Multi-stage compression cascade heat pump multi-combined supply system based on jet synergy and optimization method

Abstract

The invention relates to a multi-stage compression cascade heat pump multi-combined supply system with a jet synergistic effect and an optimization method thereof. The system comprises a low-temperature stage sub-cycle, a high-temperature stage sub-cycle, a flash evaporation cycle and a water circulation loop. Heat exchange is carried out between the low-temperature-stage sub-cycle and the high-temperature-stage sub-cycle through a three-fluid heat exchanger; the flash evaporation cycle exchanges heat with the high-temperature stage sub-cycle through a condenser; the water circulation loop supplies water flow to the low-temperature stage sub-circulation; the low-temperature stage sub-cycle is a CO2 sub-cycle with an ejector and is of a two-stage cycle structure, working fluid is compressed through a CO2 low-pressure stage compressor and a CO2 high-pressure stage compressor in the two-stage cycle structure, and the ejector is arranged at an outlet of the CO2 low-pressure stage compressor for pressurization; temperature fluctuation of an inlet and an outlet of the ejector is restrained through the subcooler and the superheater respectively. Compared with the prior art, the system integrates multiple functions of refrigeration, domestic hot water preparation and high-temperature steam preparation, and has the advantages of being high in operation energy efficiency, stable, reliable and the like.

Description

Technical Field

[0001] This invention relates to the field of combined heat pump systems, and in particular to a multi-stage compression cascade heat pump combined heat pump system based on jet enhancement and its optimization method. Background Technology

[0002] Currently, the construction of zero-carbon industrial parks helps promote the development of new productive forces, and high-temperature heat pumps will become the standard heating configuration for zero-carbon parks. However, the application of high-temperature heat pumps in industrial parks is currently less than 1%. Different industries and processes have vastly different heating needs, making the integration of high-temperature heat pumps with these processes difficult. Furthermore, heat pumps generally experience a decrease in COP under high-temperature conditions, affecting their economic competitiveness. Combined cooling and heating is the best application for heat pumps. However, transcritical CO2 refrigeration cycles suffer from significant throttling losses and low refrigeration COP; CO2 heat pump performance is significantly affected by internal circulation structure, component performance, operating conditions, and control parameters, exhibiting time-varying characteristics. Heat pump heating performance decreases under extreme conditions. Ejectors and subcoolers can help improve the performance of CO2 cooling heat pumps, but optimized design and control are still lacking.

[0003] Currently, the conventional use of multiple independent heat pump systems can meet the energy needs of different scenarios, but it also leads to increased initial investment in equipment, large space occupation in the machine room, and a high average annual idle rate of the system, resulting in serious resource waste. Essentially, the core contradiction of current industrial energy supply systems lies in the limited coverage of the advantageous operating conditions of a single device, making it impossible to simultaneously balance the energy efficiency of domestic hot water preparation, high-temperature steam generation for processes, and cooling needs, as illustrated by the air-source steam heat pump system and control method disclosed in invention publication number CN119222833A. Furthermore, the parallel implementation of multiple systems inevitably brings drawbacks such as equipment redundancy and complex operation and management. Especially when waste heat resources are unstable, existing systems struggle to establish a dynamic matching relationship between temperature rise demand and heat source conditions. Therefore, there is an urgent need to propose a flexible and efficient integrated cooling, heating, steam, and electricity system. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a flexible and efficient hybrid cycle multi-generation system based on jet enhancement and multi-stage compression, and its optimization method, which integrates multiple functions such as refrigeration, domestic hot water preparation, and high-temperature steam preparation.

[0005] The objective of this invention can be achieved through the following technical solutions: A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement includes a low-temperature stage sub-cycle, a high-temperature stage sub-cycle, a flash cycle, and a water circulation loop; The low-temperature stage sub-circuit and the high-temperature stage sub-circuit exchange heat through a three-fluid heat exchanger. The flash cycle and the high-temperature stage sub-cycle exchange heat through a condenser; The water circulation loop supplies water to the low-temperature stage sub-circulation; The cryogenic sub-cycle is a CO2 sub-cycle with an ejector, which is a two-stage cycle structure. In this two-stage cycle structure, the working fluid is compressed by a low-pressure CO2 compressor and a high-pressure CO2 compressor, respectively. The ejector is set at the outlet of the low-pressure CO2 compressor to boost the pressure. The temperature fluctuations at the inlet and outlet of the ejector are suppressed by a subcooler and a superheater, respectively.

[0006] Furthermore, the CO2 sub-cycle also includes a CO2 evaporator, a first throttle valve, a gas-liquid separator, and an exhaust cooler; The CO2 evaporator, CO2 low-pressure stage compressor, exhaust cooler, ejector, gas-liquid separator and first throttle valve are connected in sequence to form the first stage circulation loop; The ejector, gas-liquid separator, superheater, CO2 high-pressure stage compressor, three-fluid heat exchanger and subcooler are connected in sequence to form the second-stage circulation loop.

[0007] Furthermore, the water circulation loop includes a low-temperature heat source, a first water pump, a first three-way valve, a second three-way valve, a third three-way valve, and a fourth water pump; The low-temperature heat source, the first water pump, the first three-way valve, and the CO2 evaporator are connected to form a loop; the water output from the low-temperature heat source enters the first three-way valve through the first water pump, and a portion of the water output from the first three-way valve enters the CO2 evaporator for heat exchange and returns to the low-temperature heat source. Another portion of the water flow output from the first three-way valve enters the third three-way valve for further distribution. A portion of the water flow output from the third three-way valve flows into the exhaust cooler for heat exchange and mixes with the outlet water flow from the second three-way valve. Another portion of the water flow output from the third three-way valve flows into the subcooler for heat exchange and flows out of the subcooler before flowing back into the second three-way valve. A portion of the water flow output from the second three-way valve flows to the exhaust cooler, and another portion flows into the superheater for heat exchange before returning to the low-temperature heat source. The fourth water pump is connected to a hot water source and forms a hot water circulation loop with the three-fluid heat exchanger. The low-temperature heat sources include air, water, soil, industrial waste heat, solar thermal energy, and cold storage tanks. When the temperature is below the freezing point, a refrigerant is used instead of water as the working medium.

[0008] Furthermore, when the heat pump multi-generation system is operating in the CO2 sub-cycle independent mode to produce domestic hot water or for cooling, the low-temperature and low-pressure CO2 gas in the CO2 sub-cycle is compressed into medium-temperature and medium-pressure superheated steam by the CO2 low-pressure stage compressor, then flows through the exhaust cooler and is cooled by water, and finally enters the secondary inlet of the ejector and is ejected by the high-temperature and high-pressure supercritical fluid input by the ejector. The fluid output from the ejector enters the gas-liquid separator and is separated into gas and liquid phases. The gaseous CO2 gas passes through the superheater and the high-pressure stage CO2 compressor in sequence and is transformed into a high-temperature and high-pressure supercritical fluid. Then it flows through the three-fluid heat exchanger and the subcooler in sequence and is cooled by water. After that, it passes through the main nozzle of the ejector to reduce pressure and increase speed, and ejects the CO2 gas from the outlet of the low-pressure stage CO2 compressor. The liquid fluid flows into the first throttling valve to reduce pressure and then flows into the CO2 evaporator to absorb heat.

[0009] Furthermore, the water flow rate is adjusted by the first three-way valve, the second three-way valve, and the third three-way valve in the water circulation loop to optimize the control of the subcooling and superheating of the CO2 sub-circulation.

[0010] Furthermore, the high-temperature stage sub-cycle also includes a high-temperature medium compressor, a second throttle valve, and a waste heat source evaporator. The three-fluid heat exchanger, high-temperature medium compressor, condenser, second throttle valve, and waste heat source evaporator are connected in sequence to form a circulation loop. The waste heat source evaporator is also connected to a second water pump and an industrial waste heat source to form a waste heat exchange loop. Alternatively, the high-temperature stage sub-cycle may be a multi-stage compression sub-cycle or an inverse Brayton cycle, similar to the low-temperature stage sub-cycle; the high-temperature stage sub-cycle may directly supply steam or perform high-temperature heat storage.

[0011] Furthermore, the flash evaporation cycle also includes a flash evaporator, a fourth three-way valve, a third water pump, a fifth three-way valve, a sixth three-way valve, and a heat storage tank. The condenser, the fifth three-way valve, the flash evaporator, the sixth three-way valve, the fourth three-way valve, and the third water pump are connected in sequence to form a circulation loop. Steam is output from the outlet end of the flash evaporator, and one end of the fourth three-way valve is connected to a water supply pipeline. The flash evaporator, the fifth three-way valve, the heat storage tank, and the sixth three-way valve are connected in sequence to form a circulation loop.

[0012] Furthermore, when the heat pump multi-generation system is operating in the coordinated mode of high-temperature stage sub-cycle and flash cycle to produce high-temperature steam, the low-temperature and low-pressure high-temperature medium in the high-temperature stage sub-cycle is compressed into a high-temperature and high-pressure fluid by the high-temperature medium compressor, enters the condenser to exchange heat with water, and then enters the waste heat source evaporator after being throttled by the second throttling valve. After exchanging heat with waste heat in the waste heat source evaporator, it becomes a low-temperature and low-pressure high-temperature medium again. In the flash evaporation cycle, the high-temperature and high-pressure hot water from the condenser outlet is input into the flash tank, and the flash tank outputs steam to supply the user; the remaining saturated water is transported by the third water pump to participate in the circulation, and is replenished through the fourth three-way valve; When the heat pump multi-generation system operates in the superimposed cycle mode of the high-temperature sub-cycle and the CO2 sub-cycle, and in coordination with the flash cycle, the CO2 sub-cycle absorbs heat from the low-temperature heat source and releases heat to the high-temperature sub-cycle through the three-fluid heat exchanger. After absorbing heat by the high-temperature medium in the high-temperature sub-cycle, it enters the condenser and works with the flash cycle to complete the preparation of high-temperature steam.

[0013] The present invention also provides an optimization method for a multi-stage compression cascade heat pump system based on jet enhancement, as described above, comprising the following steps: The operating mode and energy supply method shall be determined based on the application scenario, operating conditions and / or energy demand. Based on the operating mode, assume the optimal intermediate pressure of the three-fluid heat exchanger, and the discharge pressure of the CO2 low-pressure stage compressor and the CO2 high-pressure stage compressor; First, based on the application scenario, operating conditions, and probability statistics of operating modes, the design of the low-temperature stage sub-cycle and the high-temperature stage sub-cycle is optimized collaboratively. Then, based on the operating conditions, control is optimized collaboratively, and heat exchange matching is achieved through a three-fluid heat exchanger. The design and control parameters of the two-stage compression cycle and ejector in the low-temperature stage sub-cycle are optimized collaboratively. The control parameters in the optimization process include compressor frequency, ejector parameters, subcooler and superheater parameters, and throttle valve opening. The ejector parameters include throat diameter, nozzle distance, ejector bypass valve, and pulse width regulating valve parameters. For large-capacity heat pumps, multiple ejectors are combined for collaborative control. The optimization process is repeated until the heat exchange capacity of the three-fluid heat exchanger is matched, the energy supply requirements are met, and the system achieves optimal energy efficiency. Then, the structure and control optimization results are output. Otherwise, the optimal intermediate pressure of the three-fluid heat exchanger and the exhaust pressure of the CO2 low-pressure stage compressor and the CO2 high-pressure stage compressor are updated.

[0014] Furthermore, the method also includes designing and optimizing the control of the injector (10), specifically including: (1) Based on the application scenario, operating mode, and inlet and outlet conditions of the injector, determine the optimization target of the injector and perform coordinated optimization of the injector design and control; the corresponding optimization process is as follows: First, a database is obtained by simulating a heterogeneous and non-equilibrium numerical model of the injector. The database is then used to train a neural network surrogate model or a machine learning model to obtain the injector optimization objective function. Then, based on the optimization objectives determined by the application scenario and the probability statistics of the operating conditions, the weights are determined using quantitative methods such as sensitivity analysis and influence weight analysis. Finally, the genetic algorithm and weighted average optimization algorithm are combined with the neural network surrogate model or machine learning model to establish an optimization framework, perform global optimization, and obtain optimized values ​​for the internal geometry of the injector suitable for different working conditions. (2) According to the operating mode, switch the adjustable ejector with different internal geometry suitable for cooling / heating and adopt different control strategies. The control strategies include: using the pressure ratio as the optimization target in the heating condition and the ejector ratio as the optimization target in the cooling condition, and coordinating the optimization of subcooling and superheating. (3) Based on the active inlet working condition of the injector, the dynamic response time of the injector is determined and real-time optimization control is performed; based on the model predictive control method, the control parameters of the injector are adaptively optimized under different working conditions according to the inlet and outlet working conditions of the injector in the cooling / heating mode.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The heat pump multi-generation system proposed in this invention is provided with a low-temperature stage sub-cycle, a high-temperature stage sub-cycle, a flash evaporation cycle and a water circulation loop. The low-temperature stage sub-cycle and the high-temperature stage sub-cycle exchange heat through a three-fluid heat exchanger. The flash evaporation cycle and the high-temperature stage sub-cycle exchange heat through a condenser. The water circulation loop supplies water to the low-temperature stage sub-cycle, realizing a flexible combination of operation modes: When domestic hot water or cooling is required, the system can operate independently in the low-temperature sub-cycle, at which time the three-fluid heat exchanger is used as an air cooler for the CO2 cycle. When there is a stable waste heat source and high-temperature steam needs to be produced, the system can switch to the high-temperature stage sub-circulation and flash evaporation cycle working mode. At this time, the three-fluid heat exchanger is effectively cut out of the system, and the high-temperature stage working fluid directly absorbs heat through the waste heat source evaporator. When there is no stable waste heat source but high-temperature steam still needs to be produced, the system can start a cascaded cycle mode of the low-temperature stage sub-cycle and the high-temperature stage sub-cycle. In this mode, the three-fluid heat exchanger acts as an intermediate heat exchanger connecting the two sub-cycles. The low-temperature stage sub-cycle absorbs heat from the natural environment and transfers the heat to the high-temperature stage cycle. This multi-mode integration and switching capability enables a single system to cover a variety of application requirements, significantly improving equipment utilization and adaptability to operating conditions.

[0016] (2) The low-temperature stage sub-cycle of the present invention adopts a two-stage compression-jet flash CO2 sub-system. This system shares the high pressure ratio of the compressor in the traditional CO2 single-stage cycle with a high-pressure stage compressor and a low-pressure stage compressor, which greatly reduces the pressure ratio of a single compressor; at the same time, an ejector is added at the outlet of the low-pressure stage compressor, and the low-pressure exhaust is mixed with the high-pressure supercritical fluid on the high-pressure side to increase the pressure, recover the expansion work of the system, increase the suction pressure of the high-pressure stage compressor, and reduce the power consumption of the high-pressure stage compressor; Because the high superheat of the low-pressure stage compressor exhaust can affect the ejector's entrainment capability when it enters the secondary flow inlet, an exhaust cooler is added to the low-pressure stage compressor exhaust port to regulate the superheat entering the secondary flow inlet and improve the ejector's entrainment capability. This innovative sub-cycle system design can significantly improve the overall system COP, while the high-pressure side compressor will also have a lower exhaust temperature than traditional single-stage compressors, reducing the risk of lubricating oil carbonization. For regions with relatively mild climates, less extreme temperature differences, and greater sensitivity to initial investment, a single-stage compression system in the low-temperature stage may be more economical and practical.

[0017] (3) Overall, the present invention has the following advantages: Functional versatility and adaptability to all operating conditions: A single system integrates multiple functions such as refrigeration, domestic hot water preparation, and high-temperature steam preparation, and can intelligently switch to the optimal mode according to conditions and needs; Significantly improved operating energy efficiency: Through mode selection, multi-level collaborative optimization of system and component design and control, efficient application of three-fluid heat exchangers, and decoupled control of subcooling / superheating in the water loop, the COP of the system under various operating conditions is effectively improved; if multi-stage compression interstage injection is used for efficiency enhancement in each stage of cascade, the limitation of COP decrease when the compression ratio increases in single-stage compression can be overcome, which helps to improve the energy efficiency of ultra-high temperature heat pumps (such as high temperature heat pumps above 500℃). Stable and reliable operation: The hybrid cycle of cascade and multi-stage compression breaks down the challenge of ultra-wide temperature range into multiple sub-temperature range challenges that are easier to implement technically. Each sub-temperature range uses a working fluid optimized for that temperature range, breaking through the limitations of a single working fluid; it avoids the exhaust temperature from exceeding the limit when using multi-stage compression and improves the reliability of the system under extreme conditions. It boasts excellent energy efficiency, environmental friendliness, and economic benefits: It fully utilizes natural heat sources and industrial waste heat, reducing the consumption of high-grade energy and meeting green and low-carbon requirements; it can also meet the needs of high-temperature-rise and high-efficiency improvement. Furthermore, it allows for flexible combination of operating modes. Controlling the intermediate pressure of the cascade cycle can enhance the safety and stability of the jet system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a multi-stage compression cascade heat pump system based on jet enhancement provided in an embodiment of the present invention; Figure 2 This is a general schematic diagram of a three-fluid heat exchanger provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the semi-circular microchannel surface structure of the heat exchange plate on the low-temperature working fluid (e.g., CO2) side of a three-fluid heat exchanger provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of the airfoil flow channel on the surface structure of the heat exchange plate on the high-temperature working fluid (e.g., R1234ze(Z)) side of a three-fluid heat exchanger provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the S-shaped flow channel on the surface structure of the heat exchange plate on the heat transfer common medium (e.g., water) side of a three-fluid heat exchanger provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the independent operation of the low-temperature stage (CO2) sub-cycle of a heat pump multi-generation system provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the coordinated operation of the high-temperature stage (R1234ze(Z)) sub-cycle and flash cycle of a heat pump multi-generation system provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the coordinated operation of a (R1234ze(Z) / CO2) cascade cycle and flash cycle in a heat pump multi-generation system provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of an optimization method for a multi-stage compression cascade heat pump system based on jet enhancement, provided in an embodiment of the present invention. In the diagram, 1. First water pump, 2. First three-way valve, 3. CO2 evaporator, 4. First throttle valve, 5. Gas-liquid separator, 6. Superheater, 7. CO2 high-pressure stage compressor, 8. Three-fluid heat exchanger, 9. Subcooler, 10. Ejector, 11. Second three-way valve, 12. Third three-way valve, 13. CO2 low-pressure stage compressor, 14. Exhaust cooler, 15. High-temperature medium compressor, 16. Condenser, 17. Second throttle valve, 18. Waste heat source evaporator, 19. Second water pump, 20. Flash evaporator, 21. Fourth three-way valve, 22. Third water pump, 23. Fourth water pump, 24. Fifth three-way valve, 25. Sixth three-way valve, 26. Heat storage tank, 27. Seventh three-way valve, 28. Eighth three-way valve, 29. Photovoltaic / thermal PV / T panel, 30. Cold storage tank / low-temperature heat source, 31. Battery, 32. Load. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0023] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0024] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0025] Example 1 like Figure 1 As shown, this embodiment provides a multi-stage compression cascade heat pump system based on jet enhancement, including a low-temperature stage sub-cycle, a high-temperature stage sub-cycle, a flash cycle, and a water circulation loop; Heat exchange occurs between the low-temperature stage sub-cycle and the high-temperature stage sub-cycle via a three-fluid heat exchanger 8; The flash cycle and the high-temperature stage sub-cycle exchange heat through condenser 16; The water circulation loop supplies water to the low-temperature stage sub-circulation; The low-temperature sub-cycle is a CO2 sub-cycle with ejector 10, which is a two-stage cycle structure. In this two-stage cycle structure, the working fluid is compressed by the CO2 low-pressure stage compressor 13 and the CO2 high-pressure stage compressor 7 respectively, and the ejector 10 is set at the outlet of the CO2 low-pressure stage compressor 13 for pressurization. The temperature fluctuations at the inlet and outlet of the ejector 10 are suppressed by the subcooler 9 and the superheater 6 respectively.

[0026] The following is a detailed description of each part.

[0027] 1. CO2 subcycle The CO2 sub-cycle specifically includes a CO2 evaporator 3, a first throttle valve 4, a gas-liquid separator 5, and an exhaust cooler 14. The CO2 evaporator 3, CO2 low-pressure stage compressor 13, exhaust cooler 14, ejector 10, gas-liquid separator 5 and first throttle valve 4 are connected in sequence to form the first stage circulation loop; The ejector 10, gas-liquid separator 5, superheater 6, CO2 high-pressure stage compressor 7, three-fluid heat exchanger 8 and subcooler 9 are connected in sequence to form the second-stage circulation loop.

[0028] The CO2 sub-cycle utilizes energy in a cascade manner to achieve flexible optimization of superheat and subcooling under varying operating conditions. Furthermore, phase change subcoolers and phase change superheaters can be used to suppress large fluctuations in the inlet and outlet pressure and temperature of the ejector, maintaining it within the optimized operating range for the ejector under different operating modes.

[0029] The subcooler 9 is a biomimetic phase change heat exchanger, which includes PCM phase change material, biomimetic structure piping, reversing valve, subcooler bypass, etc. The PCM phase change material can smooth out the fluctuations in the inlet and outlet temperatures of the ejector.

[0030] The adjustable subcooling and superheating of subcooler 9 and superheater 6 can be achieved through three-way valves. The adjustable subcooler and superheater enable cascaded energy utilization within the system.

[0031] The injector features 10 adjustable nozzles, allowing for adjustment of nozzle distance and throat area, as well as adjustable opening of the multi-ejector channel control valve and pulse width regulating valve.

[0032] The three fluids in the three-fluid heat exchanger 8 have different physical properties and pressures. Therefore, an asymmetric surface structure and wettability are used to match the heat exchange capacity of the different working fluids within the heat exchanger. Figures 2-5As shown, the surface structure of the heat exchange plate on the CO2 side of the low-temperature working fluid adopts a semi-circular microchannel, the surface structure of the heat exchange plate on the CO2 side of the high-temperature working fluid adopts an airfoil flow channel, and the surface structure of the heat exchange plate on the water side of the heat transfer medium adopts an S-shaped flow channel.

[0033] Specifically, the three-fluid heat exchanger 8 has three independent fluid channels for introducing the high-temperature refrigerant, CO2, and water, respectively. Its innovative operation lies in the following: when the CO2 cycle is running alone, by closing the CO2 flow path on the high-temperature refrigerant side, the three-fluid heat exchanger only exchanges heat between the CO2 and water, effectively acting as an air cooler; in cascade cycle mode, by closing the CO2 flow path on the water side, the three-fluid heat exchanger only exchanges heat between the CO2 and high-temperature refrigerant, efficiently achieving thermal coupling between the two cycles. Through selective opening and closing control of specific flow channels, differentiated functions of a single heat exchanger component are achieved in different system modes, forming the basis for the system's multi-functional operation.

[0034] 2. Water circulation loop The water circulation loop includes a low-temperature heat source, a first water pump 1, a first three-way valve 2, a second three-way valve 11, a third three-way valve 12, and a fourth water pump 23; The low-temperature heat source, the first water pump 1, the first three-way valve 2, and the CO2 evaporator 3 are connected to form a loop; the water output from the low-temperature heat source enters the first three-way valve 2 through the first water pump 1, and a portion of the water output from the first three-way valve 2 enters the CO2 evaporator 3 for heat exchange and returns to the low-temperature heat source. Another portion of the water output from the first three-way valve 2 enters the third three-way valve 12 for further distribution. A portion of the water output from the third three-way valve 12 flows into the exhaust cooler 14 for heat exchange and mixes with the outlet water flow from the second three-way valve 11. Another portion of the water output from the third three-way valve 12 flows into the subcooler 9 for heat exchange and flows out of the subcooler 9 before flowing back into the second three-way valve 11. A portion of the water output from the second three-way valve 11 flows to the exhaust cooler 14, and another portion flows into the superheater 6 for heat exchange before returning to the low-temperature heat source. The fourth water pump 23 is connected to a hot water source and forms a hot water circulation loop with the three-fluid heat exchanger 8.

[0035] This solution employs an innovative water circulation loop design incorporating multiple three-way valves to achieve independent and precise decoupled control of the subcooling and superheating of the CO2 working fluid: Natural water is distributed via three-way valves, with a portion entering the subcooler to exchange heat with the high-pressure CO2 working fluid, achieving deep subcooling; this portion is also heated. The heated water can be further distributed via three-way valves, with a portion directed to the superheater to superheat the compressor return gas, thus independently controlling the superheat. The remaining heated water mixes with the main natural water flow, increasing the water temperature entering the evaporator, thereby raising the CO2 evaporation temperature and pressure, and reducing the compressor compression ratio and power consumption. By adjusting the flow ratio of each branch in real time, the system can dynamically respond to changes in external conditions and load demands, ensuring the circulation is always in an optimal state. This proactive control strategy for key parameters is crucial for improving the overall energy efficiency of the system.

[0036] 3. High-temperature stage sub-cycle The high-temperature sub-cycle also includes a high-temperature medium compressor 15, a second throttle valve 17, and a waste heat source evaporator 18. The three-fluid heat exchanger 8, the high-temperature medium compressor 15, the condenser 16, the second throttle valve 17, and the waste heat source evaporator 18 are connected in sequence to form a circulation loop. The waste heat source evaporator 18 is also connected to a second water pump 19 and an industrial waste heat source to form a waste heat exchange loop.

[0037] Depending on the heating temperature, the high-temperature stage sub-cycle can utilize different working fluids, including single-stage or multi-stage heat pumps, or other types of cycles such as reverse Brayton heat pumps. High-temperature stage working fluids include: below 300°C, R718 (water), R1336mzzZZ 100–150°C, R1233zdEE 100–130°C, and R1234ze(Z) 75°C – 95°C; above 300°C, argon, helium, air, and CO2. For high-temperature stage heating temperatures exceeding 300°C, high-temperature molten salt thermal storage can be used.

[0038] 4. Flash circulation The flash evaporation cycle also includes a flash evaporator 20, a fourth three-way valve 21, a third water pump 22, a fifth three-way valve 24, a sixth three-way valve 25, and a heat storage tank 26. The condenser 16, the fifth three-way valve 24, the flash evaporator 20, the sixth three-way valve 25, the fourth three-way valve 21, and the third water pump 22 are connected in sequence to form a circulation loop. The outlet end of the flash evaporator 20 outputs steam, and one end of the fourth three-way valve 21 is connected to a water supply pipeline. The flash evaporator 20, the fifth three-way valve 24, the heat storage tank 26, and the sixth three-way valve 25 are connected in sequence to form a circulation loop.

[0039] 5. Operating modes of heat pump multi-generation systems 5.1, such as Figure 6As shown, when the heat pump multi-generation system is in the CO2 sub-cycle independent operation mode to produce domestic hot water or for cooling, the low-temperature and low-pressure CO2 gas in the CO2 sub-cycle is compressed into medium-temperature and medium-pressure superheated steam by the CO2 low-pressure stage compressor 13, then flows through the exhaust cooler 14 and is cooled by water, and finally enters the secondary inlet of the ejector 10 and is ejected by the high-temperature and high-pressure supercritical fluid input by the ejector 10. The fluid output from ejector 10 enters gas-liquid separator 5 and is separated into gas phase and liquid phase. The gas phase CO2 gas passes through superheater 6 and CO2 high-pressure stage compressor 7 in sequence and is converted into a high-temperature and high-pressure supercritical fluid. Then it flows through three-fluid heat exchanger 8 and subcooler 9 in sequence and is cooled by water. After that, it passes through the main nozzle of ejector 10 to reduce pressure and increase speed, and ejects CO2 gas from the outlet of CO2 low-pressure stage compressor 13. The liquid phase fluid flows into the first throttling valve 4 to reduce pressure and then flows into CO2 evaporator 3 to absorb heat.

[0040] 5.2, such as Figure 7 As shown, when the heat pump multi-generation system is in the coordinated operation mode of the high-temperature stage sub-cycle and the flash cycle to produce high-temperature steam, the low-temperature and low-pressure high-temperature medium in the high-temperature stage sub-cycle is compressed into a high-temperature and high-pressure fluid by the high-temperature medium compressor 15, enters the condenser 16 to exchange heat with water, and then enters the waste heat source evaporator 18 after being throttled by the second throttling valve 17. After exchanging heat with waste heat in the waste heat source evaporator 18, it becomes a low-temperature and low-pressure high-temperature medium again. In the flash evaporation cycle, the high-temperature and high-pressure hot water from the outlet of condenser 16 is input into the flash tank, and the flash tank outputs steam to supply the user; the remaining saturated water is transported by the third water pump 22 to participate in the circulation, and is replenished through the fourth three-way valve 21.

[0041] 5.3, such as Figure 8 As shown, when the heat pump multi-generation system operates in the superimposed cycle mode of the high-temperature stage sub-cycle and the CO2 sub-cycle, and in coordination with the flash cycle, the CO2 sub-cycle absorbs heat from the natural water source and releases heat to the high-temperature stage sub-cycle through the three-fluid heat exchanger 8. After absorbing heat by the high-temperature medium in the high-temperature stage sub-cycle, it enters the condenser 16 and works with the flash cycle to complete the preparation of high-temperature steam.

[0042] The following example uses R1234ze(Z) as the high-temperature circulating working fluid to illustrate a specific example of the above scheme: This example proposes a multi-stage compression cascade heat pump combined cycle system based on jet enhancement, comprising two refrigerant sub-cycles, one flash cycle, and one water circulation loop. The CO2 sub-cycle includes a CO2 evaporator 3, a first throttle valve 4, a gas-liquid separator 5, a superheater 6, a high-pressure CO2 compressor 7, a three-fluid heat exchanger 8, a subcooler 9, an ejector 10, a low-pressure CO2 compressor 13, and an exhaust cooler 14. The R1234ze(Z) sub-cycle includes a three-fluid heat exchanger 8, an R1234ze(Z) compressor 15, a condenser 16, a second throttle valve 17, and a waste heat source evaporator 18. The flash cycle includes a condenser 16, a flash tank 20, a fourth three-way valve 21, and a third water pump 22. The water circulation loop includes a first water pump 1, a first three-way valve 2, a second three-way valve 11, a third three-way valve 12, a second water pump 19, and a fourth water pump 23. The electrical circuit includes a CO2 high-pressure stage compressor 7, a CO2 low-pressure stage compressor 13, an R1234ze(Z) compressor 15, a seventh three-way valve 27, an eighth three-way valve 28, a photovoltaic / thermal PV / T panel 29, a storage battery 31, and a load 32. The seventh three-way valve 27 and the eighth three-way valve 28 are connected to the water circulation circuit and connected to the photovoltaic / thermal PV / T panel 29 to connect to the electrical circuit.

[0043] In the example, the CO2 low-pressure stage compressor 13, the CO2 high-pressure stage compressor 7, and the R1234ze(Z) compressor 15 are used to compress the working fluid to increase the temperature and pressure of the refrigerant. Different models and capacities of compressors can be selected according to the characteristics of the refrigerant and the operating conditions of the system.

[0044] Heat exchangers are used to achieve heat exchange between different media: for example, CO2 evaporator 3, superheater 6, subcooler 9, and exhaust cooler 14 achieve heat exchange between CO2 and water; condenser 16 and waste heat source evaporator 18 achieve heat exchange between R1234ze(Z) and water; and three-fluid heat exchanger 8 simultaneously facilitates heat exchange between CO2 and water, and between CO2 and R1234ze(Z). Therefore, heat exchangers of appropriate size and model must be selected according to the heat exchange medium and the amount of heat exchange.

[0045] The three-way valves are used for flow control in the water circulation loop: the first three-way valve 2 controls the flow into the third three-way valve 12, which in turn controls the flow of natural water into the subcooler 9 and the exhaust cooler 14, thereby regulating the subcooling and the superheat at the ejector secondary inlet; the second three-way valve 11 controls the flow of heated water from the subcooler 9 into the superheater 6 to regulate the suction superheat of the CO2 high-pressure stage compressor; and the fourth three-way valve 21 is used for water replenishment in the flash evaporation cycle. Therefore, the appropriate type and specification of the three-way valves must be selected according to the system control requirements and the working medium.

[0046] The ejector 10 uses the ejector fluid to increase the pressure of the ejected fluid, thereby achieving a pressurization effect. Different adjustable ejectors of different specifications can be selected according to the thermodynamic characteristics of the fluid.

[0047] In actual operation, the system has three operating modes: The CO2 sub-cycle operates independently and is used for the production of domestic hot water and refrigeration. The R1234ze(Z) sub-cycle operates in conjunction with the flash cycle to prepare high-temperature steam; The R1234ze(Z) / CO2 cascade cycle and flash cycle are used in synergistic operation to prepare high-temperature steam.

[0048] The operating mode depends on the type of medium involved in heat exchange in the three-fluid heat exchanger. In addition, the water circulation loop flexibly adjusts the subcooling and superheat of the CO2 sub-circuit through multiple three-way valves to ensure that the system maintains efficient and stable operation within a range of varying operating conditions.

[0049] like Figure 6 As shown, when the CO2 sub-cycle operates independently to produce domestic hot water or for cooling, the system works in conjunction with the water circulation loop using a jet-type two-stage compression transcritical CO2 cycle. In the CO2 cycle, low-temperature, low-pressure CO2 gas is compressed into medium-temperature, medium-pressure superheated steam by the low-pressure stage CO2 compressor 13, then flows through the exhaust cooler 14 and is cooled by water, finally entering the secondary inlet of the ejector 10 and being ejected by the high-temperature, high-pressure supercritical fluid. The two fluids mix in the mixing chamber of the ejector 10, and then, after being decelerated and pressurized in the diffuser section, enter the gas-liquid separator 5. The gas phase outlet of the gas-liquid separator 5 is connected to the superheater 6, and then to the high-pressure stage CO2 compressor 7. The CO2 pressurized by the ejector is compressed into a high-temperature and high-pressure supercritical fluid, which flows through the three-fluid heat exchanger 8 and the subcooler 9 in sequence and is cooled by water. Then, the pressure is reduced and the speed is increased through the main nozzle of the ejector 10, which ejects the CO2 from the outlet of the low-pressure stage CO2 compressor. The liquid phase outlet is connected to the CO2 evaporator 3 through the first throttling valve 4. After the CO2 is throttled and depressurized, it enters the evaporator to absorb heat.

[0050] In the water circulation loop, natural water enters the first three-way valve 2 via the first water pump 1. A portion of the water flows into the third three-way valve 12 and is further distributed; the other portion mixes with the water flowing out of the second three-way valve 11 and the exhaust cooler 14 to increase the temperature of the main water flow entering the evaporator. The third three-way valve 12 distributes the incoming flow to the subcooler 9 and the exhaust cooler 14 for heating. The water flow from the exhaust cooler 14 mixes with the water flow from the second three-way valve 11. Meanwhile, the water flow from the subcooler 9 enters the second three-way valve 11 and is redistributed: a portion enters the superheater 6 for cooling, and the remainder mixes with the exhaust cooler 14 and the main natural water flow. By adjusting the water flow through the three three-way valves, the subcooling and superheating of the CO2 cycle can be dynamically controlled under varying operating conditions.

[0051] like Figure 7 As shown, when the R1234ze(Z) sub-cycle and flash cycle operate in tandem to produce high-temperature steam, in the R1234ze(Z) sub-cycle, the low-temperature, low-pressure R1234ze(Z) gas is compressed into a high-temperature, high-pressure fluid by the R1234ze(Z) compressor 15, enters the condenser 16 to exchange heat with water, and then enters the waste heat source evaporator 18 after being throttled by the second throttling valve 17. After absorbing heat from the waste heat source, it becomes low-temperature, low-pressure gas again. In this mode, the three-fluid heat exchanger 8 does not participate in the cycle. In the flash cycle, the high-temperature, high-pressure hot water from the outlet of the condenser 16 enters the flash tank 20, and the steam is discharged from the top of the tank to supply heat users. Saturated water is transported by the third water pump 22 to participate in the cycle. To replenish the water lost due to steam output, the system replenishes water through the fourth three-way valve 21.

[0052] like Figure 8 As shown, when the R1234ze(Z) / CO2 cascade cycle and flash cycle operate in tandem to produce high-temperature steam, the waste heat source evaporator 18 in the R1234ze(Z) cycle is disconnected from the system and no longer absorbs heat from the outside. At this time, the CO2 sub-cycle maintains the same working process as the domestic hot water mode, absorbing heat from the natural water source and releasing heat to the R1234ze(Z) cycle as a low-temperature stage in the three-fluid heat exchanger 8. After absorbing heat in the intermediate heat exchanger, the R1234ze(Z) working fluid is compressed and enters the condenser 16, working in conjunction with the flash cycle to complete the production of high-temperature steam.

[0053] Example 2 like Figure 9 As shown, this embodiment provides an optimization method for a multi-stage compression cascade heat pump system based on jet enhancement, as described in Embodiment 1, including the following steps: S1: Determine the operating mode and energy supply method based on the application scenario, operating conditions and / or energy demand; S2: Based on the operating mode, assume the optimal intermediate pressure of the three-fluid heat exchanger 8, and the discharge pressure of the CO2 low-pressure stage compressor 13 and the CO2 high-pressure stage compressor 7. S3: First, based on the application scenario, operating conditions, and probability statistics of operating modes, the design of the low-temperature stage sub-cycle and the high-temperature stage sub-cycle is optimized in a coordinated manner. Then, based on the operating conditions, the control is optimized in a coordinated manner, and the heat exchange is matched through the three-fluid heat exchanger 8. The two-stage compression cycle and the ejector 10 in the low-temperature stage sub-cycle are optimized in a coordinated manner. The control parameters in the optimization process include the compressor frequency, the throat diameter and nozzle distance of the ejector 10, the parameters of the subcooler 9 and the superheater 6, and the opening degree of the throttle valve. S4: The optimization process is repeated until the heat exchange capacity of the three-fluid heat exchanger 8 is matched, meets the energy supply requirements, and achieves the optimal energy efficiency of the system. Then, the optimized structure and control results are output. Otherwise, the optimal intermediate pressure of the three-fluid heat exchanger 8 and the exhaust pressure of the CO2 low-pressure stage compressor 13 and the CO2 high-pressure stage compressor 7 are updated.

[0054] Preferably, a model-based prediction method is used to optimize the injector, as follows: (1) Based on the application scenario, operating mode, and inlet and outlet conditions (pressure, temperature, etc.) of the ejector, determine the ejector optimization target and optimize the design and control of the ejector. This includes optimizing the internal geometry of the ejector using a genetic algorithm and a weighted average optimization algorithm. (2) Based on the operating mode, switch between adjustable ejectors with different internal geometries suitable for cooling / heating and adopt different control strategies to clarify the range of optimized control parameters for the ejector. Under heating conditions, the pressure rise ratio is the optimization target, and under cooling conditions, the ejector ratio is the optimization target. The subcooling and superheating are also optimized in conjunction.

[0055] (3) Based on the active inlet state of the injector, the dynamic response time and other characteristics of the injector are identified for real-time control. The active inlet state includes the supercritical region, the quasi-critical region, and the subcritical region. Based on the inlet and outlet conditions of the injector in cooling / heating mode, the control parameters (needle position, nozzle distance) of the injector are adaptively and actively optimized under varying operating conditions.

[0056] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement, characterized in that, This includes a low-temperature stage sub-cycle, a high-temperature stage sub-cycle, a flash cycle, and a water cycle loop; The low-temperature stage sub-circuit and the high-temperature stage sub-circuit exchange heat through a three-fluid heat exchanger (8); The flash cycle and the high-temperature stage sub-cycle exchange heat through a condenser (16); The water circulation loop supplies water to the low-temperature stage sub-circulation; The low-temperature sub-cycle is a CO2 sub-cycle with an ejector (10), which is a two-stage cycle structure. In this two-stage cycle structure, the working fluid is compressed by the CO2 low-pressure stage compressor (13) and the CO2 high-pressure stage compressor (7), respectively. The ejector (10) is set at the outlet of the CO2 low-pressure stage compressor (13) for pressurization. The temperature fluctuations at the inlet and outlet of the ejector (10) are suppressed by the subcooler (9) and the superheater (6), respectively.

2. The multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 1, characterized in that, The CO2 sub-cycle also includes a CO2 evaporator (3), a first throttle valve (4), a gas-liquid separator (5), and an exhaust cooler (14). The CO2 evaporator (3), CO2 low-pressure stage compressor (13), exhaust cooler (14), ejector (10), gas-liquid separator (5) and first throttle valve (4) are connected in sequence to form the first stage circulation loop; The ejector (10), gas-liquid separator (5), superheater (6), CO2 high-pressure stage compressor (7), three-fluid heat exchanger (8) and subcooler (9) are connected in sequence to form a second-stage circulation loop.

3. The multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 2, characterized in that, The water circulation loop includes a low-temperature heat source, a first water pump (1), a first three-way valve (2), a second three-way valve (11), a third three-way valve (12), and a fourth water pump (23). The low-temperature heat source, the first water pump (1), the first three-way valve (2) and the CO2 evaporator (3) are connected to form a loop; the water output from the low-temperature heat source enters the first three-way valve (2) through the first water pump (1), and a portion of the water output from the first three-way valve (2) enters the CO2 evaporator (3) for heat exchange and returns to the low-temperature heat source; Another portion of the water flow output from the first three-way valve (2) enters the third three-way valve (12) for further distribution. A portion of the water flow output from the third three-way valve (12) flows into the exhaust cooler (14) for heat exchange and mixes with the outlet water flow from the second three-way valve (11). Another portion of the water flow output from the third three-way valve (12) flows into the subcooler (9) for heat exchange and flows out of the subcooler (9) before flowing into the second three-way valve (11). A portion of the water flow output from the second three-way valve (11) flows to the exhaust cooler (14), and another portion flows into the superheater (6) for heat exchange before returning to the low-temperature heat source. The fourth water pump (23) is connected to a hot water source and forms a hot water circulation loop with the three-fluid heat exchanger (8); The low-temperature heat sources include air, water, soil, industrial waste heat, solar thermal energy, and cold storage tanks. When the temperature is below the freezing point, a refrigerant is used instead of water as the working medium.

4. A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 3, characterized in that, When the heat pump multi-generation system is in the CO2 sub-cycle independent operation mode to produce domestic hot water or for cooling, the low-temperature and low-pressure CO2 gas in the CO2 sub-cycle is compressed into medium-temperature and medium-pressure superheated steam by the CO2 low-pressure stage compressor (13), then flows through the exhaust cooler (14) and is cooled by water, and finally enters the secondary inlet of the ejector (10) and is ejected by the high-temperature and high-pressure supercritical fluid input by the ejector (10); The fluid output from the ejector (10) enters the gas-liquid separator (5) and is separated into gas phase and liquid phase. The gas phase CO2 gas passes through the superheater (6) and the CO2 high-pressure stage compressor (7) in sequence to be converted into a high-temperature and high-pressure supercritical fluid. Then it flows through the three-fluid heat exchanger (8) and the subcooler (9) in sequence and is cooled by water. After that, it is depressurized and accelerated through the main nozzle of the ejector (10) to eject the CO2 gas from the outlet of the CO2 low-pressure stage compressor (13). The liquid phase fluid flows into the first throttle valve (4) for throttling and depressurization, and then flows into the CO2 evaporator (3) to absorb heat.

5. A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 4, characterized in that, The water flow rate is adjusted by the first three-way valve (2), the second three-way valve (11) and the third three-way valve (12) in the water circulation loop to optimize the control of the subcooling and superheat of the CO2 sub-circulation.

6. A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 1, characterized in that, The high-temperature stage sub-cycle also includes a high-temperature medium compressor (15), a second throttle valve (17), and a waste heat source evaporator (18). The three-fluid heat exchanger (8), the high-temperature medium compressor (15), the condenser (16), the second throttle valve (17), and the waste heat source evaporator (18) are connected in sequence to form a circulation loop. The waste heat source evaporator (18) is also connected to a second water pump (19) and an industrial waste heat source to form a waste heat exchange loop. Alternatively, the high-temperature stage sub-cycle may be a multi-stage compression sub-cycle or an inverse Brayton cycle, similar to the low-temperature stage sub-cycle; the high-temperature stage sub-cycle may directly supply steam or perform high-temperature heat storage.

7. A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 6, characterized in that, The flash evaporation cycle also includes a flash evaporator (20), a fourth three-way valve (21), a third water pump (22), a fifth three-way valve (24), a sixth three-way valve (25), and a heat storage tank (26). The condenser (16), the fifth three-way valve (24), the flash evaporator (20), the sixth three-way valve (25), the fourth three-way valve (21), and the third water pump (22) are connected in sequence to form a circulation loop. The outlet end of the flash evaporator (20) outputs steam. One end of the fourth three-way valve (21) is connected to a water supply pipeline. The flash evaporator (20), the fifth three-way valve (24), the heat storage tank (26), and the sixth three-way valve (25) are connected in sequence to form a circulation loop.

8. A multi-stage compression cascade heat pump combined heat and power system based on jet enhancement according to claim 7, characterized in that, When the heat pump multi-generation system is operating in the high-temperature stage sub-cycle and flash cycle coordinated mode to prepare high-temperature steam, the low-temperature and low-pressure high-temperature medium in the high-temperature stage sub-cycle is compressed into a high-temperature and high-pressure fluid by the high-temperature medium compressor (15), enters the condenser (16) to exchange heat with water, and then enters the waste heat source evaporator (18) after being throttled by the second throttle valve (17). After exchanging heat with waste heat in the waste heat source evaporator (18), it becomes a low-temperature and low-pressure high-temperature medium again. In the flash evaporation cycle, the high-temperature and high-pressure hot water from the outlet of the condenser (16) is input into the flash tank, and the flash tank outputs steam to supply the user; the remaining saturated water is transported by the third water pump (22) to participate in the cycle, and is replenished through the fourth three-way valve (21); When the heat pump multi-generation system operates in the superimposed cycle mode of the high-temperature sub-cycle and the CO2 sub-cycle, and in coordination with the flash cycle, the CO2 sub-cycle absorbs heat from the low-temperature heat source and releases heat to the high-temperature sub-cycle through the three-fluid heat exchanger (8). After absorbing heat from the high-temperature medium in the high-temperature sub-cycle, it enters the condenser (16) and works in coordination with the flash cycle to complete the preparation of high-temperature steam.

9. An optimization method for a multi-stage compression cascade heat pump combined heat and power system based on jet enhancement as described in any one of claims 1-8, characterized in that, Includes the following steps: The operating mode and energy supply method shall be determined based on the application scenario, operating conditions and / or energy demand. Based on the operating mode, assume the optimal intermediate pressure of the three-fluid heat exchanger (8), and the discharge pressure of the CO2 low-pressure stage compressor (13) and the CO2 high-pressure stage compressor (7); First, based on the application scenario, operating conditions and probability statistics of the operating mode, the design of the low-temperature stage sub-cycle and the high-temperature stage sub-cycle is optimized in a coordinated manner. Then, based on the operating conditions, the control is optimized in a coordinated manner. The heat exchange is matched by the three-fluid heat exchanger (8). The design and control parameters of the two-stage compression cycle and the ejector (10) in the low-temperature stage sub-cycle are optimized in a coordinated manner. The control parameters in the optimization process include the compressor frequency, ejector parameters, parameters of the subcooler (9) and the superheater (6) and the opening of the throttle valve. The ejector parameters include the throat diameter, nozzle distance, ejector bypass valve and pulse width regulating valve parameters. For large-capacity heat pumps, multiple ejectors are combined for coordinated control. The optimization process is repeated until the heat exchange capacity of the three-fluid heat exchanger (8) is matched, meets the energy supply requirements, and achieves the optimal energy efficiency of the system. Then the structure and control optimization results are output. Otherwise, the optimal intermediate pressure of the three-fluid heat exchanger (8) and the exhaust pressure of the CO2 low-pressure stage compressor (13) and the CO2 high-pressure stage compressor (7) are updated.

10. The method according to claim 9, characterized in that, The method also includes designing and optimizing the control of the injector (10), specifically including: (1) Based on the application scenario, operating mode, and inlet and outlet conditions of the injector, determine the optimization target of the injector and perform coordinated optimization of the injector design and control; the corresponding optimization process is as follows: First, a database is obtained by simulating a heterogeneous and non-equilibrium numerical model of the injector. The database is then used to train a neural network surrogate model or a machine learning model to obtain the injector optimization objective function. Then, based on the optimization objectives determined by the application scenario and the probability statistics of the operating conditions, the weights are determined using quantitative methods such as sensitivity analysis and influence weight analysis. Finally, the genetic algorithm and weighted average optimization algorithm are combined with the neural network surrogate model or machine learning model to establish an optimization framework, perform global optimization, and obtain optimized values ​​for the internal geometry of the injector suitable for different working conditions. (2) According to the operating mode, switch the adjustable ejector with different internal geometry suitable for cooling / heating and adopt different control strategies. The control strategies include: using the pressure ratio as the optimization target in the heating condition and the ejector ratio as the optimization target in the cooling condition, and coordinating the optimization of subcooling and superheating. (3) Based on the active inlet working condition of the injector, the dynamic response time of the injector is determined and real-time optimization control is performed; based on the model predictive control method, the control parameters of the injector are adaptively optimized under different working conditions according to the inlet and outlet working conditions of the injector in the cooling / heating mode.

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