Method and control device for operating a heat pump while stabilizing a network frequency of an electrical power network

Abstract

The invention relates to a method for operating a heat pump (10) while stabilizing a network frequency of an electrical power network (15), wherein the heat pump has a first heat exchanger (11), a compressor (12) that can be driven by an electric machine (14) connected to the electrical power network, a second heat exchanger (13), and an expansion device (16), wherein: the first heat exchanger (11) is designed to transfer thermal energy to a process medium; the compressor (12) is designed to compress the process medium downstream of the first heat exchanger; the second heat exchanger (13) is designed to transfer thermal energy of the process medium to a load; the expansion device (16) is designed to expand the process medium downstream of the second heat exchanger; and the heat pump (10) has a device by means of which a volume flow of the process medium can be adjusted. When an actual network frequency of the electrical power network (15) deviates from a setpoint network frequency, in order to stabilize the network frequency, an electrical power consumption of the electric machine (14) is controlled by controlling a rotational speed of the electric machine and / or by changing the volume flow of the process medium in such a way that, at an approximately constant pressure ratio of the compressor (12) and thus at an approximately constant temperature of the process medium in the region of the second heat exchanger (13), the actual network frequency is approximated to the setpoint network frequency.

Description

[0001] Method and control device for operating a heat pump while stabilizing a mains frequency of an electrical power grid

[0002] The invention relates to a method and a control device for operating a heat pump while stabilizing a mains frequency of an electrical power grid.

[0003] The structure of a heat pump is well known in practice. A heat pump has a first heat exchanger, which is designed to transfer thermal energy, in particular from the environment, to a process medium of the heat pump. Downstream of the first heat exchanger, a heat pump comprises a compressor, which is designed to compress the process medium of the heat pump, wherein the compressor is driven by an electric machine. Downstream of the compressor, a heat pump has a second heat exchanger, which is designed to transfer thermal energy of the process medium of the heat pump to a consumer or a process medium of a consumer. Downstream of the second heat exchanger, an expansion device is provided to expand the process medium of the heat pump.The expansion device can be a turbine and / or an expansion valve or an ejector or a pressure exchanger.

[0004] The heat pump's electrical machine, which drives its compressor, is connected to an electrical grid and supplied with electrical energy. If the grid frequency fluctuates, it is generally possible to change the electrical power consumption of the electrical machine driving the heat pump's compressor in order to stabilize the grid frequency. If the speed of the electrical machine is increased, the electrical load consumption of the heat pump increases, as does the temperature of the heat pump's process medium in the area of ​​the second heat exchanger. If the speed of the electrical machine driving the heat pump's compressor is reduced, the electrical power consumption of the heat pump decreases, and with it the temperature of the process medium in the area of ​​the second heat exchanger.

[0005] If the grid frequency of an electrical network is stabilized via the heat pump, this leads in practice to a change in the temperature of the heat pump's process fluid in the area of ​​the second heat exchanger, and thus also to fluctuations in the quality of the thermal energy transferred to the consumer. This is a disadvantage.

[0006] There is a need to operate a heat pump in such a way that, when the heat pump is used to stabilize the grid frequency of an electrical power grid, the temperature of the heat pump's process medium in the area of ​​the second heat exchanger and thus the quality of the thermal energy that can be transferred to the consumer remains unchanged or almost unchanged.

[0007] Based on this, the present invention is based on the object of creating a novel method and control device for operating a heat pump while stabilizing a mains frequency of an electrical power grid.

[0008] This object is achieved by a method according to claim 1 and a control device according to claim 9. The present invention proposes, in order to stabilize the mains frequency of an electrical power grid with the aid of a heat pump, to adapt the electrical power consumption of the electrical machine which drives the compressor of the heat pump by means of a speed control of the same and / or by changing the volume flow of the process medium of the heat pump.

[0009] If the actual grid frequency of the electrical grid deviates from the target grid frequency, the electrical power consumption is adjusted via the speed control of the electrical machine and / or by changing the volume flow of the heat pump's process medium in order to stabilize the grid frequency. The actual grid frequency of the electrical grid is brought closer to the target grid frequency at a constant or nearly constant compressor pressure ratio and thus at a constant or nearly constant process medium temperature in the area of ​​the second heat exchanger. In this way, the actual grid frequency of the electrical grid can be brought closer to the target grid frequency to stabilize the grid frequency without changing the temperature of the heat pump's medium in the area of ​​the second heat exchanger and thus the quality of the thermal energy that can be transferred to the consumer.

[0010] In order to ensure that the grid frequency is stabilized at a constant or approximately constant pressure ratio of the compressor and thus at a constant or approximately constant temperature of the process medium in the area of ​​the second heat exchanger and thus an unchanged or approximately unchanged quality of the thermal energy that can be transferred to the consumer, the electrical power consumption is preferably adjusted simultaneously by controlling the speed of the electrical machine and by changing the volume flow of the process medium of the heat pump.Preferably, when the actual grid frequency of the electrical power grid is higher than the target grid frequency, the electrical power consumption of the electrical machine is increased by increasing its speed and / or by increasing the volume flow of the heat pump's process medium. When the actual grid frequency of the electrical power grid is lower than the target grid frequency, the electrical power consumption is reduced by reducing its speed and / or by reducing the volume flow of the heat pump's process medium. This allows for a particularly advantageous stabilization of the grid frequency of an electrical power grid.

[0011] Preferably, when the actual grid frequency of the electrical power grid is higher than the target grid frequency, the electrical power consumption of the electrical machine is increased by increasing its speed and simultaneously increasing the volume flow of the process medium. When the actual grid frequency of the electrical power grid is lower than the target grid frequency, the electrical power consumption is preferably reduced by reducing the speed of the electrical machine and simultaneously reducing the volume flow of the process medium.

[0012] The speed control for the variable-speed electric machine is preferably achieved via frequency adjustment on a frequency converter connected between the electrical power grid and the electric machine. The change in the volume flow of the heat pump's process medium is preferably achieved by controlling the device for changing the volume flow, preferably by controlling the expansion device and / or the compressor and / or a separate valve or a separate throttle. In particular, this involves changing the flow resistance in the area of ​​the expansion device and / or the compressor and / or the separate valve or the separate throttle. Preferred developments of the invention emerge from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawing, without being limited thereto. In the drawing:

[0013] Fig. 1 is a diagram of a heat pump to illustrate the invention,

[0014] Fig. 2 a compressor characteristic map.

[0015] Fig. 1 shows a highly schematic embodiment of a heat pump 10.

[0016] The heat pump 10 has a first heat exchanger 11 which is configured to transfer thermal energy to a process medium of the heat pump 10.

[0017] The thermal energy transferred to the heat pump's process medium by means of the first heat exchanger 11 can be, for example, thermal energy from ambient air, thermal energy from lake or sea water, water from rivers, or municipal or industrial wastewater from a waste heat process. Waste heat from a process gas can also be used as thermal energy to heat the heat pump's process medium.

[0018] The heat pump 10 has a compressor 12 downstream of the first heat exchanger 11, as seen in the flow direction of the process medium of the heat pump 10. The compressor 12 is configured to compress the process medium of the heat pump downstream of the first heat exchanger 11 and upstream of a second heat exchanger 13 of the heat pump 10. The second heat exchanger 13 is configured to transfer thermal energy of the process medium of the heat pump 10 to a consumer or a process medium of the consumer.

[0019] The compressor 12 can be driven by an electric machine 14 of the heat pump 10. For this purpose, the electric machine 14 is connected to an electrical power grid 15. The electric machine 14 can be supplied with electrical energy from the electrical power grid 15, namely via a frequency converter 22 connected between the electric machine 14 and the electrical power grid 15. The electric machine 14 is connected to the electrical power grid 15 via the frequency converter 22. Depending on the speed and torque of the electric machine 14, the electric machine 14 takes on or takes off electrical load from the electrical power grid 15. The electric machine 14 can also be referred to as an electric motor.

[0020] The heat pump 10 further comprises an expansion device 16, which in the illustrated embodiment comprises both a turbine 17 and an expansion valve 18. The turbine 17 and the expansion valve 18 are configured to expand the process medium of the heat pump 10 downstream of the second heat exchanger 13 and upstream of the first heat exchanger 11. Energy generated in the turbine 17 can be used to drive the electric machine 14.

[0021] As an alternative to the illustrated embodiment, the expansion device 16 may also comprise exclusively the turbine 17 or exclusively the expansion valve 18. Alternatively or additionally, the expansion device 16 may also comprise an ejector or a pressure exchanger.

[0022] Fig. 1 also shows an optional bypass valve 19 to the turbine 17. The bypass valve 19 can be used to adjust the amount of process medium from the heat pump 10, which is guided past the turbine 17 directly towards the expansion valve 18.

[0023] If the grid frequency of the electrical power grid 15 changes in such a way that an actual grid frequency of the electrical power grid 15 deviates from a target grid frequency of the same, the electrical power consumption of the electrical machine 14 is adjusted in order to stabilize the grid frequency, i.e. to approximate the actual grid frequency to the target grid frequency of the electrical power grid 15, specifically by controlling the speed of the electrical machine 14 and / or by changing the volume flow of the process medium of the heat pump 10.

[0024] This adjustment of the electrical power consumption of the electrical machine 14 is carried out in such a way that, at a constant or approximately constant pressure ratio of the compressor 12 and thus at a constant or approximately constant temperature of the process medium downstream of the compressor 12 in the region of the second heat exchanger 13, the actual grid frequency of the electrical power grid 15 is approximated to the target grid frequency thereof.

[0025] If the actual grid frequency of the electrical power grid 15 is greater than the target grid frequency, the speed of the electrical machine 14 is increased and, preferably, the volume flow of the process medium of the heat pump 10 is increased simultaneously. However, if the actual grid frequency of the electrical power grid 15 is lower than the target grid frequency, the speed of the electrical machine 14 is reduced and, preferably, the volume flow of the process medium of the heat pump 10 is reduced simultaneously.

[0026] This brings the actual grid frequency closer to the target grid frequency and thus stabilizes the grid frequency of the electrical power grid 15 in a particularly advantageous manner, namely at a constant or approximately constant temperature of the process medium downstream of the compressor 12 in the region of the second heat exchanger 13.

[0027] Fig. 2 shows a characteristic diagram of a compressor 12, wherein in Fig. 2 the pressure ratio PI of the compressor 12, namely the ratio between the outlet pressure of the compressor 12 and its inlet pressure, is shown over the volume flow V of the process medium of the heat pump 10. In Fig. 2, a point 20 visualizes an operating point of the compressor 12 at a defined volume flow V and a defined pressure ratio PI. For grid stabilization within the meaning of the invention, this operating point 20 can be shifted in the direction of the double arrow 21, i.e., at a constant or approximately constant pressure ratio PI of the compressor 12 between the outlet pressure and the inlet pressure thereof. In this case, the volume flow V is adjusted, as is the speed of the electric machine 14 to maintain the constant pressure ratio PI.

[0028] Because the pressure ratio PI of the compressor 12 is kept constant, the temperature of the process medium downstream of the compressor 12 in the area of ​​the second heat exchanger 13 also remains constant, so that the quality of the thermal energy transferred to the consumer remains unchanged. Thus, a heat pump 10 can be used to stabilize a grid frequency of the electrical grid 15 without affecting the consumer.

[0029] The speed control for the speed-controlled electrical machine 14 is carried out via a load change of the electrical machine (14) and thus a change in the frequency, namely a change in the output frequency, at the frequency converter 22 connected between the electrical power grid 15 and the electrical machine 14. In order to change the volume flow of the process medium of the heat pump 10, a device for changing the volume flow of the process medium is controlled, specifically in order to change the flow resistance of the respective device for the process medium.

[0030] In the exemplary embodiment of Fig. 1, the volume flow of the process medium of the heat pump 10 can be controlled, for example, by changing the opening position of the expansion valve 18, thereby changing the flow resistance of the expansion valve 18 for the process medium. The volume flow of the process medium can also be controlled by changing the opening position of the bypass valve 19, thereby changing the flow resistance of the bypass valve 19 for the process medium. If the turbine 17 and / or the compressor 12 has adjustable guide vanes, so-called adjustable guide vanes, or adjustable rotor blades, the flow resistance for the process medium and thus the volume flow of the process medium of the heat pump 10 can also be controlled by a corresponding adjustment of the guide vanes or the rotor blades on the turbine 17 and / or the compressor 12.

[0031] In the embodiment shown, it is therefore possible that the device for changing the volume flow of the process medium of the heat pump is part of the compressor 12, part of the turbine 17 or part of the expansion device 16.

[0032] It is also possible to use a separate device for changing the volume flow of the process medium of the heat pump 10, which is designed as a separate assembly from the compressor 12 and the expansion device 16, for example as a separate valve or as a separate throttle.

[0033] The invention further relates to a control unit configured to automatically execute the method according to the invention on the control side. For this purpose, such a control unit has data interfaces for exchanging data with the components involved in executing the method according to the invention, such as the electrical power grid 15, the electric machine 14, the frequency converter 22, and the device for varying the volume flow of the process medium of the heat pump 10.The control device is configured to compare the actual grid frequency of the electrical power grid 15 with the target grid frequency thereof and, in order to stabilize the grid frequency of the electrical power grid 15, i.e., to bring the actual grid frequency closer to the target grid frequency, to change the electrical power consumption of the electrical machine 14. This is done by controlling the speed of the electrical machine 14 and / or changing the volume flow of the process medium, in such a way that the pressure ratio PI of the compressor 12 and thus the temperature of the process medium downstream of the compressor 12 in the region of the second heat exchanger 13 remains constant or approximately constant. For this purpose, the speed of the electrical machine 14 is preferably controlled and, at the same time, the volume flow of the process medium is changed.

[0034] In order to approximate the actual grid frequency to the target grid frequency for stabilizing the grid frequency, in the exemplary embodiment shown in Fig. 2, the operating point 20 is shifted along the double arrow 21 in the compressor characteristic map of Fig. 2, i.e., at a constant pressure ratio PI of the compressor 12 between the outlet pressure and the inlet pressure of the same. The electrical power consumption of the electric machine 14 is adjusted both via the speed control of the electric machine 14 and via the change in the volume flow of the process medium of the heat pump 10. This can be controlled depending on a characteristic map or also in a regulated manner.

[0035] It is also possible, depending on a deviation between the actual grid frequency and the target grid frequency, to determine a load change for the electric machine 14 that is required to bring the actual grid frequency closer to the target grid frequency. Depending on this load change, a required speed and torque for the electric machine 14 can be determined based on a motor characteristic map of the electric machine. Depending on the required torque, a control variable for the device for changing the volume flow can then be determined.

[0036] List of reference symbols

[0037] 10 heat pump

[0038] 11 first heat exchanger

[0039] 12 Compressor

[0040] 13 second heat exchanger

[0041] 14 electric machine

[0042] 15 electrical power grid

[0043] 16 Expansion device

[0044] 17 turbines

[0045] 18 Expansion valve

[0046] 19 Bypass valve

[0047] 20 operating point

[0048] 21 Double arrow

[0049] 22 frequency converters

Claims

Patent claims 1 . A method for operating a heat pump (10) while stabilizing a grid frequency of an electrical power grid (15), wherein the heat pump (10) has a first heat exchanger (11), a compressor (12) that can be driven by an electrical machine (14) connected to the electrical power grid (15), a second heat exchanger (13), and an expansion device (16), wherein the first heat exchanger (11) of the heat pump (10) is configured to transfer thermal energy to a process medium of the heat pump, wherein the compressor (12) of the heat pump (10) is configured to compress the process medium of the heat pump downstream of the first heat exchanger (11) and upstream of the second heat exchanger (13), wherein the second heat exchanger (13) of the heat pump (10) is configured to transfer thermal energy of the process medium of the heat pump to a consumer, and wherein the expansion device (16) of the heat pump (10) is configured,to expand the process medium of the heat pump downstream of the second heat exchanger (13) and upstream of the first heat exchanger (11), wherein the heat pump (10) has a device by means of which a volume flow of the process medium of the heat pump (10) can be adjusted, characterized in that when an actual grid frequency of the electrical power grid (15) deviates from a target grid frequency, in order to stabilize the grid frequency of the electrical power grid (15) and thus to approximate the actual grid frequency and the target grid frequency, an electrical power consumption of the electrical machine (14) is adjusted by means of a speed control of the same and / or by means of a change in the volume flow of the process medium of the heat pump (10) in such a way,that at a constant or approximately constant pressure ratio of the compressor (12) and thus at a constant or approximately constant temperature of the process medium in the region of the second heat exchanger (13), the actual mains frequency of the electrical power grid is approximated to the target mains frequency.

2. Method according to claim 1, characterized in that, in order to stabilize the mains frequency of the electrical power grid (15), the electrical power consumption of the electrical machine (14) is adjusted via the speed control of the electrical machine (14) and via the change in the volume flow of the process medium.

3. Method according to claim 1 or 2, characterized in that when the actual grid frequency of the electrical power grid (15) is greater than the target grid frequency, the electrical power consumption of the electrical machine (14) is increased by increasing the speed of the same and / or by increasing the volume flow of the process medium of the heat pump (10).

4. Method according to claim 1, 2 or 3, characterized in that when the actual mains frequency of the electrical power grid (15) is lower than the target mains frequency, the electrical power consumption of the electrical machine (14) is reduced by reducing the speed of the same and / or by reducing the volume flow of the process medium of the heat pump (10).

5. Method according to one of claims 1 to 4, characterized in that the speed control for the speed-controlled electrical machine (14) takes place via a load change of the electrical machine (14) or a frequency change on a frequency converter (22) connected between the electrical power network (15) and the electrical machine (14).

6. Method according to one of claims 1 to 5, characterized in that in order to change the volume flow of the process medium of the heat pump (10), the expansion device (16) is controlled as a device for changing the volume flow of the process medium, wherein the expansion device (16) has a turbine (17), the guide vanes or rotor blades of which are adjustable to change the flow resistance of the expansion device (16) and thus to change the volume flow of the process medium, and / or an expansion valve (18), the opening position of which is variable to change the flow resistance of the expansion device (16) and thus to change the volume flow of the process medium.

7. Method according to one of claims 1 to 6, characterized in that in order to change the volume flow of the process medium of the heat pump (10) as a device for changing the volume flow of the process medium, the compressor (12) whose guide vanes or rotor blades are adjustable to change the flow resistance of the compressor (12) and thus to change the volume flow of the process medium is controlled.

8. Method according to one of claims 1 to 7, characterized in that in order to change the volume flow of the process medium of the heat pump (10), a separate valve or a separate throttle is controlled as a device for changing the volume flow, the opening position of which can be changed in order to change the flow resistance thereof and thus in order to change the volume flow of the process medium.

9. Control device for operating a heat pump (10) while stabilizing a mains frequency of an electrical power network, characterized in that the same is set up to automatically carry out the method according to one of claims 1 to 8 on the control side.

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