Control method for multi-split air conditioning system

Abstract

A control method for a multi-split air conditioning system. A multi-split air conditioning system comprises an outdoor unit and at least two indoor units, each indoor unit comprising indoor expansion valves (401-40n). The control method comprises: after startup, detecting the operating state of each started indoor unit (S101); when the indoor units operate in a cooling mode, on the basis of a load coefficient corresponding to the cooling mode and the capacity of the started indoor units, calculating an initial frequency of a compressor (1) and initial opening degrees of the indoor expansion valves (401-40n) (S102), the load coefficient being determined on the basis of heat storage amount, heat loss, internal heat gain and indoor unit capacity; and, on the basis of the initial frequency of the compressor (1), regulating the frequency of the compressor (1) on the basis of an evaporation temperature, and, on the basis of the initial opening degrees of the indoor expansion valves (401-40n), regulating the opening degrees of the indoor expansion valves (401-40n) on the basis of the superheat degrees of the indoor units (S103). The multi-split air conditioning system can correspondingly regulate the compressor (1) and the indoor expansion valves (401-40n) for different building load characteristics, such that the temperature regulation capability of air conditioners match building loads, thus reducing indoor temperature fluctuation and avoiding power consumption increase caused by frequent start-stop in the case of medium or small loads, and enhancing the capability of indoor units, increasing the change speed of indoor temperature and improving the comfort for users in the case of large loads.

Description

Control method of multi-connected system

[0001] This application claims priority to Chinese Patent Application No. 202411073840.0, filed on August 6, 2024, and Chinese Patent Application No. 202411073847.2, filed on August 6, 2024, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of air conditioning, in particular to a control method of a multi-connected system. BACKGROUND

[0003] Building energy consumption accounts for 46% of total social energy consumption, and HVAC equipment energy consumption accounts for 40% of total building energy consumption. Therefore, reducing the actual operation energy consumption of HVAC equipment is crucial to achieving the dual-carbon goal.

[0004] Current multi-connected air conditioning system control is mostly preset control logic, and does not match the adjustment according to the actual use scene of the user and the building load characteristics. SUMMARY

[0005] Some embodiments of the present application propose a control method of a multi-connected system, which can adjust the frequency of the compressor and the opening degree of the expansion valve of the multi-connected system according to different building loads, improve the temperature regulation performance of the multi-connected system, and reduce the energy consumption of the multi-connected air conditioner.

[0006] According to an aspect of the present application, a control method of a multi-connected system is provided, including an outdoor unit and at least two indoor units, and the indoor unit includes an indoor expansion valve. The control method includes:

[0007] After starting, the running state of each indoor unit after starting is detected;

[0008] When the indoor unit runs in a cooling mode, the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are calculated according to the load coefficient corresponding to the cooling mode and the capacity of the indoor unit after starting;

[0009] Based on the initial frequency of the compressor, the frequency of the compressor is adjusted according to the evaporation temperature, and based on the initial opening degree of the indoor expansion valve, the opening degree of the indoor expansion valve is adjusted according to the superheat degree of the indoor unit.

[0010] According to another aspect of the present application, a control method of a multi-connected system is provided, including an outdoor unit and at least two indoor units, and the indoor unit includes an indoor expansion valve. The control method includes: after starting, the running state of each indoor unit after starting is detected;

[0011] calculating a compressor initial frequency and an indoor expansion valve initial opening degree according to a load coefficient corresponding to the cooling mode and a capacity of the indoor unit after starting;

[0012] adjusting the compressor frequency according to an evaporating temperature based on the compressor initial frequency, and adjusting the indoor expansion valve opening degree according to an indoor unit superheat degree based on the indoor expansion valve initial opening degree;

[0013] calculating a compressor initial frequency and an indoor expansion valve initial opening degree according to a load coefficient corresponding to the cooling mode and a capacity of the indoor unit after starting;

[0014] adjusting the compressor frequency according to a condensing temperature based on the compressor initial frequency in the heating state, and adjusting the indoor expansion valve opening degree according to an indoor unit subcooling degree based on the indoor expansion valve initial opening degree in the heating state.

[0015] Some embodiments of the present application provide a control method of a multi-split system, the method comprising: after starting, detecting an operation state of each indoor unit after starting; when the indoor unit operates in a cooling mode, calculating a compressor initial frequency and an indoor expansion valve initial opening degree according to a load coefficient corresponding to the cooling mode and a capacity of the indoor unit after starting; adjusting the compressor frequency according to an evaporating temperature based on the compressor initial frequency, and adjusting the indoor expansion valve opening degree according to an indoor unit superheat degree based on the indoor expansion valve initial opening degree. The method adjusts the compressor frequency according to the current evaporating temperature and adjusts the indoor expansion valve opening degree according to the indoor unit superheat degree based on the compressor initial frequency and the indoor expansion valve initial opening degree, which are calculated by the load coefficient. The load coefficient is determined by building load characteristics such as heat storage, heat leakage, and internal disturbance. Thus, the method of the present application can adjust the frequency of the compressor and the opening degree of the expansion valve according to different building loads, so that the temperature regulation performance of the system can be matched with the building load, the temperature regulation performance of the multi-split system is improved, the energy consumption is reduced, and the comfort is improved. For example, for a small or medium load building, the room temperature fluctuation is reduced and the power consumption caused by frequent start-stop is avoided. For a large load building, the temperature regulation speed of the indoor unit is improved, the room temperature change speed is accelerated, and the user comfort is improved. BRIEF DESCRIPTION OF DRAWINGS

[0016] FIG. 1 is a refrigerant circulation schematic diagram of a multi-split system in a cooling mode according to some embodiments of the present application.

[0017] FIG. 2 is a control flowchart of a multi-split system in a cooling mode according to some embodiments of the present application.

[0018] Fig. 3 is a flow chart of adjusting target evaporating temperature and target superheat according to indoor temperature variation in refrigeration mode of a multi-split system according to some embodiments of the present application.

[0019] Fig. 4 is a flow chart of adjusting compressor frequency in refrigeration mode of a multi-split system according to some embodiments of the present application.

[0020] Fig. 5 is a flow chart of adjusting indoor expansion valve in refrigeration mode of a multi-split system according to some embodiments of the present application.

[0021] Fig. 6 is a schematic diagram of refrigerant circulation in heating mode of a multi-split system according to some embodiments of the present application.

[0022] Fig. 7 is a control flow chart in heating mode of a multi-split system according to some embodiments of the present application.

[0023] Fig. 8 is a flow chart of adjusting target condensing temperature and target subcooling according to indoor temperature variation in heating mode of a multi-split system according to some embodiments of the present application.

[0024] Fig. 9 is a flow chart of adjusting compressor frequency in heating mode of a multi-split system according to some embodiments of the present application.

[0025] Fig. 10 is a flow chart of adjusting indoor expansion valve in heating mode of a multi-split system according to some embodiments of the present application.

[0026] Embodiments of the present application

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0028] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0029] The terms "first", "second", etc. are used only for the purpose of description and do not imply or indicate relative importance or imply the number of the technical features indicated. Thus, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0030] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0031] In the present application, unless otherwise explicitly specified and limited, the "upper" or "lower" of the first feature to the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, the "upper", "above" and "on" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The "under", "below" and "under" of the first feature to the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0032] The following disclosure provides many different embodiments or examples for implementing different structures of the present application. In order to simplify the disclosure of the present application, the components and arrangements of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeatedly refer to numbers and / or letters in different examples, and such repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or arrangements discussed. In addition, the present application provides examples of various specific processes and materials, but those skilled in the art can realize the application of other processes and / or the use of other materials.

[0033] The multi-split system given in the present application performs the refrigeration or heating cycle of the air conditioner by using the compressor, the condenser, the throttling device and the evaporator. The refrigeration or heating cycle includes a series of processes involving compression, condensation, expansion and evaporation, and performs refrigeration or heating for indoor space.

[0034] In the refrigeration process, low-temperature and low-pressure refrigerant enters the compressor, the compressor compresses the refrigerant gas into high-temperature and high-pressure state and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and heat is released to the surrounding environment through the condensation process.

[0035] The throttling device expands the high-temperature and high-pressure state liquid phase refrigerant condensed in the condenser into low-pressure liquid phase refrigerant. The evaporator evaporates the refrigerant expanded in the throttling device, and returns the refrigerant gas in a low-temperature and low-pressure state to the compressor. The evaporator can achieve a refrigeration effect by exchanging heat with the airflow to be cooled through the endothermic evaporation of the refrigerant. Throughout the cycle, the air conditioner can adjust the temperature of the indoor space.

[0036] The outdoor unit of the multi-split system refers to the part of the refrigeration cycle including the compressor and the outdoor heat exchanger, and the throttling device is located in the outdoor unit.

[0037] The indoor unit of the multi-split system includes an indoor heat exchanger, the multi-split system includes at least two indoor units, and each indoor unit is provided with an indoor expansion valve, and the capacity of the indoor unit is adjusted by adjusting the opening degree of the indoor expansion valve.

[0038] The indoor heat exchanger and the outdoor heat exchanger are used as a condenser or an evaporator. When the indoor heat exchanger is used as a condenser, the air conditioner is used as a heater for heating, and when the indoor heat exchanger is used as an evaporator, the air conditioner is used as a cooler for refrigeration.

[0039] The multi-split system includes an outdoor unit and at least two indoor units, the outdoor unit includes a compressor and an outdoor heat exchanger, and each indoor unit includes an indoor heat exchanger and an indoor expansion valve.

[0040] Figure 1 is a schematic diagram of a multi-split refrigeration mode refrigerant cycle. In the example of Figure 1, the multi-split system includes an outdoor unit and a first indoor unit, a second indoor unit, …, an n-th indoor unit, the outdoor unit is connected to the first indoor unit, the second indoor unit, …, the n-th indoor unit through a split pipe, forming a multi-split system.

[0041] The outdoor unit is provided with a compressor 1, an outdoor heat exchanger 2, an outdoor expansion valve 3, and a four-way valve 6, and the operating capacity of the indoor unit can be adjusted by adjusting the operating frequency of the compressor.

[0042] The first indoor unit is provided with a first indoor heat exchanger 501 and a first indoor expansion valve 401, and the operating capacity of the first indoor unit can be adjusted by adjusting the opening degree of the first indoor expansion valve 401.

[0043] The first indoor unit includes a first indoor environment temperature detection module 801, a first indoor unit liquid pipe temperature detection module 901, and a first indoor unit gas pipe temperature detection module 1001.

[0044] The second indoor heat exchanger 502 and the second indoor expansion valve 402 are arranged in the second indoor unit, and the operation capacity of the second indoor unit can be adjusted by adjusting the opening degree of the second indoor expansion valve 402.

[0045] The second indoor unit comprises a second indoor environment temperature detection module 802, a second indoor unit liquid pipe temperature detection module 902, and a second indoor unit gas pipe temperature detection module 1002.

[0046] …

[0047] The nth indoor heat exchanger 50n and the nth indoor expansion valve 40n are arranged in the nth indoor unit, and the operation capacity of the nth indoor unit can be adjusted by adjusting the opening degree of the nth indoor expansion valve 40n.

[0048] The nth indoor unit comprises an nth indoor environment temperature detection module 80n, an nth indoor unit liquid pipe temperature detection module 90n, and an nth indoor unit gas pipe temperature detection module 100n.

[0049] The ith indoor environment temperature detection module 80i is configured to detect an indoor environment temperature Tii.

[0050] The ith indoor liquid pipe temperature detection module 90i is configured to detect an indoor liquid pipe temperature Tli.

[0051] The ith indoor gas pipe temperature detection module 100i is configured to detect an indoor gas pipe temperature Tgi.

[0052] All the indoor units comprise a set temperature acquisition module.

[0053] The ith indoor set temperature acquisition module is configured to acquire an indoor set temperature Tsi.

[0054] The outdoor unit comprises an outdoor environment temperature detection module 7 configured to detect an outdoor environment temperature Ta.

[0055] The multi-split system of the embodiments of the present application proposes a control method of adjusting the compressor and the expansion valve based on the actual demand load of the building, so as to match the air conditioning capacity with the actual load of the building. In addition, it should be noted that, in the present application, the air conditioning capacity refers to the air temperature regulation capacity of the multi-split system, such as the refrigeration or heating capacity; and the actual load of the building refers to the actual required refrigeration or heating capacity of the building, such as a room, under the condition of meeting the user demand.

[0056] The multi-connected system comprises a control technology for regulating the output of the multi-connected air conditioner based on the actual load of the building, and relates to a multi-connected load control method based on self-recognition of the load characteristics of the building, so that the air conditioner control is adjusted according to different load characteristics of the building, the air conditioner capacity is matched with the building load, the room temperature fluctuation is reduced and the power consumption caused by frequent start-stop is avoided in the case of small and medium load, and the indoor unit capacity is increased to accelerate the room temperature change speed and improve the user comfort in the case of large load.

[0057] Therefore, the multi-connected system first determines the heat storage, heat leakage and internal disturbance parameters of the indoor unit corresponding room;

[0058] When the indoor unit operates in the refrigeration mode, the heat storage amount is calculated according to the heat storage parameter and the expected room temperature change amount, the heat leakage amount is calculated according to the heat leakage parameter and the difference between the outdoor temperature and the indoor temperature, and the internal disturbance amount is calculated according to the internal disturbance parameter; the load coefficient is calculated according to the sum of the heat storage amount, the heat leakage amount and the internal disturbance amount and the indoor unit capacity.

[0059] Then, the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are calculated according to the load coefficient and the indoor unit capacity, so that the initial frequency of the compressor and the initial opening degree of the indoor expansion valve can meet the indoor load to the greatest extent.

[0060] In the subsequent operation process, the frequency of the compressor is adjusted according to the evaporation temperature, and the opening degree of the indoor expansion valve is adjusted according to the superheat degree of the indoor unit. The initial target evaporation temperature and the initial target superheat degree need to be calculated; the target evaporation temperature and the target superheat degree are adjusted according to the indoor temperature change; the frequency of the compressor is adjusted according to the target evaporation temperature, and the opening degree of the indoor expansion valve is adjusted according to the target superheat degree, so that the frequency of the compressor and the opening degree of the indoor expansion valve can be adjusted following the change of the indoor load, and the indoor load requirement can be met in real time. Since the loads of each room are not necessarily the same, the heat storage, heat leakage and internal disturbance parameters are determined for each room respectively.

[0061] The load characteristic parameters ai, bi and ci in the space of the room corresponding to the i-th indoor unit are determined. i = 1, 2, …, n.

[0062] Wherein: ai is the air heat storage characteristic parameter in the space of the room corresponding to the i-th indoor unit.

[0063] bi is the heat leakage performance characteristic parameter of the room corresponding to the i-th indoor unit.

[0064] ci is the internal disturbance characteristic parameter of the room corresponding to the i-th indoor unit.

[0065] In some embodiments, the heat storage parameter ai, the heat leakage parameter bi and the internal disturbance parameter ci can be inputted after being calculated according to the size of the space in the building, the heat transfer parameter of the wall of the building and the number of heat sources in the room.

[0066] Obtaining room space size, calculating heat storage parameter ai according to room space size.

[0067] In some embodiments, heat storage parameter ai = c*Vi*ρ, wherein c is air specific heat capacity, Vi is room space size, and ρ is air density.

[0068] Obtaining room heat transfer coefficient and room area, calculating heat leakage parameter bi according to room heat transfer coefficient and room area.

[0069] In some embodiments, heat leakage parameter bi = Ki*Ai, wherein Ki is wall heat transfer coefficient, and Ai is room area.

[0070] Obtaining heat generation of heat source in room, calculating internal disturbance parameter ci according to heat generation of heat source in room.

[0071] In some embodiments, internal disturbance parameter ci = Ni+Wi, wherein Ni is heat generation corresponding to number of people in room, and Wi is heat generation of always-on equipment in room.

[0072] In the above, Vi, Ki, Ai, Ni, and Wi are user input values.

[0073] In some embodiments, the indoor unit obtains heat storage parameter ai, heat leakage parameter bi, and internal disturbance parameter ci of corresponding room respectively and sends them to the outdoor unit.

[0074] In some embodiments, indoor unit capacity is obtained, and heat storage parameter ai, heat leakage parameter bi, and internal disturbance parameter ci are calculated according to indoor unit capacity.

[0075] If the user does not input related parameters, the outdoor unit calculates heat storage parameter ai, heat leakage parameter bi, and internal disturbance parameter ci according to nominal capacity HP of the indoor unit, and the calculation method is as follows:

[0076] ai = HP i *k1.

[0077] bi = HP i *k2.

[0078] ci = HP i *k3.

[0079] Wherein, k1, k2, and k3 are constants, for example, 20≤k1≤200, 0.01≤k2≤1, and 0≤k3≤2; and HPi is the capacity of the i indoor unit.

[0080] The control process is as follows:

[0081] Step S101, after the system is started, the operating state of the indoor unit is detected, if it is in a cooling state, the following control is continued, if it is in a heating state, the following control is not performed.

[0082] Step S102, first initial value control after starting. That is, when the indoor unit runs in the cooling mode, the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are calculated according to the load coefficient corresponding to the cooling mode and the capacity of the indoor unit after starting, and the load coefficient is determined according to the heat storage amount, the heat leakage amount, the internal disturbance amount and the capacity of the indoor unit.

[0083] The initial frequency of the compressor is a constant N*∑ the product of the capacity of the indoor unit started and the load coefficient corresponding thereto.

[0084] In some embodiments, the initial frequency of the compressor H1=H10; Wherein m is the number of indoor units started.

[0085] The initial opening degree of the indoor expansion valve is a constant M, the product of the capacity of the indoor unit and the load coefficient corresponding thereto.

[0086] In some embodiments, the initial opening degree of the indoor expansion valve EVI=EVIO; EVIO=M*HP i *k i .

[0087] Wherein: N, M are constants, for example: N=15, M=100.

[0088] HP i : the capacity of the i indoor unit.

[0089] k i : load coefficient, Wherein x is a constant, for example: x=2.6;△T i is the desired room temperature change amount,△T i =f(T ii -T si ), f is a constant, for example: f=0.3;T si is the user set temperature of the i indoor unit;T ii is the indoor temperature of the i indoor unit;T a is the outdoor ambient temperature; t is the control period, for example: t=60s.

[0090] After the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are determined, the multi-split air conditioner is started to run at the initial frequency of the compressor, and the opening degree of the indoor expansion valve is adjusted to the initial opening degree of the indoor expansion valve.

[0091] Step S103, adjust the frequency of the compressor according to the evaporation temperature, and adjust the opening degree of the indoor expansion valve according to the superheat degree of the indoor unit.

[0092] In an example, the above step S103 includes:

[0093] Step S1: calculate the initial target evaporation temperature, calculate the initial target superheat degree;

[0094] Step S2: adjusting the target evaporation temperature and the target superheat degree according to the indoor temperature change; and

[0095] Step S3: adjusting the compressor frequency according to the target evaporation temperature and adjusting the indoor expansion valve opening degree according to the target superheat degree.

[0096] Wherein, the compressor frequency is controlled according to the average value Tliave of all indoor unit evaporation temperatures Tli. The indoor expansion valve is controlled according to the indoor unit superheat degree SHi=Tgi-Tli.

[0097] In some embodiments, the calculation method of step S1 is as follows:

[0098] The initial target evaporation temperature is: indoor temperature-(sum of heat storage, heat leakage and internal disturbance quantity) / indoor unit performance coefficient, the target evaporation temperature of each indoor unit is calculated respectively, and the initial target evaporation temperature is the minimum value of all indoor unit target evaporation temperatures.

[0099] The initial target evaporation temperature Tlo is calculated as follows:

[0100] The target evaporation temperature Tlio of each indoor unit is calculated respectively, and the minimum Tlio of each indoor unit is taken as the system target evaporation temperature (i.e. the initial target evaporation temperature): Tlo=min(Tlio).

[0101] di is the indoor unit performance coefficient, which is a built-in value, for example: di=0.5.

[0102] The initial target superheat degree is: (indoor unit performance coefficient*(indoor temperature-initial target evaporation temperature) / (sum of heat storage, heat leakage and internal disturbance quantity)-coefficient f1)*coefficient f2.

[0103] The initial target superheat degree SHio is calculated, and each indoor unit corresponds to an initial superheat degree, and SHio represents the initial target superheat degree of the i-th indoor unit:

[0104] f1 and f2 are coefficients, for example: f1=1, f2=10.

[0105] In step S2, the process of adjusting the target evaporation temperature according to the indoor temperature change includes: obtaining the indoor temperature of the previous period and the indoor temperature of the current period and calculating the indoor temperature difference, calculating the current expected indoor temperature change, when the indoor temperature difference exceeds the current expected indoor temperature change, the indoor unit target evaporation temperature increases by a set temperature; when the indoor temperature difference does not exceed the current expected indoor temperature change, the indoor unit target evaporation temperature decreases by a set temperature; when the indoor temperature difference is the same as the current expected indoor temperature change, the indoor unit target evaporation temperature remains unchanged.

[0106] Tlo = min(Tlio), Tlo has upper and lower limits, for example: 15≥Tlo≥2.

[0107] In the example of FIG. 2, the target evaporation temperature Tlio adjustment process of the ith indoor unit is as follows:

[0108] S211, start.

[0109] S212, read the indoor temperature Tii(j-1) of the previous period and the indoor temperature Tii(j) of the current period.

[0110] S213, calculate the current expected indoor temperature change amount ΔT = f(Tii(j)-Tsi).

[0111] S214, determine whether Tii(j-1)-Tii(j) > ΔT, if yes, go to step S215, otherwise, go to step S216.

[0112] S215, Tlio(j+1) = Tlio(j)+△Tlio. Go to step S212.

[0113] S216, determine whether Tii(j-1)-Tii(j) < ΔT, if yes, go to step S217, otherwise, go to step S218.

[0114] S217, Tlio(j+1) = Tlio(j)-△Tlio. Go to step S212.

[0115] S218, Tlio(j+1) = Tlio(j). Go to step S212.

[0116] Wherein, Tlio(j+1), Tlio(j) are the target Tlio of the next period and the current period Tlio respectively, and △Tlio is the iteration step, for example: △Tlio = 0.1.

[0117] The target evaporation temperature Tlo(j+1) of the next period = min(Tlio(j+1)).

[0118] In step S2, the process of adjusting the target superheat degree according to the indoor temperature change includes: when the indoor temperature difference exceeds the current expected indoor temperature change amount, the target superheat degree increases by a set superheat degree; when the indoor temperature difference does not exceed the current expected indoor temperature change amount, the target superheat degree decreases by a set superheat degree; when the indoor temperature difference is the same as the current expected indoor temperature change amount, the target superheat degree remains unchanged.

[0119] In the example of FIG. 3, the target superheat degree SHio adjustment process of the ith indoor unit is as follows:

[0120] S221, start.

[0121] S222, read the indoor temperature Tii(j-1) of the previous period and the indoor temperature Tii(j) of the current period.

[0122] S223, calculate the current expected room temperature change amount ΔTi=f(Tii(j)-Tsi).

[0123] S224, determine whether Tii(j-1)-Tii(j) > ΔT, if yes, go to step S225, otherwise, go to step S226.

[0124] S225, SHio(j+1)=SHio(j)+△Shio. Go to step S222.

[0125] S226, determine whether Tii(j-1)-Tii(j) < ΔT, if yes, go to step S227, otherwise, go to step S228.

[0126] S227, SHio(j+1)=SHio(j)-△Shio. Go to step S222.

[0127] S228, SHio(j+1)=SHio(j). Go to step S222.

[0128] wherein SHio(j+1), SHio(j) are the target SHio of the next period and the SHio of the current period respectively, and ΔSHio is the iteration step length, for example: ΔSHio=0.5.

[0129] In step S3, the process of adjusting the compressor frequency according to the target evaporation temperature includes: obtaining the evaporation temperature, calculating the difference between the average value of the evaporation temperature and the target evaporation temperature, increasing the compressor frequency when the difference exceeds the maximum value of the set interval; reducing the compressor frequency when the difference does not exceed the minimum value of the set interval; and keeping the compressor frequency unchanged when the difference is within the set interval.

[0130] For example, in the example of FIG. 4, the compressor frequency control flow is as follows:

[0131] S311, start.

[0132] S312, read the evaporation temperature Tli.

[0133] S313, calculate the average value Tliave of the evaporation temperature.

[0134] S314, calculate the difference between the average value Tliave of the evaporation temperature and the target evaporation temperature Tlo, Tliave-Tlo≥σ, if yes, go to step S315, otherwise, go to step S316.

[0135] S315, Hi(j+1) = Hi(j) + ΔHi. Go to step S312.

[0136] S316, Tliave-Tlo ≤ -σ, if yes, go to step S317, otherwise, go to step S318.

[0137] S317, Hi(j+1) = Hi(j) - ΔHi. Go to step S312.

[0138] S318, Hi(j+1) = Hi(j). Go to step S312.

[0139] wherein σ is a control constant, for example: σ = 0.2, Hi(j+1), Hi(j) are the next cycle target Hi, current cycle Hi respectively, ΔHi is the Hi iteration step, for example: ΔHi = 2.

[0140] In step S3, the process of adjusting the indoor expansion valve opening degree according to the target superheat degree includes: obtaining the indoor superheat degree, calculating the difference between the indoor superheat degree and the target superheat degree, increasing the indoor expansion valve opening degree when the difference exceeds the maximum value of the set interval, reducing the indoor expansion valve opening degree when the difference does not exceed the minimum value of the set high interval, and keeping the indoor expansion valve opening degree unchanged when the difference is in the set interval.

[0141] For example, in the example of FIG. 5, the indoor expansion valve control flow is as follows:

[0142] S321, start.

[0143] S322, read the indoor liquid pipe temperature Tli and the indoor gas pipe temperature Tgi.

[0144] S323, calculate the indoor superheat degree SHi = Tgi - Tli.

[0145] S324, calculate the difference between the indoor superheat degree SHi and the target superheat degree SHio, SHi - SHio ≥ δ, if yes, go to step S326, otherwise, go to step S327.

[0146] S325, EVI(j+1) = EVI(j) + ΔEVI. Go to step S322.

[0147] S326, SHi - SHio ≤ -δ, if yes, go to step S7, otherwise, go to step S328.

[0148] S327, EVI(j+1) = EVI(j) - ΔEVI. Go to step S322.

[0149] S328, EVI(j+1) = EVI(j). Go to step S322.

[0150] Wherein, δ is a control constant, for example: δ = 0.5, EVI(j+1), EVI(j) are next cycle target EVI, current cycle EVI respectively, and ΔEVI is EVI iteration step, for example: ΔEVI = 10.

[0151] In some embodiments, the multi-connected machine can run in heating mode, for example, as shown in Figure 6, which is a schematic diagram of refrigerant circulation of the multi-connected machine in heating mode. In the example of Figure 6, the outdoor unit further comprises a high pressure sensor Pd11.

[0152] The multi-connected machine system first determines the heat storage, heat leakage and internal disturbance parameters of the room corresponding to the indoor unit.

[0153] When the indoor unit runs in heating mode, the heat storage amount is calculated according to the heat storage parameter and the desired room temperature change amount, the heat leakage amount is calculated according to the heat leakage parameter and the difference between the outdoor temperature and the indoor temperature, and the internal disturbance amount is calculated according to the internal disturbance parameter; the load coefficient is calculated according to the difference between the heat storage amount, the heat leakage amount and the internal disturbance amount, and the capacity of the indoor unit.

[0154] Then, the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are calculated according to the load coefficient and the capacity of the indoor unit, so that the initial frequency of the compressor and the initial opening degree of the indoor expansion valve meet the indoor load to the greatest extent.

[0155] In the subsequent operation process, the compressor frequency is adjusted according to the condensing temperature, and the opening degree of the indoor expansion valve is adjusted according to the supercooling degree of the indoor unit. Wherein, the initial target condensing temperature needs to be calculated, and the initial target supercooling degree needs to be calculated; the target condensing temperature and the target supercooling degree are adjusted according to the indoor temperature change; the compressor frequency is adjusted according to the target condensing temperature, and the opening degree of the indoor expansion valve is adjusted according to the target supercooling degree, so that the compressor frequency and the opening degree of the indoor expansion valve are adjusted following the change of the indoor load, and the indoor load requirement is met in real time.

[0156] Since the load of each room is not necessarily exactly the same, the heat storage, heat leakage and internal disturbance parameters are determined for each room respectively.

[0157] The load characteristic parameters ai, bi and ci in the space of the room corresponding to the i-th indoor unit are determined. i = 1, 2, …, n.

[0158] Wherein: ai is the air heat storage characteristic parameter in the space of the room corresponding to the i-th indoor unit.

[0159] bi is the heat leakage performance characteristic parameter of the room corresponding to the i-th indoor unit.

[0160] ci is the internal disturbance characteristic parameter of the room corresponding to the i-th indoor unit.

[0161] In some embodiments, the heat storage parameter ai, the heat leakage parameter bi, and the internal disturbance parameter ci can be inputted according to the size of the space in the building, the heat transfer parameter of the wall of the building, and the number of heat sources in the room.

[0162] The size of the room space is obtained, and the heat storage parameter ai is calculated according to the size of the room space.

[0163] In some embodiments, the heat storage parameter ai = c * Vi * p, where c is the specific heat capacity of air, Vi is the size of the room space, and p is the air density.

[0164] The room heat transfer coefficient and the room area are obtained, and the heat leakage parameter bi is calculated according to the room heat transfer coefficient and the room area.

[0165] In some embodiments, the heat leakage parameter bi = Ki * Ai, where Ki is the wall heat transfer coefficient, and Ai is the room area.

[0166] The heat generation of the heat source in the room is obtained, and the internal disturbance parameter ci is calculated according to the heat generation of the heat source in the room.

[0167] In some embodiments, the internal disturbance parameter ci = Ni + Wi, where Ni is the heat generation corresponding to the number of people living in the room, and Wi is the heat generation of the always-on equipment in the room.

[0168] In the above, Vi, Ki, Ai, Ni, and Wi are user input values.

[0169] In some embodiments, the indoor unit obtains the heat storage parameter ai, the heat leakage parameter bi, and the internal disturbance parameter ci of the corresponding room and sends them to the outdoor unit.

[0170] In some embodiments, the capacity of the indoor unit is obtained, and the heat storage parameter ai, the heat leakage parameter bi, and the internal disturbance parameter ci are calculated according to the capacity of the indoor unit.

[0171] If the user does not input the related parameters, the outdoor unit calculates the heat storage parameter ai, the heat leakage parameter bi, and the internal disturbance parameter ci according to the nominal capacity HP of the indoor unit, and the calculation method is as follows:

[0172] ai = HP i *k1.

[0173] bi = HP i *k2.

[0174] ci = HP i *k3.

[0175] Wherein: k1, k2, and k3 are constants, for example: 20 ≤ k1 ≤ 200, 0.01 ≤ k2 ≤ 1, and 0 ≤ k3 ≤ 2; and HPi is the capacity of the i-th indoor unit.

[0176] The control process is as follows:

[0177] Step 201, after the system is started, the indoor unit operating state is detected, if it is a heating state, the following control is continued, if it is a cooling state, the following control is not performed.

[0178] Step 202, after starting, initial value control is first performed. That is, when the indoor unit operates in a heating mode, the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are calculated according to the load coefficient corresponding to the heating mode and the capacity of the indoor unit after starting. The load coefficient corresponding to the heating mode is determined according to the heat storage amount, the heat leakage amount, the internal disturbance amount, and the capacity of the indoor unit.

[0179] The initial frequency of the compressor is a constant N*∑, which is the product of the capacity of the started indoor unit and the load coefficient corresponding thereto.

[0180] In some embodiments, the initial frequency of the compressor H1=H10; Wherein, m is the number of started indoor units.

[0181] The initial opening degree of the indoor expansion valve is a constant M, which is the product of the capacity of the indoor unit and the load coefficient corresponding thereto. In some embodiments, the initial opening degree of the indoor expansion valve EVI=EVI0; EVI0=M*HP i *k i .

[0182] Wherein: N, M are constants, for example: N=15, M=800.

[0183] HP i : the capacity of the i indoor unit.

[0184] k i : the load coefficient, Wherein, y is a constant, for example: y=3;△T i is the desired room temperature change amount,△T i =f(T si -T ii ), f is a constant, for example: f=0.3; T si is the user set temperature of the i indoor unit; T ii is the indoor temperature of the i indoor unit; T a is the outdoor environment temperature; t is the control period, for example: t=60s.

[0185] After the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are determined, the multi-split air conditioner is started to operate at the initial frequency of the compressor, and the opening degree of the indoor expansion valve is adjusted to the initial opening degree of the indoor expansion valve.

[0186] Step 203, the frequency of the compressor is adjusted according to the condensing temperature, and the opening degree of the indoor expansion valve is adjusted according to the supercooling degree of the indoor unit.

[0187] In some embodiments, step 203 can include:

[0188] Step S510, calculating an initial target condensing temperature, calculating an initial target supercooling degree;

[0189] Step S530, adjusting the target condensing temperature and the target supercooling degree according to the indoor temperature change; and

[0190] Step S550, adjusting the compressor frequency according to the target condensing temperature, and adjusting the indoor expansion valve opening degree according to the target supercooling degree.

[0191] Wherein, the compressor frequency is controlled according to the current condensing temperature; the condensing temperature TC is collected by the high-pressure sensor Pd and the saturated temperature is calculated to obtain. The indoor unit expansion valve is controlled according to the indoor unit supercooling degree SCi=TC-Tli.

[0192] In step S510, the process of calculating the initial target condensing temperature includes: calculating the target condensing temperature of each indoor unit according to the indoor temperature + (the difference between the heat storage amount and the heat leakage amount, the internal disturbance amount) / the indoor unit performance coefficient, and the maximum value of all indoor unit target condensing temperatures is the initial target condensing temperature.

[0193] Calculate the initial target condensing temperature TCo:

[0194] Calculate the target condensing temperature TCio of each indoor unit, and take the maximum TCio of each indoor unit as the system target condensing temperature (i.e. the initial target condensing temperature): TCo=max(TCio).

[0195] di is the indoor unit performance coefficient, which is a built-in value, for example: di=0.6.

[0196] In step S510, the process of calculating the initial target supercooling degree includes: calculating the dimensionless supercooling degree of the indoor unit according to the formula of the indoor unit supercooling degree / (the difference between the condensing temperature and the indoor temperature), calculating the average value of all indoor unit dimensionless supercooling degrees, and calculating the initial target supercooling degree according to the formula of the average value of all indoor unit dimensionless supercooling degrees * (the difference between the condensing temperature and the indoor temperature).

[0197] Calculate the initial target supercooling degree SCio:

[0198] SCio=SCdlio*(TC-Tii), SCdlio is the target dimensionless supercooling degree of the indoor unit.

[0199] SCdlio=SCdlave, SCdlave is the average value of all indoor unit SCdli, and the indoor unit dimensionless supercooling degree SCdli=SCi / (TC-Tii), SCi is the supercooling degree of the i indoor unit.

[0200] The relationship between the dimensionless supercooling degree SCdli of the indoor unit and the capacity of the indoor unit is fixed, and is irrelevant to the ambient temperature. The influence of the supercooling degree SC on the capacity of the indoor unit is affected by the ambient temperature, so when calculating the target supercooling degree of the indoor unit, the target dimensionless supercooling degree SCdlio needs to be calculated according to the required capacity of the indoor unit first, and then the target supercooling degree SCio is calculated by using the target dimensionless supercooling degree SCdlio, which is more accurate than directly calculating the target supercooling degree SCio.

[0201] In step S530, the process of adjusting the target condensing temperature according to the indoor temperature change includes: obtaining the indoor temperature of the current period and the indoor temperature of the previous period and calculating the indoor temperature difference, calculating the current expected indoor temperature change amount, when the indoor temperature difference exceeds the current expected indoor temperature change amount, the target condensing temperature of the indoor unit is reduced by a set temperature; when the indoor temperature difference does not exceed the current expected indoor temperature change amount, the target condensing temperature of the indoor unit is increased by a set temperature; when the indoor temperature difference is the same as the current expected indoor temperature change amount, the target condensing temperature of the indoor unit is unchanged.

[0202] TCo = max (TCio), TCio has upper and lower limits, for example: 60 ≥ TCio ≥ 25.

[0203] For example, in the example of FIG. 7, the target condensing temperature TCio adjustment process of the i-th indoor unit is:

[0204] S531, start.

[0205] S532, read the indoor temperature of the previous period Tii(j-1) and the indoor temperature of the current period Tii(j).

[0206] S533, calculate the current expected indoor temperature change amount ΔT = f (Tsi-Tii(j)).

[0207] S534, judge Tii(j)-Tii(j-1) > ΔT, if yes, go to step S535, otherwise, go to step S536.

[0208] S535, TCio(j+1) = TCio(j)-△TCio. Go to step S532.

[0209] S536, judge Tii(j)-Tii(j-1) < ΔT, if yes, go to step S537, otherwise, go to step S538.

[0210] S537, TCio(j+1) = TCio(j)+△TCio. Go to step S532.

[0211] S538, TCio(j+1) = TCio(j). Go to step S532.

[0212] Wherein, TCio(j+1), TCio(j) are the next cycle target TCio, current cycle TCio respectively, △TCio is the iteration step, for example: △TCio = 0.5.

[0213] The target condensing temperature TCo(j+1) of the next cycle = max(TCio(j+1)).

[0214] In step S530, the process of adjusting the target supercooling degree according to the indoor temperature change includes: when the indoor temperature difference exceeds the current expected room temperature change amount, the indoor unit supercooling coefficient increases by a set supercooling value; when the indoor temperature difference does not exceed the current expected room temperature change amount, the indoor unit supercooling coefficient decreases by a set supercooling value; when the indoor temperature difference is the same as the current expected room temperature change amount, the indoor unit supercooling coefficient does not change, and the target supercooling degree is calculated through the indoor unit supercooling coefficient.

[0215] For example, in the example of FIG. 8, the target dimensionless supercooling degree SCdlio adjustment process of the i-th indoor unit is:

[0216] S541, start.

[0217] S542, read the i-th indoor unit supercooling degree coefficient fi. The initial value of fi is a constant, for example: fi = 10.

[0218] S543, read the indoor temperature Tii(j-1) of the previous cycle and the indoor temperature Tii(j) of the current cycle.

[0219] S544, calculate the current expected room temperature change amount △T = f(Tsi-Tii(j)).

[0220] S545, judge Tii(j)-Tii(j-1) > △T, if yes, go to step S546, otherwise, go to step S547.

[0221] S546, fi(j+1) = fi(j) + △fi. Go to step S5410.

[0222] S547, judge Tii(j)-Tii(j-1) < △T, if yes, go to step S548, otherwise, go to step S549.

[0223] S548, fi(j+1) = fi(j) - △fi. Go to step S5410.

[0224] S549, fi(j+1) = fi(j).

[0225] S5410, SCdlio(j+1) = (fi(j+1) / sum(fi(j+1)))*SCdlave(j+1)*m. Go to step S543.

[0226] Thus, SCio(j+1) = SCdlio(j+1)*(TC-Tii(j)).

[0227] Wherein, fi(j+1), fi(j) are next cycle target fi, current cycle fi respectively, sum(fi) is sum of all indoor units fi, and △fi is iteration step length, for example: △fi = 0.5.

[0228] In step S550, the process of adjusting the compressor frequency according to the target condensing temperature includes: obtaining the condensing temperature, calculating the difference between the condensing temperature and the target condensing temperature, reducing the compressor frequency when the difference exceeds the maximum value of the set interval; increasing the compressor frequency when the difference does not exceed the minimum value of the set interval; and keeping the compressor frequency unchanged when the difference is within the set interval.

[0229] For example, in the example of FIG. 9, the compressor frequency control flow is as follows:

[0230] S551, start.

[0231] S552, read the detection value of the high-pressure sensor Pd.

[0232] S553, calculate the condensing temperature TC.

[0233] S554, calculate the difference between the condensing temperature TC and the target condensing temperature TCo, TC-TCo≥σ, if yes, go to step S555, otherwise, go to step S556.

[0234] S555, Hi(j+1) = Hi(j)-△Hi. Go to step S552.

[0235] S556, TC-TCo≤-σ, if yes, go to step S557, otherwise, go to step S558.

[0236] S557, Hi(j+1) = Hi(j)+△Hi. Go to step S552.

[0237] S558, Hi(j+1) = Hi(j). Go to step S552.

[0238] Wherein, σ is a control constant, for example: σ = 0.5, Hi(j+1), Hi(j) are next cycle target Hi, current cycle Hi respectively, and △Hi is the iteration step length of Hi, for example: △Hi = 2.

[0239] In step S550, the process of adjusting the indoor expansion valve opening degree according to the target supercooling degree includes: obtaining the indoor supercooling degree, calculating the difference between the indoor supercooling degree and the target supercooling degree, increasing the indoor expansion valve opening degree when the difference exceeds the maximum value of the set interval, decreasing the indoor expansion valve opening degree when the difference does not exceed the minimum value of the set high interval, and keeping the indoor expansion valve opening degree unchanged when the difference is in the set interval.

[0240] For example, in the example of FIG. 10, the indoor expansion valve control flow is as follows:

[0241] S561, start.

[0242] S562, read the indoor liquid pipe temperature Tli and the condensing temperature TC.

[0243] S563, calculate the indoor supercooling degree SCi = TC-Tli.

[0244] S564, calculate the difference between the indoor supercooling degree SCi and the target supercooling degree SCio, and determine whether SCi-SCio≥δ, if yes, go to step S565, otherwise, go to step S566.

[0245] S565, EVI(j+1)=EVI(j)+△EVI. Go to step S562.

[0246] S566, determine whether SCi-SCio≤-δ, if yes, go to step S567, otherwise, go to step S568.

[0247] S567, EVI(j+1)=EVI(j)-△EVI. Go to step S562.

[0248] S568, EVI(j+1)=EVI(j). Go to step S562.

[0249] Wherein, δ is a control constant, for example: δ = 0.5, EVI(j+1) and EVI(j) are the next cycle target EVI and the current cycle EVI respectively, and △EVI is the EVI iteration step, for example: △EVI = 10.

[0250] The control method of the multi-split air conditioner based on the actual load of the building adjusts the compressors and expansion valves, which can match the air conditioning capacity with the actual load of the building, and solve the problems of overplay and underplay of the indoor unit capacity.

[0251] In some embodiments, the system detects the running state of the indoor unit after starting, and if it is in a cooling state, the corresponding implementation method of steps 2 and 3 is executed, and if it is in a heating state, the corresponding implementation method of steps 530 and 550 is executed.

[0252] In the description of the above-mentioned embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0253] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A control method of a multi VRF system including an outdoor unit and at least two indoor units, each indoor unit including an indoor expansion valve, wherein, The control method comprises: After starting, the running state of each indoor unit after starting is detected; When the indoor unit runs in a cooling mode, the initial frequency of the compressor and the initial opening degree of the indoor expansion valve are calculated according to the load coefficient corresponding to the cooling mode and the capacity of the indoor unit after starting, the load coefficient being determined according to the heat storage amount, the heat leakage amount, the internal disturbance amount and the capacity of the indoor unit; Based on the initial frequency of the compressor, the frequency of the compressor is adjusted according to the evaporation temperature, and based on the initial opening degree of the indoor expansion valve, the opening degree of the indoor expansion valve is adjusted according to the superheat degree of the indoor unit.

2. The control method of a VRF system according to claim 1, wherein, After the step of detecting the running state of each indoor unit after starting, the method further comprises: The heat storage, heat leakage and internal disturbance parameters of the room corresponding to each indoor unit are determined; The heat storage amount is calculated according to the heat storage parameter and the expected room temperature change amount, the heat leakage amount is calculated according to the heat leakage parameter and the difference between the outdoor temperature and the indoor temperature, and the internal disturbance amount is calculated according to the internal disturbance parameter, the expected room temperature change amount being the difference between the indoor environment temperature and the indoor set temperature; The load coefficient is calculated according to the heat storage amount, the heat leakage amount, the internal disturbance amount and the capacity of the indoor unit.

3. The control method of a VRF system according to claim 2, wherein, The step of determining the heat storage, heat leakage and internal disturbance parameters of the room corresponding to each indoor unit comprises: The room space size is obtained, and the heat storage parameter is calculated according to the room space size; The room heat transfer coefficient and the room area are obtained, and the heat leakage parameter is calculated according to the room heat transfer coefficient and the room area; The heat generation amount of the heat source in the room is obtained, and the internal disturbance parameter is calculated according to the heat generation amount of the heat source in the room.

4. The control method of a multi VRF system according to claim 2, wherein, The step of determining the heat storage, heat leakage and internal disturbance parameters of the room corresponding to each indoor unit comprises: The capacity of the indoor unit is obtained, and the heat storage, heat leakage and internal disturbance parameters are calculated according to the capacity of the indoor unit.

5. The control method of a VRF system according to claim 4, wherein, The calculation formulae of the heat storage parameter ai, the heat leakage parameter bi and the internal disturbance parameter ci are as follows: ai=HPi*k1; bi=HPi*k2; ci=HPi*k3; Wherein: k1, k2, k3 are constants, for example: 20≤k1≤200, 0.01≤k2≤1, 0≤k3≤2; HPi is the capacity of the i indoor unit.

6. The control method of a VRF system according to any one of claims 1 to 5, wherein, The compressor initial frequency is H10, The indoor expansion valve initial opening degree is EVI0, EVI0=M*HP i *k i Wherein, m is the number of started indoor units, N, M are constants, HP i is the capacity of the ith indoor unit, k i is the load coefficient.

7. The control method of a VRF system according to claim 6, wherein, where x is a constant; ΔT i is a desired room temperature change amount; ΔT i = f(T ii - T si ), f is a constant; T si is a user set temperature of the i-th indoor unit; T ii is an indoor temperature of the i-th indoor unit; T a is an outdoor ambient temperature; t is a control period, ai, bi, and ci are a heat storage parameter, a heat leakage parameter, and an internal disturbance parameter, respectively.

8. The control method of a VRF system according to any one of claims 1 to 7, wherein, The step of adjusting the frequency of the compressor according to the evaporation temperature based on the initial frequency of the compressor and adjusting the opening degree of the indoor expansion valve according to the superheat degree of the indoor unit based on the initial opening degree of the indoor expansion valve comprises: The initial target evaporation temperature and the initial target superheat degree are calculated; The target evaporation temperature and the target superheat degree are adjusted according to the change of the indoor temperature; and The frequency of the compressor is adjusted according to the target evaporation temperature based on the initial frequency of the compressor, and the opening degree of the indoor expansion valve is adjusted according to the target superheat degree based on the initial opening degree of the indoor expansion valve.

9. The control method of a VRF system according to claim 8, wherein, The step of calculating the initial target evaporation temperature comprises: the target evaporation temperature of each indoor unit is calculated according to the indoor temperature, the heat storage amount, the heat leakage amount, the internal disturbance amount and the performance coefficient of the indoor unit, and the initial target evaporation temperature is the minimum value of the target evaporation temperatures of all the indoor units.

10. The control method of a VRF system according to claim 9, wherein, The initial target evaporation temperature is Tlo, and the range of Tlo is 15≥Tlo≥2.

11. The control method of a VRF system according to any one of claims 7-10, wherein, Each indoor unit has an initial target superheat degree SHio f1, f2 are coefficients; Tlio is the target evaporation temperature of the i indoor unit; T ii is the indoor temperature of the i indoor unit; T a is the outdoor ambient temperature; t is the control period; ai, bi and ci are the heat storage parameter, heat leakage parameter and internal disturbance parameter respectively; △T i is the expected indoor temperature change of the i indoor unit; △T i = f(T ii -T si ), f is a constant, T si is the user set temperature of the i indoor unit, di is the indoor unit performance coefficient, which is a built-in value.

12. The control method of a VRF system according to any one of claims 7-11, wherein, The step of adjusting the target evaporation temperature and the target superheat degree according to the change of the indoor temperature comprises: The step of adjusting the target evaporation temperature according to the change of the indoor temperature comprises: obtaining the indoor temperature of the previous period and the indoor temperature of the current period and calculating the indoor temperature difference; calculating the current expected indoor temperature change amount, when the indoor temperature difference exceeds the current expected indoor temperature change amount, increasing the indoor unit target evaporation temperature by a set temperature, and the initial value of the indoor unit target evaporation temperature being the initial target evaporation temperature; when the indoor temperature difference does not exceed the current expected indoor temperature change amount, decreasing the indoor unit target evaporation temperature by a set temperature; and when the indoor temperature difference is equal to the current expected indoor temperature change amount, the indoor unit target evaporation temperature remains unchanged; the step of adjusting the target superheat degree according to the indoor temperature change comprises: when the indoor temperature difference exceeds the current expected indoor temperature change amount, increasing the target superheat degree by a set superheat degree, and the initial value of the target superheat degree being the initial target superheat degree; when the indoor temperature difference does not exceed the current expected indoor temperature change amount, decreasing the target superheat degree by a set superheat degree; when the indoor temperature difference is equal to the current expected indoor temperature change amount, the target superheat degree remains unchanged.

13. The control method of a VRF system according to any one of claims 7 to 12, wherein, the step of adjusting the compressor frequency according to the target evaporation temperature based on the initial compressor frequency comprises: obtaining the evaporation temperature, calculating the difference between the average value of the evaporation temperature and the target evaporation temperature, increasing the compressor frequency based on the current compressor frequency when the difference exceeds the maximum value of the set interval, the initial value of the compressor frequency being the initial compressor frequency, decreasing the compressor frequency based on the current compressor frequency when the difference does not exceed the minimum value of the set interval, and the compressor frequency remaining unchanged when the difference is within the set interval.

14. The control method of a VRF system according to claim 13, wherein, the maximum value of the set interval is σ, the minimum value of the set interval is -σ, and σ is a control constant.

15. The control method of a VRF system according to any one of claims 7 to 14, wherein, the step of adjusting the indoor expansion valve opening degree according to the target superheat degree based on the initial indoor expansion valve opening degree comprises: obtaining the indoor unit superheat degree, and calculating the difference between the indoor unit superheat degree and the target superheat degree; increasing the indoor expansion valve opening degree based on the current indoor expansion valve opening degree when the difference exceeds the maximum value of the set interval, the initial value of the indoor expansion valve opening degree being the initial indoor expansion valve opening degree; decreasing the indoor expansion valve opening degree when the difference does not exceed the minimum value of the set interval, and the indoor expansion valve opening degree remaining unchanged when the difference is within the set interval.

16. The control method of a VRF system according to claim 15, wherein, the step of obtaining the indoor unit superheat degree comprises: obtaining the indoor liquid pipe temperature and the indoor gas pipe temperature; calculating the indoor unit superheat degree based on the indoor liquid pipe temperature and the indoor gas pipe temperature.

17. The control method of a VRF system according to claim 16, wherein, the indoor unit superheat degree is the difference between the indoor gas pipe temperature and the indoor liquid pipe temperature.

18. A control method of a multi VRF system including an outdoor unit and at least two indoor units, each indoor unit including an indoor expansion valve, wherein, the control method comprises: after starting, detecting the operating state of each indoor unit after starting; when the indoor unit is running in a cooling mode, calculating the initial compressor frequency and the initial indoor expansion valve opening degree according to the load coefficient corresponding to the cooling mode and the capacity of the indoor unit after starting, and the load coefficient corresponding to the cooling mode being determined according to the heat storage amount, the heat leakage amount, the internal disturbance amount, and the capacity of the indoor unit; adjusting the compressor frequency according to the evaporating temperature based on the initial frequency of the compressor, adjusting the opening of the indoor expansion valve according to the superheat of the indoor unit based on the initial opening of the indoor expansion valve; calculating the initial frequency of the compressor and the initial opening of the indoor expansion valve according to the load coefficient corresponding to the heating mode and the capacity of the indoor unit after starting when the indoor unit operates in the heating mode, the load coefficient corresponding to the heating mode being determined according to the heat storage amount, the heat leakage amount, the internal disturbance amount and the capacity of the indoor unit; adjusting the compressor frequency according to the condensing temperature based on the initial frequency of the compressor in the heating state, adjusting the opening of the indoor expansion valve according to the subcooling degree of the indoor unit based on the initial opening of the indoor expansion valve in the heating state.

19. The control method of a VRF system according to claim 18, wherein, The condensing temperature is obtained by a high-pressure sensor and a saturation temperature is calculated, and the subcooling degree of the indoor unit is the difference between the condensing temperature and the temperature of the liquid pipe of the indoor unit, which is obtained by a liquid pipe temperature detection module.

20. The control method of a VRF system according to claim 19, wherein, The steps of adjusting the compressor frequency according to the condensing temperature based on the initial frequency of the compressor in the heating state and adjusting the opening of the indoor expansion valve according to the subcooling degree of the indoor unit based on the initial opening of the indoor expansion valve in the heating state comprise: calculating an initial target condensing temperature and an initial target subcooling degree; adjusting the target condensing temperature and the target subcooling degree according to the change of the indoor temperature; adjusting the compressor frequency according to the target condensing temperature and adjusting the opening of the indoor expansion valve according to the target subcooling degree.

21. The control method of a VRF system according to claim 20, wherein, The step of calculating the initial target condensing temperature comprises calculating the target condensing temperature of each indoor unit according to the indoor temperature, the heat storage amount, the heat leakage amount, the internal disturbance amount and the performance coefficient of the indoor unit, and the initial target condensing temperature being the maximum value of the target condensing temperatures of all the indoor units.

22. The control method of a VRF system according to claim 21, wherein, The step of calculating the initial target subcooling degree comprises calculating the dimensionless subcooling degree of the indoor unit according to the subcooling degree of the indoor unit, the condensing temperature and the indoor temperature, calculating the average value of the dimensionless subcooling degrees of all the indoor units, and calculating the initial target subcooling degree according to the average value of the dimensionless subcooling degrees of all the indoor units, the condensing temperature and the indoor temperature.

23. The control method of a VRF system according to any one of claims 21 to 22, wherein, The step of adjusting the target condensing temperature according to the change of the indoor temperature comprises: obtaining the indoor temperature of the current period and the indoor temperature of the previous period, calculating the difference of the indoor temperatures, calculating the expected change of the indoor temperature of the current period, and decreasing the target condensing temperature of the indoor unit by a set temperature when the difference of the indoor temperatures exceeds the expected change of the indoor temperature of the current period; increasing the target condensing temperature of the indoor unit by the set temperature when the difference of the indoor temperatures does not exceed the expected change of the indoor temperature of the current period; keeping the target condensing temperature of the indoor unit unchanged when the difference of the indoor temperatures is equal to the expected change of the indoor temperature of the current period.

24. The control method of a VRF system according to claim 23, wherein, The step of adjusting the compressor frequency according to the target condensing temperature comprises: obtaining the condensing temperature, calculating the difference between the condensing temperature and the target condensing temperature, decreasing the compressor frequency when the difference exceeds the maximum value of a set interval, increasing the compressor frequency when the difference does not exceed the minimum value of the set interval, and keeping the compressor frequency unchanged when the difference is within the set interval. The step of adjusting the target subcooling degree according to the change of the indoor temperature comprises: ​ 25. The control method of a VRF system according to claim 20, wherein, ​ Obtaining an indoor unit supercooling degree coefficient, an initial value of the indoor unit supercooling degree coefficient being a constant; Obtaining a current period indoor temperature and a previous period indoor temperature and calculating an indoor temperature difference value; Calculating a current expected indoor temperature change value according to a difference between an indoor set temperature and the current period indoor temperature; When the indoor temperature difference value exceeds the current expected indoor temperature change value, increasing the indoor unit supercooling degree coefficient by a set supercooling value; When the indoor temperature difference value does not exceed the current expected indoor temperature change value, decreasing the indoor unit supercooling degree coefficient by a set supercooling value; When the indoor temperature difference value is equal to the current expected indoor temperature change value, the indoor unit supercooling degree coefficient remains unchanged, and the target supercooling degree is calculated through the indoor unit supercooling degree coefficient.

26. The control method of a VRF system according to claim 25, wherein, The step of adjusting an indoor expansion valve opening degree according to the target supercooling degree comprises: Obtaining an indoor unit supercooling degree, calculating a difference value between the indoor supercooling degree and the target supercooling degree; When the difference value exceeds a maximum value of a set interval, increasing the indoor expansion valve opening degree; When the difference value does not exceed a minimum value of a set high interval, decreasing the indoor expansion valve opening degree, and when the difference value is in the set interval, the indoor expansion valve opening degree remains unchanged.

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