Capacity adjusting method and system for variable working condition refrigerating unit special for rail refrigerated vehicle

Abstract

The invention provides a capacity adjusting method and system for a special variable-working-condition refrigerating unit for a rail refrigerated vehicle, and the method comprises the steps: carrying out the temperature region division of the rail refrigerated vehicle during refrigeration mode operation and freezing mode operation, and judging the temperature region of the refrigerated vehicle based on the air supply temperature in the rail refrigerated vehicle in the refrigeration mode; in the freezing mode, the temperature area where the refrigeration vehicle is located is judged based on the return air temperature in the rail refrigeration vehicle, and refrigeration temperature control adjustment and freezing temperature control adjustment are conducted through different control strategies according to the temperature area where the refrigeration vehicle is located; whether defrosting conditions are met or not is judged in the refrigeration mode and the freezing mode, and defrosting is conducted; and whether shutdown conditions are met or not is judged in the refrigeration mode and the freezing mode, if yes, a shutdown program is started, and if not, a safety protection program is started, and data collection and monitoring, alarm monitoring and output are sequentially carried out. Precise temperature control is beneficial to keeping freshness and quality of goods, and loss caused by temperature fluctuation is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of power engineering and engineering thermophysics, and in particular to a capacity adjustment method and system for a variable-operating-condition refrigeration unit dedicated to a rail refrigerated vehicle. Background Art

[0002] The problems existing in refrigerated and frozen insulated vehicles in the cold chain supply mainly include: the cooling and heating requirements of the carriages are large, and a large amount of electricity is consumed for the conversion of cold and hot energy during normal operation.

[0003] For insulated vehicles, it is necessary to ensure the refrigeration, freezing and insulation effects throughout the year, so there is a need for heating in winter and cooling in summer. On this basis, the patent of this invention proposes to use a liquid storage tank to transform into a flash evaporator to optimize the refrigerant circulation process and build a refrigeration system for refrigerated, frozen and insulated vehicles, making full use of its powerful performance.

[0004] Another thing that needs to be considered is that refrigerated and frozen insulated vehicles have their own working characteristics. The refrigeration system with flash steam installed on the vehicle needs to adapt to specific control logic. The operating control logic should be improved according to the specific operating characteristics and needs of the application scenario. The ready-made control logic of other fields (heat pump water heaters, heat pump heating, automotive air conditioning heat pumps and thermal management, etc.) cannot be copied.

[0005] During the operation of refrigerated and frozen insulated vehicles, with the frequent loading and unloading of goods, the fluctuation of cold and hot loads in the vehicle is large, and the required margin of the heat pump air-conditioning system also increases accordingly. It cannot be designed according to the average cooling capacity or heating capacity requirements. At the same time, the requirements for humidity of the goods stored in the car are often more stringent, and precise air supply temperature needs to be controlled to ensure the humidity level in the car. When the heat pump is running in winter, try to avoid defrosting the outdoor heat exchanger. Once the system enters the defrost mode, a large range of temperature fluctuations will occur in the car. Therefore, it is also necessary to propose a frost-free control strategy. Summary of the invention

[0006] The present invention provides a capacity adjustment method and system for a variable-operating-condition refrigeration unit dedicated to a rail refrigerated vehicle, which solves the problem that a refrigeration system with a flash tank carried on a refrigerated vehicle needs to be adapted to a specific control logic, thereby achieving efficient and energy-saving operation of the refrigeration system.

[0007] To achieve the above object, the technical solution of the method of the present invention is:

[0008] A method for adjusting the capacity of a variable-operating-condition refrigeration unit for a rail refrigerated vehicle, characterized by comprising the following steps:

[0009] Step 1: Divide the temperature zones for the refrigerated mode and frozen mode operation of the rail refrigerated vehicle.

[0010] Step 2. In the refrigeration mode, the temperature zone of the refrigerated vehicle is determined based on the supply air temperature in the rail refrigerated vehicle, and different control strategies are used to adjust the refrigeration temperature according to the temperature zone; in the freezing mode, the temperature zone of the refrigerated vehicle is determined based on the return air temperature in the rail refrigerated vehicle, and different control strategies are used to adjust the freezing temperature according to the temperature zone;

[0011] Step 3. In the refrigeration mode and the freezing mode, determine whether the defrosting conditions are met respectively. If yes, start the defrost control strategy to defrost respectively. If no, proceed to the next step.

[0012] Step 4. In the refrigeration mode and the freezing mode, determine whether the shutdown conditions are met. If so, start the shutdown program. If not, start the safety protection program and perform data collection and monitoring, alarm monitoring and output in sequence.

[0013] Furthermore, in step 1, the refrigeration mode includes a refrigeration rapid cooling zone, a refrigeration cooling and frequency reduction zone, a refrigeration variable frequency capacity adjustment zone, a refrigeration fixed frequency hot air capacity adjustment zone, and a refrigeration heating and temperature rising zone; the freezing mode includes a freezing rapid cooling zone, a freezing cooling and frequency reduction zone, a freezing variable frequency capacity adjustment zone, and a freezing shutdown zone.

[0014] Further, the refrigerated rapid cooling zone in step 1 is a zone where the air supply temperature drops to 1.5°C higher than the set temperature or the air supply temperature rises to 3°C higher than the set temperature; the refrigerated cooling and frequency reduction zone is a zone where the air supply temperature drops to between the set temperature and 1.5°C higher than the set temperature or the air supply temperature rise is equal to 3°C of the set temperature; the refrigerated variable frequency capacity adjustment zone is a zone where the air supply temperature drops to between -1.5°C higher than the set temperature and the set temperature or the air supply temperature rise is 0.4°C higher than the set temperature and 3°C higher than the set temperature; the refrigerated fixed frequency hot air capacity adjustment zone is a zone where the air supply temperature drops to between -2°C higher than the set temperature and -1.5°C higher than the set temperature or the air supply temperature rise is 0.3°C higher than the set temperature and 0.4°C higher than the set temperature; the refrigerated heating and heating zone is a zone where the air supply temperature drops to below -2°C lower than the set temperature or the air supply temperature rise is 0.3°C lower than the set temperature;

[0015] The refrigeration rapid cooling zone is the zone where the return air temperature drops to 1.5℃ above the set temperature or the return air temperature rises to 3℃ above the set temperature; the refrigeration cooling frequency reduction zone is the zone where the return air temperature drops to between the set temperature and 1.5℃ above the set temperature or the return air temperature rise is equal to 3℃ of the set temperature; the refrigeration variable frequency capacity adjustment zone is the zone where the return air temperature drops to between -2℃ above the set temperature and the set temperature or the return air temperature rise is equal to the set temperature and 3℃ above the set temperature; the refrigeration shutdown zone is the zone where the return air temperature drops to below -2℃ of the set temperature or the supply air temperature rise is equal to or lower than the set temperature.

[0016] Further, the refrigerated rapid cooling zone is controlled by setting the refrigerated temperature and the evaporator superheat respectively, including: starting the compressor and increasing it at a constant frequency until the compressor runs at the maximum speed, fully opening the evaporator fan and running it at the highest gear, controlling the fan start and stop and keeping the condensing pressure within a reasonable range, and controlling the opening of the electronic expansion valve by setting the superheat;

[0017] The compressor in the refrigeration cooling and frequency reduction area is subjected to frequency reduction control, that is, the supply air temperature is collected and compared at regular intervals during the frequency reduction stage. If it is found that the supply air temperature keeps decreasing, the compressor frequency is reduced. If it is found that the temperature remains unchanged or even increases, the corresponding frequency is increased.

[0018] The refrigeration variable frequency capacity adjustment area is variable frequency capacity adjustment, including: the deviation between the air supply temperature and the set temperature is calculated through PID calculation in the programmable controller, and the compressor frequency required by the refrigeration system is output to achieve accurate matching between the refrigeration unit and the load in the box;

[0019] In the refrigerated fixed-frequency hot gas capacity adjustment area, a virtual load is added to the evaporator by introducing the high-temperature gas on the exhaust side of the compressor into the suction pipe on the inlet side of the evaporator, that is, the load inside the box plus the virtual load is re-matched with the refrigeration capacity of the refrigeration unit. The opening of the hot gas bypass valve will be obtained by PID calculation in the programmable controller according to the deviation between the supply air temperature and the set temperature;

[0020] In the refrigerated heating temperature rising zone, the high-temperature gas discharged from the compressor is introduced into the evaporator through the hot gas bypass valve, and the heat exchange between the evaporator and the air is used to increase the temperature inside the box.

[0021] Furthermore, the control steps of adjusting the hot gas bypass valve are as follows:

[0022] (1) Hot gas regulation: Control the flow of refrigerant by adjusting the opening of the hot gas bypass valve to maintain a stable temperature inside the box;

[0023] (2) Calculation of hot gas bypass valve opening: Calculate the hot gas bypass valve opening V based on the temperature deviation ΔT and the preset valve response curve. The calculation formula is:

[0024] V=V0+K v ΔT

[0025] Among them, V0 is the initial opening of the hot gas bypass valve, and Kv is the valve opening gain.

[0026] Furthermore, the rapid cooling zone of the refrigeration is controlled by a scroll compressor, an electronic expansion valve, a condenser fan and an evaporator fan respectively, and the refrigeration unit works at full load, wherein the evaporator fan is controlled by a low-speed gear, and the low-speed gear is half the air volume of the full load;

[0027] The compressor is frequency-reduced in the refrigeration and cooling frequency-reduction zone, that is, the return air temperature is collected and compared at regular intervals during the frequency-reduction stage. If the return air temperature is found to be decreasing, the compressor frequency is reduced. If the temperature is found to be unchanged or even increasing, the frequency is increased accordingly.

[0028] The refrigeration variable frequency capacity adjustment area includes the variable frequency capacity adjustment control of the scroll compressor and the start and stop capacity adjustment control of the scroll compressor. According to the deviation between the return air temperature and the set temperature, the required frequency is calculated by the PID algorithm in the programmable logic controller. The PLC transmits the calculated frequency to the inverter using the RS485 communication protocol. The inverter then controls the actual operating frequency of the compressor to achieve the best match between the refrigeration unit and the load in the box.

[0029] The refrigeration shutdown zone is the lower limit of the refrigeration capacity adjustment zone. The compressor, electronic expansion valve and condenser fan stop running, and the evaporator fan adopts low speed control to maintain air circulation in the box; when the return air temperature is higher than the target set temperature, it enters the refrigeration variable frequency capacity adjustment zone.

[0030] Furthermore, the defrost control strategy in step 3 includes manual defrost and timed defrost, specifically:

[0031] Start the defrost mode. The defrost indicator light will light up, the hot gas bypass valve will be opened, the electric heater and compressor will be started, the evaporator fan will be turned off, and the condenser fan will be turned on or off;

[0032] If the evaporator outlet temperature is greater than or equal to 25°C or the defrost time is greater than or equal to 80 minutes, the defrost will stop, the defrost indicator will go off and the timer will be reset, otherwise return to the previous step.

[0033] On the other hand, the present invention provides a capacity adjustment system for a variable-operating-condition refrigeration unit for a rail refrigerated vehicle, comprising the following steps:

[0034] Module 1. It is used to divide the temperature zones when the rail refrigerated vehicle is running in refrigeration mode and freezing mode respectively.

[0035] Module 2 is used to determine the temperature zone of the refrigerated vehicle based on the supply air temperature in the rail refrigerated vehicle in the refrigeration mode, and adopt different control strategies to adjust the refrigeration temperature according to the temperature zone; in the freezing mode, determine the temperature zone of the refrigerated vehicle based on the return air temperature in the rail refrigerated vehicle, and adopt different control strategies to adjust the freezing temperature according to the temperature zone;

[0036] Module three is used to determine whether the defrosting conditions are met in the refrigeration mode and the freezing mode respectively. If yes, the defrosting control strategy is activated to perform defrosting respectively. If no, the next step is executed.

[0037] Module four is used to determine whether the shutdown conditions are met in the refrigeration mode and the freezing mode respectively. If so, the shutdown program is started. If not, the safety protection program is started and data collection and monitoring, alarm monitoring and output are performed in sequence.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The refrigerated truck control system design of the present invention has more advanced characteristics than the existing refrigerated container control technology in terms of improving temperature control accuracy, flexibility, safety and energy efficiency, and provides a more reliable guarantee for cargo transportation. Its main advantages are as follows:

[0040] (1) Accurate temperature management: The system can achieve rapid reduction and constant maintenance of the temperature inside the box through in-box temperature management and refrigeration and freezing temperature control programs. This precise temperature control helps maintain the freshness and quality of the goods and reduce losses caused by temperature fluctuations.

[0041] (2) Flexible adjustment capability: Through the superheat adjustment of the evaporator, the variable frequency control of the compressor, and the optimization control of the intermediate pressure, the system can intelligently adjust the refrigeration capacity according to actual needs. This flexibility helps to maintain high efficiency under different working conditions, thereby saving energy.

[0042] (3) Integrated functional control and logical coordination: The system is designed with refrigeration mode and freezing mode, covering multiple adjustment areas (such as rapid cooling area, variable frequency capacity adjustment area, etc.), so that it can efficiently respond to different work needs. This partition design improves the system's response speed and adaptability.

[0043] (4) Safety protection mechanism: The system integrates a variety of safety protection mechanisms. When abnormal situations occur, it can promptly alarm and take measures to prevent equipment damage and cargo loss, thereby enhancing the safety of the overall system.

[0044] (5) Efficient energy utilization: Through variable frequency control of the compressor and adjustment of the hot gas capacity, the system can dynamically adjust energy consumption according to actual needs, thereby improving energy efficiency and reducing operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1The figure is a schematic diagram of the control flow of the refrigeration system of a refrigerated truck according to an embodiment of the present invention.

[0047] Figure 2 Schematic diagram of temperature zone division in the refrigeration mode according to an embodiment of the present invention.

[0048] Figure 3 Schematic diagram of temperature zone division in freezing mode according to an embodiment of the present invention.

[0049] Figure 4 This is a flow chart of the control strategy for the refrigeration rapid cooling zone in the refrigeration mode according to an embodiment of the present invention.

[0050] Figure 5 This is a flow chart of the control strategy for the refrigeration variable frequency capacity adjustment zone in the refrigeration mode according to an embodiment of the present invention.

[0051] Figure 6 This is a flow chart of the hot gas bypass valve control strategy in the refrigeration mode according to an embodiment of the present invention.

[0052] Figure 7 This is a schematic diagram of the capacity adjustment principle of the refrigeration mode according to an embodiment of the present invention.

[0053] Figure 8 This is a schematic diagram of variable frequency capacity regulation control of a scroll compressor in refrigeration mode according to an embodiment of the present invention.

[0054] Fig. 9 This is a defrost control flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Example 1

[0057] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0058] like Figure 1 As shown, an embodiment of the present invention provides a method for adjusting the capacity of a variable-operating-condition refrigeration unit dedicated to a rail refrigerated vehicle, which is characterized by comprising the following steps:

[0059] Step 1: Divide the temperature zones for the refrigerated mode and frozen mode operation of the rail refrigerated vehicle.

[0060] Step 2. In the refrigeration mode, the temperature zone of the refrigerated vehicle is determined based on the supply air temperature in the rail refrigerated vehicle, and different control strategies are used to adjust the refrigeration temperature according to the temperature zone; in the freezing mode, the temperature zone of the refrigerated vehicle is determined based on the return air temperature in the rail refrigerated vehicle, and different control strategies are used to adjust the freezing temperature according to the temperature zone;

[0061] Step 3. In the refrigeration mode and the freezing mode, determine whether the defrosting conditions are met respectively. If yes, start the defrost control strategy to defrost respectively. If no, proceed to the next step.

[0062] Step 4. In the refrigeration mode and the freezing mode, determine whether the shutdown conditions are met. If so, start the shutdown program. If not, start the safety protection program and perform data collection and monitoring, alarm monitoring and output in sequence.

[0063] When the temperature in the refrigerated truck reaches the preset minimum requirement, the required cooling capacity is significantly reduced, far lower than the energy required for rapid cooling when the goods are just loaded. At this time, the system will automatically adjust according to the real-time data of the temperature sensor and enter the capacity adjustment mode of the refrigeration system to reduce the cooling output, thereby achieving precise control of the temperature in the box. Studies have shown that if the refrigeration system of the refrigerated truck uses a constant speed compressor and fan, a large amount of energy will be wasted. In contrast, the use of a variable frequency fan can save about 4919 kWh of electricity per year. In addition, the energy efficiency of refrigeration equipment can be further improved by optimizing the refrigeration cycle, adopting a scientific cargo packing method, and using new defrosting technologies (such as hot gas defrosting and hot air defrosting). The present invention uses a digital scroll compressor and hot gas bypass technology to adjust the capacity of the refrigeration system. Due to its wide capacity adjustment range, the digital scroll compressor can achieve continuous and precise capacity output adjustment, thereby performing well in energy saving and reliability. Existing research reports have pointed out that in a laboratory environment, a system using a digital scroll compressor has lower energy consumption than a variable frequency system, showing superior energy saving performance.

[0064] The control system design of the refrigerated truck of the present invention covers several key aspects, including temperature management inside the box, superheat adjustment of the evaporator, frequency conversion control of the compressor, optimal intermediate pressure control, and monitoring of the liquid level of the flash tank. In addition, the system also integrates the conventional function control of the refrigerated truck and the logical coordination between its functions, as well as the safety protection mechanism of the system. The control process of the refrigeration system of the refrigerated truck is as follows: Figure 1 In the control process of the refrigerated truck, the refrigeration temperature control program and the freezing temperature control program constitute the core of the refrigeration unit control system. These programs are mainly responsible for realizing the functions of rapid reduction of the temperature inside the box, constant maintenance of the set temperature, and temperature increase regulation inside the box.

[0065] Furthermore, if Figure 2 and Figure 3 As shown, in step 1, the refrigeration mode includes a refrigeration rapid cooling zone, a refrigeration cooling and frequency reduction zone, a refrigeration variable frequency capacity adjustment zone, a refrigeration fixed frequency hot air capacity adjustment zone, and a refrigeration heating and temperature rising zone; the freezing mode includes a freezing rapid cooling zone, a freezing cooling and frequency reduction zone, a freezing variable frequency capacity adjustment zone, and a freezing shutdown zone.

[0066] When the refrigerated truck is running in the refrigeration mode, the entire temperature range can be divided into the rapid cooling zone, the rapid cooling frequency reduction zone, the variable frequency capacity adjustment zone, the hot air capacity adjustment zone, and the heating temperature rise zone. That is, the boundary temperature of the air supply temperature zone is controlled according to the zone, so as to achieve real-time adjustment of the temperature inside the refrigerated truck. The principle of the freezing mode temperature control system is as follows: Figure 3 When running in freezing mode, the return air temperature can be divided into a rapid cooling zone, a frequency reduction zone, a variable frequency capacity adjustment zone, and a start-stop control zone according to the boundary temperature of the return air temperature zone. By partitioning and using different control methods, the temperature inside the box can be accurately adjusted.

[0067] The temperature control principle of the refrigeration mode is as follows: the change of the air supply temperature is divided into a falling stage and an rising stage. Taking the set temperature as a reference, the temperature falling stage is divided into five temperature zones, corresponding to Figure 2 Similarly, the temperature rise stage is divided into four temperature zones by three temperature nodes, which correspond to E1, D1, C1 and A1 respectively along the temperature rise direction. In order to intuitively and accurately represent the control methods involved in temperature changes, the areas with the same temperature control strategies in the supply air temperature rise and fall stages are connected to obtain Figure 2 , that is, the temperature control strategy adopted when the supply air temperature drops to 1.5℃ higher than the set temperature and the supply air temperature rises to 3℃ higher than the set temperature is the same, that is, the area above the line connecting the 1.5℃ and 3℃ temperature nodes is divided into the A1 zone. The division of the C1, D1, and E1 zones is the same as the above principle. It should be pointed out that the temperature rise stage only involves 4 temperatures, and there is no rapid cooling and frequency reduction zone (B1 zone). Therefore, the triangular area enclosed by the 3℃ temperature node and the line connecting the set temperature and 1.5℃ temperature node is the B1 zone, which is slightly different from the division of other areas.

[0068] The temperature control principle of the freezing mode is as follows: the change of the return air temperature is divided into a falling stage and a rising stage. Two temperature nodes are designed with the set reference temperature as a reference, and the temperature falling stage is divided into four temperature zones, namely A2, B2, C2 and D2. Similarly, the temperature rising stage is divided into three temperature zones, corresponding to D2, C2 and A2. In order to intuitively represent the temperature control strategies adopted in different temperature zones, the areas with the same temperature control strategies in the return air temperature rising stage and falling stage are connected. Figure 3, that is, the temperature control strategy adopted when the return air temperature drops to 1.5℃ higher than the set temperature and when the return air temperature rises to 3℃ higher than the set temperature is the same, that is, the area above the line connecting the 1.5℃ and 3℃ temperature nodes is divided into the A2 zone. The division of the C2 zone and the D2 zone is the same as the above principle. It should be pointed out that there are only three temperature zones in the return air temperature rising stage, and there is no rapid frequency reduction zone (B2 zone). Therefore, the triangular area surrounded by the 3℃ temperature node and the line connecting the set temperature and 1.5℃ temperature nodes is the B2 zone, which is different from the division of other areas.

[0069] The refrigerated rapid cooling zone in step 1 is a zone where the supply air temperature drops to 1.5°C above the set temperature or the supply air temperature rise value is higher than the set temperature by 3°C; the refrigerated cooling frequency reduction zone is a zone where the supply air temperature drops to between the set temperature and 1.5°C above the set temperature or the supply air temperature rise value is equal to the set temperature by 3°C; the refrigerated variable frequency capacity adjustment zone is a zone where the supply air temperature drops to between -1.5°C above the set temperature and the set temperature or the supply air temperature rise value is higher than 0.4°C above the set temperature and 3°C above the set temperature; the refrigerated fixed frequency hot air capacity adjustment zone is a zone where the supply air temperature drops to between -2°C above the set temperature and -1.5°C above the set temperature or the supply air temperature rise value is higher than 0.3°C above the set temperature and 0.4°C above the set temperature; the refrigerated heating temperature rise zone is a zone where the supply air temperature drops to below -2°C below the set temperature or the supply air temperature rise value is lower than 0.3°C below the set temperature;

[0070] The refrigeration rapid cooling zone is the zone where the return air temperature drops to 1.5℃ above the set temperature or the return air temperature rises to 3℃ above the set temperature; the refrigeration cooling frequency reduction zone is the zone where the return air temperature drops to between the set temperature and 1.5℃ above the set temperature or the return air temperature rise is equal to 3℃ of the set temperature; the refrigeration variable frequency capacity adjustment zone is the zone where the return air temperature drops to between -2℃ above the set temperature and the set temperature or the return air temperature rise is equal to the set temperature and 3℃ above the set temperature; the refrigeration shutdown zone is the zone where the return air temperature drops to below -2℃ of the set temperature or the supply air temperature rise is equal to or lower than the set temperature.

[0071] The refrigeration mode uses the supply air temperature to indicate the temperature inside the box. This is because most of the goods loaded in the refrigeration mode are temperature-sensitive. The air in the box exchanges heat in the evaporator, and the return air temperature is high and the supply air temperature is low. In order to ensure that the goods near the air supply port are not frozen, the supply air temperature is used to limit the minimum temperature in the box. The freezing mode uses the return air temperature to indicate the temperature inside the box. This is because the goods loaded in the freezing mode are generally low-temperature and freeze-resistant. Considering that the goods will thaw due to the increase in temperature, this type of goods should pay attention to limiting the maximum temperature in the box. Generally speaking, the cooled air gradually heats up after coming out of the air supply port. When the air returns to the evaporator inlet (return air port), the temperature is the highest, so controlling the return air temperature can ensure the freezing safety of the goods in the box.

[0072] Rapid cooling control strategy in refrigeration mode

[0073] The rapid cooling function of refrigerated trucks is an effective guarantee for the rapid cooling of goods. If you want the refrigeration unit to achieve the purpose of rapid cooling, you should effectively control the scroll compressor, fan and evaporator load, let the refrigeration unit work at full load (maximum cooling capacity) as soon as possible, and speed up the cooling speed in the box. The objects of control include the scroll compressor, electronic expansion valve, condenser fan and evaporator fan. The flow chart of the rapid cooling control strategy in the refrigeration mode is as follows Figure 4 shown.

[0074] Refrigeration mode rapid cooling and frequency reduction zone

[0075] When the supply air temperature drops to 1.5℃ higher than the set refrigeration temperature, that is, the lower limit of the refrigeration rapid cooling zone (A1 zone), it enters the rapid cooling and frequency reduction zone (B1 zone). At this time, the compressor performs frequency reduction control, that is, the supply air temperature is collected and compared at regular intervals (30 seconds) during the frequency reduction stage. If it is found that the supply air temperature has been decreasing, the compressor frequency reduction process is performed. If it is found that the temperature remains unchanged or even increases, the corresponding frequency increase process is performed.

[0076] In this embodiment, the supply air temperature is collected every 30 seconds through the PLC program. If the supply air temperature continues to decrease or remains unchanged, the compressor frequency is reduced by 2Hz each time. If the temperature rises, the compressor frequency is increased by 2Hz and continues to run until the set refrigeration temperature is reached, that is, the lowest point of the rapid cooling and frequency reduction zone (B1 zone).

[0077] Capacity adjustment control strategy for cold storage mode

[0078] The refrigeration mode capacity regulation adopted by the unit studied in this embodiment includes two stages: the scroll compressor capacity regulation stage (variable frequency capacity regulation) and the compressor fixed frequency combined with hot gas regulation control stage (hot gas regulation), namely, C1 zone and D1 zone. The specific control process is as follows: When the supply air temperature continues to drop to the set temperature, it officially enters the refrigeration unit capacity regulation stage, that is, through the deviation between the supply air temperature and the set temperature, the PID operation in the programmable controller is used to output the compressor frequency required by the refrigeration system, so as to achieve accurate matching between the refrigeration unit and the load in the box. The variable frequency capacity regulation control principle of the refrigeration unit is as follows: Figure 5 The main control methods of the scroll compressor capacity adjustment stage are as follows:

[0079] (1) Set the target temperature: Set the air supply temperature T set (e.g. 8℃)

[0080] (2) Temperature deviation calculation: Real-time monitoring of supply air temperature T actual , calculate the temperature deviation ΔT = T set -T actual .

[0081] (3) Compressor frequency output: The compressor frequency f is adjusted according to the PID calculation results. The formula is:

[0082]

[0083] Where f0 is the initial frequency of the compressor.

[0084] Refrigerated fixed frequency hot gas capacity adjustment area

[0085] When the load in the box is too small, the PID control operation is output to the lowest frequency (such as 25HZ) that the compressor allows to operate normally through the variable frequency capacity adjustment method and keep running. If the cooling capacity of the system refrigeration unit is greater than the load in the box, the supply air temperature will continue to decrease. When the supply air temperature deviates from the set temperature by 1.5℃, it will enter the hot air adjustment stage. The fixed frequency of the refrigeration unit compressor combined with the hot air adjustment control principle is as follows Figure 6 shown.

[0086] like Figure 7 As shown, by introducing the high-temperature gas on the exhaust side of the compressor into the suction pipe on the inlet side of the evaporator (3-7b-7), a virtual load is added to the evaporator, that is, the load inside the box plus the virtual load is re-matched with the refrigeration capacity of the refrigeration unit. The opening of the hot gas bypass valve will be based on the deviation between the supply air temperature and the set temperature. Through the PID operation in the programmable controller, a reasonable opening of the hot gas bypass valve is obtained, thereby achieving accurate control of the supply air temperature under low load. The main control steps of hot gas bypass regulation are as follows:

[0087] (1) Hot gas regulation: The flow of refrigerant is controlled by adjusting the opening of the hot gas bypass valve to maintain a stable temperature inside the box.

[0088] (2) Valve opening calculation: Calculate the valve opening V based on the temperature deviation ΔT and the preset valve response curve. The calculation formula is:

[0089] V=V0+K v ΔT (2)

[0090] Among them, V0 is the initial opening of the valve, and Kv is the valve opening gain.

[0091] When the load in the box suddenly increases (the supply air temperature deviates from the set temperature and continues to rise, and the positive deviation becomes larger and larger), the PID controller is used to adjust the opening of the hot gas bypass valve to reduce it. When the hot gas bypass valves are all closed, the positive deviation of the supply air temperature still exists and tends to increase. The control system will switch from the compressor fixed frequency combined with hot gas regulation control to the compressor variable frequency capacity regulation control. If the supply air temperature still rises rapidly and the positive deviation exceeds 3°C, the control system will automatically switch the capacity regulation mode to the rapid cooling mode.

[0092] Refrigeration heating zone

[0093] The warming function of refrigerated trucks is also crucial, especially when passing through cold areas or when cargo ventilation operations are required. In these cases, the low temperature air outside the box may cause the temperature inside the box to drop rapidly. When the temperature inside the box drops to 2°C below the set value, the control system will start the warming control mode. In this mode, the system will introduce the high-temperature gas discharged from the compressor into the evaporator through the hot gas bypass valve, and use the heat exchange between the evaporator and the air to increase the temperature inside the box. After the high-temperature refrigerant gas exchanges heat in the evaporator, it returns to the compressor suction port and is compressed into high-temperature refrigerant gas again, thereby achieving temperature increase in the heat pump mode. During the warming operation, the refrigeration unit only involves the operation of the compressor, the evaporator low-speed fan and the hot gas bypass solenoid valve, and other components do not participate in the work. In addition, in order to speed up the warming speed, the two electric heaters (each with a power of 1500W) located at the bottom of the evaporator will also be activated. Once the supply air temperature reaches the set value, except for the evaporator low-speed fan that continues to operate, all other components of the refrigeration unit will stop working.

[0094] Rapid cooling control strategy in freezing mode

[0095] In freezing mode, the return air temperature is used as the control temperature of the refrigeration unit and represents the temperature inside the box. When running in freezing mode, the scroll compressor, electronic expansion valve, condenser fan and evaporator fan are effectively controlled to make the refrigeration unit work at full load (maximum cooling capacity) and speed up the cooling speed inside the box. Among them, the evaporator fan adopts low-speed control, which is half the air volume of full load. The saved heat load can load more goods and speed up the cooling speed inside the box.

[0096] Rapid cooling and frequency reduction zone control strategy in freezing mode

[0097] The rapid cooling and frequency reduction zone refers to when the return air temperature drops to 1.5°C above the target set temperature. At this time, the refrigeration rapid cooling zone is switched to the rapid cooling and frequency reduction zone. The compressor performs frequency reduction control, that is, the return air temperature is collected and compared at regular intervals (30 seconds) during the frequency reduction stage. If the return air temperature is found to be constantly decreasing, the compressor frequency is reduced. If the temperature is found to be unchanged or even rising, the frequency is increased accordingly. The return air temperature is collected every 30 seconds through the PLC program. If the return air temperature continues to decrease or remains unchanged, the compressor frequency is reduced by 2Hz each time. If the temperature is found to be rising, the compressor frequency is increased by 2Hz and continues to run until the set refrigeration temperature is reached, that is, the lowest point of the rapid cooling and frequency reduction zone (B2 zone).

[0098] Capacity adjustment control strategy for freezing mode

[0099] When the return air temperature gradually approaches the set value, the system will adjust by reducing the frequency. Once the return air temperature reaches the set value, the system will enter the capacity adjustment stage of the freezing mode. This stage includes two main control parts: the variable frequency capacity control of the scroll compressor and the start and stop capacity adjustment control of the scroll compressor. When the return air temperature is within the range of variable frequency capacity adjustment, the frequency of the compressor is no longer affected by the rapid freezing and cooling control, but the required frequency is calculated by the PID algorithm in the programmable logic controller (PLC) based on the deviation between the return air temperature and the set temperature. The PLC uses the RS485 communication protocol to transmit the calculated frequency to the inverter, which then controls the actual operating frequency of the compressor to achieve the best match between the refrigeration unit and the load in the box. The schematic diagram of the variable frequency capacity control of the scroll compressor in freezing mode is shown in the figure. Figure 8 shown.

[0100] When the load in the refrigerated truck is small, the PID controller will reduce the output frequency accordingly. Once the frequency drops to the lowest normal operating frequency of the scroll compressor, if the return air temperature in the box continues to drop, the scroll compressor will stop working when the temperature is 2°C lower than the set value. At this time, except for the evaporator fan in the refrigeration unit, all other components enter the shutdown state. The system will record the frequency of the scroll compressor when it stops. Due to the heat generated by the evaporator fan and the heat leakage of the box, the temperature in the box will gradually rise. When the temperature returns to the set value, the system will restart and the PLC will call the previously stored frequency command inverter to run. When the load in the box suddenly changes, the PID regulator will calculate the required operating frequency of the compressor based on the deviation between the return air temperature and the set temperature. If the return air temperature rises too quickly, the cooling capacity of the scroll compressor may not be able to match the load in the box in time, causing the return air temperature to exceed the set value of 2°C. In this case, the control system will quickly switch from the freezing capacity adjustment mode to the rapid freezing mode to avoid a large jump in the compressor frequency caused by a large deviation during the PID calculation process, thereby preventing the refrigeration system from matching imbalance and the compressor from being subjected to excessive impact, ensuring its normal operation.

[0101] Control strategy of shutdown zone in refrigeration mode

[0102] The refrigeration shutdown zone refers to when the return air temperature drops to 2°C below the target setting temperature or rises to below the target setting temperature. At this time, it is the lower limit of the refrigeration capacity adjustment zone, the compressor, electronic expansion valve and condenser fan stop running, and the evaporator fan adopts low speed control to maintain air circulation in the box; due to heat leakage of the container body and the breathing heat of the goods, when the return air temperature is higher than the target setting temperature, it enters the refrigeration variable frequency capacity adjustment zone.

[0103] Refrigerated truck temperature control strategy

[0104] The warming function of refrigerated trucks is also crucial, especially when passing through cold areas or when cargo ventilation operations are required. In these cases, the low temperature air outside the box may cause the temperature inside the box to drop rapidly. When the temperature inside the box drops to 2°C below the set value, the control system will start the warming control mode. In this mode, the system will introduce the high-temperature gas discharged from the compressor into the evaporator through the hot gas bypass valve, and use the heat exchange between the evaporator and the air to increase the temperature inside the box. After the high-temperature refrigerant gas exchanges heat in the evaporator, it returns to the compressor suction port and is compressed into high-temperature refrigerant gas again, thereby achieving temperature increase in the heat pump mode. During the warming operation, the refrigeration unit only involves the operation of the compressor, the evaporator low-speed fan and the hot gas bypass solenoid valve, and other components do not participate in the work. In addition, in order to speed up the warming speed, the two electric heaters (each with a power of 1500W) located at the bottom of the evaporator will also be activated. Once the supply air temperature reaches the set value, except for the evaporator low-speed fan that continues to operate, all other components of the refrigeration unit will stop working.

[0105] Refrigerated Truck Defrost Control Strategy

[0106] When the temperature in the refrigerated truck drops, the relative humidity will also decrease. When the temperature of the evaporator drops below zero, the water evaporated from the cargo in the box or the water vapor carried by the air during ventilation will condense into frost on the evaporator fins. If the temperature continues to drop, the frost on the evaporator coil and fins will become more serious. This severe frosting phenomenon will significantly reduce the refrigeration efficiency of the refrigeration unit, which will affect the further reduction of the temperature in the box. Therefore, the refrigerated truck must have a defrost function to ensure the long-term and efficient operation of the evaporator. The process of defrost control is as follows: Fig. 9 shown.

[0107] Example 2

[0108] This embodiment provides a capacity adjustment system for a variable-operating-condition refrigeration unit dedicated to a rail refrigerated vehicle, comprising the following steps:

[0109] Module 1. It is used to divide the temperature zones when the rail refrigerated vehicle is running in refrigeration mode and freezing mode respectively.

[0110] Module 2 is used to determine the temperature zone of the refrigerated vehicle based on the supply air temperature in the rail refrigerated vehicle in the refrigeration mode, and adopt different control strategies to adjust the refrigeration temperature according to the temperature zone; in the freezing mode, determine the temperature zone of the refrigerated vehicle based on the return air temperature in the rail refrigerated vehicle, and adopt different control strategies to adjust the freezing temperature according to the temperature zone;

[0111] Module three is used to determine whether the defrosting conditions are met in the refrigeration mode and the freezing mode respectively. If yes, the defrosting control strategy is activated to perform defrosting respectively. If no, the next step is executed.

[0112] Module 4 is used to determine whether the shutdown conditions are met in the refrigeration mode and the freezing mode respectively. If yes, the shutdown program is started. If not, the safety protection program is started and data collection and monitoring, alarm monitoring and output are performed in sequence;

[0113] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0114] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0115] Other parts not described in detail are all prior art.

Claims

1. A method for adjusting the capacity of a variable-operating-condition refrigeration unit for a rail refrigerated vehicle, characterized in that: The steps include: Step 1: Divide the temperature zones for the refrigerated mode and frozen mode operation of the rail refrigerated vehicle. Step 2. In the refrigeration mode, the temperature zone of the refrigerated vehicle is determined based on the supply air temperature in the rail refrigerated vehicle, and different control strategies are used to adjust the refrigeration temperature according to the temperature zone; in the freezing mode, the temperature zone of the refrigerated vehicle is determined based on the return air temperature in the rail refrigerated vehicle, and different control strategies are used to adjust the freezing temperature according to the temperature zone; Step 3. In the refrigeration mode and the freezing mode, determine whether the defrosting conditions are met respectively. If yes, start the defrost control strategy to defrost respectively. If no, proceed to the next step. Step 4. In the refrigeration mode and the freezing mode, determine whether the shutdown conditions are met. If so, start the shutdown program. If not, start the safety protection program and perform data collection and monitoring, alarm monitoring and output in sequence.

2. A method for adjusting the capacity of a variable-operating-mode refrigeration unit for a rail refrigerated vehicle as claimed in claim 1, characterized in that: In step 1, the refrigeration mode includes a refrigeration rapid cooling zone, a refrigeration cooling and frequency reduction zone, a refrigeration variable frequency capacity adjustment zone, a refrigeration fixed frequency hot air capacity adjustment zone, and a refrigeration heating and temperature rising zone; the freezing mode includes a freezing rapid cooling zone, a freezing cooling and frequency reduction zone, a freezing variable frequency capacity adjustment zone, and a freezing shutdown zone.

3. A method for adjusting the capacity of a variable-operating-mode refrigeration unit for a rail refrigerated vehicle as claimed in claim 2, characterized in that: The refrigerated rapid cooling zone in step 1 is a zone where the air supply temperature drops to 1.5°C higher than the set temperature or the air supply temperature rises to 3°C higher than the set temperature; the refrigerated cooling frequency reduction zone is a zone where the air supply temperature drops to between the set temperature and 1.5°C higher than the set temperature or the air supply temperature rise is equal to 3°C of the set temperature; the refrigerated variable frequency capacity adjustment zone is a zone where the air supply temperature drops to between -1.5°C higher than the set temperature and the set temperature or the air supply temperature rise is 0.4°C higher than the set temperature and 3°C higher than the set temperature; the refrigerated fixed frequency hot air capacity adjustment zone is a zone where the air supply temperature drops to between -2°C higher than the set temperature and -1.5°C higher than the set temperature or the air supply temperature rise is 0.3°C higher than the set temperature and 0.4°C higher than the set temperature; the refrigerated heating temperature rise zone is a zone where the air supply temperature drops to below -2°C or the air supply temperature rise is 0.3°C lower than the set temperature; The refrigeration rapid cooling zone is the zone where the return air temperature drops to 1.5℃ above the set temperature or the return air temperature rises to 3℃ above the set temperature; the refrigeration cooling frequency reduction zone is the zone where the return air temperature drops to between the set temperature and 1.5℃ above the set temperature or the return air temperature rise is equal to 3℃ of the set temperature; the refrigeration variable frequency capacity adjustment zone is the zone where the return air temperature drops to between -2℃ above the set temperature and the set temperature or the return air temperature rise is equal to the set temperature and 3℃ above the set temperature; the refrigeration shutdown zone is the zone where the return air temperature drops to below -2℃ of the set temperature or the supply air temperature rise is equal to or lower than the set temperature.

4. A method for adjusting the capacity of a variable-operating-mode refrigeration unit for a rail refrigerated vehicle as claimed in claim 2, characterized in that: The refrigerated rapid cooling zone is controlled by setting the refrigerated temperature and the evaporator superheat respectively, including: starting the compressor and increasing it at a constant frequency until the compressor runs at the maximum speed, fully opening the evaporator fan and running it at the highest gear, controlling the fan start and stop and keeping the condensing pressure within a reasonable range, and controlling the opening of the electronic expansion valve by setting the superheat; The compressor in the refrigeration cooling and frequency reduction area is subjected to frequency reduction control, that is, the supply air temperature is collected and compared at regular intervals during the frequency reduction stage. If it is found that the supply air temperature keeps decreasing, the compressor frequency is reduced. If it is found that the temperature remains unchanged or even increases, the corresponding frequency is increased. The refrigeration variable frequency capacity adjustment area is variable frequency capacity adjustment, including: the deviation between the air supply temperature and the set temperature is calculated through PID calculation in the programmable controller, and the compressor frequency required by the refrigeration system is output to achieve accurate matching between the refrigeration unit and the load in the box; In the refrigerated fixed-frequency hot gas capacity adjustment area, a virtual load is added to the evaporator by introducing the high-temperature gas on the exhaust side of the compressor into the suction pipe on the inlet side of the evaporator, that is, the load inside the box plus the virtual load is re-matched with the refrigeration capacity of the refrigeration unit. The opening of the hot gas bypass valve will be obtained by PID calculation in the programmable controller according to the deviation between the supply air temperature and the set temperature; In the refrigerated heating temperature rising zone, the high-temperature gas discharged from the compressor is introduced into the evaporator through the hot gas bypass valve, and the heat exchange between the evaporator and the air is used to increase the temperature inside the box.

5. A method for adjusting the capacity of a variable-operating-mode refrigeration unit for a rail refrigerated vehicle as claimed in claim 4, characterized in that: The control steps of the hot gas bypass valve adjustment are as follows: (1) Hot gas regulation: Control the flow of refrigerant by adjusting the opening of the hot gas bypass valve to maintain a stable temperature inside the box; (2) Calculation of hot gas bypass valve opening: Calculate the hot gas bypass valve opening V based on the temperature deviation ΔT and the preset valve response curve. The calculation formula is: V=V0+K v ·ΔT Among them, V0 is the initial opening of the hot gas bypass valve, and Kv is the valve opening gain.

6. A method for adjusting the capacity of a variable-operating-mode refrigeration unit for a rail refrigerated vehicle as claimed in claim 2, characterized in that: The rapid cooling zone is controlled by a scroll compressor, an electronic expansion valve, a condenser fan and an evaporator fan respectively, and the refrigeration unit works at full load, wherein the evaporator fan is controlled at a low speed, and the low speed is half the air volume of the full load; The compressor is frequency-reduced in the refrigeration and cooling frequency-reduction zone, that is, the return air temperature is collected and compared at regular intervals during the frequency-reduction stage. If the return air temperature is found to be decreasing, the compressor frequency is reduced. If the temperature is found to be unchanged or even increasing, the frequency is increased accordingly. The refrigeration variable frequency capacity adjustment area includes the variable frequency capacity adjustment control of the scroll compressor and the start and stop capacity adjustment control of the scroll compressor. According to the deviation between the return air temperature and the set temperature, the required frequency is calculated by the PID algorithm in the programmable logic controller. The PLC transmits the calculated frequency to the inverter using the RS485 communication protocol. The inverter then controls the actual operating frequency of the compressor to achieve the best match between the refrigeration unit and the load in the box. The refrigeration shutdown zone is the lower limit of the refrigeration capacity adjustment zone. The compressor, electronic expansion valve and condenser fan stop running, and the evaporator fan adopts low speed control to maintain air circulation in the box; when the return air temperature is higher than the target set temperature, it enters the refrigeration variable frequency capacity adjustment zone.

7. A method for adjusting the capacity of a variable-operating-mode refrigeration unit for a rail refrigerated vehicle as claimed in claim 2, characterized in that: The defrost control strategy in step 3 includes manual defrost and timed defrost, specifically: Start the defrost mode. The defrost indicator light will light up, the hot gas bypass valve will be opened, the electric heater and compressor will be started, the evaporator fan will be turned off, and the condenser fan will be turned on or off; If the evaporator outlet temperature is greater than or equal to 25°C or the defrost time is greater than or equal to 80 minutes, the defrost will stop, the defrost indicator will go off and the timer will be reset, otherwise return to the previous step.

8. A capacity adjustment system for variable-operating-condition refrigeration units for rail refrigerated vehicles, characterized in that: The steps include: Module 1. It is used to divide the temperature zones when the rail refrigerated vehicle is running in refrigeration mode and freezing mode respectively. Module 2 is used to determine the temperature zone of the refrigerated vehicle based on the supply air temperature in the rail refrigerated vehicle in the refrigeration mode, and adopt different control strategies to adjust the refrigeration temperature according to the temperature zone; in the freezing mode, determine the temperature zone of the refrigerated vehicle based on the return air temperature in the rail refrigerated vehicle, and adopt different control strategies to adjust the freezing temperature according to the temperature zone; Module three is used to determine whether the defrosting conditions are met in the refrigeration mode and the freezing mode respectively, and if so, to start the defrosting control strategy for defrosting respectively; Module 4 is used to determine whether the shutdown conditions are met in the refrigeration mode and the freezing mode respectively. If yes, the shutdown program is started; otherwise, the safety protection program is started and data collection and monitoring, alarm monitoring and output are performed in sequence; The capacity adjustment system for a variable-operating-condition refrigeration unit dedicated to a rail refrigerated vehicle is used to execute the steps in the capacity adjustment method for a variable-operating-condition refrigeration unit dedicated to a rail refrigerated vehicle according to any one of claims 1 to 7.

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