Control method of a photovoltaic photothermal system and photovoltaic photothermal system

Abstract

The application discloses a control method of a photovoltaic photo-thermal system and the photovoltaic photo-thermal system. The photovoltaic photo-thermal system comprises a refrigeration cycle system and a photovoltaic system. The refrigeration cycle system comprises a circulating pipeline and an evaporator, a compressor, a condenser, a liquid accumulator and a first expansion valve arranged on the circulating pipeline in sequence. The photovoltaic system comprises a photovoltaic photo-thermal assembly and a cooling pipeline. The cooling pipeline comprises a cooling pipeline arranged on the photovoltaic photo-thermal assembly, and connecting pipelines connecting the cooling pipeline to the circulating pipeline between the liquid accumulator and the evaporator and to the circulating pipeline between the evaporator and the compressor. The control method comprises an anti-explosion step. The anti-explosion step comprises: step 100, extracting and reducing refrigerant in the cooling pipeline and sending the extracted refrigerant to the liquid accumulator; step 200, disconnecting the inlet and the outlet of the cooling pipeline from the connecting pipelines after the pressure of the refrigerant in the cooling pipeline is less than a first threshold value; and step 300, keeping any two adjacent ones of the evaporator, the compressor, the condenser and the liquid accumulator in communication.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic and solar thermal technology, and in particular to a control method for a photovoltaic and solar thermal system and a photovoltaic and solar thermal system. Background Technology

[0002] Photovoltaic thermal (PVT) systems combine photovoltaic power generation with solar thermal collection. In this system, the PVT heat pump system absorbs heat through a phase change of the refrigerant within the PVT modules. This reduces the operating temperature of the PVT modules, improves power generation efficiency, and provides a high-quality heat source for the heat pump, thereby enhancing heating performance. In existing technologies, to improve energy efficiency, a direct-drive PVT direct-expansion architecture is often used, where the refrigerant evaporates and absorbs heat directly within the PVT modules.

[0003] However, when the system stops operating and solar irradiance is high, the PVT modules are exposed to prolonged sunlight. The refrigerant trapped inside will continue to absorb solar heat, causing a sharp increase in temperature and pressure. This situation leads to two main problems: first, the internal pressure of the PVT modules may exceed their pressure resistance limit, causing the modules to burst, posing a safety hazard; second, the refrigerant temperature and pressure at the compressor inlet may exceed the allowable starting range, preventing the compressor from starting normally and potentially causing damage due to liquid slugging.

[0004] Therefore, how to effectively avoid the risk of high-voltage explosion of PVT modules due to exposure to sunlight when the system is shut down is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problem in the prior art where PVT modules are prone to explosion due to exposure to sunlight after a photovoltaic (PV) thermal system is shut down. To this end, this invention provides a control method for a PV thermal system and a PV thermal system itself.

[0006] The first aspect of this invention discloses a control method for a photovoltaic-thermal system, the photovoltaic-thermal system comprising:

[0007] A refrigeration cycle system includes a circulation pipeline for refrigerant circulation and an evaporator, a compressor, a condenser, a liquid receiver, and a first expansion valve arranged sequentially on the circulation pipeline.

[0008] A photovoltaic system includes a photovoltaic thermal module and a cooling pipeline. The cooling pipeline includes a cooling pipe disposed on the photovoltaic thermal module for cooling the photovoltaic thermal module, a circulation pipeline connecting the inlet and outlet of the cooling pipe to the liquid storage tank and the evaporator respectively, and a connecting pipe connecting the evaporator and the compressor to the circulation pipeline.

[0009] The control method for the photovoltaic thermal system includes an explosion-proof step, which includes:

[0010] Step 100: Use the compressor to extract and reduce the refrigerant in the cooling pipeline and send the extracted refrigerant to the liquid storage device.

[0011] Step 200: After the pressure of the refrigerant in the cooling pipeline is less than the first threshold, disconnect both the inlet and outlet of the cooling pipeline from the connecting pipeline.

[0012] Step 300: Keep any two adjacent ones of the evaporator, compressor, condenser, and liquid storage device connected.

[0013] The control method of the photovoltaic-thermal system in this embodiment actively extracts the refrigerant in the cooling pipeline of the photovoltaic system by the compressor and recovers it to the liquid storage device, and isolates the cooling pipeline from the refrigeration cycle system, avoiding the high temperature and high pressure generated by the exposure of the refrigerant remaining in the cooling pipeline of the photovoltaic system after the system stops, thus fundamentally eliminating the safety hazard of the explosion of the photovoltaic system, and at the same time avoiding the environmental pollution and resource waste caused by the direct discharge of the refrigerant. At the same time, after the refrigerant recovery is completed, disconnect both the inlet and outlet of the cooling pipeline from the refrigeration cycle system, and keep the evaporator, compressor, condenser, and liquid storage device connected, so that the refrigerant in the main loop of the system can flow freely, preventing the high pressure caused by the local accumulation of the refrigerant, and further improving the safety of the system after it stops.

[0014] In some embodiments, before step 100, it further includes: step 110, disconnect the inlet and outlet of the evaporator from the liquid storage device and the compressor respectively.

[0015] This embodiment pre-isolates the evaporator, making the suction and recovery of the refrigerant focus on the cooling pipeline, the work of the compressor more focused, improving the work efficiency and effect, shortening the suction working time, and reducing the power consumption of the compressor.

[0016] In some embodiments, the refrigeration cycle system further includes a first on-off valve connected between the evaporator and the compressor, and the first on-off valve is used to control the on-off between the outlet of the evaporator and the compressor. Step 110 includes: closing the first expansion valve and the first on-off valve.

[0017] This embodiment can achieve reliable isolation of the evaporator by using the first on-off valve and the first expansion valve, and the control is simple and effective.

[0018] In some embodiments, step 300 includes: opening the first on-off valve and setting the opening degree of the first on-off valve to k1, where 0 < k1 < 1, then reading the pressure P at the outlet of the first on-off valve. After P remains unchanged within the first time threshold t1, open the first expansion valve and set the k1 value to 1.

[0019] In this embodiment, after completing the refrigerant extraction and isolation of the cooling pipes, the opening of the first on / off valve is adjusted, which effectively avoids the risk of high pressure differential impact and liquid slugging caused by sudden conduction, and protects the circulation pipeline and compressor. At the same time, the full opening of the first on / off valve at the end also helps to ensure pressure balance after the system stops.

[0020] In some embodiments, the connecting pipe includes a first pipe connecting the inlet of the cooling pipe to a circulation pipe between the reservoir and the first expansion valve, and a second pipe connecting the outlet of the cooling pipe to a circulation pipe between the evaporator and the compressor. The photovoltaic system also includes a second expansion valve disposed on the first pipe. Before step 100, the system further includes step 120, closing the second expansion valve.

[0021] This embodiment achieves unidirectional control of refrigerant suction in the cooling pipe by closing the second expansion valve, avoiding refrigerant backflow and thus enabling effective suction of refrigerant in the cooling pipe.

[0022] In some embodiments, the photovoltaic system further includes a second on-off valve disposed between the outlet of the cooling pipe and the connecting pipe, the second on-off valve being used to control the on-off connection between the outlet of the cooling pipe and the connecting pipe, and the control method of the photovoltaic thermal system further includes a soft-start step following the explosion-proof step, the soft-start step including:

[0023] Step 400: Keep the inlet of the cooling pipe disconnected from the connecting pipe, and set the opening degree of the second on / off valve to k2, where 0 <k2<1;

[0024] Step 500: After the second threshold time t2 has elapsed in step 400, the opening degree of the second on / off valve is set to 1.

[0025] Step 600: Connect the inlet of the cooling pipe to the connecting pipe;

[0026] Step 700: Start the compressor.

[0027] This embodiment employs a soft-start method by first partially opening the second on-off valve to gradually equalize the pressure in the cooling pipe and circulation pipe, and then fully opening the second on-off valve to connect them. This effectively prevents the rapid influx of refrigerant due to excessively low pressure in the cooling pipe, helping to prevent pipe vibration and compressor liquid slugging, and improving the reliability and lifespan of the system restart. Furthermore, this embodiment chooses to gradually open the second on-off valve at the cooling pipe outlet for pressure equalization. Compared to gradually opening the electronic expansion valve at the cooling pipe inlet, this method prevents excessive temperature stress caused by a large temperature difference between the refrigerant entering the cooling pipe and the cooling pipe itself, thus helping to protect the cooling pipe.

[0028] In some embodiments, step 100 includes: reducing the operating frequency of the compressor, and then using the compressor to extract and reduce the refrigerant in the cooling pipe.

[0029] In this embodiment, reducing the compressor frequency decreases the compressor's suction flow rate, making the refrigerant extraction process from the cooling pipes smoother and more controllable. This avoids excessive pressure differentials caused by a sudden drop in internal pressure due to rapid extraction, thus preventing deformation or damage to the cooling pipes due to excessive internal and external pressure differences. Simultaneously, low-frequency operation also reduces compressor power consumption and noise. Once the pressure inside the cooling pipes drops to near the first threshold, the frequency can be further reduced or the compressor can be stopped. This low-frequency, slow extraction method achieves gentle refrigerant recovery from the cooling pipes, balancing efficiency and safety.

[0030] A second aspect of this invention discloses a photovoltaic-thermal system, and a control method for any of the photovoltaic-thermal systems described above, wherein the photovoltaic-thermal system comprises:

[0031] A refrigeration cycle system includes a circulation pipeline for refrigerant circulation and an evaporator, a compressor, a condenser, a liquid receiver, and a first expansion valve arranged sequentially on the circulation pipeline.

[0032] A photovoltaic system includes a photovoltaic thermal module and a cooling pipeline. The cooling pipeline includes a cooling pipe disposed on the photovoltaic thermal module for cooling the photovoltaic thermal module, a circulation pipeline connecting the inlet and outlet of the cooling pipe to the liquid storage tank and the evaporator respectively, and a connecting pipe connecting the circulation pipeline between the evaporator and the compressor.

[0033] The photovoltaic-thermal system in this embodiment utilizes the aforementioned control method. The compressor actively extracts the refrigerant from the photovoltaic system's cooling pipes and recovers it to the receiver, isolating the cooling pipes from the refrigeration cycle system. This prevents the refrigerant from remaining in the cooling pipes after system shutdown, which could generate high temperatures and pressures due to exposure to sunlight. This fundamentally eliminates the safety hazard of a photovoltaic system explosion and avoids environmental pollution and resource waste caused by direct refrigerant discharge. Furthermore, after refrigerant recovery, the inlet and outlet of the cooling pipes are disconnected from the refrigeration cycle system, while the evaporator, compressor, condenser, and receiver remain connected. This allows the refrigerant in the main circuit to flow freely, preventing high pressure caused by localized refrigerant accumulation and further enhancing system safety after shutdown.

[0034] In some embodiments, the refrigeration cycle system further includes a first on / off valve connected between the evaporator and the compressor, the first on / off valve being used to control the on / off connection between the outlet of the evaporator and the compressor, the connecting pipe including a first pipe connecting the inlet of the cooling pipe to a circulation pipe between the liquid receiver and the first expansion valve and a second pipe connecting the outlet of the cooling pipe to a circulation pipe between the evaporator and the compressor, the photovoltaic system further including a second expansion valve disposed on the first pipe and a second on / off valve disposed between the outlet of the cooling pipe and the connecting pipe, the second on / off valve being used to control the on / off connection between the outlet of the cooling pipe and the connecting pipe.

[0035] In this embodiment, a first on / off valve is added to the refrigeration cycle system to isolate the evaporator together with the first expansion valve during refrigerant recovery; a second expansion valve is installed on the first pipe to control the refrigerant flow rate into the cooling pipe and to prevent refrigerant backflow during recovery; a second on / off valve is installed at the outlet of the cooling pipe to control the opening and closing of the cooling pipe outlet, and can also realize the gradual balancing of refrigerant in the cooling pipe and the circulation pipe during the soft start step. By setting controllable valve components at the above-mentioned locations, this embodiment facilitates the implementation of explosion-proof and soft start steps.

[0036] In some embodiments, the compressor is a rotary compressor.

[0037] The compressor in this embodiment is a rotary compressor, which allows for freer flow of refrigerant in the main circuit of the refrigeration cycle system after the explosion-proof steps. This helps to further reduce the risk of high pressure in the circulation pipeline of the refrigeration cycle system and further improve the safety of the system after shutdown.

[0038] Based on the control method of the photovoltaic-thermal system provided by this invention, the refrigerant in the cooling pipes of the photovoltaic system is actively extracted by the compressor and recovered to the liquid receiver, thus isolating the cooling pipes from the refrigeration cycle system. This avoids the refrigerant remaining in the cooling pipes of the photovoltaic system after system shutdown, which would generate high temperature and high pressure due to exposure to sunlight, thereby fundamentally eliminating the safety hazard of photovoltaic system explosion. It also avoids environmental pollution and resource waste caused by direct refrigerant discharge. Furthermore, after the refrigerant recovery is completed, the inlet and outlet of the cooling pipes are disconnected from the refrigeration cycle system, while the evaporator, compressor, condenser, and liquid receiver remain connected. This allows the refrigerant in the main circuit of the system to flow freely, preventing high pressure caused by local refrigerant accumulation and further improving the safety after system shutdown. The photovoltaic-thermal system of this invention can recover heat from photovoltaic-thermal components, thereby achieving energy-saving effects and belonging to energy-saving refrigeration cycle equipment.

[0039] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0040] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0041] Figure 1 This is a schematic diagram of a photovoltaic-thermal system according to an embodiment of the present invention;

[0042] Figure 2 This is a flowchart of a control method for a photovoltaic thermal system according to an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0045] In the description of this invention, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0048] The photovoltaic-thermal system in this embodiment includes a refrigeration cycle system and a photovoltaic system.

[0049] The refrigeration cycle system includes a circulation pipeline for refrigerant circulation and, sequentially arranged on the circulation pipeline, an evaporator 1, a compressor 2, a condenser 3, a liquid receiver 4, and a first expansion valve 61. These components are connected in sequence via the circulation pipeline, through which the refrigerant circulates to complete a refrigeration or heating cycle. During operation, the refrigerant circulates in the circulation pipeline, passing sequentially through the evaporator 1, compressor 2, condenser 3, liquid receiver 4, and first expansion valve. The liquid receiver 4 is connected between the condenser 3 and the first expansion valve. Figure 1 In the illustrated embodiment, a refrigerant flow pipe is provided between the condenser 3 and the first expansion valve, and a receiver is connected in series on this flow pipe, thereby connecting the condenser 3 and the first expansion valve. In some embodiments not shown in the figures, the receiver is connected in parallel with the refrigerant flow pipe between the condenser 3 and the first expansion valve, thereby connecting the condenser 3 and the first expansion valve. The refrigeration cycle system includes a heat pump system and a refrigeration system. When the evaporator 1 is used to cool the environment, the refrigeration cycle system includes a refrigeration system; when the condenser 3 is used to heat the environment, the refrigeration cycle system includes a heat pump system. Figure 1 In the embodiment shown, the condenser 3 of the refrigeration cycle system heats the water delivered from the first water pipe 83 and then outputs it from the second water pipe 85. The refrigeration cycle system includes a heat pump system.

[0050] The photovoltaic system includes photovoltaic thermal modules 5 (i.e., PVT modules) and cooling pipes. The cooling pipes include cooling pipes 93 installed on the photovoltaic thermal modules 5 for cooling the modules, a circulation pipe connecting the inlet and outlet of the cooling pipes 93 to the liquid receiver 4 and the evaporator 1 respectively, and a connecting pipe connecting the evaporator 1 and the compressor 2. The cooling pipes are used to absorb the heat generated during the photovoltaic thermal module's power generation process, reducing the module's temperature and improving power generation efficiency. Specifically, the connecting pipes connect the inlet of the cooling pipes 93 to the circulation pipe between the liquid receiver 4 and the evaporator 1, and the connecting pipes connect the outlet of the cooling pipes 93 to the circulation pipe between the evaporator 1 and the compressor 2. This makes the cooling pipes a branch connected in parallel with the evaporator of the refrigeration cycle system, through which the refrigerant can flow and carry away the heat from the photovoltaic thermal modules. In the embodiment shown in the figure, the refrigeration cycle system includes a heat pump system, and the heat carried away by the refrigerant provides a high-quality heat source for the heat pump system.

[0051] The control methods for photovoltaic and solar thermal systems include explosion-proof measures. When a photovoltaic and solar thermal system needs to be shut down for a long time (e.g., at night, or during an abnormal shutdown and may be exposed to the sun the next day), explosion-proof measures can be implemented to prevent the refrigerant remaining in the cooling pipes from rapidly increasing in temperature and pressure under the sun and causing an explosion.

[0052] Explosion-proof procedures include:

[0053] Step 100 involves using compressor 2 to extract and reduce the refrigerant in cooling pipe 93 and sending the extracted refrigerant to receiver 4. In this step, the compressor acts as a power source, and its suction port is connected to the outlet of the cooling pipe via a connecting pipe. During compressor operation, the compressor continuously extracts refrigerant from the cooling pipe. In the embodiment shown, the extracted refrigerant passes through gas-liquid separator 82 before entering the compressor. After compression, it enters the condenser to release heat and liquefy, finally flowing into the receiver for storage.

[0054] Step 200: After the refrigerant pressure in the cooling pipe 93 falls below a first threshold, both the inlet and outlet of the cooling pipe 93 are disconnected from the connecting pipe. In the embodiment shown in the figure, a pressure sensor 81 installed on the outlet side of the cooling pipe monitors the pressure inside the cooling pipe in real time. The first threshold is a preset safe pressure value (e.g., 0.2~0.5MPa), far below the burst pressure of the cooling pipe. When the pressure is detected to drop below the first threshold, it indicates that the refrigerant in the cooling pipe has been basically evacuated, with very little refrigerant remaining, making it difficult to generate dangerous high pressure even under direct sunlight. At this time, the inlet and outlet of the cooling pipe are physically isolated from the connecting pipe by a control valve. After disconnection, the cooling pipe becomes a completely closed, isolated chamber, with no further refrigerant exchange with the refrigeration cycle system.

[0055] Step 300: Ensure that any two adjacent components of the evaporator 1, compressor 2, condenser 3, and receiver 4 remain connected. After the cooling pipes are isolated, any two adjacent components in the main loop of the refrigeration cycle system ( receiver—first expansion valve—evaporator—compressor—condenser— receiver) remain connected, meaning that the pipes between any two adjacent components are not disconnected. For example, in the embodiment shown in the figure, the first expansion valve is opened to a certain degree, and the control valve between the evaporator and the compressor is opened to ensure that the refrigerant can flow freely between adjacent components for pressure balance.

[0056] After the refrigerant in the cooling pipe of the photovoltaic thermal module is extracted into the circulation pipe of the refrigeration cycle system, the amount of refrigerant in the circulation pipe increases and the pressure rises. Step 300 can prevent the refrigerant in the main circuit from being blocked and forming high pressure in local pipes (such as the circulation pipe between the condenser and the first expansion valve), thereby preventing a rapid pressure rise due to the increase in ambient temperature and the generation of new safety hazards.

[0057] The control method of the photovoltaic-thermal system in this embodiment actively extracts the refrigerant from the cooling pipe 93 of the photovoltaic system and recovers it to the liquid receiver 4 through the compressor 2, thus isolating the cooling pipe 93 from the refrigeration cycle system. This avoids the refrigerant remaining in the cooling pipe 93 of the photovoltaic system after system shutdown, which would generate high temperature and high pressure due to exposure to sunlight, thereby fundamentally eliminating the safety hazard of photovoltaic system explosion. At the same time, it avoids environmental pollution and resource waste caused by direct refrigerant discharge. Furthermore, after the refrigerant recovery is completed, both the inlet and outlet of the cooling pipe 93 are disconnected from the refrigeration cycle system. When the refrigerant in the cooling pipe 93 is recovered into the main loop of the refrigeration cycle system, the amount of refrigerant in the main loop increases, and the refrigerant pressure rises. However, the evaporator 1, compressor 2, condenser 3, and liquid receiver 4 remain connected, allowing the refrigerant in the main loop of the system to flow freely. This allows the refrigerant to flow to lower pressure areas when local refrigerant pressure becomes too high due to heating or other reasons, balancing the pressure and preventing high pressure caused by local refrigerant accumulation, further improving the safety of the system after shutdown.

[0058] In some embodiments, before step 100, the method further includes step 110, disconnecting the inlet and outlet of the evaporator 1 from the receiver 4 and the compressor 2, respectively. Before performing step 100, that is, before using the compressor to extract the refrigerant from the cooling pipes, step 110 is performed first: cutting off the connection between the evaporator inlet and the receiver 4, and simultaneously cutting off the connection between the evaporator outlet and the compressor. In this way, when the compressor starts to draw in refrigerant, the compressor's suction path mainly comes from the outlet of the cooling pipes, rather than drawing in a large amount of refrigerant from the evaporator, thereby ensuring suction efficiency and allowing the pressure in the cooling pipes to drop rapidly.

[0059] This embodiment, by pre-isolating the evaporator, concentrates the refrigerant suction and recovery on the cooling pipes, making the compressor's work more focused, improving working efficiency and performance, shortening the suction working time, and reducing compressor power consumption.

[0060] In some embodiments, the refrigeration cycle system further includes a first on / off valve 71 connected between the evaporator 1 and the compressor 2. The first on / off valve 71 is used to control the on / off connection between the outlet of the evaporator 1 and the compressor 2. Step 110 includes: closing the first expansion valve 61 and the first on / off valve 71. Figure 1 As shown, a first on / off valve is installed between the evaporator outlet and the compressor suction port. In step 110, the liquid supply channel from the receiver to the evaporator is cut off by closing the first expansion valve, such as an electronic expansion valve; simultaneously, the first on / off valve is closed, cutting off the refrigerant flow channel between the evaporator outlet and the compressor inlet. Thus, both the evaporator inlet and outlet are cut off, completely isolating the evaporator from the main circuit of the refrigeration cycle system.

[0061] In this embodiment, the reliable isolation of the evaporator can be achieved by using the first on-off valve and the first expansion valve, and the control is simple and effective.

[0062] In some embodiments, step 300 includes opening the first on-off valve 71 and setting the opening degree of the first on-off valve 71 to k1, where 0 < k1 < 1. Then, read the pressure P at the outlet of the first on-off valve 71. After P remains unchanged within the first time threshold t1, open the first expansion valve 61 and set the value of k1 to 1. After the refrigerant in the cooling pipeline is recovered and the connection between the cooling pipeline and the connecting pipeline is disconnected, step 300 is executed to restore the circulation pipeline of the refrigeration cycle system, that is, the connected state of the main circuit. First, open the first on-off valve to a smaller opening degree k1, such as 10% - 30%, to slowly conduct between the outlet of the evaporator and the inlet of the compressor. At this time, the compressor may have stopped, but the small opening degree conduction can prevent a large amount of liquid refrigerant that may be accumulated in the evaporator from suddenly pouring into the compressor, causing liquid hammer. Then, read the pressure P on the outlet side of the first on-off valve, which is obtained by reading the data of the pressure sensor 81 in the embodiment shown in the figure. Since there is a pressure difference before and after the first on-off valve, as the refrigerant slowly flows, the pressure P will gradually change. When the pressure P remains stable within the first time threshold t1, such as 30 seconds or 1 minute, it indicates that the pressures on both sides of the first on-off valve are basically balanced. At this time, open the first expansion valve to the normal opening degree and set the opening degree k1 of the first on-off valve to 1 (that is, the first on-off valve is fully open), which can make the circulation pipeline where the outlet of the evaporator is located completely unobstructed.

[0063] In this embodiment, after the refrigerant in the cooling pipeline is sucked and isolated, the adjustment of the opening degree of the first on-off valve effectively avoids the high-pressure difference impact and liquid hammer risk caused by sudden conduction, protects the circulation pipeline and the compressor, and at the same time, the full opening of the first on-off valve at the end also helps to ensure the pressure balance after the system stops.

[0064] In some embodiments, the connecting pipeline includes a first pipeline 91 that connects the inlet of the cooling pipeline 93 to the circulation pipeline between the liquid receiver 4 and the first expansion valve 61, and a second pipeline 92 that connects the outlet of the cooling pipeline 93 to the circulation pipeline between the evaporator 1 and the compressor 2. The photovoltaic system further includes a second expansion valve 62 provided on the first pipeline 91. Before step 100, it further includes: step 120, closing the second expansion valve 62.

[0065] As Figure 1As shown, the connecting pipeline is divided into a first pipeline and a second pipeline. The first pipeline connects the inlet of the cooling pipeline to the circulation pipeline between the receiver and the first expansion valve, and a second expansion valve is installed on the first pipeline. The second pipeline connects the outlet of the cooling pipeline to the circulation pipeline between the evaporator and the compressor. Before step 100, step 120 is performed: the second expansion valve is closed. Closing the second expansion valve cuts off the passage between the inlet of the cooling pipeline and the receiver, preventing the refrigerant in the receiver from flowing back into the cooling pipeline through the first pipeline during the evacuation process, thus affecting the evacuation effect. At the same time, this also ensures that the compressor's evacuation action can only be carried out through the second pipeline from the outlet of the cooling pipeline, forming a unidirectional evacuation and improving the thoroughness of refrigerant recovery.

[0066] This embodiment achieves unidirectional control of refrigerant suction in the cooling pipe by closing the second expansion valve, avoiding refrigerant backflow and thus enabling effective suction of refrigerant in the cooling pipe.

[0067] In some embodiments, the photovoltaic system further includes a second on / off valve 72 disposed between the outlet of the cooling pipe 93 and the connecting pipe. The second on / off valve 72 is used to control the on / off connection between the outlet of the cooling pipe 93 and the connecting pipe. The control method of the photovoltaic thermal system further includes a soft-start step following the explosion-proof step. The soft-start step includes:

[0068] Step 400: Keep the inlet of cooling pipe 93 disconnected from the connecting pipe, and set the opening degree of the second on / off valve 72 to k2, where 0 <k2<1;

[0069] Step 500: After the second threshold time t2 has elapsed in step 400, the opening degree of the second on / off valve 72 is set to 1.

[0070] Step 600: Connect the inlet of cooling pipe 93 to the connecting pipe;

[0071] Step 700: Start compressor 2.

[0072] After the explosion-proof steps are completed and the photovoltaic-thermal system is in a safe shutdown state, when the photovoltaic-thermal system needs to be restarted, this embodiment performs a soft-start step to avoid a sudden surge of refrigerant and a strong impact caused by excessively low pressure in the cooling pipe. Step 400: Keep the inlet of the cooling pipe disconnected from the first pipe. In the embodiment shown in the figure, this means keeping the second expansion valve closed. Open the second on / off valve to a small opening degree k2, such as 20% or 30%, so that the compressor's suction port and the cooling pipe's outlet are slowly connected through a small opening. A small amount of refrigerant gradually enters the cooling pipe, gradually increasing its internal pressure. Step 500: Maintain this small opening state for a second threshold time t2 (e.g., 0.5 min to 1.5 min) to allow the pressure in the cooling pipe to initially balance with the low-pressure side. Step 600: Then connect the inlet of the cooling pipe to the first pipe (e.g., open the second expansion valve to a suitable opening). At this time, both the inlet and outlet of the cooling pipe are connected to the refrigeration cycle system. Step 700: Finally, start the compressor, and the system begins normal operation.

[0073] This embodiment employs a soft-start method by first partially opening the second on-off valve to gradually equalize the pressure in the cooling pipe and circulation pipe, and then fully opening the second on-off valve to connect them. This effectively prevents the rapid influx of refrigerant due to excessively low pressure in the cooling pipe, helping to prevent pipe vibration and compressor liquid slugging, and improving the reliability and lifespan of the system restart. Furthermore, this embodiment chooses to gradually open the second on-off valve at the cooling pipe outlet for pressure equalization. Compared to gradually opening the electronic expansion valve at the cooling pipe inlet, this method prevents excessive temperature stress caused by a large temperature difference between the refrigerant entering the cooling pipe and the cooling pipe itself, thus helping to protect the cooling pipe.

[0074] In some embodiments, step 100 includes: reducing the operating frequency of compressor 2, and then using compressor 2 to extract and reduce the refrigerant in cooling pipe 93. Before performing the explosion-proof step, the photovoltaic thermal system is in normal operating condition, and the compressor frequency is the operating frequency during normal operation. When performing step 100, the operating frequency of compressor is first reduced to a low value (e.g., 30% to 50% of the rated frequency), and then the compressor is operated at this low frequency to extract refrigerant from the cooling pipe.

[0075] In this embodiment, reducing the compressor frequency decreases the compressor's suction flow rate, making the refrigerant extraction process from the cooling pipes smoother and more controllable. This avoids excessive pressure differentials caused by a sudden drop in internal pressure due to rapid extraction, thus preventing deformation or damage to the cooling pipes due to excessive internal and external pressure differences. Simultaneously, low-frequency operation also reduces compressor power consumption and noise. Once the pressure inside the cooling pipes drops to near the first threshold, the frequency can be further reduced or the compressor can be stopped. This low-frequency, slow extraction method achieves gentle refrigerant recovery from the cooling pipes, balancing efficiency and safety.

[0076] In some embodiments, a photovoltaic-thermal system is also disclosed, which applies any of the above-described control methods for photovoltaic-thermal systems. The photovoltaic-thermal system includes a refrigeration cycle system and a photovoltaic system.

[0077] The refrigeration cycle system includes a circulation pipeline for refrigerant circulation and an evaporator 1, a compressor 2, a condenser 3, a liquid receiver 4 and a first expansion valve 61 arranged sequentially on the circulation pipeline;

[0078] The photovoltaic system includes a photovoltaic thermal module 5 and a cooling pipeline. The cooling pipeline includes a cooling pipe 93 installed on the photovoltaic thermal module 5 for cooling the photovoltaic thermal module 5, a circulation pipeline connecting the inlet and outlet of the cooling pipe 93 to the liquid storage tank 4 and the evaporator 1 respectively, and a connecting pipe connecting the evaporator 1 and the compressor 2 to the circulation pipeline.

[0079] The photovoltaic-thermal system in this embodiment can utilize the control method described above. The compressor 2 actively extracts the refrigerant from the cooling pipe 93 of the photovoltaic system and recovers it to the receiver 4, isolating the cooling pipe 93 from the refrigeration cycle system. This prevents the refrigerant from remaining in the cooling pipe 93 after system shutdown, which could generate high temperatures and pressures due to exposure to sunlight. This fundamentally eliminates the safety hazard of a photovoltaic system explosion and avoids environmental pollution and resource waste caused by direct refrigerant discharge. Furthermore, after refrigerant recovery, the inlet and outlet of the cooling pipe 93 are disconnected from the refrigeration cycle system, while the evaporator 1, compressor 2, condenser 3, and receiver 4 remain connected. This allows the refrigerant in the main circuit to flow freely, preventing high pressure caused by localized refrigerant accumulation and further enhancing system safety after shutdown.

[0080] In some embodiments, the refrigeration cycle system further includes a first on / off valve 71 connected between the evaporator 1 and the compressor 2. The first on / off valve 71 is used to control the on / off connection between the outlet of the evaporator 1 and the compressor 2. The connecting pipe includes a first pipe 91 that connects the inlet of the cooling pipe 93 to the circulation pipe between the liquid receiver 4 and the first expansion valve 61, and a second pipe 92 that connects the outlet of the cooling pipe 93 to the circulation pipe between the evaporator 1 and the compressor 2. The photovoltaic system further includes a second expansion valve 62 disposed on the first pipe 91 and a second on / off valve 72 disposed between the outlet of the cooling pipe 93 and the connecting pipe. The second on / off valve 72 is used to control the on / off connection between the outlet of the cooling pipe 93 and the connecting pipe.

[0081] In this embodiment, a first on / off valve is added to the refrigeration cycle system to isolate the evaporator together with the first expansion valve during refrigerant recovery; a second expansion valve is installed on the first pipe to control the refrigerant flow rate into the cooling pipe and to prevent refrigerant backflow during recovery; a second on / off valve is installed at the outlet of the cooling pipe to control the opening and closing of the cooling pipe outlet, and can also realize the gradual balancing of refrigerant in the cooling pipe and the circulation pipe during the soft start step. By setting controllable valve components at the above-mentioned locations, this embodiment facilitates the implementation of explosion-proof and soft start steps.

[0082] In some embodiments, compressor 2 is a rotary compressor. The inlet and outlet of the rotary compressor can remain connected when the machine is stopped.

[0083] In this embodiment, compressor 2 is a rotary compressor, which allows the refrigerant to flow more freely in the main circuit of the refrigeration cycle system after the explosion-proof step, which helps to further reduce the risk of high pressure in the circulation pipeline of the refrigeration cycle system and further improve the safety of the system after shutdown.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A control method for a photovoltaic-thermal system, characterized in that, The photovoltaic-thermal system includes: A refrigeration cycle system, including a circulation pipeline for the refrigerant to circulate, and an evaporator, a compressor, a condenser, a liquid reservoir, and a first expansion valve sequentially arranged on the circulation pipeline; A photovoltaic system, including a photovoltaic-thermal component and a cooling pipeline. The cooling pipeline includes a cooling pipe arranged on the photovoltaic-thermal component for cooling the photovoltaic-thermal component, and connecting pipes connecting the inlet and outlet of the cooling pipe to the circulation pipeline between the liquid reservoir and the evaporator and to the circulation pipeline between the evaporator and the compressor respectively; The control method of the photovoltaic-thermal system includes an explosion-proof step, and the explosion-proof step includes: Step 100, using the compressor to extract and reduce the refrigerant in the cooling pipe and sending the extracted refrigerant to the liquid reservoir; Step 200, disconnecting both the inlet and outlet of the cooling pipe from the connecting pipe after the pressure of the refrigerant in the cooling pipe is less than a first threshold; Step 300, keeping any two adjacent ones of the evaporator, the compressor, the condenser, and the liquid reservoir connected to each other.

2. The control method for a photovoltaic-thermal system as described in claim 1, characterized in that, Before step 100, there is also included: step 110, disconnecting the inlet and outlet of the evaporator from the liquid reservoir and the compressor respectively.

3. The control method for a photovoltaic-thermal system as described in claim 2, characterized in that, The refrigeration cycle system further includes a first on-off valve connected between the evaporator and the compressor. The first on-off valve is used to control the on-off between the outlet of the evaporator and the compressor, and step 110 includes: closing the first expansion valve and the first on-off valve.

4. The control method for the photovoltaic-thermal system as described in claim 3, characterized in that, Step 300 includes opening the first on-off valve and setting the opening degree of the first on-off valve to k1, where 0 < k1 < 1. Then, read the pressure P at the outlet of the first on-off valve. After P remains unchanged within a first time threshold t1, open the first expansion valve and set the k1 value to 1.

5. The control method for a photovoltaic-thermal system as described in any one of claims 1 to 4, characterized in that, The connecting pipe includes a first pipe connecting the inlet of the cooling pipe to the circulation pipeline between the liquid reservoir and the first expansion valve, and a second pipe connecting the outlet of the cooling pipe to the circulation pipeline between the evaporator and the compressor. The photovoltaic system further includes a second expansion valve arranged on the first pipe. Before step 100, there is also included: step 120, closing the second expansion valve.

6. The control method for a photovoltaic-thermal system as described in claim 1, characterized in that, The photovoltaic system further includes a second on-off valve arranged between the outlet of the cooling pipe and the connecting pipe. The second on-off valve is used to control the on-off between the outlet of the cooling pipe and the connecting pipe. The control method of the photovoltaic-thermal system further includes a soft start step after the explosion-proof step, and the soft start step includes: Step 400, keeping the inlet of the cooling pipe disconnected from the connecting pipe and setting the opening degree of the second on-off valve to k2, where 0 < k2 < 1; Step 500, after step 400 passes a second threshold time t2, setting the opening degree of the second on-off valve to 1; Step 600, connecting the inlet of the cooling pipe to the connecting pipe; Step 700, starting the compressor.

7. The control method for a photovoltaic-thermal system as described in claim 1, characterized in that, Step 100 includes: reducing the operating frequency of the compressor, and then using the compressor to extract and reduce the refrigerant in the cooling pipe.

8. A photovoltaic-thermal system, characterized in that, The control method for the photovoltaic-thermal system as described in any one of claims 1-7 is applied, wherein the photovoltaic-thermal system comprises: A refrigeration cycle system includes a circulation pipeline for refrigerant circulation and an evaporator, a compressor, a condenser, a liquid receiver, and a first expansion valve arranged sequentially on the circulation pipeline. A photovoltaic system includes a photovoltaic thermal module and a cooling pipeline. The cooling pipeline includes a cooling pipe disposed on the photovoltaic thermal module for cooling the photovoltaic thermal module, a circulation pipeline connecting the inlet and outlet of the cooling pipe to the liquid storage tank and the evaporator respectively, and a connecting pipe connecting the circulation pipeline between the evaporator and the compressor.

9. The photovoltaic-thermal system as described in claim 8, characterized in that, The refrigeration cycle system further includes a first on / off valve connected between the evaporator and the compressor. The first on / off valve is used to control the on / off connection between the outlet of the evaporator and the compressor. The connecting pipe includes a first pipe connecting the inlet of the cooling pipe to a circulation pipe between the liquid receiver and the first expansion valve, and a second pipe connecting the outlet of the cooling pipe to a circulation pipe between the evaporator and the compressor. The photovoltaic system further includes a second expansion valve disposed on the first pipe and a second on / off valve disposed between the outlet of the cooling pipe and the connecting pipe. The second on / off valve is used to control the on / off connection between the outlet of the cooling pipe and the connecting pipe.

10. The photovoltaic-thermal system as described in claim 9, characterized in that, The compressor is a rotary compressor.

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