Multi-connected air conditioner and control method thereof

Abstract

The invention relates to a multi-connected air conditioner and a control method thereof, and belongs to the technical field of air conditioners. In the refrigeration mode of the multi-connected air conditioner, an indoor expansion valve control strategy is executed, and the rated refrigeration capacity of an indoor unit which is running and the total rated refrigeration capacity of an outdoor unit are obtained; the starting load rate is calculated according to the ratio of the sum of the rated refrigerating capacity of the running indoor units to the total rated refrigerating capacity of the outdoor units; if the starting load rate is smaller than or equal to the load threshold value, the superheat degree of the indoor heat exchanger is corrected to be a first superheat degree value, and the opening degree of an indoor expansion valve is adjusted; otherwise, the normal operation of the multi-connected air conditioner is maintained, and the opening control of the indoor expansion valve can be optimized under the conditions of long piping and small starting load.

Description

Technical Field

[0001] This invention relates to the field of air conditioner technology, specifically to a multi-split air conditioner and its control method. Background Technology

[0002] Multi-split air conditioners are evolving towards higher capacity, longer piping, and wider indoor unit capacity. Against this backdrop, when a multi-split air conditioner operates at very low load with long piping, the refrigerant circulation volume required by the indoor unit is far lower than the compressor displacement, leading to severe system mismatch. This can easily cause problems such as excessively high compressor discharge temperature and drastic fluctuations in operating frequency. Therefore, it is necessary to actively intervene in the system by dynamically correcting the superheat of the indoor heat exchanger to ensure stable operation.

[0003] Currently, multi-split air conditioners generally employ a superheat-based indoor expansion valve control strategy in cooling mode. This strategy calculates the actual superheat by detecting the refrigerant temperature at the inlet and outlet of the indoor heat exchanger and compares it with a preset, fixed target superheat. If the actual value is higher than the target value, the valve is opened wider to increase the refrigerant flow; conversely, the valve is closed narrower.

[0004] In existing technologies, under extremely low load and long piping scenarios, due to the long pipeline and large pressure loss, the normal superheat calculated on the indoor unit side cannot reflect the actual severely excessive superheat on the compressor suction side. This leads to control signal distortion and feedback lag, and can only be forced to reduce frequency and open valves after the exhaust temperature exceeds the limit, causing continuous fluctuations in compressor frequency and outlet air temperature, which seriously sacrifices system energy efficiency and user comfort. Summary of the Invention

[0005] This application provides a multi-split air conditioner and its control method to at least solve the problem in related technologies that, under extremely low load and long piping scenarios, the traditional control method based on the local overheating of the indoor unit suffers from signal distortion and adjustment lag, which forces the system to make drastic corrections only after the exhaust temperature is severely exceeded, causing operational fluctuations and seriously impairing energy efficiency and comfort.

[0006] In a first aspect, this application provides a multi-split air conditioner, comprising: The outdoor unit has a compressor; An indoor unit comprising multiple indoor units connected in parallel to an outdoor unit via refrigerant piping, wherein each indoor unit has an indoor heat exchanger and an indoor expansion valve; A controller, electrically connected to the outdoor unit and the indoor unit, is configured to execute an indoor expansion valve control strategy in the cooling mode of the multi-split air conditioner. Obtain the rated cooling capacity of the indoor unit currently in operation and the total rated cooling capacity of the outdoor unit; The operating load rate is calculated based on the ratio of the sum of the rated cooling capacities of the indoor units currently in operation to the total rated cooling capacity of the outdoor units. If the operating load rate is less than or equal to the load threshold, the superheat of the indoor heat exchanger is corrected to the first superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

[0007] By calculating the ratio of the total capacity of the indoor units to the total capacity of the outdoor units in real time, the system can accurately identify whether it is under low load conditions. This enables on-demand switching of control strategies, avoiding unnecessary control interventions under non-essential conditions. It ensures the system's operating efficiency and stability under most normal loads, while providing accurate triggering conditions for subsequent targeted optimization control under low loads. Overall, this improves the intelligence and adaptability of multi-split air conditioner control.

[0008] In some embodiments, the multi-split air conditioner further includes: An exhaust pressure sensor, which is installed at the exhaust port of the compressor and electrically connected to the controller, is used to detect the exhaust pressure; A suction pressure sensor is installed at the suction port of the compressor and electrically connected to the controller to detect suction pressure. The controller is further configured as follows: Obtain the exhaust pressure and the intake pressure; If the start-up load rate is less than or equal to the load threshold, the exhaust pressure is greater than or equal to the first threshold, and the intake pressure is less than or equal to the second threshold, then the superheat of the indoor heat exchanger is corrected to the second superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

[0009] By introducing pressure signals from both the high-pressure and low-pressure sides to comprehensively diagnose the system's load status and flow path resistance, the bottleneck condition of high exhaust pressure and low intake pressure caused by long piping can be identified more accurately. This avoids misjudgments that may occur based solely on the load rate parameter, ensuring that subsequent superheat correction control is only activated in real-world problem scenarios where both load and system pressure characteristics are met, significantly improving the accuracy and reliability of control decisions.

[0010] In some embodiments, the multi-split air conditioner further includes: An exhaust temperature sensor is installed at the exhaust port of the compressor and electrically connected to the controller to detect the current exhaust temperature and the previous exhaust temperature. The controller is further configured as follows: Obtain the exhaust temperature at the current moment and the exhaust temperature at the previous moment; If the exhaust pressure is greater than or equal to the first threshold, the intake pressure is less than or equal to the second threshold, the exhaust temperature at the current moment is greater than or equal to the third threshold, and the difference between the exhaust temperature at the current moment and the exhaust temperature at the previous moment is greater than or equal to the fourth threshold, then the superheat of the indoor heat exchanger is corrected to the third superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

[0011] By monitoring whether the current exhaust temperature exceeds the threshold and whether it is in a continuous rising state, early signs of the system entering an overheating fluctuation state can be captured, realizing an upgrade from static parameter judgment to dynamic trend prediction. This allows the controller to intervene in advance before the exhaust temperature soars out of control and the system fluctuates violently, changing the control timing from passive remediation to active prevention, thus gaining valuable time for subsequent smooth adjustment and effectively improving the control quality of the system.

[0012] In some embodiments, the controller is further configured to: The exhaust temperature correction value is calculated based on the current exhaust temperature using a preset equation. The superheat of the indoor heat exchanger is corrected to the third superheat value based on the exhaust temperature correction value.

[0013] By establishing a quantitative mathematical relationship between exhaust temperature and superheat correction, the calculation of control quantities becomes precise and predictable. The correction strength can be dynamically determined according to the severity of the system's deviation from the steady state, achieving a match between control response and fault severity. This avoids the problems of under-adjustment or over-adjustment that may be caused by fixed-value correction, thus laying the foundation for achieving rapid and stable system recovery.

[0014] In some embodiments, the preset equation is a univariate function of the exhaust temperature at the current moment, and the exhaust temperature correction value is positively correlated with the exhaust temperature at the current moment.

[0015] By ensuring a positive correlation between the exhaust temperature correction value and the exhaust temperature, a stronger correction force can be automatically applied when the exhaust temperature increases. This avoids control lag, oscillation, or instability that may be caused by nonlinear or non-monotonic relationships, and ensures the predictability and robustness of the system behavior throughout the adjustment process.

[0016] In some embodiments, the multi-split air conditioner further includes: A suction temperature sensor is installed at the suction port of the compressor and electrically connected to the controller to detect the suction temperature of the compressor. The controller is further configured as follows: Obtain the compressor suction temperature and the suction pressure; Based on the inhalation pressure, the saturation temperature corresponding to the inhalation pressure is obtained through a pre-stored pressure-to-saturation-temperature correspondence table. The exhaust temperature correction value is calculated based on the compressor intake temperature and the saturation temperature corresponding to the intake pressure.

[0017] By calculating the exhaust temperature correction value by corresponding the intake temperature and intake pressure to the saturation temperature, the core issues of pressure drop and overheating caused by long piping can be directly reflected. This makes the calculation of the correction value closer to the physical nature of the problem, providing the system with another equivalent and potentially more accurate observation perspective and control input, and enhancing the adaptability and effectiveness under different system configurations.

[0018] In some embodiments, the multi-split air conditioner further includes: A gas pipe temperature sensor is installed at the outlet of the indoor heat exchanger and electrically connected to the controller to detect the gas pipe temperature of the indoor unit. A liquid pipe temperature sensor is installed between the outlet of the indoor expansion valve and the inlet of the indoor heat exchanger, and is electrically connected to the controller, for detecting the liquid pipe temperature of the indoor unit; The controller is further configured as follows: Obtain the temperature of the indoor unit's gas pipe and the temperature of the indoor unit's liquid pipe; The target superheat value is calculated based on the indoor unit gas pipe temperature, the indoor unit liquid pipe temperature, and the exhaust temperature correction value. The superheat of the indoor heat exchanger is then corrected to the third superheat value based on the target superheat value.

[0019] By setting up gas pipe temperature sensors and liquid pipe temperature sensors and calculating the superheat target value based on their detection values ​​and correction values, the system integrates the exhaust temperature correction value reflecting the system-level state with the superheat measurement value reflecting the local state of the indoor unit. This allows the opening adjustment of the indoor expansion valve to no longer follow a fixed superheat setpoint, but instead track an optimal target that can suppress system fluctuations in advance, thus fundamentally solving the problem of local superheat control failure.

[0020] In some embodiments, the controller is further configured to: The superheat measurement value is calculated based on the indoor unit gas pipe temperature and the indoor unit liquid pipe temperature. The opening variable of the indoor expansion valve is calculated based on the difference between the measured superheat value and the target superheat value; The opening degree of the indoor expansion valve is adjusted according to the opening degree variable of the indoor expansion valve.

[0021] By calculating the difference between the measured superheat value and the target value to determine the opening variable of the indoor expansion valve, the indoor expansion valve can be adjusted according to the measured superheat value and the target superheat value. This allows for real-time compensation of the deviation in the system's refrigerant flow, ultimately stabilizing the system in an efficient and stable optimal operating state.

[0022] In some embodiments, the controller is further configured to: After adjusting the opening of the indoor expansion valve, the indoor expansion valve control strategy continues to be executed according to a preset adjustment cycle and in the cooling mode of the multi-split air conditioner.

[0023] By continuously monitoring and executing the indoor expansion valve control strategy according to a preset cycle, the control function is ensured to remain and be continuously optimized during the continuous operation of low load and long piping conditions. This effectively responds to possible dynamic changes in system conditions, prevents the recurrence of system problems caused by stopping intervention after a single adjustment, and ultimately ensures that the stability and comfort of the air conditioner can be maintained throughout the entire complex operation period.

[0024] Secondly, this application provides a method for controlling a multi-split air conditioner, including: When the multi-split air conditioner is operating in cooling mode, the rated cooling capacity of the indoor unit currently in operation and the total rated cooling capacity of the outdoor unit are obtained. The operating load rate is calculated based on the ratio of the sum of the rated cooling capacities of the indoor units currently in operation to the total rated cooling capacity of the outdoor units. If the operating load rate is less than or equal to the load threshold, the superheat of the indoor heat exchanger is corrected to the first superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

[0025] Compared to related technologies, the multi-split air conditioner control method provided by this invention calculates the start-up load rate and determines whether to correct the superheat of the indoor heat exchanger, enabling the multi-split air conditioner to autonomously and reliably switch to the optimized operating mode when facing low load challenges. This systematically improves the adaptive control level and overall energy efficiency of the air conditioner at the method level.

[0026] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects and advantages of this application more readily apparent. Attached Figure Description

[0027] The accompanying drawings, which are included to provide an understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This application provides a curve showing the fluctuation of air outlet temperature and exhaust temperature.

[0028] Figure 2 A schematic diagram of a multi-split air conditioner structure provided in this application embodiment; Figure 3 This is a schematic diagram of another multi-split air conditioner structure provided in an embodiment of this application; Figure 4 A flowchart illustrating the operation of a controller provided in an embodiment of this application; Figure 5 A flowchart illustrating the operation of another controller provided in an embodiment of this application; Figure 6 A flowchart illustrating the operation of another controller provided in an embodiment of this application; Figure 7 A flowchart illustrating the operation of another controller provided in an embodiment of this application; Figure 8 A diagram representing a preset equation provided in this application embodiment; Figure 9 A flowchart illustrating the operation of another controller provided in an embodiment of this application; Figure 10 A flowchart illustrating a multi-split air conditioner control method provided in this application embodiment.

[0029] In the picture: 1. Outdoor unit; 2. Indoor unit; 3. Controller. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application. Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0031] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0032] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may indicate singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Multiple” used in this application refers to two or more. “And / or” describes the relationship between related objects, indicating that three relationships may exist; for example, “A and / or B” can represent: A alone, A and B simultaneously, and B alone. The character " / " generally indicates that the preceding and following objects are in an "or" relationship. The terms "first," "second," and "third" used in this application are merely to distinguish similar objects and do not represent a specific ordering of the objects.

[0033] A multi-split air conditioner is a large refrigerant circulation system that can connect different types of indoor units and different piping lengths.

[0034] With the development of multi-split air conditioners and the upgrading of market products, the cooling capacity of a single outdoor unit module has now exceeded 40HP, and the maximum combined module capacity has reached 168HP.

[0035] Moreover, multi-split air conditioners are typically installed with significant elevation differences and long piping. The maximum elevation difference is 110 meters, and the total length of the system piping reaches 1200 meters.

[0036] In addition, the range of indoor unit capacities that can be matched with multi-split air conditioners is also getting wider and wider, with the most common indoor unit capacities currently ranging from 0.6HP to 6HP. In the cooling mode of an air conditioner, the opening degree of the indoor expansion valve is often controlled according to the superheat. If the superheat is higher than the target value, the valve opens; otherwise, the valve closes.

[0037] However, due to the complexity of installing and using multi-split air conditioners, the system fluctuates significantly under low load and long piping conditions.

[0038] For example, a 40HP multi-split air conditioner with a piping length of 300 meters can be used to cool a single 0.6HP indoor unit.

[0039] Because the system has a low refrigerant circulation volume and the outdoor unit has a large displacement, the two have mismatched refrigerant circulation volume requirements, which can easily lead to problems such as high exhaust temperature and compressor frequency fluctuations.

[0040] In this scenario, if the opening of the indoor expansion valve is adjusted according to the superheat of the indoor heat exchanger being 1°C in the normal cooling mode; Although the calculated superheat value of the indoor unit is 1, due to the small capacity of the indoor unit, the long refrigeration piping, and the large pressure loss along the way, the actual superheat value at the compressor suction port far exceeds 1°C, sometimes even reaching more than ten degrees Celsius. In other words, the superheat value calculated on the indoor unit side is invalid.

[0041] In addition, only a very small number of small-capacity indoor units are in operation, resulting in low refrigerant flow on the compressor suction side, high maximum cooling pressure, and high compressor load, making it easy for the compressor to discharge too high.

[0042] Normally, when the temperature exceeds a certain limit of 100°C, the only solution is to force the compressor to reduce its frequency and force the indoor expansion valve to open wider, relying on a large amount of liquid return to solve the problem of excessive exhaust.

[0043] Therefore, fluctuations in compressor frequency and forced opening of the indoor expansion valve can cause fluctuations in indoor air temperature, resulting in reduced overall energy efficiency and indoor comfort issues.

[0044] like Figure 1As shown, when an outdoor unit with a rated capacity of 40HP is operating with only one indoor unit with a capacity of 0.6HP running for cooling, the maximum cooling operating temperature is 23℃.

[0045] In the figure, the black curve represents the average air outlet temperature of the indoor unit, and the red curve represents the exhaust temperature of the compressor.

[0046] Both curves exhibit dramatic periodic fluctuations. Specifically, the indoor unit's outlet air temperature fluctuates by approximately 6°C, directly leading to significant changes in the indoor ambient temperature and severely impacting user comfort.

[0047] At the same time, the compressor exhaust temperature fluctuates by about 50°C, indicating that the system is operating in a highly unstable state.

[0048] When the exhaust temperature soars to the upper limit protection value of about 100°C, the system is forced to reduce the compressor frequency and open the indoor expansion valve to intervene. When the temperature drops, the system returns to its original state, causing the temperature to rise again, and this cycle repeats itself. This passive, remedial control mode not only results in significant energy waste but also poses a potential threat to the compressor's lifespan.

[0049] This indicates that under low load and long piping conditions, the traditional control method based on the local overheating of the indoor unit has failed and cannot maintain the stable operation of the system.

[0050] To address the aforementioned issues, this application proposes a multi-split air conditioner and its control method. By determining whether to correct the superheat of the indoor heat exchanger based on the operating load rate, the opening degree of the indoor expansion valve is adjusted. This method can optimize the control of the indoor expansion valve opening degree under conditions of long piping and low operating load.

[0051] Figure 2 This is a schematic diagram of the structure of a multi-split air conditioner provided in an embodiment of this application. Figure 2 As shown, a multi-split air conditioner includes an outdoor unit 1. The outdoor unit 1 is typically installed outside the building and is used to drive the refrigerant circulation.

[0052] In some embodiments, the multi-split air conditioner further includes an indoor unit. The indoor unit includes multiple indoor units 2, which are connected in parallel to the outdoor unit 1 via refrigerant piping.

[0053] Indoor units are typically installed on the upper part of the ceiling or wall, with their air outlets facing the indoor space, and are used to regulate indoor air for cooling in cooling mode.

[0054] In some embodiments, such as Figure 3As shown, the multi-split air conditioner also includes a compressor. The compressor is installed in the outdoor unit 1 and is used to compress the refrigerant and drive the refrigerant to circulate in the refrigeration circuit.

[0055] In some embodiments, the multi-split air conditioner also includes an indoor expansion valve. The indoor expansion valve is installed in the indoor unit 2 and is used to throttle and reduce the pressure of the refrigerant flowing into the indoor unit 2.

[0056] In some embodiments, the multi-split air conditioner also includes an indoor heat exchanger. The indoor heat exchanger is installed in the indoor unit 2 and is used to exchange heat between the throttled and depressurized refrigerant and the indoor air.

[0057] In some embodiments, the multi-split air conditioner further includes a controller 3. The controller 3 is electrically connected to the outdoor unit 1 and the indoor unit. The controller 3 can execute an indoor expansion valve control strategy in the cooling mode of the multi-split air conditioner.

[0058] In some embodiments, such as Figure 4 As shown, obtain the rated cooling capacity of the indoor unit 2 that is currently in operation and the total rated cooling capacity of the outdoor unit 1; The operating load rate is calculated based on the ratio of the sum of the rated cooling capacities of the indoor units 2 currently in operation to the total rated cooling capacity of the outdoor units 1. Determine whether the start-up load rate is less than or equal to the load threshold; If the operating load rate is less than or equal to the load threshold, the superheat of the indoor heat exchanger is corrected to the first superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the multi-split air conditioner in normal operation.

[0059] By calculating the ratio of the total capacity of indoor unit 2 to the total capacity of outdoor unit 1 in real time, the system can accurately identify whether it is under low load conditions, thereby enabling on-demand switching of control strategies.

[0060] By calculating and judging the start-up load rate, unnecessary control interventions are avoided under non-essential operating conditions, ensuring the system's operating efficiency and stability under most normal loads.

[0061] Meanwhile, calculating and determining the operating load rate provides an accurate trigger condition for implementing targeted optimization control under low load, thereby improving the intelligence and adaptability of multi-split air conditioner control as a whole.

[0062] Specifically, the problem of excessively high compressor discharge temperature mainly occurs when the system is operating at extremely low load rates, such as when only one small-capacity indoor unit is turned on. Therefore, it is necessary to determine the magnitude of the load rate relative to the load threshold.

[0063] Identify all indoor units 2 that are in cooling operation and retrieve their respective rated cooling capacities from the pre-stored system configuration data; Sum the rated cooling capacities of each of the indoor units 2 to obtain the rated cooling capacity of the currently operating indoor unit; The total rated cooling capacity of outdoor unit 1 is an inherent and unchanging capability parameter of outdoor unit 1, which is usually clearly indicated in the equipment model.

[0064] The operating load rate is obtained by dividing the rated cooling capacity of the indoor unit in operation by the total rated cooling capacity of the outdoor unit.

[0065] The load threshold can be set to 10%. Based on a deep understanding of the dynamic characteristics of multi-split air conditioners under extremely low loads, it can effectively distinguish between the stable operating zone and the potential fluctuation zone of the system.

[0066] When the operating load rate is lower than or equal to the load threshold, it indicates that the supply and demand contradiction of the refrigerant circulation in the system has begun to emerge, and the outdoor unit compressor displacement is seriously mismatched with the demand of the indoor unit. At this time, the system has a high risk of runaway exhaust temperature.

[0067] Therefore, triggering overheat correction in advance with a 10% threshold can provide the control system with valuable time to intervene, thus avoiding drastic and passive correction when the exhaust temperature rises to the protection limit.

[0068] In some embodiments, the multi-split air conditioner also includes an exhaust pressure sensor. The exhaust pressure sensor is installed at the exhaust port of the compressor and electrically connected to the controller 3 for detecting exhaust pressure.

[0069] In some embodiments, the multi-split air conditioner also includes a suction pressure sensor. The suction pressure sensor is installed at the suction port of the compressor and electrically connected to the controller 3 for detecting suction pressure.

[0070] In some embodiments, such as Figure 5 As shown, the exhaust pressure and intake pressure are obtained; If the start-up load rate is less than or equal to the load threshold, then it is further determined whether the exhaust pressure is greater than or equal to the first threshold, and whether the intake pressure is less than or equal to the second threshold. If the exhaust pressure is greater than or equal to the first threshold and the intake pressure is less than or equal to the second threshold, then the superheat of the indoor heat exchanger is corrected to the second superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the multi-split air conditioner in normal operation.

[0071] By introducing pressure signals from both the high-pressure and low-pressure sides to comprehensively diagnose the system's load status and flow path resistance, the bottleneck condition of high exhaust pressure and low intake pressure caused by long piping can be identified more accurately.

[0072] By using the above conditions to make judgments, misjudgments that may occur based on a single parameter such as load rate are avoided. This ensures that subsequent superheat correction control is only activated in real-world problem scenarios where both load and system pressure characteristics are met, significantly improving the accuracy and reliability of control decisions.

[0073] Specifically, because the system operates under extremely low operating load conditions, the refrigerant circulation demand on the evaporator side of indoor unit 2 is much smaller than the discharge capacity on the compressor suction side. At the same time, the system is characterized by excessively high discharge pressure and high compressor load.

[0074] Therefore, it is also necessary to determine the magnitude of the inhalation pressure relative to the first threshold, and the magnitude of the exhaust pressure relative to the second threshold.

[0075] The first threshold can be set to 3.65 MPa, and the second threshold can be set to 0.55 MPa, which can provide a highly specific joint criterion for identifying the specific operating condition of excessive system resistance caused by long piping.

[0076] By setting the first and second thresholds, it can be shown that the system is in a typical operating condition of high exhaust pressure and low intake pressure. This is a direct characteristic of poor refrigerant flow caused by the large friction resistance along the long piping under low load.

[0077] By using this as a prerequisite for triggering superheat correction, the control system can accurately distinguish long piping under low load problems from other faults, thereby greatly avoiding misjudgments and ensuring that the advanced control function of superheat correction is activated only in the most suitable and needed scenarios.

[0078] By using this as a prerequisite for triggering overheat correction, the intelligence and accuracy of control decisions are improved, intervention under inappropriate operating conditions is prevented, and the system's operating efficiency in other modes is guaranteed.

[0079] In some embodiments, the multi-split air conditioner also includes an exhaust temperature sensor. The exhaust temperature sensor is installed at the exhaust port of the compressor and electrically connected to the controller 3, for detecting the exhaust temperature at the current moment and the exhaust temperature at the previous moment.

[0080] In some embodiments, such as Figure 6 As shown, obtain the current exhaust temperature and the previous exhaust temperature; If the exhaust pressure is greater than or equal to the first threshold and the intake pressure is less than or equal to the second threshold, then it is further determined whether the exhaust temperature at the current moment is greater than or equal to the third threshold, and whether the difference between the exhaust temperature at the current moment and the exhaust temperature at the previous moment is greater than or equal to the fourth threshold. If the exhaust temperature at the current moment is greater than or equal to the third threshold, and the difference between the exhaust temperature at the current moment and the exhaust temperature at the previous moment is greater than or equal to the fourth threshold, then the superheat of the indoor heat exchanger is corrected to the third superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the multi-split air conditioner in normal operation.

[0081] By monitoring whether the current exhaust temperature exceeds the threshold and whether it is in a continuous rising state, early signs that the system is about to enter an overheating fluctuation state can be captured, realizing an upgrade from static parameter judgment to dynamic trend prediction.

[0082] By monitoring the exhaust temperature, the controller 3 can intervene in advance before the exhaust temperature spikes out of control and the system fluctuates violently, changing the control timing from passive remediation to active prevention, thus gaining valuable time for subsequent smooth adjustment and effectively improving the control quality of the system.

[0083] Specifically, when the conditions for judging the start-up load rate, intake pressure, and exhaust pressure are met, the exhaust temperature is monitored, and the current exhaust temperature is compared with the third threshold, and the difference between the current exhaust temperature and the previous exhaust temperature is compared with the fourth threshold.

[0084] The third threshold can be set to 90℃, and the fourth threshold can be set to 2℃.

[0085] By setting the exhaust temperature threshold to 90℃ and its minimum temperature rise trend to 2℃, an early warning system based on dynamic trends was constructed, realizing the transformation of control timing from passive remediation to proactive prevention.

[0086] The 90°C setting is lower than the general high-temperature protection limit, which is usually between 100°C and 110°C, thus providing the system with a valuable window of opportunity for early intervention. The 2°C temperature rise trend threshold effectively identifies that the exhaust temperature is in a dynamic process of continuous deterioration, rather than a short-term, self-recoverable normal fluctuation.

[0087] By combining the third and fourth thresholds, the controller 3 can keenly detect early signs of impending system instability and smoothly initiate superheat correction to adjust the indoor expansion valve before the exhaust temperature soars to a dangerous level.

[0088] By combining the third and fourth thresholds, the drastic and oscillating forced adjustment that is only required after the limit protection is triggered in traditional control is avoided, thereby greatly improving the control quality of the system, ensuring the comfortable and stable room temperature, and significantly reducing the operating stress of key components.

[0089] In some embodiments, such as Figure 7 As shown, the exhaust temperature correction value is calculated based on the current exhaust temperature using a preset equation. The superheat of the indoor heat exchanger is adjusted to the third superheat value based on the exhaust temperature correction value.

[0090] By establishing a quantitative mathematical relationship between exhaust temperature and superheat correction, the calculation of control quantities becomes accurate and predictable.

[0091] The correction intensity is dynamically determined based on the severity of the system's deviation from the steady state, achieving a match between the control response and the severity of the fault. This avoids the under-adjustment or over-adjustment problems that may result from fixed-value correction, thus laying the foundation for achieving rapid and smooth system recovery.

[0092] In some embodiments, the preset equation is a univariate function of the exhaust temperature at the current moment, and the exhaust temperature correction value is positively correlated with the exhaust temperature at the current moment.

[0093] By ensuring a positive correlation between the exhaust temperature correction value and the exhaust temperature, a stronger correction force can be automatically applied when the exhaust temperature increases.

[0094] The preset equations avoid control lag, oscillation, or instability that may be caused by nonlinear or non-monotonic relationships, ensuring the predictability and robustness of system behavior throughout the adjustment process.

[0095] Specifically, the calculation model for the preset equation is as follows:

[0096] in, The exhaust temperature at the current moment; This is the exhaust temperature correction value; like Figure 8 As shown, the solid line represents the relationship between the current exhaust temperature and the exhaust temperature correction value, obtained through experiments based on actual measurements. The dashed lines represent the expressions of the preset equations, which are derived by fitting equations that are abstracted from evidence and can be used for practical control.

[0097] The fitting process filters out random errors and noise that may exist in the experimental measurements, revealing the most essential and intrinsic quadratic function relationship between the current exhaust temperature and the exhaust temperature correction value.

[0098] By employing a specific quadratic equation as the computational model, a nonlinear mapping relationship that closely matches the actual physical process can be accurately constructed between exhaust temperature and exhaust temperature correction value.

[0099] Compared to simple linear relationships or fixed lookup table methods, pre-defined equations can more accurately describe the physical phenomenon of increased imbalance in the system as exhaust temperature rises.

[0100] When the temperature initially appears too high, the correction value provided by the preset equation increases gradually, achieving gentle fine-tuning and avoiding unnecessary disturbances to the system. When the exhaust temperature rises significantly, indicating a worsening of system imbalance, the quadratic term of the equation causes the output of the correction value to increase rapidly, thereby applying a stronger intervention force to ensure that the malignant rise in temperature can be suppressed quickly and effectively.

[0101] The preset equation settings ensure that the control response is both timely and effective, as well as smooth and stable, avoiding overshoot or oscillation in the control process. This optimizes the dynamic adjustment quality of the system and ensures its reliability and comfort across the entire operating range.

[0102] In some embodiments, the multi-split air conditioner also includes a suction temperature sensor. The suction temperature sensor is installed at the suction port of the compressor and electrically connected to the controller 3 for detecting the suction temperature of the compressor; In some embodiments, such as Figure 9 As shown, the compressor suction temperature and suction pressure are obtained; Based on the inhalation pressure, the saturation temperature corresponding to the inhalation pressure is obtained through a pre-stored table of pressure and saturation temperature correspondence. The exhaust temperature correction value is calculated based on the compressor intake temperature and intake pressure corresponding to the saturation temperature.

[0103] The exhaust temperature correction value is calculated by using the intake temperature and intake pressure to correspond to the saturation temperature, which can directly reflect the core issues of pressure drop and overheating caused by long piping.

[0104] The exhaust temperature correction value can closely approximate the physical nature of the problem, providing the system with another equivalent and potentially more accurate observation perspective and control input, thereby enhancing the adaptability and effectiveness of the invention under different system configurations.

[0105] Specifically, the calculation model for the exhaust temperature correction value is as follows:

[0106] in, This refers to the compressor suction temperature. The saturation temperature corresponds to the intake pressure; By calculating the compressor intake superheat and using it directly as the exhaust temperature correction value, the observation perspective of the control system can be elevated from local to global, and a control quantity with clear physical meaning that is directly related to the core problem of the system can be established.

[0107] By using the two parameters of compressor suction temperature and suction pressure corresponding to saturation temperature, the essential characteristics of long piping conditions can be captured with extreme sensitivity and accuracy.

[0108] With long piping, the huge frictional resistance will cause the actual suction pressure returning to the compressor to decrease significantly, and the corresponding saturation temperature will also decrease. At this time, the suction temperature Ts will be higher due to heat absorption in the piping, and the difference between the two will increase significantly.

[0109] In this way, the superheat of the indoor heat exchanger is related to the superheat of the compressor intake. If there is an abnormality in the exhaust, the superheat of the indoor heat exchanger can be adjusted in time to avoid drastic fluctuations in the system.

[0110] In addition, the calculated exhaust temperature correction value contains key information on long piping resistance and system load mismatch.

[0111] By correcting the superheat of the indoor heat exchanger using the exhaust temperature correction value, precise compensation for the pressure drop and superheat of the entire loop can be achieved, making the control response closer to the actual physical state of the system, improving control accuracy and adaptability under different system configurations.

[0112] In some embodiments, the multi-split air conditioner also includes a duct temperature sensor. The duct temperature sensor is installed at the outlet of the indoor heat exchanger and electrically connected to the controller 3 for detecting the duct temperature of the indoor unit.

[0113] In some embodiments, the multi-split air conditioner also includes a liquid pipe temperature sensor. The liquid pipe temperature sensor is installed between the outlet of the indoor expansion valve and the inlet of the indoor heat exchanger and is electrically connected to the controller 3 for detecting the liquid pipe temperature of the indoor unit.

[0114] In some embodiments, the indoor unit gas pipe temperature and the indoor unit liquid pipe temperature are obtained; The target superheat value is calculated based on the correction values ​​of the indoor unit gas pipe temperature, indoor unit liquid pipe temperature, and exhaust temperature. The superheat value of the indoor heat exchanger is then corrected to the third superheat value based on the target superheat value.

[0115] Specifically, the calculation model for the target value of superheat is as follows:

[0116] in, The target value for superheat; This refers to the temperature of the indoor unit's gas pipe. This refers to the temperature of the liquid pipe in the indoor unit.

[0117] By setting up gas pipe temperature sensors and liquid pipe temperature sensors and calculating the superheat target value based on their detection values ​​and correction values, the system achieves the fusion of the exhaust temperature correction value, which reflects the system-level state, and the superheat measurement value, which reflects the local state of the indoor unit.

[0118] The opening adjustment of the indoor expansion valve no longer follows a fixed superheat setpoint, but rather tracks an optimal target that can suppress system fluctuations in advance, thus fundamentally solving the problem of local superheat control failure.

[0119] In some embodiments, the superheat measurement value is calculated based on the indoor unit gas pipe temperature and the indoor unit liquid pipe temperature; The opening variable of the indoor expansion valve is calculated based on the difference between the measured superheat value and the target superheat value. Adjust the opening degree of the indoor expansion valve according to the opening degree variable of the indoor expansion valve.

[0120] The specific control logic for the indoor expansion valve opening variable is determined by calculating the difference between the superheat measurement value and the target value, which enables the indoor expansion valve to be adjusted according to the superheat measurement value and the superheat target value.

[0121] The above-mentioned control of the opening of the indoor expansion valve can compensate for the deviation of the refrigerant flow in the system in real time, and ultimately stabilize the system in the optimal operating state of high efficiency and stability.

[0122] In some embodiments, after adjusting the opening of the indoor expansion valve, the indoor expansion valve control strategy continues to be executed according to a preset adjustment cycle and in the cooling mode of the multi-split air conditioner.

[0123] By continuously monitoring and executing the indoor expansion valve control strategy according to a preset cycle, the control effect is ensured to remain and be continuously optimized during the continuous operation of low-load long piping conditions.

[0124] The preset cycle setting can effectively cope with the dynamic changes that may occur in the system operating conditions, prevent the recurrence of system problems caused by stopping intervention after a single adjustment, and ultimately ensure that the stability and comfort of the air conditioner can be maintained throughout the entire complex operation period.

[0125] Specifically, the preset cycle can generally be set to 60 seconds, but in special cases it can be changed to 30 seconds to speed up the adjustment.

[0126] By setting the preset cycle for adjusting the opening of the indoor expansion valve to 60 seconds, sufficient stabilization time is provided for the system adjustment process, effectively avoiding system oscillation or control instability caused by excessively frequent valve operation.

[0127] The preset cycle setting is suitable for normal operating conditions where the system disturbance is small or in a stable adjustment phase, which can ensure the smoothness of control and the energy efficiency of the system.

[0128] Based on this, the cycle can be shortened to 30 seconds under special circumstances, such as when the exhaust temperature rises sharply or the system fluctuates more intensely.

[0129] Setting the preset cycle to 30 seconds provides the system with an emergency adjustment mode to cope with severe operating conditions. By doubling the control frequency, the system can respond more quickly to sudden situations and intervene forcefully, thereby rapidly suppressing the deterioration trend of the system.

[0130] Setting the preset cycle to 30 seconds enables the control system to maintain excellent rapid recovery capabilities at critical moments while ensuring stable operation for the vast majority of the time, thus maintaining the system's high efficiency and stable operation under various complex working conditions.

[0131] Secondly, such as Figure 10 As shown, this application provides a control method for a multi-split air conditioner, including: When the multi-split air conditioner is operating in cooling mode, obtain the rated cooling capacity of the indoor unit currently in operation and the total rated cooling capacity of the outdoor unit. The operating load rate is calculated by the ratio of the sum of the rated cooling capacities of the indoor units currently in operation to the total rated cooling capacity of the outdoor units. If the operating load rate is less than or equal to the load threshold, the superheat of the indoor heat exchanger is corrected to the first superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the multi-split air conditioner in normal operation.

[0132] By calculating the start-up load rate and determining whether to correct the superheat of the indoor heat exchanger, multi-split air conditioners can autonomously and reliably switch to optimized operating mode when facing low load challenges, thereby systematically improving the adaptive control level and overall energy efficiency of the air conditioner at the methodological level.

[0133] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A multi-split air conditioner, characterized in that, include: The outdoor unit has a compressor; An indoor unit comprising multiple indoor units connected in parallel to an outdoor unit via refrigerant piping, wherein each indoor unit has an indoor heat exchanger and an indoor expansion valve; A controller, electrically connected to the outdoor unit and the indoor unit, is configured to execute an indoor expansion valve control strategy in the cooling mode of the multi-split air conditioner. Obtain the rated cooling capacity of the indoor unit currently in operation and the total rated cooling capacity of the outdoor unit; The operating load rate is calculated based on the ratio of the sum of the rated cooling capacities of the indoor units currently in operation to the total rated cooling capacity of the outdoor units. If the operating load rate is less than or equal to the load threshold, the superheat of the indoor heat exchanger is corrected to the first superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

2. The multi-split air conditioner according to claim 1, characterized in that, The multi-split air conditioner also includes: An exhaust pressure sensor, which is installed at the exhaust port of the compressor and electrically connected to the controller, is used to detect the exhaust pressure; A suction pressure sensor is installed at the suction port of the compressor and electrically connected to the controller to detect suction pressure. The controller is further configured as follows: Obtain the exhaust pressure and the intake pressure; If the start-up load rate is less than or equal to the load threshold, the exhaust pressure is greater than or equal to the first threshold, and the intake pressure is less than or equal to the second threshold, then the superheat of the indoor heat exchanger is corrected to the second superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

3. The multi-split air conditioner according to claim 2, characterized in that, The multi-split air conditioner also includes: An exhaust temperature sensor is installed at the exhaust port of the compressor and electrically connected to the controller to detect the current exhaust temperature and the previous exhaust temperature. The controller is further configured as follows: Obtain the exhaust temperature at the current moment and the exhaust temperature at the previous moment; If the exhaust pressure is greater than or equal to the first threshold, the intake pressure is less than or equal to the second threshold, the exhaust temperature at the current moment is greater than or equal to the third threshold, and the difference between the exhaust temperature at the current moment and the exhaust temperature at the previous moment is greater than or equal to the fourth threshold, then the superheat of the indoor heat exchanger is corrected to the third superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

4. The multi-split air conditioner according to claim 3, characterized in that, The controller is further configured to: The exhaust temperature correction value is calculated based on the current exhaust temperature using a preset equation. The superheat of the indoor heat exchanger is corrected to the third superheat value based on the exhaust temperature correction value.

5. The multi-split air conditioner according to claim 4, characterized in that, The preset equation is a univariate function of the exhaust temperature at the current moment, and the exhaust temperature correction value is positively correlated with the exhaust temperature at the current moment.

6. The multi-split air conditioner according to claim 3, characterized in that, The multi-split air conditioner also includes: A suction temperature sensor is installed at the suction port of the compressor and electrically connected to the controller to detect the suction temperature of the compressor. The controller is further configured as follows: Obtain the compressor suction temperature and the suction pressure; Based on the inhalation pressure, the saturation temperature corresponding to the inhalation pressure is obtained through a pre-stored pressure-to-saturation-temperature correspondence table. The exhaust temperature correction value is calculated based on the compressor intake temperature and the saturation temperature corresponding to the intake pressure.

7. The multi-split air conditioner according to claim 5 or 6, characterized in that, The multi-split air conditioner also includes: A gas pipe temperature sensor is installed at the outlet of the indoor heat exchanger and electrically connected to the controller to detect the gas pipe temperature of the indoor unit. A liquid pipe temperature sensor is installed between the outlet of the indoor expansion valve and the inlet of the indoor heat exchanger, and is electrically connected to the controller, for detecting the liquid pipe temperature of the indoor unit; The controller is further configured as follows: Obtain the temperature of the indoor unit's gas pipe and the temperature of the indoor unit's liquid pipe; The target superheat value is calculated based on the indoor unit gas pipe temperature, the indoor unit liquid pipe temperature, and the exhaust temperature correction value. The superheat of the indoor heat exchanger is then corrected to the third superheat value based on the target superheat value.

8. The multi-split air conditioner according to claim 7, characterized in that, The controller is further configured to: The superheat measurement value is calculated based on the indoor unit gas pipe temperature and the indoor unit liquid pipe temperature. The opening variable of the indoor expansion valve is calculated based on the difference between the measured superheat value and the target superheat value; The opening degree of the indoor expansion valve is adjusted according to the opening degree variable of the indoor expansion valve.

9. The multi-split air conditioner according to claim 8, characterized in that, The controller is further configured to: After adjusting the opening of the indoor expansion valve, the indoor expansion valve control strategy continues to be executed according to a preset adjustment cycle and in the cooling mode of the multi-split air conditioner.

10. A control method for a multi-split air conditioner, characterized in that, include: When the multi-split air conditioner is operating in cooling mode, the rated cooling capacity of the indoor unit currently in operation and the total rated cooling capacity of the outdoor unit are obtained. The operating load rate is calculated based on the ratio of the sum of the rated cooling capacities of the indoor units currently in operation to the total rated cooling capacity of the outdoor units. If the operating load rate is less than or equal to the load threshold, the superheat of the indoor heat exchanger is corrected to the first superheat value, and the opening of the indoor expansion valve is adjusted. Otherwise, maintain the normal operation of the multi-split air conditioner.

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