EP4705644A1

EP4705644A1 - Systems and methods for controlling capacity of a compressor

Info

Publication number: EP4705644A1
Application number: EP24726177.9A
Authority: EP
Inventors: Damien Jean Daniel Arnou; Francois Charles Andre CLUNET; Paul Eric LE SAUSSE
Original assignee: Tyco Fire and Security GmbH
Current assignee: Tyco Fire and Security GmbH
Priority date: 2023-05-12
Filing date: 2024-05-12
Publication date: 2026-03-11
Also published as: CN121285699A; KR20260010747A; TW202503172A; WO2024235884A1

Abstract

A compressor system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes one or more compressors configured to circulate a working fluid through a vapor compression system of the HVAC&R system, each compressor of the one or more compressors having a pre-rotation vane (PRV) and a variable geometry diffuser (VGD) configured to operate to regulate a capacity of the compressor system. The compressor system further includes a controller having a memory and processing circuitry, wherein the memory includes instructions stored thereon that, when executed by the processing circuitry, cause the processing circuitry to determine a head factor for each compressor of the one or more compressors, determine a compressor lift for each compressor of the one or more compressors based at least in part on the head factor, compare the compressor lift of each compressor of the one or more compressors with a low lift threshold value and a high lift threshold value, and operate each compressor of the one or more compressors in a first mode or a second mode based on comparing the compressor lift to the low lift threshold value and the high lift threshold value.

Description

SYSTEMS AND METHODS FOR CONTROLLING CAPACITY OF A COMPRESSOR

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from and the benefit of U.S. Provisional Application No. 63/466,152, entitled "SYSTEM AND METHOD FOR CONTROLLING CAPACITY OF COMPRESSOR," filed May 12, 2023, which is herein incorporated by reference in its entirety for all purposes.

BACKGROUND

This 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 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. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

Chiller systems, or vapor compression systems, utilize a working fluid (e.g., a refrigerant) that changes phases between vapor, liquid, and combinations thereof in response to exposure to different temperatures and pressures within components of the chiller system. The chiller system may place the working fluid in a heat exchange relationship with a cooling fluid (e.g., water) and may deliver the cooling fluid to conditioning equipment and/or a conditioned environment serviced by the chiller system. In such applications, the cooling fluid may be directed through downstream equipment, such as air handlers, to condition other fluids, such as air in a building. The chiller system may include one or more compressors configured to pressurize the working fluid and circulate the working fluid through a working fluid circuit. Unfortunately, implementation of multiple compressors and/or multistage compressors and the various components thereof in a chiller system increases the complexity of controlling the chiller system efficiently.

SUMMARY

A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

In one embodiment, a compressor system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes one or more compressors configured to circulate a working fluid through a vapor compression system of the HVAC&R system, each compressor of the one or more compressors having a pre-rotation vane (PRV) and a variable geometry diffuser (VGD) configured to operate to regulate a capacity of the compressor system. The compressor system further includes a controller having a memory and processing circuitry, wherein the memory includes instructions stored thereon that, when executed by the processing circuitry, cause the processing circuitry to determine a head factor for each compressor of the one or more compressors, determine a compressor lift for each compressor of the one or more compressors based at least in part on the head factor, compare the compressor lift of each compressor of the one or more compressors with a low lift threshold value and a high lift threshold value, and operate each compressor of the one or more compressors in a first mode or a second mode based on comparing the compressor lift to the low lift threshold value and the high lift threshold value.

In another embodiment, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a vapor compression system having a vapor compression circuit configured to circulate a working fluid therethrough and a compressor configured to pressurize and direct the working fluid through the vapor compression circuit, wherein the compressor comprises a pre-rotation vane (PRV) adjustable between a fully open position and a first fully closed position and a variable geometry diffuser (VGD) adjustable between a maximum allowed open position and a second fully closed position. The HVAC&R system further includes a controller having a memory and processing circuitry, wherein the memory stores instructions that, when executed by the processing circuitry, cause the processing circuitry to transition operation of the compressor between a first mode and a second mode to regulate a capacity of the compressor, wherein a first position of the VGD is independent of a second position of the PRV in the first mode, and the first position of the VGD is dependent on the second position of the PRV in the second mode.

In another embodiment, a method for controlling a capacity of a compressor having a pre-rotation vane (PRV) and a variable geometry diffuser (VGD) includes determining an actual head factor for the compressor based on one or more operating conditions of a vapor compression system employing the compressor, determining a lift of the compressor based on a ratio of the actual head factor and a maximum head factor of the compressor, comparing the lift with a low lift threshold value and a high lift threshold value to generate a comparison result, operating the compressor in a first mode in which a position of the VGD is varied independently of a position of the PRV in response to the comparison result indicating that the lift is less than the low lift threshold value, and operating the compressor in a second mode in which the position of the VGD is varied based on a correlation between the position of the VGD and the position of the PRV in response to the comparison result indicating that the lift is greater than the high lift threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 is a perspective view of an embodiment of a building that may utilize a heating, ventilating, air conditioning, and/or refrigeration (HVAC&R) system in a commercial setting, in accordance with an aspect of the present disclosure;

FIG. 2 is a perspective view of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

FIG. 3 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure; FIG. 4 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

FIG. 5 is a schematic of an embodiment of a vapor compression system having two compressors, in accordance with an aspect of the present disclosure;

FIG. 6 is a graphical representation illustrating a correlation between a position of a pre-rotation vane and a maximum allowed open position of a variable geometry diffuser of a vapor compression system, in accordance with an aspect of the present disclosure;

FIG. 7 is a flow diagram of an embodiment of a method for controlling a capacity of a compressor of a vapor compression system, in accordance with an aspect of the present disclosure; and

FIG. 8 is a flow diagram of an embodiment of a method for stall noise reduction control, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

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

When introducing elements of various embodiments of the present disclosure, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. Additionally, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

As used herein, the terms "approximately," "generally," "substantially," and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being "approximately" equal to (or, for example, "substantially similar" to) a given value, this is intended to convey that the property value may be within +/- 5%, within +/- 4%, within +/- 3%, within +/- 2%, within +/- 1%, or even closer, of the given value. Similarly, when a given feature is described as being "substantially parallel" to another feature, "generally perpendicular" to another feature, and so forth, this is intended to convey that the given feature is within +/- 5%, within +/- 4%, within +/- 3%, within +/- 2%, within +/- 1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Mathematical terms, such as "parallel" and "perpendicular," should not be rigidly interpreted in a strict mathematical sense, but should instead be interpreted as one of ordinary skill in the art would interpret such terms. For example, one of ordinary skill in the art would understand that two lines that are substantially parallel to each other are parallel to a substantial degree, but may have minor deviation from exactly parallel.

As briefly discussed above, a heating, ventilation, air conditioning, and/or refrigeration (HVAC&R) system may be used to thermally regulate a space within a building, home, or other suitable structure. For example, the HVAC&R system may include a vapor compression system (e.g., a chiller system, vapor compression circuit) that transfers thermal energy between a working fluid (e.g., refrigerant, heat transfer fluid), and a fluid to be conditioned (e.g., air, water, brine). The vapor compression system may include a first heat exchanger (e.g., a condenser) and a second heat exchanger (e.g., an evaporator) that are fluidly coupled to one another via one or more conduits (e.g., vapor compression circuit, refrigerant circuit, working fluid circuit). A compressor may be used to pressurize and circulate the working fluid through the one or more conduits and, thus, enable the transfer of thermal energy between the working fluid and the fluid to be conditioned via the condenser and the evaporator.

Compressors (e.g., centrifugal compressors) may be designed for certain operating conditions, which may include one or more characteristics or parameters of the working fluid (e.g., refrigerant). For example, compressors may be designed and/or selected for implementation in the HVAC&R system based on working fluid flow (e.g., flow rate), working fluid temperature and pressure conditions at a suction inlet of the compressor, and/or working fluid temperature and pressure conditions at a discharge outlet of the compressor. In some applications, the HVAC&R system may utilize multiple compressors (e.g., a compressor system) to achieve a desired lift (e.g., pressure differential) of the working fluid directed through the vapor compression fluid circuit. The lift or "head" of the compressor or compressor system may be defined as the work or productivity of the compressor or compressor system and may be expressed as a difference in compressor discharge pressure and compressor suction pressure. Operation of each compressor may be controlled to enable operation within various design conditions (e.g., parameters) and/or to avoid undesired operation or operating conditions (e.g., compressor surge, compressor stall).

Design conditions for a centrifugal compressor may be defined by parameters of a working fluid flow through the compressor, as well as temperature and pressure conditions at suction (e.g., inlet) and discharge (e.g., outlet) of the centrifugal compressor. The compressor may operate continuously at conditions that are close to the design conditions, or the operating environment may deviate widely from design conditions during extended periods of time. Compressors used in HVAC&R systems may be subject to wide variations. The working fluid flow through the compressor may depend on the demand for cooling load, while pressure conditions, such as a condensing pressure, may depend on ambient temperature conditions.

When operating conditions deviate from the design conditions, a centrifugal compressor may encounter instabilities, such as surge or stall, during operation. Stall or stalling is a local flow separation in one or more components of the compressor, and may be characterized by discharge pressure disturbances at certain frequencies that are less than a rotational frequency of an impeller of the compressor. Surge or surging is a transient phenomenon having oscillations in pressures and flow, and can result in complete flow reversal through the compressor. When surging, a compressor may be unable to deliver the desired working fluid flow at the desired pressure conditions. Furthermore, surging can cause excessive noise and/or vibrations in both the rotating and stationary components of the compressor, which may result in compressor damage, wear, and/or degradation. Various devices and control parameters can be used to adjust the compressor operation to desired flow and pressure conditions while avoiding compressor surging. A simple way to reduce the flow of working fluid through a centrifugal compressor is to reduce the speed of the compressor. Variable speeds of the compressor may be enabled by a turbine drives or an electric motor with electrical power supplied via a variable speed drive (VSD). When available, speed reduction can be used to a limited extent to avoid surge but may not completely avoid instances of surge. When speed reduction is not possible, another solution is to use a flow reduction device ("FRD"), such as prerotation vanes ("PRV") or a variable geometry diffuser ("VGD"), to reduce the flow of working fluid through the compressor.

For example, pre-rotation vanes ("PRV") or inlet guide vanes may be disposed at an inlet of a respective compressor and may be configured to control the flow of working fluid into the compressor (e.g., from an evaporator). In certain cases, an actuator may be used to control the opening and closing of the PRVs to adjust an amount of working fluid flowing into the compressor, thereby adjusting the cooling capacity of the system. Variable geometry diffusers ("VGD") may be disposed at an outlet of the compressor and may be utilized for stall avoidance, surge avoidance, and noise reduction associated with such conditions. In certain cases, a VGD may be utilized to control a flow of working fluid out of the compressor. For example, a VGD may include a diffuser ring configured to move into and out of a diffuser gap, which may also correspond to the outlet or discharge flow path (e.g., diffuser) for the compressed working fluid discharged by the compressor. The VGD can be adjusted to a fully open position, in which the diffuser ring is completely removed from the outlet flow path to enable an upper threshold amount of working fluid flow, to a partially or fully closed position, in which the diffuser ring occupies or extends within at least a portion of the outlet flow path, thereby restricting the working fluid flow. For example, when a stall condition is detected, an actuator may transition the VGD toward a partially or fully closed position until the stall condition is rectified, thereby avoiding surge conditions. Traditionally, PRVs are used to adjust a capacity of a compressor, while VGDs are generally controlled based on stall voltages. Depending on their availability on the compressor, the settings of aforementioned devices, namely the variable speed drive, pre-rotation vanes, and variable geometry diffuser are managed by stability control algorithms (e.g., control logic) intended to keep the machine in stable operation out of surge at the desired operating conditions, whi le enhancing efficiency. However, such control logic may not enable a respective compressor to achieve certain lift demands when a flow rate of the working fluid through the compressor is below a threshold value (e.g., at low flow rates).

Traditional HVAC&R systems employing multiple compressors or compression stages (e.g., low pressure compressor, medium pressure compressor, high pressure compressor, first stage compressor, second stage compressor, third stage compressor) may have respective capacity regulation components or flow reduction devices (FRDs) associated with each compressor (e.g., PRV systems, inlet guide vanes, VGD). Existing systems utilizing various flow reduction devices (e.g., capacity regulation components) may be configured to operate the various components utilizing a common control scheme. Unfortunately, incorporation of multiple capacity regulation components in systems having multiple compressors (e.g., a PRV system and a VGD associated with each compressor) increases costs associated with manufacture, operation (e.g., energy consumption), and/or maintenance of HVAC&R systems and increases the complexity of controlling the various capacity regulation components. Accordingly, present embodiments are directed to a vapor compression system having multiple compressors (e.g., one or more of a low pressure compressor, a medium pressure compressor, and/or a high pressure compressor, a first stage compressor, a second stage compressor, a third stage compressor, a low stage compressor, a high stage compressor) configured to operate in conjunction with one another with increased efficiency and reduced energy consumption to satisfy load and/or cooling demands. More specifically, embodiments of the present disclosure are directed to a control scheme (e.g., adaptive control logic) for a vapor compression system having multiple compressors that enables coordinated operation of the multiple compressors to satisfy a load demand of the vapor compression system, while reducing energy consumption and maintaining operation of the vapor compression system within desired operating conditions (e.g., avoiding surge and/or stall). Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system 10 in a building 12 for a typical commercial setting. The HVAC&R system 10 may include a vapor compression system 14 (e.g., a chiller) that supplies a chilled liquid, which may be used to cool the building 12. The HVAC&R system 10 may also include a boiler 16 to supply warm liquid to heat the building 12 and an air distribution system which circulates air through the building 12. The air distribution system can also include an air return duct 18, an air supply duct 20, and/or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger that is connected to the boiler 16 and the vapor compression system 14 by conduits 24. The heat exchanger in the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the mode of operation of the HVAC&R system 10. The HVAC&R system 10 is shown with a separate air handler on each floor of building 12, but in other embodiments, the HVAC&R system 10 may include air handlers 22 and/or other components that may be shared between or among floors.

FIGS. 2 and 3 illustrate embodiments of the vapor compression system 14 that can be used in the HVAC&R system 10. The vapor compression system 14 may circulate a working fluid through a circuit starting with a compressor 32. The circuit may also include a condenser 34, an expansion valve(s) or device(s) 36, and a liquid chiller or an evaporator 38. The vapor compression system 14 may further include a control panel 40 that has an analog to digital (A/D) converter 42, a microprocessor 44, a non-volatile memory 46, and/or an interface board 48.

Some examples of fluids that may be used as working fluids (e.g., refrigerants) in the vapor compression system 14 are hydrofluorocarbon (HFC) based working fluids, for example, R-410A, R-407, R-134a, hydrofluoro olefin (HFO), "natural" working fluids like ammonia (NH3), R-717, carbon dioxide (CO2), R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable working fluid. In some embodiments, the vapor compression system 14 may be configured to efficiently utilize working fluids having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at one atmosphere of pressure, also referred to as low pressure working fluids, versus a medium pressure working fluid, such as R-134a. As used herein, "normal boiling point" may refer to a boiling point temperature measured at one atmosphere of pressure. In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSDs) 52, a motor 50, the compressor 32, the condenser 34, the expansion valve or device 36, and/or the evaporator 38. The motor 50 may drive the compressor 32 and may be powered by a variable speed drive (VSD) 52. The VSD 52 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 50. In other embodiments, the motor 50 may be powered directly from an AC or direct current (DC) power source. The motor 50 may include any type of motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

The compressor 32 compresses a working fluid vapor and delivers the vapor to the condenser 34 through a discharge passage. In some embodiments, the compressor 32 may be a centrifugal compressor. The working fluid vapor delivered by the compressor 32 to the condenser 34 may transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The working fluid vapor may condense to a refrigerant liquid in the condenser 34 as a result of thermal heat transfer with the cooling fluid. The liquid working fluid from the condenser 34 may flow through the expansion device 36 to the evaporator 38. In the illustrated embodiment of FIG. 3, the condenser 34 is water cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser 34.

The liquid working fluid delivered to the evaporator 38 may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser 34. The liquid working fluid in the evaporator 38 may undergo a phase change from the liquid working fluid to a working fluid vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The cooling fluid of the evaporator 38 (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via return line 60R and exits the evaporator 38 via supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 via thermal heat transfer with the working fluid. The tube bundle 58 in the evaporator 38 can include a plurality of tubes and/or a plurality of tube bundles. In any case, the vapor working fluid exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

FIG. 4 is a schematic of the vapor compression system 14 with an intermediate circuit 64 incorporated between condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly coupled to the condenser 34. As shown in the illustrated embodiment of FIG. 4, the inlet line 68 includes a first expansion device 66 positioned upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler, an economizer, etc.). In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a "surface economizer." In the illustrated embodiment of FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to lower the pressure of (e.g., expand) the liquid working fluid received from the condenser 34. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66.

Additionally, the intermediate vessel 70 may provide for further expansion of the liquid working fluid due to a pressure drop experienced by the liquid working fluid when entering the intermediate vessel 70 (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel 70). The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel 70 may be drawn to an intermediate stage of the compressor 32 (e.g., not the suction stage). The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the liquid working fluid exiting the condenser 34 because of the expansion in the expansion device 66 and/or the intermediate vessel 70. The liquid from intermediate vessel 70 may then flow in line 72 through a second expansion device 36 to the evaporator 38.

It should be appreciated that any of the features described herein may be incorporated with embodiments of the vapor compression system 14 or any other suitable HVAC&R systems. For example, the present techniques may be incorporated with any HVAC&R system having an economizer, such as the intermediate vessel 70, and a compressor, such as the compressor 32. The discussion below describes the present techniques incorporated with embodiments of the vapor compression system 14 having multiple compressors 32. For example, vapor compression system 14 may include one compressor 32 that is a low pressure compressor or first stage compressor and another compressor 32 that is a high pressure compressor or second stage compressor. However, it should be appreciated that the techniques described herein may be incorporated with other embodiments of the compressor 32, the vapor compression system 14, and the HVAC&R system 10.

With the foregoing in mind, FIG. 5 is a schematic of an embodiment of the vapor compression system 14 (e.g., chiller, chiller system, heat pump system) having a compressor system 100 (e.g., multi-stage compressor system) in accordance with aspects of the present disclosure. It should be appreciated that the compressor system 100 and/or components thereof may be implemented with any of the systems described above, in accordance with the present techniques. Further, it should be appreciated that the compressor system 100 may be utilized in systems having fixed speed compressors. The compressor system 100 may be configured to operate according to a control algorithm (e.g., control logic, capacity control program) that transitions operation of the compressors of the compressor system 100 between a first mode and a second mode to control the capacity of each of the compressors based on certain operating conditions of the vapor compression system 14 (e.g., based on the lift of the compressor). In the first operating mode (e.g., PRV driving mode, low lift mode), the PRVs of each compressor may be adjusted or controlled to control the capacity of the compressor, and the position of the VGDs may be controlled independently of the position of the PRVs. For example, the VGD position may be set based on a stall voltage detected by one or more sensors of the vapor compression system 14. In the second operating mode (e.g., VGD driving mode, high lift mode), the VGD may be adjusted or controlled to control the capacity of the compressor, and the VGD position may be directly dependent on the position of the PRV. The controller may transition between each of the first and second operating modes discussed above based on a comparison of the lift of the compressor with a high lift threshold value and a low lift threshold value (e.g., each of which may be based on certain design conditions of the compressor), as described in greater detail below.

For example, upon a determination that the lift of a compressor in the compressor system 100 is below a low lift threshold value, the controller may operate the compressor in the first operating mode in which the PRV is utilized to control the capacity of the compressor. Upon a determination that the lift of the compressor is above the high lift threshold value, the controller may operate the compressor in the second operating mode in which the VGD is utilized (e.g., in conjunction with the PRV) to control the capacity of the compressor. Upon a determination that the lift of the compressor is between the low lift threshold value and the high lift threshold value, the controller may transition between the first operating mode and the second operating mode, as discussed in greater detail below. In this way, upper lift limits may be achieved at low compressor flow rates, while reducing or limiting a potential for surge and/or stall conditions. Further, the present techniques enable a reduction in energy consumption and an increase in efficiency associated with operation of the vapor compression system 14.

In the illustrated embodiment, the vapor compression system 14 is configured to direct a working fluid (e.g., vaporous refrigerant) from the evaporator 38 to the compressor system 100. The compressor system 100 includes a first compressor 102 (e.g., low pressure compressor, first stage compressor, low stage compressor, first compressor system) and a second compressor 104 (e.g., high pressure compressor, second stage compressor, high stage compressor, second compressor system). More specifically, the first and second compressors 102, 104 are arranged in series relative to a flow of working fluid through the compressor system 100. The compressor system 100 is configured to pressurize (e.g., lift) the working fluid to a desired pressure and direct the working fluid through the vapor compression system 14 (e.g., based on a cooling demand of the vapor compression system 14). That is, the first compressor 102 may receive working fluid from the evaporator 38, pressurize the working fluid by a first amount (e.g., first lift), and direct the working fluid to the second compressor 104. The second compressor 104 may further pressurize the working fluid by a second amount (e.g., second lift) and discharge the working fluid toward the condenser 34 of the vapor compression system 14.

The first compressor 102 may include pre-rotation vanes (PRV) 106 (e.g., PRV system) and a variable geometry diffuser (VGD) 108. As will be appreciated, the PRV 106 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the first compressor 102 and are configured to control and/or adjust flow of working fluid entering the first compressor 102 (e.g., by inducing a swirling flow or motion of the working fluid). For example, the PRV 106 may be adjustable between a fully closed position and fully open position to control the capacity (e.g., compressor stage capacity) of the first compressor 102 (e.g., of the first compressor stage). The VGD 108 may be configured to adjust a size of a diffuser gap or passage of the first compressor 102 (e.g., downstream of an impeller of the first compressor 102) to adjust and/or control flow of working fluid through the first compressor 102. Similar to the PRV 106, the VGD 108 of the compressor 102 may be adjustable between a fully closed position and an upper limit open position (e.g., maximum allowed opened position) to control the capacity of the first compressor 102. Thus, operation of the PRV 106 and the VGD 108 may be adjusted to control operation of the vapor compression system 14 (e.g., based on a load demand or cooling load of the vapor compression system 14) and/or to avoid occurrences of stall and/or surge in the first compressor 102.

The second compressor 104 may also include pre-rotation vanes (PRV) 110 (e.g., PRV system) and a variable geometry diffuser (VGD) 112. As will be appreciated, the PRV 110 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the second compressor 104 and are configured to control and/or adjust flow of working fluid entering the second compressor 104 (e.g., by inducing a swirling flow or motion of the working fluid). For example, the PRV 110 may be adjustable between a fully closed position and fully open position to control the capacity (e.g., compressor stage capacity) of the second compressor 104 (e.g., of the second compressor stage). The VGD 112 may be configured to adjust a size of a diffuser passage or gap of the second compressor 104 (e.g., downstream of an impeller of the second compressor 104) to adjust and/or control flow of working fluid through the second compressor. Similar to the PRV 106, the VGD 108 of the compressor 102 may be adjustable between a fully closed position and an upper limit open position (e.g., maximum allowed opened position) to control the capacity of the first compressor 102. Thus, operation of the PRV 110 and the VGD 112 may be adjusted to control operation of the vapor compression system 14 (e.g., based on a load demand or cooling load of the vapor compression system 14) and/or to avoid occurrences of stall and/or surge in the second compressor 104.

The compressor system 100 includes a motor system 114 (e.g., one or more motors) configured to drive rotation of the first and second compressors 102, 104. In certain embodiments, each of the compressors 102, 104 may correspond to a fixed speed motor such that each of the compressors 102, 104 are configured to operate at a fixed speed to satisfy load demands on the vapor compression system 14. For example, motors of the motor system 114 may be coupled to a fixed speed drive or may powered directly from an alternating current (AC) or direct current (DC) power source. Fixed speed drives, if used, receive AC power having a particular fixed line voltage and fixed line frequency from the AC power source and provide power having constant voltage and frequency to the motors of the motor system 114. The motor system 114 may include any type of electric motors that can be powered by a fixed speed drive or directly from an AC or DC power source. The motors of the motor system 114 can be any other suitable motor type, for example, a switched reluctance motor, an induction motor, or an electronically commutated permanent magnet motor. The speed of each of the compressors 102, 104 may be based on design operating conditions and/or expected operating conditions. For example, the speed of the first compressor 102 or the second compressor 104 may be set to operate the respective compressor 102, 104 at a lower frequency limit that corresponds to a desired lift while avoiding stall and/or surge conditions. Further, each of the compressors 102, 104 may operate at the same speed or a different speed depending on the lift demands associated with each compressor 102, 104.

In certain embodiments, the vapor compression system 14 may also include a hot gas bypass valve 116. In the illustrated embodiment, the hot gas bypass valve 116 is configured to direct compressed working fluid from a discharge outlet of the second compressor 104 to a suction inlet of the first compressor 102. However, in certain embodiments, the hot gas bypass valve 116 may be configured to direct compressed working fluid from the discharge outlet of the second compressor 104 to a location (e.g., along a circuit of the vapor compression system 14) downstream of the expansion valve 36 and upstream of the evaporator 38. Additionally, in certain embodiments, the hot gas bypass valve 116 may be configured to direct compressed working fluid from a discharge outlet of the first compressor 102 to a suction inlet of the first compressor 102, or from a discharge outlet of the second compressor 104 to a suction inlet of the second compressor 104. Further, as discussed in greater detail below, the PRVs 106, 110, the VGDs 108, 112, and the hot gas bypass valve 116 may be operated or controlled to adjust a flow rate and/or a pressure differential (e.g., lift, head) of working fluid directed through the compressor system 100 (e.g., based on a load or cooling demand of the vapor compression system 14). In certain embodiments, each of the compressors 102, 104 (e.g., each of the compressor stages) may include a stall detector 118 (e.g., stall voltage detection circuitry). The stall detectors 118 may be a stall pressure transducer disposed at a respective outlet of the first compressor 102 and/or the second compressor 104. For example, a stall detector 118A may be configured to detect (e.g., sense, measure, record) pressure pulsations at the outlet of the first compressor 102 and a stall detector 118B may be configured to detect pressure pulsations at the outlet of the second compressor 104. Each of the stall detectors 118A, 118B may then output a stall voltage signal (e.g., a DC stall voltage signal) to a controller 120. The stall voltage signal may be indicative of a magnitude of the stall noise present at the compressors 102, 104. In certain embodiments, a position of the VGD 108, 112 of each compressor 102, 104, respectively, may be adjusted to control (e.g., reduce, rectify, or eliminate) the stall noise. For example, upon detecting that a stall voltage signal detected by the stall detector 118A is above a threshold value, the controller 120 may begin to adjust the position of the VGD 108 of the first compressor 102 from the maximum allowed open position to the fully closed position until the stall noise is rectified. Once the stall noise is rectified, the VGD 108 is maintained in the same position for a predetermined amount of time (e.g., a preset wait period). After the predetermined amount of time has passed, the controller 120 may adjust (e.g., pulse, open in discrete steps or increments) the position of the VGD 108 toward the maximum allowed open position until the stall noise is detected again, or the maximum allowed open position is reached.

As described above, the vapor compression system 14 directs working fluid discharged by the compressor system 100 to the condenser 34. The condenser 34 is configured to transfer heat (e.g., thermal energy) from the working fluid to a conditioning or cooling fluid (e.g., water, air) in order to cool and/or condense the working fluid. Thereafter, the working fluid is directed through the expansion valve 36 and to the evaporator 38. The evaporator 38 may be fluidly coupled to a cooling load (e.g., cooling load 62), and the evaporator 38 may enable transfer of heat (e.g., thermal energy) from the cooling load (e.g., cooling fluid, water) to the working fluid, thereby heating the working fluid and cooling the cooling load. For example, the evaporator 38 may place the working fluid in a heat exchange relationship with a cooling fluid (e.g., water) that is circulated through the cooling load to provide cooling. However, it should be appreciated that embodiments of the present disclosure also include the vapor compression system 14 as a heat pump (e.g., chiller heat pump) configured to operate to provide heating to a load.

As mentioned above, in certain embodiments, components of the compressor system 100 and/or the vapor compression system 14 may be controlled via the controller 120 (e.g., control system, automation controller), which may correspond to the control panel 40 of FIGS. 3 and 4 or any other suitable controller (e.g., a compressor controller). For example, the controller 120 may include an interface board 122, processing circuitry 124 (e.g., one or more microprocessors), a memory 126, an analog to digital (A/D) converter 128, and a stall voltage detection board 129. The AD converter 128 may be configured to receive input signals from various components of the vapor compression system 14 that indicate the performance of the vapor compression system 14. For example, the input signals received by the controller 120 may include a temperature of a leaving chilled liquid (e.g., conditioning fluid) from the evaporator 38, working fluid pressures in the evaporator 38 and the condenser 34, an acoustic or sound pressure measurement in the discharge passages of the compressors 102, 104, saturated temperatures at the suction inlet and discharge outlet of the compressors 102, 104, and/or the pressure at the suction inlet of the compressors 102, 104.

The stall voltage detection board 129 may be configured to receive the DC stall voltage signals from the stall detectors 118A, 118B of the compressors 102, 104, respectively. The stall voltage detection board 129 may be further configured to convert the DC stall voltage signals to AC stall voltage signals. An AC stall voltage signal may further represent the magnitude of stall noise experienced by a compressor, for example, the compressors 102, 104. The stall voltage detection board 129 may be further coupled to the controller 120 to transmit the AC stall voltage signals.

The memory 126 may include volatile memory, such as random-access memory (RAM), and/or non-volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, solid-state drives, or any other non-transitory computer- readable medium storing instructions (e.g., control algorithms) that, when executed, control operation of the compressor system 100 and/or the vapor compression system 14. For example, the controller 120 may utilize (e.g., execute via the processing circuitry 124) various control algorithms (e.g., stored in the memory 126) to determine when to adjust the positions of the PRVs 106, 110 and/or the VGDs 108, 112 in response to particular compressor conditions to maintain a demanded capacity of each of the compressors 102, 104. Further, the controller 120 may use the control algorithms to determine when to adjust the position of the VGDs 108, 112 to reduce or rectify stall noise (e.g., stall noise reduction control). Further still, the controller 120 may use the control algorithms to control a position of the hot gas bypass valve 116 in response to particular compressor conditions to maintain system and compressor stability. The memory 126 may be further configured to store various threshold values demanded for maintaining system efficiency and stability, as discussed in greater detail below. The processing circuitry 124 may be configured to execute such instructions. In certain embodiments, the processing circuitry 124 may include one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more general purpose processors, or any combination thereof.

The controller 120 is configured to control operation of the compressor system 100 (e.g., control operation of one or more components of the compressor system 100, control operation of one or more components of the vapor compression system 14) to enable more efficient operation of the vapor compression system 14. In particular, the controller 120 is configured to coordinate operation of the first compressor 102 and the second compressor 104, each of which may include one or more capacity regulation components (e.g., PRVs 106, 110, VGDs 108, 112) to achieve more efficient operation of the compressor system 100 (e.g., operation with isentropic efficiency). In certain embodiments, the controller 120 may be configured to control operation of the compressor system 100 to achieve a desired lift for each of the compressors 102, 104, while limiting the occurrence of surge and/or stall in the compressor system 100. For example, the controller 120 may be configured to transition operation of each of the compressors 102, 104 between a first mode (e.g., PRV driven mode, low lift mode) and a second mode (e.g., VGD driven mode, high lift mode) based on a comparison between the lift on each compressor 102, 104 and one or more lift threshold values (e.g., high lift threshold value, low lift threshold value), as described in greater detail below. To this end, the controller 120 may be configured to output control signals to control operation (e.g., respective positions) of the PRVs 106, 110, operation (e.g., respective positions) of the VGDs 108, 112, operation of the motor system 114, and/or operation (e.g., a position) of the hot gas bypass valve 116. In some embodiments, the controller 120 may regulate operation of one or more components of the compressor system 100 based on operating conditions of the vapor compression system 14 and/or a load of the vapor compression system 14 (e.g., a respective load on each of the compressors 102, 104), or other suitable data.

In certain embodiments, the controller 120 may be configured to control operation of the compressor system 100 based on feedback received from one or more sensors 130 of the vapor compression system 14. The sensors 130 may be configured to detect one or more operating conditions (e.g., operating parameters) of the vapor compression system 14 and provide feedback indicative of the operating conditions to the controller 120. The sensors 130 may include any suitable sensor configured to detect an operating parameter of the vapor compression system 14 and/or the compressor system 100, such as pressure sensors, temperature sensors, position sensors, voltage sensors, current sensors, flow rate sensors, speed sensors, and so forth. In the illustrated embodiment, one or more sensors 130 are disposed at a respective inlet (e.g., suction side) of each of the compressors 102, 104, a respective outlet (e.g., discharge side) of each of the compressors 102, 104, an outlet of the condenser 34 (e.g., working fluid outlet, cooling fluid outlet), and/or at an outlet of the evaporator 38 (e.g., working fluid outlet, cooling fluid outlet). However, other embodiments of the vapor compression system 14 may include sensors 130 positioned at additional or alternative locations along the vapor compression system 14 (e.g., vapor compression circuit) and/or within the compressor system 100.

The sensors 130 may be configured to collect (e.g., measure, detect) data related to the working fluid, a cooling or conditioning fluid circulated by the evaporator 38, and/or a cooling or conditioning fluid circulated by the condenser 34. For example, one or more of the sensors 130 may detect temperatures, pressures, flow rates, or other operating parameters of the working fluid, a conditioning fluid, or a cooling fluid. Further, one or more sensors 130 may be associated with the PRVs 106, 110, the VGDs 108, 112, and/or the hot gas bypass valve 116. For example, the sensors 130 may be configured to detect and transmit data indicative of positions of the PRVs 106, 110, the VGDs 108, 112, and/or the hot gas bypass valve 116. The vapor compression system 14 may also include one or more sensors 130 associated with the motor system 114 (e.g., each of the motors of the motor system 114), and may be configured to detect and transmit data indicative of respective operating parameters of the motor system 114. It should be noted that the vapor compression system 14 may include fewer or more sensors 130 than those illustrated in FIG. 5, and additional or alternative sensors 130 may be configured to detect one or more operating parameters and transmit data indicative of the operating parameters to the controller 120 for use in operating the compressor system 100 and/or other components of the vapor compression system 14.

As discussed above, the PRVs 106, 110 and the VGDs 108, 112 may be operated as flow reduction devices (FRDs) configured to control or otherwise adjust flow of working fluid through a respective compressor (e.g., compressors 102, 104). One or more of the PRVs 106, 110 and the VGDs 108, 112 may be coupled to a respective actuator, each of which may be communicatively coupled to the controller 120. The actuators may be configured to operate based on control signals received from the controller 120. For example, the actuators may operate to adjust respective positions of the PRVs 106, 110 and/or the VGDs 108, 112. Depending on the operating mode of each of the compressors 102, 104, the controller 120 may instruct one or more actuators to adjust one or more of the PRVs 106, 110 toward an open position and/or to adjust one or more of the VGDs 108, 112 toward an open position. In this way, the controller 120 may control the compressor system 100 to increase flow of working fluid through the compressor system 100, thereby increasing a capacity (e.g., operating capacity) of the vapor compression system 14. Similarly, the controller 120 may instruct one or more actuators to adjust one or more of the PRVs 106, 110 toward a closed position and/or to adjust one or more of the VGDs 108, 112 toward a closed position in order to decrease flow of working fluid through the compressor system 100, thereby decreasing a capacity of the vapor compression system 14.

In certain embodiments, the controller 120 may execute a capacity control program or algorithm to transition operation of each compressor 102, 104 between the first operating mode and the second operating mode to satisfy a load demand each compressor 102, 104 based on a comparison between the lift on each compressor 102, 104 and one or more lift threshold values. The capacity control program, when executed, may cause the controller 120 to automatically operate the compressor 102, 104 in the first mode or the second mode to control the capacity at the respective compressor 102, 104 based on the lift of each compressor 102, 104. Additionally, the capacity control program may further cause the controller 120 to determine a desired position of the PRVs 106, 110 and/or the VGDs 108, 112 that would achieve the desired capacity. After determining the appropriate mode based on the lift and after determining a desired position of each of the flow reduction devices (e.g., PRVs 106, 110, VGDs 108, 112), the controller 120 may be configured to transmit control signals to the PRVs 106, 110 and/or the VGDs 108, 112 (e.g., via the interface 122) to adjust the position of the PRVs 106, 110 and/or the VGDs 108, 112. For example, when the lift on a particular compressor 102, 104 is below a low lift threshold value, the controller 120 may operate the compressor 102, 104 in the first mode in which the PRVs 106, 110 of each of the compressors 102, 104 are utilized to control the capacity of the compressor 102, 104 independent of a position of the VGDs 108, 112.

When the lift on a particular compressor 102, 104 is above a high lift threshold value, the controller 120 may operate the compressor 102, 104 in a second mode in which the VGD is utilized to control the capacity of the compressor. Accordingly, in the second mode, the VGD position is dependent (e.g., directly dependent) on the PRV position of the respective compressor 102, 104. If the lift on a particular compressor 102, 104 is between the low lift threshold value and the high lift threshold value, the controller 120 may transition between the first mode and the second mode to achieve a desired cooling capacity, as discussed in greater detail below. It should be appreciated that the controller 120 may be configured to employ continuous feedback from the sensors 130 monitoring various operational parameters of the vapor compression system 14 to monitor changes in system cooling loads. For example, the controller 120 may be configured to change the position of at least one of the PRVs 106, 110 and/or VGDs 108, 112 in each of compressors 102, 104 to maintain a demanded capacity that satisfies the updated cooling loads. That is, as a load demand on the vapor compression system 14 increases, the operating parameters of the compressors 102, 104 are correspondingly updated and/or revised to satisfy the new cooling capacity demand. Further, the controller 120 may continuously monitor compressor lift (e.g., working fluid system pressure differential) of each of the compressors 102, 104 to enhance the volumetric flow rate (e.g., the capacity) of the working fluid in the vapor compression system 14 and to maximize the resultant efficiency of the compressors 102, 104. Furthermore, while two compressors (e.g., compressor stages) are illustrated in the embodiment shown in FIG. 5, it should be appreciated that the embodiments discussed herein may include more or fewer compressor stages. That is, the present disclosure is directed to a vapor compression system having any number (e.g., one, two, three, four, five, six, or more) of compressors or stages of compression.

As will be appreciated, operation and performance of the compressors 102, 104 may be expressed and/or defined in terms of a head factor (Q) and a flow factor (0). The head factor is generally indicative of a pressure ratio or differential between discharge pressure and suction pressure of the compressor 102, 104 and the flow factor is generally indicative of a flow rate (e.g., mass flow rate) of fluid through the compressor 102, 104. During operation at a particular speed (e.g., rotational speed), an operating point of the compressor 102, 104 may be generally expressed in terms of corresponding head factor and flow factor values associated with the compressor 102, 104 at the particular speed. Indeed, at the particular operating speed, each compressor 102, 104 may be configured to operate at various operating points, where each operating point is expressly defined by particular corresponding head factor and flow factor values. The various corresponding head factor and flow factor values associated with the compressor 102, 104 may be based on particular design characteristics of the compressor 102, 104. Additionally, compressor operating points may be adjusted and/or achieved via operational adjustment of the compressor 102, 104. For example, because the compressors 102, 104 are fixed speed compressors, positions of the PRVs 106, 110 and/or VGD 108, 112 may be adjusted to adjust and/or achieve a particular operating point (e.g., corresponding head factor and flow factor values, achieve a particular capacity, achieve a particular lift) of the compressor 102, 104. However, it is desirable to avoid operation of the compressor 102, 104 at certain operating values of head factor and/or flow factor in order to avoid undesirable operating conditions or occurrences, such as surge.

For example, enhanced operating efficiency of a compressor may be achieved by operating the compressor at the lowest possible speed while avoiding surge. Thus, based on particular design conditions, a compressor having a particular speed may be selected. In certain embodiments, the minimum rotational speed and/or the minimum frequency at which compressors may operate while avoiding surge may be calculated according to techniques described in U.S. Patent No. 10,184,482 and EP2751430, each of which is hereby incorporated by reference in its entirety, or utilizing any other suitable technique. The controller 120 may then be configured to adjust the positions of the PRVs 106, 110 and/or the VGDs 108, 112 to achieve the demanded capacity. That is, the controller 120 may operate each of the compressors 102, 104 in a manner that satisfies a load or demand of the vapor compression system 14 while avoiding surge conditions and increasing overall operational efficiency of the vapor compression system 14. Moreover, the present techniques enable the above-described operations in compressor systems having multiple stages of compression (e.g., two, three, four, five, or more stages of compression).

In operation, the controller 120 may be configured to execute the capacity control program to control a capacity of each of the compressors 102, 104, which in turn, controls the capacity of the compressor system 100. For the sake of brevity, the capacity control program is described in the context of controlling operation of the first compressor 102. However, it should be appreciated that the same capacity control algorithm may be applied to the second compressor 104 to control the capacity of the compressor 104 without departing from the scope of this disclosure. Further, it should be appreciated that the same capacity control algorithm may be employed to control the capacity of compressor systems having a single stage compressor.

According to the capacity control program, the controller 120 may be configured to determine a compressor lift (e.g., compressor stage lift) for the compressor 102. Higher lift values may correspond to increased amounts of work performed by a respective compressor. In certain embodiments, the controller 120 may determine the compressor lift based on a ratio of an actual head factor Q of the compressor 102 and a maximum head factor Q_SUrge of the compressor 102. For example, as noted above, an operating point of the compressor 102 may be defined in terms of head factor (Q) and flow factor (0). It is often desirable to maintain the operating point within the operation limits of the compressor 102, for example, without stalling and surging. Further, the compressor 102 cannot exceed the maximum head factor Qsurge without going into surge. The maximum head factor Qsurge may be obtained by plotting a head factor (Q) versus flow factor (0) graph (e.g., compressor map) for a compressor or a corresponding compressor stage in the case of a multistage compressor. Typically, at a given impeller speed, the head factor (Q) increases with a decrease in the flow factor (0). The flow factor (0) can be reduced by closing flow reduction devices used in a compressor stage (e.g., PRVs 106, 110, VGDs 108, 112). The maximum head factor Qsurge corresponds to the head factor value at which the speed line for a given impeller speed intersects the surge line. The surge line may be plotted in the graph as a model of surge points given by a compressor manufacturer. The controller 120 may be configured to utilize the compressor map plotted for the compressor 102 to determine the maximum head factor _Sur_ge of the compressor 102.

The controller 120 may further be configured to process sensor readings received from the sensors 130 to determine the actual head factor Q of the compressor 102. In certain embodiments, the controller 120 may utilize equation 1 shown below to determine the actual head factor Q of the compressor 102: fl = ^ (1)

In equation 1 above, <1 refers to the actual head factor Q of the compressor 102, d//_i3 refers to the isentropic enthalpy difference between the suction and discharge of the compressor 102, and a refers to speed of sound.

The controller 120 may determine the isentropic enthalpy difference (i.e., based on sensor data received from various sensors 130 disposed at the suction inlet and the discharge outlet of the compressor 102. In certain embodiments, the controller 120 may determine the compressor lift of the compressor 102 based on a pressure ratio of discharge pressure and suction pressure of the compressor 102, a saturated temperature difference between the saturated discharge temperature and the saturated suction temperature of the compressor 102, a pressure difference between the discharge pressure and suction pressure of the compressor 102, or the like.

Upon determining the compressor lift of the compressor 102, the controller 120 may compare the determined compressor lift with a low lift threshold value and a high lift threshold value of the compressor 102. The low lift threshold value and the high lift threshold value of the compressor 102 may be stored in the memory 126. In certain embodiments, the low lift threshold value and the high lift threshold value may be determined by the operator using the user interface 122. In an exemplary embodiment, the low lift threshold value of the compressor 102 may be set to 0.8 and the high lift threshold value of the compressor 102 may be set to 0.9. It should be appreciated that the above examples are used for illustrative purposes and do not limit the scope of the disclosure in any manner. For example, the low lift threshold value and the high lift threshold value may vary for different applications of the vapor compression system 14 and can also vary for different compressor stages in a multistage compressor. Based on the comparison, the controller 120 may be configured to operate the compressor 102 in a first mode (e.g., PRV driven mode, low lift mode) and a second mode (VGD driven mode, high lift mode) to control the capacity of the first compressor 102, as described in greater detail below.

For example, based on the comparison result, the controller 120 may determine that the compressor lift of the first compressor 102 is less than the low lift threshold value of the first compressor 102. As a result, the controller 120 may operate the compressor 102 in the first mode to control the capacity of the first compressor 102. For example, the compressor lift of the first compressor 102 may be determined to be 0.68, which is less than the low lift threshold value of 0.8. Accordingly, the controller 120 may operate the compressor 102 in the first mode, in which the PRV 106 of the first compressor 102 is operated to regulate the capacity of the first compressor 102, while the VGD 108 is operated to rectify (e.g., eliminate) stall noise. Thus, in the first mode, the position of the VGD 108 may be independent of the position of the PRV 106 in the first mode.

In certain embodiments, the controller 120 may be configured to receive sensor readings from sensors 130 monitoring a position of the PRV 106. To reduce the capacity of the compressor 102 when the controller 120 is operating the compressor 102 in the first mode, the controller 120 may communicate actuation signals to an actuator of the PRV 106. The actuation signals may cause the actuator to progressively drive the PRV 106 from the current position toward the fully closed position. The current position may correspond to a fully opened position or a partially closed position. Thus, the actuator, based on the actuation signals, may close the PRV 106 in steps or increments until the desired capacity is achieved or the desired position is reached. To increase the capacity of the compressor 102 when the controller 120 is operating the compressor 102 in the first mode, the controller 120 may communicate actuation signals to the actuator of the PRV 106. The actuation signals may cause the actuator to progressively drive the PRV 106 from the current position toward the fully open position. The current position may correspond to a fully closed position or a partially opened position. Thus, the actuator, based on the actuation signals, may open the PRV 106 in steps or increments until the desired capacity is achieved or the fully opened position is reached. That is, in the first mode, the controller 120 may vary (e.g., adjust) the position of the PRV 106 of the first compressor 102 between the fully opened position and the fully closed position in response to the compressor lift of the compressor 102 being less than the low lift threshold value to control the capacity of the compressor 102.

As the controller 120 operates the compressor 102 in the first mode (e.g., while the controller 120 is regulating the capacity of the compressor 102 using the PRV 106), the controller 120 (e.g., the stall voltage detection board 129) may receive stall voltage signals from the stall detector 118A of the first compressor 102. The stall voltage signals may indicate the magnitude of stall noise detected by the stall detector 118A in the first compressor 102. The controller 120 may be configured to compare the stall voltage signals with stall voltage threshold values stored int the memory 126. The stall voltage threshold values may be indicative of an acceptable range of stall noise for the first compressor 102. For example, the stall voltage threshold values may include a low stall voltage threshold value and a high stall voltage threshold value. If the stall noise magnitude indicated by the stall voltage signal is less than the low stall voltage threshold value or greater than the high stall voltage threshold value, the stall noise may be considered unacceptable. Accordingly, based on determining that the stall noise is unacceptable (e.g., upon determining that the stall noise magnitude indicated by the stall voltage signal is less than the low stall voltage threshold value or greater than the high stall voltage threshold value), the controller 120 may communicate actuation signals to the actuator of the VGD 108. The actuation signals may cause the actuator to progressively drive the VGD 108 from a maximum allowed open position toward a closed position. For example, the actuator, based on the actuation signals, may progressively close the VGD 108 in steps or increments until the stall noise is rectified or the VGD 108 reaches the fully closed position.

Once the stall noise is rectified, the controller 120 may communicate a halt signal to the actuator of the VGD 108, which may cause the actuator to stop closing the VGD 108 and to maintain the current position for a preset wait time. Once the preset wait time has lapsed, the controller 120 may communicate actuation signals to the actuator of the VGD 108 to progressively (incrementally, step-wise) open the VGD 108. The actuator, based on the actuation signals, may open the VGD 108 in steps or increments until the stall noise is detected again or the maximum allowed open position is reached. In certain embodiments, the maximum allowed open position of the VGD 108 may correspond to a position beyond which the VGD 108 is not allowed to open without causing surge. Thus, in certain embodiments, the maximum allowed open position may be a fully opened position or a partially closed position. In certain embodiments, when the controller 120 is operating the compressor 102 in the first mode (e.g., when the controller 120 is using the PRV 106 to control the capacity of the compressor 102 independently of the VGD 108, when the compressor lift of the compressor 102 is lower than the low lift threshold value), the controller 120 may be configured to set the fully opened position as the maximum allowed open position. The controller 120 may be configured to repeat the above cycle of controlling the position of the VGD 108 between the fully closed position and the maximum allowed open position based on the stall voltage signal to maintain operation of the first compressor 102 while limiting stall noise and surging.

Thus, in the first mode, the position of the PRV 106, 110 of each compressor 102, 104 is varied to control the respective compressor capacity and the position of the VGD 108, 112 of each compressor 102, 104 is varied to reduce, rectify, and/or eliminate stall noise in the respective compressor 102, 104. For example, variation in the position of the PRVs 106, 110 for capacity control of each of the compressors 102, 104 does not result in any variation in the position of the VGDs 108, 112. In other words, when the controller 120 is operating the compressor 102, 104 in the first mode, the position of the VGDs 108, 112 is varied independent of the position of the PRVs 106, 110 associated with the compressors 102, 104, respectively.

In certain embodiments, the controller 120 may determine that the compressor lift of the first compressor 102 is greater than the high lift threshold value of the first compressor 102. As a result, the controller 120 may operate the compressor 102 in the second mode to control the capacity of the compressor 102. For example, the compressor lift of the first compressor 102 may be determined to be 0.92, which is greater than the high lift threshold value of 0.9. Accordingly, the controller 120 may operate the compressor 102 in the second mode, in which the both the PRV 106 and the VGD 108 are operated to regulate the capacity of the first compressor 102. Thus, in the second mode, the position of the VGD 108 may be dependent on the position of the PRV 106, as discussed in greater detail below.

In the second mode, the controller 120 may be configured to update or adjust the maximum allowed open position of the VGD 108 based on a varying position of the PRV 106 to control the capacity of the compressor 102. That is, the VGD 108 may be utilized in conjunction with the PRV 106 to control the capacity of the first compressor 102, and the controller 120 may set the maximum allowed open position of the VGD 108 based on a correlation between a position of the PRV 106 and the maximum allowed open position of the VGD 108. For example, the maximum allowed open position of the VGD 108 may be set to a fully closed position if the current position of the PRV 106 is within the range of 0% open (e.g., fully closed position) to 50% open. When the PRV 106 is opened beyond 50% open, the current position of the PRV 106 may have a linear relationship with the maximum allowed open position of the VGD 108. Thus, the maximum allowed open position of the VGD 108 may vary in the range of a fully closed position to a fully open position based on the current position of the PRV 106.

For example, FIG. 6 is a graph 200 illustrating a correlation between a current position of a PRV and a corresponding maximum allowed open position of a VGD associated with a compressor. For example, the graph 200 may correspond to the current position of the PRV 106 and a corresponding maximum allowed open position of the VGD 108 of the compressor 102. The graph 200 is plotted with the maximum allowed open position of the VGD (%VGDmax) on the Y-axis and the current percent open position of the PRV (%PRV) on the X-axis. Line 202 corresponds to the maximum allowed open position of the VGD when the compressor lift of the compressor (or compressor stage) is determined to be less than the low lift threshold value of the compressor. For example, as noted above, when the compressor lift on a compressor is less than a low lift threshold value of the compressor, the controller 120 may set the maximum possible open position (e.g., 100%, fully opened position) as the maximum allowed open position. Thus, the plot line 202 corresponds to operation of a compressor in the first mode. As illustrated in FIG. 6, during operation in the first mode, the maximum allowed open position of the VGD is independent of the position of the PRV.

Line 204 corresponds to the maximum allowed open position of the VGD when the compressor lift of the compressor is determined to be greater than the high lift threshold value of the compressor. For example, as noted above, when the compressor lift on a compressor is greater than the high lift threshold value of the compressor, the controller 120 may set the maximum allowed open position based on the position of the PRV. Thus, the line 204 corresponds to operation of a compressor in the second mode. The controller 120 may further utilize the line 204 while determining the value in equation 2 described below.

Returning to FIG. 5, in certain embodiments, the controller 120 may receive sensor readings from the sensors 130 monitoring a position of the PRV 106 and a position of the VGD 108. To reduce the capacity of the compressor 102 when the controller 120 is operating the compressor 102 in the second mode, the controller 120 may communicate actuation signals to an actuator of the PRV 106. The actuation signals may cause the actuator to progressively drive the PRV 106 from the current position toward the fully closed position. Thus, the actuator, based on the actuation signals, may close the PRV 106 in steps or increments until the desired capacity is achieved or the desired position is reached. Further, in response to driving the PRV 106 toward the fully closed position, the controller 120 may be configured to reduce the maximum allowed open position of the VGD 108 in accordance with the correlation between the varying position of the PRV 106 and the maximum allowed open position of the VGD 108 (e.g., illustrated in FIG. 6). For example, the controller 120 may communicate actuation signals to the actuator of the VGD 108 to progressively drive the VGD 108 toward a desired position (e.g., a maximum allowed open position that correlates with the current position of the PRV 106). Thus, the actuator, based on the actuation signals, may close the VGD 108 in steps or increments until the maximum allowed open position associated with the current position of the PRV 106 is attained. If the desired capacity is not reached, the controller 120 may generate actuation signals to further close the first stage PRV 106, which in turn, causes the controller 120 to generate actuation signals to further close the VGD 108 to an updated maximum allowed open position based on the updated position of the PRV 106.

To increase the capacity of the compressor 102 when the controller 120 is operating the compressor 102 in the second mode, the controller 120 may communicate actuation signals to the actuator of the PRV 106. The actuation signals may cause the actuator to drive (e.g., progressively drive, incrementally drive) the PRV 106 from the current position toward the fully open position. Thus, the actuator, based on the actuation signals, may open the PRV 106 in steps or increments until the desired capacity is achieved or the desired position is reached. Further, in response to driving the PRV 106 toward the fully open position, the controller 120 may be configured to increase the maximum allowed open position of the VGD 108 in accordance with the correlation between the varying position of the PRV 106 and the maximum allowed open position of the VGD 108. For example, the controller 120 may communicate actuation signals to the actuator of the VGD 108 to drive the VGD 108 toward a desired position (e.g., maximum allowed open position associated with the current position of the PRV 106). Thus, the actuator, based on the actuation signals, may open the VGD 108 in steps or increments until the maximum allowed open position associated with the current position of the PRV 106 is attained.

Notably, as the controller 120 operates the compressor 102 in the second mode, the maximum allowed open position of the VGD 108 may be more closed relative to what is demanded by stall voltages. Accordingly, stall noise rectification control (e.g., stall noise reduction control) may cause the actuator to drive the VGD 108 toward the maximum allowed open position associated with the current position of the PRV 106. The actuator, based on the actuation signals and the stall noise rectification control, may open the VGD 108 in steps or increments until the maximum allowed open position is attained. If the desired capacity is still not reached, the controller 120 may generate actuation signals to further open the PRV 106, which in turn, causes the controller 120 to generate actuation signals to further open the VGD 108 to an updated maximum allowed open position based on the updated position of the PRV 106. The controller 120 may continue opening the PRV 106 and the VGD 108 until the desired capacity is achieved or until a position of the VGD 108 causes an occurrence of stall noise.

Thus, in the second mode, the position of the PRV 106, 110 of each compressor 102, 104 and the position of the VGD 108, 112 of each compressor 102, 104, which is directly dependent on the current position of the PRV 106, 110, are varied to control the respective compressor capacity. That is, variation in the position of the PRVs 106, 110 may result in a variation in the position of the VGDs 108, 112. In other words, when the controller 120 is operating the compressor 102, 104 in the second mode, the position of the VGDs 108, 112 is varied based on the position of the PRVs 106, 110. Additionally, it should be appreciated that operation of the compressor 102, 104 in the second mode may cause the VGD 108, 112 of a respective compressor 102, 104 to be more closed relative to operation of the compressor 102, 104 in the first mode and/or relative to a degree of opening that would be demanded to rectify stall noise. Thus, in certain embodiments, operation of the compressor 102, 104 in the second mode may rectify stall noise by default.

In certain embodiments, the controller 120 may determine that the compressor lift of the first compressor 102 is between the low lift threshold value and the high lift threshold value. As a result, the controller 120 may alternate operation of the compressor 102 in the first mode and the second mode to control the capacity of the first compressor 102. For example, in embodiments in which the compressor lift is increasing in a direction toward the high lift threshold value, the controller 120 may be configured to transition operation of the compressor 102 in the first mode to operation of the compressor 102 in the second mode to control the capacity of the compressor 102. Conversely, in embodiments in which the compressor lift is decreasing in a direction toward the low lift threshold value, the controller 120 may be configured to transition operation of the compressor 102 in the second mode to operation of the compressor 102 in the first mode to control the capacity of the compressor 102.

As an example, the compressor lift for the first compressor 102 may be determined to be 0.82, which is greater than the low lift threshold value of 0.8, but less than the high lift threshold value of 0.9. Accordingly, the controller 120 may utilize the PRV 106 and the VGD 108 to regulate the capacity of the compressor 102. For example, as the compressor lift moves from the low lift threshold value to the high lift threshold value, the controller 120 may be configured to control the compressor 102 such that the contribution of the VGD 108 in capacity control increases while the contribution of the PRV 106 in capacity control decreases. Conversely, as the compressor lift moves from the high lift threshold value to the low lift threshold value, the controller 120 may be configured to control the compressor 102 such that the contribution of the VGD 108 in capacity control decreases and the contribution of the PRV 106 in capacity control increases.

To transition between the first mode and the second mode, the controller 120 may be configured to update, adjust, or modify the maximum allowed open position of the VGD 108 based on the varying position of the PRV 106. In certain embodiments, the controller 120 utilize equation 2 shown below to determine the maximum allowed open position of the VGD 108:

%KGDp_{!a Ll!!o},_8(; = 100

In equation 2 above, %TCD™rt_Biitwed refers to the maximum allowed open position of the VGD 108, £1^^ refers to the maximum head factor of the first compressor 102, £1 refers to the actual head factor of the first compressor 102, and refers to the correlation between the position of the PRV 106 and the maximum allowed open position of the VGD 108 (e.g., as described in FIG. 6) used when the controller 120 operates the compressor 102 in the second mode (e.g., when the lift of the compressor 102 is greater than the high lift threshold value).

According to equation 2, the controller 120 progressively reduces the maximum allowed open position for the VGD 108 from the maximum open position possible (e.g., 100% open) based on an increase in the compressor lift from the low lift threshold value to the high lift threshold value. Similarly, the controller 120 progressively increases the maximum allowed open position for the VGD 108 from the fully closed position (e.g., 0% open) based on a decrease in the compressor lift from the high lift threshold value to the low lift threshold value. As a result, the controller 120 is able to increase or decrease the capacity of the first compressor 102 by varying the current position of the PRV 106 and the current position of the VGD 108 based on the relationship described in equation 2. For example, when the position of the PRV 106 is between 0% open and 50% open, the maximum allowed open position of the VGD 108 is set to 100% at '0.80' compressor lift, to 90% at '0.81' compressor lift, to 80% at '0.82' compressor lift, to 70% at '0.83' compressor lift, and so on. Similarly, when the position of the PRV 106 is at 60% open, the maximum allowed open position of the VGD 108 is set to 100% at '0.80' compressor lift, to 92% at '0.81' compressor lift, to 84% at '0.82' compressor lift, and so on.

With the preceding in mind, FIG. 7 illustrates a flow chart of an embodiment of a method 300 (e.g., capacity control scheme, capacity control program, control logic) for controlling operation of the compressor system 100 (e.g., controlling operation of each of the compressors 102, 104 of the compressor system 100). That is, the method 300 may be utilized to coordinate and/or control operation of the first and second compressors 102, 104, and the respective components thereof to satisfy a load (e.g., cooling capacity, heating capacity) of the vapor compression system 14 (e.g., to operate the vapor compression system 14 at a desired capacity). For example, the controller 120 (e.g., a single controller, the processing circuitry 124) may be configured to implement and/or execute the method 300 to control various components of the vapor compression system 14 and/or to transition operation of each of the compressors 102, 104 between the first mode and the second mode based on the lift demands of the respective compressor 102, 104. In other embodiments, the method 300 may be implemented by another controller (e.g., a dedicated controller of the compressor system 100), more than one controller, or other suitable control system. Moreover, certain steps of the method 300 may be removed, modified, and/or performed in a different order.

As mentioned above, the method 300 may be implemented to control a capacity (e.g., operating capacity) of the vapor compression system 14. In some embodiments, an outlet temperature of the evaporator 38 may be monitored and evaluated to determine the operating capacity (e.g., a current operating capacity) of the vapor compression system 14. In other words, the outlet temperature of the evaporator 38 may be representative of an operating capacity of the vapor compression system 14. For example, the outlet temperature may be a temperature of cooling fluid conditioned via the evaporator 38 and exiting the evaporator 38. However, in other embodiments, the outlet temperature may be a temperature of the working fluid exiting the evaporator 38. As will be appreciated, the outlet temperature may be measured or detected by one of the sensors 130 described above.

Though the method 300 is illustrated as a series of steps, it should be understood that the method 300 may be executed or implemented on a continual or continuous control loop (e.g., a proportional integral derivative [PID] control loop) based on any suitable input, data, or feedback (e.g., feedback from sensors 130). That is, the steps of the method 300 may be repeatedly executed (e.g., in sequential order) to enable adjustment of the operating capacity of the vapor compression system 14. Indeed, the method 300 may be continually or continuously executed to dynamically control components of the vapor compression system 14 in real time (e.g., based on feedback provided by one or more of the sensors 130). The method 300 begins at block 302 with the controller 120 calculating the head (e.g., actual head, work performed, head factor) for each of the compressors 102, 104 (e.g., for each stage of compression of the compressor system 100). In certain embodiments, the head for each compressor 102, 104 may be calculated based on data indicative of working fluid temperature and/or pressure (e.g., received from sensors 130) at the corresponding inlets and outlets of the compressors 102, 104, and/or based on data indicative of working fluid and/or cooling fluid temperature and/or pressure (e.g., received from sensors 130) at the condenser 34 and evaporator 38. For example, the head for each compressor may be determined based on the saturated temperature at the suction inlet of the compressor 102, 104 and the saturated temperature at the discharge outlet of the compressor 102, 104. In some embodiments, the head for each compressor 102, 104 may be calculated according to techniques described in EP2751430, which is herein incorporated by reference in its entirety, or utilizing any other suitable technique.

At block 304, the controller 120 may determine the compressor lift based on a ratio of the actual head factor (e.g., as determined by block 302) and a maximum head factor of the compressor 102, 104. In certain embodiments, the maximum head factor may be based on design operating conditions. At block 306, the controller 120 may compare the determined compressor lift associated with a particular compressor 102, 104 with a low lift threshold value and a high lift threshold value to generate a comparison result. As noted above, the low lift threshold value and the high lift threshold value may be stored in the memory 126.

At block 308, the controller 120 may be configured to determine whether the compressor lift determined in block 304 is less than the low lift threshold value based on the comparison result generated in block 306. Upon determining that the compressor lift is less than the low lift threshold value, the method 300 may proceed to block 310, and the controller 120, at block 310, may operate the compressor 102, 104 in the first mode. Thus, as described above, when the compressor lift is less than the low lift threshold value, the controller 120 may be configured to vary the position of the PRVs 106, 110 to control compressor capacity, and may control the position of the VGDs 108, 112 to reduce and/or rectify stall noise. For example, upon selecting the first mode to operate the compressor 102, 104, the controller 120, at block 312, may set the maximum open position possible (e.g., 100%, fully open position) as the maximum allowed open position of the VGDs 108, 112. The position of the VGDs 108, 112 may then be varied to reduce, rectify, or eliminate stall noise (e.g., stall noise rectification control, stal l noise reduction control), as described in greater detail below with respect to FIG. 8.

At block 314, the controller 120 may vary the position of the PRVs 106, 110 from the fully open position to the fully closed position to control the capacity of the compressor 102, 104. For example, as noted above, to reduce the capacity of the compressor 102, 104, the controller 120 may communicate actuation signals to an actuator of the PRVs 106, 110 to drive (e.g., progressively drive, incrementally drive) the PRVs 106, 110 from the current position toward the fully closed position. Conversely, to increase the capacity of the compressor 102, 104, the controller 120 may communicate actuation signals to the actuator of the PRVs 106, 110 to drive the PRVs 106, 110 from the current position toward the fully open position. The controller 120 may continue to determine and/or evaluate any changes in the compressor lift by repeating blocks 302 and 304. Notably, the position of the VGDs 108, 112 is independent of the varying position of the PRVs 106, 110 when the controller 120 is operating the compressor 102, 104 in the first mode.

If, at block 308, the controller 120 determines that the compressor lift is not less than the low lift threshold value, the method may proceed to block 316, and the controller 120 may determine whether the compressor lift is greater than the high lift threshold value based on the comparison result generated in block 306. Upon determining that the compressor lift is greater than the high lift threshold value, the method 300 may proceed to block 318, and the controller 120, at block 318, may operate the compressor 102, 104 in the second mode. Thus, as described above, when the compressor lift is greater than the high lift threshold value, the controller 120 may be configured to vary the position of the PRVs 106, 110 and the position of the VGDs 108, 112 to control compressor capacity.

For example, upon selecting the second mode to operate the compressor 102, 104, the controller 120, at block 320, may vary the position of the PRVs 106, 110 between a fully open position and a partially or fully closed position. Further, in response to varying the position of the PRVs 106, 110, the controller 120, at block 322, may determine the maximum allowed open position of the VGDs 108, 112 based on the current position of the PRVs 106, 110. That is, the maximum allowed open position of the VGDs 108, 112 may be set based on a correlation between the current position of the PRVs 106, 110 and the maximum allowed open position of the VGDs 108, 112 (e.g., as illustrated by line 204 in FIG. 6).

At block 324, the controller 120 may vary the position of the VGDs 108, 112 to attain the set maximum allowed open position as determined by block 322 to control the capacity of the compressor 102, 104. At block 325, the controller 120 may determine whether the desired capacity is achieved. As illustrated in FIG. 7, if, at block 325, the controller 120 determines that the desired capacity is achieved, the controller 120 may continue to monitor compressor operation to determine any changes in the compressor lift (e.g., by repeating steps 302 and 304). However, if, at block 325, the controller 120 determines that the desired capacity is not achieved, the controller 120 may repeat blocks 320, 322, and 324 until the desired capacity is achieved. Additionally, the controller 120 may continue to monitor and/or detect any changes in the compressor lift by repeating blocks 302 and 304.

If, at block 316, the controller 120 determines that the compressor lift is not greater than the high lift threshold value (e.g., if the controller 120 determines that the compressor lift is between the low lift threshold value and the high lift threshold value), the method may proceed to block 326, and the controller 120, at block 326, may transition operation of the compressor 102, 104 between the first mode and the second mode to control the capacity of the compressor 102, 104.

For example, at block 328, the controller 120 may reduce or increase the maximum allowed open position of the VGDs 108, 112 as the compressor lift varies between the low lift threshold value and the high lift threshold value. As noted above, in certain embodiments, the controller 120 may utilize equation 2 to determine the maximum allowed open position of the VGDs 108, 112 based on the current position of the PRVs 106, 110. For example, as the compressor lift moves from the low lift threshold value to the high lift threshold value, the controller 120 may be configured to control the compressor 102, 104 such that the contribution of the VGDs 108, 112 in capacity control increases while the contribution of the PRVs 106, 110 in capacity control decreases. Conversely, as the compressor lift moves from the high lift threshold value to the low lift threshold value, the controller 120 may be configured to control the compressor 102, 104 such that the contribution of the VGDs 108, 112 in capacity control decreases and the contribution of the PRVs 106, 110 in capacity control increases.

At block 330, the positions of the PRVs 106, 110 and the VGDs 108, 112 are varied to achieve a desired capacity. Notably, the position of the VGDs 108, 112 is varied to attain the maximum allowed open position based on the current position of the PRVs 106, 110.

Referring now to FIG. 8, a flow chart of an embodiment of a method 400 (e.g., stall noise rectification control scheme, stall noise program, stall noise control logic) for performing stall noise rectification control is illustrated. That is, the method 400 may be utilized to minimize and/or reduce stall noise in the compressor 102, 104. For example, the controller 120 may be configured to implement and/or execute the method 400 to control various components of the vapor compression system 14 and/or the compressor system 100. In other embodiments, the method 400 may be implemented by another controller (e.g., a dedicated controller of the compressor system 100), more than one controller, or other suitable control system.

Though the method 400 is illustrated as a series of steps, it should be understood that the method 400 may be executed or implemented on a continual or continuous control loop based on any suitable input, data, or feedback (e.g., feedback from sensors 130, feedback from stall detectors 118A, 118B). That is, the steps of the method 400 may be repeatedly executed (e.g., in sequential order) to minimize and/or reduce stall noise in the compressor 102, 104. Indeed, the method 400 may be continually or continuously executed to dynamically control components of the vapor compression system 14 in real time.

The method 400 begins at block 402 with the controller 120 receiving a stall voltage signal indicative of a magnitude of stall noise in the compressor 102, 104 from the stall detector 118A, 118B. Upon receiving the stall voltage signal, the controller 120 may, at block 404, compare the stall voltage signal with one or more stall voltage threshold values stored in the memory 126. For example, the controller 120 may compare the stall voltage signal with a number of stall voltage threshold values that provide a range of acceptable stall voltage signal values. For example, if the stall voltage signal transmitted to the controller 120 by the stall detectors 118A, 118B is outside the range of stall voltage threshold values, the controller 120 may determine that the stall noise associated with the stall voltage signal is unacceptable.

If, at block 404, the controller 120 determines that the stall voltage signal is outside of the range of stall voltage threshold values, the method may proceed to block 406, and the controller 120 may vary a position of the VGD 108, 112 between the maximum allowed open position and the fully closed position based on the stall voltage signal. For example, upon determining that the stall voltage signal is indicative of unacceptable stall noise (e.g., upon determining that the stall voltage signal is outside the range of stall voltage threshold values), the controller 120 may communicate actuation signals to the actuator of the VGD 108, 112 to vary the position of the VGD 108, 112. The actuator, based on the actuation signals, may close the VGD 108, 112 in steps or increments until the stall noise is rectified or the VGD 108, 112 reaches the fully closed position. In certain embodiments, the VGD 108, 112 may be maintained at the current position that rectifies the stall noise for a preset wait period. Once the wait period is over, the controller 120 may communicate actuation signals to the actuator of the VGD 108, 112 to progressively open the VGD 108, 112 until the stall noise is detected again or the maximum allowed open position is reached. The controller 120 may be configured to repeat blocks 402, 404, and 406 to reduce, rectify, and/or eliminate occurrences of stall noise and/or surging.

The present disclosure may provide one or more technical effects useful in the operation of an HVAC&R system. In particular, the disclosed systems and methods employ capacity control algorithms that enable upper lift limits to be achieved at lower flow rates in fixed speed compressors while minimizing the occurrence of undesirable operating conditions (e.g., stall and/or surge). Additionally, the capacity control algorithms discussed herein may be applied to single stage compressors or multistage compressors for capacity control, and may enable simplified control techniques for systems having multiple stages of compression and/or multiple capacity regulation components associated with each stage of compression. Further still, the capacity control algorithms discussed herein enable efficient operation of compressor systems, thereby enabling reduced energy consumption associated with operation of HVAC&R systems employing such compressor systems.

While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, such as temperatures and pressures, mounting arrangements, use of materials, colors, orientations, and so forth, without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode, or those unrelated to enablement. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routi ne undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.

The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as "means for [perform]ing [a function]..." or "step for [perform]ing [a function]...", it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is i ntended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Claims

1. A compressor system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, the compressor system comprising: one or more compressors configured to circulate a working fluid through a vapor compression system of the HVAC&R system, each compressor of the one or more compressors comprising a pre-rotation vane and a variable geometry diffuser configured to operate to regulate a capacity of the compressor system; and a controller comprising a memory and processing circuitry, wherein the memory comprises instructions stored thereon that, when executed by the processing circuitry, cause the processing circuitry to: determine a head factor for each compressor of the one or more compressors; determine a compressor lift for each compressor of the one or more compressors based at least in part on the head factor; compare the compressor lift of each compressor of the one or more compressors with a low lift threshold value and a high lift threshold value; and operate each compressor of the one or more compressors in a first mode or a second mode based on comparing the compressor lift to the low lift threshold value and the high lift threshold value.

2. The compressor system of claim 1, wherein each compressor of the one or more compressors comprises: a pre-rotation vane (PRV) positioned proximate a suction inlet of the compressor; and a variable geometry diffuser positioned proximate a discharge outlet of the compressor.

3. The compressor system of claim 2, wherein the PRV is adjustable between a first fully closed position and a fully open position, and wherein the VGD is adjustable between a second fully closed position and a maximum allowed open position.

4. The compressor system of claim 2 or 3, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: control a first position of the PRV to regulate a capacity of each compressor of the one or more compressors in the first mode, wherein a second position of the VGD is independent of the first position of the PRV in the first mode; and control the first position of the PRV and the second position of the VGD to regulate the capacity of each compressor of the one or more compressors in the second mode, wherein the second position of the VGD is dependent on the first position of the PRV in the second mode.

5. The compressor system of claim 4, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: determine that the compressor lift for a respective compressor of the one or more compressors is lower than the low lift threshold value; and operate the respective compressor in the first mode.

6. The compressor system of claim 4 or 5, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: determine that the compressor lift for a respective compressor of the one or more compressors is greater than the low lift threshold value; and operate the respective compressor in the second mode.

7. The compressor system of any of claims 2 to 6, wherein each of the one or more compressors comprises a stall detector configured to detect pressure pulsations at the discharge outlet of the compressor, wherein the pressure pulsations are indicative of a magnitude of stall noise at the discharge outlet of the compressor.

8. The compressor system of claim 7, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: receive data from the stall detector indicative of the magnitude of stall noise; compare the magnitude of stall noise with a range of acceptable stall voltage threshold values; and control a position of the VGD to reduce the magnitude of stall noise based on the magnitude of stall noise being outside the range of acceptable stall voltage threshold values.

9. The compressor system of claim 8, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to drive the position of the VGD toward a fully closed position to reduce the magnitude of the stall noise.

10. The compressor system of any of claims 1 to 9, wherein each compressor of the one or more compressors is coupled to a fixed speed drive configured to drive operation of the compressor.

11. A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, comprising: a vapor compression system, comprising: a vapor compression circuit configured to circulate a working fluid therethough; and a compressor configured to pressurize and direct the working fluid through the vapor compression circuit, wherein the compressor comprises a pre-rotation vane (PRV) adjustable between a fully open position and a first fully closed position and a variable geometry diffuser (VGD) adjustable between a maximum allowed open position and a second fully closed position; and a controller comprising a memory and processing circuitry, wherein the memory stores instructions that, when executed by the processing circuitry, cause the processing circuitry to transition operation of the compressor between a first mode and a second mode to regulate a capacity of the compressor, wherein a first position of the VGD is independent of a second position of the PRV in the first mode, and the first position of the VGD is dependent on the second position of the PRV in the second mode.

12. The HVAC&R system of claim 11, wherein the vapor compression system comprises one or more sensors configured to detect one or more operating conditions of the vapor compression system and provide feedback indicative of the one or more operating conditions to the controller.

13. The HVAC&R system of claim 12, wherein the one or more operating conditions comprise an inlet temperature of an evaporator of the vapor compression system, an outlet temperature of the evaporator of the vapor compression system, an inlet temperature of a condenser of the vapor compression system, an outlet temperature of the condenser of the vapor compression system, or any combination thereof.

14. The HVAC&R system of claim 12 or 13, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: determine a lift of the compressor based on a ratio of an actual head factor of the compressor and a maximum head factor of the compressor; compare the lift with a low lift threshold value and a high lift threshold value; operate the compressor in the first mode when the lift is less then the low lift threshold value; and operate the compressor in the second mode when the lift is greater than the high lift threshold value.

15. The HVAC&R system of claim 14, wherein the actual head factor is based on the one or more operating conditions of the vapor compression system.

16. The HVAC&R system of any of claims 11 to 15, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to: adjust the first position of the VGD between a maximum allowed open position and a first fully closed position; and adjust the second position of the PRV between a fully open position and a second fully closed position.

17. The HVAC&R system of claim 16, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to set the maximum allowed open position of the VGD at a maximum possible open position of the VGD in the first mode.

18. The HVAC&R system of claim 16 or 17, wherein the instructions, when executed by the processing circuitry, cause the processing circuitry to set the maximum allowed open position of the VGD based on the second position of the PRV in the second mode.

19. A method for controlling a capacity of a compressor having a pre-rotation vane (PRV) and a variable geometry diffuser (VGD), the method comprising: determining an actual head factor for the compressor based on one or more operating conditions of a vapor compression system employing the compressor; determining a lift of the compressor based on a ratio of the actual head factor and a maximum head factor of the compressor; comparing the lift with a low lift threshold value and a high lift threshold value to generate a comparison result; operating the compressor in a first mode in which a position of the VGD is varied independently of a position of the PRV in response to the comparison result indicating that the lift is less than the low lift threshold value; and operating the compressor in a second mode in which the position of the VGD is varied based on a correlation between the position of the VGD and the position of the PRV in response to the comparison result indicating that the lift is greater than the high lift threshold value.

20. The method of claim 19, comprising: receiving sensor data from one or more sensors, wherein the sensor data is indicative of the one or more operating parameters of the vapor compression system; - receiving stall voltage signal data from a stall detector coupled to the compressor, wherein the stall voltage signal data is indicative of a magnitude of stall noise in the compressor; and controlling the position of the VGD based on the sensor data and the stall voltage signal data.