A variable frequency cold dryer cooperative control method based on fuzzy PID and hot gas bypass

Abstract

This invention discloses a collaborative control method for a variable frequency refrigerated dryer based on fuzzy PID and hot gas bypass, belonging to the field of refrigerated dryer control technology. This method is applied to a refrigeration system equipped with a DC inverter compressor, a hot gas bypass valve, an evaporation pressure sensor, and a variable frequency controller. Using real-time collected evaporation pressure as the control basis, the compressor operating frequency is preferentially adjusted through a fuzzy PID algorithm to achieve dynamic matching between cooling capacity and gas load. When the compressor operates at its lowest frequency but there is still excess cooling, the hot gas bypass valve is activated to supplement the heat load, forming a dual closed-loop collaborative regulation. By observing the evaporation pressure change trend after the hot gas bypass valve is closed, the method accurately distinguishes between false and real loads, correcting the control sequence to first close the hot gas bypass valve, then identify the load characteristics, and finally execute the compressor frequency increase. This achieves rapid capture and accurate response to the arrival of real gas load, improving equipment operational reliability and control accuracy.

Description

Technical Field

[0001] This invention relates to the field of freeze dryer control technology, specifically to a variable frequency freeze dryer coordinated control method based on fuzzy PID and hot gas bypass. Background Technology

[0002] Compressed air is a widely used power source in the industrial field. Refrigerated dryers are key equipment for dehydrating and drying compressed air. Their operational stability, energy efficiency, and drying effect directly affect the quality of compressed air and the operating cost of the air-using system.

[0003] Traditional fixed-frequency refrigerated dryers have compressors with a fixed speed, making it impossible to dynamically adjust the cooling capacity according to changes in compressed air consumption. The accompanying hot air bypass structure is often a manual mechanical valve with a fixed opening, unable to adjust the bypass flow in real time according to operating conditions. In scenarios with large load fluctuations, especially under extreme conditions of extremely low air consumption, this structure cannot achieve dynamic matching between cooling capacity and air load, easily leading to excess cooling capacity. This results in a significant decrease in overall machine efficiency, evaporator freezing and blockage, and large fluctuations in the moisture content of the compressed air, failing to consistently meet the drying requirements.

[0004] Existing variable frequency refrigerated dryers can adapt to different gas loads by adjusting the compressor speed, achieving dynamic adjustment of cooling capacity under normal operating conditions. However, under extremely low or even zero load conditions, even after the compressor speed drops to its minimum limit, the cooling capacity may still exceed the evaporation load, failing to completely eliminate the risk of evaporator ice blockage. More critically, existing solutions cannot distinguish the nature of the heat load on the evaporator side, nor can they differentiate between the artificially created spurious load from the hot gas bypass valve and the actual gas load from the user end. This often leads to problems such as compressor frequency erroneous increases caused by spurious loads, frequent switching of adjustment modes, and mismatch between cooling capacity and actual load. Furthermore, existing solutions often employ a control sequence of first increasing the compressor operating frequency and then closing the hot gas bypass valve, which can easily cause excessive cooling capacity, abnormal fluctuations in evaporation pressure, and even exacerbate the risk of ice blockage due to compressor frequency increases when the bypass valve is not closed. Existing solutions fail to effectively coordinate compressor frequency regulation and hot gas bypass control, making it impossible to simultaneously ensure energy-saving operation, stable drying effect, and equipment safety protection under all operating conditions, and thus difficult to adapt to the complex and ever-changing gas demand in industrial settings.

[0005] To address this, a collaborative control method for a variable frequency refrigerated dryer based on fuzzy PID and hot gas bypass is proposed. Summary of the Invention

[0006] The present invention aims to solve the problems mentioned in the background art by providing a variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass.

[0007] The specific technical solution is as follows: A collaborative control method for a variable frequency refrigerated dryer based on fuzzy PID and hot gas bypass is applied to the refrigeration system of the variable frequency refrigerated dryer. The refrigeration system includes a DC inverter compressor, a condenser, a throttling device, an evaporator, a hot gas bypass valve, an evaporation pressure sensor, and a variable frequency controller. The discharge port of the DC inverter compressor is connected to the inlet of the condenser; the outlet of the condenser is connected to the inlet of the throttling device; the outlet of the throttling device is connected to the inlet of the evaporator; the outlet of the evaporator is connected to the suction port of the DC inverter compressor; the inlet of the hot gas bypass valve is connected to the discharge port of the DC inverter compressor; the outlet of the hot gas bypass valve is connected to the inlet side of the evaporator; the evaporation pressure sensor is installed on the outlet pipe of the evaporator; and the evaporation pressure sensor, the DC inverter compressor, and the hot gas bypass valve are all electrically connected to the variable frequency controller. The collaborative control method includes the following steps: Step 1: The frequency converter completes system initialization, presets the target evaporation pressure, the compressor's minimum operating frequency, the hot gas bypass opening threshold, the hot gas bypass closing threshold, and the frequency stability determination time. Step 2: The evaporation pressure sensor collects the measured value of the evaporation pressure at the evaporator outlet in real time and transmits the measured value of the evaporation pressure to the frequency converter controller; Step 3: The frequency converter calculates the pressure deviation between the measured evaporation pressure and the target evaporation pressure, as well as the rate of change of the pressure deviation. Using the pressure deviation and the rate of change of the deviation as inputs, the target operating frequency of the DC inverter compressor is calculated using a fuzzy PID control algorithm. The frequency converter outputs a control signal to the DC inverter compressor to drive it to operate at the target operating frequency, thus performing the first closed-loop regulation of the evaporation pressure. Step 4: The frequency converter monitors the actual operating frequency of the DC inverter compressor in real time. When the actual operating frequency of the DC inverter compressor drops to the compressor's minimum operating frequency and the continuous operating time reaches the frequency stabilization judgment time, if the measured value of the evaporation pressure is still lower than the hot gas bypass opening threshold, it is determined that there is no effective real gas load or the real load on the evaporator side is extremely low, and the cooling capacity is seriously excessive. The frequency converter outputs a control signal to start the hot gas bypass valve, and the high temperature and high pressure refrigerant gas discharged from the DC inverter compressor is bypassed to the inlet side of the evaporator through the hot gas bypass valve, artificially supplementing the evaporator with a controllable false heat load, and performing a second closed-loop regulation of the evaporation pressure. Step 5: When the hot gas bypass valve is in the regulating operation state, the frequency converter synchronously maintains the first closed-loop regulation of the DC inverter compressor using the fuzzy PID control algorithm, locking the target operating frequency output by the fuzzy PID control algorithm to the compressor's minimum operating frequency, and controlling the evaporation pressure only through the regulation of the hot gas bypass valve; when the measured evaporation pressure rises above the hot gas bypass closing threshold, the frequency converter controls the hot gas bypass valve to gradually close, synchronously monitoring the evaporation pressure change trend during and after the hot gas bypass valve closure process, thus distinguishing between false loads and true loads; if the hot gas bypass valve is completely closed, the evaporation pressure... If the measured value continues to rise, it is determined that the actual gas load has arrived. The frequency converter immediately releases the compressor's operating frequency lock and resumes the normal closed-loop regulation of the DC inverter compressor by the fuzzy PID control algorithm. It drives the compressor to increase its frequency to match the actual gas load, completing the coordinated closed-loop control of the DC inverter compressor's frequency regulation and the hot gas bypass valve's load regulation. If the measured value of the evaporating pressure turns to a continuous downward trend after the hot gas bypass valve is completely closed, it is determined that the false load supplemented by the hot gas bypass valve has disappeared and there is no effective actual gas load. The frequency converter restarts the hot gas bypass valve and maintains the coordinated regulation mode of the compressor's minimum operating frequency.

[0008] Furthermore, the fuzzy PID control algorithm in step three includes the following specific steps: First, the input pressure deviation and deviation change rate are fuzzified, the fuzzy universe of discourse for pressure deviation and deviation change rate is set, and the corresponding membership function is selected. Fuzzy inference is performed based on the preset fuzzy control rule table to obtain the fuzzy correction amount of the PID parameters; The fuzzy correction values ​​of the PID parameters are defuzzified to obtain the real-time correction values ​​of the PID parameters, thus completing the online self-tuning of the proportional coefficient, integral coefficient, and derivative coefficient. Based on the tuned PID parameters, the target operating frequency of the DC inverter compressor is calculated.

[0009] Furthermore, the hot gas bypass valve is a hot gas bypass solenoid valve. In step four, the frequency converter uses an ON-OFF hysteresis control method for the hot gas bypass solenoid valve. When the measured value of the evaporation pressure is lower than the hot gas bypass opening threshold, the frequency converter outputs a signal to open the hot gas bypass solenoid valve. When the measured value of the evaporation pressure is higher than the hot gas bypass closing threshold, the frequency converter outputs a signal to close the hot gas bypass solenoid valve. The frequent start and stop of the hot gas bypass solenoid valve is avoided through hysteresis range control.

[0010] Furthermore, the hot gas bypass valve is a hot gas bypass solenoid valve. In step four, the frequency converter uses a duty cycle adjustment control method for the hot gas bypass solenoid valve. The pressure deviation between the measured evaporation pressure and the target evaporation pressure is used as the input. The duty cycle of the drive signal of the hot gas bypass solenoid valve is calculated by the PID control algorithm. The frequency converter outputs a pulse drive signal according to the corresponding duty cycle to control the on / off time ratio of the hot gas bypass solenoid valve, thereby realizing continuous adjustment of the bypass refrigerant flow.

[0011] Furthermore, the hot gas bypass valve is a hot gas bypass electronic expansion valve. In step four, the frequency converter uses a stepless opening adjustment control method for the hot gas bypass electronic expansion valve. The pressure deviation between the measured evaporation pressure and the target evaporation pressure, and the rate of change of the pressure deviation, are used as inputs. The target opening of the hot gas bypass electronic expansion valve is calculated by a fuzzy PID control algorithm. The frequency converter outputs a drive signal corresponding to the opening to control the valve opening of the hot gas bypass electronic expansion valve, thereby realizing stepless continuous adjustment of the bypass refrigerant flow.

[0012] Furthermore, the hot gas bypass opening threshold is lower than the target evaporation pressure, the hot gas bypass closing threshold is higher than the hot gas bypass opening threshold but lower than the target evaporation pressure, and the frequency stability determination time is set to 3 to 30 seconds. Through the hysteresis threshold setting and stability time determination, frequent start-stop and frequent mode switching of the hot gas bypass valve are avoided.

[0013] Furthermore, in step two, after the frequency converter receives the measured evaporation pressure value transmitted by the evaporation pressure sensor, it first performs moving average filtering and outlier removal processing on the measured evaporation pressure value, removing abnormal data that exceed the preset reasonable range, and then uses the processed measured evaporation pressure value for subsequent closed-loop control calculations.

[0014] Furthermore, in step three, after the frequency converter calculates the target operating frequency of the DC inverter compressor, it performs upper and lower limit processing and change rate limit processing on the target operating frequency. The lower limit of the upper and lower limit processing is the lowest operating frequency of the compressor, and the upper limit is the rated highest operating frequency of the compressor. The change rate limit processing limits the maximum adjustment amplitude of the compressor frequency per unit time to avoid sudden changes in the compressor operating frequency.

[0015] Furthermore, in step five, the spurious load is the controllable heat load brought by the high-temperature refrigerant gas supplied to the evaporator side when the hot gas bypass valve is opened. Its load size and trend can be precisely controlled by the opening degree of the bypass valve. It is a simulated load artificially created and has no corresponding compressed air demand. The real load is the random heat load brought by the high-temperature compressed air entering the evaporator after the gas demand end is opened. Its load size and arrival time cannot be predicted in advance and correspond to the actual compressed air drying treatment demand.

[0016] Furthermore, the frequency converter has a preset anti-icing protection threshold. When the measured value of the evaporation pressure is lower than the hot gas bypass opening threshold, the frequency converter will forcibly open the hot gas bypass valve to the maximum flow state and at the same time increase the minimum operating frequency of the compressor to quickly increase the evaporation pressure and avoid freezing and blockage of the evaporator.

[0017] The present invention has the following beneficial effects: 1. Significant Energy Saving and Consumption Reduction Advantages: This control method prioritizes adapting to changes in gas load through compressor frequency conversion adjustment. Under most conventional operating conditions, it achieves precise matching between cooling capacity and evaporation load without opening the hot gas bypass, avoiding the continuous energy loss caused by traditional fixed bypass structures and significantly improving the unit's overall operating energy efficiency. Under low-load conditions, the compressor can maintain the lowest operating frequency. Combined with the precise adjustment of the hot gas bypass valve, it avoids the additional energy consumption and equipment wear caused by frequent compressor start-stop, further reducing the unit's operating energy consumption. Compared with traditional fixed-frequency refrigerated dryers, the energy consumption level under all operating conditions is significantly optimized.

[0018] 2. Significantly improved operational stability and air supply quality: This control method, through the coordinated operation of two closed-loop regulation channels, can maintain the evaporation pressure within a stable range across the entire operating condition, greatly reducing the amplitude of operating condition fluctuations and avoiding large fluctuations in evaporation temperature. This ensures that the freeze-drying effect of compressed air remains stable, and the moisture content does not fluctuate significantly. It can reliably meet the drying requirements under different air usage conditions, thereby improving the air supply quality of compressed air.

[0019] 3. Significantly Extended Equipment Reliability and Service Life: This control method fundamentally solves the evaporator ice blockage problem caused by excess cooling capacity under extreme low-load conditions, avoiding the risks of equipment failure, downtime, and even component damage due to ice blockage, thus greatly improving the unit's operational reliability. Simultaneously, this control method avoids frequent compressor start-ups and shutdowns, reduces unnecessary frequent valve operations, lowers the mechanical and electrical shocks to critical components, effectively extending the overall service life of the unit and reducing maintenance frequency and costs.

[0020] 4. A qualitative breakthrough in control precision and operating condition response speed: This invention introduces a new logic for distinguishing between spurious and real loads. By analyzing the evaporation pressure change trend after the hot gas bypass valve is closed, it accurately differentiates between artificially added simulated loads and real loads from actual gas consumption. This completely solves the industry pain points of traditional solutions, such as compressor frequency erroneous increases, frequent mode switching, and mismatch between cooling capacity and real load caused by spurious loads. This logic can capture and identify the real gas load the instant it arrives, achieving zero-delay compressor frequency increase response. It ensures that the evaporation pressure does not fluctuate significantly during sudden load changes, and the compressed air drying effect remains stable. At the same time, it avoids energy loss caused by ineffective compressor frequency increases when there is no real load, further optimizing the energy-saving effect under all operating conditions.

[0021] 5. Comprehensive optimization of mode switching smoothness and control logic rationality: This invention corrects the traditional control timing and adopts a control logic that first closes the hot gas bypass valve, then identifies the load nature, and finally executes the compressor frequency increase. This avoids the problems of excessive cooling capacity and abnormal fluctuations in evaporation pressure caused by compressor frequency increase when the bypass valve is not closed. It realizes seamless switching between the coordinated adjustment mode and the conventional variable frequency adjustment mode, eliminates control conflicts during the mode switching process, and further improves the stability of system operation.

[0022] 6. Strong adaptability to various scenarios and wide applicability: This control method provides a variety of hot gas bypass control modes, which can be adapted to different application scenarios with different adjustment accuracy requirements and different cost budgets. It does not require major changes to the main hardware structure of the original refrigeration system. Only the corresponding controller and detection element are needed to achieve the goal. The transformation cost is low and the adaptability is strong. It can be used for the production support of new units as well as for the upgrade and transformation of existing old units, and has extremely strong applicability to be promoted.

[0023] 7. Enhanced Anti-interference Capability and Operational Safety: This control method preprocesses the collected pressure data, effectively eliminating interference signals and abnormal data in the field, ensuring the accuracy of the control logic input data, and improving the system's anti-interference capability in complex industrial environments. Simultaneously, the system has preset corresponding protection logic, which can trigger forced protection actions in extreme conditions where the evaporation pressure drops abnormally and rapidly, fundamentally preventing evaporator ice blockage. Even when abnormalities occur in the conventional control loop, it can provide effective safety protection for the equipment, further enhancing the safety and stability of the unit's operation. Attached Figure Description

[0024] Figure 1 The flowchart illustrates the variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass provided in an embodiment of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0027] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] Example This embodiment provides a fuzzy PID-based collaborative control method for a variable frequency refrigerated dryer, applied to the refrigeration system of a variable frequency refrigerated dryer. The refrigeration system includes a DC inverter compressor, a condenser, a throttling device, an evaporator, a hot gas bypass valve, an evaporation pressure sensor, and a variable frequency controller. The discharge port of the DC inverter compressor is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the throttling device, the outlet of the throttling device is connected to the inlet of the evaporator, and the outlet of the evaporator is connected to the suction port of the DC inverter compressor. The inlet of the hot gas bypass valve is connected to the discharge port of the DC inverter compressor, and the outlet of the hot gas bypass valve is connected to the inlet side of the evaporator. The evaporation pressure sensor is installed on the outlet pipe of the evaporator. The evaporation pressure sensor, the DC inverter compressor, and the hot gas bypass valve are all electrically connected to the variable frequency controller. Figure 1 As shown, the cooperative control method includes the following steps: Step 1: The frequency converter completes system initialization, presets the target evaporation pressure, the compressor's minimum operating frequency, the hot gas bypass opening threshold, the hot gas bypass closing threshold, and the frequency stability determination time. Step 2: The evaporation pressure sensor collects the measured value of the evaporation pressure at the evaporator outlet in real time and transmits the measured value of the evaporation pressure to the frequency converter controller; Step 3: The frequency converter calculates the pressure deviation between the measured evaporation pressure and the target evaporation pressure, as well as the rate of change of the pressure deviation. Using the pressure deviation and the rate of change of the deviation as inputs, the target operating frequency of the DC inverter compressor is calculated using a fuzzy PID control algorithm. The frequency converter outputs a control signal to the DC inverter compressor to drive it to operate at the target operating frequency, thus performing the first closed-loop regulation of the evaporation pressure. Step 4: The frequency converter monitors the actual operating frequency of the DC inverter compressor in real time. When the actual operating frequency of the DC inverter compressor drops to the compressor's minimum operating frequency and the continuous operating time reaches the frequency stabilization judgment time, if the measured value of the evaporation pressure is still lower than the hot gas bypass opening threshold, it is determined that there is no effective real gas load or the real load on the evaporator side is extremely low, and the cooling capacity is seriously excessive. The frequency converter outputs a control signal to start the hot gas bypass valve, and the high temperature and high pressure refrigerant gas discharged from the DC inverter compressor is bypassed to the inlet side of the evaporator through the hot gas bypass valve, artificially supplementing the evaporator with a controllable false heat load, and performing a second closed-loop regulation of the evaporation pressure. Step 5: When the hot gas bypass valve is in the regulating operation state, the frequency converter synchronously maintains the first closed-loop regulation of the DC inverter compressor using the fuzzy PID control algorithm, locking the target operating frequency output by the fuzzy PID control algorithm to the compressor's minimum operating frequency, and controlling the evaporation pressure only through the regulation of the hot gas bypass valve; when the measured evaporation pressure rises above the hot gas bypass closing threshold, the frequency converter controls the hot gas bypass valve to gradually close, synchronously monitoring the evaporation pressure change trend during and after the hot gas bypass valve closure process, thus distinguishing between false loads and true loads; if the hot gas bypass valve is completely closed, the evaporation pressure... If the measured value continues to rise, it is determined that the actual gas load has arrived. The frequency converter immediately releases the compressor's operating frequency lock and resumes the normal closed-loop regulation of the DC inverter compressor by the fuzzy PID control algorithm. It drives the compressor to increase its frequency to match the actual gas load, completing the coordinated closed-loop control of the DC inverter compressor's frequency regulation and the hot gas bypass valve's load regulation. If the measured value of the evaporating pressure turns to a continuous downward trend after the hot gas bypass valve is completely closed, it is determined that the false load supplemented by the hot gas bypass valve has disappeared and there is no effective actual gas load. The frequency converter restarts the hot gas bypass valve and maintains the coordinated regulation mode of the compressor's minimum operating frequency.

[0030] The above-mentioned scheme, through a two-stage closed-loop regulation implemented in stages, can adapt to the system's operational needs under different loads. It prioritizes compressor speed regulation to cover most conventional operating conditions, reducing unnecessary refrigerant bypass operations and lowering system energy consumption. The orderly coordination and switching of the two-stage regulation stages can reduce the fluctuation range of evaporator pressure, resulting in more stable system operation. Under extreme conditions of low load or even no load, the evaporator can be prevented from freezing and clogging by supplementing the system's heat load, while ensuring continuous and stable compressor operation without frequent start-stop cycles, and maintaining stable compressed air processing efficiency. Through load characteristic identification logic, the control malfunction problem of traditional schemes is completely solved. The corrected control timing enables seamless switching between the two regulation modes, significantly improving control accuracy and response speed.

[0031] Specifically, in this embodiment, the fuzzy PID control algorithm in step three includes the following specific steps: First, the input pressure deviation and deviation change rate are fuzzified, the fuzzy universe of discourse for pressure deviation and deviation change rate is set, and the corresponding membership function is selected. Fuzzy inference is performed based on the preset fuzzy control rule table to obtain the fuzzy correction amount of the PID parameters; The fuzzy correction values ​​of the PID parameters are defuzzified to obtain the real-time correction values ​​of the PID parameters, thus completing the online self-tuning of the proportional coefficient, integral coefficient, and derivative coefficient. Based on the tuned PID parameters, the target operating frequency of the DC inverter compressor is calculated.

[0032] By adopting the above scheme, the online self-tuning of control parameters can adapt to the operating characteristics of the system under different working conditions, offset the control deviation caused by the nonlinearity and large hysteresis characteristics of the system itself, speed up the adjustment response, improve the adjustment accuracy, avoid the overshoot or oscillation problems that occur when the conventional fixed parameter control changes the working conditions, make the compressor speed regulation more stable, and have a stronger ability to adapt to load changes.

[0033] Specifically, in this embodiment, the hot gas bypass valve is a hot gas bypass solenoid valve. In step four, the frequency converter uses an ON-OFF hysteresis control method for the hot gas bypass solenoid valve. When the measured evaporation pressure is lower than the hot gas bypass opening threshold, the frequency converter outputs a signal to open the hot gas bypass solenoid valve; when the measured evaporation pressure is higher than the hot gas bypass closing threshold, the frequency converter outputs a signal to close the hot gas bypass solenoid valve. This hysteresis range control avoids frequent starting and stopping of the hot gas bypass solenoid valve. This solution, through hysteresis range control, avoids frequent starting and stopping of the valve near the pressure critical point, extending the valve's service life. The on / off bypass control can quickly replenish the system's heat load under low load conditions, quickly curbing the continuous decline in evaporation pressure. The control logic and hardware structure are simple, with high operational reliability, suitable for application scenarios with low adjustment accuracy requirements, reducing system modification costs and maintenance difficulty.

[0034] Specifically, in this embodiment, the hot gas bypass valve is a hot gas bypass solenoid valve. In step four, the frequency converter uses a duty cycle adjustment control method for the hot gas bypass solenoid valve. Using the pressure deviation between the measured evaporation pressure and the target evaporation pressure as input, the PID control algorithm calculates the duty cycle of the drive signal for the hot gas bypass solenoid valve. The frequency converter outputs a pulse drive signal according to the corresponding duty cycle, controlling the on / off duration ratio of the hot gas bypass solenoid valve to achieve continuous adjustment of the bypass refrigerant flow. This scheme achieves continuous adjustment of the bypass flow by adjusting the valve's on / off duration ratio. Compared to on / off control, it can further reduce the fluctuation range of the evaporation pressure, making the system operation more stable and improving the stability of the compressed air treatment effect. This control method does not require replacing the valve hardware, thus improving the adjustment accuracy under low-load conditions. The control logic is easy to implement, balancing modification costs and control effects.

[0035] Specifically, in this embodiment, the hot gas bypass valve is a hot gas bypass electronic expansion valve. In step four, the frequency converter uses a stepless opening adjustment control method for the hot gas bypass electronic expansion valve. The target opening of the hot gas bypass electronic expansion valve is calculated using a fuzzy PID control algorithm, with the pressure deviation between the measured evaporation pressure and the target evaporation pressure, and the rate of change of the pressure deviation, as inputs. The frequency converter outputs a drive signal corresponding to the opening, controlling the valve opening of the hot gas bypass electronic expansion valve to achieve stepless continuous adjustment of the bypass refrigerant flow. This solution, through stepless continuous adjustment of the valve opening, can achieve fine control of the bypass flow. Combined with the corresponding control algorithm, it can quickly respond to small changes in evaporation pressure, keeping the evaporation pressure within a stable range and reducing pressure fluctuations. Even under extremely low load conditions, it can accurately control the evaporation temperature, avoiding evaporator icing and ensuring stable compressed air drying. Simultaneously, it minimizes unnecessary refrigerant bypass, reducing system energy loss.

[0036] Specifically, in this embodiment, the hot gas bypass opening threshold is lower than the target evaporation pressure, and the hot gas bypass closing threshold is higher than the hot gas bypass opening threshold but lower than the target evaporation pressure. The frequency stabilization determination time is set to 3 to 30 seconds. Through hysteresis-based threshold setting and stabilization time determination, frequent start-stop and mode switching of the hot gas bypass valve are avoided. This solution, through a reasonable threshold range and stabilization time determination, can avoid frequent switching of the regulation mode when the system experiences small load fluctuations, reduce the frequency of valve and compressor operations, and extend the service life of the main components of the equipment. At the same time, it allows the system to switch more smoothly between the two regulation modes, without sudden changes in operating conditions, ensuring the continuity and stability of system operation.

[0037] Specifically, in this embodiment, in step two, after the frequency converter receives the measured evaporation pressure value transmitted by the evaporation pressure sensor, it first performs moving average filtering and outlier removal processing on the measured evaporation pressure value, removing abnormal data that exceeds a preset reasonable range. The processed measured evaporation pressure value is then used for subsequent closed-loop control calculations. This scheme, by preprocessing the collected pressure data, can eliminate the influence of interference signals and abnormal data in the field conditions on the control calculations, ensuring the accuracy of the pressure data input to the control loop, avoiding control malfunctions caused by data distortion, making the system adjustment more precise, the operation more stable, and improving the system's anti-interference capability in complex field environments.

[0038] Specifically, in this embodiment, in step three, after the frequency converter calculates the target operating frequency of the DC inverter compressor, it performs upper and lower limit processing and change rate limit processing on the target operating frequency. The lower limit of the upper and lower limit processing is the compressor's minimum operating frequency, and the upper limit is the compressor's rated maximum operating frequency. The change rate limit processing limits the maximum adjustment amplitude of the compressor frequency per unit time, avoiding sudden changes in the compressor's operating frequency. This scheme, by constraining the upper and lower limits and adjustment rate of the compressor's operating frequency, can avoid large-scale frequency changes in the compressor, making the compressor speed adjustment more stable, reducing mechanical and electrical shocks during compressor operation, and extending the compressor's service life. It also avoids large fluctuations in system operating conditions caused by frequency mutations, making the refrigeration system operate more smoothly.

[0039] Specifically, in this embodiment, in step five, the spurious load is the controllable heat load brought by the high-temperature refrigerant gas supplied to the evaporator side when the hot gas bypass valve is opened. Its load size and trend can be precisely controlled by the opening degree of the bypass valve. It is a simulated load created artificially and has no corresponding compressed air demand. The real load is the random heat load brought by the high-temperature compressed air entering the evaporator after the gas demand end is opened. Its load size and arrival time cannot be predicted in advance and correspond to the actual compressed air drying treatment demand.

[0040] Specifically, in this embodiment, the frequency converter has a preset anti-icing protection threshold, which is lower than the hot gas bypass opening threshold. When the measured evaporation pressure is lower than the anti-icing protection threshold, the frequency converter forcibly opens the hot gas bypass valve to the maximum flow state, while simultaneously increasing the compressor's minimum operating frequency to quickly increase the evaporation pressure and prevent the evaporator from freezing and becoming blocked. This solution, through the preset protection threshold, can trigger a forced protection action in extreme conditions where the evaporation pressure drops abnormally and rapidly, quickly increasing the evaporation pressure and fundamentally preventing the evaporator from freezing and becoming blocked, thus improving the safety and reliability of the system operation. Even when abnormalities occur in the normal control circuit, it can effectively protect the main components of the system, preventing irreversible damage to the equipment.

[0041] Working principle The control method utilizes a variable frequency refrigeration dryer system, comprising a DC inverter compressor, condenser, throttling device, evaporator, hot gas bypass valve, evaporator pressure sensor, and inverter controller. The discharge port of the DC inverter compressor is connected to the condenser inlet, the condenser outlet is connected to the throttling device inlet, the throttling device outlet is connected to the evaporator inlet, and the evaporator outlet is connected to the DC inverter compressor suction port, forming a complete refrigeration cycle. The hot gas bypass valve's inlet is connected to the DC inverter compressor's discharge port, and its outlet is connected to the evaporator inlet, allowing the high-temperature, high-pressure refrigerant gas discharged from the compressor to be directly bypassed into the evaporator, supplementing the evaporator's heat load. The evaporator pressure sensor is installed on the evaporator's outlet pipe, enabling real-time acquisition of evaporator outlet pressure data. The evaporator pressure sensor, DC inverter compressor, and hot gas bypass valve are all electrically connected to the inverter controller, which collects data and outputs control commands.

[0042] After system startup, the frequency converter first completes initialization, presets the corresponding operating parameters, and the evaporator pressure sensor collects real-time measured evaporator pressure data and transmits it to the frequency converter. Based on the collected evaporator pressure, the frequency converter prioritizes adjusting the operating frequency of the DC inverter compressor to achieve dynamic matching between cooling capacity and gas load, stabilizing the evaporator pressure within the preset target range. The frequency converter calculates the deviation between the measured evaporator pressure value and the target value, as well as the rate of change of the deviation. Using these two parameters as inputs, the corresponding control algorithm adjusts the compressor's operating frequency in real-time, forming a closed-loop regulation of the evaporator pressure to adapt to the changing needs of most conventional gas loads.

[0043] When the gas load continues to decrease, the compressor's operating frequency has dropped to the preset minimum value, and after a period of stable operation, the evaporation pressure continues to decrease. This indicates that there is no effective real gas load on the evaporator side or the real load is extremely low. The compressor's cooling capacity is still greater than the gas load on the evaporator side. The frequency converter then activates the hot gas bypass valve to supplement the evaporator's heat load by bypassing high-temperature refrigerant gas, artificially creating a controllable false heat load. This forms another closed-loop regulation of the evaporation pressure, curbing the continuous decrease in evaporation pressure, preventing the refrigerant temperature in the evaporator from becoming too low and causing freezing blockage, while ensuring that the compressor continues to run without stopping.

[0044] Load identification principle: During operation in the coordinated regulation mode, the increase in evaporation pressure caused by the opening of the hot gas bypass valve originates from a spurious load. This load can only maintain stable evaporation pressure when the bypass valve is open. Once the bypass valve is closed, if there is no real gas demand, there is no continuous heat load input on the evaporator side, and the evaporation pressure will inevitably continue to decrease. On the other hand, the increase in evaporation pressure caused by real gas demand originates from the real load brought by high-temperature compressed air. This load is independent of the on / off state of the hot gas bypass valve. Even if the bypass valve is completely closed, as long as compressed air continues to flow, the heat load on the evaporator side will continue to exist, and the evaporation pressure will maintain a continuous upward trend. Based on this principle, this invention uses the trend of evaporation pressure change after the hot gas bypass valve is closed as the sole criterion for judgment, achieving accurate identification between spurious and real loads.

[0045] During the operation of the hot gas bypass valve, the frequency converter locks the compressor operating frequency at the minimum limit, regulating the evaporation pressure only through the bypass valve. When the evaporation pressure rises back to the closing threshold, the bypass valve is first controlled to gradually close, while simultaneously monitoring the evaporation pressure change trend after the valve closes: if the evaporation pressure continues to rise after the valve closes, it indicates that the actual gas load has arrived, and the compressor frequency lock is immediately released, driving the compressor to increase its frequency to match the actual load, exiting the coordinated regulation mode; if the evaporation pressure turns to decrease after the valve closes, it indicates that there is no effective actual load, and the pressure rise is only due to a false load, and the bypass valve is immediately reopened to maintain the coordinated regulation mode and prevent the compressor from erroneously increasing its frequency.

[0046] Different control methods can be adopted for hot gas bypass valves to meet different usage requirements. When using a solenoid valve, the bypass flow rate can be adjusted by switching on and off within the hysteresis range, or continuously adjusted by adjusting the proportion of on / off time. When using an electronic expansion valve, the bypass flow rate can be continuously adjusted steplessly by adjusting the valve opening. Different control methods can meet different adjustment accuracy requirements and can all effectively coordinate with the variable frequency control of the compressor.

[0047] Meanwhile, the frequency converter preprocesses the collected pressure data, eliminating abnormal data and interference signals to ensure the accuracy of the control input data; it limits the operating frequency of the compressor to avoid system operating condition fluctuations caused by large frequency changes; and it also presets corresponding protection logic, which can trigger a forced protection action when the evaporation pressure drops abnormally and rapidly to quickly increase the evaporation pressure and prevent the evaporator from ice blockage.

[0048] How to use Before the variable frequency refrigerated dryer is put into use, parameters are preset in the variable frequency controller according to the on-site gas demand and refrigerant characteristics. These parameters include the target evaporation pressure, the minimum operating frequency of the compressor, the opening and closing thresholds of the hot gas bypass, and the frequency stability judgment time. Once the parameters are set, the unit can be started.

[0049] After the unit starts up, the frequency converter automatically completes system initialization. The evaporator pressure sensor begins to collect evaporator outlet pressure data in real time and continuously transmits it to the frequency converter. The system automatically enters fully automatic operation mode without real-time manual intervention. During daily operation, the frequency converter automatically executes corresponding control logic based on the real-time collected evaporator pressure data. Under normal gas load conditions, the system prioritizes adjusting the compressor's operating frequency to adapt to load changes and maintain stable evaporator pressure. When gas consumption decreases significantly and enters low-load operation, the system automatically activates the hot gas bypass valve, working in conjunction with the compressor's frequency converter adjustment to ensure stable system operation. When the gas load recovers, the system accurately identifies the actual load through load identification logic, automatically closes the hot gas bypass valve, and resumes the normal frequency converter adjustment mode. The entire operation mode switching is completed automatically without manual operation.

[0050] To cater to different on-site operating conditions and adjustment accuracy requirements, a suitable hot gas bypass valve control method can be selected without modifying the main hardware structure of the refrigeration system. Adaptation can be achieved simply by adjusting the corresponding control logic within the frequency converter. During routine maintenance, frequent manual adjustments to the hot gas bypass valve opening are unnecessary; only regular equipment inspections are required. When long-term changes occur in on-site gas demand, simply adjusting the corresponding preset parameters within the frequency converter adapts to the new operating conditions, resulting in convenient operation and low maintenance costs.

[0051] When the system encounters extreme abnormal operating conditions and the evaporation pressure drops rapidly to the protection range, the system will automatically trigger the corresponding protection action, quickly adjust the bypass valve status and compressor operating parameters, curb the continuous drop in evaporation pressure, avoid equipment failure, and ensure the safe operation of the unit.

[0052] Implementation Example I. Technical Solution This implementation example is applied to a process with an air volume of 10 Nm. 3 The air-cooled variable frequency refrigerated dryer has a refrigeration system that includes a DC inverter compressor, an air-cooled condenser, a fixed frequency condenser fan, a throttling capillary tube, a plate evaporator, a hot gas bypass electronic expansion valve, an evaporation pressure sensor, and a variable frequency controller.

[0053] The discharge port of the DC inverter compressor is connected to the refrigerant inlet of the air-cooled condenser through a copper pipe. The refrigerant outlet of the air-cooled condenser is connected to the inlet of the throttling capillary tube through a copper pipe. The outlet of the throttling capillary tube is connected to the refrigerant side inlet of the plate evaporator through a copper pipe. The refrigerant side outlet of the plate evaporator is connected to the suction port of the DC inverter compressor through a copper pipe, forming a complete refrigeration cycle loop.

[0054] The refrigerant inlet of the hot gas bypass electronic expansion valve is connected to the discharge port of the DC inverter compressor via a copper pipe, and the refrigerant outlet of the hot gas bypass electronic expansion valve is connected to the refrigerant side inlet pipe of the plate evaporator via a copper pipe.

[0055] The evaporation pressure sensor is installed on the refrigerant side outlet pipe of the plate evaporator, with the detection position close to the suction port of the DC inverter compressor.

[0056] The signal output terminal of the evaporation pressure sensor is connected to the analog input port of the frequency converter, the drive control terminal of the DC frequency converter compressor is connected to the frequency converter drive output port of the frequency converter, the drive control terminal of the hot gas bypass electronic expansion valve is connected to the stepper motor drive output port of the frequency converter, and the control terminal of the fixed frequency condenser fan is connected to the switch output port of the frequency converter.

[0057] During the system initialization phase, the frequency converter completes parameter presets, including target evaporation pressure, minimum compressor operating frequency, maximum compressor rated operating frequency, hot gas bypass opening threshold, hot gas bypass closing threshold, anti-icing protection threshold, frequency stability judgment duration, pressure sampling cycle, initial values ​​of PID parameters, fuzzy control rule table, moving average filter window length, and frequency change rate limit amplitude.

[0058] The collaborative control method in this implementation example is fully implemented according to the following steps: 1. Upon system power-on, the frequency converter completes hardware port initialization, parameter loading, and communication self-test. The fixed-frequency condenser fan starts running synchronously, and the frequency converter drives the DC inverter compressor to start running at the starting frequency, entering normal operation.

[0059] 2. The evaporation pressure sensor collects the measured evaporation pressure at the refrigerant side outlet of the plate evaporator in real time according to a preset pressure sampling period, and transmits the analog signal to the frequency converter. After receiving the measured evaporation pressure value, the frequency converter filters the continuously collected pressure data through a moving average filter window, removes abnormal data that exceeds the preset reasonable range, and uses the processed measured evaporation pressure value for subsequent control calculations.

[0060] 3. The frequency converter calculates the pressure deviation between the processed measured evaporation pressure and the target evaporation pressure, and simultaneously calculates the change in pressure deviation between two adjacent sampling periods to obtain the deviation change rate. The frequency converter uses the pressure deviation and deviation change rate as inputs to perform fuzzy PID control calculations.

[0061] The execution process of fuzzy PID control is as follows: First, the pressure deviation and the rate of change of deviation are fuzzified, mapping the two input quantities to their corresponding fuzzy domains. The corresponding membership functions are then selected to complete the fuzzy transformation of the input quantities. Next, fuzzy inference is performed according to a preset fuzzy control rule table to obtain the fuzzy correction quantities corresponding to the proportional coefficient, integral coefficient, and derivative coefficient. The fuzzy correction quantities are then defuzzified to obtain the real-time correction values ​​of the three parameters, completing the online self-tuning of the PID parameters. Based on the tuned PID parameters, the frequency converter calculates the target operating frequency of the DC inverter compressor.

[0062] 4. The frequency converter performs upper and lower limit processing and rate of change limit processing on the calculated target operating frequency. Upper and lower limit processing restricts the target operating frequency between the compressor's minimum operating frequency and its rated maximum operating frequency. Rate of change limit processing limits the maximum adjustment amplitude of the compressor's operating frequency per unit time, preventing sudden frequency changes. The frequency converter outputs a drive signal of the corresponding frequency to the DC inverter compressor through the frequency converter drive output port, driving the DC inverter compressor to operate at the processed target operating frequency, thus forming the first closed-loop regulation of the evaporation pressure.

[0063] 5. The frequency converter monitors the actual operating frequency of the DC inverter compressor in real time. When it detects that the actual operating frequency has dropped to the compressor's minimum operating frequency and has been running for a period of time that has reached the preset frequency stabilization judgment time, and the measured value of the evaporation pressure is still lower than the hot gas bypass opening threshold, it is determined that there is no effective real gas load or the real load is extremely low on the evaporator side, and the cooling capacity is seriously excessive. The frequency converter starts the hot gas bypass control logic and enters the coordinated adjustment mode.

[0064] After entering the coordinated adjustment mode, the frequency converter locks the target operating frequency output by the fuzzy PID control algorithm to the compressor's minimum operating frequency, maintaining the DC inverter compressor at the minimum operating frequency. Simultaneously, using the pressure deviation and deviation change rate between the measured evaporation pressure and the target evaporation pressure as inputs, the fuzzy PID control algorithm calculates the target opening degree of the hot gas bypass electronic expansion valve. A corresponding drive signal is then output to the hot gas bypass electronic expansion valve via the stepper motor drive output port, controlling the valve opening and bypassing the high-temperature, high-pressure refrigerant gas discharged from the DC inverter compressor to the refrigerant-side inlet of the plate evaporator. This artificially supplements the evaporator with a controllable spurious heat load, forming a second closed-loop regulation of the evaporation pressure.

[0065] 6. During operation in the coordinated control mode, the frequency converter continuously collects the measured value of the evaporation pressure. When the measured value of the evaporation pressure rises above the hot gas bypass closure threshold, the frequency converter controls the hot gas bypass electronic expansion valve to gradually reduce its opening until it is completely closed. Simultaneously, it monitors the trend of evaporation pressure changes after the valve is closed in real time, thus distinguishing between false loads and real loads. If the measured value of the evaporation pressure continues to rise after the valve is completely closed, it is determined that a real gas load has arrived. The frequency converter immediately releases the locking of the compressor's operating frequency, restores the normal closed-loop regulation of the DC inverter compressor by the fuzzy PID control algorithm, drives the compressor to increase its frequency to match the real load, and exits the coordinated control mode. If the measured value of the evaporation pressure turns to a continuous decrease after the valve is completely closed, it is determined that there is no effective real gas load. The frequency converter reopens the hot gas bypass electronic expansion valve, maintains the coordinated control mode, and the compressor still operates at the lowest operating frequency.

[0066] 7. During the entire operation, the frequency converter continuously monitors the measured value of the evaporation pressure. When the measured value of the evaporation pressure is detected to be lower than the anti-icing blockage protection threshold, the anti-icing blockage protection logic is directly triggered, forcibly opening the hot gas bypass electronic expansion valve to the maximum opening degree, and at the same time increasing the minimum operating frequency of the compressor to quickly increase the evaporation pressure and avoid freezing blockage faults in the plate evaporator.

[0067] II. Experimental Data The control group for this experiment consisted of a traditional fixed-frequency refrigerated dryer with the same air volume, equipped with a fixed-frequency compressor and a manually operated hot gas bypass valve with a fixed opening. All other refrigeration components were identical to those in this implementation example. The experimental environment was standard atmospheric pressure, ambient temperature 30℃, inlet pressure 0.7MPa, and inlet temperature 38℃. The single-condition stable operation test duration was no less than 24 hours, and the total continuous operation test duration under all operating conditions was 720 hours. The measured data under different load conditions are as follows: 1. Rated load condition, compressed air consumption 10 Nm³ 3 / min In this implementation example, the evaporation pressure fluctuates between 0.48 MPa and 0.52 MPa, the average operating power of the unit is 2.1 kW, the compressed air outlet pressure dew point is stable between 2°C and 4°C, there is no ice blockage during continuous operation, and there is no mode switching action.

[0068] The control group fixed-frequency refrigerated dryer had an evaporation pressure fluctuation range of 0.42MPa to 0.58MPa, an average operating power of 3.2kW, a compressed air outlet pressure dew point fluctuation range of 1℃ to 7℃, and no ice blockage during continuous operation.

[0069] 2.50% load condition, compressed air consumption 5 Nm³ 3 / min In this implementation example, the evaporation pressure fluctuates between 0.47 MPa and 0.53 MPa, the average operating power of the unit is 1.2 kW, the compressed air outlet pressure dew point is stable between 2°C and 4°C, there is no ice blockage during continuous operation, and there is no mode switching action.

[0070] The control group fixed-frequency refrigerated dryer had an evaporation pressure fluctuation range of 0.38MPa to 0.60MPa, an average operating power of 3.0kW, a compressed air outlet pressure dew point fluctuation range of 0℃ to 8℃, and no ice blockage during continuous operation.

[0071] Under 3.20% load conditions, compressed air consumption is 2 Nm³. 3 / min In this implementation example, the evaporation pressure fluctuates between 0.46 MPa and 0.54 MPa, the average operating power of the unit is 0.8 kW, the compressed air outlet pressure dew point is stable between 2°C and 4°C, there is no ice blockage during continuous operation, and there is no mode switching action.

[0072] The control group of fixed-frequency refrigerated dryers had an evaporation pressure fluctuation range of 0.32MPa to 0.62MPa, an average operating power of 2.9kW, a compressed air outlet pressure dew point fluctuation range of -2℃ to 9℃, and experienced slight frost formation during operation without ice blockage shutdown.

[0073] 4.10% load condition, compressed air consumption 1 Nm³ 3 / min In this implementation example: the evaporation pressure fluctuates between 0.47MPa and 0.53MPa, the average operating power of the unit is 0.6kW, the compressed air outlet pressure dew point is stable between 2℃ and 4℃, there is no ice blockage during continuous operation, it stably enters the coordinated regulation mode, the opening of the hot gas bypass electronic expansion valve is maintained between 15% and 25%, there is no compressor frequency increase action, and there is no fluctuation during mode switching.

[0074] The control group of fixed-frequency refrigerated dryers had an evaporation pressure fluctuation range of 0.25MPa to 0.60MPa, an average operating power of 2.8kW, and a compressed air outlet pressure dew point fluctuation range of -5℃ to 10℃. During operation, severe frost appeared in the evaporator flow channel, accompanied by intermittent ice blockage.

[0075] 5.0 load condition, compressed air consumption 0 Nm³ 3 / min This implementation example shows that the evaporation pressure fluctuates between 0.46 MPa and 0.54 MPa, the average operating power of the unit is 0.5 kW, the compressed air outlet pressure dew point is stable between 3°C and 5°C, there is no ice blockage after 720 hours of continuous operation, the coordinated regulation mode is stably maintained, the opening of the hot gas bypass electronic expansion valve is maintained between 30% and 40%, there is no frequent mode switching, and no compressor malfunction.

[0076] The control group of fixed-frequency refrigerated dryers had an evaporation pressure that remained below 0.3 MPa, an average operating power of 2.8 kW, and after running for 2 hours, the evaporator flow channel was completely frozen and blocked. The compressor suction pressure was too low, triggering the protection shutdown, and the unit could not continue to operate.

[0077] 6. Sudden load change condition (from zero load to rated load) In this implementation example: the identification is completed within one sampling cycle after the actual load arrives, the compressor increases frequency without delay, the maximum fluctuation of the evaporation pressure does not exceed 0.05MPa, the outlet dew point does not fluctuate significantly, and there is no risk of ice blockage.

[0078] Existing inverter solutions: false loads cause compressors to erroneously increase frequency, mode switching conflicts occur, the maximum fluctuation of evaporating pressure exceeds 0.2MPa, the outlet dew point fluctuation range exceeds 5℃, and there is a problem of insufficient cooling capacity in the short term.

[0079] Long-term operation test results: After 720 hours of full-condition cyclic testing in this implementation example, the compressor, hot gas bypass electronic expansion valve, and evaporator showed no abnormal wear or malfunctions, the evaporation pressure control deviation did not drift, and the outlet dew point stability remained unchanged. In contrast, after 720 hours of cyclic testing, the control group's fixed-frequency refrigerated dryer showed slight sticking in the manual hot gas bypass valve, residual scale and ice blockage damage in the evaporator flow channel, and the compressor started and stopped more than 2000 times.

[0080] III. Technical Effects This implementation example brings many practical operational advantages through a complete collaborative control scheme, all of which can be directly derived and verified through experimental data and scheme logic.

[0081] In terms of energy saving and consumption reduction, this implementation example shows that the unit's operating power is much lower than that of a traditional fixed-frequency refrigerated dryer under rated load conditions. The energy consumption advantage is even more pronounced under low load conditions, with a significant reduction in operating energy consumption across the entire operating range. This is because the system prioritizes adapting to load changes through compressor frequency conversion adjustment, eliminating the need for continuous hot gas bypass operation. This avoids the ineffective energy consumption associated with traditional fixed bypass structures. Under low load conditions, the compressor can operate at its lowest frequency, supplementing the heat load only through a small-scale hot gas bypass, ensuring stable system operation while minimizing energy consumption.

[0082] Regarding the stability of the drying effect, this implementation example shows that the fluctuation range of the evaporation pressure is much smaller than that of a traditional fixed-frequency refrigerated dryer across the entire operating range. The compressed air outlet pressure dew point remains within a stable range without significant fluctuations. This is because the coordinated operation of the two closed-loop controls allows for rapid response to load changes, consistently maintaining the evaporation pressure within the target range and avoiding large fluctuations in evaporation temperature. Consequently, the refrigeration drying effect of the compressed air remains stable, consistently meeting the drying requirements under different air usage conditions.

[0083] Regarding equipment operational reliability, this implementation example demonstrates stable, continuous operation for extended periods under extreme zero-load conditions without ice blockage, whereas traditional fixed-frequency refrigerated dryers would experience ice blockage and shutdown within a short time under the same conditions. This is because the collaborative control scheme can precisely supplement the heat load through hot gas bypass under extremely low-load conditions, fundamentally solving the evaporator ice blockage problem caused by excess cooling capacity and avoiding equipment failure and shutdown risks associated with ice blockage. Simultaneously, this scheme avoids frequent compressor start-stop cycles, reduces unnecessary valve movements, and lowers the mechanical and electrical impact on critical equipment components. After long-term operation, the equipment exhibits no abnormal wear or failures, significantly extending its service life and reducing maintenance costs.

[0084] In terms of operating condition adaptability, this implementation example covers the entire operating range from 0 load to rated load, achieving stable control under different loads without the need for manual parameter adjustments. Traditional fixed-frequency refrigerated dryers, on the other hand, can only achieve stable operation near the rated load, and are prone to problems such as frosting and ice blockage under low load conditions, making them unsuitable for industrial applications with significant fluctuations in gas load. This solution's full-condition adaptability meets the needs of different industries and gas usage scenarios, demonstrating strong practicality.

[0085] In terms of control precision and response speed, this implementation example completely solves the industry pain points of traditional solutions through the identification logic of false load and real load. It can complete the identification and response the moment the real load arrives, without control malfunctions. The evaporation pressure does not fluctuate significantly when the load changes suddenly, and the outlet dew point remains stable. At the same time, it avoids the ineffective frequency increase of the compressor when there is no real load, further optimizing the energy-saving effect.

[0086] Regarding the smoothness of mode switching, this implementation example adopts a control timing sequence of closing the valve first, then screening, and then increasing the frequency, which completely eliminates control conflicts during the mode switching process, realizes the seamless switching between the two regulation modes, and further improves the stability of system operation.

[0087] In terms of anti-interference and protection capabilities, this implementation example eliminates interference signals during the pressure acquisition process through filtering, ensuring the accuracy of control calculations and enabling stable operation even in complex industrial environments. Simultaneously, the pre-set anti-icing protection logic can respond quickly to sudden changes in operating conditions, forming a safety net. Even under extreme abnormal circumstances, it can prevent irreversible damage to the equipment, further enhancing the safety and stability of the unit's operation.

[0088] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for coordinated control of a variable frequency refrigerated dryer based on fuzzy PID and hot gas bypass, characterized in that, A refrigeration system for a variable frequency refrigerated dryer includes a DC inverter compressor, a condenser, a throttling device, an evaporator, a hot gas bypass valve, an evaporating pressure sensor, and a variable frequency controller. The discharge port of the DC inverter compressor is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the throttling device, the outlet of the throttling device is connected to the inlet of the evaporator, the outlet of the evaporator is connected to the suction port of the DC inverter compressor, the inlet of the hot gas bypass valve is connected to the discharge port of the DC inverter compressor, and the outlet of the hot gas bypass valve is connected to the inlet side of the evaporator. The evaporating pressure sensor is installed on the outlet pipe of the evaporator. The evaporating pressure sensor, the DC inverter compressor, and the hot gas bypass valve are all electrically connected to the variable frequency controller. The coordinated control method includes the following steps: Step 1: The frequency converter completes system initialization, presets the target evaporation pressure, the compressor's minimum operating frequency, the hot gas bypass opening threshold, the hot gas bypass closing threshold, and the frequency stability determination time. Step 2: The evaporation pressure sensor collects the measured value of the evaporation pressure at the evaporator outlet in real time and transmits the measured value of the evaporation pressure to the frequency converter controller; Step 3: The frequency converter calculates the pressure deviation between the measured evaporation pressure and the target evaporation pressure, as well as the rate of change of the pressure deviation. Using the pressure deviation and the rate of change of the deviation as inputs, the target operating frequency of the DC inverter compressor is calculated using a fuzzy PID control algorithm. The frequency converter outputs a control signal to the DC inverter compressor to drive it to operate at the target operating frequency, thus performing the first closed-loop regulation of the evaporation pressure. Step 4: The frequency converter monitors the actual operating frequency of the DC inverter compressor in real time. When the actual operating frequency of the DC inverter compressor drops to the compressor's minimum operating frequency and the continuous operating time reaches the frequency stabilization judgment time, if the measured value of the evaporation pressure is still lower than the hot gas bypass opening threshold, it is determined that there is no effective real gas load or the real load on the evaporator side is extremely low, and the cooling capacity is seriously excessive. The frequency converter outputs a control signal to start the hot gas bypass valve, and the high temperature and high pressure refrigerant gas discharged from the DC inverter compressor is bypassed to the inlet side of the evaporator through the hot gas bypass valve, artificially supplementing the evaporator with a controllable false heat load, and performing a second closed-loop regulation of the evaporation pressure. Step 5: When the hot gas bypass valve is in the regulating operation state, the frequency converter synchronously maintains the first closed-loop regulation of the DC inverter compressor using the fuzzy PID control algorithm, locking the target operating frequency output by the fuzzy PID control algorithm to the compressor's minimum operating frequency, and controlling the evaporation pressure only through the regulation of the hot gas bypass valve; when the measured evaporation pressure rises above the hot gas bypass closing threshold, the frequency converter controls the hot gas bypass valve to gradually close, synchronously monitoring the evaporation pressure change trend during and after the hot gas bypass valve closure process, thus distinguishing between false loads and true loads; if the hot gas bypass valve is completely closed, the evaporation pressure... If the measured value continues to rise, it is determined that the actual gas load has arrived. The frequency converter immediately releases the compressor's operating frequency lock and resumes the normal closed-loop regulation of the DC inverter compressor by the fuzzy PID control algorithm. It drives the compressor to increase its frequency to match the actual gas load, completing the coordinated closed-loop control of the DC inverter compressor's frequency regulation and the hot gas bypass valve's load regulation. If the measured value of the evaporating pressure turns to a continuous downward trend after the hot gas bypass valve is completely closed, it is determined that the false load supplemented by the hot gas bypass valve has disappeared and there is no effective actual gas load. The frequency converter restarts the hot gas bypass valve and maintains the coordinated regulation mode of the compressor's minimum operating frequency.

2. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, The fuzzy PID control algorithm in step three includes the following specific steps: First, the input pressure deviation and deviation change rate are fuzzified, the fuzzy universe of discourse for pressure deviation and deviation change rate is set, and the corresponding membership function is selected. Fuzzy inference is performed based on the preset fuzzy control rule table to obtain the fuzzy correction amount of the PID parameters; The fuzzy correction values ​​of the PID parameters are defuzzified to obtain the real-time correction values ​​of the PID parameters, thus completing the online self-tuning of the proportional coefficient, integral coefficient, and derivative coefficient. Based on the tuned PID parameters, the target operating frequency of the DC inverter compressor is calculated.

3. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, The hot gas bypass valve is a hot gas bypass solenoid valve. In step four, the frequency converter uses an ON-OFF hysteresis control method for the hot gas bypass solenoid valve. When the measured value of the evaporation pressure is lower than the hot gas bypass opening threshold, the frequency converter outputs a signal to open the hot gas bypass solenoid valve. When the measured value of the evaporation pressure is higher than the hot gas bypass closing threshold, the frequency converter outputs a signal to close the hot gas bypass solenoid valve. The frequent start and stop of the hot gas bypass solenoid valve is avoided by controlling the hysteresis range.

4. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, The hot gas bypass valve is a hot gas bypass solenoid valve. In step four, the frequency converter uses a duty cycle adjustment control method for the hot gas bypass solenoid valve. The pressure deviation between the measured evaporation pressure and the target evaporation pressure is used as the input. The duty cycle of the drive signal of the hot gas bypass solenoid valve is calculated by the PID control algorithm. The frequency converter outputs a pulse drive signal according to the corresponding duty cycle to control the on / off time ratio of the hot gas bypass solenoid valve, thereby realizing continuous adjustment of the bypass refrigerant flow.

5. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, The hot gas bypass valve is a hot gas bypass electronic expansion valve. In step four, the frequency converter uses a stepless opening adjustment control mode for the hot gas bypass electronic expansion valve. The pressure deviation between the measured evaporation pressure and the target evaporation pressure, and the rate of change of the pressure deviation, are used as inputs. The target opening of the hot gas bypass electronic expansion valve is calculated by a fuzzy PID control algorithm. The frequency converter outputs a drive signal corresponding to the opening to control the valve opening of the hot gas bypass electronic expansion valve, thereby realizing stepless continuous adjustment of the bypass refrigerant flow.

6. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, The hot gas bypass opening threshold is lower than the target evaporation pressure, the hot gas bypass closing threshold is higher than the hot gas bypass opening threshold but lower than the target evaporation pressure, and the frequency stability determination time is set to 3 to 30 seconds. By using hysteresis threshold setting and stability time determination, frequent start-stop and mode switching of the hot gas bypass valve are avoided.

7. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, In step two, after the frequency converter receives the measured evaporation pressure value transmitted by the evaporation pressure sensor, it first performs moving average filtering and outlier removal processing on the measured evaporation pressure value, removing abnormal data that exceed the preset reasonable range, and then uses the processed measured evaporation pressure value for subsequent closed-loop control calculations.

8. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass according to claim 1, characterized in that, In step three, after the frequency converter calculates the target operating frequency of the DC inverter compressor, it performs upper and lower limit processing and change rate limit processing on the target operating frequency. The lower limit of the upper and lower limit processing is the lowest operating frequency of the compressor, and the upper limit is the rated highest operating frequency of the compressor. The change rate limit processing limits the maximum adjustment amplitude of the compressor frequency per unit time to avoid sudden changes in the compressor operating frequency.

9. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass as described in claim 1, characterized in that, In step five, the spurious load is the controllable heat load brought by the high-temperature refrigerant gas supplied to the evaporator side when the hot gas bypass valve is opened. Its load size and trend can be precisely controlled by the opening degree of the bypass valve. It is a simulated load created artificially and has no corresponding compressed air demand. The real load is the random heat load brought by the high-temperature compressed air entering the evaporator after the gas demand end is opened. Its load size and arrival time cannot be predicted in advance and correspond to the actual compressed air drying treatment demand.

10. The variable frequency refrigerated dryer coordinated control method based on fuzzy PID and hot gas bypass according to any one of claims 1-9, characterized in that, The frequency converter has a preset anti-icing protection threshold. When the measured value of the evaporation pressure is lower than the hot gas bypass opening threshold, the frequency converter will forcibly open the hot gas bypass valve to the maximum flow state and at the same time increase the minimum operating frequency of the compressor to quickly increase the evaporation pressure and avoid freezing and blockage of the evaporator.

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