Method for controlling cycle system and compression equipment - Patents.com

Abstract

The present invention relates to a method for controlling a cycle system using a physical model. The cycle system includes a circuit containing a working substance, in which at least one expansion device (43, 44) and at least one compression device (20) are arranged, and the cycle system includes at least one heat consuming device and at least one heat transport device (41). The method includes calculating a working substance flow rate in the circuit based on the thermal output of the at least one heat consuming device, and then controlling a manipulated variable of the compression device (20) according to the calculated working substance flow rate. Furthermore, the expansion devices (43, 44) are controlled such that a first predetermined pressure of the working substance at the time of exiting from the expansion devices (43, 44) is set.

Description

[Technical field]

[0001] The present invention relates to a method for controlling a cycle system, a computing unit and a computer program for implementing the method, and a compression installation. [Background technology]

[0002] Refrigeration cycle systems, such as heat pumps and air conditioning systems, include a refrigerant circuit in which a compressor, a condenser, an expansion valve and an evaporator are arranged. The heat output of such a refrigeration cycle system is controlled by an expansion valve, through which the amount of refrigerant to be evaporated reaches the evaporator. A compressor is arranged downstream of the evaporator, which sucks in the evaporated refrigerant and thereby keeps the pressure constant during evaporation. The evaporation pressure is set in particular by the rotation speed of the compressor, which compresses the evaporated refrigerant, which then reaches the condenser with an increased pressure and temperature, where it is liquefied again.

[0003] To prevent damage to the compressor due to the liquid component of the refrigerant, the amount of refrigerant to be evaporated can be controlled so that at the end of the evaporation process the refrigerant is present as a superheated gas. Now, in a refrigeration cycle system, the temperature after the evaporator can be the control / regulation variable for the expansion valve. If more refrigerant reaches the evaporator than is needed for the required heat output, the temperature will drop and the expansion valve will reduce the amount of refrigerant and vice versa.

[0004] However, such indirect control / adjustment of the refrigerant amount requires a sufficient safety margin between the specified superheat temperature (target superheat temperature) and the saturation temperature of the refrigerant, with a corresponding loss in system efficiency. Summary of the Invention

[0005] According to the invention, a method for controlling a cycle system by means of a physical model of the cycle system, a compression installation and a computing unit and a computer program for implementing the method are proposed with the features of the independent claims. Advantageous configurations are the subject of the dependent claims and the following description.

[0006] The present invention provides control of a refrigeration cycle system that controls the flow of refrigerant within the system according to the laws of physics. The cycle system comprises a circuit containing a working substance, in which at least one expansion device and at least one compression device are arranged. The working substance has certain thermodynamic properties, such as a boiling point curve, a dew point curve and latent heat, depending on the pressure and temperature. The term "latent heat" refers to the enthalpy absorbed or released during a phase change. The circuit is preferably a closed conduit system in which the working substance circulates. Hereinafter, this circuit is also referred to as the primary side of the cycle system.

[0007] The working substance is liquid before the expansion device and is expanded in the expansion device to a first predetermined pressure, where the working substance evaporates according to its thermodynamic properties at a saturation temperature corresponding to the first predetermined pressure, where it absorbs heat from the environment. The first predetermined pressure after passing through the expansion device can be determined based on the vapor pressure curve of the working substance used according to the desired cooling performance. For example, the refrigerant R134a (C2H2F4) has a saturation temperature of -26°C at a pressure of 1 bar.

[0008] The term "environment" should be understood as any medium to which heat can be transferred from the circuit or from which heat can be transferred to the circuit. In the following, the "environment" is also called the secondary side of the cycle system.

[0009] The gaseous working substance is then compressed in the compressor to a second predetermined pressure, which increases the pressure and temperature of the working substance. The temperature of the working substance in the circuit after passing through the compressor is preferably higher than the temperature on the secondary side of the cycle system, and the working substance releases heat to the cycle system. If the temperature falls below a saturation temperature, which has a higher value at a higher second predetermined pressure depending on the thermodynamic properties of the working substance, the working substance condenses in the circuit and becomes liquid again before the expansion device. For example, the refrigerant R124a (C2H2F4) has a saturation temperature of 60°C at a pressure of 17 bar. This allows condensation of the refrigerant with moderate compression even at high ambient temperatures.

[0010] Preferably, the cycle system is a heat pump that can be used for both cooling and heating. Particularly preferably, the cycle system is an air conditioning system, in particular an air conditioning system for a motor vehicle with an electric drive. Preferably, the working substance is a refrigerant such as R134a (C2H2F4), R1234yf (C3H2F4) or R744 (CO2).

[0011] The expansion device may be an expansion valve with a variable cross-sectional area. The expansion valve may be mechanically, electrically or electronically controlled. Preferably, the expansion device is an electronically controlled expansion valve with a variable cross-sectional area. The compression device is preferably a compressor, such as a scroll compressor, a vane compressor, a piston compressor, a swash plate compressor, etc.

[0012] The working substance is evaporated in the circuit in the flow direction between the expansion device and the compression device. In this region, the circuit can include, for example, a pipe loop, which can provide a larger surface area for heat transfer from the secondary side to the primary side of the cycle system. This region of the circuit is referred to below as the evaporator. Alternatively, the evaporator can be a separate component connected to the circuit in the flow direction between the expansion device and the compression device.

[0013] Furthermore, the working substance is condensed in the circuit in the flow direction between the compression device and the expansion device. In this region, the circuit can also include a pipe loop, which can provide a larger surface area for heat transfer from the primary side to the secondary side of the cycle system. This region of the circuit is hereinafter referred to as the condenser. Alternatively, the condenser can be a separate component connected to the circuit in the flow direction between the compression device and the expansion device.

[0014] Furthermore, the cycle system includes at least one heat consuming device and at least one heat transporting device. A heat consuming device is to be understood as a (space) volume and / or (part) mass from which heat is removed or to which heat is delivered. This means that at least one heat consuming device is arranged on the secondary side of the cycle system. Preferably, the heat consuming device is a room, in particular a passenger compartment of an (electric) vehicle, and / or a part, preferably a part of a vehicle, in particular a battery for storing electricity for driving an electric vehicle.

[0015] For example, the optimum temperature range for lithium-ion batteries, currently preferably used in electric vehicles, is 15°C to 35°C, and temperature control of the battery is usually achieved by connection to the refrigerant circuit of the vehicle's air conditioning system. This results in a cycle system with two parallel subcircuits, one of which provides interior temperature control and the other battery temperature control.

[0016] A heat transport device is to be understood as a part / component that supports the heat transport from the primary side to the secondary side of a cycle system. In particular, the heat transport device is used to transfer heat that can be dissipated during condensation of a working substance to a medium on the secondary side of the cycle system. The heat transport device can be integrated into a condenser, whereby the condenser is designed, for example, as a working substance / air exchanger or a working substance / liquid heat exchanger. Alternatively or additionally, the heat transport device can comprise a ventilator that is arranged on the secondary side of the cycle system in the area of ​​the condenser. Particularly preferably, the heat transport device is a condenser designed as a working substance / air heat exchanger and equipped with a ventilator.

[0017] The physical model of the cycle system preferably uses physical models that represent the physical properties of the components on the primary and secondary sides of the system. That is, there are preferably sub-models of at least one expansion and compression device, a piping system with an evaporator and a condenser, as well as at least one heat transport device and at least one heat consuming device. Preferably, the thermodynamic properties of the working substances and fluids used in the heat transfer on the secondary side of the cycle system are also incorporated into the physical model. Thus, the working substance flow rate in the circuit on the primary side of the cycle system, the fluid flow rate on the secondary side, and the pressure and temperature at key points of the cycle system can be calculated. These variables can be used both for controlling the system and for providing target values ​​for the control / regulation of the individual components. Here, different target values ​​are available compared to known control / regulation methods, which allows different regulation strategies and even provides additional optimization possibilities.

[0018] According to the invention, the working substance flow rate in the circuit is determined or calculated, and the calculated working substance flow rate is based on the thermal output of at least one heat consuming device, which means that the working substance flow rate required in the circuit on the primary side of the cycle system is calculated based on the required thermal output of a heat consuming device on the secondary side of the cycle system (e.g. temperature control of the passenger compartment or battery of a car).

[0019] The working substance flow rate can be a volumetric flow rate of the working substance and / or a mass flow rate of the working substance. Preferably, the working substance flow rate is a mass flow rate of the working substance. The heat output of a heat consuming device is to be understood as the heat flow to be dissipated or supplied that is required to achieve a desired temperature in the heat consuming device.

[0020] The functional form of the physical model is described below on the basis of very simplified equations: The physical model also describes the heat transfer between the individual components of the cycle system and the behavior of the working substance depending on the aggregate state.

[0021] The required heat output of the consumer on the secondary side of the cycle system is calculated using a physical model of the cycle system to obtain the desired / required outlet temperature of the fluid on the secondary side.

[0022]

number

[0023] Based on this, it can be calculated according to equation (1).

[0024]

number

[0025] Where:

[0026]

number

[0027] represents the thermal power at the secondary side,

[0028]

number

[0029] represents the mass flow rate of the heat transfer fluid on the secondary side, and c s represents the heat storage capacity of the fluid on the secondary side,

[0030]

number

[0031] represents the inlet temperature of the fluid on the secondary side. The flow rate of the working substance to be evaporated on the primary side is proportional to the required heat output on the secondary side.

[0032]

number

[0033] and the thermal output to be provided on the primary side

[0034]

number

[0035] This is calculated from the conservation of energy. Primary heat output

[0036]

number

[0037] follows equation (2).

[0038]

number

[0039] Where:

[0040]

number

[0041] is the mass flow rate of the working substance to be evaporated on the primary side, and Δh νrepresents the enthalpy change of the working substance flow due to vaporization caused by the thermodynamic properties of the working substance at a first predetermined pressure.

[0042] therefore,

[0043]

number

[0044] is the mass flow rate of the working substance to be evaporated on the primary side

[0045]

number

[0046] If we ignore heat transfer losses and phase-dependent changes in the temperature behavior of the working material, we get

[0047]

number

[0048] Calculated working material flow rate

[0049]

number

[0050] In other words, the compressor is controlled in response to the calculated working material flow rate.

[0051]

number

[0052] The compressor is controlled by suitable manipulated variables so that the working material flow rate is provided. For this purpose, the compressor can have, for example, a characteristic curve which shows the value of the manipulated variable as a function of the working material flow rate. This characteristic curve can be stored, for example, in a computing unit of the compressor or in a central computing unit of the cycle system.

[0053] The manipulated variable of the compression device is preferably the compressor speed, which is controlled by a computing unit according to the compressor characteristic curve using pulse width modulation or via a data bus system (e.g. via a local interconnect network (LIN)).

[0054] Furthermore, the expansion device is controlled such that a first predetermined pressure of the working substance at the outlet from the expansion device is set, where outlet from the expansion device should be understood to mean in particular the outlet from the evaporator, and by controlling the expansion device to the first predetermined pressure in accordance with the thermodynamic properties of the working substance, the associated saturation temperature is set.

[0055] The first predefined pressure is preferably selected based on the boundary conditions of the cycle system (ambient conditions, working substance) and the requirements of the heat consuming device. For example, the first predefined pressure should not be selected too low to avoid freezing of the evaporator. On the other hand, in the case of an air conditioning system for a vehicle cabin, the pressure should not be selected too high, for example to avoid odor problems. Thus, the pressure level after the expansion device can be set differently for various applications.

[0056] Preferably, the opening cross-sectional area and / or the opening duration of the expansion valve are controlled as a function of a first predetermined pressure at the outlet from the expansion device, whereby the pressure can be determined using a physical model and the expansion valve can be controlled such that the opening cross-sectional area and / or the opening duration is set, whereby the first predetermined pressure is achieved. Preferably, the expansion valve is a valve whose opening cross-sectional area is adjusted by a corresponding valve position, for example using a LIN bus connection.

[0057] The above-mentioned physics-based control of the cycle system allows the superheat temperature of the working material flow at the inlet of the compressor to be set more easily and accurately. As a result, the superheat temperature can be selected lower, thereby improving the efficiency of the cycle system. Furthermore, the control according to the present invention can reduce losses in the compressor and fluctuations of the operating variables of the compressor, and avoid noise and vibration problems during the operation of the cycle system.

[0058] Preferably, in the calculation of the working substance flow rate, a first predetermined temperature of the working substance at the time of entry into the compression device is taken into account. In other words, the working substance is preferably superheated to the first predetermined temperature after evaporation in order to prevent damage to the compression device by the liquid components of the refrigerant. The change in enthalpy of the working substance required to reach a predetermined temperature (superheating temperature) at the first predetermined pressure, Δh', is calculated as ν can be obtained from the thermodynamic properties of the working substance. Thus, for the required working substance mass flow rate, taking into account the superheat temperature, we obtain:

[0059]

number

[0060] Preferably, furthermore, the heat power for condensing the working substance in the circuit after the discharge from the compressor is calculated based on a second predetermined pressure of the working substance and the calculated working substance flow rate, the second predetermined pressure corresponding to the pressure after the compressor and derived from the rotational speed.

[0061] Since the temperature of the working substance after compression is higher than the saturation temperature, the working substance must first be cooled to its saturation temperature. Therefore, the enthalpy that can be lost from the working substance Δh' k is the enthalpy required for condensation, Δh k Higher than.

[0062] Therefore, the heat power that can be dissipated due to the condensation of the working substance in the circuit after the discharge from the compression device

[0063]

number

[0064] is calculated as follows:

[0065]

number

[0066] Where:

[0067]

number

[0068] represents the heat power required to condense the working substance,

[0069]

number

[0070] is the mass flow rate of the working substance to be evaporated in a quasi-steady state in a closed circuit.

[0071]

number

[0072] represents the mass flow rate of the working substance to be condensed, which is equal to Δh' k represents the enthalpy that can be lost due to condensation of the working substance at a second predetermined pressure resulting from the thermodynamic properties of the working substance.

[0073] Calculated heat output for condensation of the working substance

[0074]

number

[0075] Based on this, a physical model of the cycle system is preferably then used to calculate the fluid flow rate through the heat transport device, and the manipulated variables of the heat transport device are controlled accordingly. According to the conservation of energy between the primary and secondary sides of the cycle system, the fluid flow rate on the secondary side is calculated by neglecting heat transfer losses and phase-dependent changes in the temperature behavior of the working substance.

[0076]

number

[0077] is calculated as follows:

[0078]

number

[0079] where c s represents the heat storage capacity of the fluid on the secondary side,

[0080]

number

[0081] represents the inlet temperature of the fluid at the secondary side of the cycle system;

[0082]

number

[0083] represents the outlet temperature. The fluid on the secondary side of the cycle system is a gaseous fluid, such as air, or a liquid. The manipulated variable of the heat transport device is, for example, the ventilator speed when using a working flow / air heat exchanger, which is proportional to the fluid mass flow rate and can therefore be very easily controlled as a function of the fluid mass flow rate.

[0084] Particularly preferably, in the calculation of the fluid flow rate through the heat transport device, the second predetermined temperature of the working substance at the time of entry into the expansion device is taken into account. In other words, after condensation, the working substance is subcooled to the second predetermined temperature, ensuring that no vapor bubbles are generated in front of the expansion device. The enthalpy of the working substance required to reach the second predetermined temperature (subcooling temperature) at the second predetermined pressure

[0085]

number

[0086] The change in can be obtained from the thermodynamic properties of the working substance. Therefore, the required fluid mass flow rate

[0087]

number

[0088] Taking the supercooling temperature into account, we get the following:

[0089]

number

[0090] By calculating the fluid flow rate required on the secondary side of the cycle system to cool the working substance to a desired temperature level before the expansion device, the heat dissipation through the heat transport device can be optimized and thus the performance of the cycle system can be improved.

[0091] According to a preferred embodiment, the circuit on the primary side of the cycle system comprises a first partial circuit with a first expansion device for a first consumer on the secondary side of the cycle system and a second partial circuit with a second expansion device for a second consumer on the secondary side of the cycle system. Particularly preferably, the partial circuits are arranged parallel to one another and merge into a common line before the compression device.

[0092] This embodiment can be used, for example, when, as described above, the air conditioning system of an electric vehicle is used to control the temperature of the battery in addition to controlling the temperature of the passenger compartment. Here, a first working substance flow is first calculated in a first partial circuit on the basis of the thermal output of a first consumer. A calculation of a second working substance flow in a second partial circuit is then performed on the basis of the thermal output of a second consumer. The calculation of the individual working substance partial flows is performed in the same way as described above for a single consumer. The calculation of the individual working substance partial flows ensures the required superheat temperature at the inlet to the compressor even in the case of two parallel heat consumers.

[0093] The sum of the first and second working substance flows is used to calculate the total working substance flow in the circuit, on the basis of which the manipulated variable of the compressor is controlled, which means that the compressor can be controlled in the same way as for a single consumer.

[0094] The first expansion device is preferably controlled in such a way that a first predetermined pressure of the working substance at the outflow from the first expansion device is set. Here, this pressure can be selected depending on the operating mode of the cycle system. If the battery is the first consumer, the first predetermined pressure can be selected only according to the requirements of the temperature control of the battery, for example, if no temperature control of the vehicle compartment is required. If both heat consumers are active, the pressure must be selected according to the requirements of both consumers. The control of the first predetermined pressure according to the requirements for both consumers is preferably performed by the first expansion device, i.e. this pressure also occurs after passing through the second expansion device.

[0095] Preferably, the control of the second expansion device is performed depending on the calculated working substance flow rate in the second partial circuit and the first predetermined pressure of the working substance at the outflow from the first expansion device. In other words, the pressure after passing through the second expansion device is predetermined by the control of the first expansion device, and thus the working substance partial flow rate through the second partial circuit can be set by the opening cross-sectional area / opening duration of the second expansion device. The required working substance flow rate for the first partial circuit is automatically obtained, since the compression device provides the total working substance flow rate required for both partial circuits. This allows an improved control of the pressure after passing through the expansion device in the case of two parallel working substance flow circuits compared to the control of the pressure by means of a compression device.

[0096] According to a preferred embodiment, the (current) working substance flow rate in the circuit is determined and the determined working substance flow rate is compared to the calculated working substance flow rate. An operating variable of the compression device is then set or controlled based on the difference between the determined working substance flow rate and the calculated working substance flow rate. Preferably, the operating variable of the compression device is set such that the determined working substance flow rate corresponds to the calculated working substance flow rate. According to one embodiment, the working substance flow rate is measured at a first predetermined position in the circuit by means of a flow sensor. Alternatively or additionally, the working substance flow rate can be estimated based on a measured temperature at the inlet to the compression device and / or a measured pressure after passing through the compression device.

[0097] Preferably, the compression device itself is equipped with a flow sensor. Alternatively or additionally, the predetermined location of the flow sensor may be between the expansion device and the compression device. Particularly preferably, in this case, the flow sensor is arranged at a predetermined distance before the inlet to the compression device, for example to avoid measurement errors due to backflow. Volumetric or mass flow sensors can be used. Particularly preferably, mass flow sensors are used.

[0098] Control of the compressor manipulated variable based on the measured working material flow rate has the advantage that deviations between the physical model of the cycle system and the real system can be compensated for, and thus changes associated with system aging can be accommodated, for example.

[0099] The manipulated variable of the compression device is preferably the compressor speed, which is controlled by a computing unit according to the compressor characteristic curve using pulse width modulation or via a data bus system (e.g. via a local interconnect network (LIN)).

[0100] Preferably, the compression device itself is equipped with a calculation unit that receives the calculated and measured values ​​of the working material flow rate and controls the manipulated variables based on the received values. In this calculation unit, additional parameters of the compression device, such as minimum and maximum values ​​of the manipulated variables and / or performance limits of the compression device, can be stored, which can be taken into account during the adjustment. A corresponding compression installation with a compression device (or a pump in general), a calculation unit and a flow rate sensor are also the subject of the present invention.

[0101] Preferably, the pressure of the working substance is further measured at a second predetermined position in the circuit by means of a pressure sensor. The predetermined position of the pressure sensor in the circuit is preferably downstream of the evaporator, between the evaporator and the compressor. Particularly preferably, the pressure sensor is located immediately after the evaporator.

[0102] The measured working substance pressure is compared to a first predetermined pressure of the working substance at exit from the expansion device, and the at least one expansion valve is controlled based on a difference between the measured working substance pressure and the first predetermined pressure.

[0103] Preferably, the opening cross-sectional area and / or the opening duration of the expansion valve are controlled such that the actual working substance pressure corresponds to a first predetermined pressure at the outlet from the expansion device, whereby depending on the distance from the outlet from the expansion device to the pressure sensor position, pressure losses in the line can be taken into account and the measured working substance pressure can therefore also be adjusted to a value different from the first predetermined pressure.

[0104] Preferably, the temperature of the working substance is further measured at a third predetermined location in the circuit by means of a temperature sensor, the predetermined location of the temperature sensor being preferably downstream of the condenser and between the condenser and the at least one expansion device, particularly preferably immediately before the expansion device.

[0105] The measured temperature is then compared to a predetermined temperature of the working substance at the inlet to the expansion device, and the operating variable of the heat transport device is controlled based on the difference between the measured working substance temperature and the predetermined temperature, whereby depending on the distance from the inlet to the expansion device to the temperature sensor location, temperature losses in the line can be taken into account and therefore the measured working substance temperature can be adjusted to a value different from the predetermined temperature.

[0106] Regulation of the working substance pressure and temperature can compensate for deviations of the real cycle system from the physical model that may occur, for example, due to ageing processes in the system, thereby improving the accuracy of the cycle control even with long system operating times.

[0107] A computing unit according to the invention, for example a control device of a motor vehicle, is designed, in particular from a programming point of view, to carry out the method according to the invention. The implementation of the method according to the invention in the form of a computer program or computer program product containing program code for implementing all the method steps is also advantageous. This is particularly advantageous as it is particularly cost-effective, especially when the executing control device is also used for further purposes and is therefore present in any case. Finally, a machine-readable storage medium is provided on which a computer program as described above is stored. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories such as hard drives, flash memories, EEPROMs, DVDs, etc. Downloading of the program via a computer network (such as the Internet or an intranet) is also possible. Here, such downloading can be performed via a wired or cabled connection or wirelessly (e.g., via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

[0108] Further advantages and features of the present invention will become apparent from the specification and accompanying drawings. The invention is illustrated diagrammatically on the basis of exemplary embodiments in the following drawings and will be described below with reference to the drawings. [Brief description of the drawings]

[0109] [Figure 1] FIG. 1 is a schematic diagram of an example of a refrigeration cycle system that includes a compression facility according to a preferred embodiment of the present invention and that can be controlled / regulated according to a preferred embodiment of the claimed method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0110] In Fig. 1, an example of a cycle system that can be controlled / regulated according to a preferred embodiment of the present invention is shown in a schematic manner. The cycle system is preferably an air conditioning system in an electric vehicle (not shown). The air conditioning system comprises a refrigerant circuit, in which there are two parallel partial circuits 450, 451, each of which comprises an expansion valve 43, 44 (expansion device) and an evaporator 50, 60. Furthermore, the refrigerant circuit comprises a compression installation, which comprises a compressor 20 (compression device), a compressor control unit (calculation unit) 21 and a flow sensor 22, an accumulator 70 and a condenser 40, the latter of which is provided on the secondary side with a ventilator 41 (heat transport device). Alternatively or additionally, the flow rate can be estimated based on a measured temperature at the inlet of the compressor and / or a measured pressure after the compressor.

[0111] The first partial circuit 450, including the first evaporator 60, is used for temperature control of the traction battery (not shown) of the electric vehicle. For this purpose, a working substance / liquid heat exchanger (indicated by arrow 61) is arranged on the secondary side of the first evaporator 60, which conducts the coolant to a cooling plate (not shown), for example connected to the battery. The second partial circuit 451, including the second evaporator 50, is provided for temperature control of the passenger compartment (not shown). For this purpose, a ventilator 51 is arranged on the secondary side of the second evaporator 50, which conducts the cooled air at the secondary side of the second evaporator 50 to the passenger compartment. The two partial circuits merge into a common line 500, in which a pressure sensor is arranged for monitoring / measuring a first predetermined pressure of the refrigerant at the outlet of the evaporators 50, 60. Through the line 500, the gaseous refrigerant is fed to the compressor 20 via an accumulator 70. Within the accumulator 70, the liquid component of the refrigerant may be separated.

[0112] Based on the required heat output of the two heat consumers connected to the partial circuits 450, 451, the refrigerant mass flow required in the individual partial circuits is calculated, in particular according to formula (3) or (4). From the sum of the first and second refrigerant mass flows, the total refrigerant mass flow in the refrigerant circuit is calculated, on the basis of which the speed of the compressor 20 is controlled.

[0113] In the illustrated refrigerant circuit, the vehicle traction battery, which must be temperature controlled continuously, is the first heat consumer. In contrast, the temperature control of the passenger compartment, which is the second heat consumer, is only switched on when necessary. Thus, a first predefined pressure after the two evaporators 50, 60 is set according to the requirements of the battery, unless an additional temperature control of the passenger compartment is required. If both heat consumers are active, the pressure after the evaporators must be selected according to the requirements of both consumers.

[0114] The first expansion valve 44 is preferably controlled such that a first predetermined pressure of the working substance after passing through the evaporator 60 is set. Due to the parallel arrangement of the partial circuits, this pressure also exists after passing through the second expansion valve 43. In other words, the pressure after passing through the second expansion valve 43 is predefined by controlling the first expansion valve 44, and thus the partial refrigerant flow rate through the second partial circuit 451 can be set by the opening cross-sectional area / opening duration of the second expansion valve 43. The required refrigerant flow rate for the first partial circuit 450 is automatically obtained, since the compressor 20 provides the total required refrigerant flow rate for both partial circuits 450, 451. This allows an improved control of the pressure after passing through the evaporators 50, 60 in the case of two parallel refrigerant circuits 450, 451 compared to the control of the pressure by means of the compressor 20.

[0115] The compressor 20 compresses the refrigerant to a second predetermined pressure and sends it through a line 200 to a condenser 40. The condenser 40 is equipped with a ventilator 41 by means of which the air mass flow rate at the secondary side of the condenser can be controlled. Here, the second predetermined pressure is preferably selected such that the associated saturation temperature is higher than the ambient temperature. In the condenser, the compressed refrigerant is first cooled to its saturation temperature and then liquefied.

[0116] The heat power required for condensation of the refrigerant is calculated from the enthalpy that can be lost at a second predetermined pressure and the refrigerant mass flow rate in the circuit according to equation (5). Then, based on the calculated heat power of the condenser, the air mass flow rate on the secondary side of the condenser is determined according to equation (6) or (7), and the rotation speed of the ventilator 41 is controlled accordingly to provide the required heat transport.

[0117] The liquefied refrigerant is again fed to the expansion valves 43, 44 through lines 400, 450. A temperature sensor 42 is disposed before the expansion valves 43, 44, and the temperature sensor 42 makes it possible to monitor / measure the subcooling temperature of the refrigerant.

[0118] The illustrated air conditioning system for an electric vehicle further comprises a calculation unit 10 for controlling the individual components of the air conditioning system. A physical model of the air conditioning system is stored in the calculation unit 10, with the aid of which the described calculations can be carried out. The calculation unit 10 receives the signals of the flow sensor 22, the temperature sensor 42 and the pressure sensor 62 and adjusts the respective variables on the basis of the associated setpoint values ​​determined on the basis of the physical model. Furthermore, the calculation unit 10 is electrically connected to the compressor control unit 21, the ventilators 41, 51 and the expansion valves 43, 44, and can carry out the control of the air conditioning system using the manipulated variables of the associated components.

[0119] In particular, data exchange can take place between the calculation unit 10 and the compressor control unit 21 for adjusting the refrigerant mass flow rate. The data exchange can take place, for example, via a data bus system (for example, via a local interconnect network (LIN)). Here, the calculation unit 10 first transmits the required refrigerant mass flow rate (target mass flow rate) determined on the basis of a physical model to the compressor control unit 21. In addition to the target mass flow rate, the compressor control unit 21 further receives the flow rate signal of the flow sensor 22, calculates the difference between the target mass flow rate and the current mass flow rate, and sets the speed of the compressor 20 on the basis of the calculated mass flow rate difference. This has the advantage that additional parameters, such as a minimum or maximum speed of the compressor 20, a maximum permissible temperature, and / or a maximum power, can be stored in the compressor control unit 21 and can be taken into account by the compressor control unit 21 during adjustment.

[0120] Alternatively or additionally, the calculation unit 10 can receive the signal of the flow sensor 22, calculate the difference in the refrigerant mass flow rates and transmit this difference to the compressor control unit 21. The compressor control unit 21 can set the required compressor speed based on the received mass flow rate difference.

[0121] The above-mentioned physics-based control of the cycle system allows the superheat temperature of the working material flow at the inlet of the compression device to be set more easily and accurately. As a result, the superheat temperature can be selected lower, thereby improving the efficiency of the cycle system. Furthermore, the control according to the present invention can reduce the fluctuations of the operating variables of the compression device, thus avoiding noise and vibration problems during the operation of the cycle system.

Claims

1. A method for controlling a cycle system using a physical model, the cycle system comprising a circuit containing a working substance, at least one heat consuming device, and at least one heat transporting device (41, 51), in which at least one expansion device (43, 44) and at least one compression device (20) are arranged; calculating a working material flow rate in the circuit based on the heat output of the at least one heat consuming device; controlling a manipulated variable of the compression device (20) in response to the calculated working material flow rate; controlling the expansion device (43, 44) to set a first predetermined pressure of the working substance upon exiting the expansion device (43, 44); The method includes:

2. 2. The method of claim 1, wherein the calculation of the working material flow rate takes into account a first predetermined temperature of the working material upon entry into the compression device (20).

3. calculating a heat output for condensing the working substance in the circuit after exiting the compression device (20) based on a second predetermined pressure of the working substance and the calculated working substance flow rate; calculating a fluid flow rate through the heat transport device (41, 51) based on the calculated heat output for condensing the working substance; controlling a manipulated variable of the heat transport device (41, 51) in response to the calculated fluid flow rate through the heat transport device (41, 51); The method of claim 1 or 2, further comprising:

4. 4. The method of claim 3, wherein the calculation of the fluid flow rate through the heat transport device (41, 51) takes into account a second predetermined temperature of the working substance upon entry into the expansion device (43, 44).

5. measuring the temperature of the working substance in the circuit using a temperature sensor (42); comparing the measured working substance temperature to the second predetermined temperature of the working substance upon entry into the expansion device (43, 44); controlling the manipulated variable of the heat transport device (41, 51) based on a difference between the measured working substance temperature and the second predetermined temperature of the working substance upon entering the expansion device (43, 44); The method of claim 4 further comprising:

6. the circuit comprises a first partial circuit (450) including a first expansion device (44) for a first consumer and a second partial circuit (451) including a second expansion device (43) for a second consumer, calculating a first working material flow rate in the first partial circuit (450) based on the heat output of the first consumer; calculating a second working substance flow rate in the second partial circuit (451) based on the heat output of the second consumer; calculating a working substance flow rate in said circuit as the sum of said calculated working substance flows through said first and second partial circuits (450, 451); controlling the manipulated variable of the compression device (20) in response to the calculated working material flow rate; controlling the first expander (43, 44) to set a first predetermined pressure of the working substance upon exiting the first expander (44); controlling the second expansion device (43) in response to the calculated working substance flow rate in the second partial circuit and the first predetermined pressure of the working substance at the exit from the first expansion device (44); The method of claim 1 , further comprising:

7. determining a flow rate of a working substance in the circuit; comparing the determined working substance flow rate with the calculated working substance flow rate; controlling the manipulated variable of the compression device (20) based on a difference between the determined work flow rate and the calculated work flow rate; The method of any one of claims 1 to 6, further comprising:

8. measuring the pressure of the working substance in the circuit with a pressure sensor (62); comparing the measured working substance pressure to the first predetermined pressure of the working substance at the exit from the expansion device (43, 44); controlling the at least one expansion device (43, 44) based on a difference between the measured working substance pressure and the first predetermined pressure of the working substance; The method of any one of claims 1 to 7, further comprising:

9. A computing unit (10) designed to carry out all the method steps of the method according to any one of the claims 1 to 8.

10. A computer program which, when executed on a computing unit (10), causes said computing unit to carry out all the method steps of the method according to any one of the claims 1 to 8.

11. A machine-readable storage medium having stored thereon the computer program of claim 10.

12. A compression installation comprising a compression device (20), a calculation unit (21) and a flow sensor (22), the calculation unit (21) being designed to receive a target value for a working flow rate that can be delivered by the compression device (20), to compare the target value with a measured value for the working flow rate received by the flow sensor (22), and to control an operating variable of the compression device (20) based on a difference between the target value and the measured value.

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