge; determine the surge threshold; determine the relationship between motor speed and surge events; adjust the control margin to provide a greater surge margin; and determine whether to take protective actions, such as generating warnings or stopping machine operation, when a surge event occurs. These steps can also prevent catastrophic failures of the centrifugal compressor by: enabling more accurate scheduling of preventative maintenance; increasing the sensitivity of surge prevention control; improving reliability by limiting the severity of surge at startup by keeping the centrifugal compressor at a lower speed until it stabilizes; allowing the system to continue providing cooling by increasing the running time on the centrifugal compressor before failure and shutdown; and improving reliability by limiting the severity of surge by operating the unloading device according to surge detection rather than estimation diagrams.

[0033] Reference Figure 1 The compressor 100, illustrated as a two-stage refrigerant compressor, is generally designated 100. The compressor 100 generally includes a compressor housing 102, which forms at least one sealed cavity within which each stage of refrigerant compression is performed. The compressor 100 includes a first refrigerant inlet 110 that introduces refrigerant vapor into the first compression stage (in...). Figure 1 (Not marked in the text); First refrigerant outlet 114; Refrigerant transfer conduit 112, which transfers compressed refrigerant from the first compression stage to the second compression stage; Second refrigerant inlet 118, which introduces refrigerant vapor into the second compression stage (in... Figure 1 (Not shown in the diagram); and a second refrigerant outlet 120. Refrigerant delivery conduits 112 are operatively connected at opposite ends to a first refrigerant outlet 114 and a second refrigerant inlet 118, respectively. The second refrigerant outlet 120 delivers compressed refrigerant from the second compression stage to a cooling system in which the compressor 100 is integrated.

[0034] Reference Figure 2The 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 increase kinetic energy to the refrigerant entering via a 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 into increased refrigerant pressure as the refrigerant velocity decreases during its transmission to a sealed cavity (e.g., a diffuser) formed within the volute 132. Similarly, the second compression stage 126 includes a second compression mechanism 116 configured to increase kinetic energy to the refrigerant entering via a second refrigerant inlet 118, which is transmitted 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 into increased refrigerant pressure as the refrigerant velocity decreases during its transfer to the sealed cavity (e.g., diffuser) formed within the volute 132. The compressed refrigerant exits through the second refrigerant outlet 120 (not at...). Figure 2 (As shown in the image) Exiting the second compression stage 126.

[0035] Reference Figure 2 The first-stage compression mechanism 106 and the second-stage compression mechanism 116 are connected at opposite ends of the drive shaft 104. The drive shaft 104 is operatively connected to a motor 108 positioned between the first-stage compression mechanism 106 and the second-stage compression mechanism 116, such that the first-stage compression mechanism 106 and the second-stage compression mechanism 116 rotate at a selected rotational speed to compress the refrigerant to exit the second refrigerant outlet 120 (at...). Figure 2 A pre-selected mass flow rate (not shown). Any suitable motor can be incorporated into the compressor 100, including but not limited to electric motors. The drive shaft 104 is supported by a gas foil bearing assembly 300 positioned within a sleeve 202 in each bearing housing 200 / 200a, as described in further detail below. Figure 2 As shown, each bearing housing 200 / 200a includes a mounting structure (not shown) for connecting the respective bearing housing 200 / 200a to the compressor housing 102.

[0036] Reference Figure 2 Each bearing housing 200 / 200a supports a drive shaft 104, which protrudes through the bearing housing 200 / 200a opposite to the sleeve 202, and a compression mechanism 106 is connected to the protruding end of the drive shaft 104. (See reference...) Figure 3 and Figure 5A gas foil bearing assembly 300 is positioned within a cylindrical bore 206 within a bearing housing 200. A drive shaft 104 is tightly fitted within the gas foil bearing assembly 300, which includes: an outer compliant foil or outer compliant foil layer 302 positioned adjacent to the inner wall of a sleeve 202; an inner compliant foil or inner compliant foil layer 306 (also referred to as a "top foil") positioned adjacent to the drive shaft 104; and a corrugated foil or corrugated foil layer 310 positioned 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 a substantially cylindrical tube sized to receive the drive shaft 104 through a relatively small gap or no gap, as determined by existing foil bearing design methods. Components of the foil bearing assembly 300, such as the outer foil layer 302, the inner foil layer 306, and the corrugated foil layer 310, can be made 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, each of the outer foil layer 302, the inner foil layer 306, and the corrugated foil layer 310 is made of stainless steel (e.g., 17-4 stainless steel).

[0037] Refer again Figure 3 The foil bearing assembly 300 in the illustrated embodiment further includes a pair of foil retainers 312a / 312b, which are positioned adjacent to the opposite ends of layers 302 / 306 / 310 to prevent the layers 302 / 306 / 310 from sliding axially within the cylindrical bore 206 of the sleeve 202. A pair of foil retaining clips 314a / 314b, positioned adjacent to the foil retainers 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 can be removably connected to the bearing housing 200.

[0038] In other implementations, such as Figure 4 As shown, each bearing housing 200a includes a foil retaining lip 214, which is integrally formed (e.g., cast) with the bearing housing 200a and projects radially inward from the radially inner surface 204 defining a cylindrical bore 206. In the illustrated embodiment, the foil retaining lip 214 is positioned near the compression mechanism 116 of the cylindrical bore 206. Figure 2Near the compression mechanism end 216 (shown in the diagram). A foil retaining lip 214 is sized and dimensioned to protrude radially from a radially inner surface 204, which overlaps at least a portion of layers 302 / 306 / 310 of the foil bearing assembly 300. The foil retaining lip 214 may extend circumferentially completely around the radially inner surface 204, or the foil retaining lip may comprise two or more segments extending over a portion of the circumferential direction of the radially inner surface 204 and spaced apart by spaces flush with adjacent radially inner surfaces 204. The bearing housing 200 (in...) Figure 4 (Not shown in the image) is formed in a similar manner.

[0039] Figure 4 The foil bearing assembly 300 of the embodiment illustrated in the figure also includes a single foil retaining clip 314, which is positioned adjacent to the end of layers 302 / 306 / 310 opposite to the foil retaining lip 214 to inhibit axial movement of layers 302 / 306 / 310 within the cylindrical bore 206 of the sleeve 202. In this embodiment, the foil retaining clip 314 engages in a circumferential groove 212 formed within the radially inner surface 204 of the cylindrical bore 206 near the motor end 218 of the cylindrical bore 206.

[0040] The foil retaining lip 214 can be positioned in any region of the cylindrical aperture 206 near the compression mechanism end 216, including but not limited to a position immediately adjacent to the opening of the cylindrical aperture 206 at the compression mechanism end 216. Alternatively, the foil retaining lip 214 can be positioned in any region of the cylindrical aperture 206 near the motor end 218, including but not limited to a position immediately adjacent to the opening of the cylindrical aperture 206 at the motor end 218. In such an embodiment, the foil retaining clip 314 is positioned in conjunction with... Figure 4 The arrangement shown is substantially the opposite of the arrangement, engaging in a circumferential groove 212 formed within the radial inner surface 204 of the cylindrical bore 206 near the end 216 of the compression mechanism.

[0041] Refer again Figure 4 The foil bearing assembly 300 is installed within the bearing housing 200 as follows: the foil bearing assembly 300 is inserted into the cylindrical bore 206 of the bearing housing 200 at the motor end 218. The foil bearing assembly 300 is then axially advanced into the cylindrical bore 206 toward the compression mechanism end 216 until layers 302 / 306 / 310 contact the foil retaining lip 214. The foil retaining clip 314 then engages with a circumferential groove 212 in the cylindrical bore 206 near the motor end 218 to lock the foil bearing assembly 300 in place.

[0042] In other embodiments, any suitable method for attaching the foil bearing assembly 300 to the sleeve 202 may be used. Non-limiting examples of suitable methods include retainers and retaining clips, adhesives, fixing screws, and any other suitable fastening method.

[0043] The bearing housing 200 / 200a can also be used as a mounting structure for various components, including but not limited to radial bearings such as the aforementioned foil bearing assembly 300, thrust bearings, and sensing devices (not shown) used for feedback to passive or active control schemes, such as proximity probes, pressure transducers, thermocouples, key phasers, etc.

[0044] The foil bearing assembly 300 can be arranged in any suitable form without limitation. For example, the foil bearing assembly 300 can be provided with two layers, three layers, four layers, or additional layers without limitation. The corrugated foil 310 of the foil bearing assembly 300 can be formed of a radially resilient structure to provide a resilient surface for the rotating drive shaft 104 during operation of the compressor 100. The corrugated foil 310 can be formed of any suitable radially resilient structure without limitation, including but not limited to: an array of deformable corrugations or other features designed to deform and spring back under intermittent compressive radial loads, and any other elastically resilient material capable of compressing and springing back under intermittent compressive radial loads. The corrugated foil 310 can 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 corrugated foil 310 can be connected to both the outer layer 302 and the inner layer 306. In other embodiments, the corrugated foil 310 can be free-floating and not connected to any layer of the foil bearing assembly 300.

[0045] Reference Figure 6An example embodiment of system 400 includes a power compressor 404. In one embodiment, the power compressor is a centrifugal compressor. In other embodiments, the power compressor is an axial compressor. 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. System 400 also includes a variable frequency drive (VFD) 416 having a current sensor 408 and a motor interface 413 communicating with the motor 406. In other 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 example embodiment, the compression mechanism 407 is an impeller, and the power compressor 404 is a centrifugal compressor. In other embodiments, the compression mechanism 407 is blades, and the power compressor 404 is an axial compressor. The compressor housing 405 and the compressor 404, including the motor 406, the compression mechanism 407 and the gas foil bearing 409, can be connected with Figures 1 to 5 The compressor 100 described herein is constructed similarly, or may be constructed in a different manner. The compressor 404 is not limited to the specific construction in system 400. The compressor 404 includes a controller 410 for controlling the operation of the compressor 404, determining when a surge event occurs, and determining whether to take protective action if one or more surge events have occurred. The controller 410 includes a processor 411, a memory 412, and an unloading interface 414. The memory 412 includes instructions executed by the processor 411 to control the compressor and perform methods for determining whether and when a surge event has occurred and whether to take protective action in response.

[0046] The unloading device 401 in system 400 removes and / or reduces the load on the compressor during startup and shutdown routines, as well as during surge event detection, to limit the severity of the surge event. In an example embodiment, the unloading device 401 is a bypass valve. Regardless of how slowly the compressor motor 406 accelerates during startup or decelerates during shutdown, the bypass valve, such as a refrigerant bypass valve, provides an alternative path for the gas, thereby stopping the pressure rise of the compressor 404 and limiting any potential surge. In other embodiments, the unloading device 401 is an expansion valve. In other embodiments, the unloading device 401 can be a variable orifice or variable diameter valve, such as a servo valve, and a fixed orifice or fixed diameter valve, such as a solenoid valve or a pulse width modulation (PWM) valve configured to control opening and closing according to a duty cycle. In other embodiments, the unloading device 401 can be, but is not limited to, a variable diffuser or a variable inlet guide vane (VIGV). While many types of unloading devices have been described herein, the unloading device 401 can also be any suitable device or combination of these devices that reduces the load on the compressor 404.

[0047] The unloading device 401 is operatively coupled to the controller 410, and the controller 410 is configured to control at least one operating parameter of the unloading device 401, such as the opening of a bypass valve. A current sensor 408 measures the current of the motor 406, and the controller 410 determines whether and when a surge event has occurred in the compressor 404 by detecting spikes in the measured current of the motor 406. The controller 410 also determines when the surge event has ended and when normal operation should resume when the measured current of the motor 406 is substantially constant. Other embodiments may use other techniques, such as detecting voltage changes, detecting pressure changes, sensing vibrations caused by surge, etc., to detect the occurrence and termination of surge events. The controller 410 also determines whether to take protective action if a surge event has occurred. Non-limiting examples of suitable sensors used in one or more control schemes include temperature sensors, pressure sensors, flow sensors, current sensors, voltage sensors, rotational speed sensors, and any other suitable sensors.

[0048] The control system 400 includes a motor interface 413 for connecting the VFD 416 to the motor 406, an interface for connecting the controller 410 to the VFD 416, and an unloading interface 414 for connecting the controller 410 to the unloading device 401. The processor 411 can then execute instructions stored in the memory 412 to determine, at least in part, when a surge event occurs based on received signals representing current from the VFD 416 to the motor 406, and to determine whether to take protective action when the processor 411 determines that a surge event has occurred.

[0049] The control system 400 includes a user interface 415 configured to output (e.g., display) and / or receive (e.g., from a user) information associated with the system 400. In some embodiments, the user interface 415 is configured to receive enable and / or disable inputs from the user to enable and disable (i.e., turn on and off) operation of the system 400 or otherwise implement operation of the system 400. Furthermore, in some embodiments, the user interface 415 is configured to output information associated with one or more operating characteristics of the system 400, such as, but not limited to, warning indications like severity warnings, occurrence warnings, fault warnings, and motor speed warnings, as well as the status of the gas foil bearing 409, and any other suitable information.

[0050] User interface 415 may include any suitable input and output devices that enable user interface 415 to function as described herein. For example, user interface 415 may include input devices, including but not limited to keyboards, mice, touchscreens, joysticks, throttles, buttons, switches, and / or other input devices. Furthermore, user interface 415 may include output devices, including but not limited to displays (e.g., liquid crystal displays (LCDs) or organic light-emitting diode (OLED) displays), speakers, indicator lights, instruments, and / or other output devices. Additionally, user interface 415 may be part of various components such as a system controller (not shown). Other embodiments do not include user interface 415.

[0051] In some implementations, system 400 can be controlled by a remote control interface. For example, system 400 may include a communication interface (not shown) configured to connect to a wireless control interface that enables remote control and activation of system 400. The wireless control interface may be implemented on a portable computing device, such as a tablet or smartphone.

[0052] Controller 410 is typically configured to control the operation of compressor 404. Controller 410 controls operation through programming and instructions from another device or controller, or through integration with control system 400 via a system controller. In some embodiments, for example, controller 410 receives user input from user interface 415, and controller 410 controls one or more components of system 400 in response to such user input. For example, controller 410 may control motor 406 based on user input received from user interface 415.

[0053] 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 can be communicatively coupled to each other and can operate independently or in association with each other (e.g., controller 410 may form all or part of a controller network). Controller 410 may include one or more modules or devices, one or more of which are enclosed within system 400 or can be located remotely from system 400. Controller 410 may be part of or separate from compressor 404, and may be part of the system controller in an HVAC system. Controller 410 and / or components of controller 410 may be integrated or incorporated into other components of system 400. In some embodiments, for example, controller 410 may be incorporated into motor 406 or unloading device 401. Controller 410 may include one or more processors 411 configured to perform various computer-implemented functions (e.g., performing calculations, determinations, and functions disclosed herein) and associated memory devices 412. As used herein, the term "processor" refers not only to an integrated circuit but also to a controller, microcontroller, microcomputer, programmable logic controller (PLC), application-specific integrated circuit (ASIC), and other programmable circuits. Additionally, the memory device 412 of the controller 410 may typically be or include memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact optical disc-read-only memory (CD-ROM), magneto-optical disc (MOD), digital versatile disc (DVD), and / or other suitable memory elements. Such a memory device 412 may typically be configured to store suitable computer-readable instructions that, when implemented by the processor 411, configure or cause the controller 410 to perform the 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 the operator via the user interface 415, controlling the unloading device 401, and / or various other suitable computer-implemented functions.

[0054] Reference Figure 7 The surge current characteristic curve 600 during startup is shown, including the speed curve 601 and the motor current curve 602. Figure 7The diagram illustrates accelerating the motor speed to a first speed and operating the motor 406 at that first speed for a certain period of time 605. During this period of time 605, the oscillations in the motor current curve 602 identify potential surge regions 603. The compressor 404 remains at the first speed until the surge current oscillation pattern has ceased 604 and the compressor 404 is indicated to be fully started.

[0055] Figure 8 and Figure 9 It is used by the system to detect surge (e.g., in Figure 7 The signal trace that occurred during the time period 605. Figure 8 It is the velocity curve graph 800, and Figure 9 It's the current curve graph 900. About... Figure 8 The actual speed 801 of the compressor motor is shown together with a reference speed line 803, which can be used as a reference point to determine whether surge has occurred. The reference speed line 803 is also referred to as the speed setpoint or command speed. Regarding... Figure 9 The diagram shows the actual current 901 supplied to the motor (as detected using current sensor 408) and the average current 902. The average current 902 can be: the current detected immediately before the surge event, the average of all current measurements prior to the surge event, the average of a predetermined or variable number of current measurements prior to the surge event, or any other suitable current average. When compressor 404 enters a surge event, the mass flow through the compressor decreases significantly, thereby reducing the load on compressor 404 and causing the unloaded motor 406 to rise above the reference speed line 803. VFD 416 then reduces the actual current 901 in response to the increased speed via a control algorithm, so that the actual speed 801 returns to the reference speed line 803. When the surge ends, the load on compressor 404 (and motor 406) recovers, causing the speed 801 to drop rapidly. VFD 416 increases the current to restore the motor speed to the reference speed 803. As a result, before the speed and current recover to their approximate pre-surge levels, Figure 8 and Figure 9The surge event is characterized by an overshoot of the actual current 901 and an undershoot of the actual speed 801 visible at the end of the surge event. The controller uses the drop in the actual current 901 relative to the average current 902 to detect the occurrence of a surge event. When the current change relative to the average current 902 exceeds a threshold, the controller determines that a surge event has occurred. The speed curve 800 shows the speed surge severity 802 during a surge event, and the current curve 900 shows the current surge severity 904 during a 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 can be recorded in the memory 412.

[0056] Reference Figure 10 An example graphical relationship 1100 between the current swing percentage and the speed percentage is shown to illustrate the threshold current swing used to detect surge events. The linear surge curve 1103 represents the threshold used to detect surge. At the compressor's current speed (expressed as a percentage of maximum speed), the current swing on or beyond the linear surge curve 1103 (e.g., ...) Figure 9 The surge severity (904) is determined as an indicator of the occurrence of a surge event. If the current swing is below the linear surge curve (1103), a surge event will not be detected. Alternatively, only current swings exceeding the linear surge curve (1103) can be considered surge events, while current swings below the linear surge curve may not be considered surge events.

[0057] Reference Figure 11 The diagram illustrates an operational envelope, or operational figure 1000, for an example centrifugal compressor 404. Operational figure 1000 graphically estimates and illustrates the compressor's performance in terms of flow rate, head, and speed. The figure shows the relationship between head, expressed as a percentage of its value, and inlet mass flow rate at the compressor 404's design point. Inlet mass flow rate is a measure of the amount of working fluid, such as refrigerant, flowing through the compression unit 407. Head is the total pressure ratio of outlet pressure to inlet pressure. Operational figure 1000 shows multiple compressor speed lines 1007. In this example, there are five speed lines 1007, ranging from 110% of the design speed to 70% of the design speed, with each speed line spaced 10% apart. While these specific speed lines are shown in this example, any number of speed lines at any different percentage of the compressor's design speed can be shown for any type of compressor.

[0058] Surge limit line 1004 indicates the maximum load condition prior to surge in surge region 1006 (i.e., to the left of surge limit line 1004). Surge control line 1003 generally indicates the maximum load condition under which compressor 404 can operate safely without the risk of slipping into surge. Surge control line 1003 is defined by surge margin 1005 relative to surge limit line 1004. By operating to the right of surge control line 1003, the compressor should avoid surge. An operating point 1009 for compressor 404 in operating diagram 1000 is shown as the intersection of the speed line, inlet mass flow rate, and total pressure ratio. For example, operating point 1009 shown in operating diagram 1000 is at 80% inlet mass flow rate, 108% head, and 100% speed. If surge occurs during operation at operating point 1009, the surge margin 1005 may be increased, for example, by an amount 1008, to shift the surge control line 1003 to a new surge control line 1002. The choke line 1001 is shown in operating diagram 1000.

[0059] Reference Figure 12 A method 1200 for determining when a surge event occurs is shown. Method 1200 begins by operating motor 406 1201 using VFD 416 to compress a working fluid. In some embodiments, the working fluid is a refrigerant. Once motor 1201 is operated, method 1200 continues by receiving 1202 a signal representing the current from VFD 416 to motor 406. Method 1200 ends by determining 1203 when a surge event occurs, at least in part, based on the received signal representing the current from VFD 416 to motor 406. Method 1200 in… Figure 6 This is implemented on the control system 400 shown. Specifically, the controller 410 implements method 1200 via processor 411 using instructions stored in memory 412. Measurements of the current to motor 406 are provided by current sensor 408 included by VFD 416. Other embodiments may use any other suitable detection or estimation of the current supplied to motor 406. In the operation 1201 of motor 406, compression of the working fluid is accomplished by compression mechanism 407.

[0060] Determining that a surge event has occurred (1203) includes determining the difference between a previous current and a current based on a received signal representing the current from VFD 416 to motor 406. In some implementations, the previous current is determined by averaging multiple signals representing the current from VFD 416 to motor 406 received by processor 411 before receiving the signal representing the current current from VFD 416 to motor 406. A surge event has occurred when the difference between the previous current and the current current exceeds a surge threshold. For example, the surge threshold is a variable threshold (e.g., as shown in the image). Figure 10 (as shown in the diagram), and can be pre-loaded to the controller 410 by the user and then changed via the user interface 415. When a signal representing the current current is received, a variable surge threshold is determined at least in part based on the speed detected from the speed sensor 417 of the motor 406. In other embodiments, determining the difference between the previous current and the current current based on the received signal representing the current from the VFD 416 to the motor 406 includes determining the surge amplitude based on the difference between the previous current and the current current. The processor 411 stores an indication of the occurrence of a surge event and the determined surge amplitude in memory 412.

[0061] Reference Figure 13 It shows the source Figure 12 A flowchart 1300 is provided as an example implementation of the method 1200 for determining a surge event. Flowchart 1300 begins upon startup of compressor 404. Flowchart 1300 illustrates both normal operation and startup operation of compressor 404 when determining whether a surge event has occurred. Compressor 404 starts operating, and current sensor 408 continuously measures the current I. 当前 And the speed sensor 417 continuously measures the speed S 实际 When compressor 404 is operating, N previously measured currents I 先前 Using rolling dataset I 滚动 ={I 先前1 I 先前 2, ... I 先前N The data is stored in memory 412 in a manner described above. (Scrolling dataset I) 滚动 This can include within a certain time period in I 当前 Any N currents I previously measured 先前 To create a subset. Once the scrolling dataset I is created... 滚动 And store it in memory 412, then the rolling average In relation to the scrolling dataset I 滚动 Generated over a related time period. The "rolling average" is the average of a series of measured current values ​​with a fixed subset size. Once the current value I is obtained over a certain time period via controller 410... 滚动 The first average of the first subset I 平均 The subset is then modified by shifting the first current value in the rolling dataset forward or excluding the first current value and adding a new (e.g., the most recent) current value, thus creating the new subset I. 滚动2 ={I 先前2 I 先前 3, ... I (先前N+1)The data is then generated and stored in memory 412 at different time intervals. This is done continuously over the entire current dataset throughout the lifetime of compressor 404. A subset I is then created and stored. 滚动 The rate can be set by the OEM or adjusted by the user via user interface 415. Controller 410 calculates the rolling average I. 平均 With the current I 当前 The difference between I 差 The controller 410 then checks whether the compressor 404 is in startup operation. If the compressor 404 is in startup operation, it will... 差 =I 平均 -I 当前 With the preset starting current I 启动 A comparison is made. In some implementations, the starting current I... 启动 It is 2 amperes. In other embodiments, the starting current I... 启动 It is any other suitable fixed or variable current. If the difference I 差 Greater than or equal to the starting current I 启动 If a surge event is detected, its occurrence is stored in memory 412. If the compressor is operating normally, the controller 410 determines the speed based on the detected compressor 404 speed S. 实际 Determine the surge threshold current I 阈值 Surge threshold current I 阈值 It is through the use of the above Figure 10 The relationship between the current swing percentage and the speed percentage of the compressor 404 described herein is found in the graphical relationship 1100. That is, in the example embodiment, the surge threshold current I... 阈值 The linear surge curve 1103 is at the detected velocity S 实际 The percentage of current swing at a given velocity percentage. Other implementations can define the threshold based on absolute velocity, absolute current swing, or any suitable combination. Some implementations may list the surge threshold current in a lookup table or any other suitable form. If the difference I 差 Greater than or equal to surge threshold current I 阈值 If a surge event has occurred, it has been detected. If a surge event has occurred, its occurrence is stored in memory 412, and the associated difference I... 差 The magnitude of the surge is stored in memory 412 as the surge severity. During both startup and normal operation of compressor 404, if no surge event is detected, compressor 404 continues either startup or normal operation until a surge event with a new subset of the measured current is detected in the future.

[0062] Reference Figure 14This illustrates a method 1400 for determining whether to take protective action when processor 411 determines that a surge event has occurred. Method 1400 occurs during... Figure 12 The illustrated method 1200 determines after a surge event has occurred. While the preceding method 1200 can be used simultaneously to determine the occurrence of a surge event, method 1400 can be used in any situation where a surge event has already been detected in a power compressor (by any detection device). Method 1400 begins by operating motor 406 at a motor speed 1401 greater than the predicted minimum surge speed plus a control margin to compress the working fluid. The method continues to determine 1402 when the surge event occurred. In some embodiments, this step may utilize method 1200 to determine that a surge event has occurred. Method 1400 continues by storing an indication of each surge event determined by processor 411 in memory 412. Method 1400 ends by determining 1404 whether to take protective action when processor 411 determines that a surge event has occurred. In some embodiments, protective action includes generating an alert. This alert may be a warning signal sent to a remotely located system controller, a visual or audible alert located near the compressor, or any other suitable alert. In some embodiments, protective action includes stopping motor 406. In some implementations, the protection action includes adjusting the control margin. Similar to the previous method 1200, method 1400 includes... Figure 6 This is implemented on the control system 400 shown. Specifically, the controller 410 implements method 1400 via processor 411 using instructions stored in memory 412. When operating motor 406 1401, the compression of the working fluid is accomplished by compression mechanism 407.

[0063] If step 1404 of method 1400 concludes that generating an alert is a necessary protective action after processor 411 determines that a surge event has occurred, then in various embodiments, the following steps are also taken. Generating an alert may include generating an alert when the number of surge events with indications stored in memory 412 is greater than or equal to an alarm occurrence limit. Generating an alert may include generating a fault alert when the number of surge events with indications stored in memory 412 is greater than or equal to a fault limit greater than an alarm occurrence limit. In some embodiments, when a fault alert is generated, then the control margin of the power compressor 404, such as... Figure 11The control margin 1005 of the operation diagram 1000 shown is increased. In some embodiments, the indication of each surge event includes an indication of the magnitude of the surge event, and generating an alert includes generating a critical alert when the sum of the magnitudes of determined surge events stored in memory 412 is greater than or equal to a critical alarm limit. In some embodiments, generating an alert also includes generating a fault alert when the sum of the magnitudes of determined surge events stored in memory 412 is greater than or equal to a critical fault limit, which is greater than a critical alarm limit. Then, as described above, when a fault alert is generated, the control margin can be increased. In some embodiments, when the working fluid is a refrigerant, an alert is generated if the speed of motor 406 exceeds the sum of the predicted minimum surge speed, the control margin, and the charge margin during a surge event. Then, as described above, when an alert is generated, the control margin is increased.

[0064] If step 1404 of method 1400 concludes that stopping motor 406 is a necessary protective action after a surge event has been determined to have occurred, wherein the indication of each surge event includes the amplitude of the surge event, then the method may include the following. In some embodiments, motor 406 stops when the number of detected surge events is greater than or equal to a shutdown threshold. Alternatively or additionally, motor 406 may be stopped when the sum of the amplitudes of the determined surge events is greater than or equal to a cumulative shutdown threshold.

[0065] Reference Figure 15 It shows the source Figure 14 A flowchart 1500 illustrates an example implementation of a method 1400 for determining whether to take protective action when a surge event has occurred in a power compressor 404. Flowchart 1500 begins when a surge event i = 1, 2, ..., N is detected. Once detected, the surge number N increases to N = N + 1. Simultaneously, as the surge number N increases to N = N + 1, a cumulative surge severity is calculated. This cumulative surge severity is the sum of the amplitudes of all N detected surge events. Next, examine the surge number N and the cumulative surge severity. To observe whether the compressor 404 shutdown condition is met. If the surge number N is greater than or equal to the shutdown surge number limit N. 关闭 (N≥N 关闭 ), or if the cumulative severity of dyspnea Greater than or equal to the surge severity limit Then the control system 400 begins to shut down and the compressor 404 is locked. If the shutdown conditions described above are not met, a fault check is performed using a threshold lower than the threshold used in the shutdown determination. If the surge number N is greater than or equal to the fault surge number limit N...故障 (N≥N 故障 ), or if the cumulative severity of dyspnea Greater than or equal to the fault surge severity limit The control system 400 increases the surge speed control margin of the power compressor 404, such as by Figure 11 The operation shown in Figure 1000 is indicated by the control margin shift 1008. The surge speed control margin can be increased by a fixed amount, a fixed percentage, or a variable. After increasing the surge speed control margin, a surge fault is issued to controller 410. In some embodiments, the surge fault is issued to a separate system controller of the HVAC system (in... Figure 6 An alarm (not shown) is issued for power compressor 404, which is part of the HVAC system. If the above fault conditions are not met, an alarm limit check is performed using a threshold lower than the threshold used in the fault check. If the surge number N is greater than or equal to the alarm number limit N... 警报 (N≥N 警报 ), or if the cumulative severity of dyspnea Greater than or equal to the alarm surge severity limit The control system 400 then sends a surge warning to the controller 410. In some embodiments, the surge warning is an alarm sent to a separate system controller for the HVAC system. Furthermore, when a surge event is detected, the speed S of the power compressor 404 is measured and compared with the predicted surge speed S. 预测 Add filling margin S 裕度 Compare the values. If the velocity S is greater than the predicted surge velocity S0, then... 预测 Add filling margin S 裕度 (S>S 预测 +S 裕度 If this occurs, the surge speed control margin increases. When this happens, a low charge warning is issued to controller 410, indicating that the system may require additional working fluid (e.g., refrigerant). In some implementations, the low charge warning is sent to a separate system controller for the HVAC system. Figure 6 An alarm is issued (not shown in the diagram) by a power compressor 404, which is part of the HVAC system. Other implementations may perform the above comparisons in reverse order. That is, an alarm limit check may be performed first, followed by a fault check, and finally a shutdown check. In such an implementation, if the alarm limit check determines that no surge warning is issued, the comparison can be stopped because the thresholds used for the fault check and shutdown check are greater than the threshold used for the alarm limit check, and if the lower alarm limit threshold (N) is not exceeded... 警报 If the threshold is not exceeded, it cannot exceed the threshold used for fault checking and shutdown checking.

[0066] In some implementations, when a surge event is detected, an unloading device is activated as a protective action to unload the compressor, thereby reducing the severity of the surge. In an example implementation, the unloading device is a load balancing valve, and it is activated at time T before restoring the load on compressor 404. 延迟 Within minutes, the load on compressor 404 is reduced.

[0067] The technical benefits of the methods and systems described in this paper are as follows: (a) continuous monitoring of the number and severity of surge events as observed by compressors in HVAC systems; (b) comparison of surge events and surge severity with the maximum number of surges that a compressor can handle in an HVAC system; and (c) comparison of the compressor speed during a surge event with the predicted surge speed at the current pressure ratio.

[0068] When describing elements of this disclosure or embodiments thereof, the articles “a,” “an,” “the,” and “described” are intended to indicate that one or more of these elements are provided. The terms “comprising,” “including,” “containing,” and “having” are intended to be inclusive and mean that additional elements may be provided in addition to the listed elements. The use of terms indicating a particular orientation (e.g., “top,” “bottom,” “side,” etc.) is for ease of description and does not require any particular orientation of the described item.

[0069] Various changes may be made to the above construction and method without departing from the scope of this disclosure. It is intended that all content contained in the above description and shown in the accompanying drawings should be interpreted as illustrative and not restrictive.

Claims

1. A system comprising: A power compressor, the power compressor comprising: A motor having a drive shaft rotatably supported within the power compressor; and A compression mechanism connected to the drive shaft and operable to compress the working fluid as the drive shaft rotates; A variable frequency drive (VFD) including a sensor configured to sense the current supplied to the motor; and A controller connected to the motor, the controller including a processor and a memory, wherein the memory stores instructions for programming the processor to perform the following: The variable frequency drive is used to operate the motor to compress the working fluid; Receive a signal representing the current from the frequency converter to the motor; and The timing of the surge event is determined at least in part based on the received signal representing the current from the variable frequency drive to the motor. The memory also stores instructions for programming the processor to perform the following: determining, based on a received signal representing the current from the inverter driver to the motor, the difference between a previous current and a current to determine that a surge event has occurred. The memory also stores instructions for programming the processor to perform the following: determine that a surge event has occurred when the difference exceeds a surge threshold. Wherein, the surge threshold is a variable threshold, and The memory also stores instructions for programming the processor to perform the following: upon receiving a signal representing the current current, determine the surge threshold based at least in part on the detected speed of the motor.

2. The system according to claim 1, wherein, The memory also stores instructions to program the processor to perform the following: determine the previous current by averaging a plurality of signals representing the current from the frequency converter to the motor received by the processor before receiving the current signal representing the current from the frequency converter to the motor from the frequency converter driver.

3. The system of claim 1 further includes a speed sensor configured to detect the speed of the motor.

4. The system according to claim 1, wherein, The memory also stores instructions for programming the processor to perform the following: determining the amplitude of the surge based on the difference between the previous current and the current current.

5. The system according to claim 4, wherein, The memory also stores instructions for programming the processor to perform the following: storing an indication of the surge event occurring and the determined amplitude of the surge in the memory.

6. The system according to claim 1, wherein, The power compressor is a centrifugal compressor, and the compression mechanism is an impeller.

7. The system according to claim 6, wherein, The system is an HVAC system, and the working fluid is a refrigerant.

8. A method for detecting surge events in a power compressor, the power compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operated, the method comprising: Operate the motor to compress the working fluid; Receive a signal indicating the current supplied to the motor to operate the motor; as well as The timing of a surge event is determined solely based on the received signal representing the current supplied to the motor and a surge threshold. Determining when a surge event occurs includes: The difference between the previous current and the current current is determined based on the received signal representing the current supplied to the motor; and When the difference exceeds the surge threshold, it is determined that the surge event has occurred, and The surge threshold is a variable threshold, and determining when a surge event occurs includes determining the surge threshold at least in part based on the detected speed of the motor when a signal representing the current is received.

9. The method according to claim 8, wherein, Determining the previous current includes averaging multiple received signals representing the current supplied to the motor before receiving a signal representing the current supplied to the motor.

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