Capacity regulation method and system of variable working condition refrigerating unit special for rail refrigeration vehicle

Abstract

The application provides a variable-condition refrigerating unit capacity adjustment method and system for a rail refrigerated vehicle, which comprises the following steps: dividing temperature zones when the rail refrigerated vehicle is in a refrigeration mode and a freezing mode respectively, determining the temperature zone of the rail refrigerated vehicle based on the supply air temperature in the refrigeration mode, determining the temperature zone of the rail refrigerated vehicle based on the return air temperature in the freezing mode, and performing refrigeration temperature control adjustment and freezing temperature control adjustment by using different control strategies according to the temperature zone; determining whether the defrosting condition is met in the refrigeration mode and the freezing mode respectively and performing defrosting; determining whether the shutdown condition is met in the refrigeration mode and the freezing mode respectively, starting the shutdown program if the shutdown condition is met, and starting the safety protection program if the shutdown condition is not met, and then performing data acquisition and monitoring, alarm monitoring and outputting in sequence. The accurate temperature control is helpful to keep the freshness and quality of goods and reduce the loss caused by temperature fluctuation.

Description

Technical Field

[0001] This invention relates to the fields of power engineering and engineering thermophysics, specifically to a method and system for adjusting the capacity of a variable-condition refrigeration unit for rail refrigerated vehicles. Background Technology

[0002] The main problems with refrigerated and insulated vehicles in the cold chain supply chain include: the large demand for cooling and heating in the vehicle compartment, and the consumption of a large amount of electricity for the conversion of cold and heat energy during normal operation.

[0003] For refrigerated trucks, it is necessary to ensure their refrigeration, freezing, and insulation effects throughout the year, thus requiring heating in winter and cooling in summer. Based on this, this invention patent proposes to optimize the refrigerant circulation process and build a refrigeration system for refrigerated and frozen insulated trucks by modifying a liquid storage tank into a flash evaporator, fully utilizing its powerful performance.

[0004] It is also necessary to consider that refrigerated and frozen insulated vehicles have their own working characteristics. The refrigeration system with flash vapor installed on the vehicle needs to be adapted to specific control logic. The operation control logic should be improved according to the specific operating characteristics and needs of the application, and the existing control logic of other fields (heat pump water heaters, heat pump heating, vehicle air conditioning heat pumps and thermal management, etc.) cannot be copied.

[0005] During the operation of refrigerated and frozen insulated trucks, the cooling and heating loads inside the truck fluctuate significantly due to frequent loading and unloading of goods. This necessitates a larger margin in the heat pump air conditioning system, which cannot be designed based on average cooling or heating capacity requirements. Furthermore, the humidity requirements of the goods stored in the truck are often quite stringent, requiring precise control through air supply temperature to ensure adequate humidity levels within the truck. During winter operation of the heat pump, defrosting of the outdoor heat exchanger should be avoided as much as possible. Once the system enters defrosting mode, significant temperature fluctuations will occur inside the truck. Therefore, a frost-free control strategy is also necessary. Summary of the Invention

[0006] This invention provides a method and system for adjusting the capacity of a variable-condition refrigeration unit specifically for refrigerated rail vehicles, which solves the problem that the refrigeration system with a flash tank on the refrigerated vehicle needs to be adapted to specific control logic to achieve efficient and energy-saving operation of the refrigeration system.

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

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

[0009] Step 1. Divide the temperature zones for the refrigerated railcars in refrigerated and frozen modes respectively.

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

[0011] Step 3. Determine whether the defrosting conditions are met in both refrigeration and freezer modes. If so, activate the defrosting control strategy to defrost; otherwise, proceed to the next step.

[0012] Step 4. Determine whether the shutdown conditions are met in both refrigeration and freezing modes. If so, start the shutdown procedure; otherwise, start the safety protection procedure and perform data acquisition and monitoring, alarm monitoring and output in sequence.

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

[0014] Further, in step 1, the rapid cooling zone for refrigeration is the area where the supply air temperature drops to 1.5℃ above the set temperature or the supply air temperature rises to 3℃ above the set temperature; the frequency reduction zone for refrigeration cooling is the area where the supply air temperature drops to between the set temperature and 1.5℃ above the set temperature or the supply air temperature rises to 3℃ above the set temperature; the variable frequency capacity adjustment zone for refrigeration is the area where the supply air temperature drops to between -1.5℃ and the set temperature or the supply air temperature rises to between 0.4℃ and 3℃ above the set temperature; the fixed frequency hot air capacity adjustment zone for refrigeration is the area where the supply air temperature drops to between -2℃ and -1.5℃ above the set temperature or the supply air temperature rises to between 0.3℃ and 0.4℃ above the set temperature; and the heating zone for refrigeration is the area where the supply air temperature drops to below -2℃ or the supply air temperature rises to below 0.3℃ above the set temperature.

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

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

[0017] In the refrigeration cooling and frequency reduction zone, the compressor is controlled to reduce its frequency. That is, during the frequency reduction phase, the supply air temperature is collected and compared at regular intervals. If the supply air temperature is found to be continuously decreasing, the compressor frequency is reduced. If the temperature is found to remain unchanged or even increase, the corresponding frequency is increased.

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

[0019] In the refrigeration fixed-frequency hot gas capacity adjustment zone, a virtual load is added to the evaporator by introducing high-temperature gas from the compressor exhaust side into the suction pipe on the evaporator inlet side. This allows the load inside the unit to be rematched with the cooling capacity of the refrigeration unit. The opening of the hot gas bypass valve will be determined by PID calculation in the programmable controller based on the deviation between the supply air temperature and the set temperature.

[0020] In the refrigeration heating zone, the high-temperature gas discharged from the compressor is introduced into the evaporator through a hot gas bypass valve, and the temperature inside the chamber is increased by utilizing the heat exchange between the evaporator and the air.

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

[0022] (1) Hot gas regulation: The flow rate of refrigerant is controlled 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: Based on the temperature deviation ΔT and the preset valve response curve, calculate the hot gas bypass valve opening V. The calculation formula is as follows:

[0024] V = V0 + K v ·ΔT

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

[0026] Furthermore, the rapid cooling zone is controlled by a scroll compressor, an electronic expansion valve, a condenser fan, and an evaporator fan, respectively. The refrigeration unit operates at full load, and the evaporator fan is controlled at a low speed, with the low speed setting being half the air volume of the full load.

[0027] In the refrigeration cooling frequency reduction zone, the compressor is controlled to reduce its frequency. That is, during the frequency reduction phase, the return air temperature is collected and compared at regular intervals. If the return air temperature is found to be continuously decreasing, the compressor frequency is reduced. If the temperature is found to remain unchanged or even increase, the frequency is increased accordingly.

[0028] The refrigeration inverter capacity regulation zone includes the inverter capacity regulation control of the scroll compressor and the start-stop capacity regulation control of the scroll compressor. Based on 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 uses the RS485 communication protocol to transmit the calculated frequency to the inverter. The inverter then controls the actual operating frequency of the compressor to achieve the best match between the refrigeration unit and the load inside the unit.

[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, while the evaporator fan is controlled at a low speed to maintain air circulation inside the unit. When the return air temperature is higher than the target set temperature, it enters the refrigeration inverter capacity adjustment zone.

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

[0031] When the defrost mode is activated, the defrost indicator light will illuminate. Open the hot gas bypass valve, start the electric heater and compressor, turn off the evaporator fan, and turn the condenser fan on or off.

[0032] If the evaporator outlet temperature is greater than or equal to 25°C or the defrosting time is greater than or equal to 80 minutes, defrosting will stop, the defrosting indicator light will turn off and the timer will 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 specifically for refrigerated rail vehicles, comprising the following steps:

[0034] Module 1. It is used to divide the temperature zones for refrigerated rail vehicles in refrigerated and frozen modes, respectively.

[0035] Module 2 is used to determine the temperature zone of the refrigerated vehicle based on the supply air temperature inside the refrigerated vehicle in refrigeration mode, and to adjust the refrigeration temperature according to different control strategies based on the temperature zone. In freezing mode, it determines the temperature zone of the refrigerated vehicle based on the return air temperature inside the refrigerated vehicle, and to adjust the freezing temperature according to different control strategies based on the temperature zone.

[0036] Module 3 is used to determine whether the defrosting conditions are met in both refrigeration and freezing modes. If so, the defrosting control strategy is activated to perform defrosting; otherwise, the next step is executed.

[0037] Module 4 is used to determine whether the shutdown conditions are met in both refrigeration and freezing modes. If so, the shutdown procedure is initiated; otherwise, the safety protection procedure is initiated and data acquisition and monitoring, alarm monitoring and output are performed sequentially.

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

[0039] The refrigerated truck control system of this invention exhibits more advanced characteristics than existing refrigerated container control technologies in terms of improved temperature control accuracy, flexibility, safety, and energy efficiency, providing a more reliable guarantee for cargo transportation. Its main advantages are as follows:

[0040] (1) Precise temperature management: The system can rapidly reduce and maintain a constant temperature inside the container through internal temperature management and refrigeration / freezing temperature control programs. This precise temperature control helps maintain the freshness and quality of goods and reduces losses caused by temperature fluctuations.

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

[0042] (3) Integrated functional control and logical coordination: The system is designed with separate refrigeration and freezing modes, covering multiple adjustment zones (such as rapid cooling zone, variable frequency capacity adjustment zone, etc.), enabling it to efficiently meet different work requirements. This partitioned design improves the system's response speed and adaptability.

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

[0044] (5) High-efficiency energy utilization: By controlling the compressor by frequency conversion and adjusting the heat capacity, the system can dynamically adjust energy consumption according to actual needs, thereby improving the efficiency of energy use and reducing operating costs. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] Figure 1This 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 This is a schematic diagram of the temperature zone division in the refrigeration mode according to an embodiment of the present invention.

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

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

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

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

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

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

[0054] Figure 9 This is a flowchart illustrating the defrosting control process according to an embodiment of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0056] Example 1

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

[0058] like Figure 1 As shown in the figure, this embodiment of the invention provides a method for adjusting the capacity of a variable-condition refrigeration unit for rail refrigerated vehicles, characterized by the following steps:

[0059] Step 1. Divide the temperature zones for the refrigerated railcars in refrigerated and frozen modes respectively.

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

[0061] Step 3. Determine whether the defrosting conditions are met in both refrigeration and freezer modes. If so, activate the defrosting control strategy to defrost; otherwise, proceed to the next step.

[0062] Step 4. Determine whether the shutdown conditions are met in both refrigeration and freezing modes. If so, start the shutdown procedure; otherwise, start the safety protection procedure and perform data acquisition and monitoring, alarm monitoring and output in sequence.

[0063] When the temperature inside the refrigerated truck reaches the preset minimum requirement, the required cooling capacity is significantly reduced, far below the energy needed for rapid cooling when the goods are first loaded. At this point, the system automatically adjusts based on real-time data from the temperature sensor, entering a capacity regulation mode to reduce cooling output and achieve precise temperature control inside the truck. Studies have shown that using a constant-speed compressor and fan in the refrigeration system of a refrigerated truck leads to significant energy waste. In contrast, using a variable-frequency fan can save approximately 4919 kWh of electricity annually. Furthermore, optimizing the refrigeration cycle, employing scientific cargo packing methods, and using novel defrosting technologies (such as hot gas defrosting and hot air defrosting) can further improve the energy efficiency of refrigeration equipment. This invention uses a digital scroll compressor and hot gas bypass technology to regulate the capacity of the refrigeration system. The digital scroll compressor, due to its wide capacity adjustment range, enables continuous and precise capacity output adjustment, resulting in excellent energy efficiency and reliability. Existing research reports indicate that in laboratory environments, systems using digital scroll compressors have lower energy consumption than variable-frequency systems, demonstrating superior energy-saving performance.

[0064] The refrigerated truck control system design of this invention covers several key aspects, including in-cabin temperature management, evaporator superheat regulation, compressor frequency conversion control, optimal intermediate pressure control, and flash tank level monitoring. Furthermore, the system integrates the conventional function control of the refrigerated truck and the logical coordination between these functions, as well as the system's safety protection mechanisms. The control flow of the refrigeration system of the refrigerated truck is as follows: Figure 1 As shown. In the control process of a 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 functions such as rapid reduction of the temperature inside the compartment, constant maintenance of the set temperature, and temperature regulation of the compartment.

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

[0066] When a refrigerated truck is operating in refrigeration mode, the entire temperature range can be divided into a rapid cooling zone, a rapid cooling frequency reduction zone, a variable frequency capacity adjustment zone, a hot air capacity adjustment zone, and a heating zone. This means that the temperature is controlled in zones based on the boundary temperatures of the air supply temperature zones, achieving real-time adjustment of the temperature inside the refrigerated truck compartment. The principle of the temperature control system in freezing mode is as follows: Figure 3 As shown. When running in refrigeration mode, the 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 based on the boundary temperature of the return air temperature area. By dividing the zone, different control methods can be used to achieve precise temperature regulation inside the cabinet.

[0067] The temperature control principle of the refrigeration mode is as follows: the change in air supply temperature is divided into a decreasing phase and a increasing phase. Taking the set temperature as a reference, the temperature decreasing phase is divided into five temperature zones, corresponding to... Figure 2 The temperature rise phase is divided into four zones: A1, B1, C1, D1, and E1. Similarly, the temperature rise phase is divided into four zones using three temperature nodes, corresponding to zones E1, D1, C1, and A1 along the direction of temperature rise. To intuitively and accurately represent the control methods involved in temperature changes, areas with the same temperature control strategies during the rise and fall phases of the supply air temperature are connected to obtain... Figure 2 The temperature control strategy is the same when the supply air temperature drops to 1.5℃ above the set temperature and when the supply air temperature rises to 3℃ above the set temperature. The area above the line connecting the 1.5℃ and 3℃ temperature nodes is designated as zone A1. The division of zones C1, D1, and E1 follows the same principle. It should be noted that the temperature rise phase only involves four temperatures; there is no rapid cooling / frequency reduction zone (zone B1). Therefore, the triangular area enclosed by the line connecting the 3℃ temperature node, the set temperature, and the 1.5℃ temperature node is zone B1, which differs slightly from the division of other zones.

[0068] The temperature control principle in refrigeration mode is as follows: The return air temperature change is divided into a decreasing phase and a increasing phase. Two temperature nodes are designed with a reference temperature as the reference. The decreasing phase is divided into four temperature zones: A2, B2, C2, and D2. Similarly, the increasing phase is divided into three temperature zones: D2, C2, and A2. To visually represent the temperature control strategies used in different temperature zones, areas with the same temperature control strategies during the increasing and decreasing phases of the return air temperature are connected. Figure 3The temperature control strategy is the same when the return air temperature drops to 1.5℃ above the set temperature and when it rises to 3℃ above the set temperature. The area above the line connecting the 1.5℃ and 3℃ temperature nodes is designated as zone A2. The division of zones C2 and D2 follows the same principle. It should be noted that during the return air temperature rise phase, there are only three temperature zones; there is no rapid frequency reduction zone (zone B2). Therefore, the triangular area enclosed by the line connecting the 3℃ temperature node, the set temperature, and the 1.5℃ temperature node is zone B2, which differs from the division of other zones.

[0069] In step 1, the rapid cooling zone for refrigeration is the area where the supply air temperature drops to 1.5℃ above the set temperature or the supply air temperature rises to 3℃ above the set temperature; the frequency reduction zone for refrigeration cooling is the area where the supply air temperature drops to between the set temperature and 1.5℃ above the set temperature or the supply air temperature rises to 3℃ above the set temperature; the variable frequency capacity adjustment zone for refrigeration is the area where the supply air temperature drops to between -1.5℃ and the set temperature or the set temperature or the supply air temperature rises to between 0.4℃ and 3℃ above the set temperature; the fixed frequency hot air capacity adjustment zone for refrigeration is the area where the supply air temperature drops to between -2℃ and -1.5℃ above the set temperature or the supply air temperature rises to between 0.3℃ and 0.4℃ above the set temperature; and the heating zone for refrigeration is the area where the supply air temperature drops to below -2℃ or the supply air temperature rises to below 0.3℃ above the set temperature.

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

[0071] In refrigerated mode, the supply air temperature is used to indicate the internal temperature of the container. This is because most of the goods packed in refrigerated mode are temperature-sensitive. The air inside the container exchanges heat in the evaporator, resulting in a high return air temperature and a low supply air temperature. To ensure that goods near the air outlet are not damaged by freezing, the supply air temperature is used to limit the minimum internal temperature. In frozen mode, the return air temperature is used to indicate the internal temperature. This is because goods packed in frozen mode are generally low-temperature resistant. Considering that goods may thaw due to temperature increases, the maximum internal temperature for these goods must be limited. Generally, the cooled air gradually warms up after exiting the air outlet, reaching its highest temperature when it returns to the evaporator inlet (return air outlet). Therefore, controlling the return air temperature ensures the safe freezing of the goods inside the container.

[0072] Rapid cooling control strategy in refrigeration mode

[0073] The rapid cooling function of a refrigerated truck is essential for effectively cooling its cargo. To achieve rapid cooling, the load on the scroll compressor, fan, and evaporator must be effectively controlled, allowing the refrigeration unit to operate at full load (maximum cooling capacity) as quickly as possible to accelerate the cooling rate inside the compartment. The controlled components include the scroll compressor, electronic expansion valve, condenser fan, and evaporator fan. A flowchart of the rapid cooling control strategy in refrigerated mode is shown below. Figure 4 As 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, which is the lower limit of the rapid cooling zone (A1 zone), it enters the rapid cooling frequency reduction zone (B1 zone). At this time, the compressor performs frequency reduction control. That is, during the frequency reduction stage, the supply air temperature is collected and compared every 30 seconds. If the supply air temperature is found to be continuously decreasing, the compressor frequency is reduced. If the temperature is found to remain unchanged or even rise, the corresponding frequency is increased.

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

[0077] Refrigeration mode capacity adjustment control strategy

[0078] The refrigeration unit studied in this embodiment employs a refrigeration mode capacity adjustment system comprising two stages: a scroll compressor capacity adjustment stage (variable frequency capacity adjustment) and a compressor fixed frequency combined with hot gas regulation control stage (hot gas regulation), namely zones C1 and D1. The specific control process is as follows: When the supply air temperature continuously decreases to the set temperature, the refrigeration unit capacity adjustment stage officially begins. This involves using PID calculations in the programmable controller based on the deviation between the supply air temperature and the set temperature to output the compressor frequency required by the refrigeration system, achieving precise matching between the refrigeration unit and the load inside the unit. The variable frequency capacity adjustment control principle of the refrigeration unit is as follows: Figure 5 As shown. The main control methods for the capacity regulation stage of a scroll compressor are as follows:

[0079] (1) Set target temperature: Set the supply air 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: Adjust the compressor frequency f according to the PID calculation result, 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 inside the chamber is too low, the PID control output is adjusted to the lowest frequency (e.g., 25Hz) allowed for normal compressor operation via variable frequency capacity regulation and continues to operate. If the cooling capacity of the system's refrigeration unit exceeds the load inside the chamber, 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 conditioning stage. The refrigeration unit's compressor operates on a fixed frequency combined with hot air conditioning control principle as follows: Figure 6 As shown.

[0086] like Figure 7 As shown, by introducing high-temperature gas from the compressor exhaust side into the suction pipe (3-7b-7) on the evaporator inlet side, a virtual load is added to the evaporator. This virtual load re-matches the load inside the unit with the cooling capacity of the refrigeration unit. The opening degree of the hot gas bypass valve is determined by PID calculations in the programmable controller based on the deviation between the supply air temperature and the set temperature, thus achieving precise 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 rate 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: Based on the temperature deviation ΔT and the preset valve response curve, calculate the valve opening V. The calculation formula is as follows:

[0089] V = V0 + K v ·ΔT (2)

[0090] Where V0 is the initial valve opening and Kv is the valve opening gain.

[0091] When the load inside the box suddenly increases (the supply air temperature deviates from the set temperature and continues to rise, with the positive deviation becoming larger and larger), the PID controller adjusts the opening of the hot air bypass valve to reduce it. When the hot air bypass valve is completely closed, the positive deviation of the supply air temperature still exists and has an increasing trend. The control system will switch from compressor fixed frequency combined with hot air regulation control to 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 rapid cooling mode.

[0092] Refrigeration heating zone

[0093] The heating function of a refrigerated truck is equally crucial, especially when traversing cold regions or requiring cargo ventilation. In these situations, the low-temperature outside air can cause the interior temperature to drop rapidly. When the interior temperature falls below the set value by 2°C, the control system activates the heating control mode. In this mode, the system introduces high-temperature gas discharged from the compressor into the evaporator through a hot gas bypass valve, utilizing the heat exchange between the evaporator and the air to raise the interior temperature. After heat exchange in the evaporator, the high-temperature refrigerant gas returns to the compressor suction port, where it is compressed again into high-temperature refrigerant gas, thus achieving temperature increase in heat pump mode. During the heating operation, only the compressor, the evaporator low-speed fan, and the hot gas bypass solenoid valve operate; other components remain inactive. Additionally, to accelerate the heating process, two electric heaters (each with a power of 1500W) located at the bottom of the evaporator are activated. Once the supply air temperature reaches the set value, all other components of the refrigeration unit, except for the evaporator low-speed fan which continues to operate, will cease operation.

[0094] Rapid cooling control strategy in freezing mode

[0095] In refrigeration mode, the return air temperature is used as the control temperature of the refrigeration unit and represents the internal temperature of the container. During refrigeration mode operation, the scroll compressor, electronic expansion valve, condenser fan, and evaporator fan are effectively controlled, allowing the refrigeration unit to operate at full load (maximum cooling capacity) and accelerating the cooling rate inside the container. The evaporator fan operates at a low speed, which is half the airflow of the full load. This saved heat load allows for the loading of more goods, further accelerating the cooling process inside the container.

[0096] Freezing mode rapid cooling and frequency reduction zone control strategy

[0097] The rapid cooling and frequency reduction zone refers to the zone where the compressor switches from the rapid cooling zone to the rapid cooling and frequency reduction zone when the return air temperature drops below 1.5°C above the target set temperature. During this zone, the compressor performs frequency reduction control, meaning that the return air temperature is collected and compared every 30 seconds. If the return air temperature continues to decrease, the compressor frequency is reduced; if the temperature remains unchanged or even rises, the frequency is increased accordingly. The PLC program collects the return air temperature every 30 seconds. If the return air temperature continues to decrease or remains unchanged, the compressor frequency decreases by 2Hz each time. If the temperature rises, the compressor frequency increases by 2Hz and continues to operate until the set refrigeration temperature is reached, which is the lowest point of the rapid cooling and frequency reduction zone (zone B2).

[0098] Freezing mode capacity regulation control strategy

[0099] As 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 switch to the capacity adjustment stage of the refrigeration mode. This stage includes two main control parts: variable frequency capacity control of the scroll compressor and start-stop capacity adjustment control of the scroll compressor. When the return air temperature is within the range of variable frequency capacity adjustment, the compressor frequency is no longer affected by the rapid refrigeration cooling control. Instead, 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 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 inside the unit. The schematic diagram of the variable frequency capacity control of the scroll compressor in refrigeration mode is shown below. Figure 8 As shown.

[0100] When the load inside the refrigerated truck is low, the PID controller will correspondingly reduce the output frequency. Once the frequency drops to the minimum normal operating frequency of the scroll compressor, if the return air temperature inside the compartment continues to decrease, the scroll compressor will stop working when the temperature is 2°C below the set value. At this time, all components in the refrigeration unit except the evaporator fan will enter a shutdown state. The system will record the frequency at which the scroll compressor stops. Due to the heat generated by the evaporator fan and heat leakage from the compartment, the temperature inside the compartment 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 to run the inverter. When the load inside the compartment changes abruptly, the PID controller 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 inside the compartment in time, causing the return air temperature to exceed the set value by 2°C. In this case, the control system will quickly switch from the refrigeration capacity adjustment mode to the rapid freezing mode to avoid large jumps in the compressor frequency caused by large deviations during the PID calculation process, thereby preventing refrigeration system mismatch and excessive impact on the compressor, ensuring its normal operation.

[0101] Freezing mode shutdown zone control strategy

[0102] The refrigeration shutdown zone refers to the lower limit of the refrigeration capacity adjustment zone when the return air temperature drops to 2°C below the target set temperature or rises to below the target set temperature. At this time, the compressor, electronic expansion valve and condenser fan stop running, while the evaporator fan is controlled at a low speed to maintain air circulation inside the container. Due to heat leakage from the container body and breathing heat from the cargo, when the return air temperature is higher than the target set temperature, the refrigeration inverter capacity adjustment zone is entered.

[0103] Refrigerated truck temperature control strategy

[0104] The heating function of a refrigerated truck is equally crucial, especially when traversing cold regions or requiring cargo ventilation. In these situations, the low-temperature outside air can cause the interior temperature to drop rapidly. When the interior temperature falls below the set value by 2°C, the control system activates the heating control mode. In this mode, the system introduces high-temperature gas discharged from the compressor into the evaporator through a hot gas bypass valve, utilizing the heat exchange between the evaporator and the air to raise the interior temperature. After heat exchange in the evaporator, the high-temperature refrigerant gas returns to the compressor suction port, where it is compressed again into high-temperature refrigerant gas, thus achieving temperature increase in heat pump mode. During the heating operation, only the compressor, the evaporator low-speed fan, and the hot gas bypass solenoid valve operate; other components remain inactive. Additionally, to accelerate the heating process, two electric heaters (each with a power of 1500W) located at the bottom of the evaporator are activated. Once the supply air temperature reaches the set value, all other components of the refrigeration unit, except for the evaporator low-speed fan which continues to operate, will cease operation.

[0105] Refrigerated truck defrosting control strategy

[0106] As the temperature inside a refrigerated truck decreases, the relative humidity also decreases. When the evaporator temperature drops below zero degrees Celsius, moisture evaporated from the goods inside the truck or water vapor carried by the air during ventilation will condense into frost on the evaporator fins. If the temperature continues to drop, the frost buildup on the evaporator coils and fins will become more severe. This severe frost buildup will significantly reduce the cooling efficiency of the refrigeration unit, thus affecting further temperature reduction inside the truck. Therefore, refrigerated trucks must have a defrosting function to ensure the long-term efficient operation of the evaporator. The defrosting control process is as follows: Figure 9 As shown.

[0107] Example 2

[0108] This embodiment provides a capacity regulation system for a variable-condition refrigeration unit specifically designed for refrigerated rail vehicles, comprising the following steps:

[0109] Module 1. It is used to divide the temperature zones for refrigerated rail vehicles in refrigerated and frozen modes, respectively.

[0110] Module 2 is used to determine the temperature zone of the refrigerated vehicle based on the supply air temperature inside the refrigerated vehicle in refrigeration mode, and to adjust the refrigeration temperature according to different control strategies based on the temperature zone. In freezing mode, it determines the temperature zone of the refrigerated vehicle based on the return air temperature inside the refrigerated vehicle, and to adjust the freezing temperature according to different control strategies based on the temperature zone.

[0111] Module 3 is used to determine whether the defrosting conditions are met in both refrigeration and freezing modes. If so, the defrosting control strategy is activated to perform defrosting; otherwise, the next step is executed.

[0112] Module 4 is used to determine whether the shutdown conditions are met in refrigeration mode and freezing mode respectively. If so, the shutdown procedure is started; otherwise, the safety protection procedure is started and data acquisition and monitoring, alarm monitoring and output are performed in sequence.

[0113] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0114] Obviously, those skilled in the art can make various modifications and variations 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 to the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

[0115] All other parts not described in detail are existing technologies.

Claims

1. A method for adjusting the capacity of a variable-condition refrigeration unit specifically for refrigerated rail vehicles, characterized in that, Includes the following steps: Step 1. Divide the temperature zones for the operation of the refrigerated railcar in refrigeration mode and freezing mode respectively. The refrigeration mode includes a rapid cooling zone, a cooling frequency reduction zone, a variable frequency capacity adjustment zone, a fixed frequency hot gas capacity adjustment zone, and a heating zone. The freezing mode includes a rapid cooling zone, a cooling frequency reduction zone, a variable frequency capacity adjustment zone, and a freezing shutdown zone. The refrigeration rapid cooling zone is the area where the supply air temperature drops to 1.5℃ above the set temperature or rises to 3℃ above the set temperature; the refrigeration cooling frequency reduction zone is the area where the supply air temperature drops to between the set temperature and 1.5℃ above the set temperature or rises to 3℃ above the set temperature; the refrigeration variable frequency capacity adjustment zone is the area where the supply air temperature drops to between -1.5℃ and the set temperature or rises to between 0.4℃ and 3℃ above the set temperature; the refrigeration fixed frequency hot air capacity adjustment zone is the area where the supply air temperature drops to between -2℃ and -1.5℃ above the set temperature or rises to between 0.3℃ and 0.4℃ above the set temperature; the refrigeration heating zone is the area where the supply air temperature drops to below -2℃ or rises to below 0.3℃. Step 2. In refrigeration mode, the temperature zone of the refrigerated vehicle is determined based on the supply air temperature inside the refrigerated vehicle, and different control strategies are adopted to adjust the refrigeration temperature according to the temperature zone. In freezing mode, the temperature zone of the refrigerated vehicle is determined based on the return air temperature inside the refrigerated vehicle, and different control strategies are adopted to adjust the freezing temperature according to the temperature zone. The rapid cooling zone of the refrigeration is controlled by setting the refrigeration temperature and the evaporator superheat, including: starting the compressor and increasing it at a constant frequency until the compressor runs at its maximum speed, fully opening the evaporator fan and running it at the highest level, controlling the start and stop of the condenser fan and keeping the condensing pressure within a reasonable range, and controlling the opening of the electronic expansion valve by setting the superheat. In the refrigeration cooling and frequency reduction zone, the compressor is controlled to reduce its frequency. That is, during the frequency reduction phase, the supply air temperature is collected and compared at regular intervals. If the supply air temperature is found to be continuously decreasing, the compressor frequency is reduced. If the temperature is found to remain unchanged or even increase, the corresponding frequency is increased. The variable frequency capacity adjustment area for refrigeration is for variable frequency capacity adjustment, including: the deviation between the supply air temperature and the set temperature is calculated by PID in the programmable controller, and the compressor frequency required by the refrigeration system is output to achieve precise matching between the refrigeration unit and the load inside the cabinet; In the refrigeration fixed-frequency hot gas capacity adjustment zone, a virtual load is added to the evaporator by introducing high-temperature gas from the compressor exhaust side into the suction pipe on the evaporator inlet side. This allows the load inside the unit to be rematched with the cooling capacity of the refrigeration unit. The opening of the hot gas bypass valve will be determined by PID calculation in the programmable controller based on the deviation between the supply air temperature and the set temperature. In the refrigeration heating zone, the high-temperature gas discharged from the compressor is introduced into the evaporator through the hot gas bypass valve, and the temperature inside the chamber is increased by the heat exchange between the evaporator and the air. Step 3. Determine whether the defrosting conditions are met in both refrigeration and freezer modes. If so, activate the defrosting control strategy to defrost; otherwise, proceed to the next step. Step 4. Determine whether the shutdown conditions are met in both refrigeration and freezing modes. If so, start the shutdown procedure; otherwise, start the safety protection procedure and perform data acquisition and monitoring, alarm monitoring and output in sequence.

2. The method for adjusting the capacity of a variable-condition refrigeration unit for rail refrigerated vehicles as described in claim 1, characterized in that, In step 1, the rapid cooling zone is the area where the return air temperature drops to 1.5°C above the set temperature or rises to 3°C above the set temperature; the cooling frequency reduction zone is the area where the return air temperature drops to between the set temperature and 1.5°C above the set temperature or rises to 3°C above the set temperature; the variable frequency capacity adjustment zone is the area where the return air temperature drops to between -2°C and the set temperature or rises to between the set temperature and 3°C above the set temperature; and the refrigeration shutdown zone is the area where the return air temperature drops to below -2°C or rises to equal to or below the set temperature.

3. The method for adjusting the capacity of a special variable-condition refrigeration unit for rail refrigerated vehicles as described in claim 1, characterized in that, The control steps for regulating the hot gas bypass valve are as follows: (1) Hot gas regulation: The flow rate of refrigerant is controlled 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: Based on the temperature deviation ΔT and the preset valve response curve, calculate the hot gas bypass valve opening V. The calculation formula is as follows: in, V 0 represents the initial opening degree of the hot gas bypass valve. K v is the valve opening gain.

4. The method for adjusting the capacity of a variable-condition refrigeration unit for rail refrigerated vehicles as described in claim 1, characterized in that, The rapid cooling zone is controlled by a scroll compressor, an electronic expansion valve, a condenser fan, and an evaporator fan. The refrigeration unit operates at full load, with the evaporator fan controlled at low speed, which is half the air volume of the full load. In the refrigeration cooling frequency reduction zone, the compressor is controlled to reduce frequency. That is, during the frequency reduction stage, the return air temperature is collected and compared at regular intervals. If the return air temperature is found to be continuously decreasing, the compressor frequency is reduced. If the temperature is found to remain unchanged or even increase, the frequency is increased accordingly. The refrigeration inverter capacity regulation zone includes the inverter capacity regulation control of the scroll compressor and the start-stop capacity regulation control of the scroll compressor. Based on 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 uses the RS485 communication protocol to transmit the calculated frequency to the inverter. The inverter then controls the actual operating frequency of the compressor to achieve the best match between the refrigeration unit and the load inside the unit. The refrigeration shutdown zone is the lower limit of the refrigeration capacity adjustment zone. The compressor, electronic expansion valve, and condenser fan stop running, while the evaporator fan is controlled at a low speed to maintain air circulation inside the unit. When the return air temperature is higher than the target set temperature, it enters the refrigeration inverter capacity adjustment zone.

5. The method for adjusting the capacity of a variable-condition refrigeration unit for rail refrigerated vehicles as described in claim 1, characterized in that, The defrosting control strategy in step 3 includes manual defrosting and timed defrosting, specifically: When the defrost mode is activated, the defrost indicator light will illuminate. Open the hot gas bypass valve, start the electric heater and compressor, turn off the evaporator fan, and turn the condenser fan on or off. If the evaporator outlet temperature is greater than or equal to 25℃ or the defrosting time is greater than or equal to 80 minutes, defrosting will stop, the defrosting indicator light will turn off and the timer will reset; otherwise, defrosting will continue.

6. A capacity regulation system for a variable-condition refrigeration unit specifically designed for refrigerated rail vehicles, characterized in that, include: Module 1. It is used to divide the temperature zones for refrigerated rail vehicles in refrigerated and frozen modes, respectively. Module 2 is used to determine the temperature zone of the refrigerated vehicle based on the supply air temperature inside the refrigerated vehicle in refrigeration mode, and to adjust the refrigeration temperature according to different control strategies based on the temperature zone. In freezing mode, it determines the temperature zone of the refrigerated vehicle based on the return air temperature inside the refrigerated vehicle, and to adjust the freezing temperature according to different control strategies based on the temperature zone. Module 3 is used to determine whether the defrosting conditions are met in both refrigeration and freezing modes. If so, the defrosting control strategy is activated to perform defrosting. Module 4 is used to determine whether the shutdown conditions are met in refrigeration mode and freezing mode respectively. If so, the shutdown procedure is started; otherwise, the safety protection procedure is started and data acquisition and monitoring, alarm monitoring and output are performed in sequence. The variable-condition refrigeration unit capacity adjustment system for rail refrigerated vehicles is used to perform the steps in the variable-condition refrigeration unit capacity adjustment method for rail refrigerated vehicles as described in any one of claims 1-5.

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