A refrigeration system variable frequency fluid mechanical speed regulation control method based on condensing pressure rising speed

Abstract

This invention provides a variable frequency fluid machinery speed control method for refrigeration systems based on the rate of increase of condensing pressure, belonging to the field of refrigeration system control technology. This method addresses the problems of poor adaptability of the initial speed setting of existing variable frequency fluid machinery in refrigeration systems, incompatibility with different condenser specifications, and large fluctuations in condensing pressure. It adopts the following control flow: When the refrigeration system starts, the compressor is started first. The initial speed of the variable frequency fluid machinery is determined based on the rate of increase of condensing pressure during the compressor's operation. When the condensing pressure reaches the starting threshold, the fluid machinery starts at this initial speed. After a preset holding time, fuzzy PID control is engaged to adjust the speed. When the condensing pressure drops to the shutdown threshold, the fluid machinery stops, and the initial speed for the next start is re-matched. This method has strong adaptability, is compatible with different condenser specifications, effectively stabilizes the condensing pressure, ensures stable operation of the refrigeration system, and reduces operating energy consumption.

Description

Technical Field

[0001] This invention relates to the field of refrigeration system control technology, and specifically to a variable frequency fluid mechanical speed control method for refrigeration systems based on the rate of rise of condensing pressure. Background Technology

[0002] During the operation of a refrigeration system, it is necessary to maintain a suitable condensing pressure to ensure the internal liquid supply driving force and ensure the stable and normal operation of the system. This requires speed control of the variable frequency fluid machinery that delivers the cooling medium on the condenser side to regulate the condensing pressure and keep it within a relatively constant range.

[0003] In conventional control methods within the industry, the initial starting speed of variable frequency fluid machinery is often determined based on ambient temperature or condenser surface temperature. This method does not consider the operational differences caused by variations in the condenser's heat transfer area and coefficient, making it unsuitable for different condenser specifications. The initial speed setting has a low match with the actual operating requirements of the system, easily leading to significant fluctuations in condensing pressure after startup. This can result in either insufficient liquid supply driving force, affecting the cooling effect and operational stability, or ineffective operation of the fluid machinery, increasing unnecessary energy consumption. Consequently, it fails to balance the operational stability and energy efficiency of the refrigeration system.

[0004] To address this, a variable frequency fluid mechanical speed control method for refrigeration systems based on the rate of increase of condensing pressure is proposed. Summary of the Invention

[0005] The present invention aims to solve the problems mentioned in the background art by providing a variable frequency fluid mechanical speed control method for refrigeration systems based on the condensation pressure rise rate.

[0006] The specific technical solution is as follows: A variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure includes the following steps: Step 1: When starting the refrigeration system, first start the compressor, keep the variable frequency fluid machinery on the condenser side in a stopped state, and collect the condensing pressure of the refrigeration system in real time through the condensing pressure sensor; Step 2: Based on the real-time collected condensing pressure, calculate the rate of increase of condensing pressure after the compressor starts and before the variable frequency fluid machinery starts. According to the preset rule that the rate of increase of condensing pressure is proportional to the initial speed, determine the initial speed of the variable frequency fluid machinery. Step 3: When the absolute value of the real-time collected condensation pressure is higher than the preset start-up pressure threshold, control the variable frequency fluid machinery to start operation at the determined initial start-up speed; Step 4: After the variable frequency fluid machinery starts running at the initial speed and maintains the preset initial speed for a set time, it switches to fuzzy PID control mode. Based on the deviation between the real-time collected condensing pressure and the preset condensing pressure setpoint, the speed adjustment signal is output through fuzzy PID calculation to adjust the running speed of the variable frequency fluid machinery in real time and maintain the condensing pressure stable near the preset condensing pressure setpoint. Step 5: When the absolute value of the real-time collected condensing pressure is lower than the preset shutdown pressure threshold, control the variable frequency fluid machinery to stop running, and repeat steps 1 and 2 to determine a new initial starting speed for the next start-up of the variable frequency fluid machinery.

[0007] As a preferred embodiment of the present invention, the rate of increase of condensing pressure in step two is the change in condensing pressure per unit time, which is obtained by linear fitting calculation through multiple sets of continuously collected condensing pressure data.

[0008] As a preferred embodiment of the present invention, the preset rule in step two is that the initial starting speed is equal to the preset reference speed multiplied by the ratio of the condensing pressure rise rate to the preset reference rise rate.

[0009] As a preferred embodiment of the present invention, the starting pressure threshold in step three is preset based on the rated condensing pressure of the refrigeration system and the liquid supply driving force requirement of the throttling device, and the starting pressure threshold is higher than the preset condensing pressure setting value.

[0010] As a preferred embodiment of the present invention, the initial rotational speed maintenance time in step four is preset according to the starting characteristics of the variable frequency fluid machinery and the volume of the refrigeration system, and the value range is from 5 seconds to 30 seconds.

[0011] As a preferred embodiment of the present invention, in the fuzzy PID control mode in step four, the deviation between the real-time value of the condensing pressure and the set value of the condensing pressure, and the rate of change of the deviation are used as input quantities. The proportional coefficient, integral coefficient, and derivative coefficient of the PID are corrected in real time through preset fuzzy rules, and the corresponding speed adjustment signal is output.

[0012] As a preferred embodiment of the present invention, the shutdown pressure threshold in step five is preset based on the minimum stable operating condensing pressure of the refrigeration system, and the shutdown pressure threshold is lower than the preset condensing pressure setting value.

[0013] As a preferred embodiment of the present invention, the variable frequency fluid machinery is a variable frequency condensing fan or a variable frequency cooling water pump that drives the flow of cooling medium in the condenser.

[0014] In a preferred embodiment of the present invention, the condensing pressure sensor is installed on the refrigerant inlet pipe of the condenser or the exhaust port pipe of the compressor, and the condensing pressure collected is the exhaust condensing pressure of the refrigeration system.

[0015] As a preferred embodiment of the present invention, the initial starting speed determined in step two shall not exceed the rated maximum speed of the variable frequency fluid machinery, and shall not be lower than the minimum stable operating speed of the variable frequency fluid machinery.

[0016] The present invention has the following beneficial effects: This method determines the initial rotational speed of the fluid machinery by the rate of increase of condensing pressure. It can directly adapt to the actual heat load of the refrigeration system and the actual heat exchange characteristics of the condenser without having to consider the differences in parameters such as the heat transfer area and heat transfer coefficient of the condenser. It is compatible with condensers of different specifications and models, greatly expanding the scope of application of the control method and solving the problems of poor adaptability and insufficient compatibility of conventional control methods.

[0017] The initial rotation speed is precisely matched with the actual operating requirements of the system, which can avoid large fluctuations in condensing pressure after the fluid machinery is started, prevent pressure overshoot or insufficient liquid supply driving force, effectively ensure the stability of the refrigeration system during operation, and avoid abnormal cooling effect or equipment failure caused by pressure fluctuations.

[0018] The start-up, shutdown, and speed regulation of the fluid machinery perfectly match the actual condensing pressure requirements of the system, avoiding ineffective operation of the fluid machinery, reducing unnecessary energy consumption, and balancing system stability and energy efficiency. Furthermore, after starting, the fluid machinery initially operates at a fixed initial speed before switching regulation modes, ensuring a smooth transition between operating modes and preventing system oscillations during mode switching. This improves the smoothness and accuracy of speed regulation, allowing the condensing pressure to be maintained more stably within the set range.

[0019] Each time the fluid machinery stops, the initial speed for the next startup is recalculated and matched. This allows for real-time adaptation to dynamic changes in heat load, environmental conditions, and other operating conditions during system operation, continuously ensuring that the system receives appropriate control parameters under different operating conditions and maintains a stable and reliable operating state over the long term. This method does not require significant modifications to the original hardware structure of the refrigeration system; it can be implemented simply by optimizing the control logic. It has low implementation costs and is easy to promote and apply in various refrigeration systems.

[0020] Stable and controllable condensing pressure can continuously ensure the liquid supply driving force inside the system, avoid abnormal liquid supply from the throttling device, effectively reduce the operating load of the core components of the refrigeration system, and extend the overall service life of the equipment. Attached Figure Description

[0021] Figure 1 A flowchart of a variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, provided in an embodiment of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] Example The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure provided in this embodiment, such as... Figure 1 As shown, it includes the following steps: Step 1: When starting the refrigeration system, first start the compressor, keep the variable frequency fluid machinery on the condenser side in a stopped state, and collect the condensing pressure of the refrigeration system in real time through the condensing pressure sensor; Step 2: Based on the real-time collected condensing pressure, calculate the rate of increase of condensing pressure after the compressor starts and before the variable frequency fluid machinery starts. According to the preset rule that the rate of increase of condensing pressure is proportional to the initial speed, determine the initial speed of the variable frequency fluid machinery. Step 3: When the absolute value of the real-time collected condensation pressure is higher than the preset start-up pressure threshold, control the variable frequency fluid machinery to start operation at the determined initial start-up speed; Step 4: After the variable frequency fluid machinery starts running at the initial speed and maintains the preset initial speed for a set time, it switches to fuzzy PID control mode. Based on the deviation between the real-time collected condensing pressure and the preset condensing pressure setpoint, the speed adjustment signal is output through fuzzy PID calculation to adjust the running speed of the variable frequency fluid machinery in real time and maintain the condensing pressure stable near the preset condensing pressure setpoint. Step 5: When the absolute value of the real-time collected condensing pressure is lower than the preset shutdown pressure threshold, control the variable frequency fluid machinery to stop running, and repeat steps 1 and 2 to determine a new initial starting speed for the next start-up of the variable frequency fluid machinery.

[0027] By adopting the above technical solution and executing control according to a predetermined start-up and shutdown sequence, the control process can be progressively advanced to match the actual operating state of the refrigeration system, avoiding operational anomalies caused by disordered equipment start-up and shutdown sequences. Matching the start-up speed based on the pressure changes in the early stages of system operation ensures that the equipment startup state adapts to the actual operating needs of the system at present, reducing large fluctuations in system operating parameters after startup. Fixing the operating state before switching the adjustment mode after startup ensures a smooth transition of the system state, avoiding operational oscillations caused by mode switching. After the equipment stops, the startup parameters are rematched for the next startup, ensuring that each equipment startup matches the current operating conditions of the system, continuously guaranteeing the stability of system operation, and reducing energy consumption caused by ineffective equipment operation.

[0028] Specifically, in this embodiment, the rate of increase in condensing pressure in step two is the change in condensing pressure per unit time, which is calculated by linear fitting of multiple sets of continuously collected condensing pressure data. This scheme calculates pressure changes using multiple sets of continuously collected data, allowing the obtained parameters to better reflect the actual pressure change trend of the system, avoiding errors caused by single-point data collection, providing a more realistic basis for determining subsequent equipment operating parameters, and reducing system operation fluctuations caused by parameter deviations.

[0029] Specifically, in this embodiment, the preset rule in step two is that the initial startup speed is equal to the preset reference speed multiplied by the ratio of the condensing pressure rise rate to the preset reference rise rate. This scheme determines the equipment startup speed through proportional conversion of reference parameters, enabling a stable correspondence between the equipment startup speed and system pressure changes. This adapts to the actual needs of different system operating loads, ensuring that the system obtains suitable startup parameters under different operating conditions, and improving the system's adaptability to different operating conditions.

[0030] Specifically, in this embodiment, the start-up pressure threshold in step three is preset based on the rated condensing pressure of the refrigeration system and the liquid supply driving force requirement of the throttling device, and the start-up pressure threshold is higher than the preset condensing pressure setting value. This scheme combines the rated operating parameters of the system with the basic liquid supply requirements to set the critical pressure value for equipment start-up, ensuring that the system has a stable operating foundation when the equipment starts up, while avoiding energy waste caused by premature equipment start-up, and also preventing the system pressure from exceeding the reasonable range due to delayed equipment start-up, thus ensuring the stability of the system's liquid supply and the safety of operation.

[0031] Specifically, in this embodiment, the initial speed maintenance time in step four is preset based on the start-up characteristics of the variable frequency fluid machinery and the volume of the refrigeration system, with a value ranging from 5 to 30 seconds. This scheme, by combining the equipment's own start-up characteristics with the actual volume of the system to set a fixed speed operating time, allows the equipment to reach a stable operating state after startup, while also stabilizing the internal pressure state of the system. This provides a stable operating foundation for subsequent mode switching and avoids system instability during mode switching.

[0032] Specifically, in this embodiment, in the fuzzy PID control mode of step four, the deviation between the real-time value of the condensing pressure and the setpoint value of the condensing pressure, as well as the rate of change of the deviation, are used as inputs. The proportional coefficient, integral coefficient, and derivative coefficient of the PID controller are corrected in real time using preset fuzzy rules, and a corresponding speed adjustment signal is output. This scheme uses the actual deviation of the system pressure and the trend of its change as the input basis for adjustment. It can adapt to changes in the operating conditions during system operation in real time, dynamically adjust the adjustment parameters, and keep the system pressure within a stable operating range. This reduces pressure deviation caused by fluctuations in operating conditions and improves the stability and anti-interference capability of system operation.

[0033] Specifically, in this embodiment, the shutdown pressure threshold in step five is preset based on the minimum stable operating condensing pressure of the refrigeration system, and the shutdown pressure threshold is lower than the preset condensing pressure setting value. This scheme sets the equipment shutdown pressure threshold based on the system's minimum stable operating pressure requirement, ensuring that the system can maintain a basic stable operating state after the equipment stops, avoiding a rapid pressure rebound caused by premature shutdown, and also preventing unnecessary energy consumption caused by delayed shutdown, thus balancing system stability and energy efficiency.

[0034] Specifically, in this embodiment, the variable frequency fluid machinery is a variable frequency condenser fan or a variable frequency cooling water pump that drives the flow of the cooling medium in the condenser. This solution clarifies the types of equipment to which the method is applicable, allowing the control method to cover refrigeration systems with different cooling medium forms, broadening the applicable scenarios of the method, and ensuring that refrigeration systems with different cooling forms can achieve stable operation control through this method.

[0035] Specifically, in this embodiment, the condensing pressure sensor is installed on the refrigerant inlet pipe of the condenser or the exhaust pipe of the compressor, and the collected condensing pressure is the exhaust condensing pressure of the refrigeration system. This scheme clearly defines the pressure data collection location, enabling direct acquisition of pressure data that best reflects the actual operating state of the system, avoiding pressure data distortion caused by sampling location deviations, providing accurate basic data for subsequent parameter calculations and operational adjustments, and improving the precision of system control.

[0036] Specifically, in this embodiment, the initial starting speed determined in step two does not exceed the rated maximum speed of the variable frequency fluid machinery, and is not lower than the minimum stable operating speed of the variable frequency fluid machinery. This scheme limits the upper and lower operating range of the equipment's starting speed, which can prevent the starting speed from exceeding the normal operating range of the equipment, prevent the equipment from being overloaded and damaged due to excessive speed, and also prevent the equipment from becoming unstable due to excessively low speed, ensuring that the equipment always operates within a safe and stable range and extending the service life of the equipment.

[0037] Working principle: During the operation of the refrigeration system, after the compressor starts, the refrigerant circulates within the system, and the condensing pressure will continue to rise as the compressor runs. The rate of increase in condensing pressure can directly reflect the actual heat load state of the refrigeration system, as well as the heat exchange characteristics of the condenser itself and the actual operating requirements, and is not affected by differences in condenser specifications and models.

[0038] Based on this characteristic, the control process first starts the compressor independently while the fluid machinery remains shut down. By continuously collecting condensing pressure data, the rate of increase in condensing pressure before the fluid machinery starts is calculated, thus determining the initial speed of the fluid machinery and ensuring that the initial speed precisely matches the actual cooling demand of the system. After the fluid machinery starts, it first runs at the determined initial speed for a period of time to allow the condensing pressure inside the system to stabilize. Then, it switches to the corresponding adjustment mode, dynamically adjusting the operating speed of the fluid machinery based on the deviation between the real-time condensing pressure and the set value. This maintains the condensing pressure within a stable operating range, ensuring stable liquid supply driving force for the system.

[0039] When the condensing pressure drops to the shutdown threshold, the fluid machinery stops operating. Then, the condensing pressure data is collected again to calculate the rise rate, and the corresponding initial speed is matched for the next startup. This adapts to the dynamic changes in system operating conditions and continuously ensures the stability of system operation.

[0040] How to use: When this control method is applied to a refrigeration system, it is executed according to a predetermined process. When the refrigeration system is started, the compressor in the system is started first, while the variable frequency fluid machinery on the condenser side is kept in a stopped state. The condensing pressure data of the refrigeration system is continuously collected in real time through the condensing pressure sensor installed at the corresponding location in the system.

[0041] During the compressor operation and fluid machinery shutdown phases, the change in condensing pressure per unit time is calculated based on continuously collected condensing pressure data to obtain the condensing pressure rise rate. According to a preset correlation, the initial starting speed of the variable frequency fluid machinery is determined. When the real-time collected condensing pressure reaches the preset starting threshold, a control command is issued to start the variable frequency fluid machinery, allowing it to operate at the predetermined initial speed.

[0042] After the variable frequency fluid machinery runs at its initial speed for a preset time, it switches to the adjustment mode. Based on the deviation between the real-time collected condensing pressure and the preset condensing pressure setting, it outputs a speed adjustment signal through the corresponding calculation logic to dynamically adjust the operating speed of the variable frequency fluid machinery in real time, so that the condensing pressure is always maintained near the preset setting value, ensuring the stability of the system's liquid supply driving force.

[0043] When the real-time collected condensing pressure drops to the preset shutdown threshold, a control command is issued to stop the variable frequency fluid machinery. After the fluid machinery stops, the above process of collecting condensing pressure, calculating the rise rate, and determining the initial speed is repeated to match a new initial speed for the next startup of the variable frequency fluid machinery, thereby adapting to changes in operating conditions during system operation.

[0044] This method can be directly applied to various refrigeration systems equipped with variable frequency condenser fans or variable frequency cooling water pumps without requiring significant modifications to the original hardware structure of the system. Only the control logic of the system needs to be adjusted for implementation.

[0045] In summary, the variable frequency fluid mechanical speed control method for refrigeration systems based on the rate of rise of condensing pressure provided by this invention has the following advantages: This method determines the initial rotational speed of the fluid machinery by the rate of increase of condensing pressure. It can directly adapt to the actual heat load of the refrigeration system and the actual heat exchange characteristics of the condenser without having to consider the differences in parameters such as the heat transfer area and heat transfer coefficient of the condenser. It is compatible with condensers of different specifications and models, greatly expanding the scope of application of the control method and solving the problems of poor adaptability and insufficient compatibility of conventional control methods.

[0046] The initial rotation speed is precisely matched with the actual operating requirements of the system, which can avoid large fluctuations in condensing pressure after the fluid machinery is started, prevent pressure overshoot or insufficient liquid supply driving force, effectively ensure the stability of the refrigeration system during operation, and avoid abnormal cooling effect or equipment failure caused by pressure fluctuations.

[0047] The start-up, shutdown, and speed regulation of the fluid machinery perfectly match the actual condensing pressure requirements of the system, avoiding ineffective operation of the fluid machinery, reducing unnecessary energy consumption, and balancing system stability and energy efficiency. Furthermore, after starting, the fluid machinery initially operates at a fixed initial speed before switching regulation modes, ensuring a smooth transition between operating modes and preventing system oscillations during mode switching. This improves the smoothness and accuracy of speed regulation, allowing the condensing pressure to be maintained more stably within the set range.

[0048] Each time the fluid machinery stops, the initial speed for the next startup is recalculated and matched. This allows for real-time adaptation to dynamic changes in heat load, environmental conditions, and other operating conditions during system operation, continuously ensuring that the system receives appropriate control parameters under different operating conditions and maintains a stable and reliable operating state over the long term. This method does not require significant modifications to the original hardware structure of the refrigeration system; it can be implemented simply by optimizing the control logic. It has low implementation costs and is easy to promote and apply in various refrigeration systems.

[0049] Stable and controllable condensing pressure can continuously ensure the liquid supply driving force inside the system, avoid abnormal liquid supply from the throttling device, effectively reduce the operating load of the core components of the refrigeration system, and extend the overall service life of the equipment.

[0050] Furthermore, this invention also provides an implementation example of a variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of increase of condensing pressure. I. Technical Solution This implementation example applies to an air-cooled chiller unit, which includes a screw compressor, a finned air-cooled condenser, multiple parallel variable frequency condenser fans, an electronic expansion throttling device, a shell-and-tube evaporator, a condensing pressure sensor, and a programmable frequency converter. The condensing pressure sensor is installed on the compressor's exhaust pipe to directly collect the unit's exhaust condensing pressure. The frequency converter is electrically connected to the compressor, the condensing pressure sensor, and each variable frequency condenser fan, executing the corresponding control logic.

[0051] After receiving the start-up command, the inverter controller first outputs a start signal to start the compressor, while keeping all inverter condenser fans in a stopped state. After the compressor starts, the condensing pressure sensor continuously transmits real-time condensing pressure data to the inverter controller at a fixed sampling frequency.

[0052] The variable frequency controller receives continuously collected condensing pressure data and calculates the change in condensing pressure per unit time after the compressor starts and before the condenser fan starts. It then performs linear fitting on multiple sets of continuously collected data to obtain the condensing pressure rise rate. The variable frequency controller has preset reference speed and reference rise rate. Following the rule that the initial starting speed equals the reference speed multiplied by the ratio of the condensing pressure rise rate to the reference rise rate, the initial starting speed of the variable frequency condenser fan is calculated. The calculated initial starting speed does not exceed the rated maximum speed of the variable frequency condenser fan, and is not lower than the minimum stable operating speed of the variable frequency condenser fan.

[0053] The variable frequency controller has a preset starting pressure threshold, which is set according to the unit's rated condensing pressure and the liquid supply driving force requirement of the throttling device, and is higher than the preset condensing pressure setting. When the real-time collected absolute value of the condensing pressure is higher than the starting pressure threshold, the variable frequency controller outputs an operating signal to all variable frequency condensing fans, controlling the variable frequency condensing fans to start operation at the calculated initial starting speed.

[0054] The variable frequency controller has a preset initial speed maintenance time, which is set according to the start-up characteristics of the variable frequency condenser fan and the system volume of the unit. The variable frequency condenser fan runs continuously at the initial start-up speed, and after reaching the preset initial speed maintenance time, it automatically switches to fuzzy PID control mode. In fuzzy PID control mode, the variable frequency controller uses the deviation between the real-time value of the condensing pressure and the set value of the condensing pressure, as well as the rate of change of the deviation, as input. Through preset fuzzy rules, it corrects the proportional coefficient, integral coefficient, and derivative coefficient of the PID controller in real time, and outputs the corresponding speed adjustment signal to adjust the operating speed of the variable frequency condenser fan in real time, maintaining the condensing pressure near the set value of the condensing pressure.

[0055] The variable frequency controller has a preset shutdown pressure threshold, which is set based on the unit's minimum stable operating condensing pressure, and the shutdown pressure threshold is lower than the set condensing pressure value. When the real-time collected absolute value of the condensing pressure is lower than the shutdown pressure threshold, the variable frequency controller outputs a shutdown signal, controlling all variable frequency condensing fans to stop operating. After the condensing fans stop, the variable frequency controller re-executes the process of condensing pressure data acquisition, condensing pressure rise rate calculation, and initial startup speed determination to determine a new initial startup speed for the next startup of the variable frequency condensing fans.

[0056] II. Working Principle: The working principle of this implementation example is based on the operating characteristics of the refrigeration unit. After the compressor starts, the refrigerant is compressed into a high-temperature, high-pressure gaseous state and sent into the air-cooled condenser. At this time, the condenser fan is not running, and the heat exchange capacity of the condenser is at its lowest. The condensing pressure will continuously rise as the compressor continues to run. The rate of increase in condensing pressure directly reflects the actual heat load of the unit at present, and also directly reflects the heat exchange capacity of the condenser itself, unaffected by differences in the condenser's heat transfer area, heat transfer coefficient, and other specifications.

[0057] Based on this characteristic, determining the initial startup speed of the condenser fan by the rate of increase in condensing pressure allows the fan's startup airflow to directly match the unit's actual cooling needs, avoiding the mismatch between the initial speed and actual requirements caused by traditional methods that only determine the initial speed based on ambient temperature or condenser surface temperature. After the fan starts, it first runs at a fixed initial speed to stabilize the condensing pressure within the unit, then switches to fuzzy PID control mode. This avoids system oscillations caused by mode switching, making the speed adjustment process smoother. After the fan stops, the initial startup speed is re-matched, adapting to dynamic changes in ambient temperature, terminal heat load, and other operating conditions during unit operation, ensuring that each fan startup matches the unit's current actual operating state.

[0058] III. Experimental Data: This test was conducted in a fixed environment with the ambient dry-bulb temperature maintained at 35°C, and the unit's inlet and outlet water temperatures kept constant to ensure stable terminal heat load. Multiple parallel tests were performed using both the control method described in this implementation example and the industry-standard control method that uses ambient temperature to determine the initial speed. Different condenser specifications were also used to verify compatibility. The test data obtained are as follows.

[0059] In the basic operating condition test, the condensing pressure setpoint was 1.85 MPa, the start-up pressure threshold was 2.0 MPa, the shutdown pressure threshold was 1.7 MPa, and the initial speed maintenance time was 10 seconds, with the unit operating at rated load. Using the method of this implementation example, after the condenser fan started, the condensing pressure rose to a maximum of 2.08 MPa, and it took 12 seconds to stabilize near the setpoint. During operation, the condensing pressure fluctuated between 1.82 MPa and 1.88 MPa. Using the method of setting the initial speed at a conventional ambient temperature, after the condenser fan started, the condensing pressure rose to a maximum of 2.27 MPa, and it took 38 seconds to stabilize near the setpoint. During operation, the condensing pressure fluctuated between 1.76 MPa and 1.94 MPa.

[0060] In the energy consumption test, the above test environment and load conditions were kept unchanged, and the unit ran continuously for 24 hours. Using the method of this implementation example, the cumulative power consumption of the variable frequency condenser fan was 128 kWh. Using the method of setting the initial speed at a conventional ambient temperature, the cumulative power consumption of the variable frequency condenser fan was 156 kWh.

[0061] In the compatibility test of different condensers, three sets of finned air-cooled condensers with different heat transfer areas and coefficients were used without modifying any preset parameters in the control program and keeping other test conditions consistent. Using the method of this implementation example, the condensing pressure stabilization time of all three sets of condensers did not exceed 15 seconds, and the pressure fluctuation range did not exceed ±0.04 MPa. Using the method of setting the initial speed at a normal ambient temperature, the shortest condensing pressure stabilization time of the three sets of condensers was 29 seconds, and the longest was 56 seconds. The minimum pressure fluctuation range was ±0.12 MPa, and the maximum was ±0.21 MPa. One set of condensers experienced a situation where the condensing pressure remained overpressure after startup, triggering the unit's high-pressure protection.

[0062] In the variable load test, while maintaining a constant ambient temperature, the unit load was gradually reduced from the rated load to 30% of the rated load. Using the method described in this example, the condenser fan started and stopped three times during the load adjustment process, and the condensing pressure quickly stabilized after each start-up, without any overpressure or excessively low pressure. Using the conventional method of setting the initial speed based on ambient temperature, the condenser fan started and stopped five times during the load adjustment process. Two of these starts resulted in a rapid drop in condensing pressure below the shutdown threshold, leading to frequent fan start-stops.

[0063] IV. Technical Effects The technical effectiveness of this implementation example can be directly demonstrated from the actual test results. By determining the initial fan speed by the rate of increase of condensing pressure, the actual cooling requirements of the unit can be accurately matched, significantly reducing the overshoot of condensing pressure, shortening the time for the unit to stabilize, avoiding unit instability caused by large fluctuations in condensing pressure, effectively ensuring the stability of the liquid supply driving force of the throttling device, and avoiding abnormal cooling effects.

[0064] This method does not require consideration of differences in the specifications of the condenser, such as heat transfer area and heat transfer coefficient. After replacing the condenser with a different specification, it can operate normally and stably without modifying the control parameters, which greatly improves the adaptability and compatibility of the control method. It can be applied to different models of air-cooled refrigeration units without the need to adjust the control parameters separately for different condensers, thus reducing the on-site commissioning cost of the unit.

[0065] This method allows the start-up, shutdown, and speed adjustment of the condenser fan to perfectly match the actual operating needs of the unit, reducing ineffective operation of the fan and avoiding frequent start-up and shutdown of the fan, thus significantly reducing the operating energy consumption of the condenser fan and improving the overall energy efficiency of the unit.

[0066] This method achieves a smooth transition in operating modes by operating at a fixed initial speed before switching the adjustment mode. This avoids system oscillations during speed adjustment, keeps the condensing pressure within a stable range, reduces the operating load on the compressor and condenser fan, minimizes frequent start-stop losses, and extends the service life of the unit's core components.

[0067] This method does not require any modification to the original hardware structure of the unit. It can be achieved simply by optimizing the control logic within the frequency converter. It is easy to implement, suitable for upgrading existing units, and easy to apply directly to newly produced units. It has high promotional value.

[0068] 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 variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, characterized in that, Includes the following steps: Step 1: When starting the refrigeration system, first start the compressor, keep the variable frequency fluid machinery on the condenser side in a stopped state, and collect the condensing pressure of the refrigeration system in real time through the condensing pressure sensor; Step 2: Based on the real-time collected condensing pressure, calculate the rate of increase of condensing pressure after the compressor starts and before the variable frequency fluid machinery starts. According to the preset rule that the rate of increase of condensing pressure is proportional to the initial speed, determine the initial speed of the variable frequency fluid machinery. Step 3: When the absolute value of the real-time collected condensation pressure is higher than the preset start-up pressure threshold, control the variable frequency fluid machinery to start operation at the determined initial start-up speed; Step 4: After the variable frequency fluid machinery starts running at the initial speed and maintains the preset initial speed for a set time, it switches to fuzzy PID control mode. Based on the deviation between the real-time collected condensing pressure and the preset condensing pressure setpoint, the speed adjustment signal is output through fuzzy PID calculation to adjust the running speed of the variable frequency fluid machinery in real time and maintain the condensing pressure stable near the preset condensing pressure setpoint. Step 5: When the absolute value of the real-time collected condensing pressure is lower than the preset shutdown pressure threshold, control the variable frequency fluid machinery to stop running, and repeat steps 1 and 2 to determine a new initial starting speed for the next start-up of the variable frequency fluid machinery.

2. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... The rate of increase of condensing pressure in step two is the change in condensing pressure per unit time, which is obtained by linear fitting calculation through multiple sets of continuously collected condensing pressure data.

3. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... The preset rule in step two is that the initial starting speed is equal to the preset reference speed multiplied by the ratio of the condensing pressure rise rate to the preset reference rise rate.

4. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... The starting pressure threshold in step three is preset based on the rated condensing pressure of the refrigeration system and the liquid supply driving force requirement of the throttling device, and the starting pressure threshold is higher than the preset condensing pressure setting value.

5. The variable frequency fluid mechanical speed control method for a refrigeration system based on the condensing pressure rise rate according to claim 1, characterized in that, The initial speed maintenance time in step four is preset based on the start-up characteristics of the variable frequency fluid machinery and the volume of the refrigeration system, with a value range of 5 to 30 seconds.

6. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... In the fuzzy PID control mode in step four, the deviation between the real-time value of the condensing pressure and the set value of the condensing pressure, as well as the rate of change of the deviation, are used as inputs. The proportional coefficient, integral coefficient, and derivative coefficient of the PID are corrected in real time through preset fuzzy rules, and the corresponding speed adjustment signal is output.

7. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... The shutdown pressure threshold in step five is preset based on the minimum stable operating condensing pressure of the refrigeration system, and the shutdown pressure threshold is lower than the preset condensing pressure setting value.

8. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... The variable frequency fluid machinery is a variable frequency condenser fan or a variable frequency cooling water pump that drives the flow of cooling medium in the condenser.

9. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, as described in claim 1, is characterized in that... The condensing pressure sensor is installed on the refrigerant inlet pipe of the condenser or the exhaust pipe of the compressor, and the condensing pressure collected is the exhaust condensing pressure of the refrigeration system.

10. The variable frequency fluid mechanical speed control method for a refrigeration system based on the rate of rise of condensing pressure, according to any one of claims 1-9, is characterized in that, The initial starting speed determined in step two shall not exceed the rated maximum speed of the variable frequency fluid machinery, and shall not be lower than the minimum stable operating speed of the variable frequency fluid machinery.

Images