Carbon dioxide low circulation ratio system based on low superheat degree regulation and control

Abstract

The invention discloses a carbon dioxide low circulation rate system based on low superheat degree regulation and control, which relates to the technical field of refrigeration and comprises a loop, a plurality of tail end heat exchange branches and a controller, the execution controllability evaluation module is used for calculating the branch outlet superheat degree based on the pressure and temperature measurement values and judging whether the branch outlet superheat degree is in a preset outlet superheat degree target window or not; the branch type judgment module reduces the valve opening degree step by step under the safety constraint to obtain a reducible valve allowance, and accordingly, branches are divided into an over-supply redundancy type, an under-supply sensitive type and an execution limited type to form a redundancy supply set and a protection set; a target pump frequency solving module summarizes the reducible valve margin of the redundant supply set, calculates the pump frequency pressing amplitude and the target pump frequency in combination with the bottleneck margin determined by the protection set, and generates valve bias for redundant branches; according to the invention, on the premise of ensuring stable operation of each tail end, the reduction of the system circulation ratio and the optimization of the pump power consumption are realized.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, and more specifically, to a low-cycle-rate carbon dioxide system based on low superheat regulation. Background Technology

[0002] Existing carbon dioxide refrigeration systems typically require periodic defrosting after evaporator frosting. Common defrosting methods in engineering applications include electric defrosting and hot carbon dioxide defrosting. While electric defrosting is relatively simple to control, it often results in high energy consumption. Furthermore, uneven heating and frost distribution can easily cause localized overheating of the evaporator, increasing thermal stress on materials and affecting the long-term reliability of the heat exchanger. Hot carbon dioxide defrosting achieves rapid defrosting by introducing a high-temperature working fluid, but in multi-branch systems, it can easily lead to flow redistribution due to valve switching, resulting in significant system pressure and temperature fluctuations. Temperature shocks can also affect the fit and expansion performance of copper tubes and heat sink fins, reducing heat transfer consistency and posing reliability risks. Simultaneously, the defrosting process involving high-temperature, high-pressure working fluids places higher demands on control stability and safety protection. Therefore, there is an urgent need for a defrosting control and system coordination solution that can reduce defrosting energy consumption, suppress pressure fluctuations, minimize temperature shocks, and avoid localized overheating while meeting safety constraints.

[0003] To address the above problems, this invention proposes a solution. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide a low-cycle carbon dioxide system based on low superheat regulation to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A low-cycle-rate carbon dioxide system based on low superheat regulation, comprising: circuit, AND Several end heat exchange branches connected in the loop and with The controller (10) is connected to the loop and several terminal heat exchange branches.

[0007] The system includes the following modules: The controllability assessment module acquires the pressure measurement value, suction temperature measurement value, valve opening degree, and pump operating frequency of the terminal heat exchange branch; it looks up the saturation temperature based on the pressure measurement value and the pre-stored saturation temperature; it obtains the branch outlet superheat by the difference between the suction temperature measurement value and the saturation temperature, filters it to obtain the smoothed superheat, and calculates the superheat fluctuation; based on the smoothed superheat and the superheat fluctuation, it determines whether each terminal heat exchange branch is within the preset outlet superheat target window and outputs the corresponding window status quantity.

[0008] The branch type determination module determines the branch type for the end heat exchange branch whose window status indicates that it is within the outlet superheat target window. Under the constraints of the preset minimum stable valve opening and the upper limit safety margin of superheat, the valve opening is gradually reduced to obtain the valve margin that can be reduced. Based on the valve margin that can be reduced, the superheat fluctuation and the valve controllability margin, the branch type is determined, forming a redundant supply set and a protection set. Among them, the valve controllability margin is obtained by normalizing the valve opening relative to the preset minimum stable valve opening.

[0009] The target pump frequency solving module sums the reducible valve margins of the redundant supply set to obtain the total extractable redundancy. It then calculates the downward pressure of the pump operating frequency and the corresponding target pump frequency by combining the bottleneck margin determined by the protection set, and generates the valve bias applied to the redundant supply set. Under the constraints of the preset minimum stable pump frequency and the upper limit of pump frequency ramping, it issues the execution command corresponding to the target pump frequency and valve bias.

[0010] In a preferred embodiment, the The circuit includes reservoir, and The shielded pump, and the plurality of terminal heat exchange branches including a through-flow air cooler, a medium-temperature storage chamber, and a high-temperature heat exchanger, are provided at the inlet of each terminal heat exchange branch. Electronic expansion valve; each terminal heat exchange branch is equipped with a pressure sensor, a suction temperature probe, and an outlet air temperature probe or a suction air temperature probe. The pressure measurement value, suction temperature measurement value, and valve opening are all read by the controller, and the air side temperature measurement value is obtained by the outlet air temperature probe or the suction air temperature probe.

[0011] In a preferred embodiment, the smooth superheat is obtained by: performing low-pass filtering on the branch outlet superheat obtained by each terminal heat exchange branch in each sampling period in an exponentially weighted manner, and using the filtered result as the smooth superheat of the terminal heat exchange branch, wherein the low-pass filtering is characterized by the filtering coefficient parameter; and updating the smooth superheat within a preset sliding time window.

[0012] In a preferred embodiment, hysteresis logic is used to determine whether each terminal heat exchange branch is within a preset outlet superheat target window. Specifically, when the smooth superheat is continuously within the outlet superheat target window and the superheat fluctuation is less than or equal to the preset entry stability threshold for a duration that reaches the entry dwell time, the window status quantity of the corresponding terminal heat exchange branch is set to indicate that it is within the outlet superheat target window; when the smooth superheat continuously exceeds the upper release threshold or is lower than the lower release threshold for a duration that reaches the release dwell time, the window status quantity of the corresponding terminal heat exchange branch is set to indicate that it is not within the outlet superheat target window.

[0013] In a preferred embodiment, the method for obtaining the reducible valve margin is as follows: for the end heat exchange branch where the window status indicator is within the outlet superheat target window, when the valve controllability margin is greater than or equal to the test margin threshold and the superheat fluctuation is less than or equal to the test fluctuation threshold, the valve opening of the end heat exchange branch where the window status indicator is within the outlet superheat target window is gradually reduced according to a preset valve opening step size, and a preset dwell time is maintained after each reduction; if the preset safety conditions are met during the dwell period, the reduction amount is accumulated and the next reduction is continued; otherwise, the gradual reduction is terminated, and the accumulated valve opening reduction amount before termination is determined as the reducible valve margin of the end heat exchange branch;

[0014] The preset safety condition is: when the superheat at the branch outlet does not exceed the value obtained by subtracting the preset superheat upper limit safety margin from the upper limit of the outlet superheat target window, and the valve opening is not less than the value obtained by adding the preset minimum stable opening safety interval, it is determined that the preset safety condition is met.

[0015] If the superheat at the branch outlet exceeds the value obtained by subtracting the superheat upper limit safety margin from the target window for superheat, or if the valve opening is less than the value obtained by adding the minimum stable valve opening to the minimum stable opening safety interval, it is determined that the preset safety conditions are not met.

[0016] In a preferred embodiment, the branch type is determined based on the reducible valve margin, superheat fluctuation and valve controllability margin by comparing the reducible valve margin, superheat fluctuation and valve controllability margin of a certain terminal heat exchange branch with its corresponding preset threshold.

[0017] If the reduceable valve margin of a certain terminal heat exchange branch is greater than or equal to the redundancy significant threshold, and the superheat fluctuation is less than or equal to the redundancy stability threshold, and the valve controllability margin is greater than or equal to the redundancy margin threshold, then the branch type of the terminal heat exchange branch is determined to be over-supply redundancy type; if the valve controllability margin of a certain terminal heat exchange branch is less than or equal to the limited margin threshold or the superheat fluctuation is greater than or equal to the limited fluctuation threshold, then the branch type of the terminal heat exchange branch is determined to be execution-limited type; the remaining window status indicators are within the outlet superheat target window and the terminal heat exchange branches that are not determined to be over-supply redundancy type branches or execution-limited type branches are determined to be under-supply sensitive type.

[0018] The terminal heat exchange branches with the branch type of oversupply redundancy and whose window status indicators are within the outlet superheat target window are formed into a redundant supply set, and the terminal heat exchange branches with the branch type of undersupply sensitive or execution restricted and whose window status indicators are within the outlet superheat target window are formed into a protection set.

[0019] In a preferred embodiment, the bottleneck margin is determined as follows: a protection margin is constructed for each end heat exchange branch in the protection set, wherein the protection margin is the smaller value of the superheat margin term and the valve margin mapping term, wherein the superheat margin term is the difference between the upper limit of the outlet superheat target window and the smoothed superheat of the end heat exchange branch; the valve margin mapping term is a linear function of the valve controllability margin of the end heat exchange branch; and the minimum value of each protection margin in the protection set is taken as the bottleneck margin; which represents the maximum allowable space for the pump operating frequency to decrease in pressure without causing instability in any end heat exchange branch in the protection set.

[0020] In a preferred embodiment, the method for calculating the downward pressure of the pump operating frequency and the corresponding target pump frequency is as follows: the total amount of extractable redundancy is obtained by summing the reducible valve margins of each terminal heat exchange branch in the redundant supply set, and candidate pump operating frequency downward pressure is constructed in combination with the bottleneck margin; the candidate pump operating frequency downward pressure is used as the target reference for the pump operating frequency downward pressure, and a feasibility check is performed on the candidate pump operating frequency downward pressure. Under the premise that the feasibility check is passed, the actual pump operating frequency downward pressure is determined by combining the minimum stable frequency of the pump and the upper limit of the pump frequency ramp, and the target pump frequency is obtained by subtracting the pump operating frequency downward pressure from the current pump operating frequency.

[0021] In a preferred embodiment, the specific steps of the feasibility verification are as follows: the pump operating frequency is gradually reduced according to a preset pump frequency step size, and a preset steady-state residence time is maintained after each reduction. During the steady-state residence time, the smooth superheat, superheat fluctuation, and valve controllability margin of each terminal heat exchange branch in the protection set are monitored. When the smooth superheat of all terminal heat exchange branches in the protection set does not exceed the value obtained by subtracting the superheat upper limit safety margin from the upper limit of the outlet superheat target window, the superheat fluctuation does not exceed the preset fluctuation limit, and the valve controllability margin is not lower than the preset safety margin threshold, the pump operating frequency reduction of this stage is determined to be feasible and the next stage reduction is continued. When any terminal heat exchange branch in the protection set does not meet any of the above criteria, the current stage reduction is determined to be infeasible and the gradual reduction is stopped. The pump operating frequency reduction amplitude of the previous feasible stage is used as the actual reduction amplitude, and the corresponding target pump frequency is obtained accordingly.

[0022] In a preferred embodiment, the system further includes an execution constraint steady-state determination module, used to perform a coordinated steady-state determination after executing the execution command corresponding to the target pump frequency and valve bias. The coordinated steady-state determination includes: monitoring the smooth superheat and superheat fluctuation changes of each terminal heat exchange branch in the protection set within a preset coordinated steady-state determination time window; when the smooth superheat of each terminal heat exchange branch in the protection set remains within the value obtained by subtracting the superheat upper limit safety margin from the upper limit of the outlet superheat target window, and the superheat fluctuation does not exceed a preset stability threshold, the system is determined to be in a coordinated steady state and maintains the current target pump frequency and valve bias; when the above conditions are not met, the system does not... Upon reaching a coordinated steady state, the bias scaling factor is decreased by a preset attenuation factor, and the pump frequency command is maintained or slightly reverted until the preset steady state criterion is met again. When the bias scaling factor is decreased to the preset minimum execution factor but still does not meet the preset steady state criterion, the pump frequency command is reverted and the steady state determination is re-entered. When a coordinated steady state is determined, a low cycle rate holding state is entered. While maintaining the target pump frequency and valve bias, the return liquid redundancy and two-phase effective utilization coefficient of the redundant supply set are monitored. When the total redundancy of the redundant supply set decreases or the end heat exchange branch in any protection set becomes execution-restricted, the low cycle rate holding state is exited and a holding exit dwell time is set to suppress frequent exits caused by short-term disturbances.

[0023] The technical effects and advantages of this invention, a low-superheat control-based carbon dioxide low-cycle-rate system, are as follows: By identifying and coordinating the control of redundant supply capacity, this invention reduces the cycle rate and pump power while suppressing pressure fluctuations caused by flow redistribution during operating condition switching and defrosting disturbances. This reduces the risk of local overheating and temperature overshoot, thereby minimizing the additional energy consumption associated with defrosting and improving system operational stability and long-term heat exchanger reliability. Its beneficial effects are mainly reflected in the following aspects: First, the system can automatically identify and quantify the reducible valve margin of each branch, accurately distinguishing between over-supply redundant, under-supply sensitive, and execution-limited branches, providing a clear and safe source for redundancy extraction. Second, by constructing a protection set and bottleneck margin, it can effectively protect unstable branches when the pump frequency is reduced, preventing their overheating from exceeding the safe window and ensuring the stability and reliability of the system during depressurization. Furthermore, by employing a feasibility verification and collaborative steady-state determination mechanism, the dynamic matching of pump frequency reduction and valve position adjustment is adaptively matched, which suppresses disturbances caused by flow redistribution and improves the overall robustness under low circulation rate conditions. Finally, while maintaining low superheat, this invention achieves optimized reduction of pump power, improves system energy efficiency, and has clear and reproducible control logic, making it suitable for actual operating scenarios with varying loads. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the hardware structure of a low-cycle-rate carbon dioxide system based on low superheat regulation according to the present invention.

[0025] Figure 2 This is a schematic diagram of a module implementation of a low-cycle rate carbon dioxide system based on low superheat control according to the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example

[0028] Please see Figure 1 As shown, this invention discloses a low-cycle carbon dioxide system based on low superheat regulation, the hardware structure of which includes: a Freon parallel compressor unit (1), a Freon-oil separator (2), a Freon condenser (3), a Freon receiver (4), an expansion valve (5), and a condenser-evaporator (6). Liquid reservoir (7) Shielded pump (8), through-ventilation air cooler (9), controller (10) Electronic expansion valve (11), pressure sensor (12), suction temperature probe (13), outlet air temperature probe or suction air temperature probe (14), medium temperature chamber (15), high temperature heat exchanger (16); wherein, the present invention will use Liquid reservoir (7) The circuit with the shielded pump (8) as the core and connecting each terminal heat exchange branch is defined as follows: The circuit is defined as several terminal heat exchange branches between the through-hall air cooler (9), the medium-temperature warehouse (15), and the high-temperature heat exchanger (16), and each branch inlet is equipped with The electronic expansion valve 11 is controlled by the controller (10); during the operation of the system, the data collected by each sensor is processed and a control quantity is generated, which in turn drives the electronic expansion valve and the shielded pump to complete the regulation.

[0029] Based on the above hardware structure, please refer to Figure 2 As shown, this invention discloses a low-cycle-rate carbon dioxide system based on low superheat regulation, comprising the following modules:

[0030] The controllability assessment module acquires the pressure measurement value, suction temperature measurement value, valve opening degree and pump operating frequency of the terminal heat exchange branch. Based on the pressure measurement value and the pre-stored saturation temperature, the saturation temperature is obtained by looking up a table. The branch outlet superheat is obtained by the difference between the suction temperature measurement value and the saturation temperature, and the superheat is smoothed by filtering. The superheat fluctuation is calculated. Based on the smoothed superheat and the superheat fluctuation, it is determined whether each terminal heat exchange branch is within the preset outlet superheat target window, and the corresponding window status quantity is output.

[0031] In one specific embodiment, the controller (10) operates according to the sampling period parameter. The cyclic task is executed periodically, and the measurement data of each end heat exchange branch i is read, including but not limited to: pressure measurement values ​​obtained by pressure sensor (12). The measured value of the inhalation temperature obtained by the inhalation temperature probe (13) The air-side temperature measurement value obtained by the outlet air temperature probe or the intake air temperature probe (14) Simultaneously read the valve opening degree of the terminal heat exchange branch. and pump operating frequency Among them, the sampling period parameter Its initial value is set to a second-level sampling period to balance actuator response and computational load. An example initial value is... The logic for setting the initial value is as follows: branch superheat and valve action have a significant impact on system stability, and the typical response time of valves and pumps is usually on the order of several seconds. Using second-level sampling can simultaneously obtain sufficient dynamic resolution and stable computing resources.

[0032] After data acquisition, the branch outlet superheat is constructed, and pressure measurements are obtained. With the measured value of inhalation temperature Then, the working fluid saturation temperature is pre-stored in the controller (10) and looked up in the table. It stores discrete points indexed by pressure measurements and uses linear interpolation to obtain the saturation temperature under the current pressure measurement. The difference between the suction temperature and the saturation temperature is defined as the outlet superheat according to its physical meaning. Specifically: under a given pressure measurement, if the suction temperature is higher than the saturation temperature, superheat exists; the superheat is equal to the difference between the two. Therefore, the instantaneous superheat of the terminal heat exchange branch i is constructed. The instantaneous overheating of the branch The following formula can be used as a reference: ;in, This refers to the pressure measurement value corresponding to the terminal heat exchange branch i. This refers to the measured suction temperature of the corresponding terminal heat exchange branch i; where i is the identifier of the terminal heat exchange branch and N represents the total number of terminal heat exchange branches;

[0033] It should be noted that the pre-stored working fluid saturation temperature is obtained from a table. Used to characterize the saturation temperature corresponding to pressure P, it stores multiple pressure discrete points and the saturation temperature corresponding to each discrete point using the pressure measurement value as an index; when the pressure measurement value is between two adjacent pressure discrete points, the controller (10) uses linear interpolation to calculate the saturation temperature under the current pressure measurement value; when the pressure measurement value exceeds the coverage range of the pressure discrete points, the controller (10) uses the saturation temperature corresponding to the boundary pressure discrete point as the saturation temperature to ensure the determinism and reproducibility of the outlet superheat calculation;

[0034] To ensure that the judgment is not affected by transient noise in the low superheat range, the instantaneous superheat of the branch is formed. Further construction of smooth superheat That is, using an exponentially weighted method to measure the instantaneous overheat of the branch. Low-pass filtering suppresses fast noise while preserving the true changes in the branches. Its mathematical expression is: Where k is the index of the discrete time step. These are the filter coefficient parameters; their initial values ​​can be: The initial value setting logic is as follows: under second-level sampling, the filter coefficient parameters... Setting the value close to 1 can effectively suppress measurement jitter while still being able to track load changes within tens of seconds; if the noise level is higher at the site, the filter coefficient parameter can be adjusted through calibration. However, the system defaults to using this initial value;

[0035] When a smooth superheat is obtained Subsequently, it does not directly use a single smooth superheat. The result determines whether the terminal heat exchange branch enters the target operating state; instead, it first generates fluctuation results for stability assessment. Specifically: in a length of... Calculate smooth superheat on the sliding sequence The discrete standard deviation is used to obtain the superheat fluctuation. Its mathematical expression is: ;in The initial value can be taken from dozens of sampling points to cover a characteristic range of a valve or pump response. An example initial value is... ;

[0036] Subsequently, based on smooth superheat With fluctuations in superheat Perform outlet superheat target window determination and output window status. And further mapped to branch pattern Specifically: the target window for outlet superheat Based on the preset window lower limit With preset window limit The definition and its setting logic are as follows: when the outlet superheat is within the target window, the outlet of the terminal heat exchange branch is close to saturation but still retains the necessary margin. After considering measurement errors and dynamic fluctuations, this can be used as the preliminary operating state for subsequent cycle redundancy evaluation and cycle rate reduction control; the lower limit of the preset window With preset window limit The initial values ​​are 0K and 1K respectively, which are used as the initial calibration values ​​when the system is put into operation;

[0037] Preferably, to avoid frequent switching at window boundaries, an entry stability threshold is set. With entry and length of stay And set the release upper limit threshold. Release lower threshold With release of stay time This constitutes hysteresis; specifically: when smoothing superheat... The export overheating target window has been continuously falling. And the degree of overheating fluctuates Less than or equal to the stability threshold The duration reaches the entry stay time At that time, set the window state variable ;

[0038] When smoothing overheating Continuously exceeding the upper limit threshold or below the lower release threshold The duration reaches the release dwell time At that time, set the window state variable ;

[0039] Among them, the stability threshold The initial value is set to a degree level of, for example, 0.2K, and the dwell time is entered. The initial value is set to a minute level, for example, 60 seconds; release upper limit threshold. The initial value is slightly higher than the preset window limit. And preset window lower limit The initial value is slightly lower than the lower release threshold. For example, 1.2K and -0.2K; based on the requirement to release the window state quickly once an out-of-bounds trend appears, and at the same time to release the dwell time by suppressing boundary jitter through hysteresis. The initial value is taken in the tens of seconds range, for example, 30 seconds;

[0040] After the window state variable is formed, the output branch mode is output. Its construction logic is as follows: the window state variable is used to characterize whether the branch is in the operating state where the outlet overheat target window is available; when the window state variable At that time, branch mode Take the target window mode for outlet superheat; when the window state quantity Branch mode Take the normal mode;

[0041] Preferably, to ensure that subsequent modules naturally avoid the unstable execution region when performing redundancy assessments and pump reduction derivations, this module outputs execution controllability margin results within the same cycle of the output branch mode. This result is used to quantify the remaining space between the valve and the pump and their stable operable boundary. Specifically, it is based on the preset minimum stable valve opening. With preset pump minimum stable frequency Set the current valve opening degree Relative to the preset minimum stable opening of the valve Normalization is performed to obtain the valve controllability margin. ; Set the current pump frequency The pump controllability margin is obtained by normalizing relative to the pump's minimum stable frequency. Its corresponding mathematical expression is as follows: ;in, The initial value for the pump's highest frequency can be taken as the rated highest frequency, such as... , The maximum valve opening is usually taken as 100%;

[0042] It should be noted that the preset valve minimum stable opening degree With preset pump minimum stable frequency Preset initial values ​​are used and can be calibrated during installation and commissioning: The initial value was selected based on the valve's resolution and minimum stable flow test results in the small opening region, with an example initial value of 8%. The initial value is selected based on the pump's minimum stable flow rate and the experimental results to avoid cavitation and a sharp drop in efficiency. An example initial value is... .

[0043] The branch type determination module determines the branch type for the terminal heat exchange branch whose window status indicator is within the outlet superheat target window. Under the constraints of the preset minimum stable valve opening and the upper limit safety margin of superheat, the valve opening is gradually reduced to obtain the valve margin that can be reduced. Based on the valve margin that can be reduced, the superheat fluctuation and the valve controllability margin, the branch type is determined, including: oversupply redundancy type, execution restricted type and undersupply sensitive type.

[0044] In one specific embodiment, only the window state quantity is considered. The target window mode for export overheating is... The terminal heat exchange branch performs two-phase efficient utilization and return liquid redundancy assessment, and evaluates the window state quantity. For the conventional mode, the direct output of the terminal heat exchange branch can reduce valve margin to 0 and return liquid redundancy to 0, and change the branch type. Set to normal to prevent non-target window conditions from entering subsequent redundant extraction links;

[0045] Under the export overheating target window model, the two-phase effective utilization coefficient is first constructed. This is used to characterize the effectiveness of the two-phase heat transfer contribution when the outlet is close to saturation; its construction logic is as follows: a dimensionless coefficient is formed by the ratio of the latent heat contribution scale of the phase change to the sensible heat contribution scale of the terminal, where the sensible heat contribution of the terminal is determined by... Characterization; in one embodiment, a preset steam specific heat parameter With latent heat parameters of phase change Their initial values ​​can be taken as follows: and The initial value setting logic is to select approximate thermal properties under typical operating conditions to ensure resolution within the 0–1K range and avoid complex online property calculations; accordingly, the two-phase effective utilization coefficient The following expression can be used as a reference: ;

[0046] After obtaining the two-phase effective utilization coefficient Then, further construction can reduce valve margin. This is used to quantify the liquid supply adjustment space that can be safely reduced in the terminal heat exchange branch while maintaining the stability of the outlet superheat target window; it should be noted that the reduceable valve margin... It is not inferred from a single point of overheating, but obtained through a deterministic online reduction, dwell, judgment, and recovery trial process, thus providing a reproducible quantitative basis for subsequent cyclic redundancy extraction;

[0047] Preferably, the triggering of the probing process is constrained by both stability and controllability: when and Probing is permitted at certain times; otherwise, the valve margin can be reduced. ;in, To test the margin threshold, To test the fluctuation threshold and avoid introducing test disturbances that could lead to distorted judgments when the valve is close to its minimum stable opening or when there is significant superheat fluctuation, the following can be done: The initial value is set to 0.15. The initial value is set to 0.2K;

[0048] When the testing conditions are met, the valve opening step size is used. The valve opening is gradually reduced, and a dwell time is maintained after each reduction. To observe the instantaneous overheating of the branch circuit With fluctuations in superheat The response; if it is determined to be safe, the reduction amount is accumulated and the next step is continued; otherwise, the process terminates and the accumulated reduction amount is output as the reducible valve margin. Among them, the valve opening step size The initial value can be 1%, and the dwell time The initial value can be 10s, and the initial value setting logic is to match the valve resolution and cover the branch thermal inertia response time.

[0049] To ensure that the probe does not push the branch to the window boundary, an overheat limit safety margin is set. Safety interval with minimum stable opening During the stay Or the temporary valve opening is less than or equal to If the reduction is deemed unacceptable, the trial is terminated; the upper limit of superheat safety margin is included. The initial value can be taken as 0.1K, and the minimum stable opening safety interval is... The initial value can be set to 2%. The logic for setting the initial value is to maintain a margin within the window while considering measurement errors and dynamic fluctuations, and to prevent the valve from entering an unstable small opening region. After termination, the dwell time is restored. To return to the original control point, The initial value can be 20s, and its setting logic is to eliminate the short-term bias caused by trial and error and maintain the comparability of the evaluation in the next cycle.

[0050] Obtaining a reduceable valve margin Then, construct the return fluid redundancy. To achieve cross-branch comparability: normalize the reducible margin relative to the current available opening range and introduce protection parameters. Avoid making the denominator too small; among which, the protection parameters The initial value can be 0.5%, and the logic is set to be consistent with the valve's minimum resolution level; return fluid redundancy. The expression is: ;

[0051] Furthermore, based on the ability to reduce valve margin Fluctuations in superheat With valve controllability margin Output branch type This allows subsequent modules to select redundancy extraction sources by type and identify bottleneck branches; preferably, a significant redundancy threshold is set. Redundancy stability threshold Redundancy threshold Constrained redundancy threshold With restricted volatility threshold Its initial values ​​can be 3%, 0.25K, 0.2, 0.1, and 0.35K respectively. The logic for setting the initial values ​​is as follows: the redundant type must simultaneously satisfy sufficient reduction amount, stability within the window, and sufficient valve margin; the restricted type is used to identify non-extractable objects where the margin is close to the boundary or fluctuates significantly. Accordingly, when and and Time-set branch type For oversupply redundancy; when or Time-set branch type For restricted execution; other branch types under the outlet superheat target window mode. It is a sensitive type due to supply shortage.

[0052] The target pump frequency solution module sums the reducible valve margins of the redundant supply set to obtain the total extractable redundancy, calculates the downward pressure of the pump operating frequency and the corresponding target pump frequency in combination with the bottleneck margin determined by the protection set, and generates the valve bias applied to the redundant supply set; under the constraints of the preset minimum stable pump frequency and the upper limit of pump frequency ramping, it issues the execution command corresponding to the target pump frequency and valve bias.

[0053] Based on the obtained branch type This forms a branch set state, used to clarify the sources of redundancy extraction and the objects to be protected, including: those that meet the branch type... It is an over-supply redundancy type, and the window state quantity The terminal heat exchange branch is included in the redundant supply set D and its element index is denoted as . The terminal heat exchange branch number corresponding to its d-th element is denoted as ; will satisfy branch type For those with supply shortages or execution restrictions, and with window state variables The terminal heat exchange branch is included in the protection set P and its element index is denoted as . The terminal heat exchange branch number corresponding to its p-th element is denoted as Other window state variables or branch type Conventional terminal heat exchange branches are categorized into the conventional set. Among them, the redundant supply set D serves as the sole source of cyclic redundancy extraction, the protection set P is used to limit the downward pressure to avoid window instability or execution saturation, and the regular set... Not involved in the pressure solution; among them, and All taken from And any d and any p satisfy ; Regular set In addition to the above and The set of numbers for the remaining terminal heat exchange branches, excluding those mentioned above;

[0054] After the set state is formed, the total amount of extractable redundancy is calculated. Its construction logic is as follows: the reduceable valve margin of each end heat exchange branch in the redundant supply set. This characterizes the liquid supply adjustment space that can be reduced while maintaining a stable outlet superheat target window for this terminal heat exchange branch. At the system level, summing this space yields the total extractable space available for the down-pressure pump. Based on this, the total extractable redundancy can be obtained using the following expression: Preferably, to avoid blindly lowering the redundancy level when there is insufficient redundancy, causing the end heat exchange branch in the protection set to go out of bounds, a redundancy activation threshold is preset. The total amount of redundancy that can be extracted With redundancy activation threshold When comparing, At that time, the actual downward pressure amplitude is directly output. Target pump frequency Bias all valves Among them, the redundancy activation threshold Initial values ​​can be taken and redundancy thresholds are significant. For the same magnitude, such as 3%, the setting logic is to require that the system has at least a significantly reducible source of redundancy before triggering downpressure;

[0055] when At the same time, further build bottleneck margins This is to quantify the ability of the protection set to limit the downward pressure. Its construction logic is as follows: after the pump supply pressure decreases, the first branch to become unstable is usually the bottleneck branch in the protection set. The bottleneck risk is mainly manifested in the outlet superheat approaching the upper boundary of the target window and the valve opening approaching the minimum stable opening. Therefore, for each branch in the protection set P... Construction protection margin The smaller value between the superheat margin term and the valve clearance mapping term is taken as the bottleneck margin; where the superheat margin term is composed of... Characterization, valve redundancy mapping term is derived from Characterization; then the protection margin Based on the obtained protection margin Bottleneck margin can be obtained ;in The mapping coefficient parameter can have an initial value of [value]. The initial value setting logic is to retain a limited margin baseline when the valve margin is small, and to significantly increase the withstand pressure space as the valve margin increases.

[0056] Obtain the total amount of extractable redundancy With bottleneck margin Then, the frequency down-pressure amplitude of the candidate pump is generated. The construction logic is as follows: the candidate downsampling amplitude increases with the total amount of extractable redundancy and with the bottleneck margin, and the size of the redundant supply set is normalized to avoid over-excitation caused by a small amount of branch redundancy; preferably, a pump reduction scale parameter is introduced. With normalized scaling parameters The candidate downward pressure amplitude can be obtained by referring to the following expression: Among them, the pump scale parameters The initial value can be set to 10Hz, and the logic is set to limit the single pressure drop to a controllable range within the pump's adjustable range; normalized scale parameters. The initial value can be 10%, and the logic is set to convert the percentage reduction in valve opening into a frequency-based pressure scale; to ensure that the output pressure amplitude can be realized under the current execution constraints, candidate pressure amplitudes are... Perform feasibility verification and converge to the actual downward pressure range. ;

[0057] Preferably, a preset step size is used. Duration of stay Conduct step-by-step trials: adjust the pump frequency according to... Decrease gradually at each level and maintain the dwell time at each level. During this period, for each of the protection sets P The corresponding smooth superheat sequence takes the maximum value, if any satisfy or the corresponding valve controllability margin The temperature drops to a level that does not meet the minimum safety margin, i.e., is less than or equal to the limited margin threshold, or its corresponding superheat fluctuation. Exceeding the fluctuation limit If the current level is deemed infeasible, the trial is stopped, and the previous feasible level is taken as the actual downward pressure level; accordingly: actual downward pressure level Then the target pump frequency ;in, The initial value can be 0.5Hz. The initial value can be 20s. The initial value setting logic is to match the stable adjustment resolution of the frequency converter and cover the main response of the pump-valve-thermal inertia coupling. The constraint level can be consistent with that of the branch type determination module, for example, 0.35K. The valve safety margin is set using the branch type determination module to ensure consistency across the entire link boundary. For the number Smooth superheating of the terminal heat exchange branch;

[0058] After obtaining the target pump frequency Then, construct the cycle multiplier result quantity. This is used to characterize the circulation rate level after pressure reduction; its construction logic is as follows: under the approximation of pump characteristics, the circulation flow rate is approximately positively correlated with the pump frequency, therefore, the ratio of the pump frequency relative to the reference is used to approximate the ratio of the circulation rate relative to the reference; for this purpose, the window state quantity is first satisfied. and Latch pump frequency reference when triggering downpressure And set the cycle ratio benchmark. Initial value, for example, 2; based on this: ;in To protect parameters, the initial value is taken from the minimum resolution level of the pump frequency, and the logic is set to avoid an excessively small denominator. Furthermore, to ensure that redundant extraction actions are concentrated on the redundant supply set and consistent with the pump's downward pressure amplitude, the output valve is biased. Its construction logic is as follows: bias the valve according to the ratio of the actual downward pressure amplitude to the realized candidate downward pressure amplitude. Scaling is performed, and a negative bias is applied to the redundant supply set; preferably, an implementation ratio is defined. Then for have ,right have And all have ;in To protect parameters, the initial value is taken as... Use fractions of the same order of magnitude to avoid having an excessively small denominator.

[0059] The execution constraint steady-state determination module performs execution-layer constraint shaping on the target pump frequency to form a pump command frequency that satisfies the minimum stable frequency constraint and the upper limit of pump frequency ramp-up. It also performs executable bias shaping on the valve bias to output the valve command opening, applying negative valve bias only to over-supply redundant branches of the redundant supply set. After the pump and valve commands are issued, it performs coordinated steady-state determination and redistribution suppression. In the non-steady-state condition, the bias scaling factor is decreased according to a preset attenuation factor. If the non-steady-state condition persists even after decreasing to a preset minimum execution factor, the pump frequency command is called back. In the steady-state condition, it enters a low-cycle rate holding state and exits after a holding exit dwell time.

[0060] First, the target pump frequency... Perform execution layer constraint shaping and output executable pump command frequency. The construction logic is as follows: the pump frequency command should meet the minimum stable frequency constraint and the inverter ramp rate constraint, and prioritize window stability when a window mode branch exists; therefore, an upper limit for pump frequency ramp rate is set. pump frequency command lower limit and with sampling period By limiting the rate of change of the instruction, we get: ;in For amplitude limiting operator; ramp limit The initial value can be taken as 2Hz / s. Its setting logic is to limit the pressure difference step caused by sudden changes in pump frequency, thereby reducing the probability of the terminal valve shaking and flow redistribution in the small opening range; if the pump frequency ramp-up limit is... The indicator pump is approaching the stability boundary and If the number of branch roads is greater than zero, the upper limit for climbing will be further tightened to [value missing]. ,in The initial value can be 0.5, and the logic is set to use a gentler frequency change in a low redundancy state to ensure system controllability;

[0061] After obtaining the pump command frequency Subsequently, executable bias shaping is performed on the valve bias of each terminal heat exchange branch, and the output valve command opening degree is determined. Its construction logic is as follows: valve bias should primarily act on redundant supply branches to achieve redundant return fluid extraction, while simultaneously satisfying the minimum stable valve opening constraint and avoiding bias on each of the protection sets P. Applying a negative bias causes the upper boundary of the window to approach; therefore, the current valve opening is used. Valve bias output by the target pump frequency solver module Construct candidate valve commands and introduce a minimum stable opening safety interval. Forming hard constraints: ;in Setting it to 100% ensures that the bias matches the branch state, depending on the branch type. For over-supply redundancy and The branch allows the above negative bias to be performed; for branch type For terminal heat exchange branches that are under-supply sensitive or have limited operation, if Then force zeroing; for The side road will Set to zero and only maintain the original local overheat control to avoid the conventional mode branch from participating in redundant extraction;

[0062] After the pump and valve commands are issued simultaneously, a coordinated steady-state determination and redistribution suppression are performed to handle common branch flow grabbing and local valve saturation problems under low cycle rate conditions, ensuring that the downward pressure amplitude obtained by the target pump frequency solution module is not offset by pressure fluctuation amplification. Its construction logic is as follows: changes in pump frequency will cause changes in the supply pressure differential, leading to a redistribution of the actual flow in each branch; if this redistribution causes each branch in the protection set P to... If the smoothed overheating approaches the upper limit of the window or the overheating fluctuation increases, the downward pressure should be temporarily suspended and the bias action should be converged; therefore, a steady-state determination time window should be set. And monitor each of the protection sets P within this time window. corresponding and Changes; during the steady-state determination time window All internal conditions are met and The system is determined to enter a cooperative steady state if the condition is met; otherwise, it is determined to be in an unstable state and a protection strategy is executed. The steady-state determination time window... The initial value can be 60s, and its setting logic is the time for the pressure field and terminal thermal inertia to reconverge after the pump frequency adjustment. The pressure field and flow redistribution disturbance can be triggered by pump frequency adjustment, valve switching, loop switching during defrosting, hot gas introduction and exit, etc. Therefore, it is necessary to suppress pressure fluctuation amplification and temperature overshoot through collaborative steady-state determination and self-convergence strategy.

[0063] When the condition is determined to be non-steady, the execution quantity is self-converged: the current bias scaling factor is adjusted. According to the preset attenuation factor Decrease the frequency and maintain or slightly reduce the pump frequency command until the steady-state criterion is met again; specifically, set... When any satisfy or When, execute And bias the valves of the redundant supply branches to Calculate after scaling ;in The initial value can be 0.7, and the logic is set to rapidly reduce the bias strength over several sampling periods to suppress flow redistribution impacts; simultaneously, if the bias scaling factor... It has been reduced to the preset minimum execution coefficient. If the steady-state criterion is still not met, then... Callback to And re-enter steady state determination; among which The initial value can be 0.2. The logic is set so that when the bias is almost ineffective and still unstable, the bottleneck branch constraint should be released by restoring part of the liquid supply capacity.

[0064] When the condition is determined to be in a cooperative steady state, the system enters a low-cycle-rate hold state and outputs a status flag. The logic for maintaining the state is as follows: while maintaining... and At the same time, continuously monitor the return fluid redundancy of the redundant supply collection branch. With two-phase effective utilization coefficient Change; when the total redundancy of redundant supply branches decreases, If the branch type in any protection set changes to execution-restricted, the hold state is exited and the branch type determination module is triggered to reassess redundancy; therefore, a hold exit dwell time is set. To avoid frequent exits caused by short-term disturbances; The initial value can be 30s, and its setting logic is to match the magnitude of the window hysteresis time of the execution controllability assessment module, thereby maintaining the consistency of the entire system's state switching.

[0065] The constraint steady-state determination module ultimately generates and issues the pump command frequency. Command opening degree of each branch valve and output cooperative steady-state identifier. As a system operating state variable, the target pump frequency reduction and redundant extraction actions obtained by the target pump frequency solving module satisfy the stability boundary constraints at the execution layer and the window stability constraints at the system layer, thereby realizing a reproducible control process of reduced pump power and controlled pressure fluctuations under low cycle rate conditions.

[0066] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0067] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0068] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0069] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0070] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0071] In conclusion, the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-cycle-rate carbon dioxide system based on low superheat regulation, characterized in that, include circuit, AND Several end heat exchange branches connected in the loop and with A controller that controls the circuit and several terminal heat exchange branches; The system includes the following modules: The controllability assessment module acquires the pressure measurement value, suction temperature measurement value, valve opening degree, and pump operating frequency of the terminal heat exchange branch; it looks up the saturation temperature based on the pressure measurement value and the pre-stored saturation temperature; it obtains the branch outlet superheat by the difference between the suction temperature measurement value and the saturation temperature, filters it to obtain the smoothed superheat, and calculates the superheat fluctuation; based on the smoothed superheat and the superheat fluctuation, it determines whether each terminal heat exchange branch is within the preset outlet superheat target window and outputs the corresponding window status quantity. The branch type determination module determines the branch type for the end heat exchange branch whose window status indicates that it is within the outlet superheat target window. Under the constraints of the preset minimum stable valve opening and the upper limit safety margin of superheat, the valve opening is gradually reduced to obtain the valve margin that can be reduced. Based on the valve margin that can be reduced, the superheat fluctuation and the valve controllability margin, the branch type is determined, forming a redundant supply set and a protection set. Among them, the valve controllability margin is obtained by normalizing the valve opening relative to the preset minimum stable valve opening. The target pump frequency solving module sums the reducible valve margins of the redundant supply set to obtain the total extractable redundancy. It then calculates the downward pressure of the pump operating frequency and the corresponding target pump frequency by combining the bottleneck margin determined by the protection set, and generates the valve bias applied to the redundant supply set. Under the constraints of the preset minimum stable pump frequency and the upper limit of pump frequency ramping, it issues the execution command corresponding to the target pump frequency and valve bias.

2. The low-superheat control carbon dioxide low-cycle-rate system according to claim 1, characterized in that, The The circuit includes reservoir and The shielded pump, and the plurality of terminal heat exchange branches including a through-hall air cooler, a medium-temperature storage chamber, and a high-temperature heat exchanger, are provided at the inlet of each terminal heat exchange branch. Electronic expansion valve; each terminal heat exchange branch is equipped with a pressure sensor, a suction temperature probe, and an outlet air temperature probe or a suction air temperature probe. The pressure measurement value, suction temperature measurement value, and valve opening are all read by the controller, and the air side temperature measurement value is obtained by the outlet air temperature probe or the suction air temperature probe.

3. The low-superheat control carbon dioxide low-cycle-rate system according to claim 1, characterized in that, The smooth superheat is obtained by: performing low-pass filtering on the branch outlet superheat obtained in each sampling period of each terminal heat exchange branch in an exponential weighted manner, and using the filtered result as the smooth superheat of the terminal heat exchange branch, wherein the low-pass filtering is characterized by the filtering coefficient parameter; and updating the smooth superheat within a preset sliding time window.

4. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 3, characterized in that, Hysteresis logic is used to determine whether each terminal heat exchange branch is within the preset outlet superheat target window. Specifically, when the smooth superheat is continuously within the outlet superheat target window and the superheat fluctuation is less than or equal to the preset entry stability threshold for a duration that reaches the entry residence time, the window status quantity of the corresponding terminal heat exchange branch is set to indicate that it is within the outlet superheat target window; when the smooth superheat continuously exceeds the upper release threshold or is lower than the lower release threshold for a duration that reaches the release residence time, the window status quantity of the corresponding terminal heat exchange branch is set to indicate that it is not within the outlet superheat target window.

5. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 1, characterized in that, The method to obtain the reducible valve margin is as follows: For the end heat exchange branch where the window status indicator is within the outlet superheat target window, when the valve controllability margin is greater than or equal to the test margin threshold and the superheat fluctuation is less than or equal to the test fluctuation threshold, the valve opening of the end heat exchange branch where the window status indicator is within the outlet superheat target window is gradually reduced according to the preset valve opening step size, and the preset dwell time is maintained after each reduction. If the preset safety conditions are met during the residence period, the reduction amount is accumulated and the next reduction is continued; otherwise, the step-by-step reduction is terminated, and the cumulative valve opening reduction amount before termination is determined as the reducible valve margin of the terminal heat exchange branch. The preset safety condition is: when the superheat at the branch outlet does not exceed the value obtained by subtracting the preset superheat upper limit safety margin from the upper limit of the outlet superheat target window, and the valve opening is not less than the value obtained by adding the preset minimum stable opening safety interval, it is determined that the preset safety condition is met. If the superheat at the branch outlet exceeds the value obtained by subtracting the superheat upper limit safety margin from the target window for superheat, or if the valve opening is less than the value obtained by adding the minimum stable valve opening to the minimum stable opening safety interval, it is determined that the preset safety conditions are not met.

6. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 5, characterized in that, The method for determining the branch type based on the reducible valve margin, superheat fluctuation and valve controllability margin is as follows: compare the reducible valve margin, superheat fluctuation and valve controllability margin of a certain terminal heat exchange branch with its corresponding preset threshold. If the valve margin that can be reduced in a certain terminal heat exchange branch is greater than or equal to the redundancy significant threshold, and the superheat fluctuation is less than or equal to the redundancy stability threshold, and the valve controllability margin is greater than or equal to the redundancy margin threshold, then the branch type of the terminal heat exchange branch is determined to be over-supply redundancy type; if the valve controllability margin of a certain terminal heat exchange branch is less than or equal to the limited margin threshold or the superheat fluctuation is greater than or equal to the limited fluctuation threshold, then the branch type of the terminal heat exchange branch is determined to be execution-limited type. The remaining window status indicators are within the outlet superheat target window and the terminal heat exchange branches that are not identified as over-supply redundant branches or execution restricted branches are identified as under-supply sensitive branches. The terminal heat exchange branches with the branch type of oversupply redundancy and whose window status indicators are within the outlet superheat target window are formed into a redundant supply set, and the terminal heat exchange branches with the branch type of undersupply sensitive or execution restricted and whose window status indicators are within the outlet superheat target window are formed into a protection set.

7. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 6, characterized in that, The bottleneck margin is determined as follows: a protection margin is constructed for each end heat exchange branch in the protection set. The protection margin is the smaller value of the superheat margin term and the valve redundancy mapping term, wherein the superheat margin term is the difference between the upper limit of the outlet superheat target window and the smoothed superheat of the end heat exchange branch; the valve redundancy mapping term is a linear function of the valve controllability margin of the end heat exchange branch; and the minimum value of each protection margin in the protection set is taken as the bottleneck margin. It represents the maximum allowable pressure reduction at the pump operating frequency without causing instability in any end heat exchange branch of the protection set.

8. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 1, characterized in that, The method for calculating the downward pressure of pump operating frequency and the corresponding target pump frequency is as follows: the total amount of extractable redundancy is obtained by summing the reducible valve margins of each terminal heat exchange branch in the redundant supply set, and candidate pump operating frequency downward pressure is constructed in combination with the bottleneck margin; the candidate pump operating frequency downward pressure is used as the target reference for pump operating frequency downward pressure, and a feasibility check is performed on the candidate pump operating frequency downward pressure. Under the premise that the feasibility check is passed, the actual pump operating frequency downward pressure is determined by combining the pump minimum stable frequency and the pump frequency ramp-up upper limit, and the target pump frequency is obtained by subtracting the pump operating frequency downward pressure from the current pump operating frequency.

9. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 8, characterized in that, The specific steps for feasibility verification are as follows: The pump operating frequency is gradually reduced according to a preset pump frequency step size, and a preset steady-state dwell time is maintained after each reduction. During the steady-state dwell time, the smooth superheat, superheat fluctuation, and valve controllability margin of each terminal heat exchange branch in the protection set are monitored. When the smooth superheat of all terminal heat exchange branches in the protection set does not exceed the value obtained by subtracting the superheat upper limit safety margin from the upper limit of the outlet superheat target window, the superheat fluctuation does not exceed the preset fluctuation limit, and the valve controllability margin is not lower than the preset safety margin threshold, the pump operating frequency reduction for that stage is deemed feasible, and the next stage reduction continues. When any terminal heat exchange branch in the protection set fails to meet any of the above criteria, the current stage reduction is deemed infeasible, and the gradual reduction stops. The pump operating frequency reduction amplitude of the previous feasible stage is used as the actual reduction amplitude, and the corresponding target pump frequency is obtained accordingly.

10. A low-superheat-controlled carbon dioxide low-cycle-rate system according to claim 1, characterized in that, It also includes an execution constraint steady-state determination module, used to perform coordinated steady-state determination after executing the execution command corresponding to the target pump frequency and valve bias. The coordinated steady-state determination includes: monitoring the smooth superheat and superheat fluctuation changes of each terminal heat exchange branch in the protection set within a preset coordinated steady-state determination time window; when the smooth superheat of each terminal heat exchange branch in the protection set within the coordinated steady-state determination time window remains within the value obtained by subtracting the superheat upper limit safety margin from the upper limit of the outlet superheat target window and the superheat fluctuation does not exceed the preset stability threshold, the system is determined to be in a coordinated steady state and maintains the current target pump frequency and valve bias; when the above conditions are not met, the system is determined to have not reached a coordinated steady state. The bias scaling factor is reduced by a preset attenuation factor, and the pump frequency command is maintained or slightly reduced until the preset steady-state criterion is met again. When the bias scaling factor is reduced to the preset minimum execution factor and the preset steady-state criterion is still not met, the pump frequency command is reduced and the steady-state determination is re-entered. When the cooperative steady state is determined, the low cycle rate holding state is entered. While maintaining the target pump frequency and valve bias, the return liquid redundancy and two-phase effective utilization coefficient of the redundant supply set are monitored. When the total redundancy of the redundant supply set decreases or the end heat exchange branch in any protection set becomes execution-restricted, the low cycle rate holding state is exited and a holding exit dwell time is set to suppress frequent exits caused by short-term disturbances.

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