DE102021214679A1 - Process for controlling a cycle process system and compression arrangement - Google Patents

Abstract

The invention relates to a method for controlling a cycle process system using a physical model. The cyclic process system contains a circuit with a working substance, in which at least one expansion device (43, 44) and at least one compression device (20) are arranged, as well as at least one thermal consumer and at least one heat transport device (41). The method calculates a working substance flow in the circuit based on a thermal output of the at least one thermal consumer and then controls a manipulated variable of the compression device (20) as a function of the calculated working substance flow. In addition, the expansion device (43, 44) is controlled in such a way that a first predetermined pressure of the working substance is set at an outlet from the expansion device (43, 44).

Description

The present invention relates to a method for controlling a cyclic process system, a computing unit and a computer program for its implementation, and a compression arrangement.

Background of the Invention

A refrigeration cycle system, such as a heat pump or an air conditioner, contains a refrigerant circuit in which a compressor, a condenser, an expansion valve and an evaporator are arranged. The control of the thermal output of such a refrigeration circuit process system is carried out by means of the expansion valve, through which the amount of refrigerant to be evaporated reaches the evaporator. The compressor is arranged downstream of the evaporator, which sucks off the evaporated refrigerant and thus keeps the pressure constant during evaporation. The evaporation pressure is set in particular by means of the speed of the compressor, which compresses the evaporated refrigerant before it reaches the condenser at increased pressure and temperature, where it is liquefied again.

The amount of refrigerant to be evaporated can be controlled in such a way that the refrigerant is present as superheated gas at the end of the evaporation process in order to prevent damage to the compressor by liquid components of the refrigerant. In a refrigeration circuit process system, the temperature after the evaporator can represent the control/regulated variable for the expansion valve. If more refrigerant enters the evaporator than is required for the requested thermal capacity, the temperature will drop, causing the expansion valve to reduce the refrigerant charge, and vice versa.

However, such an indirect control/regulation of the amount of refrigerant requires a sufficient safety margin between the specified overheating temperature (set value of the overheating temperature) and the saturation temperature of the refrigerant, which is associated with corresponding losses in efficiency of the system.

Disclosure of Invention

According to the invention, a method for controlling a cyclic process system using a physical model of the cyclic process system, a compression arrangement and a computing unit and a computer program for carrying out the method with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

The invention provides a controller for a refrigeration cycle system that controls the refrigerant flow in accordance with the physical laws in the system.

The cyclic process system contains a circuit with a working substance, at least one expansion device and at least one compression device being arranged in the circuit. The working substance has predetermined thermodynamic properties, such as a boiling line, a dew line and latent heat as a function of pressure and temperature. The term "latent heat" refers to the enthalpy absorbed or released during a phase transition. The cycle is preferably a closed line system in which the working substance circulates. In the following, this circuit is also referred to as the primary side of the cycle process system.

The working substance is in liquid form before the expansion device and is expanded in the expansion device to a first predetermined pressure. The working substance evaporates at a saturation temperature corresponding to the first predetermined pressure according to its thermodynamic material properties and in the process absorbs heat from the environment. The first predetermined pressure after the expansion device can be determined based on the vapor pressure curve of the working material used according to the desired cooling capacity. For example, the refrigerant R134a (C ₂ H ₂ F ₄ ) has a saturation temperature of -26°C at a pressure of 1 bar.

The term "environment" should be understood to mean any medium to which heat can be transferred from the circuit or from which heat can be transferred into the circuit. In the following, the "environment" is also referred to as the secondary side of the cycle process system.

The gaseous working material is subsequently compressed in the compression device to a second predetermined pressure, thereby increasing the pressure and temperature of the working material. The temperature of the working substance in the circuit after the compression device is preferably higher than a temperature of the secondary side of the cycle process system, so that the working substance gives off heat to it. If the temperature falls below the saturation temperature, which has a higher value at the increased second predetermined pressure depending on the thermodynamic material properties of the working material, then con the working substance in the circuit densifies and is again in liquid form before the expansion device. For example, the refrigerant R124a (C ₂ H ₂ F ₄ ) has a saturation temperature of 60° C. at a pressure of 17 bar. This allows this refrigerant to condense with moderate compression even at higher ambient temperatures.

The cycle process system is preferably a heat pump that can be used both for cooling and for heating. The cycle process system is particularly preferably an air conditioning system, in particular an air conditioning system in a motor vehicle with an electric drive. The working substance is preferably a refrigerant, such as R134a (C ₂ H ₂ F ₄ ), R 1234yf (C ₃ H ₂ F ₄ ), or R744 (CO ₂ ).

The expansion device may be an expansion valve with a variable opening area. The expansion valve can be controlled mechanically, electrically or electronically. Preferably, the expansion device is an electronically controlled expansion valve with a variable opening area. The compression device is preferably a compressor (compressor) such as a scroll compressor, a vane compressor, a piston compressor or a swash plate compressor.

The working substance is vaporized in the circuit downstream between the expansion and compression devices. In this area, the circuit can contain pipe loops, for example, which means that a larger surface area can be provided for heat transfer from the secondary side to the primary side of the cycle process system. This area of the circuit is referred to below as the evaporator. Alternatively, the evaporator can also be a separate component that is connected to the circuit in the direction of flow between the expansion and the compression device.

Furthermore, the working material in the circuit is condensed in the flow direction between the compression and the expansion device. In this area, the circuit can also contain pipe loops, which means that a larger surface area can be provided for heat transfer from the primary side to the secondary side of the cycle process system. This area of the circuit is referred to below as the condenser. Alternatively, the condenser can also be a separate component which is connected to the circuit in the direction of flow between the compression and the expansion device.

Furthermore, the cyclic process system comprises at least one thermal consumer and at least one heat transport device.

A thermal consumer should be understood to mean a (room) volume and/or a (component) mass from which heat is to be removed or to which heat is to be supplied. This means that the at least one thermal consumer is arranged on the secondary side of the cyclic process system. The thermal consumer is preferably an interior, in particular an interior of an (electric) vehicle, and/or a component, preferably a component of a vehicle, in particular a battery, which stores the electricity for driving an electric vehicle.

For example, the optimum temperature range for lithium-ion batteries, which are currently the preferred choice in electric vehicles, is between 15 °C and 35 °C, so that the temperature of the battery is usually controlled via the connection to the refrigerant circuit of the vehicle's air conditioning system. This results in a cycle process system with two parallel sub-cycles, one of which provides the interior temperature control and the other the battery temperature control.

A heat transfer device should be understood as a part/component that supports the transfer of heat from the primary side to the secondary side of the cycle system. In particular, the heat transport device should serve to transfer the heat to be dissipated during the condensation of the working substance to a medium on the secondary side of the cyclic process system. The heat transport device can be integrated into the condenser, in that this is designed, for example, as a working material/air or working material/liquid heat exchanger. Alternatively or additionally, the heat transport device can have a fan which is arranged on the secondary side of the cycle process system in the area of the condenser. The heat transport device is particularly preferably a condenser which is designed as a working fluid/air heat exchanger and has a fan.

The physical model of the cyclic process system preferably uses physical models that depict the physics of the components on the primary side and the secondary side of the system, i.e. there are preferably sub-models of the at least one expansion and compression device, the line system with evaporator and condenser and the at least one heat transport device and the at least one thermal consumer. The thermodynamic material properties are also preferred of the working substance and the fluids that are used for heat transfer on the secondary side of the cyclic process plant are integrated into the physical model. Thus, the flow of working substance in the circuit on the primary side of the cyclic process system, the fluid flows on the secondary side and the pressure and the temperature at the relevant points of the cyclic process system can be calculated. These variables can be used both to control the system and to provide target values for the control/regulation of individual components. In comparison to known control/regulation methods, different target values are available, which enable a different control strategy and additional optimization potential.

According to the invention, a working substance flow in the circuit is determined or calculated, with the calculated working substance flow being based on a thermal output of the at least one thermal consumer. This means that a required working substance flow in the circuit on the primary side of the cycle process system is calculated based on a requested thermal output of a thermal consumer (e.g. vehicle interior or battery temperature control) on the secondary side of the cycle process system.

The flow of working substance can be a volume flow of the working substance and/or a mass flow of the working substance. The flow of working substance is preferably a mass flow of the working substance. The thermal output of the thermal load is to be understood as meaning the heat flow that is required to be removed or supplied in order to achieve a desired temperature in/at the thermal load.

The mode of operation of the physical model is described below using greatly simplified formulas. The physical model also depicts the heat transfer between the individual components of the cyclic process system and the behavior of the working substance depending on its physical state.

The required thermal output of a consumer on the secondary side of the cyclic process system can be calculated using the physical model of the cyclic process system based on the desired/required outlet temperature T _{S out of} of the fluid on the secondary side can be calculated according to formula (1): $${\dot{Q}}_S={\dot{m}}_S\cdot c_S\cdot \left(T_{S_{ein}}-T_{S_{a\mathrm{and}s}}\right)$$

Q̇ _S denotes the thermal power on the secondary side, ṁ _S the mass flow of the heat-transferring fluid on the secondary side, c _S the heat storage capacity of the fluid on the secondary side and T _{S a} the inlet temperature of the fluid on the secondary side.

The working substance flow to be evaporated on the primary side is calculated from the energy conservation between the required thermal output Q̇ _S on the secondary side and the thermal output Q̇ _Pv to be provided on the primary side.

wobei ${\dot{m}}_{Pv}$

den zu verdampfenden Arbeitsstoffmassenstrom auf der Primärseite und Δh_v die Änderung der Enthalpie des Arbeitsstoffstroms durch die Verdampfung bezeichnet, die sich aus den thermodynamischen Stoffeigenschaften des Arbeitsstoffs bei dem ersten vorbestimmten Druck ergibt.According to formula (2), the thermal output Q̇ _Pv on the primary side is: $${\dot{Q}}_{Pv}={\dot{m}}_{Pv}\cdot \Delta H_v$$

whereby ${\dot{m}}_{Pv}$

denotes the working substance mass flow to be evaporated on the primary side and Δh _v denotes the change in the enthalpy of the working substance flow due to the evaporation, which results from the thermodynamic material properties of the working substance at the first predetermined pressure.

With Q̇ _S = Q̇ _P , it follows for the working substance mass flow ṁ _Pv to be evaporated on the primary side, neglecting heat transfer losses and phase-dependent changes in the temperature behavior of the working substance: $${\dot{m}}_{Pv}=\frac{{\dot{m}}_S\cdot c_S\cdot \left(T_{S_{ein}}-T_{S_{a\mathrm{and}s}}\right)}{\Delta H_v}$$

wird eine Stellgröße der Kompressionsvorrichtung gesteuert. Mit anderen Worten wird die Kompressionsvorrichtung mittels einer geeigneten Stellgröße derart gesteuert, dass der berechnete Arbeitsstoffstrom ${\dot{m}}_{Pv}$

bereitgestellt wird. Dazu kann die Kompressionsvorrichtung beispielsweise eine Kennlinie aufweisen, welche die Werte der Stellgröße in Abhängigkeit von dem Arbeitsstoffstrom angibt. Diese Kennlinie kann beispielsweise in einer Recheneinheit der Kompressionsvorrichtung oder in einer zentralen Recheneinheit der Kreisprozessanlage gespeichert sein.Depending on the calculated working substance flow ${\dot{m}}_{Pv}$

a manipulated variable of the compression device is controlled. In other words, the compression device is controlled by means of a suitable manipulated variable in such a way that the calculated flow of working substance ${\dot{m}}_{Pv}$

provided. For this purpose, the compression device can have a characteristic curve, for example, which indicates the values of the manipulated variable as a function of the working substance flow. This characteristic curve can be stored, for example, in a computing unit of the compression device or in a central computing unit of the cyclic process system.

The manipulated variable of the compression device is preferably a speed of a compressor, which is controlled by a computing unit by means of pulse width modulation or via a data bus system (e.g. via Local Interconnect Network (LIN)) according to the characteristic curve of the compressor.

Furthermore, the expansion device is controlled in such a way that a first predetermined pressure of the working substance is established at an outlet from the expansion device. Under the exit from the expansion device should ins be understood especially the exit from the evaporator. In accordance with the thermodynamic material properties of the working substance, an associated saturation temperature is set by controlling the expansion device at the first predetermined pressure.

The first predetermined pressure is preferably selected on the basis of the boundary conditions of the cyclic process system (ambient conditions, working material) and the requirements of the thermal consumers. For example, the first predetermined pressure must not be chosen too low in order to avoid icing of the evaporator. On the other hand, in the case of an air conditioning system for a vehicle interior, the pressure selected must not be too high either, in order to avoid odor problems, for example. Therefore, the pressure level after the expansion device can be set differently for the different applications.

An opening cross section and/or an opening duration of an expansion valve are preferably controlled as a function of the first predetermined pressure at the outlet from the expansion device. The pressure can be determined by means of the physical model and the expansion valve can be controlled in such a way that an opening cross section and/or an opening duration are established, with which the first predetermined pressure is reached. The expansion valve is preferably a valve in which the opening cross section is set via a corresponding valve position, e.g. with a LIN bus connection.

The described physically based control of the cyclic process system enables a simpler and more precise adjustment of the overheating temperature of the working substance flow at the inlet of the compression device. As a result, the superheat temperature can be selected to be smaller, which improves the efficiency of the cyclic process plant. Furthermore, the control according to the invention reduces losses in the compression device and fluctuations in its manipulated variable, so that noise and vibration problems can be avoided during operation of the cyclic process system.

des Arbeitsstoffs zum Erreichen der vorbestimmten Temperatur (Überhitzungstemperatur) bei dem ersten vorbestimmten Druck kann den thermodynamischen Stoffeigenschaften des Arbeitsstoffs entnommen werden. Somit folgt für den benötigten Arbeitsstoffmassenstrom unter Berücksichtigung der Überhitzungstemperatur $${\dot{m}}_{Pv}^{\text{'}}=\frac{{\dot{m}}_S\cdot c_S\cdot \left(T_{S_{ein}}-T_{S_{aus}}\right)}{\Delta h_v}\text{mit }\Delta {\text{h}}_v^{\text{'}}>\Delta h_v$$

When calculating the flow of working substance, a first predetermined temperature of the working substance at an inlet into the compression device is preferably taken into account. In other words, the working substance is preferably overheated after evaporation to the first predetermined temperature in order to prevent damage to the compression device by liquid components of the refrigerant. The required change in enthalpy $\Delta H_v^{\text{'}}$

of the working substance to reach the predetermined temperature (superheating temperature) at the first predetermined pressure can be taken from the thermodynamic substance properties of the working substance. Thus follows for the required working substance mass flow taking into account the overheating temperature $${\dot{m}}_{Pv}^{\text{'}}=\frac{{\dot{m}}_S\cdot c_S\cdot \left(T_{S_{ein}}-T_{S_{a\mathrm{and}s}}\right)}{\Delta H_v}\text{with}\Delta {\text{H}}_v^{\text{'}}>\Delta H_v$$

In addition, a thermal output for condensing the working substance in the circuit after it has exited the compression device is preferably calculated. This calculation is based on a second predetermined pressure of the working substance and the calculated working substance flow. The second predetermined pressure corresponds to the pressure after the compression device and results from the speed.

höher als die zur Kondensation benötigte Enthalpie Δh_k.Since the temperature of the working substance after compression is higher than the saturation temperature, the working substance must first be cooled down to the saturation temperature. Thus, the enthalpy to be removed from the working substance is $\Delta H_k^{\text{'}}$

higher than the enthalpy Δh _k required for condensation.

The thermal power Q̇ _Pk to be dissipated for the condensation of the working substance in the circuit after exiting the compression device is thus calculated as follows $${\dot{Q}}_{Pk}={\dot{m}}_{Pk}\cdot \Delta H_k^{\text{'}}\text{with}{\dot{m}}_{Pk}\cdot =m_{Pv}^{\text{'}}$$

den zu kondensierenden Arbeitsstoffmassenstrom, der bei quasistationärer Betrachtung in dem geschlossenen Kreislauf gleich dem zu verdampfenden Arbeitsstoffmassenstrom $m^{;}{}_{Pv}$

ist, und $\Delta h_K^{\text{'}}$

zur Kondensation des Arbeitsstoffs bei dem zweiten vorbestimmten Druck abzuführende Enthalpie, die sich aus den thermodynamischen Stoffeigenschaften des Arbeitsstoffs ergibt.Q _Pk denotes the thermal power required to condense the working substance, ${\dot{m}}_{Pk}$

the working substance mass flow to be condensed, which is equal to the working substance mass flow to be evaporated in a quasi-stationary view in the closed circuit $m^{;}{}_{Pv}$

is and $\Delta H_K^{\text{'}}$

enthalpy to be dissipated for condensing the working substance at the second predetermined pressure, which enthalpy results from the thermodynamic material properties of the working substance.

Based on the calculated thermal power Q _Pk for condensing the working substance, a fluid flow through the heat transport device is then preferably calculated using the physical model of the cycle process system, depending on which a manipulated variable of the heat transport device is controlled.

auf der Sekundärseite unter Vernachlässigung von Wärmeübergangsverlusten und phasenabhängiger Änderung des Temperaturverhaltens des Arbeitsstoffs zu $${\dot{m}}_{Sk}=\frac{{\dot{m}}_{Pk}\cdot \Delta h_k^{\text{'}}}{c_S\cdot \left(T_{S_{ein}}-T_{S_{aus}}\right)}$$

wobei c_S die Wärmespeicherkapazität des Fluids auf der Sekundärseite, T_Sein die Eingangstemperatur und T_Saus die Ausgangstemperatur des Fluids auf der Sekundärseite der Kreisprozessanlage bezeichnet. Bei dem Fluid auf der Sekundärseite der Kreisprozessanlage kann es sich sowohl um ein gasförmiges Fluid, wie Luft, oder um eine Flüssigkeit handeln.The fluid flow is calculated according to the conservation of energy between the primary and secondary side of the cyclic process system ${\dot{m}}_{Sk}$

on the secondary side, neglecting heat transfer losses and phase-dependent changes in the temperature behavior of the working substance $${\dot{m}}_{Sk}=\frac{{\dot{m}}_{Pk}\cdot \Delta H_k^{\text{'}}}{c_S\cdot \left(T_{S_{ein}}-T_{S_{a\mathrm{and}s}}\right)}$$

where _cS is the heat storage capacity of the fluid on the secondary side, _{TS a} the inlet temperature and T _{S out of} denotes the outlet temperature of the fluid on the secondary side of the cycle process system. The fluid on the secondary side of the cyclic process system can be either a gaseous fluid, such as air, or a liquid.

The manipulated variable of the heat transport device can be, e.g. when using a working flow/air heat exchanger, the speed of a fan, which is proportional to the fluid mass flow and can therefore be controlled very easily as a function of this.

des Arbeitsstoffs zum Erreichen der zweiten vorbestimmten Temperatur (Unterkühlungstemperatur) bei dem zweiten vorbestimmten Druck kann den thermodynamischen Stoffeigenschaften des Arbeitsstoffs entnommen werden. Somit folgt für den benötigten Fluidmassenstrom $m_{Sk}$

unter Berücksichtigung der Unterkühlungstemperatur $${\dot{m}}_{Sk}{}^{\text{'}}=\frac{{\dot{m}}_{Pk}\cdot \Delta h_k^{"}}{c_S\cdot \left(T_{S_{ein}}-T_{S_{aus}}\right)}\text{mit }\Delta h_k^{"}>\Delta h_k^{\text{'}}$$

A second predetermined temperature of the working substance at an inlet into the expansion device is particularly preferably taken into account when calculating the fluid flow through the heat transport device. In other words, after condensation, the working fluid is subcooled to a second predetermined temperature to ensure that vapor locks do not form in front of the expansion device. The required change in enthalpy $\Delta H_k^{"}$

of the working material to reach the second predetermined temperature (supercooling temperature) at the second predetermined pressure can be found in the thermodynamic material properties of the working material. Thus follows for the required fluid mass flow $m_{Sk}$

considering the subcooling temperature $${\dot{m}}_{Sk}{}^{\text{'}}=\frac{{\dot{m}}_{Pk}\cdot \Delta H_k^{"}}{c_S\cdot \left(T_{S_{ein}}-T_{S_{a\mathrm{and}s}}\right)}\text{with}\Delta H_k^{"}>\Delta H_k^{\text{'}}$$

The calculation of a required fluid flow on the secondary side of the cyclic process system for cooling the working substance to a desired temperature level before the expansion device enables optimization of the heat dissipation via the heat transport device and thus an increase in the performance of the cyclic process system.

According to a preferred embodiment, the circuit on the primary side of the cyclic process plant contains a first sub-circuit with a first expansion device for a first consumer on the secondary side of the cyclic process plant and a second sub-circuit with a second expansion device for a second consumer on the secondary side of the cyclic process plant. The partial circuits are particularly preferably arranged parallel to one another and open into a common line upstream of the compression device.

This embodiment can be used, for example, when, as described above, the air conditioning system of an electric vehicle is used not only to control the temperature of the vehicle interior but also to control the temperature of the battery. In this case, a first flow of working substance is initially calculated in the first partial circuit based on a thermal output of the first consumer. A second working substance flow is then calculated in the second partial circuit based on a thermal output of the second consumer. The calculation of the individual partial flows of working material is carried out in the same way as described above for a single consumer. The calculation of the individual partial flows of working material ensures that the required superheating temperature at the entry into the compression device is also ensured with two parallel thermal consumers.

The total working substance flow in the circuit is calculated from the sum of the first and second working substance flow and is used to control the manipulated variable of the compression device. This means that the compression device can be controlled in the same way as for a single consumer.

The first expansion device is preferably controlled in such a way that a first predetermined pressure of the working substance is established at an outlet from the first expansion device. This pressure can be selected depending on the operating mode of the cyclic process system. In the event that the battery represents the first consumer, the first predetermined pressure can be selected, for example, only according to the requirements for temperature control of the battery if no vehicle interior temperature control is required. If both thermal 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 carried out via the first expansion device, i.e. it is also present after the second expansion device.

The second expansion device is preferably controlled as a function of the calculated flow of working substance in the second partial circuit and the first predetermined pressure of the working substance at the outlet from the first expansion device. In other words, the pressure downstream of the second expansion device is predetermined by the control of the first expansion device, so that the partial working substance flow through the second partial circuit can be adjusted with the opening cross section/opening duration of the second expansion device. Since the compression device requires all the working substance current for both sub-cycles, the required flow of working material for the first sub-cycle results automatically. This enables improved control of the pressure after the expansion device in the case of two parallel working fluid circuits compared to control of the pressure by means of the compression device.

According to a preferred embodiment, an (actual) working material flow is determined in the circuit and the working material flow determined is compared with the calculated working material flow. The manipulated variable of the compression device is then adjusted or controlled based on a difference between the determined and the calculated working substance flow. The manipulated variable of the compression device is preferably set in such a way that the determined working substance flow corresponds to the calculated one. According to one embodiment, the working substance flow is measured at a first predetermined position in the circuit using a flow sensor. Alternatively or additionally, the working substance flow can be estimated based on a measured temperature at the entrance to the compression device and/or a measured pressure after the compression device.

Preferably, the compression device itself is equipped with the flow sensor. Alternatively or additionally, the predetermined position of the flow sensor may be between the expansion device and the compression device. In the latter case, the flow sensor is particularly preferably arranged at a predetermined distance from the entry into the compression device in order to avoid measurement errors, for example due to backflows. A volume flow sensor or a mass flow sensor can be used. A mass flow sensor is particularly preferably used.

Controlling the manipulated variable of the compression device based on the measured flow of working substance offers the advantage that deviations between the physical model of the cyclic process system and the real system can be compensated for. Thus, for example, it is possible to react to age-related changes in the system.

The manipulated variable of the compression device is preferably a speed of a compressor, which is controlled by a computing unit by means of pulse width modulation or via a data bus system (e.g. via Local Interconnect Network (LIN)) according to the characteristic curve of the compressor.

The compression device itself is preferably equipped with a computing unit which receives the values of the calculated and measured working substance flow and controls the manipulated variable on the basis of the received values. Additional parameters of the compression device, such as minimum and maximum values of the manipulated variable and/or power limits of the compression device, can be stored in this arithmetic unit, which can be taken into account in the regulation. A corresponding compression arrangement with a compression device (or generally a pump), a computing unit and a flow sensor is also itself the subject of the invention.

In addition, a pressure of the working substance is preferably 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 compression device. The pressure sensor is particularly preferably located directly after the evaporator.

The measured working fluid pressure is compared to the first predetermined pressure of working fluid at the outlet of the expansion device and the at least one expansion valve is controlled based on a difference between the measured working fluid pressure and the first predetermined pressure.

The opening cross section and/or the opening duration of the expansion valve are preferably controlled in such a way that the actual working fluid pressure corresponds to the first predetermined pressure at the outlet from the expansion device. Depending on the distance between the pressure sensor position and the outlet from the expansion device, pressure losses in the line can be taken into account, so that the measured working substance pressure can also be regulated to a value that differs from the first predetermined pressure.

In addition, a temperature of the working substance is preferably measured at a third predetermined position in the circuit by means of a temperature sensor. The predetermined position of the temperature sensor is preferably downstream of the condenser, between the condenser and the at least one expansion device. The temperature sensor is particularly preferably located directly in front of the expansion device.

The measured temperature is then compared to the predetermined temperature of the working fluid at the entrance to the expansion device and the manipulated variable of the heat transport device based on a difference between the measured sen working temperature and the predetermined temperature controlled. Depending on the distance between the temperature sensor position and the entry into the expansion device, temperature losses in the line can be taken into account, so that the measured working fluid temperature can also be regulated to a value that differs from the predetermined temperature.

By controlling the pressure and temperature of the working substance, deviations in the real cycle process system from the physical model, which can occur in the system as a result of aging processes, for example, can be compensated for. This enables an improved accuracy of the cycle process control even with a longer running time of the plant.

A computing unit according to the invention, e.g. a control unit of a motor vehicle, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is advantageous because this causes particularly low costs, especially if an executing control device is also used for other tasks and is therefore available anyway. Finally, a machine-readable storage medium is provided with a computer program stored thereon as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical storage devices such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.). Such a download can be wired or wired or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

Further advantages and refinements of the invention result from the description and the attached drawing.

The invention is shown schematically using an exemplary embodiment in the following drawings and is described below with reference to the drawing.

character list

• 1 Figure 12 shows schematically an example of a refrigeration cycle plant including a compression arrangement according to a preferred embodiment of the invention, and which can be controlled according to a preferred embodiment of the claimed method.

embodiment(s) of the invention

In 1 an example of a cycle process system is shown schematically, which can be controlled / regulated according to a preferred embodiment of the invention. The cyclic process system is preferably an air conditioning system in an electric vehicle (not shown). The air conditioning system includes a refrigerant circuit in which there are two parallel sub-circuits 450, 451, each of which has an expansion valve 43, 44 (expansion device) and an evaporator 50, 60. Furthermore, the refrigerant circuit includes a compression assembly having a compressor 20 (compression device), a compressor control unit (arithmetic unit) 21 and a flow sensor 22, and an accumulator 70 and a condenser 40, which is provided with a fan 41 (heat transport device) on the secondary side . Alternatively or additionally, the flow can be estimated using a measured temperature at the inlet of the compressor and/or a measured pressure after the compressor.

The first partial circuit 450 with the first evaporator 60 is used to control the temperature of a traction battery (not shown) of the electric vehicle. For this purpose, a working material/liquid heat exchanger (indicated by the arrows 61) is arranged on the secondary side of the first evaporator 60, which, for example, conducts cooling liquid to a cooling plate (not shown) connected to the battery. The second partial circuit 451 with the second evaporator 50 is provided for temperature control of the vehicle interior (not shown). For this purpose, a fan 51 is arranged on the secondary side of the second evaporator 50 and directs the cooled air on the secondary side of the second evaporator 50 into the vehicle interior. The two partial circuits open into the common line 500, in which a pressure sensor for monitoring/measuring a first predetermined pressure of the refrigerant at the outlet of the evaporators 50, 60 is arranged. The gaseous refrigerant is fed to the compressor 20 via the accumulator 70 via the line 500 . Any liquid components of the refrigerant can be separated in the accumulator 70 .

Based on the required thermal output of the two thermal 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 flow, the total refrigerant mass flow in the refrigerant circuit is calculated, based on which the speed of the compressor 20 is controlled.

In the refrigerant circuit shown, the traction battery of the vehicle, which has to be continuously temperature-controlled, represents the first thermal consumer. The temperature control of the vehicle interior, which represents the second thermal consumer, is only switched on when required. A first predetermined pressure is thus set after the two evaporators 50, 60 according to the requirements of the battery, as long as no additional temperature control of the vehicle interior is required. If both thermal consumers are active, the pressure after the evaporator must be selected according to the requirements of both consumers.

The first expansion valve 44 is preferably controlled in such a way that the first predetermined pressure of the working substance after the evaporator 60 is set. This pressure is then also present after the second expansion valve 43 due to the parallel arrangement of the partial circuits. In other words, the pressure after the second expansion valve 43 is predetermined by the control of the first expansion valve 44, so that the partial refrigerant flow through the second partial circuit 451 can be adjusted via an opening cross section/an opening duration of the second expansion valve 43. Since the compressor 20 provides the required total refrigerant flow for both sub-circuits 450, 451, the required refrigerant flow for the first sub-circuit 450 results automatically. This enables improved control of the pressure after the evaporators 50, 60 in the case of two parallel refrigerant circuits 450, 451 compared to controlling the pressure by means of the compressor 20.

The compressor 20 compresses the refrigerant to a second predetermined pressure and conveys it via a line 200 to a condenser 40. The condenser 40 has a fan 41 with which an air mass flow on the secondary side of the condenser can be controlled. The second predetermined pressure is preferably selected in such a way that the associated saturation temperature is above the ambient temperature. In the condenser, the compressed refrigerant is first cooled to the saturation temperature and then liquefied.

The required thermal power for condensing the refrigerant is calculated from the enthalpy to be dissipated at the second predetermined pressure and the refrigerant mass flow in the circuit according to formula (5). Based on the calculated thermal output of the condenser, the air mass flow on the secondary side of the condenser is then determined according to formula (6) or (7), using which the speed of fan 42 is controlled in order to provide the required heat transport.

The liquefied refrigerant is then fed back to the expansion valves 43, 44 via the line 400, 450. A temperature sensor 42 is arranged upstream of the expansion valves 43, 44, with which the subcooling temperature of the refrigerant can be monitored/measured.

The air conditioning system shown for an electric vehicle also includes a computing unit 10 for controlling the individual components of the air conditioning system. A physical model of the air conditioning system is stored in the computing unit 10, with which the calculations described can be carried out. The computing unit 10 receives the signals from the flow sensor 22, the temperature sensor 42 and the pressure sensor 62 for controlling the respective variables based on the associated setpoint values that were determined using the physical model. Furthermore, the computing unit 10 is electrically connected to the compressor control unit 21, the fans 41, 51 and the expansion valves 43, 44 in order to be able to control the air conditioning system using the manipulated variables of the relevant components.

In particular, a data exchange can take place between the computing unit 10 and the compressor control unit 21 for controlling the refrigerant mass flow. The data can be exchanged, for example, via a data bus system (e.g. via Local Interconnect Network (LIN)). The computing unit 10 first sends the required refrigerant mass flow (target mass flow) determined using the physical model to the compressor control unit 21. In addition to the target mass flow, this also receives the flow signal from the flow sensor 22 and calculates the difference between the target and the actual -mass flow and adjusts the speed of the compressor 20 based on the calculated mass flow difference. This has the advantage that additional parameters, such as the minimum or maximum speed, the maximum permissible temperature and/or the maximum output of the compressor 20, can be stored in the compressor control unit 21, which the compressor control unit 21 can take into account in the regulation.

As an alternative or in addition, the computing unit 10 can receive the signal from the flow sensor 22 , calculate the refrigerant mass flow difference and send this to the compressor control unit 21 . This can then the required com Set the pressor speed based on the received mass flow difference.

The described physically based control of the cyclic process system enables a simpler and more precise adjustment of the overheating temperature of the working substance flow at the inlet of the compression device. As a result, the superheat temperature can be selected to be smaller, which improves the efficiency of the cyclic process plant. Furthermore, the control according to the invention reduces fluctuations in the manipulated variable of the compression device, so that noise and vibration problems can be avoided during the operation of the cyclic process system.

Claims (12)

Method for controlling a cyclic process system using a physical model, the cyclic process system having a circuit with a working substance, at least one thermal consumer and at least one heat transport device (41, 51), with at least one expansion device (43, 44) and at least one compression device in the circuit (20) are arranged, comprising the steps of: - Calculating a working substance flow in the circuit based on a thermal output of the at least one thermal consumer, - Controlling a manipulated variable of the compression device (20) depending on the calculated flow of working substance; and - Controlling the expansion device (43, 44) in such a way that a first predetermined pressure of the working substance is set at an outlet from the expansion device (43, 44). procedure according to claim 1 , A first predetermined temperature of the working substance at an entry into the compression device (20) being taken into account when calculating the flow of working substance. procedure according to claim 1 or 2 , wherein the method comprises the further steps: - calculating a thermal power for condensing the working substance in the circuit after an exit from the compression device (20) based on a second predetermined pressure of the working substance and the calculated working substance flow; - Calculating a fluid flow through the heat transport device (41, 51) based on the calculated thermal power for condensing the working substance; and - controlling a manipulated variable of the heat transport device (41, 51) depending on the calculated fluid flow through the heat transport device (41, 51). procedure according to claim 3 , wherein in the calculation of the fluid flow through the heat transport device (41, 51) a second predetermined temperature of the working substance at an entry into the expansion device (43, 44) is taken into account. procedure according to claim 4 , comprising the further steps: - measuring a temperature of the working substance in the circuit by means of a temperature sensor (42); - comparing the measured working fluid temperature with the second predetermined temperature of the working fluid at the entrance to the expander (43, 44); and - 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 at the inlet to the expansion device (43, 44). Method according to one of the preceding claims, wherein the circuit contains a first sub-circuit (450) with a first expansion device (44) for a first consumer and a second sub-circuit (451) with a second expansion device (43) for a second consumer, comprising the further Steps: - Calculating a first flow of working substance in the first partial circuit (450) based on a thermal output of the first consumer, and - Calculating a second flow of working substance in the second partial circuit (451) based on a thermal output of the second consumer; - Calculating a working material flow in the circuit as a sum of the calculated working material flows through the first and second partial circuits (450, 451); - Controlling the manipulated variable of the compression device (20) depending on the calculated flow of working substance; - Controlling the first expansion device (43, 44) in such a way that a first predetermined pressure of the working substance is set at an outlet from the first expansion device (44), and - Controlling the second expansion device (43) depending on the calculated flow of working material in the second partial circuit and the first predetermined pressure of the working material at the outlet from the first expansion device (44). Method according to one of the preceding claims, comprising the further steps: - Determining a working substance flow in the cycle; - Comparing the determined working substance flow with the calculated working substance flow; and - Controlling the manipulated variable of the compression device (20) based on a difference between the determined and the calculated working flow. Method according to one of the preceding claims, comprising the further steps: - measuring a pressure of the working substance in the circuit by means of a pressure sensor (62); - comparing the measured working fluid pressure with the first predetermined pressure of the working fluid at the exit from the expansion device (43, 44); and - controlling the at least one expansion device (43, 44) based on a difference between the measured working fluid pressure and the first predetermined pressure of the working fluid. Arithmetic unit (10) which is set up to carry out all method steps of a method according to one of the preceding claims. Computer program that causes a computing unit (10) to all method steps of a method according to one of Claims 1 until 8th to be performed when it is executed on the computing unit. Machine-readable storage medium with a computer program stored on it claim 10 . Compression arrangement with a compression device (20), a computing unit (21) and a flow sensor (22), wherein the computing unit (21) is set up to receive a target value for a working flow to be delivered by the compression device (21), this with one of to compare the measured value for the working flow received from the flow sensor (21) and to control a manipulated variable of the compression device (20) based on a difference between the desired value and the measured value.

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