Variable-frequency double-unit cascade refrigeration system based on multi-parameter cooperative control and control method of variable-frequency double-unit cascade refrigeration system

Abstract

The control method comprises the steps that the rotating speed of a high-temperature-stage inverter compressor is mainly comprehensively determined by the high-temperature-stage exhaust temperature, the high-temperature-stage condenser temperature, the high-temperature-side outlet temperature of an intermediate heat exchanger and the high-temperature-stage return air temperature; through dynamic adjustment of the first fuzzy PID controller, the working condition and energy efficiency of the high-pressure side of the system are optimized; the rotating speed of the low-temperature-stage frequency conversion compressor is mainly comprehensively determined by the temperature in the box, the real-time rotating speed of the high-temperature-stage compressor, the low-temperature-stage exhaust temperature, the temperature of the intermediate heat exchanger and the low-temperature-stage return air temperature, and the rotating speed is dynamically adjusted through the second fuzzy PID controller so as to ensure that the temperature in the box is accurate and stable and is matched with the high-temperature-stage capacity in real time. Through cooperative control of the parameter groups, the problems of low efficiency and unstable operation caused by mismatching of two-stage capabilities of the cascade system are solved, and efficient, stable and reliable operation of the system under all working conditions is realized.

Description

Technical Field

[0001] This invention relates to the field of refrigeration system technology, and in particular to a variable frequency dual-machine cascade refrigeration system and its control method based on multi-parameter coordinated control. Background Technology

[0002] Cascade refrigeration systems utilize two or more independent refrigeration cycles connected in series. The high-temperature stage cycle cools the condenser of the low-temperature stage cycle, thus overcoming the thermodynamic limitations of a single refrigerant. This is a typical technical solution for achieving ultra-low temperature environments below -40°C. Such systems are widely used in fields such as biopharmaceutical refrigeration, low-temperature experiments, industrial material processing, and the freezing of specialty foods.

[0003] Currently, in most implemented cascade refrigeration systems, the control strategies are still relatively traditional and rudimentary, mainly reflected in the following aspects: 1. Isolated control architecture with unbalanced inter-level coupling. Traditional control typically treats the high- and low-temperature compressor stages as independent units, starting and stopping or adjusting them via PID control based on the temperature or pressure of their respective evaporators. This "separate control" approach ignores the inherent strong coupling characteristics of cascade systems: the cooling capacity of the high-temperature stage directly affects the condensing temperature of the low-temperature stage, thus determining its cooling efficiency and pressure ratio. In actual operation, because the capacities of the two stages cannot be matched in real time, significant fluctuations in the intermediate heat exchange temperature (condenser-evaporator temperature) often occur. If the high-temperature stage capacity is insufficient, the intermediate temperature rises, the low-temperature stage condensing pressure becomes too high, efficiency drops sharply, or even shutdown occurs; if the high-temperature stage capacity is excessive, the intermediate temperature becomes too low, which may cause the low-temperature stage evaporating pressure to be too low, reducing cooling capacity and increasing the risk to the compressor. This inter-stage mismatch not only results in low overall system energy efficiency but also exacerbates the mechanical load on critical components.

[0004] 2. Single control parameter, resulting in sluggish dynamic response. Common control schemes often use only the evaporation temperature or the internal temperature as the sole feedback parameter, employing a fixed-parameter PID controller for regulation. However, in cascade systems, under varying operating conditions such as changes in external ambient temperature, fluctuations in the chamber's heat load, and door opening, the system's thermal inertia and the response time constants of various components differ significantly. Single-parameter control cannot fully reflect the system state, leading to lag in regulation and a tendency for significant overshoot or continuous oscillation of the internal temperature, making it difficult to meet the stability requirements of high-precision temperature control applications. Furthermore, fixed-parameter PID controllers struggle to maintain optimal regulation performance over a wide operating range, further impacting the system's adaptability and stability.

[0005] 3. The protection mechanism lacks a systematic approach, and its reliability is questionable. Traditional control systems often rely solely on simple protection devices integrated into the compressor (such as overcurrent and overheat protection) without providing coordinated protection at the system level. During transient processes such as startup, defrosting, and sudden load changes, there is a lack of coordinated monitoring and limiting control of key parameters such as intermediate pressure, discharge temperature, and pressure ratio. For example, a low-temperature stage compressor may start before the high-temperature stage has been sufficiently cooled, causing a rapid increase in condensing pressure, resulting in motor overload or poor lubrication. In extreme high-temperature environments, the system may operate under continuous high load, leading to excessive discharge temperature, which over time accelerates lubricant deterioration and compressor wear, severely impacting system reliability and service life.

[0006] As cryogenic applications continue to expand, users are increasingly demanding higher energy efficiency, temperature stability, and operational reliability from refrigeration systems. The shortcomings of existing control strategies in terms of inter-stage coordination, dynamic adaptability, and system protection have become bottlenecks restricting the upgrading of cascade refrigeration technology towards higher efficiency and intelligence. Therefore, developing an intelligent collaborative control strategy capable of real-time capability matching between high and low temperature stages, rapid adjustment to adapt to changing operating conditions, and embedding a systematic protection mechanism is of urgent technical necessity and significant application value for improving the overall performance and reliability of cascade refrigeration systems. Summary of the Invention

[0007] In order to overcome the above-mentioned problems in the prior art, the present invention proposes a variable frequency dual-machine cascade refrigeration system and its control method based on multi-parameter collaborative control.

[0008] The technical solution adopted by this invention to solve its technical problem is: a control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control, comprising the following steps: Step 1: Real-time acquisition of high-temperature stage exhaust temperature, high-temperature stage condenser temperature, high-temperature side outlet temperature of intermediate heat exchanger, and high-temperature stage return gas temperature parameters; Based on the parameters, the target speed of the high-temperature stage variable frequency compressor is calculated by the first control algorithm, and its operation is controlled. Step 2: Real-time acquisition of parameters including the internal temperature of the chamber, the real-time speed of the high-temperature stage compressor, the exhaust temperature of the low-temperature stage, the low-temperature side temperature of the intermediate heat exchanger, and the return gas temperature of the low-temperature stage; based on these parameters, the target speed of the low-temperature stage variable frequency compressor is calculated using the second control algorithm, and its operation is controlled. In step 2, when controlling the speed of the low-temperature stage variable frequency compressor, if the real-time speed of the high-temperature stage variable frequency compressor continuously reaches more than 90% of the rated speed and the temperature inside the chamber is still higher than the set value, the second control algorithm will limit the rate of increase of the low-temperature stage compressor speed to prevent the intermediate heat exchanger temperature from rising too quickly and causing the high-temperature stage capacity to be unable to keep up in time.

[0009] The control method of the variable frequency dual-machine cascade refrigeration system based on multi-parameter collaborative control mentioned above, wherein the first control algorithm is a fuzzy PID control algorithm, specifically: comparing the exhaust temperature of the high-temperature stage with a first preset safety value, and using the deviation and the rate of change of the deviation as control variables to suppress overheating; The temperature of the high-temperature stage condenser is compared with the first preset target value, and the deviation and the rate of change of the deviation are used as control variables to optimize the heat dissipation capacity. The high-temperature side outlet temperature of the intermediate heat exchanger is used as a demand signal reflecting the load of the low-temperature stage. When its value increases, the demand for increasing the speed of the high-temperature stage compressor is output.

[0010] The control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter collaborative control described above, wherein the second control algorithm is a fuzzy PID control algorithm, specifically: comparing the temperature inside the chamber with the user-set temperature value, and using the deviation and the rate of change of the deviation as the core control variables; The real-time speed of the high-temperature stage variable frequency compressor is used as a feedforward signal. When its value increases, it will correspondingly allow or trigger an increase in the speed of the low-temperature stage compressor to ensure that the capabilities of the two stages are matched. The exhaust temperature of the low-temperature stage is compared with the second preset safety value, and the deviation and the rate of change of the deviation are used as control variables to suppress overheating of the low-temperature stage.

[0011] The control method of the variable frequency dual-machine cascade refrigeration system based on multi-parameter collaborative control described above, in the cooling stage, the system control process is as follows: when the temperature inside the chamber is much higher than the set value, the controller will output a command to gradually increase the speed of the low-temperature stage variable frequency compressor; at the same time, the temperature of the intermediate heat exchanger rises accordingly, the high-temperature stage control loop detects the rise in the temperature of the intermediate heat exchanger, and then increases the speed of the high-temperature stage variable frequency compressor. The low-temperature stage controller simultaneously detects that the speed of the high-temperature stage variable frequency compressor is rising, knows that the high-temperature stage capability is increasing, and continues to safely increase the speed of the low-temperature stage until the chamber temperature reaches the set value.

[0012] The control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter collaborative control described above, under high-temperature conditions, specifically involves the following process: A sudden rise in ambient temperature leads to an increase in the high-temperature stage condensing temperature. The high-temperature stage controller prioritizes ensuring the exhaust temperature does not exceed limits using a first control algorithm, appropriately reducing the speed of the high-temperature stage variable frequency compressor. At this time, the low-temperature stage controller detects this feedforward signal of the high-temperature stage variable frequency compressor speed decrease. Even if the internal temperature has not yet recovered, it actively reduces the speed of the low-temperature stage variable frequency compressor, thereby preventing the intermediate heat exchanger temperature from continuing to rise and placing additional burden on the already limited high-temperature stage, thus preventing the system from entering a vicious cycle and shutting down.

[0013] A variable frequency dual-machine cascade refrigeration system based on multi-parameter collaborative control applies the control method described above, specifically including a high-temperature stage circulation loop, a low-temperature stage circulation loop, a sensor group, and a system controller. The high-temperature stage circulation loop includes a high-temperature stage variable frequency compressor, a high-temperature stage condenser, a high-temperature stage throttling device, and a high-temperature stage evaporation channel installed in an intermediate heat exchanger. The low-temperature stage circulation loop includes a low-temperature stage variable frequency compressor, a low-temperature stage condensation channel installed in the intermediate heat exchanger, a low-temperature stage throttling device, and a low-temperature stage evaporator; The sensor group includes a high-temperature stage exhaust temperature sensor, a high-temperature stage condenser temperature sensor, a high-temperature side outlet temperature sensor of the intermediate heat exchanger, a high-temperature stage return gas temperature sensor, an internal temperature sensor, a low-temperature stage exhaust temperature sensor, a low-temperature side outlet temperature sensor of the intermediate heat exchanger, and a low-temperature stage return gas temperature sensor. The system controller receives data collected by the sensor group and executes the speed control steps for the high-temperature stage variable frequency compressor and the low-temperature stage variable frequency compressor.

[0014] The beneficial effects of this invention are: 1. Coordination and dynamic matching capabilities. In traditional solutions, the high- and low-temperature stage controllers do not communicate with each other. This invention, by constructing a real-time parameter sharing mechanism between stages, uses the real-time rotational speed (RPMH) of the high-temperature stage compressor as the feedforward input of the low-temperature stage controller, achieving deep coupling and active coordination of the two-stage refrigeration cycles. The controller dynamically calculates and allocates the optimal capacity output of the two stages based on the total system load and real-time status, ensuring that the intermediate heat exchange temperature remains stable within the preset optimal range. This not only completely avoids problems such as intermediate temperature runaway, system oscillation, or sudden efficiency drops caused by capacity mismatch, but also significantly improves the system's smooth transition capability under varying loads, laying the foundation for overall efficient operation.

[0015] 2. Predictive and Adaptive Adjustment Capabilities. Traditional PID control is a "reactive" type. This invention, by real-time acquisition and fusion of temperature and pressure signals from multiple key nodes in the system (such as intake / exhaust temperatures at each stage, intermediate temperatures, and chamber temperatures), incorporates an intelligent algorithm that can identify system operating trends in advance. Based on this, the controller can proactively fine-tune the compressor speed or expansion valve opening before the temperature or pressure significantly exceeds the limit, achieving smooth "preventative" adjustment. This significantly reduces the fluctuation range of the chamber temperature, and revolutionarily enhances the system's anti-interference capability and long-term operational stability.

[0016] 3. High Efficiency and Energy Saving Optimization. By achieving precise matching of inter-stage capabilities and predictive optimization of operating conditions, this invention enables the system to automatically track and maintain operation near its theoretical optimal operating point throughout the entire operating cycle. Both the high-temperature and low-temperature compressor stages operate within more efficient load ranges, avoiding energy losses caused by frequent single-stage start-stops or long-term deviations from design operating conditions. Practical applications show that systems employing this collaborative control strategy achieve a significantly improved Comprehensive Energy Performance Ratio (COP) compared to traditional control methods, resulting in considerable energy savings and reduced long-term operating costs.

[0017] 4. Safety and Reliability of Active Protection. This invention upgrades the system safety design from "passive alarm and post-event protection" to "active control and pre-event protection." Key protective parameters (such as exhaust temperatures at each stage, intermediate pressures, and pressure ratios) are no longer merely thresholds for triggering alarms or shutdowns, but are deeply integrated into the core control algorithm, directly participating in real-time compressor speed decisions as continuous constraints. For example, when the controller anticipates that the exhaust temperature may be approaching the limit, it will proactively and gradually reduce the speed to eliminate the risk, rather than waiting until it exceeds the limit before emergency shutdown. This multi-layered active protection mechanism embedded in the control loop greatly reduces the risk of compressor overload, overheating, or liquid slugging under extreme operating conditions, thereby effectively extending the service life of core components and improving the overall system's operational reliability and safety.

[0018] In summary, the intelligent collaborative control strategy of this invention systematically solves the key technical bottlenecks in traditional cascade refrigeration control, such as matching imbalance, response hysteresis, low energy efficiency, and insufficient protection, through the innovation of four core mechanisms: inter-level collaboration, trend prediction, efficiency optimization, and active protection. This achieves a comprehensive improvement in the system's stability, efficiency, adaptability, and reliability. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the refrigeration system of the present invention; Figure 2 This is a schematic diagram of the refrigeration system control of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figure 1 As shown, this embodiment discloses a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control, including: The high-temperature stage circulation loop includes a high-temperature stage variable frequency compressor (101), a high-temperature stage condenser (102), a high-temperature stage throttling device (103), and a high-temperature stage evaporation channel disposed in an intermediate heat exchanger (300).

[0022] The low-temperature stage circulation loop includes a low-temperature stage variable frequency compressor (201), a low-temperature stage condensation channel installed in an intermediate heat exchanger (300), a low-temperature stage throttling device (203), and a low-temperature stage evaporator (204).

[0023] System controller (400), high-temperature stage exhaust temperature sensor (401), high-temperature stage condenser temperature sensor (402), intermediate heat exchanger high-temperature side outlet temperature sensor (403), high-temperature stage return gas temperature sensor (404), chamber temperature sensor (405), low-temperature stage exhaust temperature sensor (406), intermediate heat exchanger low-temperature side outlet temperature sensor (407), low-temperature stage return gas temperature sensor (408).

[0024] Based on the above system, this embodiment also discloses a control method.

[0025] I. Speed ​​Control Logic of High-Temperature Inverter Compressor The core task of the high-temperature stage is to provide a stable condensation environment (i.e., a stable intermediate temperature) for the low-temperature stage. This invention abandons the method of relying solely on intermediate temperature control and innovatively employs the following parameter group: High-temperature stage exhaust temperature (T_dish): directly reflects the compressor's operating intensity and lubrication condition. Excessive temperature will trigger frequency throttling protection.

[0026] High-temperature stage condenser temperature (T_condh): reflects the heat dissipation status of the high-pressure side of the system. By controlling this temperature near its optimal value, the fan speed or compressor speed can be adjusted to optimize energy efficiency.

[0027] The high-temperature side outlet temperature of the intermediate heat exchanger (T_exh): This temperature indirectly reflects the heat load applied to the intermediate heat exchanger by the low-temperature stage cycle. An increase in T_exh means that the low-temperature stage load is increasing, requiring an increase in the high-temperature stage compressor speed to enhance heat dissipation capacity.

[0028] High-temperature stage return gas temperature (T_sugh): Used to calculate superheat, prevent liquid slugging, and ensure compressor safety.

[0029] High-temperature compressor speed control steps: The controller (400) inputs the above four parameters into the first fuzzy PID controller. The controller has target values ​​or safety thresholds for each parameter set internally, and calculates a comprehensive control output through fuzzy rules, which is finally converted into a speed command to drive the high-temperature variable frequency compressor (101).

[0030] The specific processing procedure of the fuzzy PID controller is as follows: the high-temperature stage exhaust temperature (T_dish) is compared with the first preset safety value, and the deviation and the rate of change of the deviation are used as control variables to suppress overheating; the high-temperature stage condenser temperature (T_condh) is compared with the first preset target value, and the deviation and the rate of change of the deviation are used as control variables to optimize heat dissipation capacity; the high-temperature side outlet temperature (T_exh) of the intermediate heat exchanger is used as a demand signal reflecting the load of the low-temperature stage, and when its value increases, the demand to increase the speed of the high-temperature stage compressor is output.

[0031] II. Speed ​​Control Logic of Low-Temperature Inverter Compressor The core task of the cryogenic stage is to ensure that the internal temperature reaches the set value quickly and stably. Its rotational speed is determined not only by the internal temperature but also by the capabilities of the high-temperature stage. This invention employs the following parameter group: Internal temperature (T_cab): The main control target, its deviation from the set value and its trend of change are the main basis for control.

[0032] High-temperature stage compressor real-time speed (RPMh): This is a critical feedforward signal. It represents the maximum cooling capacity that the high-temperature stage can currently provide. Increases in the low-temperature stage compressor speed must be matched with RPMh. If RPMh is already high, further increases in the low-temperature stage speed are limited to prevent a sudden rise in the intermediate heat exchanger temperature (T_exl) from overwhelming the high-temperature stage and causing a system shutdown for protection.

[0033] Low-temperature stage exhaust temperature (T_disl): reflects the working intensity and lubrication condition of the low-temperature stage compressor. If the temperature is too high, frequency reduction protection is required.

[0034] The low-temperature side temperature of the intermediate heat exchanger (T_exl) is the condensation temperature of the low-temperature stage. This temperature directly affects the compression ratio and efficiency of the low-temperature stage and needs to be kept within a reasonable range.

[0035] Low-temperature stage return gas temperature (T_sugl): Used to calculate superheat and ensure the safe operation of the compressor.

[0036] The steps for controlling the speed of the cryogenic compressor are as follows: The controller (400) inputs these parameters into the second fuzzy PID controller. The controller comprehensively judges the cooling demand inside the chamber and the capacity status of the high-level system, and outputs a coordinated speed command to the cryogenic inverter compressor (201).

[0037] The specific processing procedure of the second fuzzy PID controller is as follows: the internal temperature (T_cab) is compared with the user-set temperature value, and the deviation and the rate of change of the deviation are used as the core control variables; the real-time speed (RPMh) of the high-temperature stage compressor is used as a feedforward signal, and an increase in its value will correspondingly allow or trigger an increase in the speed of the low-temperature stage compressor to ensure that the capabilities of the two stages are matched; the exhaust temperature (T_disl) of the low-temperature stage is compared with the second preset safety value, and the deviation and the rate of change of the deviation are used as control variables to suppress overheating of the low-temperature stage.

[0038] In the cryogenic compressor speed control step, when the real-time speed (RPMh) of the high-temperature compressor is continuously monitored to reach more than 90% of the rated speed and the internal temperature (T_cab) is still higher than the set value, the second control algorithm will limit the rate of increase of the cryogenic compressor speed to prevent the intermediate heat exchanger temperature (T_exl) from rising too quickly and causing the high-temperature stage capacity to be unable to keep up in time.

[0039] Cooling Phase: When the chamber temperature (T_cab) is significantly higher than the set value, the controller will output a command to gradually increase the speed of the cryogenic stage compressor (201). Simultaneously, the intermediate heat exchanger temperatures (T_exl, T_exh) rise accordingly. The high-temperature stage control loop detects the increase in T_exh and subsequently increases the speed of the high-temperature stage compressor (101). The cryogenic stage controller also detects an increase in RPMh, indicating that the high-temperature stage capability is improving. Therefore, it can safely continue to increase the cryogenic stage speed until the chamber temperature reaches the set value.

[0040] Protection under high-temperature conditions: A sudden rise in ambient temperature causes the high-temperature stage condensing temperature (T_condh) to increase. The high-temperature stage controller prioritizes ensuring that the exhaust temperature (T_dish) does not exceed the limit, which may appropriately reduce the high-temperature stage speed (RPMh). At this time, the low-temperature stage controller detects this feedforward signal of RPMh decrease. Even if the chamber temperature (T_cab) has not yet recovered, it will proactively and preventively reduce the low-temperature stage speed in advance. This avoids the intermediate heat exchanger temperature (T_exl) from continuing to rise, placing additional burden on the already limited high-temperature stage and preventing the system from entering a vicious cycle and shutting down.

[0041] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its scope and spirit, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control, characterized in that, Includes the following steps: Step 1: Real-time acquisition of high-temperature stage exhaust temperature, high-temperature stage condenser temperature, high-temperature side outlet temperature of intermediate heat exchanger, and high-temperature stage return gas temperature parameters; Based on the parameters, the target speed of the high-temperature stage variable frequency compressor is calculated by the first control algorithm, and its operation is controlled. Step 2: Real-time acquisition of parameters including the temperature inside the chamber, the real-time speed of the high-temperature stage compressor, the low-temperature stage exhaust temperature, the low-temperature side temperature of the intermediate heat exchanger, and the low-temperature stage return gas temperature. Based on the parameters, the target speed of the cryogenic stage variable frequency compressor is calculated by the second control algorithm, and its operation is controlled accordingly. In step 2, when controlling the speed of the low-temperature stage variable frequency compressor, if the real-time speed of the high-temperature stage variable frequency compressor continuously reaches more than 90% of the rated speed and the temperature inside the chamber is still higher than the set value, the second control algorithm will limit the rate of increase of the low-temperature stage compressor speed to prevent the intermediate heat exchanger temperature from rising too quickly and causing the high-temperature stage capacity to be unable to keep up in time.

2. The control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control according to claim 1, characterized in that, The first control algorithm is a fuzzy PID control algorithm, specifically: the exhaust temperature of the high-temperature stage is compared with a first preset safety value, and the deviation and the rate of change of the deviation are used as control variables to suppress overheating; The temperature of the high-temperature stage condenser is compared with the first preset target value, and the deviation and the rate of change of the deviation are used as control variables to optimize the heat dissipation capacity. The high-temperature side outlet temperature of the intermediate heat exchanger is used as a demand signal reflecting the load of the low-temperature stage. When its value increases, the demand for increasing the speed of the high-temperature stage compressor is output.

3. The control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control according to claim 1, characterized in that, The second control algorithm is a fuzzy PID control algorithm, specifically: the temperature inside the chamber is compared with the temperature set by the user, and the deviation and the rate of change of the deviation are used as the core control variables; The real-time speed of the high-temperature stage variable frequency compressor is used as a feedforward signal. When its value increases, it will correspondingly allow or trigger an increase in the speed of the low-temperature stage compressor to ensure that the capabilities of the two stages are matched. The exhaust temperature of the low-temperature stage is compared with the second preset safety value, and the deviation and the rate of change of the deviation are used as control variables to suppress overheating of the low-temperature stage.

4. The control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control according to claim 1, characterized in that, During the cooling phase, the system control process is as follows: when the temperature inside the chamber is much higher than the set value, the controller will output a command to gradually increase the speed of the low-temperature stage inverter compressor; at the same time, the temperature of the intermediate heat exchanger rises accordingly, the high-temperature stage control loop detects the rise in the intermediate heat exchanger temperature, and then increases the speed of the high-temperature stage inverter compressor. The low-temperature stage controller also detects that the speed of the high-temperature stage inverter compressor is rising, knows that the high-temperature stage capability is increasing, and continues to safely increase the speed of the low-temperature stage until the chamber temperature reaches the set value.

5. The control method for a variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control according to claim 1, characterized in that, Under high-temperature conditions, the specific control process of the system is as follows: when the ambient temperature rises sharply, the high-temperature stage condensing temperature rises. The high-temperature stage controller prioritizes ensuring that the exhaust temperature does not exceed the limit through the first control algorithm and appropriately reduces the speed of the high-temperature stage variable frequency compressor. At this time, the low-temperature stage controller detects the feedforward signal of the high-temperature stage variable frequency compressor speed decreasing. Even if the temperature inside the chamber has not yet risen, it actively reduces the speed of the low-temperature stage variable frequency compressor to avoid the intermediate heat exchanger temperature from continuing to rise and putting additional burden on the high-temperature stage, which is already in a limited capacity state, thus preventing the system from entering a vicious cycle and shutting down.

6. A variable frequency dual-machine cascade refrigeration system based on multi-parameter coordinated control, characterized in that, The control method described in any one of claims 1-5 specifically includes a high-temperature stage circulation loop, a low-temperature stage circulation loop, a sensor group, and a system controller. The high-temperature stage circulation loop includes a high-temperature stage variable frequency compressor, a high-temperature stage condenser, a high-temperature stage throttling device, and a high-temperature stage evaporation channel disposed in an intermediate heat exchanger. The low-temperature stage circulation loop includes a low-temperature stage variable frequency compressor, a low-temperature stage condensation channel installed in the intermediate heat exchanger, a low-temperature stage throttling device, and a low-temperature stage evaporator; The sensor group includes a high-temperature stage exhaust temperature sensor, a high-temperature stage condenser temperature sensor, a high-temperature side outlet temperature sensor of the intermediate heat exchanger, a high-temperature stage return gas temperature sensor, an internal temperature sensor, a low-temperature stage exhaust temperature sensor, a low-temperature side outlet temperature sensor of the intermediate heat exchanger, and a low-temperature stage return gas temperature sensor. The system controller receives data collected by the sensor group and executes the speed control steps for the high-temperature stage variable frequency compressor and the low-temperature stage variable frequency compressor.

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