A step-by-step dehumidification system operating in all seasons and a control method thereof

Abstract

The present application relates to air treatment technical field, specifically to a kind of four seasons all operating condition operation's cascade dehumidification system and its control method, comprising: air supply air duct;First refrigeration system, first internal heat exchanger being arranged in air supply air duct;Second refrigeration system, second internal heat exchanger being arranged in air supply air duct;Third refrigeration system, third condenser and third evaporator are arranged in air supply air duct;First internal heat exchanger, second internal heat exchanger are sequentially arranged along air flow direction;Third evaporator is located third condenser upstream;Three steam compression refrigeration cycles that are independent of each other using first refrigeration system, second refrigeration system and third refrigeration system, realize air cascade cooling, cascade dehumidification and condensing heat recovery.

Description

Technical Field

[0001] This invention relates to the field of air treatment technology, specifically to a cascade dehumidification system and its control method that can operate under all conditions in all four seasons. Background Technology

[0002] Industrial dehumidifiers mainly employ two technological approaches: adsorption dehumidification and refrigeration dehumidification. Refrigeration dehumidification technology uses an evaporator to cool air below its dew point, causing moisture to condense and be released.

[0003] Traditional refrigeration dehumidifiers, such as the invention patent with application number CN202110227618.1, disclose a dehumidification system, control method, computer equipment, and storage medium for an air conditioner, including: a compressor, a condenser, a throttling device, an evaporator, a fan unit, and a temperature compensation device. This system uses a refrigerant circuit composed of the compressor, condenser, throttling device, and evaporator to dehumidify indoor air after it passes through the evaporator. By installing a temperature compensation device in the air supply path, with its heat-releasing side partially in contact with the air supply path, the dehumidified air is heated by the temperature compensation device before being blown out from the air outlet, reducing the temperature difference between the inlet and outlet air.

[0004] However, traditional refrigeration dehumidifiers have many obvious drawbacks: (1) In order to regulate the temperature and humidity of the supplied air, they need to use electric heating to adjust the air temperature before supplying air. Electric heating wastes a lot of energy. (2) In order to obtain a lower dew point, these dehumidifiers often require an evaporation temperature below zero degrees Celsius. The low evaporation temperature causes the evaporator to frost, and the compressor to reduce its frequency for defrosting or stop, which seriously affects the stability of the supplied air. (3) In addition, the heating capacity of the compression cycle of traditional dehumidifiers is significantly reduced when the temperature is low in winter. It is difficult to achieve stable and efficient operation in all seasons and cannot flexibly adapt to the supply air demand of different seasons. Summary of the Invention

[0005] The purpose of this invention is to provide a cascade dehumidification system and its control method that can operate under all conditions in all four seasons. It adopts three independent vapor compression refrigeration cycles to achieve efficient and stable operation in three operating modes: refrigeration, heating and dehumidification, so as to solve the defects mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A cascade dehumidification system that operates year-round under all conditions includes: Air supply duct; The first refrigeration system includes a first compressor assembly, a first four-way valve, a first external heat exchanger, a first expansion valve, and a first internal heat exchanger disposed in the air supply duct. The first refrigeration system switches between a refrigeration mode and a heating mode through the first four-way valve. The second refrigeration system includes a second compressor assembly, a second four-way valve, a second external heat exchanger, a second expansion valve, and a second internal heat exchanger disposed in the air supply duct. The second refrigeration system switches between refrigeration mode and heating mode through the second four-way valve. The third refrigeration system includes a third compressor assembly, a third condenser, a third expansion valve, and a third evaporator, wherein the third condenser and the third evaporator are both disposed within the air supply duct. The first internal heat exchanger, the second internal heat exchanger, and the third condenser are arranged sequentially along the airflow direction; the third evaporator is located upstream of the third condenser. The first refrigeration system, the second refrigeration system, and the third refrigeration system are three independent vapor compression refrigeration cycles.

[0007] As a further improvement, the third evaporator is located upstream of the first internal heat exchanger, or the third evaporator is located between the first internal heat exchanger and the second internal heat exchanger, or the third evaporator is located between the second internal heat exchanger and the third condenser.

[0008] As a further improvement, the air supply duct is also equipped with a filter and an air supply fan.

[0009] As a further improvement, an electric heater is also provided in the air supply duct, and the electric heater is located downstream of the third condenser.

[0010] As a further improvement, the first compressor assembly is a single compressor, or the first compressor assembly includes a first compressor and a second compressor connected in series or in parallel; the second compressor assembly is a single compressor, or the second compressor assembly includes a third compressor and a fourth compressor connected in series or in parallel.

[0011] A control method for a cascade dehumidification system that operates under all conditions in all four seasons, including cooling mode, heating mode and dehumidification mode; In refrigeration mode, the first and second refrigeration systems operate, while the third refrigeration system does not operate. Both the first four-way valve and the second four-way valve are set to refrigeration mode. Air undergoes two-stage cooling through the first and second internal heat exchangers. In heating mode, the first and second refrigeration systems operate, while the third refrigeration system does not operate. Both the first four-way valve and the second four-way valve are set to heating mode. Air undergoes two-stage heating through the first and second internal heat exchangers. In dehumidification mode, the first refrigeration system, the second refrigeration system, and the third refrigeration system operate simultaneously, and the first four-way valve and the second four-way valve are both set to refrigeration mode; the air undergoes three stages of cooling and dehumidification through the first internal heat exchanger, the second internal heat exchanger, and the third evaporator, and is then heated by the third condenser.

[0012] As a further improvement, the control system collects the supply air temperature in real time. Based on the deviation between the supply air temperature and the set value, it uses a PID algorithm to jointly adjust the frequencies of the first and second compressors of the first refrigeration system, as well as the third and fourth compressors of the second refrigeration system. As the cooling or heating load increases, the first compressor, the third compressor, the second compressor, and the fourth compressor are started sequentially. When the cooling or heating load decreases, the fourth compressor, the second compressor, the third compressor, and the first compressor are shut down sequentially.

[0013] As a further improvement, in heating mode, when the first compressor, the second compressor, the third compressor, and the fourth compressor all reach their output limits but the air supply temperature is still insufficient, the electric heater is started for auxiliary heating; when the heating load decreases, the electric heater is turned off first, and then the fourth compressor, the second compressor, the third compressor, and the first compressor are turned off in sequence.

[0014] As a further improvement, in heating mode, the first four-way valve of the first refrigeration system or the second four-way valve of the second refrigeration system is briefly placed in cooling mode for defrosting, while the electric heater is activated to compensate for the supply air temperature; the first refrigeration system and the second refrigeration system do not defrost at the same time.

[0015] As a further improvement, the control system collects the supply air humidity in real time, and uses a PID algorithm to independently adjust the frequency of the third compressor component of the third refrigeration system based on the deviation between the supply air humidity and the set value.

[0016] Compared with the prior art, the beneficial effects of the present invention are: This application employs three independent vapor compression refrigeration cycles—a first refrigeration system, a second refrigeration system, and a third refrigeration system—to achieve cascaded air cooling, cascaded dehumidification, and condensation heat recovery. Compared to single-system dehumidifiers, it has higher energy efficiency and lower supply air dew point. In this application, under dehumidification conditions, the third refrigeration system is equipped with a third condenser and a third evaporator in the air duct. The heat obtained by the third refrigeration system during cooling and dehumidification, as well as the work done by the compressor, are used to heat and regulate the temperature of the processed air through the third condenser. This reduces the reliance on electric heaters under dehumidification conditions and is more energy-efficient. This application employs a first refrigeration system and a second refrigeration system to regulate temperature, and a third refrigeration system to regulate humidity, thereby achieving decoupled control of temperature and humidity. This allows the supply air temperature and humidity to be automatically adjusted according to the set values, improving control accuracy. The first compressor, second compressor, third compressor and fourth compressor in the first refrigeration system and the second refrigeration system of this application adopt stage loading, stage unloading and PID joint control, so that all heat exchangers still have a high utilization rate under partial load and improve the overall energy efficiency throughout the year; This application can switch the working states of the first refrigeration system, the second refrigeration system and the third refrigeration system according to different operating conditions, so as to achieve efficient cooling in summer, deep dehumidification and reheating in dehumidification mode, and stable heat pump heating in winter. When the first or second refrigeration system is frosted, this application switches the corresponding system for short-term reverse defrosting while the other system continues to heat, and at the same time starts the electric heater to compensate for the supply air temperature, so as to achieve continuous and stable heating. The third evaporator of the third refrigeration system of this application can be arranged upstream of the first internal heat exchanger, or between the first internal heat exchanger and the second internal heat exchanger, or between the second internal heat exchanger and the third condenser, depending on the different models. The arrangement is flexible. The third condenser is always located at the downstream end of all heat exchangers to complete reheating, so as to adapt to different product structure designs. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a structural schematic diagram of an embodiment of the present invention; Figure 2 This is a schematic diagram of the heating operation in an embodiment of the present invention; Figure 3 This is a schematic diagram of the dehumidification process according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the first four-way valve according to an embodiment of the present invention.

[0019] In the diagram: 1-Air supply duct; 2-First refrigeration system; 3-Second refrigeration system; 4-Third refrigeration system; 5-First compressor; 6-Second compressor; 7-First four-way valve; 8-First external heat exchanger; 9-First expansion valve; 10-First internal heat exchanger; 11-Third compressor; 12-Fourth compressor; 13-Second four-way valve; 14-Second external heat exchanger; 15-Second expansion valve; 16-Second internal heat exchanger; 17-Fifth compressor; 18-Third condenser; 19-Third expansion valve; 20-Third evaporator; 21-Filter; 22-Air supply fan; 23-Electric heater. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figures 1 to 4 As shown, a cascade dehumidification system capable of operating under all conditions in all seasons includes an air supply duct 1 and three independent vapor compression refrigeration cycles. The three vapor compression refrigeration cycles are designated as a first refrigeration system 2, a second refrigeration system 3, and a third refrigeration system 4.

[0022] The first refrigeration system 2 includes a first compressor assembly, which may be a single compressor or include a first compressor 5 and a second compressor 6 connected in series or in parallel. In this embodiment, the first compressor 5 and the second compressor 6 are connected in parallel. It also includes a first four-way valve 7, a first external heat exchanger 8, a first expansion valve 9, and a first internal heat exchanger 10 disposed in the air supply duct 1.

[0023] The exhaust ports of the first compressor 5 and the second compressor 6 are connected in parallel to the D port of the first four-way valve 7. The intake ports of the first compressor 5 and the second compressor 6 are connected in parallel to the S port of the first four-way valve 7. The C port of the first four-way valve 7 is connected to one end of the first external heat exchanger 8. The E port of the first four-way valve 7 is connected to one end of the first internal heat exchanger 10. The other end of the first external heat exchanger 8 and the other end of the first internal heat exchanger 10 are connected to the first expansion valve 9.

[0024] The first refrigeration system 2 switches between refrigeration mode and heating mode via the first four-way valve 7: In cooling mode, such as Figure 1 and Figure 4As shown, the first four-way valve 7 connects the D port to the C port and the E port to the S port. Refrigerant flows out from the exhaust ports of the first compressor 5 and the second compressor 6, enters the first external heat exchanger 8, and condenses into a liquid state. Then, the refrigerant enters the first expansion valve 9, where its pressure decreases. Next, the refrigerant enters the first internal heat exchanger 10, evaporates, absorbs heat, and exchanges heat with the air in the air duct 1. Finally, the refrigerant returns to the suction ports of the first compressor 5 and the second compressor 6. At this time, the first external heat exchanger 8 functions as a condenser, and the first internal heat exchanger 10 functions as an evaporator.

[0025] In heating mode, such as Figure 2 As shown, the first four-way valve 7 connects the D port to the E port and the C port to the S port. Refrigerant flows out from the exhaust ports of the first compressor 5 and the second compressor 6, enters the first internal heat exchanger 10, condenses and releases heat, exchanging heat with the air in the air duct 1; then the refrigerant enters the first expansion valve 9, where the pressure decreases; next, the refrigerant enters the first external heat exchanger 8, evaporates and absorbs heat; finally, the refrigerant returns to the suction ports of the first compressor 5 and the second compressor 6. At this time, the first internal heat exchanger 10 is used as a condenser, and the first external heat exchanger 8 is used as an evaporator.

[0026] The second refrigeration system 3 includes a second compressor assembly, which may be a single compressor or include a third compressor 11 and a fourth compressor 12 connected in series or in parallel. In this embodiment, the third compressor 11 and the fourth compressor 12 are connected in parallel. It also includes a second four-way valve 13, a second external heat exchanger 14, a second expansion valve 15, and a second internal heat exchanger 16 disposed in the air supply duct 1.

[0027] The exhaust ports of the third compressor 11 and the fourth compressor 12 are connected in parallel to the D port of the second four-way valve 13. The intake ports of the third compressor 11 and the fourth compressor 12 are connected in parallel to the S port of the second four-way valve 13. The C port of the second four-way valve 13 is connected to one end of the second external heat exchanger 14. The E port of the second four-way valve 13 is connected to one end of the second internal heat exchanger 16. The other end of the second external heat exchanger 14 and the other end of the second internal heat exchanger 16 are connected to the second expansion valve 15.

[0028] The second refrigeration system 3 switches between cooling and heating modes via the second four-way valve 13. The adjustment method of the second refrigeration system 3 is the same as that of the first refrigeration system 2. In cooling mode, the second four-way valve 13 connects the D port to the C port and the E port to the S port. Refrigerant flows out from the exhaust ports of the third compressor 11 and the fourth compressor 12, enters the second external heat exchanger 14, and condenses into a liquid state. Then, the refrigerant enters the second expansion valve 15, where its pressure decreases. Next, the refrigerant enters the second internal heat exchanger 16, where it evaporates and absorbs heat, exchanging heat with the air in the air duct 1. Finally, the refrigerant returns to the suction ports of the third compressor 11 and the fourth compressor 12. At this time, the second external heat exchanger 14 functions as a condenser, and the second internal heat exchanger 16 functions as an evaporator.

[0029] In heating mode, the second four-way valve 13 connects the D port to the E port and the C port to the S port. Refrigerant flows out from the exhaust ports of the third compressor 11 and the fourth compressor 12, enters the second internal heat exchanger 16, condenses and releases heat, exchanging heat with the air in the air duct 1; then the refrigerant enters the second expansion valve 15, where its pressure decreases; next, the refrigerant enters the second external heat exchanger 14, evaporates and absorbs heat; finally, the refrigerant returns to the suction ports of the third compressor 11 and the fourth compressor 12. At this time, the second internal heat exchanger 16 functions as a condenser, and the second external heat exchanger 14 functions as an evaporator.

[0030] The third refrigeration system 4 includes a third compressor assembly, specifically a single fifth compressor 17; it also includes a third condenser 18, a third expansion valve 19, and a third evaporator 20. Both the third condenser 18 and the third evaporator 20 are located within the air supply duct 1, with the third condenser 18 situated at the downstream end of all heat exchangers. The exhaust port of the fifth compressor 17 is connected to one end of the third condenser 18, the other end of the third condenser 18 is connected to one end of the third expansion valve 19, the other end of the third expansion valve 19 is connected to one end of the third evaporator 20, and the other end of the third evaporator 20 is connected to the suction port of the fifth compressor 17.

[0031] When the third refrigeration system 4 is working, the refrigerant flows out from the exhaust port of the fifth compressor 17 and first enters the third condenser 18, which is located at the downstream end of all heat exchangers. While condensing into a liquid state, it heats the air in the air supply duct 1. Then the refrigerant enters the third expansion valve 19, where the pressure decreases. Next, it enters the third evaporator 20, where it evaporates and absorbs heat, exchanging heat with the air in the air supply duct 1. Finally, it returns to the suction port of the fifth compressor 17.

[0032] In this embodiment, the first internal heat exchanger 10, the second internal heat exchanger 16, and the third condenser 18 are arranged sequentially along the airflow direction. The third evaporator 20 is located upstream of the third condenser 18. The third evaporator 20 can be located upstream of the first internal heat exchanger 10, or between the first internal heat exchanger 10 and the second internal heat exchanger 16, or between the second internal heat exchanger 16 and the third condenser 18, allowing for flexible arrangement to adapt to different product structure designs. In this embodiment, the third evaporator 20 is arranged between the second internal heat exchanger 16 and the third condenser 18.

[0033] In this embodiment, the air supply duct 1 is also provided with a filter 21 and an air supply fan 22, wherein the filter 21 is located on the air inlet side of the air supply duct 1 and the air supply fan 22 is located on the air outlet side of the air supply duct 1.

[0034] In this embodiment, an electric heater 23 is also provided in the air supply duct 1. The electric heater 23 is located downstream of the third condenser 18 and between the air supply fan 22.

[0035] A control method for a cascade dehumidification system that operates under all conditions in all four seasons, including cooling mode, heating mode and dehumidification mode.

[0036] Under refrigeration conditions, such as Figure 1 As shown, the first refrigeration system 2 and the second refrigeration system 3 are operating, while the third refrigeration system 4 is not operating. The first four-way valve 7 and the second four-way valve 13 are both set to refrigeration mode. In the air supply duct 1, the processed air first passes through the filter 21; then it passes through the first internal heat exchanger 10 of the first refrigeration system 2, where it is cooled and dehumidified; next, it passes through the second internal heat exchanger 16 of the second refrigeration system 3, where it is further cooled and dehumidified; finally, it enters the air supply fan 22, where it is pressurized and delivered to the user end.

[0037] Under heating conditions, such as Figure 2 As shown, the first refrigeration system 2 and the second refrigeration system 3 are operating, while the third refrigeration system 4 is not operating. Both the first four-way valve 7 and the second four-way valve 13 are set to heating mode. In the air supply duct 1, the processed air first passes through filter 21; then it passes through the first internal heat exchanger 10 of the first refrigeration system 2 and is heated; next, it passes through the second internal heat exchanger 16 of the second refrigeration system 3 and is further heated; finally, it enters the air supply fan 22, is pressurized, and delivered to the user end. Under certain operating conditions, when the air supply temperature cannot meet the user's needs, the electric heater 23 located upstream of the air supply fan 22 will be activated as needed, further increasing the temperature of the processed air.

[0038] In winter, when temperatures are low, the evaporation temperatures of both the first refrigeration system 2 and the second refrigeration system 3 may fall below zero degrees Celsius. At this time, both the first external heat exchanger 8 of the first refrigeration system 2 and the second external heat exchanger 14 of the second refrigeration system 3 may frost over. When the suction pressure of either the first refrigeration system 2 or the second refrigeration system 3 remains below the set frosting pressure, the control system determines that it is entering the defrosting procedure.

[0039] Taking the first refrigeration system 2 as an example, the first four-way valve 7 is briefly placed in the refrigeration mode for defrosting, while the second refrigeration system 3 continues to operate in the heating mode. At the same time, the electric heater 23 is activated to compensate for the supply air temperature. Therefore, the entire unit can provide continuous heating without shutting down the entire unit. After the defrosting mode is maintained for a period of time, the first four-way valve 7 and the electric heater 23 are restored to their state before entering the defrosting mode.

[0040] The defrosting time is very short, much shorter than the duration of normal operation in heating mode. Therefore, the defrosting phases of the first refrigeration system 2 and the second refrigeration system 3 will not overlap. This ensures that at least one system is in heating mode, providing stable heating. At the same time, the electric heater 23 will also automatically operate to ensure that the system can maintain the required supply air temperature.

[0041] Under dehumidification conditions, such as Figure 3 As shown, the first refrigeration system 2, the second refrigeration system 3, and the third refrigeration system 4 operate simultaneously, with the first four-way valve 7 and the second four-way valve 13 both set to refrigeration mode. In the air supply duct 1, the processed air first passes through filter 21; then through the first internal heat exchanger 10 of the first refrigeration system 2 to complete the first stage of cooling and dehumidification; next, through the second internal heat exchanger 16 of the second refrigeration system 3 to complete the second stage of cooling and dehumidification; then through the third evaporator 20 of the third refrigeration system 4 to achieve deep dehumidification; finally, through the third condenser 18 of the third refrigeration system 4, it is reheated to restore the air supply to the set temperature while maintaining a low humidity content; finally, it enters the air supply fan 22, is pressurized, and delivered to the user end.

[0042] In this embodiment, the control system collects the supply air temperature in real time. Based on the deviation between the supply air temperature and the set value, a PID algorithm is used to jointly adjust the frequencies of the first compressor 5 and the second compressor 6 of the first refrigeration system 2, as well as the third compressor 11 and the fourth compressor 12 of the second refrigeration system 3. As the cooling or heating load increases, the first compressor 5, the third compressor 11, the second compressor 6, and the fourth compressor 12 are started sequentially; when the cooling or heating load decreases, the fourth compressor 12, the second compressor 6, the third compressor 11, and the first compressor 5 are shut down sequentially.

[0043] The following are the specific rules for loading and unloading the first and second refrigeration systems: The loading rules are as follows: Start the first compressor 5 and perform PID adjustment. When the first compressor 5 reaches the shift upper limit threshold, start the third compressor 11 and run it at the upshift starting value. At the same time, reduce the load of the first compressor 5 to the upshift starting value. PID regulation is performed on the first compressor 5 and the third compressor 11. When the first compressor 5 reaches the upper limit threshold of the shift again, the second compressor 6 is started and runs at the starting value of the upshift. At the same time, the first compressor 5 is unloaded to the starting value of the upshift. The first compressor 5 and the second compressor 6 maintain the same output for PID regulation. The first compressor 5, the second compressor 6 and the third compressor 11 are PID regulated. When the third compressor 11 reaches the upper limit threshold of the shift, the fourth compressor 12 is started and runs at the starting value of the upshift. At the same time, the third compressor 11 is unloaded to the starting value of the upshift. The third compressor 11 and the fourth compressor 12 maintain the same output for PID regulation.

[0044] The load reduction rules are as follows: When the first compressor 5, the second compressor 6, the third compressor 11, and the fourth compressor 12 are all turned on for PID regulation, when the third compressor 11 and the fourth compressor 12 are simultaneously reduced to the lower limit of the system output, the fourth compressor 12 is turned off, and the third compressor 11 is loaded to the downshift starting value; the first compressor 5 and the second compressor 6 maintain the same output, and the PID regulation of the first compressor 5, the second compressor 6, and the third compressor 11 continues; When the first compressor 5 and the second compressor 6 are simultaneously unloaded to the lower limit of the system output, the second compressor 6 is turned off, and the first compressor 5 is loaded to the downshift starting value; the PID control of the first compressor 5 and the third compressor 11 continues. When the third compressor 11 is reduced to the lower limit of the system output, the third compressor 11 is turned off, and the first compressor 5 is loaded to the downshift starting value; the PID adjustment of the first compressor 5 continues until the first compressor 5 is reduced to the lowest frequency and then the first compressor 5 is turned off.

[0045] In addition, under heating conditions, when the first compressor 5, the second compressor 6, the third compressor 11 and the fourth compressor 12 all reach their upper output limits but the air supply temperature is still insufficient, the electric heater 23 is started for auxiliary heating; when the heating load decreases, the electric heater 23 is turned off first, and then the fourth compressor 12, the second compressor 6, the third compressor 11 and the first compressor 5 are turned off in sequence.

[0046] The control system collects the supply air humidity in real time and uses a PID algorithm to independently adjust the frequency of the fifth compressor 17 in the third refrigeration system 4 based on the deviation between the supply air humidity and the set value. Therefore, the supply air temperature and supply air humidity can be controlled independently, achieving decoupled temperature and humidity regulation and improving control accuracy.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A cascade dehumidification system that operates under all conditions in all four seasons, characterized in that, include: Air supply duct; The first refrigeration system includes a first compressor assembly, a first four-way valve, a first external heat exchanger, a first expansion valve, and a first internal heat exchanger disposed in the air supply duct. The first refrigeration system switches between a refrigeration mode and a heating mode through the first four-way valve. The second refrigeration system includes a second compressor assembly, a second four-way valve, a second external heat exchanger, a second expansion valve, and a second internal heat exchanger disposed in the air supply duct. The second refrigeration system switches between refrigeration mode and heating mode through the second four-way valve. The third refrigeration system includes a third compressor assembly, a third condenser, a third expansion valve, and a third evaporator, wherein the third condenser and the third evaporator are both disposed within the air supply duct. The first internal heat exchanger, the second internal heat exchanger, and the third condenser are arranged sequentially along the airflow direction; the third evaporator is located upstream of the third condenser. The first refrigeration system, the second refrigeration system, and the third refrigeration system are three independent vapor compression refrigeration cycles.

2. The cascade dehumidification system for all-season operation as described in claim 1, characterized in that: The third evaporator is located upstream of the first internal heat exchanger, or the third evaporator is located between the first internal heat exchanger and the second internal heat exchanger, or the third evaporator is located between the second internal heat exchanger and the third condenser.

3. The cascade dehumidification system for all-season operation as described in claim 1, characterized in that: The air supply duct is also equipped with a filter and an air supply fan.

4. The cascade dehumidification system for all-season operation as described in claim 1, characterized in that: An electric heater is also installed in the air supply duct, and the electric heater is located downstream of the third condenser.

5. A cascade dehumidification system for all-season operation as described in claim 1, characterized in that: The first compressor assembly is a single compressor, or the first compressor assembly includes a first compressor and a second compressor connected in series or in parallel; the second compressor assembly is a single compressor, or the second compressor assembly includes a third compressor and a fourth compressor connected in series or in parallel.

6. A control method for a cascade dehumidification system operating under all conditions in all four seasons as described in any one of claims 1-5, characterized in that: This includes cooling, heating, and dehumidification modes. In refrigeration mode, the first and second refrigeration systems operate, while the third refrigeration system does not operate. Both the first four-way valve and the second four-way valve are set to refrigeration mode. Air undergoes two-stage cooling through the first and second internal heat exchangers. In heating mode, the first and second refrigeration systems operate, while the third refrigeration system does not operate. Both the first four-way valve and the second four-way valve are set to heating mode. Air undergoes two-stage heating through the first and second internal heat exchangers. In dehumidification mode, the first refrigeration system, the second refrigeration system, and the third refrigeration system operate simultaneously, and the first four-way valve and the second four-way valve are both set to refrigeration mode; the air undergoes three stages of cooling and dehumidification through the first internal heat exchanger, the second internal heat exchanger, and the third evaporator, and is then heated by the third condenser.

7. The control method as described in claim 6, characterized in that: The control system collects the supply air temperature in real time, and uses a PID algorithm to jointly adjust the frequencies of the first and second compressors of the first refrigeration system and the third and fourth compressors of the second refrigeration system based on the deviation between the supply air temperature and the set value. As the cooling or heating load increases, the first compressor, the third compressor, the second compressor, and the fourth compressor are started sequentially. When the cooling or heating load decreases, the fourth compressor, second compressor, third compressor, and first compressor are shut down in sequence.

8. The control method as described in claim 7, characterized in that: In heating mode, when the first compressor, the second compressor, the third compressor, and the fourth compressor all reach their output limits but the air supply temperature is still insufficient, the electric heater is started for auxiliary heating; when the heating load decreases, the electric heater is turned off first, and then the fourth compressor, the second compressor, the third compressor, and the first compressor are turned off in sequence.

9. The control method as described in claim 6, characterized in that: In heating mode, the first four-way valve of the first refrigeration system or the second four-way valve of the second refrigeration system is briefly placed in cooling mode for defrosting, while the electric heater is activated to compensate for the supply air temperature; the first refrigeration system and the second refrigeration system do not defrost at the same time.

10. The control method as described in claim 6, characterized in that: The control system collects the supply air humidity in real time and uses a PID algorithm to independently adjust the frequency of the third compressor component of the third refrigeration system based on the deviation between the supply air humidity and the set value.

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