Surge control system and method for dynamic compressors

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 of related applications This application claims priority to U.S. Patent Applications No. 17 / 247,724 and 17 / 247,725, filed on 21 December 2020, the disclosures of which are incorporated herein by reference in their entirety.

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

[0003] Dynamic compressors, including centrifugal compressors, are used in many applications such as HVAC. A centrifugal compressor has a drive shaft operably connected to a motor between impeller stages or a compression mechanism supported by a gas foil bearing. The drive shaft can be positioned between the impeller stages so that the impeller rotates at a certain rotational speed to compress the refrigerant to a selected pressure in the HVAC system. Compressor bearings typically have 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 foil away from the shaft so that contact does not occur. The shaft and gas foil bearing are separated by the high pressure of the gas, which is generated by the rotation drawing the gas into the bearing by a viscous effect. A high speed of the shaft relative to the gas foil bearing is required to initiate a gas gap, and once this is achieved, no contact occurs. These bearings offer several advantages over other bearings, including lighter weight, stable operation at high speeds and temperatures, low power loss at high speeds, and a long service life with minimal maintenance.

[0004] Compressor surge events accelerate wear on the compressor and its components (including bearings). A surge is a characteristic operation of a dynamic compressor that can occur when the head (lift) generated by the compressor to overcome the system pressure during compressor discharge is insufficient. When a surge occurs, the compressor's output pressure drops significantly, resulting in a reversal of the flow within the compressor. When a dynamic compressor surges, there is an actual reversal of the gas flow through the impeller. A surge usually begins in one stage of a multistage compressor and can occur very rapidly. Compressors are particularly susceptible to surge events during startup or shutdown due to their low operating speed. The severity of a surge event and the damage it causes increases with compressor speed.

[0005] This background technology section is intended to introduce readers to various aspects of the technology that may be relevant to the various aspects of the disclosure described and / or claimed below. This discussion is intended to help readers better understand the various aspects of the disclosure by providing background information. Therefore, it should be understood that these statements should be read in this context and not as an endorsement of prior art. [Overview of the Initiative]

[0006] One aspect of the present disclosure is a system comprising 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 the current supplied to the motor. The controller is connected to the motor and includes a processor and memory. The memory stores instructions for operating the motor to compress a working fluid using the VFD, receiving a signal representing the current from the VFD to the motor, and programming the processor to determine when a surge event has occurred, at least in part, based on the received signal representing the current from the VFD to the motor.

[0007] Another embodiment is a controller for a dynamic compressor, which includes a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operating. The controller includes a processor and memory. The memory stores instructions for operating the motor to compress the working fluid, receiving a signal representing the current supplied to the motor to operate the motor, and determining when a surge event has occurred based at least in part on the received signal representing the current supplied to the motor.

[0008] Another embodiment is a method for detecting the occurrence of a surge event in a dynamic compressor, which includes a motor and a compression mechanism connected to the motor and operable to compress a working fluid when the motor is operating. The method includes the steps of operating the motor to compress a working fluid, receiving a signal representing the current supplied to the motor to operate the motor, and determining when the surge event occurred based only on the received signal representing the current supplied to the motor and a surge threshold.

[0009] Another embodiment 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 as the drive shaft rotates. The controller is connected to the motor and includes a processor and memory. The memory operates the motor to compress the working fluid at a motor speed greater than the predicted minimum surge speed plus a control margin, determines when a surge event has occurred, stores an indication for each surge event that the processor has determined has occurred, and stores instructions to program the processor to determine whether to perform a protective action when the processor has determined that a surge event has occurred.

[0010] Another aspect is a controller for a dynamic compressor including a motor and a compression mechanism connected to the motor and operable to compress a working fluid during operation of the motor. The controller includes a processor and a memory. The memory stores instructions to operate the motor to compress the working fluid at a motor speed greater than the predicted minimum surge speed plus a control margin, to determine when a surge event has occurred, to store an indication of each surge event determined by the processor to have occurred in the memory, and to program the processor to determine whether to take a protection 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 during operation of the motor. The method includes operating the motor to compress the working fluid at a motor speed greater than the predicted minimum surge speed plus a control margin, determining when a surge event has occurred, storing an indication of each surge event determined by the processor to have occurred, and determining whether to take a protection action when the processor determines that a surge event has occurred.

[0012] Notable features associated with the above aspects have various improvements. Further features may be incorporated into the above aspects. These improvements 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 alone or in any combination.

Brief Description of the Drawings

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

[0014] [Figure 1] It is a perspective view of an assembled compressor.

[0015] [Figure 2]This is a cross-sectional view of the compressor in Figure 1, taken along line 2-2, with the external conduit removed.

[0016] [Figure 3] Figure 2 is a cross-sectional view through the sleeve of the bearing housing, showing the drive shaft supported within the foil bearing assembly, which is held in place within the sleeve of the bearing housing using a pair of retaining clips.

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

[0018] [Figure 5] This is an exploded view of the elements of a foil bearing assembly positioned relative to the bearing housing and drive shaft.

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

[0020] [Figure 7] This is a surge current characteristic graph for a dynamic centrifugal compressor.

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

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

[0023] [Figure 10] This is a graphical representation of the relationship between the current fluctuation rate and the speed rate of a dynamic centrifugal compressor.

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

[0025] [Figure 12] This is a flowchart showing how to determine when a surge event occurred in a dynamic centrifugal compressor.

[0026] [Figure 13] Figure 12 is a flowchart illustrating an exemplary embodiment of the method.

[0027] [Figure 14] This is a flowchart showing how to determine whether or not to perform protective action when a surge event occurs in a dynamic centrifugal compressor.

[0028] [Figure 15] Figure 14 is a flowchart illustrating an exemplary embodiment of the method.

[0029] Throughout the drawing, corresponding reference numerals indicate corresponding parts. [Modes for carrying out the invention]

[0030] For brevity, an example relating to a centrifugal compressor equipped with a gas foil bearing (GFB) will be described. However, the methods and systems described herein may 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 occur, monitoring the severity of surge events, determining the surge threshold, determining the relationship between motor speed and surge events, adjusting the control margin to provide a larger surge margin, and deciding whether to take protective actions such as issuing alerts or stopping the machine when a surge event occurs can prevent damage and extend the life of the centrifugal compressor. These steps can further prevent catastrophic failures of centrifugal compressors by enabling more precise scheduling of preventative maintenance, increasing the sensitivity of surge prevention controls, improving reliability by limiting the severity of surges during startup by holding the centrifugal compressor at a low speed until it stabilizes, allowing the system to continue providing cooling by increasing the operating time of the centrifugal compressor before it fails and stops, and improving reliability by limiting the severity of surges by activating the unloading device with surge detection rather than an estimated map.

[0031] Referring to Figure 1, a compressor shown in the form of a two-stage refrigerant compressor is generally denoted as 100. Compressor 100 generally includes a compressor housing 102 in which each stage of refrigerant compression is achieved, forming at least one sealed cavity therein. Compressor 100 includes a first refrigerant inlet 110 for introducing refrigerant vapor into a first compression stage (not labeled in Figure 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 a second compression stage (not labeled in Figure 1), and a second refrigerant outlet 120. The refrigerant transfer conduit 112 is connected at both ends to the first refrigerant outlet 114 and the second refrigerant inlet 118, respectively. The second refrigerant outlet 120 delivers compressed refrigerant from the second compression stage to the cooling system in which compressor 100 is incorporated.

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

[0033] Referring to Figure 2, the first compression mechanism 106 and the second compression mechanism 116 are connected to the ends of the drive shaft 104. The drive shaft 104 is operably 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 pre-selected mass flow rate exiting the second refrigerant outlet 120 (not shown in Figure 2). Any suitable motor, including but not limited to an electric motor, may be incorporated into the compressor 100. The drive shaft 104 is supported by gasfoil bearing assemblies 300 located within sleeves 202 of each bearing housing 200 / 200a, as will be described in more detail below. Each bearing housing 200 / 200a includes mounting structures (not shown) for connecting each bearing housing 200 / 200a to the compressor housing 102, as shown in Figure 2.

[0034] Referring to Figure 2, each bearing housing 200 / 200a supports the drive shaft 104, which protrudes through the bearing housing 200 / 200a opposite to the sleeve 202, and the compression mechanism 106 is connected to the protruding end of the drive shaft 104. Referring to Figures 3 and 5, the gasfoil bearing assembly 300 is located within a cylindrical bore 206 in the bearing housing 200. The drive shaft 104 is tightly fitted into the gasfoil bearing assembly 300, which includes an outer compliant foil or foil layer 302 located adjacent to the inner wall of the sleeve 202, an inner compliant foil or foil layer 306 (also called the “top foil”) located adjacent to the drive shaft 104, and a bump foil or foil layer 310 located between the inner foil layer 306 and the outer foil layer 302. The foil or layers 302 / 306 / 310 of the gas foil bearing assembly form an essentially cylindrical tube sized to accept the drive shaft 104 with a relatively small gap or no gap, as determined 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 made of any suitable material that enables the foil bearing assembly 300 to function as described herein. Suitable materials include, for example, metal alloys. In some embodiments, for example, each of the outer foil layer 302, the inner foil layer 306, and the bump foil layer 310 is made of stainless steel (e.g., 17-4 stainless steel).

[0035] Referring again to Figure 3, the illustrated embodiment of the foil bearing assembly 300 further includes a pair of foil keepers 312a / 312b positioned adjacent to both ends of the layers 302 / 306 / 310 to restrain the axial sliding of the layers 302 / 306 / 310 within the cylindrical bore 206 of the sleeve 202. A pair of foil retaining clips 314a / 314b positioned adjacent to the foil keepers 312a / 312b each 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 other embodiments, as shown in Figure 4, each bearing housing 200a includes a foil retaining lip 214 formed integrally with the bearing housing 200a (e.g., by casting) and projecting radially inward from a radial inner surface 204 defining a cylindrical bore 206. In the illustrated embodiment, the foil retaining lip 214 is positioned near the compression mechanism end 216 of the cylindrical bore 206 proximal to the compression mechanism 116 (shown in Figure 2). The foil retaining lip 214 is sized and dimensioned to project radially from the radial inner surface 204, overlapping with at least a portion of layers 302 / 306 / 310 of the foil bearing assembly 300. The foil retaining lip 214 may extend entirely around the radial inner surface 204, or it may extend over a portion of the circumference of the radial inner surface 204 and include two or more segments separated by a space flush with adjacent radial inner surfaces 204. The bearing housing 200 (not shown in Figure 4) is formed similarly.

[0037] The foil bearing assembly 300 of the embodiment shown in Figure 4 further includes a single foil retaining clip 314 positioned adjacent to the foil retaining lip 214 and the end of the layers 302 / 306 / 310 opposite to the foil retaining lip 214 in order to restrain the axial movement of the layers 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 region of the cylindrical bore 206 near the compression mechanism end 216, including but not limited to a position directly adjacent to the opening of the cylindrical bore 206 at the compression mechanism end 216. Alternatively, the foil retaining lip 214 may be located in any region of the cylindrical bore 206 near the motor end 218, including but not limited to a position directly adjacent to the opening of the cylindrical bore 206 at the motor end 218. In such embodiments, the foil retaining clip 314 fits into a circumferential groove 212 formed within the radial inner surface 204 of the cylindrical bore 206 near the compression mechanism end 216, in an arrangement essentially opposite to that shown in Figure 4.

[0039] Referring again to Figure 4, the foil bearing assembly 300 is installed in 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 then advances axially 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 is then fitted 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 for mounting the foil bearing assembly 300 within the sleeve 202 may be used. Non-limiting examples of suitable methods include keepers and retaining clips, adhesives, fixing screws, and any other suitable mounting methods.

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

[0042] The foil bearing assembly 300 may be provided in any suitable form, without limitation. For example, the foil bearing assembly 300 may comprise two, three, four, or additional layers, without limitation. The bump foil 310 of the foil bearing assembly 300 may be formed from a radially elastic structure to provide an elastic surface for the drive shaft 104 that rotates during the 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 layer of the foil bearing assembly 300.

[0043] Referring to Figure 6, an exemplary embodiment of system 400 includes a dynamic compressor 404. In one embodiment, the dynamic compressor is a centrifugal compressor. In other embodiments, the dynamic 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 further includes a variable frequency drive (VFD) 416 having a current sensor 408, and a motor interface 413 that communicates 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 exemplary embodiments, 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 flow compressor. The compressor housing 405, including the motor 406, the compression mechanism 407, and the gas foil bearing 409, and the compressor 404 may be configured similarly to the compressor 100 shown in Figure 1-5, or in a different manner. The compressor 404 is not limited to a specific 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 has occurred and whether to take protective action when one or more surge events have occurred. The controller 410 includes a processor 411, memory 412, and an unload interface 414. The memory 412 includes instructions executed by the processor to control the compressor 404 and to perform a method for determining whether a surge event has occurred, when it occurred, and whether to take protective action in response to the surge event.

[0044] The unloading device 401 within the system 400 removes and / or reduces the compressor load during start-up and stop routines and detected surge events, limiting the severity of surge events. In exemplary embodiments, the unloading device 401 is a bypass valve. A 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 surges, regardless of how slowly the compressor motor 406 is accelerating during start-up or decelerating during stop-down. 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 pulse-width modulation (PWM) valve, configured to control opening and closing according to a duty cycle. In yet another embodiment, the unloading device 401 can be a variable diffuser or a variable inlet guide vane (VIGV), but is not limited. Although many types of unloading devices are described here, the unloading device 401 can be any suitable device or combination of devices that reduces the load on the compressor 404.

[0045] The unloading device 401 is operably coupled to the 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 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 further determines when the surge event has completed and when normal operation resumes when the measured current of the motor 406 is substantially constant. Other embodiments may use other techniques, such as detecting changes in voltage, detecting changes in pressure, or sensing vibrations caused by the surge, to detect the occurrence and completion of the surge event. The controller 410 further determines whether to take 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 sensors, current sensors, voltage sensors, rotational rate sensors, and any other suitable sensors.

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

[0047] The control system 400 includes a user interface 415 configured to output (e.g., display) and / or receive information related to the system 400 (e.g., from the user). In some embodiments, the user interface 415 is configured to receive activation and / or deactivation inputs from the user and to enable the system 400 to be activated and deactivated (i.e., turned on and off) or otherwise operated. Furthermore, in some embodiments, the user interface 415 is configured to output information related to one or more operating characteristics of the system 400, including, 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 gasfoil bearing 409 and other appropriate 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, but is not limited to, input devices such as a keyboard, mouse, touchscreen, joystick(s), throttle(s), buttons, switches, and / or other input devices. Furthermore, the user interface 415 may include, but is not limited to, output devices such as a display (e.g., a liquid crystal display (LCD) or organic light-emitting diode (OLED) display), speaker, indicator light, instrument, and / or other output devices. Furthermore, the user interface 415 may be part of a different component such as a system controller (not shown). Other embodiments do not include the user interface 415.

[0049] In some embodiments, the system 400 may be controlled by a remote control interface. For example, the system 400 may include a communication interface (not shown) configured to connect to a wireless control interface that enables remote control and activation of the system 400. The wireless control interface may be implemented 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 by programming and commands 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 user input received from the user interface 415.

[0051] The controller 410 may include any suitable computer and / or other processing units, including any suitable combination of computers, processing units and / or similar, which can generally be coupled together in a communicative manner and can operate independently or in conjunction with each other (for example, 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 separately from the system 400. The controller 410 may be part of the compressor 404, or separate from it, or may be part of a system controller in the HVAC system. The controller 410 and / or components of the controller 410 may be integrated or incorporated into other components of the system 400. In some embodiments, for example, the controller 410 may be incorporated into a motor 406 or an unloading device 401. The controller 410 may include one or more processors 411 and associated memory devices 412 configured to perform various computer-implemented functions (e.g., performing calculations, decisions and functions disclosed herein). As used herein, the term “processor” means not only integrated circuits but also controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application-specific integrated circuits, and other programmable circuits. Furthermore, the memory device(s) 412 of the controller 410 may include, but are not limited to, computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk read-only memory (CD-ROM), magneto-optical disks (MODs), digital general-purpose disks (DVDs), and / or other suitable memory elements.Such memory devices 412 may generally be configured to store appropriate computer-readable instructions that, when implemented by a processor 411, set up 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 the operator via the user interface 415, controlling the unloading device 401, and / or other appropriate computer implementation functions.

[0052] Referring to Figure 7, a surge current characteristic graph 600 at startup is shown, including a speed curve 601 and a motor current curve 602. Figure 7 shows the motor speed being accelerated to a first speed, and the motor 406 being operated at that first speed for a period 605. While the motor 406 is operating at the first speed for the period 605, the region of possible surge 603 is identified by the oscillation in the motor current curve 602. The compressor 404 is held at the first speed until the surge current oscillation pattern stops, indicating that the compressor 404 has fully started up.

[0053] Figures 8 and 9 are traces of signals used by the system to detect the occurrence of a surge (e.g., during period 605 in Figure 7). Figure 8 is a speed graph 800, and Figure 9 is a current graph 900. With respect to Figure 8, the actual speed 801 of the compressor motor is shown along with a baseline speed line 803, which can be used as a reference point for determining whether a surge occurs. The baseline speed line 803 is also called the speed setpoint or command speed. With respect to Figure 9, the actual current 901 (detected using current sensor 408) and average current 902 supplied to the motor are shown. The average current 902 may 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 the compressor 404 enters a surge event, the mass flow rate through the compressor decreases significantly, thereby reducing the load on the compressor 404 and causing the speed of the unloaded motor 406 to rise above the baseline speed line 803. Next, VFD416, via its control algorithm, reduces the actual current 901 in proportion to the increased speed in order to return the actual speed 801 back to the baseline speed line 803. Once the surge ends, the load on the compressor 404 (and motor 406) returns, causing the speed 801 to decrease rapidly. VFD416 increases the current to return the motor speed back to the baseline speed 803. The result is a characteristic overshoot of the actual current 901 and an undershoot of the actual speed 801, as seen at the end of the surge event in Figures 8 and 9, before the speed and current return to approximate levels before the surge. The decrease 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. Speed ​​graph 800 shows the speed surge severity 802, and 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 can be recorded in memory 412.

[0054] Referring to Figure 10, an exemplary graphical relationship 1100 between the current swing rate and the rate rate is shown to illustrate the threshold current swing for detecting a surge event. The linear surge curve 1103 represents the threshold for detecting a surge. A current swing on or above the linear surge curve 1103 at the current compressor speed (expressed as a percentage of the maximum speed) (e.g., surge severity 904 in Figure 9) is determined to indicate the occurrence of a surge event. If the current swing is smaller than the linear surge curve 1103, no surge event is detected. Alternatively, only current swings above the linear surge curve 1103 may be considered surge events, and current swings below the linear surge curve may not be considered surge events.

[0055] Referring to Figure 11, an exemplary dynamic centrifugal compressor 404 is shown as an operating envelope or operating map 1000. The operating map 1000 graphically estimates and displays the compressor's performance with respect to flow rate, head, and speed. The map shows the head versus inlet mass flow rate at the design point of the compressor 404 as a percentage of those values. The inlet mass flow rate is a measure of the amount of working fluid, such as 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 shows multiple compressor speed lines 1007. In this example, there are five speed lines 1007 ranging from 110% design speed to 70% design speed, with each line separated by a 10% difference. While these specific speed lines are shown in this example, any number of speed lines at any different percentages of the compressor's design speed can be shown for any type of compressor.

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

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

[0058] 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 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, which are received by the processor 411 before receiving a signal from the VFD representing the current current from the VFD 416 to the motor 406. A surge event occurs when the difference between the previous current and the current exceeds a surge threshold. For example, the surge threshold may be a variable threshold (e.g., as shown in Figure 10) which is preloaded by the user into the controller 410 and subsequently modified via the user interface 415. The variable surge threshold is determined at least in part based on the speed detected from the speed sensor 417 of the motor 406 when a signal representing the current is received. In other embodiments, determining the difference between a previous current and a current based on a received signal representing the current from the VFD 416 to the motor 406 includes determining the magnitude of the surge based on the difference between the previous current and the current. The processor 411 stores the instruction for the occurrence of a surge event and the determined magnitude of the surge in memory 412.

[0059] Referring to Figure 13, a flowchart 1300 of an exemplary embodiment of method 1200 from Figure 12 for determining a surge event is shown. Flowchart 1300 begins when the compressor 404 is started. Flowchart 1300 shows both the normal operation and start operation cases of the compressor 404 when determining whether a surge event has occurred. The compressor 404 has started operation and the current sensor 408 is at the current I present The speed sensor 417 continuously measures the speed S actual The current I is measured continuously. When the compressor 404 is operating, N previously measured currents I previous is a rolling dataset

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

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

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

[0063] Referring to Figure 15, a flowchart 1500 of an exemplary embodiment of method 1400 from Figure 14 for determining whether or not to take protective action in the event of a surge event in the dynamic compressor 404 is shown. Flowchart 1500 shows the surge event i=1,2, …N When a surge is detected, the surge count N is incremented to N=N+1. Simultaneously, the surge severity cumulative is calculated. The surge severity cumulative 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 acts as a protective action to unload the compressor and reduce the severity of the surge. In an exemplary embodiment, the unloading device is a load balance valve and unloads the compressor 404 for a time T before returning the load. delay Reduce the load on compressor 404 for a minute.

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

[0066] When describing elements of this disclosure or its embodiments, the articles “a,” “an,” “the,” and “said” are intended to indicate that there are one or more elements. The terms “have,” “include,” and “have” are intended to be inclusive and mean that there may be additional elements other than those listed. The use of terms indicating a particular orientation (e.g., “top,” “bottom,” “side,” etc.) is for explanatory convenience and does not require a specific orientation of the items described.

[0067] Because various modifications can be made to the above configuration and method without exceeding the scope of disclosure, all matters included in the above description and shown in the attached drawings are intended to be interpreted as illustrative, not restrictive.

Claims

1. It is a dynamic compressor: A motor having a drive shaft rotatably supported within the aforementioned dynamic compressor; and A compression mechanism connected to the drive shaft and capable of operating to compress the working fluid when the drive shaft rotates; Dynamic compressor and; A variable frequency drive (VFD) including a sensor configured to sense the current supplied to the motor; A controller connected to the motor, the controller having a processor and memory, the memory being: The motor is operated using the VFD to compress the working fluid; The VFD receives a signal representing the current to the motor; Based on at least a portion of the received signal representing the current from the VFD to the motor, it is determined when the surge event occurred; A device that stores instructions for programming the aforementioned processor. It has a controller; The memory stores further instructions for programming the processor to determine that the surge event has occurred by determining the difference between a previous current and the current based on the received signal representing the current from the VFD to the motor, and further instructions for programming the processor to determine that the surge event has occurred when the difference exceeds a surge threshold. The aforementioned surge threshold is a variable threshold. system.

2. The memory stores further instructions for programming 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 before the VFD received a signal representing the current from the VFD to the motor. The system according to claim 1.

3. The system further comprises a speed sensor configured to detect the speed of the motor, and the memory stores further instructions for programming the processor to determine the surge threshold based at least in part on the detected speed of the motor when the signal representing the current is received. The system according to claim 1.

4. The memory stores further instructions for programming the processor to determine the severity of the surge event based on the difference between the previous current and the current. The system according to claim 1.

5. The memory stores instructions for the occurrence of the surge event and further instructions for programming the processor to store the determined severity of the surge event in the memory. The system according to claim 4.

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

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

8. A controller for a dynamic compressor, comprising a motor and a compression mechanism connected to the motor and capable of operating to compress a working fluid when the motor is operating, wherein the controller: Processor and; Memory, wherein the memory is: The motor is operated to compress the working fluid; The system receives a signal representing the current supplied to the motor in order to operate the motor; Based at least in part on the received signal representing the current supplied to the motor, it is determined when the surge event occurred; Thus, a memory for storing instructions for programming the processor; It has, The memory stores further instructions for programming the processor to determine that the surge event has occurred by determining the difference between a previous current and the current based on the received signal representing the current supplied to the motor, and further instructions for programming the processor to determine that the surge event has occurred when the difference exceeds a surge threshold. The surge threshold is a variable threshold, and the memory stores further instructions for programming the processor to determine the surge threshold based at least in part on the detected speed of the motor when the signal representing the current is received. controller.

9. The memory stores further instructions for programming the processor by averaging a plurality of signals representing the current supplied to the motor, which have been received by the processor, before receiving a signal representing the current supplied to the motor. The controller according to claim 8.

10. The aforementioned memory is: The severity of the surge event is determined based on the difference between the previous current and the current; The instruction for the occurrence of the surge event and the determined severity of the surge event are stored in the memory; To store further instructions for programming the processor, The controller according to claim 8.

11. A method for detecting the occurrence of a surge event in a dynamic compressor, which includes a motor and a compression mechanism connected to the motor and capable of operating to compress a working fluid when the motor is operating, the method being: The steps include: operating the motor to compress the working fluid; The steps include: receiving a signal representing the current supplied to the motor in order to operate the motor; The steps include: determining when a surge event occurred based solely on the received signal representing the current supplied to the motor and a surge threshold; The steps to determine when the aforementioned surge event occurred are: The steps include determining the difference between a previous current and a current based on the received signal representing the current supplied to the motor; The steps include: determining that a surge event has occurred when the difference exceeds the surge threshold; The surge threshold is a variable threshold, and the step of determining when the surge event occurred includes determining the surge threshold at least in part based on the detected speed of the motor when the signal representing the current current was received. method.

12. Determining the aforementioned prior current includes averaging a plurality of signals representing the current supplied to the motor that are received, before receiving a signal representing the current supplied to the motor. The method according to claim 11.

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