Control of refrigeration circuit

Abstract

A controller (100) for a refrigeration circuit (10) is disclosed, the controller (100) configured to monitor a current set of conditions (50) associated with the refrigeration circuit, the current set of conditions (50) including a space temperature of a temperature controlled space associated with the refrigeration circuit. The controller (100) has a simulation module (102) configured to determine a limit setting (152) for a control variable of the refrigeration circuit by an iterative optimization process based on a model (110) corresponding to the refrigeration circuit. The objective function for optimization is related to the operating efficiency. The controller further includes a dynamic control module (160) configured to: based on monitoring of the performance parameter during operation of the refrigeration circuit, adjust an operational setting of the control variable over an operational range to target a performance threshold for the monitored performance parameter; and applying the limit setting received from the simulation module as a limit of the operating range.

Description

Technical Field

[0001] The present invention relates to controlling a refrigeration circuit (such as may be used in an HVAC-R system), and in particular to controlling control variables of a refrigeration circuit based on minimum performance parameters and efficiency-related optimization. Background Art

[0002] It is known to provide a refrigeration circuit that can be operated using an operating map of operating conditions. It is known to adjust various operating parameters (e.g., compressor speed or expansion valve setting) during operation of the refrigeration circuit. Such control is typically based on target thermodynamic parameters in or around the refrigeration circuit (e.g., a target superheat upstream of the compressor) or a target temperature of the process medium that exchanges heat with the refrigerant of the refrigeration circuit at a heat exchanger in the refrigeration circuit.

[0003] It would be desirable to provide an improved method of controlling a refrigeration circuit based on the performance requirements of the system. Summary of the Invention

[0004] According to a first aspect, a controller for a refrigeration circuit is disclosed;

[0005] wherein the controller is configured to monitor a set of current conditions associated with the refrigeration circuit, the set of current conditions including a space temperature of a temperature-controlled space associated with the refrigeration circuit;

[0006] wherein the controller has a simulation module configured to determine limit settings of control variables for the refrigeration circuit through an iterative optimization process based on a model corresponding to the refrigeration circuit;

[0007] wherein the iterative optimization process is defined based on an objective function related to the operating efficiency of the refrigeration circuit and is determined based on evaluating the model for corresponding simulated operating points;

[0008] wherein the simulated operating point is defined by the set of monitored current conditions and by the simulated settings for the control variables that are iteratively varied during the optimization process, and

[0009] The controller further includes a dynamic control module configured to: adjust an operational setting of a control variable within an operating range based on monitoring a performance parameter during operation of the refrigeration circuit to target a performance threshold for the monitored performance parameter; and apply limit settings received from the simulation module as limits of the operating range.

[0010] The limit settings for the control variables are defined based on the simulated operating point determined to correspond to the objective function being at an optimal value (e.g., maximum value) or within a range including the optimal value (e.g., maximum value) corresponding to near-optimal performance.

[0011] The dynamic control module may be configured to adjust operational settings of the control variables during operation of the refrigeration circuit based on concurrent monitoring of performance parameters during operation of the refrigeration circuit.

[0012] The model can have uncertain performance parameters.

[0013] The objective function may be a coefficient of performance.

[0014] The coefficient of performance may be determined based on a simulated heat transfer capability (eg, cooling capability) and a corresponding simulated power consumption, both of which are determined based on a model.

[0015] When the current conditions relate to operation of the refrigeration circuit in a cooling mode in which the second heat exchanger operates as an evaporator for cooling the associated temperature-controlled environment, the heat transfer capacity may correspond to the cooling capacity. When the current conditions relate to operation of the refrigeration circuit in a cooling mode in which the second heat exchanger operates as a condenser for heating the associated temperature-controlled environment, the heat transfer capacity may correspond to the heating capacity.

[0016] The controller may be configured to simulate the operation of the refrigeration circuit at a simulated operating point using the digital twin.

[0017] The monitored performance parameter may be a rate of change of a monitored condition associated with the refrigeration circuit.

[0018] The target performance threshold for the monitored performance parameter can be selected from the group consisting of: (i) a heat transfer parameter related to the heat transfer capacity of the refrigeration circuit, such as: a predetermined minimum heat transfer capacity of the refrigeration circuit; or a predetermined minimum amplitude of the rate of change of the space temperature of the monitored temperature-controlled space; and (ii) a predetermined minimum refrigerant superheat at a superheat monitoring location along the suction line of the refrigeration circuit.

[0019] The dynamic control module includes a PI or PID control module configured to control a control variable of the refrigeration circuit during operation of the refrigeration circuit. The PI or PID control module can be configured to change the control variable based on an error signal associated with a difference between a performance threshold and a monitored performance parameter. A limit setting for the control variable can be applied as a saturation limit for the PI or PID controller.

[0020] The target performance threshold for the monitored performance parameter may be a predetermined minimum magnitude of a rate of change of the monitored space temperature. The PI or PID control module may (i) be configured to control an operating parameter of the compressor as a controlled variable; and (ii) be configured to determine an error signal as a difference between the predetermined minimum magnitude of the rate of change of the space temperature and the rate of change of the monitored space temperature.

[0021] The model can be configured to determine the simulated power consumption based on one or more of: (i) operating parameters of the compressor as control variables or derived from a current set of conditions; (ii) operating parameters of a first fan associated with the first heat exchanger as control variables or derived from a current set of conditions; and / or (iii) operating parameters of a second fan associated with the second heat exchanger as control variables or derived from a current set of conditions.

[0022] The controller may be configured to repeat the optimization process and update the limit settings. The controller may be configured to repeat the optimization process at predetermined intervals; and / or to repeat the optimization process based on a threshold change or rate of change in determining a current condition in a set of current conditions.

[0023] The simulation module may be configured to determine limit settings for a plurality of control variables of the refrigeration circuit through an iterative optimization process. A simulated operating point may be defined by a set of monitored current conditions and corresponding simulated settings for the plurality of control variables. For each control variable, the simulation control module may be configured to determine a corresponding limit setting through the optimization process. The dynamic control module may be configured to adjust each corresponding operating setting of the control variable within a corresponding operating range to target a performance threshold for the monitored performance parameter, and to apply each corresponding limit setting received from the simulation module as a limit of the corresponding operating range.

[0024] When there are multiple control variables, the above references to the variation, determination and setting of a control variable or corresponding limit are to be interpreted as corresponding to the (corresponding) variation, determination and setting of each corresponding control variable or limit.

[0025] According to a second aspect, a refrigeration circuit is disclosed comprising a compressor, a first heat exchanger, an expansion device, a second heat exchanger, and the controller according to the first aspect.

[0026] According to a third aspect, a method of controlling a refrigeration circuit (e.g., a control circuit according to the second aspect) using the controller according to the first aspect is disclosed, wherein a control variable of the refrigeration circuit is variable during operation of the refrigeration circuit, the method comprising:

[0027] monitoring a set of current conditions associated with the refrigeration circuit, the set of current conditions including a space temperature of a temperature-controlled space associated with the refrigeration circuit;

[0028] The simulation module conducts an iterative optimization process to determine the limit settings of the control variables for the refrigeration circuit;

[0029] Apply limit settings as limits to the operating range for the control variable;

[0030] monitoring performance parameters for the refrigeration circuit during operation of the refrigeration circuit;

[0031] The dynamic control module adjusts an operational setting of the control variable within an operating range to target a performance threshold for the monitored performance parameter;

[0032] Whereby, the dynamic control module biases operation of the refrigeration circuit to the limit setting of the control variable determined by the optimization process when the limit setting corresponds to compliance with the performance threshold during operation of the refrigeration circuit; and

[0033] Thus, when the limit setting corresponds to a failure to meet a performance threshold during operation of the refrigeration circuit, the dynamic control module biases operation of the refrigeration circuit away from the limit setting of the controlled variable to achieve the target performance threshold.

[0034] According to a fourth aspect, there is provided a non-transitory machine-readable medium comprising instructions which, when executed by a processor, cause the performance of the method according to the third aspect.

[0035] The controllers described herein may include a processor. The controller and / or processor may include any suitable circuitry to perform the methods described herein and as shown. The controller or processor may include: at least one application-specific integrated circuit (ASIC); and / or at least one field-programmable gate array (FPGA); and / or a single-processor architecture or a multi-processor architecture; and / or a sequential (von Neumann) / parallel architecture; and / or at least one programmable logic controller (PLC); and / or at least one microprocessor; and / or at least one microcontroller; and / or a central processing unit (CPU) to perform the methods and / or the functions for which the controller or processor is configured.

[0036] The controller may include, or the processor may include, or be in communication with, one or more memories that store data described herein and / or store machine-readable instructions (e.g., software) for performing the processes and functions described herein (e.g., determination of parameters and execution of control routines).

[0037] The memory can be any suitable non-transitory computer-readable storage medium, one or more data storage devices, and can include a hard disk and / or solid-state memory (e.g., flash memory). In some examples, the computer-readable instructions can be transmitted to the memory via a wireless signal or via a wired signal. The memory can be a permanent, non-removable memory, or it can be a removable memory (e.g., a Universal Serial Bus (USB) flash drive). The memory can store a computer program including computer-readable instructions that, when read by a processor or controller, causes the methods described herein and / or illustrated in the figures to be performed. The computer program can be software or firmware, or a combination of software and firmware.

[0038] Those skilled in the art will understand that, unless mutually exclusive, features described in connection with any one of the above aspects may be applied to any other aspect after mutatis mutandis. In addition, unless mutually exclusive, any feature described herein may be applied to any aspect and / or combined with any other feature described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be described with reference to the accompanying drawings, in which:

[0040] Figure 1 The refrigeration circuit is schematically shown;

[0041] Figure 2 A flow chart schematically illustrates control actions performed by a simulation module of a controller for a refrigeration circuit;

[0042] Figure 3 The analog module and dynamic module of the controller are schematically shown;

[0043] Figure 4 A flow chart schematically illustrates control actions performed by a dynamic module of a controller for a refrigeration circuit;

[0044] Figure 5 and Figure 6 a graph showing performance and efficiency parameters of a refrigeration circuit over an entire operating range of control variables for the refrigeration circuit;

[0045] Figure 7 Schematically illustrates example operating ranges for control variables for a refrigeration circuit;

[0046] Figure 8 is a flow chart of a method of controlling a refrigeration circuit; and

[0047] Figure 9 A machine-readable medium and a processor are schematically shown. DETAILED DESCRIPTION

[0048] Figure 1 An example refrigeration circuit 10 (e.g., a heat pump or vapor compression cycle) for transferring heat from one heat exchange medium to another heat exchange medium (e.g., between a controlled environment 2 (e.g., a temperature-controlled space) and an ambient environment) is schematically illustrated. Example applications of such refrigeration circuits include chiller systems (e.g., for centralized heating and cooling of process fluids (e.g., water circulated within a building or other facility to a heat transfer terminal (e.g., for room heating)) or refrigeration systems (e.g., HVAC systems or transport refrigeration systems).

[0049] Figure 1 The refrigeration circuit 10 comprises a compressor 12, a first heat exchanger 14, an expansion device 16 and a second heat exchanger 18. The first heat exchanger 14 and the second heat exchanger 18 are provided with respective fans 15,19.

[0050] The refrigeration circuit 10 may be configured to define two flow paths through a heat pump (commonly referred to as a reversible heat pump) for operating in different modes (ie, a cooling mode and a heating mode).

[0051] The terms "heating" and "cooling" refer to the direction of heat transfer relative to a heat exchange medium that is actively heated or cooled, for example, to maintain a set point temperature in a temperature-controlled space (e.g., air in a cargo space, or process fluid / water in a chiller system). In this disclosure, this is referred to as a conditioned heat exchange medium.

[0052] Figure 1 A refrigeration circuit is shown in cooling mode whereby there is a flow path (indicated by arrows) extending (in flow order) through the compressor 12 , a first heat exchanger 14 acting as a condenser for rejecting heat to an ambient heat exchange medium (e.g., ambient air), an expansion device 16 , a second heat exchanger 18 acting as an evaporator for receiving heat from the conditioned heat exchange medium in the temperature-controlled space 2 , and back to the compressor 12 . Figure 1 The flow path of the first heat exchanger 14 is used to cool the conditioned heat exchange medium, and the second heat exchanger 18 is in thermal communication with the conditioned heat exchange medium. Accordingly, the fan 15 associated with the first heat exchanger 14 can be referred to as a condenser fan 15, and the fan 19 associated with the second heat exchanger 18 can be referred to as an evaporator fan 19.

[0053] As is known in the art, a suitable valve arrangement may be provided to reverse the flow direction for heating mode so that the second heat exchanger 18 acts as a condenser for rejecting heat to the conditioned heat exchange medium and the first heat exchanger 14 acts as an evaporator for receiving heat from the ambient heat exchange medium.

[0054] Further description reference Figure 1Refrigeration circuit in cooling mode shown. The portion of the flow path between compressor 12 and condenser 14 is called the discharge line, the portion of the flow path between condenser 14 and expansion device 16 is called the liquid line, the portion of the flow path between expansion device 16 and evaporator 18 is called the distribution line, and the portion of the flow path between evaporator 18 and compressor 12 is called the suction line.

[0055] A suction line heat exchanger 20 is provided for heat exchange between the refrigerant in the liquid line and the suction line. The suction line heat exchanger 20 has a liquid line portion 22 along the liquid line and a suction line portion 24 along the suction line. In other examples, such a suction line heat exchanger may not be present.

[0056] exist Figure 1 When used in the cooling mode, the gaseous refrigerant is compressed to a high pressure at compressor 12 and condensed in condenser 14 to reject heat to the ambient heat exchange medium, thereby providing high-pressure and high-temperature condensed refrigerant in the liquid line. The condensed refrigerant is expanded at expansion device 16 to provide a multiphase refrigerant stream to evaporator 18. This stream evaporates in evaporator 18 before being provided to compressor 12. The evaporation at evaporator 18 cools the conditioned heat exchange medium associated with the evaporator.

[0057] When the suction line heat exchanger 20 is present, it transfers heat from the high-temperature liquid refrigerant in the liquid line to the relatively lower temperature refrigerant in the suction line. This can be thought of as temporarily removing thermal energy from the refrigerant for the portion of the circuit that includes the expansion device and the evaporator. This can allow the refrigerant to expand to a relatively lower pressure and saturation temperature, absorbing heat from the ambient heat exchange medium at the evaporator. The thermal energy is returned to the refrigerant at the suction line portion 24 of the suction line heat exchanger, which can correspond to further evaporation and / or superheating of the refrigerant upstream of the compressor 12.

[0058] Figure 1 Further monitoring and control equipment of, or associated with, the refrigeration circuit 10 is shown. A controller 100 is provided and operatively connected to control operating variables of the compressor 12 and / or the expansion device 16. The controller 100 may control only one of the compressor 12 and the expansion device 16, or may control both. For example, the expansion valve 16 may be provided with its own controller (e.g., as an electronic expansion valve (EXV)) or may be configured as a thermostatically controlled valve.

[0059] The controller 100 is also coupled to one or more sensors around the refrigeration circuit for monitoring one or more current conditions of the refrigeration circuit, which may include one or more thermodynamic parameters of the refrigerant, and / or one or more parameters associated with the ambient heat exchange medium and / or the conditioned heat exchange medium.

[0060] Figure 1 Monitoring locations for such sensors are shown, including a discharge line monitoring location 32 along the discharge line, a first liquid line monitoring location 34 along the liquid line upstream of the suction line heat exchanger 20, a second liquid line monitoring location 35 along the liquid line downstream of the suction line heat exchanger 20, a distribution line monitoring location 36 along the distribution line, a first suction line monitoring location 38 along the suction line upstream of the suction line heat exchanger 20, and a second suction line monitoring location 39 along the suction line downstream of the suction line heat exchanger 20. Another monitoring location 40 is associated with the conditioned heat exchange medium; for example, a temperature sensor may be provided to monitor the flow rate of supply air provided to or / and return air provided from the temperature-controlled space 2, or a temperature sensor may be provided within the temperature-controlled space 2. Similarly, another monitoring location 42 is associated with the ambient heat exchange medium 4; for example, a temperature sensor may be provided to monitor the temperature of the ambient airflow delivered to the condenser 14 (e.g., by the condenser fan 15). The temperature sensor can be co-located with the condenser 14 or condenser fan 15 for such monitoring, or otherwise disposed in the ambient heat exchange medium. Any one or more monitoring locations can be used in a refrigeration circuit according to the present disclosure. Furthermore, any monitoring location where at least one sensor is disposed can be provided with a temperature sensor and / or a pressure sensor.

[0061] Although not shown schematically with a link between the monitoring location and the controller 100, signals from the pressure and / or temperature sensors may be provided to the controller 100 for use in controlling the refrigeration circuit, as will be discussed below.

[0062] Figure 2 The flowchart schematically shows a control action implemented by the simulation module 102 of the controller 100. The simulation module 102 includes a model 110 or is configured to reference (eg, remotely access) the model 110.

[0063] The model is configured to correlate one or more parameters associated with an operating point of the refrigeration circuit with one or more performance parameters of the refrigeration circuit. The term "operating point" refers to a state of the refrigeration circuit, such that example parameters associated with the operating point describe thermodynamic parameters or operating parameters associated with the corresponding portion of the refrigeration circuit. For example, such parameters may include one or more of the following: the temperature of the temperature-controlled space 2 (e.g., the temperature monitored by the temperature sensor at monitoring location 40), the temperature of the ambient heat exchange medium (e.g., the temperature monitored by the temperature sensor at monitoring location 42), an operating parameter of the condenser fan 15 (e.g., fan speed or a power parameter associated with the power supplied to the fan (e.g., power, frequency, voltage, or current)), an operating parameter of the evaporator fan 19 (which may be similar to the operating parameter of the condenser fan), an operating parameter of the expansion device 16 (e.g., a valve setting associated with the state of the valve, such as a parameter associated with the degree to which the valve is open and / or whether the valve is in a closed state), and an operating parameter of the compressor 12 (e.g., a compressor speed parameter (e.g., rotational speed (e.g., revolutions per minute), angular velocity, or frequency of rotation), or a power parameter associated with the power supplied to the compressor (e.g., power, frequency, voltage, or current)). Furthermore, such parameters may include one or more temperatures or pressures of the refrigerant surrounding the refrigeration circuit. As is known in the art, refrigerant pressure can be used to determine the saturation temperature of the refrigerant and thereby allow determination of the amount of subcooling or superheating of the refrigerant at an associated location.

[0064] exist Figure 2 In the example of FIG, a model 110 is configured to correlate four parameters 50, 150 (operating point parameters) related to the operating point of a refrigeration circuit with two performance parameters 112, 114. In this example, the operating point parameters are the temperature of the ambient heat exchange medium, the temperature of the temperature-controlled space, the condenser fan speed, and the compressor speed parameter. The model 110 is configured to correlate these parameters with the cooling capacity of the refrigeration circuit and the power consumption of the refrigeration circuit. The expression cooling capacity has a well-known meaning in the art and refers to the amount of heat that can be removed by the system. The SI unit is the watt (W), and the cooling capacity is typically derived as the product of the mass flow rate (e.g., the mass flow rate of the ambient heat exchange medium or the regulated heat exchange medium), the corresponding specific heat capacity (Cp), and the observed temperature change.

[0065] Although specific examples of relationships between operating point parameters and performance parameters have been described, it should be understood that in other examples, model 110 can be configured to implement various similar relationships relating different or overlapping sets of operating point parameters to different or overlapping sets of performance parameters. Such relationships can be based on any suitable number of operating point parameters (rather than four parameters as in the above example).

[0066] like Figure 2 As shown, three of the example operating point parameters 50 are received as inputs from outside the simulation module 102 (e.g., from sensors at corresponding monitoring locations), while at least one of the operating point parameters 150 is iteratively derived by the simulation module 102 and corresponds to a control variable of the refrigeration circuit. In this example, the corresponding control variable 150 is a compressor speed parameter 150. Figure 2 As shown, this may be derived externally from the simulation module (102) (e.g., as an output of a motor or motor controller for the compressor) or iteratively derived within the simulation module 102. An initial value for the control variable 150 may be obtained by observation, and subsequent values ​​for the control variable 150 may be determined by the simulation module 102 without corresponding changes to the control variable 150 as applied to the refrigeration circuit, as will be described in further detail below.

[0067] In this example, another performance parameter 120 is derived based on the performance parameters 112, 114. Specifically, a coefficient of performance (COP) is determined based on the cooling capacity 112 of the refrigeration circuit and the power consumption 114 of the refrigeration circuit. In other examples, the model 110 can directly relate the operating point parameters 50, 150 to a single performance parameter (e.g., COP).

[0068] At block 130, the simulation module 102 is configured to iteratively evaluate a performance parameter (e.g., COP) to determine a value for the control variable that corresponds to an optimal (e.g., maximum) value of the performance parameter (e.g., COP). It should be understood that this evaluation occurs iteratively, rather than based on a single value of the control variable and a single variation of the corresponding performance parameter. Thus, block 130 of the simulation module 102 can be considered to implement iterative adjustment of the control variable to search for an optimal value of the performance parameter. As is known in the art, it is contemplated that many suitable methods for performing such iterative optimization or search can be implemented. Thus, block 130 and the simulation module 102 can be considered to implement an optimization process in which an objective function is defined based on the performance parameter (e.g., to maximize the COP), and the independent variable is the control variable 150.

[0069] Figure 2 It shows how the control variables are iteratively adjusted (140) and the adjusted values ​​are provided to the model 110 for further iteration. The iterative adjustment of the control variables within the simulation module 102 occurs only within the simulation module 102, without the need for corresponding direct adjustment of the values ​​of the control variables applied to the refrigeration circuit during the iterative adjustment. Therefore, the model 110 can be considered to operate based on a combination of the current operating conditions 50 derived from monitoring of the refrigeration circuit and the simulated settings 150 for the control variables.

[0070] When block 130 determines that the optimal performance parameter is achieved, a corresponding value 152 for the controlled variable is output as a limit setting 152 for the controlled variable. The limit setting is provided to the dynamic control module, as will now be described.

[0071] like Figure 3 As schematically shown in FIG, controller 100 includes a simulation module 102 and a dynamic control module 160. Simulation module 102 is configured to derive limit settings for a control variable based on current conditions associated with the operating point of the refrigeration circuit (i.e., without directly adjusting the control variable as applied in the refrigeration circuit—for example, without directly adjusting the compressor speed). In contrast, dynamic control module 160 is configured to adjust the operation of the refrigeration circuit by adjusting the control variable as applied in the refrigeration circuit (e.g., directly adjusting the compressor speed). However, rather than simply utilizing the value 152 for the control variable determined by simulation module 102, dynamic control module 160 determines whether to adopt value 152 based on one or more other performance-related objectives.

[0072] Figure 4 FIG. 1 is a flow chart showing the control actions of the dynamic control module 160. Figure 4 As indicated by the dashed arrows in FIG, various parameters are provided from outside of dynamic control module 160, while other parameters may be determined or stored locally within the dynamic control module. First, dynamic control module 160 receives limit settings 152 from simulation module 102. Second, dynamic control module 160 receives performance parameters related to the performance of the refrigeration circuit. The performance parameters may be observed performance parameters (e.g., derived from monitoring signals from one or more sensors). In this example, the performance parameter is the rate of change of temperature in temperature-controlled space 2, as derived from a series of temperature observations obtained by controller 100 from temperature sensors at corresponding monitoring locations 42.

[0073] Dynamic control module 160 stores or references performance thresholds 130 for corresponding performance parameters. For example, a performance threshold may correspond to a minimum magnitude of the rate of temperature change in temperature-controlled space 2 during cooling operation (eg, a minimum magnitude of 0.21°C / minute).

[0074] The dynamic control module 160 is configured to determine a value 154 for the controlled variable based on comparing the performance parameter to the performance threshold; and / or based on the limit setting 152 received from the simulation module 102, so as to (i) target compliance with the performance threshold, and (ii) apply the limit setting 152 if the limit setting 152 from the simulation module 102 corresponds to compliance with the performance threshold.

[0075] The dynamic control module 160 may determine the value 154 for the controlled variable in any suitable manner to achieve this effect. For example, the dynamic control module 160 may be configured to implement a gradual change in the controlled variable based on performance parameter comparisons and / or limit settings.

[0076] While specific examples of performance thresholds and associated performance parameters have been described, it should be understood that other performance parameters and thresholds may be applied, and that two or more such performance parameters may be monitored and two or more such thresholds may be targeted. For example, in addition to or in lieu of a minimum heat transfer capacity of the refrigeration circuit and / or a minimum amplitude of the rate of change of the space temperature of the temperature-controlled space, the dynamic control module may monitor a performance parameter related to a thermodynamic property associated with the refrigeration circuit (e.g., superheat at a superheat monitoring location along the suction line of the refrigeration circuit (e.g., upstream of the compressor, optionally upstream or downstream of any suction line heat exchanger (when provided))). Monitoring such parameters may be desirable when associated with the operational requirements or benefits of the refrigeration circuit. For example, it may be desirable to have a minimum superheat in the refrigerant supplied to the compressor to prevent liquid hammer and associated adverse effects.

[0077] A preferred embodiment of the dynamic control module 160 is as a PID (Proportional-Integral-Derivative) or PI (Proportional-Integral) controller. This type of controller is configured to adjust a variable based on a target, such as to reduce the error between two signals while minimizing overshoot and related behavior. A PI (or PID) controller can be used in the dynamic control module 160 to adjust a controlled variable (e.g., a compressor speed parameter) to minimize an error signal determined as the difference between a performance parameter (e.g., the observed rate of change of temperature in a temperature-controlled space) and a performance threshold for the performance parameter (e.g., a minimum rate of change of that temperature).

[0078] When the dynamic control module is implemented as a PI or PID controller, the limits set for the controlled variables are applied as saturation limits for the PI or PID controller, specifically the lower saturation limit (minimum value). The saturation limit of a PI or PID controller is a term used in the relevant technical field and relates to the limit value (e.g., maximum or minimum value) that the PI or PID controller can output.

[0079] By applying the limit setting as a saturation lower limit, the PI or PID controller is configured to ensure that the control variable is set to a value that is equal to or greater than the value determined by the simulation module 102 for optimal operation, but is free to adjust to a higher setting that may be required to achieve a minimum performance threshold (e.g., a minimum temperature change rate). This provides a particularly efficient implementation of the desired control function that minimizes control complexity and equipment cost.

[0080] Figure 5 and Figure 6 Graphs are shown for performance parameters of a refrigeration circuit. In each graph, the X-axis corresponds to the change in a controlled variable, which in this example is the compressor speed parameter. The plotted physical quantities are in different units, with solid lines 502 and 506 corresponding to coefficients of performance (COPs), and dashed lines 504 and 530 corresponding to cooling capacities. Solid line 502 corresponds to the compressor COP, while solid line 506 corresponds to the overall COP. Dashed line 504 corresponds to the system cooling capacity, while dashed line 530 corresponds to a performance threshold (e.g., minimum cooling capacity) for the corresponding performance parameter.

[0081] Point 508 on the overall COP line 506 corresponds to the maximum efficiency for the refrigeration circuit.

[0082] Figure 5 Two points on the cooling capacity line 504 are shown: a first point 510 corresponding to the intersection with the performance threshold line 503 ; and a second point 512 corresponding to the maximum efficiency point 508 .

[0083] The controller 100 described above is configured to determine the limit setting 152 for the controlled variable using the simulation module 102 such that the limit setting 152 for the controlled variable corresponds to the maximum efficiency point 508 and the second point 512 on the cooling capacity line 504 .

[0084] The dynamic control module is configured such that, in the absence of a limit setting, the value of the control variable is adjusted to target a performance threshold (eg, minimum cooling capacity represented by line 530). Figure 5 The first point 510 on the cooling capability line 504 is shown above and is annotated as "Performance Threshold" where it intersects the X-axis for the controlled variable.

[0085] exist Figure 5 In the example shown, the value of the controlled variable corresponding to the performance threshold is lower than the value of the limit setting for the controlled variable (corresponding to optimal operation). When the controlled variable is a compressor speed parameter, this effectively means that it is more efficient to operate at a compressor speed higher than that required to simply meet the performance threshold (e.g., a minimum temperature change rate). The dynamic control module 160 is configured to apply the limit setting as a limit (particularly a lower limit) to the operating range of the controlled variable, and therefore, the dynamic control module 160 causes the limit setting for the controlled variable to be applied. The dynamic control module maintains the controlled variable at the limit setting, despite the bias of the limit setting toward targeting the performance threshold, because the bias would simply drive the controlled variable to a lower value and, therefore, be prevented by the limit setting (e.g., as applied by a lower saturation limit in a PI or PID controller).

[0086] exist Figure 6In the illustrated comparative example, the same COP and cooling capacity lines are shown, but the performance threshold is higher, such that the first point 610 where the cooling capacity line 504 intersects the performance threshold 630 corresponds to a value of the controlled variable above the limit setting (corresponding to optimal performance). The dynamic control module still applies the limit setting as the limit (particularly the lower limit) of the operating range of the controlled variable, but is free to adjust to higher values ​​of the controlled variable to target the performance threshold. For example, the dynamic control module can be adjusted within a range above the limit setting until a value is found that results in performance at the performance threshold (e.g., at a minimum threshold cooling capacity).

[0087] These comparison examples are Figure 7 As schematically shown in Figure 7 A range of values ​​for a controlled variable is schematically illustrated as a horizontal line, with various settings for the controlled variable indicated along the range. In example (A), the performance setting corresponding to a performance threshold (e.g., minimum cooling rate) is lower than the limit setting corresponding to optimal performance. The dynamic control module applies the limit setting as the lower limit of the operating range, effectively constraining the refrigeration circuit to operate at the limit setting of the controlled variable. In example (B), the performance setting corresponding to the performance threshold is higher than the limit setting corresponding to optimal performance and is therefore within the operating range defined by the limit settings. Therefore, the dynamic control module adjusts the value of the controlled variable toward the performance setting.

[0088] Figure 8 A flow chart of a method 800 of controlling a refrigeration circuit to change a control variable of the refrigeration circuit during operation of the refrigeration circuit is schematically shown. By way of example only, reference will be made to the above description of Figures 1 to 4 The controller 100 and the refrigeration circuit 10 are described.

[0089] In block 802 , a controller monitors current conditions of a refrigeration circuit (eg, a space temperature of a temperature-controlled space associated with the refrigeration circuit), and optionally one or more other operating conditions as described above.

[0090] In block 804, the simulation module of the controller determines limit settings for the control variables of the refrigeration circuit. The simulation module performs an iterative optimization process to determine the limit settings. The iterative optimization process is defined based on an objective function related to the operating efficiency of the refrigeration circuit. The objective function is determined based on evaluating the model and is determined by evaluating the model for the refrigeration circuit at corresponding simulated operating points (i.e., operating points that vary based on iterative changes in the control variables). The simulated operating points are defined by a set of monitored current conditions and by the simulated settings for the control variables.

[0091] like Figure 8As shown, the determined limit settings 805 resulting from the optimization process are stored, for example, in a memory of the controller.

[0092] At block 806, the controller's dynamic control module monitors a performance parameter (e.g., a performance parameter related to the rate of change of the temperature-controlled space or the cooling capacity of the monitored system). At block 808, the dynamic control module adjusts the operational setting of the control variable (i.e., the setting applied to the refrigeration circuit, not just the simulated setting) within an operating range to target a performance threshold 807 (e.g., a predetermined performance threshold stored in the controller's memory) for the monitored performance parameter. The limit settings received from the simulation module are applied as limits to the operating range, for example, as described above.

[0093] Figure 9 Schematically, a machine readable medium 900 is shown that includes instructions 902. The instructions are defined such that when executed by a compressor 904, the method described herein (e.g., as described with reference to FIG. Figure 8 and / or reference Figures 1 to 7 any of the methods described in ).

Claims

1. A controller (100) for a refrigeration circuit (10); in, The controller (100) is configured to monitor a set of current conditions (50) associated with the refrigeration circuit, the set of current conditions (50) including a space temperature of a temperature-controlled space associated with the refrigeration circuit; The controller includes a simulation module (102) configured to determine, based on a model (110) corresponding to the refrigeration circuit, a limit setting (152) for a control variable of the refrigeration circuit through an iterative optimization process; wherein the iterative optimization process is defined based on an objective function related to the operating efficiency (120) of the refrigeration circuit and is determined based on evaluating the model for corresponding simulated operating points; wherein the simulated operating point is defined by a set of monitored current conditions (50) and by simulated settings (150) for the control variables that are iteratively varied during the optimization process, and The controller further comprises a dynamic control module (160), wherein the dynamic control module (160) is configured to: adjusting an operational setting of the control variable within an operating range based on monitoring a performance parameter during operation of the refrigeration circuit to target a performance threshold for the monitored performance parameter; The limit settings received from the simulation module are applied as limits of the operating range.

2. The controller according to claim 1, wherein: The dynamic control module is configured to adjust the operational setting of the control variable during operation of the refrigeration circuit based on concurrent monitoring of the performance parameter during operation of the refrigeration circuit.

3. The controller according to claim 1 or 2, wherein: The model does not determine the performance parameters.

4. A controller according to any preceding claim, wherein: The objective function is the performance coefficient.

5. The controller according to claim 4, wherein: The coefficient of performance is determined based on a simulated heat transfer capability and a corresponding simulated power consumption, both of which are determined based on the model.

6. A controller according to any preceding claim, wherein: The monitored performance parameter is a rate of change of a monitored condition associated with the refrigeration circuit.

7. A controller according to any preceding claim, wherein: The target performance threshold for the monitored performance parameter is selected from the group consisting of: Heat transfer parameters related to the heat transfer capacity of the refrigeration circuit, such as: a predetermined minimum heat transfer capacity of the refrigeration circuit; or a predetermined minimum magnitude of the rate of change of the monitored space temperature of the temperature-controlled space; a predetermined minimum refrigerant superheat at a superheat monitoring location along the suction line of the refrigeration circuit.

8. A controller according to any preceding claim, wherein: The dynamic control module includes a PI or PID control module configured to control the control variable of the refrigeration circuit during operation of the refrigeration circuit; wherein the PI or PID control module is configured to change the control variable based on an error signal related to a difference between the performance threshold and the monitored performance parameter; and Therein, the limit setting for the control variable is applied as a saturation limit of the PI or PID controller.

9. The controller according to claim 8, wherein: The target performance threshold for the monitored performance parameter is a predetermined minimum magnitude of the rate of change of the monitored space temperature; and Wherein, the PI or PID control module: configured to control an operating parameter of the compressor as the controlled variable; The method is configured to determine the error signal as a difference between the predetermined minimum magnitude of the rate of change of the space temperature and the rate of change of the monitored space temperature.

10. A controller according to claim 6 and optionally according to any one of claims 7 to 9, wherein The model is configured to determine simulated power consumption based on one or more of: an operating parameter of the compressor as said control variable or derived from said current set of conditions; an operating parameter of a first fan associated with a first heat exchanger as the control variable or derived from the current set of conditions; and / or An operating parameter of a second fan associated with a second heat exchanger is derived as the control variable or from the current set of conditions.

11. A controller according to any preceding claim, configured to: repeat the optimisation process and update the limit settings; optionally wherein: The controller is configured to: Repeating the optimization process at predetermined intervals; and / or The optimization process is repeated based on determining a threshold change or rate of change of current conditions in the set of current conditions.

12. A controller according to any preceding claim, wherein The simulation module is configured to determine limit settings for a plurality of control variables of the refrigeration circuit through the iterative optimization process; wherein the simulated operating point is defined by a set of monitored current conditions and by corresponding simulation settings for the plurality of control variables; wherein, for each control variable, the simulation control module is configured to determine a corresponding limit setting through the optimization process; wherein the dynamic control module is configured to adjust each respective operating setting of the control variable within a respective operating range to target the performance threshold for the monitored performance parameter and to apply each respective limit setting received from the simulation module as a limit of the respective operating range.

13. A refrigeration circuit (10), comprising a compressor (12), a first heat exchanger (14), an expansion device (16), a second heat exchanger (18), and a controller (100); in, The controller (100) is a controller according to any preceding claim.

14. A method of controlling a refrigeration circuit using a controller according to any preceding claim, wherein: The control variable of the refrigeration circuit is variable during operation of the refrigeration circuit, and the method comprises: monitoring a set of current conditions associated with the refrigeration circuit, the set of current conditions including a space temperature of a temperature-controlled space associated with the refrigeration circuit; The simulation module performs the iterative optimization process to determine limit settings for control variables of the refrigeration circuit; applying the limit settings as limits for an operating range of the control variable; monitoring a performance parameter for the refrigeration circuit during operation of the refrigeration circuit; the dynamic control module adjusting an operational setting of the control variable within the operating range to target a performance threshold for the monitored performance parameter; whereby the dynamic control module biases operation of the refrigeration circuit to the limit setting of the control variable determined by the optimization process when the limit setting corresponds to compliance with the performance threshold during operation of the refrigeration circuit; and Thus, when the limit setting corresponds to a failure to meet the performance threshold during operation of the refrigeration circuit, the dynamic control module biases operation of the refrigeration circuit away from the limit setting of the controlled variable to achieve a target performance threshold.

15. A non-transitory machine-readable medium comprising instructions that, when executed by a processor, cause the method of claim 14 to be performed.

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