Systems and Methods for Controlling Refrigerant Pressure Differential

Abstract

A system and method are provided for controlling a compressor system to ensure sufficient differential pressure to provide cooling. The compressor system includes a compressor, a suction pressure sensor at the suction inlet of the compressor, a discharge pressure sensor, a condenser, an expansion device, a liquid line, a liquid line pressure sensor, an evaporator, a condenser blower, and a controller. The method includes: determining a pressure target based on an intermediate pressure within the compressor and a cooling differential pressure threshold; determining a pressure ratio setpoint based on the pressure target and the liquid line pressure measured by the liquid line pressure sensor; controlling the condenser blower to operate based on the determined pressure ratio setpoint; determining a subcooling setpoint based on the pressure target and the liquid line pressure in the compressor system; and controlling the expansion device to operate based on the subcooling setpoint.

Description

Technical Field

[0001] The present disclosure relates to a compressor system and a method of operating a compressor system to control an air flow and an expansion valve opening to ensure a sufficient refrigerant pressure difference for cooling components of the compressor system. Background Art

[0002] Cooling systems for certain compressors utilize a pressure difference within the compressor system to provide cooling for components of the compressor system (such as a compressor motor or an inverter). The pressure difference may need to be maintained at or above a threshold to ensure proper operation of the cooling system. In some compressor systems, the pressure difference may vary based on ambient temperature, the water temperature at an evaporator in a chiller system, and operating parameters of the compressor system. Summary of the Invention

[0003] The present disclosure relates to a compressor system and a method of operating a compressor system to control an air flow and an expansion valve opening to ensure a sufficient refrigerant pressure difference for cooling components of the compressor system.

[0004] A refrigerant pressure difference (e.g., a pressure difference between an intermediate pressure within a compressor of a compressor system and a liquid line of the compressor system) can be used to provide cooling for components of the compressor system (such as a motor, an inverter, bearings, etc.). In some compressor systems, the refrigerant pressure difference must be maintained at or above a threshold to properly cool these components.

[0005] By adjusting a pressure ratio target and a cooling setpoint, the operation of the compressor system can be adjusted to ensure that a refrigerant pressure difference sufficient for cooling is maintained by controlling the air flow and the aperture of an expansion device.

[0006] In an embodiment, a method of controlling a compressor system includes determining a pressure target based on an intermediate pressure within a compressor of the compressor system and a cooling pressure difference threshold. The method further includes determining a pressure ratio setpoint based on the pressure target and a liquid line pressure within a liquid line of the compressor system. The method includes operating a condenser blower at a speed determined based on the determined pressure ratio setpoint. The method further includes determining a subcooling setpoint based on the pressure target and the liquid line pressure in the compressor system; and operating an expansion device based on the determined subcooling setpoint.

[0007] In an embodiment, the intermediate pressure is determined based on a suction pressure of the compressor and a discharge pressure of the compressor.

[0008] In an embodiment, determining a pressure ratio setpoint includes: comparing a pressure target with a liquid line pressure; when the pressure target exceeds the liquid line pressure, setting the pressure ratio setpoint to the product of the current pressure ratio and the ratio of the pressure target to the liquid line pressure; when the liquid line pressure reaches or exceeds the pressure target, setting the pressure ratio setpoint to the current pressure ratio.

[0009] In an embodiment, determining the speed includes referring to a mathematical model that correlates the pressure ratio with the speed of a condenser blower. In an embodiment, the method further includes applying a smoothing function to control the rate of change of the pressure ratio setpoint.

[0010] In an embodiment, the method further includes comparing the determined pressure ratio setpoint with a pressure ratio limit and setting the pressure ratio setpoint to the pressure ratio limit when the determined pressure ratio setpoint exceeds the pressure ratio limit.

[0011] In an embodiment, determining a subcooling setpoint includes: determining a liquid pressure difference based on the pressure target and the liquid line pressure; determining a subcooling offset based on the liquid pressure difference; determining the subcooling setpoint based on the subcooling offset and the current subcooling value.

[0012] In an embodiment, determining the subcooling offset includes referring to a mathematical model that correlates the subcooling offset with the liquid pressure difference. In an embodiment, the method further includes applying a smoothing function to control the rate of change of the subcooling setpoint.

[0013] In an embodiment, operating an expansion device based on the subcooling setpoint includes setting an aperture size of the expansion device based on the subcooling setpoint.

[0014] In an embodiment, a compressor system includes: a compressor; a condenser; an expansion device that is fluidly connected to the condenser via a liquid line; a liquid line pressure sensor at the liquid line of the compressor system; an evaporator; a blower configured to drive an air flow over the condenser; and a controller. The controller is configured to: determine a pressure target based on an intermediate pressure within the compressor and a cooling pressure difference threshold; determine a pressure ratio setpoint based on the pressure target and the liquid line pressure measured by the liquid line pressure sensor; control the blower to operate at a speed determined based on the determined pressure ratio setpoint; determine a subcooling setpoint based on the pressure target and the liquid line pressure in the compressor system; and control the expansion device to operate based on the subcooling setpoint.

[0015] In an embodiment, the expansion device is a controllable electronic expansion valve. In an embodiment, a processor is configured to control the expansion device to operate based on the subcooling setpoint by setting an aperture size of the controllable electronic expansion valve.

[0016] In an embodiment, the processor is further configured to determine an intermediate pressure within the compressor based on the suction pressure measured by the suction pressure sensor and the discharge pressure measured by the discharge pressure sensor.

[0017] In an embodiment, the controller is configured to determine a pressure ratio setpoint by: comparing a pressure target with a liquid line pressure; when the pressure target exceeds the liquid line pressure, setting the pressure ratio setpoint to the product of the current pressure ratio and the ratio of the pressure target to the liquid line pressure; and when the liquid line pressure reaches or exceeds the pressure target, setting the pressure ratio setpoint to the current pressure ratio.

[0018] In an embodiment, the controller is configured to determine a subcooling setpoint by: determining a liquid pressure difference based on the pressure target and the liquid line pressure; determining a subcooling offset based on the liquid pressure difference; and determining the subcooling setpoint based on the subcooling offset and the current subcooling value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A compressor system according to an embodiment is shown.

[0020] Figure 2 A flowchart of a method of controlling a compressor system according to an embodiment is shown.

[0021] Figure 3 A flowchart of an exemplary method for determining a pressure ratio setpoint according to an embodiment is shown.

[0022] Figure 4 A flowchart of an exemplary method for determining a subcooling setpoint according to an embodiment is shown. DETAILED DESCRIPTION

[0023] The present disclosure relates to a compressor system and a method of operating a compressor system to control an air flow and an expansion valve opening to ensure a sufficient refrigerant pressure difference for cooling components of the compressor system.

[0024] Figure 1FIG. 0 shows a compressor system 100 according to an embodiment. The compressor system 100 includes a compressor 102, a condenser 104, an expansion device 106, and an evaporator 108 that are fluidly connected to each other. The compressor system 100 further includes a controller 110. The compressor system 100 further includes a suction pressure sensor 112 at the suction port 114 of the compressor 102, a discharge pressure sensor 116 at the discharge port 118 of the compressor 102, and a liquid line sensor 120 that is positioned between the condenser 104 and the expansion device 106 along a liquid line 122 relative to the flow of the working fluid through the compressor system 100. A cooling line 126 may extend from the liquid line 122 to the compressor 102 and / or other components of the compressor system 100.

[0025] The compressor 102 is a compressor that compresses the working fluid of the compressor system 100. The compressor 102 may be, for example, a centrifugal compressor or any other suitable type of compressor. The compressor 102 may include a motor. In an embodiment, the motor of the compressor 102 is configured to be cooled by the working fluid of the compressor system 100. In an embodiment, the cooling of the motor of the compressor 102 may be affected by the pressure difference within the compressor system 100. In an embodiment, cooling may be provided by introducing the working fluid from the liquid line 122 into the components of the compressor 102 via the cooling line 126. The working fluid introduced into these components of the compressor 102 expands, thereby absorbing heat and cooling the components of the compressor 102, and then the working fluid merges with the other working fluid of the compressor system 100 and is compressed by the compressor 102. The compressor 102 receives the working fluid at the suction port 114, and the compressed working fluid leaves the compressor 102 at the discharge port 118. The compressed working fluid then reaches the condenser 104. The compressor 102 may have a pressure ratio determined by dividing the pressure at the discharge port 118 by the pressure at the suction port 114.

[0026] The condenser 104 includes a heat exchanger. The condenser 104 receives the compressed working fluid from the compressor 102, and the working fluid rejects heat through the heat exchanger at the condenser 104. The heat rejection at the condenser 104 condenses the working fluid into a liquid. The condenser 104 may be in thermal communication with the surrounding environment and reject heat to the surrounding environment. One or more blowers 124 may provide an air flow over the condenser 104. One or more blowers may be controlled by the controller 110 to provide a variable air flow. In an embodiment, one or more blowers operate at a value corresponding to a percentage of the air flow that may be provided by one or more blowers 124. One or more blowers may affect the heat transfer of the working fluid within the condenser 104. The heat transfer at the condenser 104 affects the pressure at the condenser 104 and may affect the suction pressure at the suction port 114 and the pressure ratio of the compressor. The heat transfer at the condenser 104 affected by the operation of one or more blowers 124 may also affect the liquid line pressure at the liquid line 122.

[0027] The liquid line 122 provides a fluid connection between the condenser 104 and the expansion device 106. One or more liquid line sensors 120 may be positioned along the liquid line 122. One or more liquid line sensors 120 include pressure sensors to measure the pressure of the fluid within the liquid line 122. The pressure sensor may be any suitable pressure sensor for measuring the pressure of the fluid within the liquid line 122. In an embodiment, one or more liquid line sensors 120 further include temperature sensors.

[0028] The cooling line 126 may provide a fluid connection between the liquid line 122 and a component of the compressor system 100 to be cooled. The cooling line 126 may deliver some of the working fluid from the liquid line 122 to a component of the compressor system 100 to be cooled, such as the motor and / or inverter of the compressor 102. The working fluid from the cooling line 126 may be expanded, thereby absorbing heat at the component of the compressor system 100 to be cooled. For the components of the compressor 102, the expansion of the working fluid from the cooling line 126 may be the expansion of the intermediate pressure of the compressor 102.

[0029] The expansion device 106 is a device configured to reduce the pressure of the working fluid. As a result, a portion of the working fluid is converted into a gaseous form. The expansion device 106 can be, for example, an expansion valve, an orifice, or other suitable expander for reducing the pressure of a refrigerant such as the working fluid. In an embodiment, the expansion device 106 includes a plurality of orifices. In an embodiment, the plurality of orifices of the expansion device 106 have different sizes. The expansion device 106 can be a controllable expansion device with a variable aperture. In an embodiment, the expansion device 106 is an electronic expansion valve. The expansion device 106 can be controlled by the controller 110 to adjust the effect of the expansion device 106 on the flow and expansion of the working fluid, for example, by controlling the aperture size of the expansion valve or controlling the number and size of the orifices in use based on a signal from the controller 110.

[0030] The evaporator 108 receives the working fluid from the expansion device 106. The evaporator 108 includes a heat exchanger in which the working fluid can absorb heat, for example, absorb heat from the air stream to be provided to the building to cool the air stream. The compressor system 100 can be part of an HVACR system. The HVACR system can be, for example, an air-cooled chiller. The air stream exchanges heat with the working fluid in the evaporator 108, which causes the heat in the air stream to be absorbed and the working fluid to evaporate.

[0031] The controller 110 is a controller that can be operably coupled to at least the suction pressure sensor 112, the discharge pressure sensor 116, one or more liquid line sensors 120, the expansion device 106, and one or more blowers 124. The controller 110 can be operably coupled to the suction pressure sensor 112, the discharge pressure sensor 116, and one or more liquid line sensors 120 such that the controller 110 receives pressure readings from each of the above sensors. The controller 110 can also be operably connected to one or more liquid line sensors 120 such that the controller 110 receives the liquid line temperature. The controller 110 can be operably coupled to the expansion device 106 such that the controller 110 can provide commands to the expansion device 106. The controller 110 can be operably connected to one or more blowers 124 such that the controller 110 can provide commands to one or more blowers 124. The controller 110 can include one or more processors and one or more memories.

[0032] The controller 110 can be configured to determine a pressure target based on the intermediate pressure within the compressor 102 and a cooling pressure differential threshold. In an embodiment, the pressure target can be the sum of the intermediate pressure in the compressor 102 and the cooling pressure differential threshold. In an embodiment, the cooling pressure differential threshold is a value stored in the memory of the controller 110.

[0033] The controller 110 can be configured to determine an intermediate pressure in the compressor 102. In an embodiment, the controller 110 is configured to determine the intermediate pressure based on the suction pressure measured by 112 and the discharge pressure measured by 116. In an embodiment, the controller 110 determines the intermediate pressure in the compressor 102 by taking the square root of the product of the suction pressure measured by 112 and the discharge pressure measured by 116.

[0034] The controller 110 can be configured to determine a pressure ratio setpoint based on a pressure target and the liquid line pressure measured by one or more liquid line sensors 120. The pressure ratio setpoint can be a desired pressure ratio. The pressure ratio can be defined as the discharge pressure of the compressor 102 divided by the suction pressure of the compressor 102. The air flow across the condenser 104 can affect the condensation of the working fluid received from the discharge port 118 of the compressor 102 in the condenser 104 and the pressure within the condenser 104. The air flow across the condenser 104 can thus affect the discharge pressure of the compressor 102 and the pressure ratio. In an embodiment, the pressure ratio setpoint is determined by comparing the pressure target with the pressure in the liquid line 122 measured by one or more liquid line sensors 120, and when the pressure target exceeds the pressure in the liquid line 122, the pressure ratio target is set to the current pressure ratio multiplied by the ratio of the pressure target to the pressure in the liquid line 122. When the pressure in the liquid line 122 exceeds the pressure target, the pressure ratio setpoint can be maintained at the current level.

[0035] The controller 110 can be configured to control one or more blowers to operate at a speed determined based on the determined pressure ratio setpoint. The control of the blowers can be any suitable control loop for controlling the air flow from one or more blowers 124 to achieve the determined pressure ratio setpoint. In an embodiment, the control loop for controlling the air flow is a closed-loop control. In an embodiment, the control loop for controlling the air flow includes a proportional integral derivative (PID) control loop.

[0036] The controller 110 can be configured to determine a subcooling setpoint based on a pressure target and the liquid line pressure in the compressor system. The subcooling setpoint is a setpoint that can be used as a control parameter for the expansion device 106. The expansion device 106 controls the outflow of the liquid line 122, and thus the subcooling setpoint and the corresponding control of the expansion device 106 can affect the pressure differential in the compressor system 100. In an embodiment, the controller 110 is configured to determine the subcooling setpoint by determining a liquid pressure differential, which is determined based on the difference between the pressure target and the actual pressure within the liquid line 122 measured by one or more liquid line sensors 120. The pressure differential can be converted into a temperature offset for subcooling. The temperature offset can then be applied to the current subcooling value to obtain the subcooling setpoint. The controller 110 can be configured to control the expansion device 106 based on the subcooling setpoint, such as by adjusting the orifice size within the expansion device 106. The control of the expansion valve 106 can be achieved through any suitable control loop to control the expansion device 106 based on the subcooling setpoint. In an embodiment, the control of the expansion device 106 can refer to the liquid line temperature measured by one or more liquid line sensors 120. In an embodiment, the control loop for controlling the expansion device 106 is a closed-loop control. In an embodiment, the control loop for controlling the expansion device 106 includes a PID control loop.

[0037] Figure 2 A flowchart showing a method 200 for controlling a compressor system according to an embodiment is shown. A pressure target 202 is determined. A liquid line pressure 204 is received. A pressure ratio setpoint 206 is determined, and a condenser blower 208 is operated based on the pressure ratio setpoint. Additionally, a subcooling setpoint 210 is determined, and an expansion device 212 is operated based on the subcooling setpoint.

[0038] Determine a pressure target 202. The pressure target can be a pressure level that maintains the cooling of one or more compressor system components, such as a compressor motor, an inverter, or any other component that is at least partially cooled using the working fluid of the compressor system. The pressure target can be determined based on the pressure differential used to provide cooling to one or more compressor system components. The pressure target can be based on an intermediate pressure within the compressor and a cooling pressure differential threshold. In an embodiment, the pressure target is determined by adding a minimum compressor cooling pressure differential value to the intermediate pressure within the compressor. Optionally, in an embodiment, the intermediate pressure 218 is determined based on the measured suction pressure and discharge pressure. The minimum compressor cooling pressure differential value can be a value stored in a memory. The cooling pressure differential threshold can be determined based on the cooling requirements of the components of the compressor system. In an embodiment, the cooling pressure differential threshold can be a value calculated based on one or more operating parameters of the compressor. In an embodiment, the cooling pressure differential threshold can be determined based on a mathematical model that correlates the pressure required for cooling with one or more operating parameters of the compressor.

[0039] Receive a liquid line pressure 204. The liquid line pressure can be a value measured by a pressure sensor positioned along the liquid line, such as one or more liquid line sensors 120 along the liquid line 122 as shown and described above. Figure 1 as shown and described above.

[0040] Determine a pressure ratio setpoint 206. The pressure ratio setpoint can be based on the pressure target determined at 202 and the liquid line pressure received at 204. The pressure ratio can be defined as the discharge pressure of the compressor of the compressor system divided by the suction pressure of the compressor. The airflow across the condenser of the compressor system can affect the discharge pressure and thus the pressure ratio. Therefore, the pressure ratio setpoint can be used to control the airflow across the condenser, the pressure at the compressor discharge port, and the liquid line pressure. This, in turn, affects the difference between the liquid line pressure and the intermediate pressure and thus affects the cooling provided to the components of the compressor system. In an embodiment, the pressure ratio setpoint can be determined by comparing the pressure target and a liquid line target and determining the pressure ratio setpoint based on that comparison, as Figure 3 shown and described below.

[0041] Operate the condenser blower 208 based on a pressure ratio setpoint. The operation 208 of the condenser blower based on the pressure ratio setpoint can be achieved through a control loop for the condenser blower air flow, which includes the pressure ratio setpoint as a variable. In an embodiment, the condenser blower 208 can be operated according to the pressure ratio setpoint with reference to a mathematical model that correlates the pressure ratio setpoint with the air flow. In an embodiment, the rotational speed of the condenser blower is adjusted according to the control loop. In an embodiment, the control loop for controlling the air flow is a closed-loop control. In an embodiment, the control loop for controlling the air flow includes a proportional-integral-derivative (PID) control loop.

[0042] Determine a subcooling setpoint 210. The subcooling setpoint can be a subcooling value for controlling an expansion device of the compressor system. The expansion device can control the outflow of the liquid line of the compressor system, so the expansion device can control the liquid line pressure of the compressor system. For example, when the cooling system relies on the pressure difference between the liquid line and the intermediate pressure in the compressor, the liquid line pressure can affect whether one or more compressor system components can be cooled by such a cooling system. The subcooling setpoint can be based on a subcooling value and an offset, which is calculated based on the pressure target determined at 202 and the liquid line pressure received at 204. In an embodiment, the subcooling setpoint can be determined by determining a liquid pressure difference, determining a subcooling offset, and adding the subcooling offset to the current subcooling value, as Figure 4 shown and described below.

[0043] Operate the expansion device 212 based on the subcooling setpoint. The operation 212 of the expansion device according to the subcooling setpoint can be achieved through a control loop that includes the subcooling setpoint as a variable. The expansion device can be, for example, Figure 1 the expansion device 106 shown and described above. The expansion device can have a controllable aperture size. In an embodiment, the expansion device is an electronic expansion valve. In an embodiment, the aperture size 212 of the expansion device is controlled based on the subcooling setpoint. In an embodiment, the expansion device is operated with reference to a mathematical model that correlates the expansion device position with the subcooling setpoint. The control based on the subcooling setpoint can refer to the current liquid line temperature. In an embodiment, the liquid line temperature can be measured by a temperature sensor. In an embodiment, the control loop for controlling the expansion device is a closed-loop control. In an embodiment, the control loop for controlling the expansion device includes a PID control loop.

[0044] Optionally, method 200 can include receiving the suction pressure 214, receiving the discharge pressure 216, and / or determining the intermediate pressure in the compressor 218. In an embodiment, the suction pressure can be received from a pressure sensor at the suction port of the compressor, such as Figure 1The suction pressure sensor 112 as shown and described above. In an embodiment, the discharge pressure can be received from a pressure sensor at the discharge port of the compressor, for example Figure 1 The discharge pressure sensor 116 as shown and described above. In an embodiment, the intermediate pressure 218 is determined based on one or more of the suction pressure received at 214 and the discharge pressure received at 216. In an embodiment, the intermediate pressure 218 is determined by taking the square root of the product of the suction pressure received at 214 and the discharge pressure received at 216. In an embodiment, the intermediate pressure determined at 218 is used to determine the pressure target 202.

[0045] During operation, the method 200 can iterate, for example, by returning from operating the condenser blower 208 and the expansion device 212 to receiving the suction pressure 214, receiving the discharge pressure 216, or returning to determining the pressure target 202. The iteration can be continuous, periodic, or triggered based on certain conditions, such as changes in the operating conditions of the compressor system, changes in the component temperatures of the compressor system, or changes in the ambient environmental conditions.

[0046] Figure 3 A flowchart showing an exemplary method for determining a pressure ratio set value according to an embodiment is shown. In Figure 3 The shown embodiment, when the liquid line pressure 204 is received, the pressure target determined at 202 is compared with the liquid line pressure received at 204 at 302.

[0047] When it is found in the comparison at 302 that the pressure target determined at 202 exceeds the liquid line pressure received at 204, the pressure ratio set value is determined at 304 based on the product of the current pressure ratio multiplied by the ratio of the pressure target to the liquid line pressure. In an embodiment, the formula for determining the pressure ratio set value is:

[0048]

[0049] When it is found that the liquid line pressure received at 204 exceeds the pressure target determined at 202, the pressure ratio set value can be maintained at the current pressure ratio at 306.

[0050] Once the pressure ratio set value is established at 304 or 306 based on the comparison at 302, the condenser blower 208 can be controlled based on the pressure ratio set value 204, as described above.

[0051] Figure 4A flowchart showing an exemplary method for determining a subcooling setpoint according to an embodiment is shown. After determining a target pressure at 202 and receiving a liquid line pressure at 204, a liquid pressure difference 402 is determined, a subcooling offset 404 is determined, and the subcooling offset is added to the current subcooling value 406.

[0052] Determine the liquid pressure difference 402. The liquid pressure difference can be a value in units of pressure, such as kPa. The liquid pressure difference can be the difference between the target pressure determined at 202 and the liquid line pressure received at 204. In an embodiment, the liquid pressure difference 402 is determined by subtracting the liquid line pressure received at 204 from the target pressure determined at 202.

[0053] Determine the subcooling offset 404 based on the liquid pressure difference determined at 402. The subcooling offset can be a temperature value in units of °F, °C, or K. In an embodiment, a function is used to convert the liquid pressure difference determined at 402 into a subcooling offset. In an embodiment, a mathematical model that correlates the liquid pressure difference with the subcooling offset is referred to. In an embodiment, a look-up table that correlates the liquid pressure difference with the subcooling offset is referred to. In an embodiment, the subcooling offset determined at 404 is proportional to the liquid pressure difference determined at 402.

[0054] Add the subcooling offset to the current subcooling value 406. The subcooling setpoint determined by adding the subcooling offset to the current subcooling value at 406 can then be used to control the expansion device 212 as described above.

[0055] Multiple aspects

[0056] It should be understood that any one of aspects 1-10 can be combined with any one of aspects 11-16.

[0057] Aspect 1. A method of controlling a compressor system, comprising:

[0058] Determine a pressure target based on an intermediate pressure within a compressor of the compressor system and a cooling pressure difference threshold;

[0059] Determine a pressure ratio setpoint based on the pressure target and a liquid line pressure within a liquid line of the compressor system;

[0060] Operate a condenser blower at a speed determined based on the determined pressure ratio setpoint;

[0061] Determine a subcooling setpoint based on the pressure target and the liquid line pressure in the compressor system; and

[0062] Operate an expansion device based on the determined subcooling setpoint.

[0063] Aspect 2. The method according to Aspect 1, wherein the intermediate pressure is determined based on the suction pressure of the compressor and the discharge pressure of the compressor.

[0064] Aspect 3. The method according to any one of Aspects 1-2, wherein determining the pressure ratio set value includes:

[0065] Comparing the pressure target with the liquid pipeline pressure;

[0066] When the pressure target exceeds the liquid pipeline pressure, setting the pressure ratio set value to the product of the current pressure ratio multiplied by the ratio of the pressure target to the liquid pipeline pressure;

[0067] When the liquid pipeline pressure reaches or exceeds the pressure target, setting the pressure ratio set value to the current pressure ratio.

[0068] Aspect 4. The method according to Aspect 3, wherein determining the speed includes referring to a mathematical model that correlates the pressure ratio with the speed of the condenser blower.

[0069] Aspect 5. The method according to any one of Aspects 3-4, further comprising applying a smoothing function to control the rate of change of the pressure ratio set value.

[0070] Aspect 6. The method according to any one of Aspects 3-5, further comprising comparing the determined pressure ratio set value with a pressure ratio limit, and setting the pressure ratio set value to the pressure ratio limit when the determined pressure ratio set value exceeds the pressure ratio limit.

[0071] Aspect 7. The method according to any one of Aspects 1-6, wherein determining the subcooling set value includes:

[0072] Determining a liquid pressure difference based on the pressure target and the liquid pipeline pressure;

[0073] Determining a subcooling offset based on the liquid pressure difference;

[0074] Determining the subcooling set value based on the subcooling offset and the current subcooling value.

[0075] Aspect 8. The method according to Aspect 7, wherein determining the subcooling offset includes referring to a mathematical model that correlates the subcooling offset with the liquid pressure difference.

[0076] Aspect 9. The method according to any one of Aspects 7-8, further comprising applying a smoothing function to control the rate of change of the subcooling set value.

[0077] Aspect 10. The method according to any one of Aspects 7 - 9, wherein operating the expansion device based on the subcooling set value includes setting the aperture size of the expansion device based on the subcooling set value.

[0078] Aspect 11. A compressor system, comprising:

[0079] A compressor;

[0080] A condenser;

[0081] An expansion device fluidly connected to the condenser through a liquid pipeline;

[0082] A liquid pipeline pressure sensor at the liquid pipeline of the compressor system;

[0083] An evaporator;

[0084] A blower configured to drive an air flow over the condenser; and

[0085] A controller configured to:

[0086] Determine a pressure target based on an intermediate pressure within the compressor and a cooling pressure difference threshold;

[0087] Determine a pressure ratio set value based on the pressure target and the liquid pipeline pressure measured by the liquid pipeline pressure sensor;

[0088] Control the blower to operate at a speed determined based on the determined pressure ratio set value;

[0089] Determine a subcooling set value based on the pressure target and the liquid pipeline pressure in the compressor system; and

[0090] Control the expansion device to operate based on the subcooling set value.

[0091] Aspect 12. The compressor system according to Aspect 11, wherein the expansion device is a controllable electronic expansion valve.

[0092] Aspect 13. The compressor system according to Aspect 12, wherein the processor is configured to control the expansion device to operate based on the subcooling set value by setting the aperture size of the controllable electronic expansion valve.

[0093] Aspect 14. The compressor system according to any one of Aspects 11-13 further includes a suction pressure sensor located at the suction port of the compressor and a discharge pressure sensor located at the discharge port of the compressor, and wherein the processor is further configured to determine an intermediate pressure within the compressor based on the suction pressure measured by the suction pressure sensor and the discharge pressure measured by the discharge pressure sensor.

[0094] Aspect 15. The compressor system according to any one of Aspects 11-14, wherein the controller is configured to determine a pressure ratio set value by:

[0095] Comparing the pressure target with the liquid line pressure;

[0096] When the pressure target exceeds the liquid line pressure, setting the pressure ratio set value to the product of the current pressure ratio and the ratio of the pressure target to the liquid line pressure; and

[0097] When the liquid line pressure reaches or exceeds the pressure target, setting the pressure ratio set value to the current pressure ratio.

[0098] Aspect 16. The compressor system according to any one of Aspects 11-15, wherein the controller is configured to determine a subcooling set value by:

[0099] Determining a liquid pressure difference based on the pressure target and the liquid line pressure;

[0100] Determining a subcooling offset based on the liquid pressure difference; and

[0101] Determining the subcooling set value based on the subcooling offset and the current subcooling value.

[0102] In all aspects, the examples disclosed in this application should be considered illustrative rather than restrictive. The scope of the present invention is defined by the appended claims rather than by the foregoing description; and all changes within the meaning and scope of the equivalents of the claims are intended to be included in the present invention.

Claims

1. A method for controlling a compressor system, comprising: Determining a pressure target based on a cooling pressure difference threshold and an intermediate pressure within a compressor of the compressor system; Determining a pressure ratio set value based on the pressure target and a liquid line pressure within a liquid line between a condenser and an expansion device of the compressor system; Operating a condenser blower at a speed determined based on the determined pressure ratio set value; Determining a subcooling set value based on the pressure target and the liquid line pressure in the compressor system; And Operating the expansion device based on the determined subcooling set value.

2. The method according to claim 1, wherein, Determining the intermediate pressure based on a suction pressure of the compressor and a discharge pressure of the compressor.

3. The method according to claim 1, wherein, Determining the pressure ratio set value includes: Comparing the pressure target with the liquid line pressure; When the pressure target exceeds the liquid line pressure, setting the pressure ratio set value to a product of a current pressure ratio and a ratio of the pressure target to the liquid line pressure; When the liquid line pressure reaches or exceeds the pressure target, setting the pressure ratio set value to the current pressure ratio.

4. The method according to claim 3, wherein, Determining the speed includes referring to a mathematical model that correlates the pressure ratio with the speed of the condenser blower.

5. The method according to claim 3, further comprising applying a smoothing function to control a rate of change of the pressure ratio set value.

6. The method according to claim 3, further comprising comparing the determined pressure ratio set value with a pressure ratio limit and setting the pressure ratio set value to the pressure ratio limit when the determined pressure ratio set value exceeds the pressure ratio limit.

7. The method according to any one of claims 1 - 6, wherein Determining the subcooling set value includes: Determining a liquid pressure difference based on the pressure target and the liquid line pressure; Determining a subcooling offset based on the liquid pressure difference; Determining the subcooling set value based on the subcooling offset and a current subcooling value.

8. The method according to claim 7, wherein Determining the subcooling offset includes referring to a mathematical model that correlates the subcooling offset with the liquid pressure difference.

9. The method according to claim 7, further comprising applying a smoothing function to control a rate of change of the subcooling set value.

10. The method according to claim 7, wherein, Operating the expansion device based on the subcooling set value includes setting an aperture size of the expansion device based on the subcooling set value.

11. A compressor system, comprising: A compressor; A condenser; An expansion device fluidly connected to the condenser via a liquid line; A liquid line pressure sensor at a liquid line of the compressor system; An evaporator; A blower configured to drive an air flow over the condenser; And A controller configured to: Determine a pressure target based on a cooling pressure difference threshold and an intermediate pressure within the compressor; Determine a pressure ratio set value based on the pressure target and a liquid line pressure within a liquid line between the condenser and the expansion device measured by the liquid line pressure sensor; Control the blower to operate at a speed determined based on the determined pressure ratio set value; Determine a subcooling set value based on the pressure target and the liquid line pressure in the compressor system; and Control the expansion device to operate based on the subcooling setpoint.

12. The compressor system according to claim 11, wherein, The expansion device is a controllable electronic expansion valve.

13. The compressor system according to claim 12, wherein, The controller is configured to control the expansion device to operate based on the subcooling setpoint by setting the aperture size of the controllable electronic expansion valve.

14. The compressor system according to claim 11 further includes a suction pressure sensor located at the suction inlet of the compressor and a discharge pressure sensor located at the discharge outlet of the compressor, and wherein, The controller is further configured to determine the intermediate pressure within the compressor based on the suction pressure measured by the suction pressure sensor and the discharge pressure measured by the discharge pressure sensor.

15. The compressor system according to claim 11, wherein, The controller is configured to determine the pressure ratio setpoint by: Comparing the pressure target with the liquid line pressure; When the pressure target exceeds the liquid line pressure, setting the pressure ratio setpoint to the product of the current pressure ratio and the ratio of the pressure target to the liquid line pressure; And When the liquid line pressure reaches or exceeds the pressure target, setting the pressure ratio setpoint to the current pressure ratio.

16. The compressor system according to any one of claims 11-15, wherein, The controller is configured to determine the subcooling setpoint by: Determining a liquid pressure difference based on the pressure target and the liquid line pressure; Determining a subcooling offset based on the liquid pressure difference; And Determining the subcooling setpoint based on the subcooling offset and the current subcooling value.

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