Dual-system frequency conversion cascade control system

Abstract

The invention relates to a dual-system frequency conversion cascade control system, and belongs to the technical field of heat pump control systems. According to the system, the working state can be adjusted according to the real-time environment change through frequency adjustment of the variable-frequency press, reasonable starting and stopping of the fixed-frequency press and intelligent control over the defrosting mode, and frequent mechanical abrasion is avoided, the service life of equipment is prolonged and the optimal energy efficiency is achieved by reducing unnecessary press starting and stopping and delay control.

Description

Technical Field

[0001] The invention belongs to the technical field of heat pump control systems, and in particular relates to a dual-system variable frequency cascade control system. Background Art

[0002] With the improvement of living standards, the requirements for clean energy are getting higher and higher. Heat pumps are now widely used in domestic hot water, heating and other fields, and the scope of application is constantly expanding. Although heat pumps have many advantages such as safety and cleanliness, they have certain limitations. For example, single-stage compressors cannot heat the temperature to a very high temperature. General water heaters are heated to about 55°C. Therefore, heat pumps need to be specially designed in application places where high-temperature heat sources are required, and heat pumps in the form of two-stage heating have come into being. However, when both stages of the heat pump use fixed-frequency compressors, since the compressor cannot be started and stopped frequently, the conventional practice is to start the compressor again after at least 3 minutes. Frequent startup not only shortens the life of the compressor, but also wastes electricity, causing grid shocks and affecting the normal use of other electrical appliances. To avoid frequent startup, the system design must be very precise, which increases the difficulty of system design; if both stages use variable-frequency compressors, although the problem of frequent compressor startup is solved, it is intuitive to see that the cost of electronic control will increase greatly. Summary of the invention

[0003] In order to solve at least one of the above problems existing in the prior art, the present invention provides a dual-system variable frequency cascade control system.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A control system includes a dual system consisting of a fixed frequency system and a variable frequency system, wherein the fixed frequency system includes a fixed frequency compressor and a fixed frequency four-way valve, and the variable frequency system includes a variable frequency compressor and a variable frequency four-way valve;

[0006] After the system is turned on, the water inlet temperature is detected to control whether the system is running heating work;

[0007] When the system starts to operate the heating operation, the variable frequency compressor is turned on and the condensing temperature is detected. If the condensing temperature is not less than the first temperature, the fixed frequency compressor is turned on after the variable frequency compressor is turned on for the first time; if the condensing temperature is less than the first temperature, the fixed frequency compressor is turned on after the condensing temperature on the variable frequency side rises to the first temperature;

[0008] Among them, when the fixed-frequency compressor is turned on, the system notifies the detection and judgment of the condensing temperature;

[0009] When the system stops heating, the variable frequency compressor is turned off, and the fixed frequency compressor is turned off after the variable frequency compressor has a delay of the second time.

[0010] In a further embodiment of the present invention, when the system starts the compressor in heating operation, the frequency is increased to 50 Hz and maintained for 5 minutes, and then the operating frequency of the variable frequency compressor is adjusted according to the ambient temperature, the condensing temperature and the condensing target temperature;

[0011] The condensation target temperature is a preset value switched according to the ambient temperature;

[0012] Among them, when the condensing temperature on the frequency conversion side is not greater than the difference between the condensing target temperature and 1, the frequency of the frequency conversion compressor increases at a rate of 1Hz / 10s to a maximum operating frequency of 85Hz;

[0013] When the condensing temperature on the variable frequency side is less than the sum of the condensing target temperature and 1 and greater than the difference between the condensing target temperature and 1, the frequency of the variable frequency compressor remains unchanged;

[0014] When the condensing temperature on the variable frequency side is not less than the sum of the condensing target temperature and 1, the frequency of the variable frequency compressor decreases at a rate of 1 Hz / 10s.

[0015] In a further embodiment of the present invention, when the water inlet temperature is not greater than the difference between the preset heating setting temperature and the preset return temperature, the system starts to operate the heating operation;

[0016] When the inlet water temperature is not less than the preset heating set temperature, the system stops heating.

[0017] In a further embodiment of the present invention, the system further comprises a fan and a water pump;

[0018] The system is set with a defrost mode. When the system enters the defrost mode, the defrost work will be performed;

[0019] The system performs the following operations when running defrost:

[0020] Step S101: The variable frequency four-way valve is powered on, the compressor is reduced to 30 Hz, and step S102 is executed after 55 seconds;

[0021] Step S102: Turn off the fan, open the main electronic expansion valve and the auxiliary electronic expansion valve to the defrosting opening, and execute step S103 after 5 seconds;

[0022] Step S103: the press starts to rise;

[0023] Step S104: the water pump keeps running;

[0024] The system performs the following operations when it exits defrosting operation:

[0025] Step S201: the compressor is reduced to 30 Hz, and step S202 is executed after 50 seconds;

[0026] Step S202: the variable frequency four-way valve is powered off, the fan is started, and step S203 is executed after 10 seconds;

[0027] Step S203: The compressor returns to normal control frequency.

[0028] In a further embodiment of the present invention, the condition for the system to enter the defrost mode when operating the heating operation is:

[0029] Condition 101: The cumulative operation time of the compressor is not less than 70 minutes and the continuous operation time of the compressor is not less than 5 minutes. At the same time, the temperature of the external coil is less than -3 degrees Celsius;

[0030] Condition 102: The difference between the ambient temperature and the external coil temperature is not less than 8°C, and at the same time, the ambient temperature is not less than -7°C and the ambient temperature is not greater than the preset defrost ambient temperature and lasts for 30 seconds;

[0031] Condition 103: The difference between the ambient temperature and the external coil temperature is not less than 8°C and the ambient temperature is less than -7°C and maintained for 30 seconds;

[0032] When the system satisfies condition 101 and satisfies any one of condition 102 and condition 103 , the system enters the defrost mode.

[0033] In a further embodiment of the present invention, when the system meets the conditions for operating the heating operation, it also meets the following conditions:

[0034] Condition 201: System shutdown, system standby or compressor power-off time shall not be less than 30 minutes;

[0035] Condition 202: The ambient temperature is not less than -7°C and not more than 3°C, and the coil temperature is less than the preset defrost entry temperature;

[0036] The system stops heating and enters defrost mode.

[0037] In a further embodiment of the present invention, the condition for the system to exit the defrost mode is: the temperature of the external coil is not less than a preset defrost exit temperature or the defrost time reaches 10 minutes.

[0038] In a further embodiment of the present invention, the system further comprises an electronic expansion valve; when the system is powered on, the electronic expansion valve of the frequency conversion system is reset and the opening is adjusted to the initial opening;

[0039] When the exhaust temperature is not greater than the preset main expansion valve regulated exhaust temperature, the main expansion valve is controlled according to the EV action;

[0040] When the difference between the exhaust temperature and the preset exhaust temperature adjusted by the main expansion valve is not less than 5°C, the main expansion valve opens 10 steps every 30 seconds;

[0041] The EV action is:

[0042] EXV n =(EXV n-1 )+[K P *(DTC n -DST)+K D *(DTC n -DTC n-1 )],

[0043] DTCn=T S -T p ,

[0044] When the system is equipped with a pressure sensor:

[0045] DTCn=T S -T Z ,

[0046] Among them, EXV n is the actual opening of the electronic expansion valve; EXV n-1 K is the last opening of the electronic expansion valve; P is the superheat proportional coefficient; K D is the superheat differential coefficient; DTC n is the actual target superheat; DST is the set target superheat; DTC n-1 is the last target overheat; T S is the compressor return air temperature; T Z is the low pressure temperature; T p is the outdoor coil temperature.

[0047] In a further embodiment of the present invention, after the electronic expansion valve of the variable frequency system is reset, the opening is adjusted to 350P; and then the expansion valve of the fixed frequency system is adjusted to an opening of 230P;

[0048] The main expansion valve of the frequency conversion system is adjusted to the corresponding opening degree according to the adjustment mode and ambient temperature.

[0049] In a further embodiment of the present invention, the system is also provided with a fault detection function, including but not limited to communication fault, ambient temperature fault, water inlet temperature fault, and water outlet temperature fault.

[0050] The beneficial effects of the present invention are as follows: through frequency regulation of the variable frequency compressor, reasonable start and stop of the fixed frequency compressor and intelligent control of the defrost mode, the system can adjust the working state according to real-time environmental changes, and by reducing unnecessary compressor start and stop and delay control, frequent mechanical wear is avoided, the use of the equipment is extended, and optimal energy efficiency is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0052] Figure 1 A system operation flow chart provided in one embodiment of the present invention;

[0053] Figure 2 This is a control flow chart of a variable frequency compressor provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0055] Please refer to Figure 1 The present embodiment provides a dual-system variable frequency cascade control system, the control system includes a dual system consisting of a fixed frequency system and a variable frequency system, the fixed frequency system includes a fixed frequency compressor and a fixed frequency four-way valve, the variable frequency system includes a variable frequency compressor and a variable frequency four-way valve;

[0056] After the system is turned on, the water inlet temperature is detected to control whether the system is running heating work;

[0057] When the system starts heating, the variable frequency compressor is turned on and the condensing temperature is detected. If the condensing temperature is not less than the first temperature of 20°C, the fixed frequency compressor is turned on after the variable frequency compressor is turned on for the first time; if the condensing temperature is less than the first temperature, the fixed frequency compressor is turned on after the condensing temperature on the variable frequency side rises to the first temperature;

[0058] Among them, when the fixed-frequency compressor is turned on, the system notifies the detection and judgment of the condensing temperature;

[0059] When the system stops heating, the variable frequency compressor is turned off, and the fixed frequency compressor is turned off after the variable frequency compressor has a delay of the second time.

[0060] The first time is 5s, the second time is 30s, the first temperature is 20℃, the system has 3-minute protection for the compressor, and the compressor must wait at least three minutes after shutting down before it can be turned on again (there is no 3-minute protection for the first power-on). At the same time, either the variable frequency compressor or the fixed frequency compressor triggers the shutdown protection and enters the shutdown state, and both the variable frequency compressor and the fixed frequency compressor stop running.

[0061] In this embodiment, a dual-system variable frequency cascade control system is proposed, including a fixed frequency system and a variable frequency system. The fixed frequency system includes a fixed frequency compressor and a fixed frequency four-way valve, while the variable frequency system includes a variable frequency compressor and a variable frequency four-way valve. The system accurately controls the start and stop and working status of the equipment through real-time monitoring and adjustment of multiple parameters such as inlet water temperature, condensation temperature, and ambient temperature. After the system is turned on, the inlet water temperature is detected, and the heating mode is determined by detecting the inlet water temperature. Only when the inlet water temperature meets the preset conditions will the system start to operate the heating work.

[0062] The dual-system cascade machine is a combination of two single-system cascade machines, designed to adapt to the occasions of greater heat supply. After power-on, system 1 starts first, and after 30 seconds, system 2 starts. This can avoid the simultaneous startup of the two systems, which will cause too much impact on the power grid. In order to achieve higher efficiency, the two systems are started and run at the same time.

[0063] The cascade heat pump includes the first stage (low temperature, variable frequency) and the second stage (high temperature, fixed frequency). The cascade method is adopted to firstly exchange heat between the first stage evaporator and the air to absorb the low-grade heat of the air, and then the heat exchange between the first stage and the second stage is carried out through the evaporative condenser in the middle, and then the second stage increases the higher-grade heat provided by the first stage to a higher-grade heat. That is, the second stage (high-temperature side compressor) and the first stage (low-temperature side compressor) work together, the low-temperature side provides a stable heat source to the high-temperature side, and each raises the temperature to its own target temperature within its own capacity, and finally reaches the user's target temperature.

[0064] The first-stage condenser and the second-stage evaporator are the central hubs for heat exchange on both sides, and are also important data collection points for the control logic on the low-temperature side. The traditional method of directly collecting the temperature of the corresponding pipeline position using thermocouples is low-cost, but due to the influence of the refrigerant flow, there is a certain error between the detected temperature and the actual refrigerant saturation temperature in the pipeline. Therefore, these two temperatures are detected by pressure sensors, which improves accuracy and real-time performance compared to the method of using thermocouples.

[0065] Through real-time detection and control of the condensing temperature, the compressor can be started and stopped as needed to avoid unnecessary energy consumption. The mechanism of delayed start of the fixed-frequency compressor can effectively extend the service life of the equipment, reduce the damage caused by frequent start-ups, avoid premature or unnecessary start-up of the fixed-frequency compressor, improve the operating efficiency and stability of the system, reduce mechanical wear, thereby extending the service life of the equipment and reducing maintenance costs.

[0066] Please refer to Figure 2 , in a further embodiment of the present invention, when the system starts the compressor in heating operation, the frequency is increased to 50 Hz and maintained for 5 minutes, and then the operating frequency of the variable frequency compressor is adjusted according to the ambient temperature, the condensing temperature and the condensing target temperature;

[0067] When the ambient temperature is not less than 25°C, the condensation target temperature is the preset first condensation target temperature; the first condensation target temperature adjustment range is 10-40°C, and the initial value is 25°C; when the ambient temperature is less than 25°C and not less than 15°C, the condensation target temperature is the preset second condensation target temperature; the second condensation target temperature adjustment range is 10-40°C, and the initial value is 25°C; when the ambient temperature is less than 15°C and not less than 5°C, the condensation target temperature is the preset third condensation target temperature; the third condensation target temperature adjustment range is 10-40°C, and the initial value is 24°C; when the ambient temperature is less than 5°C and not less than -2°C, the condensation target temperature is the preset fourth condensation target temperature; the fourth condensation target temperature adjustment range is 10-40°C, and the initial value is 24°C; When the ambient temperature is less than -2°C and not less than -9°C, the condensation target temperature is the preset fifth condensation target temperature; the fifth condensation target temperature adjustment range is 10-40°C, and the initial value is 24°C; when the ambient temperature is less than -9°C and not less than -15°C, the condensation target temperature is the preset sixth condensation target temperature; the sixth condensation target temperature adjustment range is 10-40°C, and the initial value is 24°C; when the ambient temperature is less than -15°C and not less than -22°C, the condensation target temperature is the preset seventh condensation target temperature; the seventh condensation target temperature adjustment range is 10-40°C, and the initial value is 23°C; when the ambient temperature is less than -22°C, the condensation target temperature is the preset eighth condensation target temperature; the eighth condensation target temperature adjustment range is 10-40°C, and the initial value is 22°C. Among them, when the condensing temperature on the frequency conversion side is not greater than the difference between the condensing target temperature and 1, the frequency of the frequency conversion compressor increases at a speed of 1Hz / 10s to the maximum operating frequency of 85Hz; when the condensing temperature on the frequency conversion side is less than the sum of the condensing target temperature and 1 and greater than the difference between the condensing target temperature and 1, the frequency of the frequency conversion compressor remains unchanged; when the condensing temperature on the frequency conversion side is not less than the sum of the condensing target temperature and 1, the frequency of the frequency conversion compressor decreases at a speed of 1Hz / 10s.

[0068] In this embodiment, when the system is running, the frequency of the variable frequency compressor is adjusted according to the difference between the ambient temperature, the condensing temperature and the condensing target temperature. According to different ambient temperatures, the system sets different condensing target temperatures, and optimizes the system efficiency by accurately adjusting the frequency of the variable frequency compressor. It ensures that the compressor can adjust the frequency according to actual needs. Accurately adjusting the frequency of the variable frequency compressor enables the system to automatically optimize the operating state according to environmental changes, while ensuring the efficient operation of the system, avoiding system overload or inefficient operation, and avoiding excessive energy consumption.

[0069] In a further embodiment of the present invention, after the system is turned on, the inlet water temperature is detected; when the inlet water temperature is not greater than the difference between the preset heating setting temperature and the preset return temperature, the system starts to operate the heating operation; when the inlet water temperature is not less than the preset heating setting temperature, the system stops operating the heating operation.

[0070] In this embodiment, this control method ensures that the system starts working only when heating is needed by real-time monitoring of the inlet water temperature, avoiding overheating or energy waste. Through precise control of the inlet water temperature, the system avoids overheating or energy waste, while also improving the system's adaptive ability and overall operating efficiency.

[0071] In a further embodiment of the present invention, the system further comprises a fan and a water pump; the system is provided with a defrost mode, and when the system enters the defrost mode, the defrost operation is performed; when the system performs the defrost operation, the following operations are performed:

[0072] Step S101: The variable frequency four-way valve is powered on, the compressor is reduced to 30 Hz, and step S102 is executed after 55 seconds;

[0073] Step S102: Turn off the fan, open the main electronic expansion valve and the auxiliary electronic expansion valve to the defrosting opening, and execute step S103 after 5 seconds;

[0074] Among them, the defrost opening is a preset value, the adjustment range is 20-450P, and the initial value is 400P;

[0075] Step S103: the press starts to rise;

[0076] Step S104: the water pump keeps running;

[0077] The system performs the following operations when it exits defrosting operation:

[0078] Step S201: the compressor is reduced to 30 Hz, and step S202 is executed after 50 seconds;

[0079] Step S202: the variable frequency four-way valve is powered off, the fan is started, and step S203 is executed after 10 seconds;

[0080] Step S203: The compressor returns to normal control frequency.

[0081] In this embodiment, the system is set with a defrost mode, and automatically enters the defrost mode under certain conditions in a low-temperature environment. The defrost operation involves the coordinated work of the variable frequency four-way valve, the electronically controlled expansion valve, the compressor, the fan and the water pump. The defrost mode ensures that the system can effectively defrost in a low-temperature environment to prevent frost from affecting the system efficiency. At the same time, this process ensures that the system can effectively defrost and restore the heat exchange efficiency by precisely controlling the operation of the fan, the water pump and the expansion valve, thereby improving the heating efficiency and stability of the system.

[0082] In a further embodiment of the present invention, the condition for the system to enter the defrost mode when operating the heating operation is:

[0083] Condition 101: The cumulative operation time of the compressor is not less than 70 minutes and the continuous operation time of the compressor is not less than 5 minutes. At the same time, the temperature of the external coil is less than -3 degrees Celsius;

[0084] Condition 102: The difference between the ambient temperature and the external coil temperature is not less than 8°C, and at the same time, the ambient temperature is not less than -7°C and the ambient temperature is not greater than the preset defrost ambient temperature and lasts for 30 seconds;

[0085] Condition 103: The difference between the ambient temperature and the external coil temperature is not less than 8°C and the ambient temperature is less than -7°C and maintained for 30 seconds;

[0086] When the system satisfies condition 101 and satisfies any one of condition 102 and condition 103 , the system enters the defrost mode.

[0087] When only one system in the fixed frequency system or variable frequency system meets the conditions for entering defrost, when the temperature of the external coil of the other system is lower than the defrost exit temperature, it also enters the defrost mode at the same time; when the temperature of the external coil of the other system is not lower than the defrost exit temperature, it stops and waits.

[0088] The defrost exit temperature is a preset value, the setting range is 1-40℃, and the initial value is 12℃.

[0089] In this embodiment, the system determines whether to enter the defrost mode based on multiple conditions. The conditions such as the cumulative running time of the compressor, the difference between the ambient temperature and the temperature of the external coil, etc. need to be met. Through multiple condition judgments, it is intelligently determined whether to enter the defrost state. The system ensures that the defrost mode is started only when necessary, avoiding ineffective defrosting, avoiding unnecessary defrosting operations, improving energy efficiency, and reducing energy waste caused by excessive defrosting, saving energy.

[0090] In a further embodiment of the present invention, when the system meets the conditions for running the heating operation (water temperature is lower than the hysteresis / the machine is turned on, but not started), the following conditions are met at the same time:

[0091] Condition 201: System shutdown, system standby or compressor power-off time shall not be less than 30 minutes;

[0092] Condition 202: The ambient temperature is not less than -7°C and not more than 3°C, and the coil temperature is less than the preset defrost entry temperature;

[0093] The defrost entry temperature adjustment range is -15℃-1℃, and the initial value is -3℃.

[0094] The system stops heating and enters defrost mode.

[0095] In this embodiment, the system determines whether to enter the defrost mode based on multiple conditions. The conditions such as the cumulative running time of the compressor, the difference between the ambient temperature and the temperature of the external coil, etc. need to be met. Through multiple condition judgments, it is intelligently determined whether to enter the defrost state. The system ensures that the defrost mode is started only when necessary, avoiding ineffective defrosting, avoiding unnecessary defrosting operations, improving energy efficiency, and reducing energy waste caused by excessive defrosting, saving energy.

[0096] In a further embodiment of the present invention, the condition for the system to exit the defrost mode is: the temperature of the external coil is not less than a preset defrost exit temperature or the defrost time reaches 10 minutes.

[0097] The defrost exit temperature is a preset value, the setting range is 1-40℃, and the initial value is 12℃.

[0098] In this embodiment, when the temperature of the external coil reaches a certain value or the defrosting time reaches the set time limit, the system will automatically exit the defrosting mode and resume normal operation. This mechanism ensures that the defrosting time does not exceed the necessary range, and avoids excessive defrosting affecting normal heating work. By setting reasonable exit conditions, the system avoids the decrease in heating efficiency caused by excessive defrosting time, thereby improving the economy and work efficiency of the system.

[0099] In a further embodiment of the present invention, the system further comprises an electronic expansion valve; when the system is powered on, the electronic expansion valve of the frequency conversion system is reset and the opening is adjusted to the initial opening;

[0100] When the exhaust temperature is not greater than the preset main expansion valve regulated exhaust temperature, the main expansion valve is controlled according to the EV action;

[0101] When the difference between the exhaust temperature and the preset exhaust temperature adjusted by the main expansion valve is not less than 5°C, the main expansion valve opens 10 steps every 30 seconds;

[0102] The EV action is:

[0103] EXV n =(EXV n-1 )+[K P *(DTC n -DST)+K D *(DTC n -DTC n-1 )],

[0104] DTCn=T S -T p ,

[0105] When the system is equipped with a pressure sensor:

[0106] DTCn=TS -T Z ,

[0107] Among them, EXV n is the actual opening of the electronic expansion valve; EXV n-1 K is the last opening of the electronic expansion valve; P is the superheat proportional coefficient; K D is the superheat differential coefficient; DTC n is the actual target superheat; DST is the set target superheat; DTC n-1 is the last target overheat; T S is the compressor return air temperature; T Z is the low pressure temperature; T p is the outdoor coil temperature.

[0108] Among them, the electronic expansion valve action time cycle is a preset value, the adjustment range is 20s-90s, and the initial value is 20s.

[0109] During defrosting, the opening of the electronic expansion valve is adjusted to 400P.

[0110] In this embodiment, the system adjusts the refrigerant flow rate through an electronic expansion valve to ensure the optimal superheat and achieve more efficient heat exchange. Accurately adjusting the opening of the expansion valve can optimize the heat exchange process. Fine expansion valve adjustment improves the stability and thermal efficiency of the system, avoids the influence of improper refrigerant flow on the heat exchange efficiency, and thus improves the energy utilization efficiency of the system, reduces overheating and overcooling, and further reduces energy consumption.

[0111] In a further embodiment of the present invention, after the electronic expansion valve of the variable frequency system is reset, the opening is adjusted to 350P; and then the expansion valve of the fixed frequency system is adjusted to an opening of 230P;

[0112] The main expansion valve of the frequency conversion system is adjusted to the corresponding opening degree according to the adjustment mode and ambient temperature;

[0113] When the main expansion valve of the frequency conversion system is in the first adjustment mode:

[0114] When the ambient temperature is not less than 10℃, the initial opening of the main expansion valve is 240P; when the ambient temperature is less than 10℃ and not less than 3℃, the initial opening of the main expansion valve is 160P; when the ambient temperature is less than 3℃ and not less than -3℃, the initial opening of the main expansion valve is 150P; when the ambient temperature is less than -3℃ and not less than -10℃, the initial opening of the main expansion valve is 130P; when the ambient temperature is less than -10℃ and not less than -15℃, the initial opening of the main expansion valve is 110P; when the ambient temperature is less than -15℃ and not less than -22℃, the initial opening of the main expansion valve is 100P; when the ambient temperature is less than -22℃, the initial opening of the main expansion valve is 100P; the opening degree of the main expansion valve is a preset value, and the adjustment range is 0P-480P.

[0115] When the main expansion valve of the frequency conversion system is in the second adjustment mode:

[0116] When the ambient temperature is not less than 10℃, the initial opening of the main expansion valve is 200P; when the ambient temperature is less than 10℃ and not less than 3℃, the initial opening of the main expansion valve is 90P; when the ambient temperature is less than 3℃ and not less than -3℃, the initial opening of the main expansion valve is 60P; when the ambient temperature is less than -3℃ and not less than -10℃, the initial opening of the main expansion valve is 50P; when the ambient temperature is less than -10℃ and not less than -15℃, the initial opening of the main expansion valve is 50P; when the ambient temperature is less than -15℃ and not less than -22℃, the initial opening of the main expansion valve is 50P; when the ambient temperature is less than -22℃, the initial opening of the main expansion valve is 50P.

[0117] The lower limit of the electronic expansion valve of the frequency conversion system is the preset value, and its adjustment range is 0P-480P;

[0118] The lower limit of adjustment of the electronic expansion valve of the frequency conversion system is:

[0119] When the ambient temperature is not less than 10℃, the initial value of the lower limit of adjustment is 156P; when the ambient temperature is less than 10℃ and not less than 3℃, the initial value of the lower limit of adjustment is 136P; when the ambient temperature is less than 3℃ and not less than -3℃, the initial value of the lower limit of adjustment is 130P; when the ambient temperature is less than -3℃ and not less than -10℃, the initial value of the lower limit of adjustment is 114P; when the ambient temperature is less than -10℃ and not less than -15℃, the initial value of the lower limit of adjustment is 88P; when the ambient temperature is less than -15℃ and not less than -22℃, the initial value of the lower limit of adjustment is 78P; when the ambient temperature is less than -22℃, the initial value of the lower limit of adjustment is 74P.

[0120] The lower limit of the electronic expansion valve in the fixed frequency system is:

[0121] The lower limit of the fixed-frequency electronic expansion valve is a preset value, and its adjustment range is 0P-480P; when the return air temperature is not less than 26°C, the initial value of the lower limit of adjustment is 220P; when the return air temperature is less than 26°C and not less than 21°C, the initial value of the lower limit of adjustment is 200P; when the return air temperature is less than 21°C and not less than 16°C, the initial value of the lower limit of adjustment is 160P; when the return air temperature is less than 16°C and not less than 10°C, the initial value of the lower limit of adjustment is 152P; when the return air temperature is less than 10°C and not less than 0°C, the initial value of the lower limit of adjustment is 150P; when the return air temperature is less than 0°C, the initial value of the lower limit of adjustment is 150P.

[0122] Among them, the main expansion valve of the variable frequency system is the expansion valve installed on the evaporation side (indoor unit), which is mainly responsible for adjusting the pressure difference of the refrigerant between indoors and outdoors, and controlling the refrigerant flow rate to ensure the stability of the indoor temperature; the auxiliary expansion valve of the variable frequency system is the expansion valve installed on the condensing side (outdoor unit), which is mainly used to reduce the pressure of the compressor and increase the refrigeration efficiency.

[0123] In this embodiment, the initial opening of the main expansion valve is also set in detail. According to the adjustment mode and the ambient temperature, the initial opening of the main expansion valve is set at different values ​​to ensure the best operation effect of the system under different environmental conditions. This design takes into account both the heating efficiency of the system and the stability and durability of the system.

[0124] In a further embodiment of the present invention, the system is further provided with an auxiliary electronic expansion valve.

[0125] Before the system is powered on and the motor is started, the electronic expansion valve is first returned to zero position; during defrosting, the opening of the auxiliary electronic expansion valve is 0P; during heating, when the ambient temperature is not greater than 11°C, the auxiliary electronic expansion valve is allowed to be opened, and when the ambient temperature is greater than 11°C, the auxiliary electronic expansion valve is closed.

[0126] In a further embodiment of the present invention, the system is further provided with a plurality of electrical appliances, including but not limited to:

[0127] Water pump: When starting up, the water pump will start 60 seconds in advance; when shutting down, the water pump will shut down 90 seconds after the press. Fan: When starting up, the fan will start 5 seconds in advance; when shutting down, the fan will shut down 90 seconds after the press; during defrosting, the fan stops running.

[0128] Crankshaft electric heating: when the ambient temperature is not greater than 7°C and the compressor is turned off, the crankshaft electric heating is turned on; when the ambient temperature is not less than 9°C or the compressor is turned on, the crankshaft electric heating is turned off.

[0129] Enthalpy-increasing solenoid valve, in heating operation, when the exhaust temperature is not less than 100℃, the enthalpy-increasing valve is forced to open; when the exhaust temperature is not greater than 95℃, it is controlled according to the ambient temperature: when the ambient temperature is not greater than 11℃, the enthalpy-increasing valve is opened; when the ambient temperature is not less than 13℃, the enthalpy-increasing valve is closed. Chassis electric heating; in heating, the ambient temperature is not greater than 2℃ to open, and the ambient temperature is not less than 4℃ to close. Among them, it is forced to open during defrosting.

[0130] In a further embodiment of the present invention, the system is also provided with a fault detection function, including but not limited to communication fault, ambient temperature fault, water inlet temperature fault, and water outlet temperature fault.

[0131] Exhaust temperature protection: 1) When the exhaust temperature is not less than 120℃ and lasts for 5 seconds, the compressor will shut down; 2) When the exhaust temperature is not less than 110℃ and less than 120℃, the compressor operating frequency will be controlled to decrease at a rate of 1Hz / s until it reaches the lowest operating frequency; 3) When the exhaust temperature is not less than 105℃ and less than 110℃, the compressor operating frequency will be controlled to decrease at a rate of 1Hz / 5s until it reaches the lowest operating frequency; 4) When the exhaust temperature is not less than 100℃ and less than 105℃, the compressor operating frequency will be controlled to decrease at a rate of 1Hz / 10s until it reaches the lowest operating frequency; 5) When the exhaust temperature is not less than 95℃ and less than 100℃, the compressor operating frequency is prohibited from rising; 6) When the exhaust temperature is less than 95℃ and remains for 1 minute, the compressor operating frequency will resume normal control. Among them, after the exhaust temperature protection is shut down for 3 minutes, when the exhaust temperature is not greater than 95℃, the compressor will resume normal operation.

[0132] When the exhaust temperature is high but has not reached the shutdown threshold, the system will gradually adjust the operating frequency of the compressor according to the temperature value. This gradual frequency reduction method avoids drastic changes in the compressor frequency and can reduce compressor load fluctuations. Directly changing the compressor frequency may produce mechanical stress. Gradually reducing the frequency can ensure a smooth transition and avoid excessive impact on the compressor. At the same time, it can also prevent the temperature from continuing to rise. By reducing the operating frequency of the compressor, the heat generated by the compressor is reduced, thereby reducing the exhaust temperature.

[0133] When the temperature is too high, the system will shut down for three minutes and wait for the temperature to drop to a safe range. This can effectively prevent the equipment from starting and stopping frequently. Frequent shutdown and startup will cause mechanical load on the compressor and other parts of the system and shorten the life of the equipment. By setting the downtime and temperature recovery conditions, the risk of frequent start and stop can be reduced. At the same time, when the exhaust temperature exceeds a certain limit, it will shut down directly and wait for the temperature to recover to ensure the safety of the compressor and the system.

[0134] External coil high temperature protection: 1) When the external coil temperature is not less than 65℃ and maintained for 10 seconds, the compressor will shut down; 2) When the external coil temperature is less than 65℃ and not less than 60℃, the compressor operating frequency will be controlled to decrease at a rate of 1Hz / 5s until it reaches the minimum operating frequency. The system burden and temperature will be reduced by gradually reducing the compressor frequency; 3) When the external coil temperature is less than 60℃ and not less than 55℃, the compressor operating frequency will be prohibited from rising to avoid aggravating the increase in the external coil temperature; 4) When the external coil temperature is less than 55℃, the compressor operating frequency will resume normal control. Among them, 3 minutes after the external coil high temperature protection is shut down, when the external coil temperature is not greater than 55℃, the compressor will resume normal operation. Communication failure: When the mainboard is disconnected from the line control communication for 60 seconds, a communication failure will be reported and the unit will continue to run.

[0135] When the temperature of the outer coil is too high, the heat exchange efficiency inside the outer coil may drop sharply, and even cause pipeline damage, component aging, and even affect the overall operation of the system. At the same time, too high a temperature will not only cause a decrease in heat exchange efficiency, but may also damage other important components inside the system, such as the compressor. Therefore, shutting down can avoid the system from being in an abnormal operating state for a long time and keep the heat pump working efficiently.

[0136] Ambient temperature fault: Detected after the unit is powered on; if the ambient temperature sensor is detected to be short-circuited or open-circuited at any time, it is judged as an ambient temperature sensor fault and the system does not shut down; when this fault occurs, the system antifreeze detection is cancelled; this fault can be automatically restored; when a fault occurs, the wire controller reports a maintenance fault.

[0137] Even if the ambient temperature sensor has a short circuit or open circuit fault, the system can still continue to operate, avoiding a complete system shutdown due to sensor failure and ensuring the user's heating or cooling needs. At the same time, if the antifreeze protection function cannot work properly due to the ambient temperature sensor failure, canceling the antifreeze protection function can effectively prevent misoperation or unnecessary shutdown.

[0138] Inlet water temperature failure: Detected after the unit is powered on; if the inlet water temperature sensor is detected to be short-circuited or open-circuited at any time, it is judged as an inlet water temperature sensor failure and the system shuts down for protection; this failure can be automatically recovered; in the event of a failure, the wire controller reports a maintenance failure.

[0139] Outlet water temperature failure: Detected after the unit is powered on; if the outlet water temperature sensor is detected to be short-circuited or open-circuited at any time, it is judged as an outlet water temperature sensor failure and the system shuts down for protection; when this failure occurs, the system antifreeze detection is cancelled; this failure can be automatically restored; when a failure occurs, the wire controller reports a maintenance failure.

[0140] The outlet water temperature sensor is used to monitor the water temperature output by the heat pump system, helping the system to determine whether the set temperature requirements are met and adjust the system operation. If the outlet water temperature sensor is short-circuited or open-circuited, it cannot provide accurate temperature information, and the system will not be able to reasonably adjust the temperature, which may cause the equipment to overheat or overcool, thereby affecting the efficiency or safety of the system. The system is equipped with output temperature fault protection to ensure the safe and stable operation of the heat pump system through reasonable protection measures. When a fault in the outlet water temperature sensor is detected, the system will automatically shut down to prevent equipment damage or reduced efficiency caused by incorrect temperature control; at the same time, due to sensor failure, the antifreeze protection function may fail, so the antifreeze protection function is canceled to prevent unnecessary protection actions caused by incorrect temperature judgment. When the outlet water temperature sensor returns to normal, the system can automatically resume normal operation, reducing the user's operating burden.

[0141] External coil temperature failure: Detection after the unit is powered on; if a short circuit or open circuit is detected at any time, it is judged as an external coil temperature failure, and the corresponding system will not shut down; when this failure occurs, the main electronic expansion valve is opened to the manual step number in the heating mode (when the pressure sensor is not detected); this failure can be automatically recovered, and the defrost is timed defrost when this failure occurs; when a failure occurs, the wire controller reports a corresponding system maintenance failure.

[0142] The system is equipped with external coil temperature fault protection, which is a processing mechanism for the failure of the external coil temperature sensor. The external coil temperature sensor is used to monitor the temperature on the external heat exchanger (such as the evaporator or condenser). Since the temperature of the external coil directly affects the heating and cooling effect of the system, the failure of the temperature sensor may cause the loss of temperature data and affect the operation of the heat pump system. However, in order to ensure that the system can still operate safely when the temperature sensor fails, while avoiding excessive shutdowns or operation interruptions, this protection mechanism is designed with specific countermeasures when the external coil temperature sensor fails. After the unit is powered on, the system will perform a self-test to check the working status of all sensors. If the external coil temperature sensor is short-circuited or open-circuited (such as circuit failure or sensor damage), the system will detect and record the fault in time; if a short-circuit or open-circuit fault is detected in the external coil temperature sensor during system operation, the system will determine it as a temperature sensing fault and perform protection. In this regard, the system will not shut down due to sensor failure, but continue to run; when the external coil temperature sensor fails, the system will set the main circuit electronic expansion valve to manual control steps to avoid automatic adjustment failure caused by sensor failure. This measure is common when the pressure sensor is not detected, and the purpose is to maintain the stability of system operation. The system is equipped with external coil temperature fault protection. Even if the external coil temperature sensor fails, the system continues to run, avoiding shutdown of the entire system due to a single fault point, thus improving the stability and availability of the equipment. When the sensor fails, the system sets the electronic expansion valve to manual control to avoid misadjustment of the expansion valve due to lack of accurate temperature data. Through the timed defrost mechanism, even if the external coil temperature sensor fails, the system can still perform defrost operations normally to ensure that the system is not affected by frost. After the fault is repaired, the system can automatically resume operation, and the wire controller will display maintenance fault information, allowing users to perform repairs and maintenance in a timely manner.

[0143] Fixed-frequency coil temperature failure: Detect after the unit is powered on; if a short circuit or open circuit is detected in the external coil temperature sensor at any time, it is judged as an external coil temperature sensor failure, and the corresponding system will not shut down; when this failure occurs, the fixed-frequency electronic expansion valve of the corresponding system is opened to the manual step number; in the event of a failure, the wire controller reports a maintenance failure of the corresponding system.

[0144] Inverter condensing temperature fault: Detected after the unit is powered on; if the inverter condensing temperature sensor is detected to be short-circuited or open-circuited at any time, it is judged as an inverter condensing temperature sensor fault and the corresponding system is shut down; this fault can be automatically restored; in the event of a fault, the wire controller reports a corresponding system maintenance fault.

[0145] The system is equipped with variable frequency condensing temperature fault protection, which is a protective measure for the condensing temperature sensor in the variable frequency heat pump system when it fails. The condensing temperature sensor is responsible for monitoring the temperature of the condenser to ensure that the condensing process is carried out within the normal range. If the condensing temperature is too high, it may cause a decrease in refrigeration efficiency or even damage key components in the system. Therefore, when the condensing temperature sensor is short-circuited or open-circuited, protective measures need to be taken immediately to ensure the safe operation of the system. When the unit is powered on, the system will perform a self-test to detect the working status of all sensors and related equipment. The short circuit or open circuit fault of the condensing temperature sensor will be discovered in time when the unit is turned on; during the operation of the unit, if the variable frequency condensing temperature sensor is detected to be short-circuited or open-circuited (such as circuit failure, sensor damage, etc.), the system will determine it as a sensor failure and immediately enter the shutdown protection state. After the condensing temperature sensor fails, the system cannot accurately determine the condensing temperature, which may cause equipment such as the compressor and condenser to operate under unsafe temperature conditions, so it is necessary to shut down for protection in time; when the variable frequency condensing temperature sensor is short-circuited or open-circuited, if the problem is solved and returns to normal, the system will automatically resume operation. This means that after the sensor fault disappears, the system can automatically restart and return to normal operation; when the system detects that the condensing temperature sensor has failed, it will report the fault information through the wired controller or display screen to remind the user to repair it. The system usually displays the specific fault type or maintenance requirements. By real-time detection of the working status of the condensing temperature sensor, it ensures that the system can be shut down for protection in time when a fault occurs, preventing safety problems such as equipment damage and overheating caused by sensor failure; the failure of the condensing temperature sensor may cause the system to be unable to accurately determine the condensing temperature, which may cause the equipment to overheat or operate inefficiently. Through shutdown protection, the system can avoid operating in an unsafe working state and reduce the risk of equipment damage; the system can automatically resume operation after the fault is restored, reducing manual intervention, improving the automation and stability of the system, and improving the user experience; reporting fault information to the user through the wired controller enables the user to find problems and perform repairs in time to ensure the stability and long-term operation of the equipment.

[0146] Return air temperature failure: Detected after the unit is powered on; if the return air temperature sensor is detected to be short-circuited or open-circuited at any time, it is judged as a return air temperature sensor failure and the corresponding system will not shut down; when this failure occurs, the main electronic expansion valve opens to the manual step; this failure can be automatically restored; when a failure occurs, the wire controller reports a corresponding system maintenance failure.

[0147] Fixed frequency return air temperature fault: Detected after the unit is powered on; if the return air temperature sensor is detected to be short-circuited or open-circuited at any time, it is judged as a return air temperature sensor fault, and the corresponding system is shut down; this fault can be automatically restored; when a fault occurs, the wire controller reports a corresponding system maintenance fault. Exhaust temperature fault: If the exhaust temperature sensor is detected to be short-circuited or open-circuited 5 minutes after the compressor is turned on, it is judged as an exhaust temperature sensor fault, and the corresponding system is shut down for protection; this fault can be automatically restored; when a fault occurs, the wire controller reports a corresponding system maintenance fault.

[0148] Fixed-frequency exhaust temperature failure: If the exhaust temperature sensor is detected to be short-circuited or open-circuited 5 minutes after the fixed-frequency compressor is turned on, it is judged as an exhaust temperature sensor failure and the corresponding system is shut down for protection; this failure can be automatically restored; in the event of a failure, the wire controller reports a corresponding system maintenance failure.

[0149] The system is equipped with fixed-frequency exhaust temperature fault protection, which is an automatic shutdown protection measure taken when the exhaust temperature sensor in the fixed-frequency compressor system fails. The exhaust temperature sensor is used to monitor the exhaust temperature of the compressor to ensure that it operates within the normal operating range. If the exhaust temperature sensor fails, the system will not be able to accurately obtain the exhaust temperature information, which may lead to incorrect operating conditions or equipment damage, so protective measures need to be taken. After the fixed-frequency compressor is started, the system will wait for 5 minutes to ensure that the compressor can operate stably and allow the exhaust temperature sensor temperature to change to the normal operating range. During this time, the system will not immediately perform temperature sensing fault detection, avoiding false faults due to temperature fluctuations when it is just started. When the system detects a short circuit or open circuit fault in the exhaust temperature sensor after 5 minutes, the system will immediately enter the shutdown protection state. The failure of the exhaust temperature sensor means that the exhaust temperature of the compressor cannot be accurately read, and the system cannot adjust the working state according to the actual temperature, which may cause the compressor to overheat, inefficiency or other unsafe operations; when the exhaust temperature sensor is short-circuited or open-circuited, the system can automatically resume operation after the sensor failure recovers; specifically, if the sensor restores the normal signal, the system will automatically release the shutdown protection and continue normal operation; when the exhaust temperature sensor is short-circuited or open-circuited, the system will report the fault information to the user through the wire controller (or display), prompting the user to check and repair the temperature sensor. By setting a 5-minute delay, false alarms caused by temperature fluctuations in the early stage after the compressor is started can be avoided, and the accuracy of fault detection can be improved. At the same time, when the exhaust temperature sensor is short-circuited or open-circuited, the system immediately enters shutdown protection to prevent equipment damage or overheating due to the inability to read the accurate exhaust temperature.

[0150] System high-voltage protection: After the compressor is turned on, if the high-voltage switch is detected to be disconnected for 5 consecutive seconds, the system will shut down for protection accordingly; if this fault occurs three times within 60 minutes, the power must be turned off to recover (the first two times can be automatically recovered); in the event of a fault, the wire controller will report a corresponding system maintenance fault.

[0151] Fixed-frequency high-voltage protection: After the fixed-frequency compressor is turned on, if the high-voltage switch is detected to be disconnected for 5 consecutive seconds, the system will shut down for protection accordingly; if this fault occurs three times within 60 minutes, the power must be turned off to recover (the first two times can be automatically recovered); in the event of a fault, the wire controller will report a corresponding system maintenance fault.

[0152] System low-voltage protection: 5 minutes after the compressor is turned on, if the low-voltage switch is detected to be disconnected for 5 consecutive seconds, the system will shut down for protection; if this fault occurs three times within 60 minutes, the power must be turned off to recover (the first two times can be automatically recovered).

[0153] Fixed-frequency low-voltage protection: 5 minutes after the fixed-frequency compressor is turned on, if the low-voltage switch is detected to be disconnected for 5 consecutive seconds, the corresponding system will shut down for protection; if this fault occurs three times within 60 minutes, the power must be turned off to recover (the first two times can be automatically recovered).

[0154] Exhaust temperature is too high protection: the exhaust temperature is detected 1 minute after the compressor is turned on. When the exhaust temperature is detected to be ≥120℃, the exhaust temperature protection is activated and the corresponding system is shut down. When the exhaust temperature is detected to be ≤95℃, the exhaust temperature protection is activated and normal operation is resumed. If this fault occurs three times within 60 minutes, the machine cannot be restored without power off (the first two times can be automatically restored).

[0155] Exhaust temperature over-temperature protection is a safety protection measure taken for compressor exhaust temperature that is too high. Exhaust temperature is an important indicator for measuring the working state of the compressor and the stability of system operation. Excessive exhaust temperature may cause the compressor to overheat and damage, and even affect the long-term reliability of the entire system. Therefore, monitoring and controlling the exhaust temperature is a key link to ensure the safe and efficient operation of the heat pump system. This protection mechanism effectively avoids the damage of high temperature to the equipment through real-time monitoring and fault handling of the exhaust temperature. Among them, the 1-minute detection period after the compressor is started is to establish a stable working state for the compressor and the system. At this time, the compressor has just started to operate and may not have reached a stable exhaust temperature, so it is necessary to wait for a while. The 1-minute delay can ensure that the compressor enters the normal working state before temperature monitoring. By automatically shutting down when the exhaust temperature is too high, the compressor is prevented from being damaged due to overheating and the long-term stable operation of the equipment is ensured; when the exhaust temperature returns to a safe range, the system can automatically resume operation to avoid long-term shutdown and ensure system efficiency; and when faults occur frequently, limiting automatic recovery can prevent the system from continuing to operate in a high temperature environment, prompting technicians to conduct inspections and repairs.

[0156] Fixed-frequency exhaust temperature over-temperature protection The fixed-frequency compressor detects the exhaust temperature 1 minute after it is turned on. When the exhaust temperature is detected to be ≥120℃, it enters the exhaust temperature over-temperature protection and the corresponding system shuts down; when the exhaust temperature is detected to be ≤95℃, it exits the exhaust temperature over-temperature protection and resumes normal operation; if this fault occurs three times within 60 minutes, it cannot be restored without power off (the first two times can be automatically recovered).

[0157] Heating water outlet over-high protection: During heating, when the outlet water temperature is detected to be ≥75℃, the heating overheat protection is entered, and the compressor and fan stop running; when the outlet water temperature is detected to be ≤70℃, the heating overheat protection is exited and normal operation is restored; if this fault occurs three times within 60 minutes, the power must be turned off to recover (the first two times can be automatically recovered).

[0158] Water flow protection: The water flow switch is detected 15 seconds after the water pump is started. If the switch is detected to be disconnected for 10 consecutive seconds, the pump will be shut down for protection. When this fault occurs, if the fault is not restored, the water pump will be restarted every 4 minutes to detect the water flow. If the water flow switch is still not closed after the water pump is automatically restarted 5 times within 60 minutes, the water pump will not be started again until the water flow switch is closed.

[0159] After the water pump is started, the system needs to confirm whether the water flow starts smoothly, so a delay detection is set (15 seconds after starting). If the water flow switch is in normal state (closed) after the water pump is started, it means that the water flow is normal; if the water flow switch is not closed, it means that the water flow is not established or an abnormality occurs. Among them, the 15-second delay is to give the water pump enough time to start and establish water flow, ensuring that the system can effectively monitor the state of the water flow. If the system does not detect water flow within a short period of time after starting, it may be due to abnormal operation of the water pump, blocked water pipes, or other system failures. Through delay detection, it can ensure that the system can respond quickly after the water pump is started to avoid continued operation when there is insufficient or no water flow, and prevent damage to the equipment. After the water pump is started, the water flow switch is disconnected for 10 seconds, indicating that the water pump cannot push enough water flow, or the water flow is abnormal. The system will immediately trigger the shutdown protection and stop the operation of the water pump. The lack of sufficient water flow in the water pump may cause the equipment to overheat or overload, especially the compressor may not be effectively cooled due to insufficient water flow, which will affect the normal operation of the system. Shutdown protection ensures that the pump does not continue to run without water flow, thus avoiding damage to critical equipment. At the same time, if the pump continues to run without water flow, it may cause energy waste and increase electricity consumption. Shutdown protection helps prevent this ineffective operation and save energy.

[0160] Fan overload protection: The fan overload switch is detected 5 seconds after the fan is turned on. If the switch is detected to be disconnected for 5 consecutive seconds, the system will shut down for protection. If this fault occurs three times within 60 minutes, the power must be turned off to recover (the first two times can be automatically recovered).

[0161] System antifreeze: During standby or shutdown protection, when the ambient temperature is ≤5℃ and the outlet water temperature is ≤4℃, the system enters the first-level antifreeze protection, and the water pump is turned on for 60 seconds every 10 minutes and runs in a cycle; when the ambient temperature is ≥8℃ or the outlet water temperature is ≥15℃, the system exits the first-level antifreeze protection; when the ambient temperature is ≤5℃ and the outlet water temperature is ≤2℃, the system enters the second-level antifreeze protection, and automatically turns on the heating; when the ambient temperature is ≥8℃ or the outlet water temperature is ≥15℃, the system exits the second-level antifreeze protection; when the ambient temperature fails, the system enters the first or second level antifreeze according to the outlet water temperature; among them, if the outlet water temperature fails, the inlet water temperature replaces the outlet water temperature for antifreeze; if the ambient, outlet water and inlet water temperatures all fail, the system enters the first level antifreeze.

[0162] In this embodiment, the system monitors multiple parameters such as communication, ambient temperature, water inlet temperature, and water outlet temperature through sensors. If an abnormality occurs, the system will automatically detect and alarm. Through multiple monitoring and alarm functions, the system can detect possible problems in real time and take corresponding measures. Timely fault detection can reduce system downtime, avoid equipment damage or system operation failures, and improve system reliability and long-term stability.

[0163] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A dual-system variable frequency cascade control system, characterized in that: The control system includes a dual system consisting of an independently set fixed frequency system and an independently set variable frequency system, wherein the fixed frequency system includes a fixed frequency compressor and a fixed frequency four-way valve, and the variable frequency system includes a variable frequency compressor and a variable frequency four-way valve; After the system is turned on, the water inlet temperature is detected to control whether the system is running heating work; When the system starts to operate the heating work, the variable frequency compressor is turned on and the condensing temperature is detected. If the condensing temperature is not less than the first temperature, the fixed frequency compressor is turned on for the first time after the variable frequency compressor is turned on; if the condensing temperature is less than the first temperature, the fixed frequency compressor is turned on after the condensing temperature on the variable frequency side rises to the first temperature; Among them, when the fixed-frequency compressor is turned on, the system notifies the detection and judgment of the condensing temperature; When the system stops heating, the variable frequency compressor is turned off, and the fixed frequency compressor is turned off at a delayed time, followed by the variable frequency compressor.

2. A dual-system variable frequency cascade control system according to claim 1, characterized in that: When the system starts the compressor for heating operation, the frequency is increased to 50Hz and kept running for 5 minutes, and then the operating frequency of the variable frequency compressor is adjusted according to the ambient temperature, condensing temperature and condensing target temperature; The condensation target temperature is a preset value switched according to the ambient temperature; Among them, when the condensing temperature on the frequency conversion side is not greater than the difference between the condensing target temperature and 1, the frequency of the frequency conversion compressor increases at a rate of 1Hz / 10s to a maximum operating frequency of 85Hz; When the condensing temperature on the variable frequency side is less than the sum of the condensing target temperature and 1 and greater than the difference between the condensing target temperature and 1, the frequency of the variable frequency compressor remains unchanged; When the condensing temperature on the variable frequency side is not less than the sum of the condensing target temperature and 1, the frequency of the variable frequency compressor decreases at a rate of 1 Hz / 10s.

3. A dual-system variable frequency cascade control system according to claim 1, characterized in that: After the system is turned on, the inlet water temperature is tested; When the inlet water temperature is not greater than the difference between the preset heating set temperature and the preset return temperature, the system starts to operate the heating operation; When the inlet water temperature is not less than the preset heating set temperature, the system stops heating.

4. A dual-system variable frequency cascade control system according to claim 1, characterized in that: The system also includes fans and water pumps; The system is set with a defrost mode. When the system enters the defrost mode, the defrost work will be performed; The system performs the following operations when running defrost: Step S101: The variable frequency four-way valve is powered on, the compressor is reduced to 30 Hz, and step S102 is executed after 55 seconds; Step S102: Turn off the fan, open the main electronic expansion valve and the auxiliary electronic expansion valve to the defrosting opening, and execute step S103 after 5 seconds; Step S103: the press starts to rise; Step S104: the water pump keeps running; The system performs the following operations when it exits defrosting operation: Step S201: the compressor is reduced to 30 Hz, and step S202 is executed after 50 seconds; Step S202: the variable frequency four-way valve is powered off, the fan is started, and step S203 is executed after 10 seconds; Step S203: The compressor returns to normal control frequency.

5. A dual-system variable frequency cascade control system according to claim 4, characterized in that: The conditions for the system to enter defrost mode when running heating are: Condition 101: The cumulative operation time of the compressor is not less than 70 minutes and the continuous operation time of the compressor is not less than 5 minutes. At the same time, the temperature of the external coil is less than -3 degrees Celsius; Condition 102: The difference between the ambient temperature and the external coil temperature is not less than 8°C, and at the same time, the ambient temperature is not less than -7°C and the ambient temperature is not greater than the preset defrost ambient temperature and lasts for 30 seconds; Condition 103: The difference between the ambient temperature and the external coil temperature is not less than 8°C and the ambient temperature is less than -7°C and maintained for 30 seconds; When the system satisfies condition 101 and satisfies any one of condition 102 and condition 103 , the system enters the defrost mode.

6. A dual-system variable frequency cascade control system according to claim 4, characterized in that: When the system meets the conditions for heating operation, it also meets the following conditions: Condition 201: System shutdown, system standby or compressor power-off time shall not be less than 30 minutes; Condition 202: The ambient temperature is not less than -7°C and not more than 3°C, and the coil temperature is less than the preset defrost entry temperature; The system stops heating and enters defrost mode.

7. A dual-system variable frequency cascade control system according to any one of claims 4 to 6, characterized in that: The conditions for the system to exit the defrost mode are: the external coil temperature is not less than the preset defrost exit temperature or the defrost time reaches 10 minutes.

8. A dual-system variable frequency cascade control system according to claim 1, characterized in that: The system also includes an electronic expansion valve; when the system is powered on, the electronic expansion valve of the frequency conversion system is reset and the opening is adjusted to the initial opening; When the exhaust temperature is not greater than the preset main expansion valve regulated exhaust temperature, the main expansion valve is controlled according to the EV action; When the difference between the exhaust temperature and the preset exhaust temperature adjusted by the main expansion valve is not less than 5°C, the main expansion valve opens 10 steps every 30 seconds; The EV action is: EXV n =(EXV n-1 )+[K P *(DTC n -DST)+K D *(DTC n -DTC n-1 )], DTCn=T S -T p , When the system is equipped with a pressure sensor: DTCn=T S -T Z , Among them, EXV n is the actual opening of the electronic expansion valve; EXV n-1 K is the last opening of the electronic expansion valve; P is the superheat proportional coefficient; K D is the superheat differential coefficient; DTC n is the actual target superheat; DST is the set target superheat; DTC n-1 is the last target overheat; T S is the compressor return air temperature; T Z is the low pressure temperature; T p is the outdoor coil temperature.

9. A dual-system variable frequency cascade control system according to claim 8, characterized in that: After the electronic expansion valve of the variable frequency system is reset, adjust the opening to 350P; then adjust the expansion valve of the fixed frequency system to 230P; The main expansion valve of the frequency conversion system is adjusted to the corresponding opening degree according to the adjustment mode and ambient temperature.

10. A dual-system variable frequency cascade control system according to claim 1, characterized in that: The system is also equipped with fault detection functions, including communication fault, ambient temperature fault, water inlet temperature fault, and water outlet temperature fault.

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