Dual cascade heat pump defrosting control method, system and dual cascade heat pump system

Abstract

The application discloses a double-cascade heat pump defrosting control method, a system and a double-cascade heat pump system. The heat pump system comprises a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger and a fourth heat exchanger. The first compressor, the first heat exchanger and the second heat exchanger form a front-stage temperature processing unit, and the second compressor, the second heat exchanger and the third heat exchanger form a rear-stage temperature processing unit. The fourth heat exchanger is connected to the second heat exchanger in parallel through a one-way valve. The defrosting control method comprises the following steps: the first compressor is reduced to an initial starting frequency; the first cooling medium is reversely flowed to switch from the second heat exchanger to the fourth heat exchanger; the second compressor is stopped; the first compressor is increased to a defrosting set frequency for defrosting; and a second pipeline is turned on. The defrosting control method effectively improves the reliability and stability of the system defrosting process and improves the defrosting efficiency, and effectively avoids the possibility of failure of the double-cascade heat pump system during the defrosting process.

Description

Technical Field

[0001] This invention relates to the field of air conditioning defrosting technology, and in particular to a double cascade heat pump defrosting control method, system, and double cascade heat pump system. Background Technology

[0002] In the field of heat pump systems, cascade heat pump units are widely used due to their efficient heating capabilities in low-temperature environments. Traditional cascade heat pump systems, in heating mode, typically achieve heat exchange between the high-temperature refrigerant in the low-temperature stage and the low-temperature refrigerant in the high-temperature stage via a heat exchanger, allowing the high-temperature stage to output hot water at temperatures above 80°C. However, under low-temperature operating conditions, frost easily forms on the surface of the copper tube finned evaporator in the low-temperature stage, leading to a significant decrease in system heating efficiency or even system shutdown. To address the frost problem, existing technologies mainly employ two defrosting solutions: hot gas bypass defrosting and four-way valve reversing defrosting.

[0003] One method, hot gas bypass defrosting, involves bypassing the high-temperature refrigerant discharged from the low-temperature stage compressor to the evaporator inlet for defrosting. However, this method has a significant drawback: when the evaporator is severely frosted, the heat output from the compressor is insufficient to completely melt the frost layer, potentially leading to frost accumulation and ice formation, or even liquid slugging in the compressor, severely impacting system reliability. Another method, four-way valve reversing defrosting, changes the refrigerant flow direction by switching the direction of the four-way valves in the high and low temperature stage systems. However, frequent switching of the four-way valves exacerbates mechanical wear, increasing the probability of system failure. Furthermore, the high-temperature stage needs to operate continuously during defrosting, leading to increased energy consumption and limited defrosting efficiency. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the aforementioned technical problems by providing a double cascade heat pump defrosting control method, system, and double cascade heat pump system that can balance defrosting efficiency, system reliability, and operational continuity.

[0005] To achieve the above objectives, the present invention provides a double-cascade heat pump defrosting control method. The heat pump system includes a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, and a fourth heat exchanger. The first compressor, the first heat exchanger, and the second heat exchanger constitute a front-stage temperature processing unit. The second compressor, the second heat exchanger, and the third heat exchanger constitute a rear-stage temperature processing unit. A first cooling medium circulating in the front-stage temperature processing unit and a second cooling medium circulating in the rear-stage temperature processing unit exchange heat in the second heat exchanger. The first heat exchanger exchanges heat with the external environmental medium. The third heat exchanger exchanges heat with water in a first pipeline. The fourth heat exchanger is connected in parallel with the second heat exchanger via a one-way valve and exchanges heat with water in the second pipeline. Both the first and second pipelines are connected to a main circulating water pipeline.

[0006] When the heat pump system enters the heating mode and meets the defrosting conditions, the defrosting control method controls the heat pump system to enter the defrosting working state based on a first method, the first method including:

[0007] The first compressor is reduced to its initial starting frequency;

[0008] The first cooling medium flows in reverse to switch from the second heat exchanger to the fourth heat exchanger;

[0009] The second compressor stopped running;

[0010] The first compressor is frequency-increased to the defrosting set frequency for defrosting;

[0011] The second pipeline is opened so that at least a portion of the water in the main circulating water pipeline enters the fourth heat exchanger.

[0012] Preferably, after the first compressor is reduced to its initial start-up frequency, the fan of the first heat exchanger is reduced to its first target frequency; and when the second compressor stops running, the fan is turned off.

[0013] Preferably, after the first compressor reduces its frequency to the initial start-up frequency, it waits for a first period of time before the fan of the first heat exchanger reduces its frequency to the first target frequency.

[0014] Preferably, when the fan of the first heat exchanger is reduced to the first target frequency, a second time is waited before the first cooling medium is controlled to flow in reverse into the fourth heat exchanger.

[0015] Preferably, after the fan is shut down for a third period of time, the opening of the main expansion valve connected to the first compressor is adjusted to the maximum, and after waiting for a fourth period of time, the first compressor is controlled to increase its frequency to the defrosting set frequency.

[0016] Preferably, when the heat pump system is in defrost operation and the defrost exit conditions are met, the defrost control method controls the heat pump system to exit the defrost operation based on a second method, the second method comprising:

[0017] The first compressor is reduced to the initial starting frequency;

[0018] The first cooling medium flows in the reverse direction again to switch from the fourth heat exchanger to the second heat exchanger;

[0019] The second compressor starts;

[0020] The second pipeline is disconnected to prevent water in the main circulating water pipeline from entering the fourth heat exchanger.

[0021] Preferably, when the first compressor reduces its frequency to the initial start-up frequency, after waiting for a fifth time period, the opening degree of the main expansion valve connected to the first compressor is adjusted to the target number of steps, and after waiting for a sixth time period, the opening degree of the main expansion valve is put into an automatic control state.

[0022] Preferably, after the main expansion valve opening is in automatic control mode, when the high pressure value of the front-stage temperature processing unit is greater than the preset target high pressure, the fan in the first heat exchanger is controlled to run at a second target frequency, which is less than the rated frequency. After waiting for a seventh time, the first cooling medium is controlled to flow in reverse again to switch from the fourth heat exchanger to the second heat exchanger.

[0023] Preferably, after the first cooling medium is switched from the fourth heat exchanger to the second heat exchanger, the second compressor is started when the condensation temperature in the pre-stage temperature processing unit is greater than the preset first target temperature.

[0024] Preferably, when the condensation temperature in the pre-stage temperature processing unit is greater than the preset second target temperature, and the second target temperature is greater than the first target temperature, the second pipeline is disconnected.

[0025] This invention also provides a dual cascade heat pump system, comprising a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, and a controller; the first compressor, the first heat exchanger, and the second heat exchanger constitute a front-stage temperature processing unit, and the second compressor, the second heat exchanger, and the third heat exchanger constitute a rear-stage temperature processing unit; a first cooling medium circulating in the front-stage temperature processing unit and a second cooling medium circulating in the rear-stage temperature processing unit exchange heat in the second heat exchanger; the first heat exchanger exchanges heat with an external environmental medium; the third heat exchanger exchanges heat with water in a first pipeline for the second cooling medium; the fourth heat exchanger is connected in parallel with the second heat exchanger via a one-way valve, and exchanges heat between the first cooling medium and water in the second pipeline; both the first and second pipelines are connected to a main circulating water pipeline;

[0026] The controller controls the operating state of the heat pump system based on the dual cascade heat pump defrosting control method described above.

[0027] The present invention also provides a dual cascade heat pump defrosting control system, which includes:

[0028] One or more processors;

[0029] Memory;

[0030] And one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the programs including instructions for performing the dual cascade heat pump defrosting control method as described above.

[0031] The present invention also provides a computer-readable storage medium, characterized in that it includes a computer program, which can be executed by a processor to perform the dual cascade heat pump defrosting control method as described above.

[0032] Compared with the prior art, the dual cascade heat pump defrosting control method provided by the above-mentioned technical solution of the present invention uses water in the circulating water main pipeline as a stable heat source (through the fourth heat exchanger) to exchange heat with the first cooling medium flowing through the first heat exchanger, so as to quickly remove the frost on the first heat exchanger. Compared with the traditional hot gas bypass relying on the heat of the compressor exhaust, the low temperature stage does not need to be equipped with a gas bypass valve, and the high temperature stage does not need to be equipped with a four-way valve, which can provide more sufficient and controllable defrosting energy, especially suitable for ultra-low temperature conditions below -25℃; in addition, the low temperature stage absorbs heat from the water side through the fourth heat exchanger to realize the system's circulating defrosting, while the high temperature stage enters standby during the defrosting process, which effectively improves the reliability and stability of the system's defrosting process and improves the defrosting efficiency, and also effectively avoids the possibility of failure during the defrosting process of the cascade heat pump system. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the heat pump system in one embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the heat pump system in another embodiment of the present invention.

[0035] Figure 3 This is a flowchart of the first method in an embodiment of the present invention.

[0036] Figure 4 This is a flowchart of the second method in an embodiment of the present invention. Detailed Implementation

[0037] To illustrate the technical content, structural features, objectives, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0038] This embodiment discloses a defrosting control method for a dual cascade heat pump, which is used to automatically control the defrosting operation of a dual cascade heat pump system.

[0039] First, such as Figure 1 The heat pump system in this embodiment includes a first compressor ML, a second compressor MH, a first heat exchanger TH1, a second heat exchanger TH2, a third heat exchanger TH3, a fourth heat exchanger TH4, and a controller.

[0040] The first compressor ML, via a four-way valve 4WV, forms the pre-stage temperature processing unit SM1 with the first heat exchanger TH1 and the second heat exchanger TH2. This pre-stage temperature processing unit SM1 is a low-temperature unit; that is, when the heat pump system is heating, the first heat exchanger TH1 is used to exchange heat with the external environment, absorbing heat from the environment, either from the air or wastewater. Therefore, when the heat pump system is heating, the first heat exchanger TH1 is prone to frosting. Excessive frosting can affect the operation of the heat pump system, requiring timely defrosting.

[0041] The second compressor MH, together with the second heat exchanger TH2 and the third heat exchanger TH3, constitutes the downstream temperature processing unit SM2.

[0042] The first cooling medium circulating in the pre-stage temperature treatment unit SM1 and the second cooling medium circulating in the post-stage temperature treatment unit SM2 exchange heat in the second heat exchanger TH2.

[0043] The post-stage temperature processing unit SM2 is a high-temperature stage unit. That is, when the heat pump system is heating, the temperature of the second cooling medium, which has been heated by the first cooling medium in the pre-stage temperature processing unit SM1, is further increased by the post-stage temperature processing unit SM2, thereby raising the temperature of the second cooling medium to a higher level.

[0044] The third heat exchanger TH3 is used to exchange heat between the second cooling medium and the water in the first pipe G1 to heat the water in the first pipe G1 to the target temperature, and then introduce the water in the first pipe G1 into the indoor environment that needs heating.

[0045] The fourth heat exchanger TH4 is connected in parallel with the second heat exchanger TH2 through one-way valves D1 and D2. The fourth heat exchanger TH4 is used for heat exchange between the first cooling medium and the water in the second pipeline G2. The first pipeline G1 and the second pipeline G2 are both connected to the main circulating water pipeline G0.

[0046] It should be noted that for heat pump systems, the water temperature at the inlet of the main circulating water line G0 is generally much higher than normal temperature, for example, 80°C. After passing through the third heat exchanger TH3, the water temperature is heated to 85°C.

[0047] Before describing the defrosting control method in this embodiment, the heating operation principle of the above-mentioned heat pump system will be explained in detail.

[0048] First, the state of the four-way valve 4WV in the front-end temperature processing unit SM1 is controlled so that the high-temperature first cooling medium output by the first compressor ML flows to the second heat exchanger TH2. During this process, due to the action of the one-way valve D2, the first cooling medium is prevented from flowing into the fourth heat exchanger TH4.

[0049] In the fourth heat exchanger TH4, the first cooling medium exchanges heat with the second cooling medium in the subsequent temperature processing unit SM2. After the heat exchange, the temperature of the first cooling medium decreases, and the temperature of the second cooling medium increases. The cooled first cooling medium returns from the second heat exchanger TH2 to the first heat exchanger TH1.

[0050] In the first heat exchanger TH1, the first cooling medium receives heat energy from the environment and is heated. The heated first cooling medium then flows back to the first compressor ML through the four-way valve 4WV, and the cycle continues.

[0051] In the downstream temperature processing unit SM2, the second cooling medium is heated in the second heat exchanger TH2 and then flows into the second compressor MH. After being processed by the second compressor MH, the temperature of the second cooling medium is further increased, and the high-temperature second cooling medium enters the third heat exchanger TH3.

[0052] In the third heat exchanger TH3, the second cooling medium exchanges heat with the water in the first pipeline G1. After the heat exchange, the temperature of the second cooling medium decreases and the water temperature increases.

[0053] The cooled second cooling medium flows from the third heat exchanger TH3 into the second heat exchanger TH2, where it exchanges heat with the first cooling medium in the second heat exchanger TH2 again, and so on.

[0054] In addition, to ensure the energy efficiency of the heat pump system, two parallel front-end temperature processing units SM1 and rear-end temperature processing units SM2 can be configured. For example... Figure 2 The two front-end temperature processing units SM1 share a fourth heat exchanger TH4, and the two back-end temperature processing units SM2 share a third heat exchanger TH3.

[0055] When the heat pump system is in heating mode, the first heat exchanger TH1 performs heat absorption. Therefore, it is prone to frost formation when the ambient temperature is low, which requires real-time monitoring of the frost formation status.

[0056] Currently, the industry generally uses one or more of the following methods for frost detection: temperature-time combined judgment method, temperature difference method, pressure sensor monitoring, and intelligent algorithm.

[0057] For the temperature-time combined judgment method: when the surface temperature of the evaporator (such as the first heat exchanger TH1) is detected to be continuously lower than the set value (such as -5℃) and the running time exceeds the preset cycle (such as 30 minutes), it is determined that the frost is severe and defrosting is initiated. In addition, in low temperature and high humidity environments, the temperature sensor and timer are linked to shorten the defrosting trigger interval.

[0058] For the temperature difference method: by comparing the temperature difference between the evaporator inlet and outlet (e.g., temperature difference > 5°C for 10 minutes), it is shown that frost formation on the fins leads to a decrease in heat exchange efficiency, triggering defrosting.

[0059] For pressure sensor monitoring: When heating, a significant decrease in low-pressure side pressure (e.g., below 0.5 MPa) indicates that heat exchange in the evaporator is obstructed, and the system automatically enters defrosting mode.

[0060] For intelligent algorithms: By taking into account multiple parameters such as outdoor temperature, humidity, and operating time, the defrosting threshold is dynamically adjusted to reduce ineffective defrosting and improve energy efficiency.

[0061] When the heat pump system meets the defrosting conditions, the controller controls the heat pump system to enter the defrosting working state based on the first method, such as... Figure 1 and Figure 3 The first method includes:

[0062] S10: The first compressor ML is reduced to its initial starting frequency;

[0063] S11: The state of the four-way valve 4WV changes, causing the first cooling medium to flow in reverse, so as to switch from the second heat exchanger TH2 to the fourth heat exchanger TH4.

[0064] S12: The second compressor MH stops running;

[0065] S13: The first compressor ML is frequency-upgraded to the defrosting set frequency for defrosting;

[0066] S14: Open the water valve on the second pipeline G2, so that at least part of the water in the main circulating water pipeline G0 enters the fourth heat exchanger TH4.

[0067] Therefore, it can be seen that after the first method is started, the first compressor ML and the first heat exchanger TH1 switch from cyclic operation with the second heat exchanger TH2 to cyclic operation with the fourth heat exchanger TH4.

[0068] In response, the high-temperature cooling medium output from the first compressor ML first enters the first heat exchanger TH1, where it releases heat to melt the frost. The cooled cooling medium then flows to the fourth heat exchanger TH4. At this point, due to the action of the one-way valve D1, the cooling medium does not flow into the second heat exchanger TH2.

[0069] Since the second pipeline G2 is already open at this time, the water at the inlet of the main circulating water pipeline G0 will enter the fourth heat exchanger TH4 through the second pipeline G2.

[0070] In the fourth heat exchanger TH4, the first cooling medium exchanges heat with water (at 80°C). After the heat exchange occurs, the water temperature decreases, and the temperature of the first cooling medium increases.

[0071] The heated first cooling medium returns to the first compressor ML via the four-way valve 4WV, thus creating a cycle.

[0072] Therefore, it can be seen that, firstly, by eliminating the traditional hot gas bypass valve, the high-temperature stage four-way valve 4WV, and adopting the fourth heat exchanger TH4 parallel structure and one-way valve switching flow path, the risk of mechanical failure caused by frequent valve operation (such as the four-way valve 4WV jamming, bypass valve leakage, etc.) is fundamentally eliminated.

[0073] The second compressor MH completely shuts down during defrosting, avoiding system pressure fluctuations caused by continuous operation of the high-temperature stage in traditional solutions and reducing the risk of compressor overload.

[0074] Secondly, utilizing the water in the main circulating water line G0 as a stable heat source (through the fourth heat exchanger TH4) provides more abundant and controllable defrosting energy compared to traditional hot gas bypass that relies on compressor exhaust heat, making it particularly suitable for ultra-low temperature conditions below -25℃. Furthermore, reusing the main circulating water line G0 as a defrosting heat source eliminates the need for additional auxiliary electric heating devices, effectively reducing equipment investment costs.

[0075] The first compressor ML's dynamic adjustment strategy of frequency reduction and increase (initial start frequency → defrost set frequency) achieves a smooth transition of system pressure in the early stage of defrost and a precise match with the high heat flux density output in the later stage. Experimental data shows that it can improve the defrost rate by at least 30%.

[0076] Furthermore, the dual-compressor time-sharing control strategy (front-stage variable frequency operation + rear-stage shutdown) can effectively reduce the overall power consumption during the defrosting stage compared to the traditional two-stage continuous operation scheme.

[0077] The first compressor ML's frequency reduction start-up strategy effectively suppresses the backflow of liquid refrigerant. Combined with the water circuit heat source buffering effect of the fourth heat exchanger TH4, it can extend the compressor's service life.

[0078] On the other hand, after the first compressor ML reduces its frequency to the initial start-up frequency, the fan of the first heat exchanger TH1 reduces its frequency to the first target frequency. Furthermore, when the second compressor MH stops running, the fan is shut down.

[0079] In this embodiment, firstly, after the compressor frequency is reduced, the fan frequency is reduced to a first target frequency (e.g., 50% of the rated frequency). This reduces the sudden drop in surface temperature of the first heat exchanger TH1 caused by forced air convection, preventing the humid air drawn in from the low-temperature environment from accelerating frost formation. Experiments show that this design can reduce the frost formation rate of the first heat exchanger TH1 by approximately 40%.

[0080] Secondly, shutting down the fan after the second compressor MH has completely stopped can completely block the interference of external cold sources on the system's thermal cycle, allowing the heat of the first cooling medium to be concentrated and transferred to the fourth heat exchanger TH4 for defrosting, while reducing the ineffective power consumption of the fan.

[0081] On the other hand, after the first compressor ML is reduced to the initial start-up frequency, it waits for a first period of time, and then the fan of the first heat exchanger TH1 is reduced to the first target frequency.

[0082] In this embodiment, the first duration is 2 seconds, and the first target frequency is 50% of the rated frequency.

[0083] In this embodiment, after the first compressor ML completes frequency reduction, a 2-second delay is allowed until the refrigerant flow and pressure field reach dynamic equilibrium before the fan frequency is reduced. This effectively avoids evaporator overheating oscillations caused by sudden frequency changes in the first compressor ML. This buffering mechanism ensures precise matching between fan speed regulation and the thermodynamic system response characteristics. It prevents secondary frosting on the evaporator (i.e., the first heat exchanger TH1) surface caused by premature frequency reduction and avoids ineffective airflow loss due to delayed regulation. Furthermore, by reducing synchronous disturbances in the electromechanical system, it effectively lowers the failure rate of control components.

[0084] On the other hand, when the fan of the first heat exchanger TH1 reduces its frequency to the first target frequency, a second time period is waited before the first cooling medium is controlled to flow in reverse into the fourth heat exchanger TH4. Specifically, the second time period is 15 seconds.

[0085] In this embodiment, a time-series linkage mechanism between fan frequency reduction and medium reversal is established to achieve precise coupling of multiple physical fields in the thermodynamic system. Specifically, after the fan completes frequency reduction, a 15-second delay (corresponding to the evaporator surface frost softening time window under typical operating conditions) is established, allowing the air vortex intensity between the fins to decay to a critical value (typically <0.3 m / s) before triggering the medium reversal flow. This strategy ensures a more stable heat source supply during defrosting of the fourth heat exchanger TH4 (temperature fluctuation reduced by ±2℃), while avoiding the risk of refrigerant backflow caused by premature reversal.

[0086] On the other hand, after the fan has been off for a third period of time, the opening of the main expansion valve connected to the first compressor ML is adjusted to the maximum, and after a fourth period of time, the frequency of the first compressor ML is controlled to increase to the defrost set frequency. Specifically, the third period of time is 5 seconds, and the fourth period of time is 20 seconds.

[0087] In this embodiment, precise control of energy release in the heat pump system is achieved by establishing a gradient control sequence between valve opening and compressor frequency. Specifically, 5 seconds after the fan is turned off (ensuring that residual condensate on the surface of the first heat exchanger TH1 is completely drained), the main expansion valve is fully opened, allowing the system to quickly establish a refrigerant pressure gradient. A subsequent 20-second buffer period allows the refrigerant to achieve a stable phase distribution, ultimately resulting in smoother load characteristics when the first compressor ML increases its frequency. This design improves the uniformity of heat output during the defrosting stage while avoiding the liquid slugging risk associated with traditional direct frequency increases, significantly enhancing the operational reliability of the first compressor ML.

[0088] In another preferred embodiment of the present invention, when the heat pump system is in the defrosting working state, and defrosting ends and the conditions for exiting defrosting are met, the controller controls the heat pump system to exit the defrosting working state based on the second method, such as... Figure 1 and Figure 4 The second method includes:

[0089] S20: The first compressor ML reduces its frequency from the defrost set frequency to the initial start frequency;

[0090] S21: Control the four-way valve 4WV to operate, so that the first cooling medium flows in reverse again, so as to switch from the fourth heat exchanger TH4 to the second heat exchanger TH2.

[0091] S22: Second compressor MH starts;

[0092] S23: The second pipeline G2 is disconnected to prevent water in the main circulating water pipeline G0 from entering the fourth heat exchanger TH4.

[0093] The second method allows the heat pump system to automatically return to normal operation once defrosting is complete, thus achieving unattended control of automatic defrosting and automatic heating.

[0094] On the other hand, when the first compressor ML is reduced to the initial start-up frequency, after waiting for the fifth time, the opening of the main expansion valve connected to the first compressor ML is adjusted to the target number of steps, and after waiting for the sixth time, the opening of the main expansion valve is put into automatic control state.

[0095] Specifically, the fifth duration is 2 seconds, the sixth duration is 60 seconds, and the target number of steps is 20% of the total number of steps taken.

[0096] In this embodiment, a multi-level buffer exit mechanism is constructed to achieve a zero-impact transition during mode switching. Specifically, after the first compressor ML frequency is reduced, a 2-second delay is made (to ensure the frequency feedback signal is stable) to limit the opening of the main expansion valve to 20%, forming a controllable throttling effect to suppress sudden changes in system pressure. Subsequently, a 60-second main expansion valve holding phase (covering the thermal inertia response cycle of the high and low temperature stage heat exchangers) allows the refrigerant phase distribution and pipeline temperature field to be fully balanced. Finally, when switching to automatic control, the system is already in a quasi-steady state (superheat deviation < ±1.5℃). This design effectively shortens the heating mode recovery time and avoids the liquid hammer phenomenon caused by traditional direct valve cutting.

[0097] On the other hand, after the main expansion valve opening is in automatic control state, when the high pressure value of the current stage temperature processing unit SM1 is greater than the preset target high pressure, the fan in the first heat exchanger TH1 is controlled to run at the second target frequency. The second target frequency is less than the rated frequency. After waiting for seven hours, the first cooling medium is controlled to flow in reverse again to switch from the fourth heat exchanger TH4 to the second heat exchanger TH2.

[0098] Specifically, the second target frequency is 50% of the rated frequency, and the seventh duration is 5 seconds.

[0099] In this embodiment, adaptive protection under high-pressure conditions is achieved by constructing a closed-loop control logic of pressure feedback, fan frequency, and flow channel switching. Specifically, when the upstream high pressure exceeds the limit, the fan frequency is immediately reduced to 50%, and the system pressure is rapidly reduced by decreasing the heat dissipation intensity of the first heat exchanger TH1. Then, after a 5-second delay, flow channel switching is performed, which can effectively avoid the risk of refrigerant congestion caused by direct reversal in traditional solutions.

[0100] On the other hand, after the first cooling medium is switched from the fourth heat exchanger TH4 to the second heat exchanger TH2, when the condensing temperature in the current stage temperature processing unit SM1 is greater than the preset first target temperature, the second compressor MH is started.

[0101] In this embodiment, a precise coordination of the two-stage system is achieved by establishing a condensation temperature threshold triggering mechanism. Specifically, after the upstream flow channel switching is completed, the second compressor MH is only started after the condensation temperature reaches a preset value (e.g., 80°C), ensuring a stable heat source input for the high-temperature stage system (temperature fluctuation < ±2°C). This design maintains the suction superheat of the downstream second compressor MH within a safe range of 5-8°C, while also avoiding the risk of lubricating oil carbonization caused by low-temperature startup.

[0102] On the other hand, when the condensation temperature in the current stage temperature processing unit SM1 is greater than the preset second target temperature, the second target temperature is greater than the first target temperature, and the second pipeline G2 is disconnected.

[0103] In this embodiment, when the condensation temperature exceeds the second target temperature (e.g., 85°C) above the higher threshold, the second pipeline G2 is forcibly disconnected, which can effectively prevent the fourth heat exchanger TH4 from ineffective heat exchange under high temperature conditions. At the same time, by cutting off the water bypass, the heat of the main circulation is ensured to be concentratedly supplied to the third heat exchanger TH3.

[0104] In summary, this invention discloses a defrosting control method for a dual-cascade heat pump system. The heat pump system includes a pre-stage temperature processing unit SM1 and a post-stage temperature processing unit SM2, with inter-stage heat exchange achieved through a second heat exchanger TH2. During defrosting, multi-stage coordinated control is employed: the first compressor ML in the pre-stage system reduces its frequency and switches the first cooling medium to the fourth heat exchanger TH4 to absorb heat from the water circuit; the second compressor MH in the post-stage system shuts down. This invention also introduces a timing control strategy (including fan frequency division slow-stop, main expansion valve gradient adjustment, and cooling medium reversal delay) and a temperature threshold triggering mechanism. Through multi-dimensional parameter coupling of pressure, temperature, and time, precise heat distribution and zero-impact transition during mode switching are achieved during the defrosting stage. This solution completely eliminates the traditional four-way valve 4WV and bypass valve structure, improving defrosting rate while reducing energy consumption and enhancing system reliability. It is particularly suitable for stable and efficient operation in ultra-low temperature and high humidity environments below -25℃.

[0105] This invention also discloses a dual-cascade heat pump defrosting control system, which includes one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors. The programs include instructions for performing the heat pump defrosting control method as described above. The processors may be general-purpose central processing units (CPUs), microprocessors, application-specific integrated circuits (ASICs), or one or more integrated circuits, used to execute relevant programs to implement the functions required by the modules in the heat pump defrosting control system of this application embodiment, or to execute the heat pump defrosting control method of this application method embodiment.

[0106] This invention also discloses a computer-readable storage medium comprising a computer program executable by a processor to perform the heat pump defrosting control method described above. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center integrating one or more available media. The available medium can be read-only memory (ROM), random access memory (RAM), or magnetic media, such as floppy disks, hard disks, magnetic tapes, magnetic disks, or optical media, such as digital versatile discs (DVDs), or semiconductor media, such as solid-state disks (SSDs).

[0107] This application also discloses a computer program product or computer program, which includes computer instructions stored in a computer-readable storage medium. A processor of an electronic device reads the computer instructions from the computer-readable storage medium and executes the computer instructions, causing the electronic device to perform the aforementioned heat pump defrosting control method.

[0108] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A defrosting control method for a dual-cascade heat pump, characterized in that, The heat pump system includes a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, and a fourth heat exchanger. The first compressor, the first heat exchanger, and the second heat exchanger constitute a front-stage temperature processing unit. The second compressor, the second heat exchanger, and the third heat exchanger constitute a rear-stage temperature processing unit. A first cooling medium circulating in the front-stage temperature processing unit and a second cooling medium circulating in the rear-stage temperature processing unit exchange heat in the second heat exchanger. The first heat exchanger exchanges heat with the external environmental medium. The third heat exchanger exchanges heat with water in the first pipeline through the second cooling medium. The fourth heat exchanger is connected in parallel with the second heat exchanger via a one-way valve and exchanges heat with water in the second pipeline through the first cooling medium. Both the first pipeline and the second pipeline are connected to the main circulating water pipeline. When the heat pump system enters the heating mode and meets the defrosting conditions, the defrosting control method controls the heat pump system to enter the defrosting working state based on a first method, the first method including: The first compressor is reduced to its initial starting frequency; The first cooling medium flows in reverse to switch from the second heat exchanger to the fourth heat exchanger; The second compressor stopped running; The first compressor is frequency-increased to the defrosting set frequency for defrosting; The second pipeline is opened so that at least a portion of the water in the main circulating water pipeline enters the fourth heat exchanger; After the first compressor reduces its frequency to the initial start-up frequency, the fan of the first heat exchanger reduces its frequency to the first target frequency; and when the second compressor stops running, the fan is turned off. When the heat pump system is in defrosting operation and the conditions for exiting defrosting are met, the defrosting control method controls the heat pump system to exit the defrosting operation based on a second method, the second method including: The first compressor is reduced to the initial starting frequency; The first cooling medium flows in the reverse direction again to switch from the fourth heat exchanger to the second heat exchanger; The second compressor starts; The second pipeline is disconnected to prevent water in the main circulating water pipeline from entering the fourth heat exchanger; After the first cooling medium is switched from the fourth heat exchanger to the second heat exchanger, the second compressor starts when the condensing temperature in the front-stage temperature processing unit is greater than the preset first target temperature. When the condensation temperature in the pre-stage temperature processing unit is greater than the preset second target temperature, and the second target temperature is greater than the first target temperature, the second pipeline is disconnected.

2. The defrosting control method for a dual-cascade heat pump according to claim 1, characterized in that, After the first compressor reduces its frequency to the initial start-up frequency, it waits for a first duration, and then the fan of the first heat exchanger reduces its frequency to the first target frequency.

3. The defrosting control method for a dual-cascade heat pump according to claim 1, characterized in that, When the fan of the first heat exchanger is reduced to the first target frequency, wait for a second duration, and then control the first cooling medium to flow in reverse into the fourth heat exchanger.

4. The defrosting control method for a dual-cascade heat pump according to claim 1, characterized in that, After the fan has been shut down for a third period of time, the opening of the main expansion valve connected to the first compressor is adjusted to the maximum, and after waiting for a fourth period of time, the first compressor is controlled to increase its frequency to the defrosting set frequency.

5. The defrosting control method for a dual-cascade heat pump according to claim 1, characterized in that, In the second method, when the first compressor is reduced to the initial start-up frequency, after waiting for a fifth time period, the opening degree of the main expansion valve connected to the first compressor is adjusted to the target number of steps, and after waiting for a sixth time period, the opening degree of the main expansion valve is put into an automatic control state.

6. The defrosting control method for a dual-cascade heat pump according to claim 5, characterized in that, After the main expansion valve opening is in automatic control mode, when the high pressure value of the front-stage temperature processing unit is greater than the preset target high pressure, the fan in the first heat exchanger is controlled to run at the second target frequency. The second target frequency is less than the rated frequency. After waiting for seven hours, the first cooling medium is controlled to flow in reverse again to switch from the fourth heat exchanger to the second heat exchanger.

7. A dual cascade heat pump system, characterized in that, The system includes a first compressor, a second compressor, a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, and a controller. The first compressor, the first heat exchanger, and the second heat exchanger constitute a pre-stage temperature processing unit. The second compressor, the second heat exchanger, and the third heat exchanger constitute a post-stage temperature processing unit. A first cooling medium circulating in the pre-stage temperature processing unit and a second cooling medium circulating in the post-stage temperature processing unit exchange heat in the second heat exchanger. The first heat exchanger exchanges heat with the external environmental medium. The third heat exchanger exchanges heat with water in a first pipeline. The fourth heat exchanger is connected in parallel with the second heat exchanger via a one-way valve and exchanges heat with water in a second pipeline. Both the first and second pipelines are connected to a main circulating water pipeline. The controller controls the operating state of the heat pump system based on the double cascade heat pump defrosting control method according to any one of claims 1 to 6.

8. A dual-cascade heat pump defrosting control system, characterized in that, include: One or more processors; Memory; And one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the programs including instructions for performing the dual cascade heat pump defrosting control method as claimed in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, Includes a computer program that can be executed by a processor to perform the dual cascade heat pump defrosting control method as described in any one of claims 1 to 6.

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