System and method for mass flow rate interpolation for dynamic compressors

Abstract

A method for determining a mass flow rate of a dynamic compressor not including a mass flow sensor while the compressor is operating to compress a working fluid includes determining, by a processor, a current operating point of the compressor. If the current operating point is the same as one in a map of a plurality of predetermined operating points stored in a memory, the mass flow rate of the predetermined operating point is taken as the mass flow rate of the current operating point. If not, the processor calculates the mass flow rate at the current operating point from the mass flow rates of a subset of the predetermined operating points that are closest to the current operating point. The dynamic compressor continues to operate to compress the working fluid based at least in part on the calculated mass flow rate for the current operating point.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 17 / 243,787, filed April 29, 2021, the disclosure of which is incorporated by reference in its entirety herein.

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

[0003] Dynamic compressors, including centrifugal compressors, are commonly used in HVAC systems. The compressor is operatively connected to a motor via a drive shaft that supports multiple compression mechanisms or impeller stages. The motor rotates the impeller at speed and load conditions to compress the refrigerant to a specified demand. The motor speed and load can be controlled to operate the compressor over a wide range of operating conditions. Knowing the exact operating point of the compressor helps to avoid operation in regions of inefficiency (e.g., choked flow) or instability (e.g., surge).

[0004] Choked flow occurs when the load on a compressor at a particular speed is low enough to achieve a minimum pressure rise of the working fluid through the machine. Although a compressor can safely operate choked for extended periods of time, it is an inefficient and undesirable mode of operation. Surge is a highly unstable flow region that occurs when the head generated by the compressor is insufficient to overcome the pressure at the compressor discharge, resulting in a reversal of flow through the impeller. Operating in this unstable flow region for even a short period of time can damage bearings and other components of the machine, thereby reducing the life of the compressor.

[0005] To avoid operation in undesirable flow regions, it is desirable to have real-time data on the key parameters that define the compressor's operating point: rotational speed, pressure rise, and mass flow rate. By including these parameters in the compressor's control strategy, other operating parameters can be adjusted to keep the compressor within a specific operating range. Motor speed and compressor inlet and outlet pressures are easily measured using standard instrumentation. However, sensors that measure mass flow rate are often cost-prohibitive. It is therefore desirable to determine the compressor's mass flow rate without the cost of additional instrumentation.

[0006] This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. As such, it should be understood that these statements are to be read in this light, and not as admissions of prior art. Summary of the Invention

[0007] One aspect of the disclosure is directed to a system having a dynamic compressor operable to compress a working fluid and a controller. The controller is connected to the dynamic compressor and has a processor and a memory. The memory stores a map of predefined operating points of the dynamic compressor, each predefined operating point including a mass flow rate of the dynamic compressor at the predefined operating point. The memory further stores instructions to program the processor to operate the dynamic compressor to compress the working fluid and determine a current operating point of the compressor while operating the dynamic compressor. If the operating point is one of the predefined operating points, the instructions stored in the memory program the processor to obtain a mass flow rate of the current operating point from the map. If the operating point is not one of the predefined operating points, the instructions stored in the memory program the processor to calculate a mass flow rate of the current operating point from mass flow rates of a subset of the re-determined operating points that are closest to the current operating point. The instructions stored in the memory further program the processor to continue operating the dynamic compressor to compress the working fluid based at least in part on the calculated mass flow rate for the current operating point.

[0008] Another aspect of the disclosure is directed to a controller for a dynamic compressor without a mass flow sensor. The controller has a processor and a memory. The memory stores a map of a plurality of predetermined operating points of the dynamic compressor, each predetermined operating point including a mass flow rate of the dynamic compressor at the predetermined operating point. The memory further stores instructions to program the processor to operate the dynamic compressor to compress a working fluid and determine a current operating point of the compressor while operating the dynamic compressor. If the current operating point is one of the predetermined operating points, the instructions stored in the memory program the processor to obtain a mass flow rate for the current operating point from the map. If the current operating point is not one of the predetermined operating points, the instructions stored in the memory program the processor to calculate a mass flow rate for the current operating point from the mass flow rates of a subset of the predetermined operating points closest to the current operating point. The instructions stored in the memory further program the processor to continue operating the dynamic compressor to compress the working fluid based at least in part on the calculated mass flow rate for the current operating point.

[0009] Another aspect of the disclosure is directed to a method for compressing a working fluid and determining a mass flow rate of a dynamic compressor that does not include a mass sensor, the method including: operating the dynamic compressor to compress a working fluid, determining a current operating point of the compressor, if the current operating point is one of a plurality of predefined operating points of the dynamic compressor in a map, obtaining a mass flow rate of the current operating point from a map of predefined operating points stored in a memory, each predefined operating point in the map including a mass flow rate of the dynamic compressor at the predefined operating point, if the current operating point is not one of the predefined operating points in the map, calculating a mass flow rate of the current operating point from mass flow rates of a subset of the predefined operating points that are closest to the current operating point, and continuing to operate the dynamic compressor to compress the working fluid based at least in part on the calculated mass flow rate for the current operating point.

[0010] Various refinements exist for the features described in relation to the above aspects. Further features may be incorporated into the above aspects. These refinements and further features may exist individually or in any combination. For example, various features described below in relation to any of the illustrated embodiments may be incorporated into any of the above aspects, either alone or in any combination. [Brief description of the drawings]

[0011] The following figures illustrate various aspects of the present disclosure.

[0012] [Figure 1] FIG. 2 is a perspective view of an assembled dynamic compressor.

[0013] [Diagram 2] FIG. 2 is a cross-sectional view of the compressor of FIG. 1 taken along line 2-2 with the external conduit removed.

[0014] [Diagram 3] FIG. 2 is a block diagram of a control system for the dynamic compressor.

[0015] [Figure 4] 2 is an operation map of a dynamic compressor.

[0016] [Diagram 5] 4 is a map of predetermined operating points and an example current operating point of a dynamic compressor.

[0017] [Figure 6] 1 is a flowchart of a method for determining a mass flow rate of a dynamic compressor that compresses a working fluid.

[0018] [Figure 7A] 1 is a first graphical representation of a subset of a current operating point and a nearest predetermined operating point;

[0019] [Figure 7B]11 is a second graphical representation of a subset of the current operating point and the nearest predetermined operating point.

[0020] [Figure 8] 11 is a third graphical representation of a subset of a current operating point and a nearest predetermined operating point.

[0021] [Figure 9] 11 is a fourth graphical representation of a subset of a current operating point and a nearest predetermined operating point.

[0022] [Figure 10] 13 is a fifth graphical representation of a subset of a current operating point and a nearest predetermined operating point;

[0023] [Figure 11] 13 is a sixth graphical representation of a subset of the current operating point and the nearest predetermined operating point;

[0024] [Figure 12] 13 is a flowchart of a method for calculating an inlet mass flow rate at a current operating point using two subsets of predetermined operating points at first and second VIGV positions.

[0025] [Figure 13] 1 is a graphical representation of a current operating point, two intermediate mass flows, and two subsets of predetermined operating points.

[0026] [Figure 14] 4 is a flow chart of an example control algorithm for operation of a dynamic compressor using inlet mass flow rate as an input.

[0027] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] For brevity, a centrifugal compressor example is described. However, the methods and systems described herein can be applied to any suitable dynamic compressor. Dynamic compressor performance and life can be improved by real-time measurements of key operating parameters including speed, pressure ratio and inlet mass flow rate. Such measurements can be used as inputs to control algorithms to limit the likelihood of the compressor experiencing undesirable operating conditions such as surge or choke. To obtain operating mass flow information without the need for additional instrumentation, a set of prior data points can be used to interpolate the value of mass flow rate at the current operating point. The prior data points can be obtained from simulation, experiment, a combination of the two, or other suitable means.

[0029] Referring to FIG. 1, a two-stage refrigerant compressor is generally designated 100. The compressor 100 includes a compressor housing 102 that defines at least one sealed cavity within which each stage of refrigerant compression is accomplished. The compressor 100 includes a first refrigerant inlet 110 that introduces refrigerant vapor into a first compression stage (not labeled in FIG. 1), a first refrigerant outlet 114, a refrigerant transfer conduit 112 that transfers compressed refrigerant from the first compression stage to a second compression stage, a second refrigerant inlet 118 that introduces refrigerant vapor into the second compression stage (not labeled in FIG. 1), and a second refrigerant outlet 120. The refrigerant transfer conduit 112 is connected at each end 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 a refrigeration system in which the compressor 100 is incorporated.

[0030] Referring to FIG. 2, the compressor housing 102 encloses a first compression stage 124 and a second compression stage 126 at opposite ends of the compressor 100. The first compression stage 124 includes a first compression mechanism 106 configured to add kinetic energy to the refrigerant entering through the first refrigerant inlet 110. In some embodiments, the first compression mechanism 106 is an impeller. The kinetic energy imparted to the refrigerant by the first compression mechanism 106 is converted to an increased refrigerant pressure as the refrigerant velocity is reduced as it travels to a closed 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 transferred from the first compression stage 124 entering 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 to increased refrigerant pressure as the refrigerant velocity is slowed as it travels to a sealed cavity (e.g., a diffuser) formed within the volute 132. The compressed refrigerant exits the second compression stage 126 via a second refrigerant outlet 120 (not shown in FIG. 2).

[0031] The first stage compression mechanism 106 and the second stage compression mechanism 116 are connected to opposite ends of a drive shaft 104. The drive shaft 104 is operatively connected to a motor 108 located between the first 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 are rotated at a selected rotational speed to compress the refrigerant to a preselected pressure that exits a second refrigerant outlet 120 (not shown in FIG. 2 ). The compressor 100 may incorporate any suitable motor, including, but not limited to, an electric motor.

[0032] The drive shaft 104 is supported by a gas foil bearing assembly 300 disposed within the sleeve 202 of each bearing housing 200 / 200a. Each bearing housing 200 / 200a includes mounting structure (not shown) for connecting each bearing housing 200 / 200a to the compressor housing 102, as shown in Figure 2. The bearing housing 200 / 200a may further serve as a mounting structure for various elements including, but not limited to, radial bearings, thrust bearings, such as the gas foil bearing assemblies 300 described above, and sensing devices (not shown) used as feedback for passive or active control schemes, such as proximity probes, pressure transducers, thermocouples, key phasors, etc.

[0033] 3, an exemplary embodiment of a system 350 includes a dynamic compressor 304 operable to compress a working fluid. The compressor 304 includes a compressor housing 305, a compression mechanism 307, a motor 306, a speed sensor 317, a pressure sensor 309, and a controller 310. In this embodiment, the dynamic compressor 304 is a centrifugal compressor and the compression mechanism 307 is an impeller. In other embodiments, the dynamic compressor 304 may be an axial compressor and the compression mechanism 307 may be an axial rotor. The speed sensor 317 measures the rotational speed of the compressor and the pressure sensor 309 measures the pressure at various points along the compressor flowpath, including the refrigerant inlet and the refrigerant outlet. Additional sensors may be attached to the compressor 304 to provide data regarding its operation, including, but not limited to, temperature sensors, flow sensors, current sensors 308, voltage sensors, rotational rate sensors, and other suitable sensors. Compressor 304 is not limited to a particular configuration in system 350 and may be configured similarly to compressor 100 described in Figures 1-2 or may be configured differently. System 350 further includes an unloading device 301, a variable frequency drive 316, and a user interface 315.

[0034] A controller 310 is operatively connected to the compressor 304 for controlling its operation based in part on the measured parameters described above. The controller 310 includes a processor 311, a memory 312, and an unload interface 314. The memory 312 stores a map 500 (FIG. 5) of a plurality of operating points of the compressor 304, which may be stored in any suitable data structure, such as a table, a matrix, etc. The memory 312 further stores instructions that are executed by the processor 311 to operate the compressor 304 to compress the working fluid and to perform a method of mass flow rate interpolation. The map 500 and the method of mass flow rate interpolation are discussed in further detail below.

[0035] System 350 includes a motor interface for connection of controller 310 to VFD 316 and a motor interface 313 for connection of VFD 316 to motor 306. In certain embodiments, VFD 316 operates under the control of controller 310. In further embodiments, VFD 316 is part of controller 310. System 350 further includes an unload interface 314 for connection of controller 310 to unload device 301.

[0036] The controller 310 is operatively coupled to the unloading device 301 via an unloading interface 314, which removes and / or reduces detected surge events to limit the load of the compressor 304 during start-up and shutdown routines and the severity of the surge events. In an exemplary embodiment, the unloading device 301 is a variable diffuser or variable inlet guide vanes (VIGV). The controller 310 is configured to control at least one operating parameter of the unloading device 301, such as the position of the VIGV. In another embodiment, the unloading device 301 is a bypass valve. A bypass valve, such as a refrigerant bypass valve, provides an alternative path for gas, thereby stopping the pressure rise of the compressor 304 and limiting any potential surge, regardless of how slowly the compressor motor 306 is accelerating during start-up or decelerating during shutdown. In another embodiment, the unloading device 301 is an expansion valve. In yet other embodiments, the unloading device 301 may be a variable orifice or diameter valve, such as a servo valve, a fixed orifice or diameter valve, such as a solenoid valve or a pulse width modulated (PWM) valve configured to control opening and closing according to a duty cycle. Although many types of unloading devices are described herein, the unloading device 301 may be any suitable device or combination of devices that reduces the load on the compressor 304.

[0037] System 350 further includes a user interface 315 configured to output (e.g., display) and / or receive (e.g., from a user) information related to system 350. In some embodiments, user interface 315 is configured to receive activation and / or deactivation input from a user to activate and deactivate (i.e., turn on and off) or otherwise enable operation of system 350. Additionally, in some embodiments, user interface 315 is configured to output information related to one or more operational characteristics of system 350, including, for example, but not limited to, warning indicators such as severity alerts, occurrence alerts, fault alerts, motor speed alerts, and other suitable information.

[0038] The user interface 315 may include any suitable input and output devices that enable the user interface 315 to function as described herein. For example, the user interface 315 may include input devices including, but not limited to, a keyboard, a mouse, a touch screen, joystick(s), throttle(s), buttons, switches, and / or other input devices. Additionally, the user interface 315 may include output devices including, but not limited to, for example, a display (e.g., a liquid crystal display (LCD) or an organic light emitting diode (OLED) display), a speaker, indicator lights, gauges, and / or other output devices. Additionally, the user interface 315 may be part of a different component, such as a system controller (not shown). Other embodiments do not include a user interface 315.

[0039] The controller 310 is generally configured to control the operation of the compressor 304. The controller 310 controls the operation via programming and instructions from other devices or controllers or is integrated with the system 350 via a system controller. In some embodiments, for example, the controller 310 receives user input from a user interface 315 and controls one or more components of the system 350 in response to such user input. For example, the controller 310 may control the motor 306 based on the user input received from the user interface 315. In some implementations, the system 350 may be controlled by a remote control interface. For example, the system 350 may include a communication interface (not shown) configured for connection to a wireless control interface that allows for remote control and activation of the system 350. The wireless control interface may be embodied on a portable computing device such as a tablet or smartphone.

[0040] The controller 310 may generally include any suitable computer and / or other processing unit, including any suitable combination of computers, processing units, and / or the like, communicatively coupled to each other and capable of operating independently or in conjunction with each other (e.g., the controller 310 may form all or part of a controller network). The controller 310 may include one or more modules or devices, one or more of which may be enclosed within the system 350 or may be located remotely from the system 350. The controller 310 may be part of the compressor 304 or may be separate and may be part of a system controller in an HVAC system. The controller 310 and / or components of the controller 310 may be integrated or incorporated within other components of the system 350. The controller 310 may include one or more processors 311 and associated memory devices 312 configured to perform various computer-implemented functions (e.g., performing the calculations, decisions, and functions disclosed herein). As used herein, the term "processor" refers not only to integrated circuits, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Additionally, the memory device(s) 312 of the controller 310 may generally 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 disk read only memory (CD-ROM), magneto-optical disks (MODs), digital versatile disks (DVDs), and / or other suitable memory elements.Such memory device(s) 312 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 311, configure or cause the controller 310 to perform various functions described herein, including, but not limited to, controlling the system 350, controlling the operation of the motor 306, receiving input from the user interface 315, providing output to an operator via the user interface 315, controlling the unloading apparatus 301, and / or various other suitable computer-implemented functions.

[0041] Referring to FIG. 4, an operating envelope or operating map 400 of an example dynamic centrifugal compressor 304 is shown. The operating map 400 is a graphical representation of one of a number of predefined operating point maps stored in memory 312. The operating map 400 illustrates compressor performance in terms of flows, head, and speed. The map shows head versus inlet mass flow rate as a percentage of their values ​​at the design point of the compressor 304. Head is the total pressure ratio of the outlet pressure to the inlet pressure. Inlet mass flow rate is a measure of the amount of working fluid, such as refrigerant, flowing through the compression mechanism 307. The operating map 400 shows a number of compressor speed lines 407. In this example, there are five speed lines 407 ranging from 70% design speed to 110% design speed, each line separated by 10%. Although these particular 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.

[0042] The surge limit line 404 indicates the maximum load condition before a surge occurs in the surge region 406 (i.e., to the left of the surge limit line 404). The surge control line 403 indicates roughly the maximum load condition at which the compressor 304 can safely operate without risk of going into surge. The surge control line 403 is defined by a surge margin 405 from the surge limit line 404. By operating to the right of the surge control line 403, the compressor should avoid surge. The choke line 401 indicates that operating to the right will cause the compressor to operate in a choke condition. An operating point 409 of the operating map 400 of the compressor 304 is shown as the intersection of the speed line, the inlet mass flow rate, and the total pressure ratio. For example, the operating point 409 shown in the operating map 400 is 80% inlet mass flow rate, 108% head, and 100% speed, although any number of operating points can be shown for any type of compressor. The operating point defines the current operating parameters of the compressor, and the operating map 400 indicates how close the current operating point is to operating in an unstable condition (ie, surge) or inefficient condition (ie, choke).

[0043] FIG. 5 illustrates a map 500 of predetermined operating points 50. Map 500 is another representative view of a map of predetermined operating points stored in memory 312. Each predetermined operating point 50 is illustrated as an intersection of a compressor speed value and a compressor pressure ratio value. All of the predetermined operating points in map 500 have the same VIGV location. Similar maps may be stored in memory 312 for different VIGV locations and include predetermined operating points for the same speed and pressure ratio combinations as map 500. An inlet mass flow rate is defined for each predetermined operating point 50. Speeds at surge (522) and choke (532), and pressure ratios at surge (524) and choke (534) are also defined for each predetermined operating point 50. Map 500 includes a range of operating points 50 up to and including points along surge line 520 and choke line 530. Memory 312 stores a surge point mass flow rate for each predetermined surge point and a choke point mass flow rate for each predetermined choke point. Map 500 does not include points above surge line 520 or below choke line 530 because these should be avoided and are therefore not "operating points". Other embodiments may include inlet mass flow rates above surge line 520 or below choke line 530. In this map 500, the predetermined operating points 50 range from 10% to 35% speed and from 5% to 50% pressure ratio, with each point spaced 5% apart on both axes. Although these particular operating points are shown in this example, any number of operating points may be shown for any type of compressor at any value and with any resolution. The values ​​of speed, pressure ratio, inlet mass flow rate, and VIGV position for each predetermined operating point 50 may be generated by simulating the operation of the dynamic compressor on a computer, by testing the dynamic compressor in a controlled environment, by a combination of simulation and testing, or by any other suitable method for pre-determining the values ​​of speed, pressure ratio, inlet mass flow rate, and VIGV position for each predetermined operating point 50.

[0044] The memory 312 further stores instructions to program the processor 311 to determine the compressor mass flow rate, a method 600 of which is shown in FIG. 6. During operation of the dynamic compressor to compress the working fluid 602, the processor 311 determines 604 a current operating point of the compressor 304. The current operating point is defined by the measured speed, pressure ratio, and VIGV position at which the compressor 304 is operating at a given time. For example, the current operating point 710 shown in the map 500 represents a current operation at 22% speed, 28% pressure ratio, and VIGV position that is all VIGV positions of the points in the map 500. If the current operating point has the same speed, pressure ratio, and VIGV position values ​​as one of the predefined operating points 50, the processor determines 606 that the current operating point is one of the predefined operating points 50. In such a case, memory 312 stores instructions that program processor 311 to obtain 608 the value of the inlet mass flow rate for that given operating point 50 and return it as the value of the inlet mass flow rate at the current operating point.

[0045] If the current operating point does not have the same speed, pressure ratio, and VIGV position as any of the predefined operating points 50, the processor 606 determines that the current operating point is not one of the predefined operating points 50. In such a case, the memory 312 includes instructions to program the processor 311 to determine a subset of the predefined operating points 50 that is closest to the current operating point. The processor 311 then performs linear or envelope interpolation to calculate 610 the mass flow rate at the current operating point from the mass flow rate values ​​of the subset of the predefined operating points 50 that is closest to the current operating point. The procedures for determining the points that comprise the subset and performing the envelope interpolation are described in more detail below.

[0046] Envelope interpolation is described with reference to Figure 7A. Figure 7A is a first graphical representation of a current operating point 710 and a subset 700 of predefined operating points 701, 702, 703, 704 that are closest to the current operating point 710. The current operating point 710 does not have the same speed or pressure ratio value as any of the predefined operating points 701-704 and is not adjacent to the surge line 520 or the choke line 530. Thus, instructions stored in memory 312 program processor 311 to form subset 700 by identifying the four predefined operating points that are closest to the current operating point 710. Subset 700 includes four predefined points 701-704, designated by coordinates (x1, y1), (x2, y1), (x1, y2) and (x2, y2), where x is the compressor speed and y is the compressor pressure ratio at the operating point. Each of the four predetermined points 701-704 is 11 , K 21 , K 12 and K 22 In further embodiments, the subset may include less than four predefined operating points.

[0047] The mass flow rate J at the current operating point 710 is calculated using a process of envelope interpolation. A first intermediate mass flow rate L1 defined at the same speed as the current operating point 710 is calculated using the mass flow rate K 11 and the mass flow rate difference (K ) between the second predetermined operating point and the first predetermined operating point 702, 701 scaled by the ratio of the velocity difference (x-x1) between the current operating point 710 and the first predetermined operating point 701 and the velocity difference (x2-x1) between the second predetermined operating point 702 and the first predetermined operating point 701. 21 -K 11 ) and L1 is then calculated as the sum of L1 and L2. Therefore, L1 is determined as follows:

number

[0048] Similarly, a second intermediate mass flow rate L2, defined at the same speed as the current operating point 710, is calculated as a mass flow rate K 12 and the mass flow rate difference (K ) between the third and fourth predetermined operating points 703, 704 scaled by the ratio of the velocity difference (x-x1) between the current operating point 710 and the third predetermined operating point 703 and the velocity difference (x2-x1) between the fourth predetermined operating point 704 and the third predetermined operating point 703. 22 -K 12 ) and L2 is then calculated as the sum of L2 and L3. Therefore, L2 is determined as follows:

number

[0049] Finally, the mass flow rate J may be calculated as the sum of the first intermediate mass flow rate L1 and the second and first intermediate mass flow rates (L2-L1) scaled by the ratio of the difference (y-y1) between the pressure ratio at the current operating point 710 and the pressure ratio at the first and second predetermined operating points and the difference (y2-y1) between the pressure ratio at the third and fourth predetermined operating points 703, 704 and the pressure ratio at the first and second predetermined operating points 701, 702. Thus, J is determined as follows:

number

[0050] 7B shows a second graphical representation of the current operating point 710 and the subset 700 of nearest predetermined operating points 701-704. The above envelope interpolation process may alternatively be performed by defining first and second intermediate mass flow values ​​L1, L2 at the same pressure ratio as the current operating point 710, but not at the same speed. In this case, the calculation of the intermediate mass flow values ​​L1, L2 uses the ratio of the pressure ratio difference as a scaling factor. Thus, L1 is determined as follows:

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[0051] 8 shows a third graphical representation of a current operating point 810 and a subset 800 of predefined operating points that are closest to the current operating point 810. The current operating point 810 has the same pressure ratio value y1 as the two closest predefined operating points 801, 802, but has a different speed value x, and is not adjacent to the surge line 520 or the choke line 530. Thus, the subset of closest points 800 is formed from the two closest points that have the same pressure ratio value. For example, 11 and K. 21 The mass flow rate is shown at coordinates (x1, y1) and (x2, y1).

[0052] The mass flow rate J at the current operating point 810 is calculated by multiplying the mass flow rate K at the first predetermined operating point 801 by 11 and the mass flow rate difference (K ) between the first and second predetermined operating points 801, 802 scaled by the ratio of the speed difference (x-x1) between the current operating point 810 and the first predetermined operating point 801 to the speed difference (x2-x1) between the second predetermined operating point 802 and the first predetermined operating point 801. 21 -K 11 ) J is then calculated as the sum of J and J = 1. Therefore, J is determined as follows:

number

[0053] 9 illustrates a fourth graphical representation of a current operating point 910 and a subset 900 of predefined operating points that are closest to the current operating point 910. The current operating point 910 has the same speed value x1 as the two closest predefined operating points 901, 902, but has a different pressure ratio value y, and is not adjacent to the surge line 520 or the choke line 530. Thus, the subset of closest points 900 includes the two closest points that have the same speed value, e.g., K 11 and K 12 The mass flow rate is formed from the mass flow rates shown at coordinates (x1, y1) and (x1, y2).

[0054] The mass flow rate J at the current operating point 910 is calculated by multiplying the mass flow rate K at the first predetermined operating point 901 by 11 and the mass flow rate difference (K) between the first and second predetermined operating points 902, 901 scaled by the ratio of the pressure ratio difference (y-y1) between the current operating point 910 and the first predetermined operating point 901 to the pressure ratio difference (y2-y1) between the second predetermined operating point 902 and the first predetermined operating point 901. 12 -K 11 ) is calculated as the sum of J and J. Therefore, J is determined as follows:

number

[0055] 10 illustrates a fifth graphical representation of a current operating point 1010 and a subset 1000 of predefined operating points that are closest to the current operating point 1010. Because the current operating point 1010 is adjacent to the surge line 520 and the map of predefined operating points is not defined above the surge line 520, the subset of closest points 1000 is formed of the three predefined operating points 1001, 1002, 1003 that are closest to the current operating point 1010. In this example, the subset 1000 is formed of the three predefined operating points 1001, 1002, 1003 that are closest to the current operating point 1010, each of which has a mass flow value K 11 , K 21 , and K 22 The points indicated at coordinates (x1, y1), (x2, y1), and (x2, y2) have the following coordinates:

[0056] The mass flow rate at the current operating point 1010 is calculated based on the distance from the current operating point 1010 relative to the known mass flow rate K at each of the predetermined operating points 1001, 1002, 1003. 11 , K 21 , and K 22 to the current operating point 1010. K11 , W K21 , W K22 is the mass flow rate K at each of the predetermined operating points 1001, 1002, and 1003 that satisfies the following three equations: 11 , K 21 , K 22 Prescribed for:

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number

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[0057] 11 illustrates a sixth graphical representation of a current operating point 1110 and a subset 1100 of predefined operating points that are closest to the current operating point 1110. Because the current operating point 1110 is adjacent to the choke line 530 and the map of predefined operating points is not defined below the choke line 530, the subset of closest points 1100 is formed of the three predefined operating points 1101, 1102, 1103 that are closest to the current operating point 1110. In this example, the subset 1100 is formed of the three predefined operating points 1101, 1102, 1103 that are closest to the current operating point 1110, each of which has a mass flow value K 11 , K 12 , and K 22 The points indicated at coordinates (x1, y1), (x1, y2), and (x2, y2) have the coordinates (x1, y1), (x1, y2), and (x2, y2).

[0058] Similar to the procedure described in FIG. 10 above, the mass flow rate at the current operating point 1110 is calculated based on the distance from the current operating point 1110 relative to the known mass flow rate K at each of the predetermined operating points 1101, 1102, 1103. 11 , K 12 , and K 22to the current operating point 1110. K11 , W K12 , W K22 is the mass flow rate K at each of the predetermined operating points 1101, 1102, and 1103 that satisfies the following three equations: 11 , K 12 , K 22 Prescribed for:

number

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[0059] 7A-11, the current operating point is at the same VIGV position as the corresponding subset of the predetermined operating points. If the current operating point does not have the same VIGV position value as any of the predetermined operating points, a modified procedure can be followed, which is described in detail below.

[0060] 12 is a flow chart of a method for determining mass flow rate at a current operating point when the current operating point does not have the same VIGV position value as any of the predetermined operating points. A first subset 1210 of predetermined operating points is determined from a map of predetermined operating points at a first VIGV position less than the VIGV position 1205 of the current operating point. The subset includes predetermined operating points having speed and pressure ratio values ​​closest to those of the current operating point. Processor 311 determines a first intermediate mass flow rate J, according to the associated interpolation procedure 1215 described above, that represents mass flow rate at an operating point with the same speed and pressure ratio as the current operating point, but at a lower VIGV position. A Calculate.

[0061] Similarly, a second subset 1220 of predetermined operating points is determined from the map of predetermined operating points at a second VIGV position greater than the VIGV position 1205 of the current operating point. The subset includes the predetermined operating points having speed and pressure ratio values ​​closest to the current operating point's values. Processor 311 derives a second intermediate mass flow rate J, according to the associated interpolation procedure 1225 described above, that represents the mass flow rate at an operating point with the same speed and pressure ratio as the current operating point, but at a higher VIGV position. B Calculate.

[0062] Finally, the processor performs linear interpolation 1230 to calculate the mass flow rate of the current operating point as a function of the first intermediate mass flow, the second intermediate mass flow, and the calculated distances between the current VIGV position, the first VIGV position, and the second VIGV position. Referring to FIG. 13, the mass flow rate J is calculated as the first intermediate mass flow rate J A and the difference between the current VIGV position and the first VIGV position (zz A ) and the difference between the second VIGV position and the first VIGV position (z B -z A ) is the difference between the second and first intermediate mass flows (J B -J A ) The mass flow rate J is therefore determined as:

number

[0063] The processor 311 may use the calculated inlet mass flow rate K for the current operating point as an input to a control algorithm for operation of the dynamic compressor 304, one embodiment of which is shown in Figure 14. In other embodiments, the calculated inlet mass flow rate may be used in any other control algorithm that uses the inlet mass flow rate as a parameter.

[0064] The above method can also be used to calculate a surge point corresponding to the current operating point, i.e., a mass flow rate and pressure ratio at a point where the compressor would surge if it did not maintain the same speed and pressure ratio as the current operating point. The above method can additionally or alternatively be used to calculate a choke point corresponding to the current operating point, i.e., a mass flow rate and pressure ratio at a point where the compressor would experience choked flow if it did not maintain the same speed and pressure ratio as the current operating point. Thus, in some embodiments, the system calculates one or more of the inlet mass flow rate at the current operating point, and the inlet mass flow rate and pressure ratio at a surge for the current operating point, and the inlet mass flow rate and pressure ratio at a choke point for the current operating point.

[0065] Technical advantages of the methods and systems described herein are: (a) obtaining real-time mass flow data without the expense of mass flow instrumentation; and (b) providing input for active control of unloading devices such as VIGVs to prevent compressor surge.

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

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

Claims

1. A dynamic compressor operable to compress a working fluid; a controller connected to the dynamic compressor, the controller having a processor and a memory, the memory comprising: a map of a plurality of predetermined operating points of the dynamic compressor, each of the predetermined operating points including a mass flow rate of the dynamic compressor at the predetermined operating point; and The instruction: operating the dynamic compressor to compress the working fluid; determining a current operating point of the dynamic compressor while operating the dynamic compressor; if the current operating point is one of the predetermined operating points, obtain the mass flow rate for the current operating point from the map; if the current operating point is not one of the predetermined operating points, calculating the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points that are closest to the current operating point; continuing to operate the dynamic compressor to compress the working fluid based at least in part on the mass flow rate calculated for the current operating point. storing the instruction; system.

2. The instructions stored in the memory calculate the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points closest to the current operating point by: identifying the subset of the predetermined operating points that are closest to the current operating point; determining a distance between the current operating point and the subset of the predetermined operating points that are closest to the current operating point; calculating the mass flow rate of the current operating point as a function of the determined distance and the mass flow rate of each predetermined operating point of the subset of the predetermined operating points that is closest to the current operating point; and programming the processor to determine The system of claim 1 .

3. the dynamic compressor has a motor, and each of the predetermined operating points and the current operating point is defined by a speed of the motor and an operating pressure ratio of the dynamic compressor. The system of claim 2.

4. The dynamic compressor has a motor and a variable inlet guide vane (VIGV), and each of the predetermined operating points and the current operating point are defined by a speed of the motor, an operating pressure ratio, and a position of the VIGV. The system of claim 2.

5. The instructions stored in the memory may include calculating the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points that are closest to the current operating point by: identifying a first subset of the predetermined operating points closest to the current operating point, the first subset of the predetermined operating points having a same first VIGV position that is less than a current VIGV position of the current operating point; determining a distance between the current operating point and the predetermined operating point in the first subset, the current VIGV position being replaced by the first VIGV position; calculating a first intermediate mass flow rate for the current operating point replacing the current VIGV position with the first VIGV position as a function of the determined distance and the mass flow rate for each predetermined operating point of the first subset; identifying a second subset of the predetermined operating points closest to the current operating point, the second subset of the predetermined operating points having a same second VIGV position that is greater than the current VIGV position of the current operating point; determining a distance between the current operating point and the predetermined operating point of the second subset, the current VIGV position being replaced by the second VIGV position; calculating a second intermediate mass flow rate for the current operating point by replacing the current VIGV position with the second VIGV position as a function of the determined distance and the mass flow rate for each predetermined operating point of the second subset; calculating the mass flow rate at the current operating point as a function of the first intermediate mass flow rate, the second intermediate mass flow rate, and distances between the current VIGV position and the first and second VIGV positions; and programming the processor to determine The system of claim 4.

6. The dynamic compressor includes a centrifugal compressor. The system of claim 1 .

7. The instructions stored in the memory program the processor to input the determined mass flow rate for the current operating point into a control algorithm for operation of the dynamic compressor. The system of claim 1 .

8. The memory further stores a map of a plurality of predetermined surge points, a surge point mass flow rate for each predetermined surge point, a plurality of predetermined choke points, and a choke point mass flow rate for each predetermined choke point, and the instructions stored in the memory cause the processor to: determining a current surge point for the current operating point based on the map of the plurality of predetermined surge points; determining a current choke point for the current operating point based on the map of the plurality of predetermined choke points; if the current surge point is one of the predetermined surge points, obtain the mass flow rate for the current surge point from the map; if the current choke point is one of the predetermined choke points, obtain the mass flow rate for the current choke point from the map; if the current surge point is not one of the predetermined surge points, calculating a surge point mass flow rate for the current surge point from the mass flow rates of a subset of the plurality of predetermined surge points that is closest to the current surge point; if the current choke point is not one of the predetermined choke points, calculating a choke point mass flow rate for the current choke point from the mass flow rates of a subset of the plurality of predetermined choke points that are closest to the current choke point; Program it like this: The system of claim 1 .

9. The dynamic compressor does not include a mass flow sensor. A system according to any preceding claim.

10. 1. A controller for a dynamic compressor without a mass flow sensor, the controller comprising: A processor; A memory, the memory comprising: a map of a plurality of predetermined operating points of the dynamic compressor, each predetermined operating point including a mass flow rate of the dynamic compressor at the predetermined operating point; and Instructions for causing the processor to: operating the dynamic compressor to compress a working fluid; determining a current operating point of the dynamic compressor while operating the dynamic compressor; if the current operating point is one of the predetermined operating points, obtaining the mass flow rate for the current operating point from the map; if the current operating point is not one of the predetermined operating points, calculating the mass flow rate for the current operating point from the mass flow rates of a subset of the predetermined operating points that are closest to the current operating point; continuing to operate the dynamic compressor to compress the working fluid based at least in part on the mass flow rate calculated for the current operating point; To program it, to memorize instructions, a memory; controller.

11. The instructions stored in the memory calculate the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points closest to the current operating point by: identifying the subset of the predetermined operating points that are closest to the current operating point; determining a distance between the current operating point and the subset of the predetermined operating points that are closest to the current operating point; calculating the mass flow rate of the current operating point as a function of the determined distance and the mass flow rate of each predetermined operating point of the subset of predetermined operating points that is closest to the current operating point; and programming the processor to determine The controller of claim 10.

12. The dynamic compressor has a motor, and each of the predetermined operating points and the current operating point is defined by a speed and an operating pressure ratio of the motor. The controller of claim 11.

13. The dynamic compressor has a motor and a variable inlet guide vane (VIGV), and each of the predetermined operating points and the current operating point are defined by a speed of the motor, an operating pressure ratio, and a position of the VIGV. The controller of claim 11.

14. The instructions stored in the memory may include calculating the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points that are closest to the current operating point by: identifying a first subset of the predetermined operating points closest to the current operating point, the first subset of the predetermined operating points having a same first VIGV position that is less than a current VIGV position of the current operating point; determining a distance between the current operating point and the predetermined operating point in the first subset, the current VIGV position being replaced by the first VIGV position; calculating a first intermediate mass flow rate for the current operating point replacing the current VIGV position with the first VIGV position as a function of the determined distance and the mass flow rate for each predetermined operating point of the first subset; identifying a second subset of the predetermined operating points closest to the current operating point, the second subset of the predetermined operating points having a same second VIGV position that is greater than the current VIGV position of the current operating point; determining a distance between the current operating point and the predetermined operating point of the second subset, the current VIGV position being replaced by the second VIGV position; calculating a second intermediate mass flow rate for the current operating point by replacing the current VIGV position with the second VIGV position as a function of the determined distance and the mass flow rate for each predetermined operating point of the second subset; calculating the mass flow rate at the current operating point as a function of the first intermediate mass flow rate, the second intermediate mass flow rate, and distances between the current VIGV position and the first and second VIGV positions; and programming the processor to determine The controller of claim 13.

15. The instructions stored in the memory program the processor to input the determined mass flow rate for the current operating point into a control algorithm for operation of the dynamic compressor. The controller of claim 10.

16. The memory further stores a map of a plurality of predetermined surge points, a surge point mass flow rate for each predetermined surge point, a plurality of predetermined choke points, and a choke point mass flow rate for each predetermined choke point, and the instructions stored in the memory cause the processor to: determining a current surge point for the current operating point based on the map of the plurality of predetermined surge points; determining a current choke point for the current operating point based on the map of the plurality of predetermined choke points; if the current surge point is one of the predetermined surge points, obtain the mass flow rate for the current surge point from the map; if the current choke point is one of the predetermined choke points, obtain the mass flow rate for the current choke point from the map; if the current surge point is not one of the predetermined surge points, calculating a surge point mass flow rate for the current surge point from the mass flow rates of a subset of the plurality of predetermined surge points that is closest to the current surge point; if the current choke point is not one of the predetermined choke points, calculating a choke point mass flow rate for the current choke point from the mass flow rates of a subset of the plurality of predetermined choke points that are closest to the current choke point; Program it like this:

16. A controller according to any one of claims 10 to 15.

17. 1. A method for determining a mass flow rate of a dynamic compressor that compresses a working fluid and does not include a mass flow sensor, the method comprising: operating the dynamic compressor to compress the working fluid; determining a current operating point of the dynamic compressor while operating the dynamic compressor; if the current operating point is one of a plurality of predetermined operating points for the dynamic compressor within a map of predetermined operating points stored in a memory, obtaining a mass flow rate for the current operating point from the map, each predetermined operating point in the map including a mass flow rate for the dynamic compressor at the predetermined operating point; if the current operating point is not one of the predetermined operating points in the map, calculating the mass flow rate for the current operating point from the mass flow rates of a subset of the predetermined operating points that are closest to the current operating point; continuing to operate the dynamic compressor to compress the working fluid based at least in part on the mass flow rate calculated for the current operating point; method.

18. Determining the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points closest to the current operating point comprises: identifying the subset of the predetermined operating points that are closest to the current operating point; determining a distance between the current operating point and the subset of the predetermined operating points that are closest to the current operating point; calculating the mass flow rate of the current operating point as a function of the determined distance and the mass flow rate of each predetermined operating point of the subset of predetermined operating points that is closest to the current operating point; 20. The method of claim 17.

19. The dynamic compressor has a motor and a variable inlet guide vane (VIGV), each of the predetermined operating points and the current operating point being defined by a speed of the motor, an operating pressure ratio, and a position of a VIGV, and determining the mass flow rate for the current operating point from the mass flow rates of the subset of the predetermined operating points closest to the current operating point comprises: identifying a first subset of the predetermined operating points closest to the current operating point, the first subset of the predetermined operating points having a same first VIGV position that is less than a current VIGV position of the current operating point; determining a distance between the current operating point and the predetermined operating point in the first subset, the current VIGV position being replaced by the first VIGV position; calculating a first intermediate mass flow rate for the current operating point replacing the current VIGV position with the first VIGV position as a function of the determined distance and the mass flow rate for each predetermined operating point of the first subset; identifying a second subset of the predetermined operating points closest to the current operating point, the second subset of the predetermined operating points having a same second VIGV position that is greater than the current VIGV position of the current operating point; determining a distance between the current operating point and the predetermined operating point of the second subset, the current VIGV position being replaced by the second VIGV position; calculating a second intermediate mass flow rate for the current operating point by replacing the current VIGV position with the second VIGV position as a function of the determined distance and the mass flow rate for each predetermined operating point of the second subset; calculating the mass flow rate at the current operating point as a function of the first intermediate mass flow rate, the second intermediate mass flow rate, and distances between the current VIGV position and the first and second VIGV positions; Including, 20. The method of claim 18.

20. determining a current surge point for the current operating point based on a map of a plurality of predefined surge points, the map including a surge point mass flow rate for each predefined surge point; determining a current choke point for the current operating point based on a map of a plurality of predefined choke points, the map including a choke point mass flow rate for each predefined choke point; if the current surge point is one of the predetermined surge points, obtaining the mass flow rate for the current surge point from the map; if the current choke point is one of the predetermined choke points, obtaining the mass flow rate for the current choke point from the map; if the current surge point is not one of the predetermined surge points, calculating a surge point mass flow rate for the current surge point from the mass flow rates of a subset of the plurality of predetermined surge points closest to the current surge point; if the current choke point is not one of the predetermined choke points, calculating a choke point mass flow rate for the current choke point from the mass flow rates of a subset of a plurality of predetermined choke points closest to the current choke point; Including, 20. The method according to any one of claims 17 to 19.

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