A method and system for energy-saving control of chiller units

Abstract

This invention relates to the field of general control system technology, specifically to an energy-saving control method and system for a chiller unit. The method includes: dividing the CNC machine tool machining process into several monitoring periods; determining the chiller unit's demand during the CNC machine tool machining process within each monitoring period to select a target monitoring period; determining the chiller unit's cooling effect during the target monitoring period; determining the energy consumption of the chiller unit during the target monitoring period by combining the time interval between the rise in cutting temperature and the change in compressor speed; and determining the control coefficient of the variable frequency drive control system during the target monitoring period by combining the rise and fall of cutting temperature and ambient temperature, thereby controlling the compressor operating speed of the chiller unit. This invention achieves energy-saving control of the chiller unit by obtaining the control coefficient for energy-saving control of the chiller unit in the variable frequency control system and controlling the operating speed of the chiller unit's compressor.

Description

Technical Field

[0001] This invention relates to the field of general control system technology, and specifically to an energy-saving control method and system for a chiller unit. Background Technology

[0002] Chillers are primarily used to provide low-temperature cooling water and are widely used in air conditioning systems, industrial cooling, and food processing. With economic development, the frequency of use and load fluctuations of chillers have increased significantly, leading to a continuous rise in their energy consumption. Statistics show that the energy efficiency ratio of chillers is affected by ambient temperature, load changes, and the unit's operating status. To reduce energy consumption and improve system energy utilization efficiency, effective energy-saving control of chillers is urgently needed.

[0003] Existing problems: Although existing energy-saving control methods for chiller units have achieved energy saving and consumption reduction to a certain extent, there are still some shortcomings. For example, in the operation of existing energy-saving control methods, the distribution of hot and cold water in the water circulation system may be uneven, which leads to unstable cooling effect of the evaporator. In addition, during the exchange of hot and cold water, the heat transfer efficiency of the heat exchanger may be reduced due to water quality, resulting in insufficient heat exchange. Under this condition, the refrigerant cannot effectively absorb heat, thereby affecting the cooling capacity of the chiller unit and further increasing the energy consumption of the chiller unit. Summary of the Invention

[0004] This invention provides an energy-saving control method and system for chiller units to solve existing problems.

[0005] The present invention provides an energy-saving control method and system for a chiller unit, which adopts the following technical solution:

[0006] One embodiment of the present invention provides an energy-saving control method for a chiller unit, the method comprising the following steps:

[0007] During CNC machine tool processing, the cutting force, cutting temperature, machine tool vibration data, chiller inlet water temperature, chiller outlet water temperature, compressor speed, ambient temperature, and the time when the compressor speed changes at each moment are acquired.

[0008] The CNC machine tool machining process is divided into several monitoring periods. Based on the changes in cutting force, cutting temperature, and machine tool vibration data during the monitoring periods, the demand for chiller units during the CNC machine tool machining process is determined.

[0009] Based on the magnitude of the demand, target monitoring periods are selected; based on the rise and change of cutting temperature and the difference between the inlet and outlet water temperatures of the chiller unit during the target monitoring period, the cooling effect of the chiller unit during the target monitoring period is determined.

[0010] Based on the cooling effect, and combined with the time interval between the rise in cutting temperature and the change in compressor speed, the energy consumption of the chiller unit during the target monitoring period is determined.

[0011] Based on the energy consumption and the changes in cutting temperature and ambient temperature, the control coefficient of the variable frequency drive control system during the target monitoring period is determined.

[0012] The operating speed of the chiller unit's compressor is adjusted based on the aforementioned control coefficient and the compressor speed.

[0013] Furthermore, the specific steps for determining the demand for chiller units during CNC machine tool processing within the monitoring period are as follows:

[0014] During the t-th monitoring period, the information entropy of all extreme values ​​of the cutting force at all times is obtained. The average of the absolute values ​​of the differences between all adjacent extreme values ​​of the machine tool vibration data at all times is taken as the first average. The average of the time intervals between all adjacent extreme values ​​of the machine tool vibration data at all times is taken as the second average. The product of the ratio of the first average to the second average and the information entropy is taken as the instantaneous state of the CNC machine tool during the t-th monitoring period.

[0015] Obtain the mean square error between cutting force and cutting temperature at all times within the t-th monitoring period, and record the ratio of the instantaneous state to the mean square error as the demand of the chiller unit during the CNC machine tool machining process within the t-th monitoring period.

[0016] Furthermore, the specific steps for selecting the target monitoring period based on the magnitude of the demand are as follows:

[0017] In all monitoring periods, the monitoring periods are sorted in ascending order of the demand for chiller units during CNC machine tool processing to obtain a monitoring period sequence;

[0018] In the monitoring time period sequence, the maximum value of the absolute difference of the demand of the chiller unit during the CNC machine tool processing in all adjacent monitoring time periods is obtained, and the monitoring time period sequence is divided into the left segment and the right segment of the monitoring time period sequence from the middle of the adjacent monitoring time period corresponding to the maximum value.

[0019] Each monitoring period in the right segment of the monitoring period sequence is designated as the target monitoring period.

[0020] Furthermore, the specific steps for determining the cooling effect of the chiller unit during the target monitoring period are as follows:

[0021] During the i-th target monitoring period, the difference between the cutting temperature at time j and the cutting temperature at time j-1 is taken as the cutting temperature trend at time j. The time when the cutting temperature trend is positive is recorded as the cutting temperature rise time. The absolute value of the difference between the inlet and outlet water temperatures of the chiller unit at the x-th cutting temperature rise time is calculated. The ratio of the cutting temperature trend at the x-th cutting temperature rise time to the absolute value of the difference is recorded as the first ratio at the x-th cutting temperature rise time. The inverse proportional value of the mean of the first ratios at all cutting temperature rise times is taken as the cooling effect of the chiller unit during the i-th target monitoring period.

[0022] Furthermore, the specific steps for determining the energy consumption of the chiller unit during the target monitoring period are as follows:

[0023] Record the moment when the compressor speed changes each time as the speed adjustment moment;

[0024] Obtain the first corresponding speed adjustment time after the x-th cutting temperature rise time in the i-th target monitoring period;

[0025] Based on the time interval between the cutting temperature rise time and the response speed adjustment time, the response delay of the chiller unit control system in the i-th target monitoring period is determined;

[0026] The ratio of the response delay to the cooling effect of the chiller unit during the i-th target monitoring period is taken as the energy consumption of the chiller unit during the i-th target monitoring period.

[0027] Furthermore, the specific steps for determining the response delay of the chiller unit control system during the i-th target monitoring period based on the time interval between the cutting temperature rise time and the corresponding speed adjustment time are as follows:

[0028] During the i-th target monitoring period, the time interval between the x-th cutting temperature rise time and the corresponding speed adjustment time during the x-th cutting temperature rise time is obtained as the response duration of the x-th cutting temperature rise time. The average of the response durations of all cutting temperature rise times is used as the response delay of the chiller unit control system during the i-th target monitoring period.

[0029] Furthermore, the specific steps for determining the control coefficient of the variable frequency drive control system during the target monitoring period are as follows:

[0030] During the i-th target monitoring period, the difference between the ambient temperature at time y and the ambient temperature at time y-1 is taken as the ambient temperature trend at time y. The time when the ambient temperature trend is positive is recorded as the ambient temperature rise time. The mean of the ambient temperature at all times is calculated as the third mean. The absolute value of the difference between the ambient temperature trend and the cutting temperature trend at the g-th ambient temperature rise time is calculated as the trend difference value at the g-th ambient temperature rise time. The mean of the trend difference values ​​at all ambient temperature rise times is calculated as the fourth mean. The ratio of the third mean to the fourth mean is taken as the cooling loss of the chiller unit caused by the ambient temperature during the i-th target monitoring period.

[0031] Based on the cooling loss and energy consumption of the chiller caused by the ambient temperature during the i-th target monitoring period, the control coefficient of the variable frequency drive control system during the i-th target monitoring period is determined.

[0032] Furthermore, the specific steps for determining the control coefficient of the variable frequency drive control system during the i-th target monitoring period based on the cooling loss and energy consumption of the chiller caused by the ambient temperature during the i-th target monitoring period are as follows:

[0033] The normalized value of the product of the chiller's cooling loss caused by ambient temperature during the i-th target monitoring period and the chiller's energy consumption during the i-th target monitoring period is used as the control coefficient of the variable frequency drive control system during the i-th target monitoring period.

[0034] Furthermore, the specific steps for regulating the compressor operating speed of the chiller unit based on the regulation coefficient and the compressor speed are as follows:

[0035] If the current monitoring period is the target monitoring period, the compressor speed at the current moment is calculated as the product of the variable frequency drive control system's regulation coefficient during the current monitoring period. If the regulation coefficient of the variable frequency drive control system during the current monitoring period is greater than a preset judgment threshold, the sum of the compressor speed at the current moment and the product is taken as the regulated compressor operating speed. If the regulation coefficient of the variable frequency drive control system during the current monitoring period is less than or equal to the preset judgment threshold, the difference between the compressor speed at the current moment and the product is taken as the regulated compressor operating speed.

[0036] The present invention also proposes an energy-saving control system for a chiller unit, including a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the computer program stored in the memory to implement the steps of the aforementioned energy-saving control method for a chiller unit.

[0037] The beneficial effects of the technical solution of the present invention are:

[0038] In this embodiment, the CNC machine tool machining process is divided into several monitoring periods. Based on the changes in cutting force, cutting temperature, and machine tool vibration data within each monitoring period, the demand for chiller units during the CNC machine tool machining process is determined, thus identifying target monitoring periods. This is achieved by analyzing the actual machining state of the machining equipment and whether the machining state generates a large amount of heat, ensuring the accuracy of the timing for control. Furthermore, the cooling effect of the chiller unit is evaluated by observing the change in the outlet water temperature of the chiller unit during the temperature rise process. The energy consumption of the chiller unit during machining is explained by combining the response delay of the frequency converter control system to temperature changes. Then, the cooling loss under environmental conditions is analyzed by considering the temperature state of the environment in which the chiller unit is located. Finally, the control coefficient for energy-saving control of the chiller unit in the frequency converter control system is obtained. Thus, through the analysis of the instability of the cooling effect and the heat transfer efficiency of the hot and cold water exchange process, the control coefficient is obtained to ensure the cooling capacity of the chiller unit. Finally, the control coefficient is used to precisely control the compressor operating speed of the chiller unit. Thus, this invention achieves the goal of energy-saving control of the chiller unit by obtaining the control coefficient for energy-saving control of the chiller unit in the variable frequency control system and accurately controlling the operating speed of the chiller unit compressor. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart illustrating the steps of an energy-saving control method for a chiller unit according to the present invention.

[0041] Figure 2 This is a schematic diagram of the curve showing how machine tool vibration data changes over time. Detailed Implementation

[0042] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a chiller unit energy-saving control method and system proposed according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0044] The following description, in conjunction with the accompanying drawings, details a specific scheme for an energy-saving control method and system for a chiller unit provided by the present invention.

[0045] Please see Figure 1 The diagram illustrates a flowchart of an energy-saving control method for a chiller unit according to an embodiment of the present invention. The method includes the following steps:

[0046] Step S001: During the CNC machine tool machining process, acquire the cutting force, cutting temperature, machine tool vibration data, chiller inlet water temperature, chiller outlet water temperature, compressor speed, ambient temperature, and the time when the compressor speed changes each time.

[0047] It should be noted that in industrial production, especially in machinery manufacturing, electronic equipment production, and food processing, chillers serve as critical cooling equipment, responsible for maintaining the optimal operating temperature of equipment and processes. When a large machinery manufacturing plant's main products are high-precision CNC machine tools, these tools generate significant cutting heat during processing, leading to increased temperatures in tools and workpieces, thus affecting machining accuracy and tool lifespan. Increased energy consumption of chillers is due to the inability of existing energy-saving control systems to achieve precise load regulation and a lack of adaptive capabilities. Especially under drastic load changes, the equipment may experience over-cooling or under-cooling because traditional fixed-frequency and simple variable-frequency control systems lack flexibility and cannot respond to load changes in real time. Furthermore, under rapid load fluctuations, the response time of existing systems may be too long, causing the chiller unit to fail to adjust in time, resulting in energy waste.

[0048] During CNC machine tool processing, data such as cutting force, cutting temperature, machine tool vibration, inlet water temperature, outlet water temperature of the chiller unit, compressor speed, ambient temperature, and the time when the compressor speed changes are collected at every moment.

[0049] It should be noted that the data collection frequency is once per second, and this is used as an example for description. In this embodiment, the minimum-maximum normalization method is used to standardize the data of each dimension, unifying the dimensions of data in different dimensions. This is a well-known technique. Piezoelectric sensors, temperature sensors, and vibration sensors installed on the machine tool are used to directly measure the cutting force, cutting temperature, and machine tool vibration data generated during CNC machine tool machining. Temperature sensors and speed sensors at the water inlet and outlet are used to collect the inlet and outlet water temperatures of the chiller unit and the compressor speed, thereby statistically analyzing the time of each change in compressor speed. Temperature sensors are used to collect the ambient temperature of the CNC machine tool. The schematic diagram of the machine tool vibration data changing over time is shown below. Figure 2 As shown, Figure 2 The horizontal and vertical axes represent time in seconds, while the vertical axis represents machine tool vibration data (vibration velocity) in millimeters per second.

[0050] It should be further explained that in the energy-saving control methods and systems for chiller units, data acquisition is a key link in achieving precise control and optimizing energy efficiency. The main data includes, but is not limited to: temperature data (cooling water inlet temperature, outlet temperature, refrigerant evaporation temperature, and refrigerant condensation temperature), flow data (cooling chamber flow rate and refrigerant flow rate), pressure data (evaporator pressure and condenser pressure), and energy efficiency ratio data (real-time energy efficiency ratio and seasonal energy efficiency ratio). Sensors that meet environmental conditions should be selected and installed in key locations of the chiller unit, including the evaporator, condenser, cooling water pipes, and coolant pump. A data acquisition device (such as a PLC, embedded controller, or industrial computer) should be selected to collect signals, ensuring that it can receive multiple input signals. Appropriate communication interfaces should be configured to transmit sensor data to the data acquisition system. When the chiller unit starts working, the data acquisition system should be activated to record the collected data in real time to the database for subsequent data analysis and processing.

[0051] Step S002: Divide the CNC machine tool machining process into several monitoring periods; based on the changes in cutting force, cutting temperature, and machine tool vibration data during the monitoring periods, determine the demand for chiller units during the CNC machine tool machining process during the monitoring periods.

[0052] It should be noted that the actual machining state during the CNC machine tool processing is analyzed. By analyzing the changes in the machining state, it can be determined whether a lot of cutting heat is generated during the CNC machine tool processing. Frequent generation of cutting heat requires the chiller unit to respond quickly to ensure that the cooling effect matches the actual needs.

[0053] Preferably, in one embodiment of the present invention, the method for obtaining the demand for chiller units during CNC machine tool processing within a monitoring period includes:

[0054] A preset duration threshold S is used, which is 20 minutes in this embodiment. This will be used as an example for the description.

[0055] The CNC machine tool processing process is divided into several monitoring periods of duration S.

[0056] It should be noted that during the CNC machine tool processing, every 20 minutes is considered a monitoring period starting from the first moment. If the last monitoring period in which the current moment is located does not meet the 20-minute requirement, it is also considered a monitoring period.

[0057] During the t-th monitoring period, the extreme values ​​of the cutting force at all times are obtained using the first derivative method, and then the information entropy H of all extreme values ​​is obtained.

[0058] During the t-th monitoring period, the extreme values ​​of the machine tool vibration data at all times are obtained using the first derivative method. The absolute value of the difference between any two adjacent extreme values ​​and the time interval are calculated. The mean of the absolute values ​​of the differences between all two adjacent extreme values ​​is taken as the first mean, and the mean of the time intervals between all two adjacent extreme values ​​is taken as the second mean. The product of the ratio of the first mean to the second mean and the information entropy H is taken as the instantaneous state of the CNC machine tool during the t-th monitoring period.

[0059] It should be noted that both the first derivative method and information entropy are well-known techniques, and their specific methods will not be described here. Extreme values ​​include both maximum and minimum values. A higher information entropy indicates more frequent changes in the maximum and minimum values ​​of the cutting force data during machining, meaning that different degrees of load variation occurred during machining. The first mean reflects the average vibration amplitude during CNC machine tool machining, and the second mean reflects the vibration frequency during machining. Therefore, a greater instantaneous state indicates more frequent instantaneous changes in the actual machining process, meaning a higher frequency of switching in the chiller unit's operating state.

[0060] It should be noted that during CNC machine tool processing, changes in cutting force and vibration amplitude can indicate frequent switching of processing states to a certain extent. However, for chiller units, if the processing equipment does not generate corresponding temperature changes, there is no issue of untimely sensing by the chiller unit.

[0061] Obtain the mean square error between cutting force and cutting temperature at all times within the t-th monitoring period. The ratio of the instantaneous state of the CNC machine tool within the t-th monitoring period to this mean square error is denoted as the demand for chiller units during the CNC machine tool machining process within the t-th monitoring period.

[0062] It should be noted that the mean square error is a well-known technique, and the specific method will not be described here. The smaller the mean square error, the more similar the changes in cutting force and cutting temperature are within the monitoring period, that is, the closer the relationship between temperature changes and actual load within the monitoring period. The larger the ratio of instantaneous state to mean square error, the more frequent the switching of processing modes during the machining process generates a large amount of heat, which needs to be transferred by the chiller unit, that is, the higher the demand for the chiller unit.

[0063] Using the above method, the demand for chiller units during CNC machine tool processing is obtained for each monitoring period.

[0064] Step S003: Select the target monitoring period based on the magnitude of the demand; determine the cooling effect of the chiller during the target monitoring period based on the rise and change of the cutting temperature and the difference between the inlet and outlet water temperatures of the chiller unit.

[0065] It should be noted that during CNC machine tool machining, frequent switching of machining modes can generate a large amount of cutting heat, necessitating the use of chillers to dissipate this heat. If the chiller's detection of these heat changes is delayed, it will increase energy consumption, potentially leading to overheating or even damage to the machining equipment. Therefore, analyzing the chiller's perception of the machining status under frequent changes in CNC machine tool machining conditions is crucial to determining whether its actual operating response aligns with energy-saving control measures.

[0066] Preferably, in one embodiment of the present invention, the method for obtaining the cooling effect of the chiller unit during the target monitoring period includes:

[0067] In all monitoring periods, the monitoring periods are sorted in ascending order of the demand for chiller units during CNC machine tool processing to obtain a monitoring period sequence.

[0068] In the monitoring time period sequence, calculate the absolute value of the difference in the demand for chiller units during CNC machine tool processing in any two adjacent monitoring time periods, obtain the maximum value among the absolute values ​​of the difference in the demand for chiller units during CNC machine tool processing in all adjacent monitoring time periods, and divide the monitoring time period sequence into the left segment and the right segment of the monitoring time period sequence from the middle of the adjacent monitoring time period corresponding to the maximum value.

[0069] It should be noted that the demand in the monitoring time series increases sequentially from left to right. Therefore, the left segment of the monitoring time series can be considered a monitoring period with lower demand for chiller units, during which the switching frequency of CNC machine tool processing modes is lower. The right segment is considered a monitoring period with higher demand for chiller units, during which the switching frequency of CNC machine tool processing modes is higher.

[0070] Each monitoring period in the right segment of the monitoring period sequence is designated as the target monitoring period.

[0071] During the i-th target monitoring period, the difference between the cutting temperature at time j and the cutting temperature at time j-1 is taken as the cutting temperature trend at time j.

[0072] It should be noted that in this embodiment, the cutting temperature trend at the first moment of each target monitoring period is not analyzed. When the cutting temperature trend is positive, it indicates that the cutting temperature is showing an upward trend.

[0073] During the i-th target monitoring period, the moment when the cutting temperature trend is positive is recorded as the cutting temperature rise moment.

[0074] During the i-th target monitoring period, the absolute value of the difference between the inlet and outlet water temperatures of the chiller unit at the x-th cutting temperature rise time is calculated. The ratio of the cutting temperature trend at the x-th cutting temperature rise time to the absolute value of this difference is recorded as the first ratio at the x-th cutting temperature rise time. The inverse proportional value of the mean of the first ratios at all cutting temperature rise times is taken as the cooling effect of the chiller unit during the i-th target monitoring period.

[0075] It should be noted that in this implementation, the reciprocal of the mean is taken, and the mean is processed inversely proportionally, as illustrated by this example. The smaller the difference between the inlet and outlet water temperatures of the chiller unit, the less heat is discharged under the current rising cutting temperature, resulting in a greater temperature rise in the cutting process. Conversely, the smaller the temperature difference between the inlet and outlet water (i.e., the larger the first ratio), the worse the cooling effect of the chiller unit during operation. This means that the expectation of the cooling system needing to discharge more heat when the cutting temperature rises, which implies an increase in heat generated during the cutting process, is not met.

[0076] Step S004: Based on the cooling effect and the time interval between the rise in cutting temperature and the change in compressor speed, determine the energy consumption of the chiller unit during the target monitoring period.

[0077] It should be noted that the energy efficiency and cooling effect of a chiller unit are mutually reinforcing. A high-efficiency unit typically provides more stable cooling, while good cooling helps the unit operate efficiently and reduce energy consumption. Modern chillers are equipped with variable frequency drive systems. When the system load increases, causing the temperature to rise, the chiller unit can adjust the compressor speed to increase the refrigerant flow. Since the control system typically activates its corresponding measures after the temperature has risen, the compressor's adjustment time generally occurs after the temperature begins to rise.

[0078] Preferably, in one embodiment of the present invention, the method for obtaining the energy consumption of the chiller unit during the target monitoring period includes:

[0079] The moment when the compressor speed changes each time is recorded as the speed adjustment moment.

[0080] Obtain the first speed adjustment time after the x-th cutting temperature rise time in the i-th target monitoring period, and use it as the corresponding speed adjustment time for the x-th cutting temperature rise time.

[0081] It should be noted that if there is no corresponding speed adjustment time at a certain cutting temperature rise time, then this cutting temperature rise time will not be analyzed.

[0082] During the i-th target monitoring period, the time interval between the x-th cutting temperature rise time and the corresponding speed adjustment time during the x-th cutting temperature rise time is obtained as the response duration of the x-th cutting temperature rise time. The average of the response durations of all cutting temperature rise times is used as the response delay of the chiller unit control system during the i-th target monitoring period.

[0083] It should be noted that when the cutting temperature rises during the machining process, the variable frequency control system of the chiller does not respond to this temperature change in a timely manner, which leads to an increase in the energy consumption of the chiller. In other words, the longer the response time, the greater the delay in the operation time of the control system when the cutting temperature rises, that is, the higher the response delay of the control system.

[0084] The ratio of the response delay of the chiller control system to the cooling effect of the chiller during the i-th target monitoring period is taken as the energy consumption of the chiller during the i-th target monitoring period.

[0085] It should be noted that the greater the response delay, the greater the energy consumption, while the better the cooling effect, the lower the energy consumption. Therefore, the larger the ratio, the higher the energy consumption of the chiller unit under the current processing state of the CNC machine tool. This is because the energy consumption of the chiller unit increases due to the lag in the response of the frequency conversion control system to temperature changes.

[0086] Step S005: Based on the energy consumption and the changes in cutting temperature and ambient temperature, determine the control coefficient of the variable frequency drive control system during the target monitoring period.

[0087] It should be noted that in high-temperature environments, chiller units need to provide greater cooling capacity to maintain the normal operating temperature of equipment or processes. To cope with higher loads, the units may need to operate for longer periods, leading to increased energy consumption. In assessing the environmental conditions of the chiller unit under current conditions, it is generally found that chiller units consume more energy at higher ambient temperatures because the compressor must overcome higher exhaust temperatures to achieve cooling. This manifests as increased electricity required per unit of cooling capacity, thereby reducing overall energy efficiency.

[0088] Preferably, in one embodiment of the present invention, the method for obtaining the control coefficient of the variable frequency drive control system during the target monitoring period includes:

[0089] During the i-th target monitoring period, the difference between the ambient temperature at time y and the ambient temperature at time y-1 is taken as the trend of the ambient temperature at time y.

[0090] It should be noted that in this embodiment, the trend of ambient temperature at the first moment in each target monitoring period is not analyzed. When the ambient temperature trend is positive, it indicates that the ambient temperature is showing an upward trend.

[0091] During the i-th target monitoring period, the moment when the ambient temperature trend is positive is recorded as the moment of ambient temperature rise.

[0092] During the i-th target monitoring period, the mean of the ambient temperature at all times is calculated as the third mean. The absolute value of the difference between the trend of ambient temperature and the trend of cutting temperature at the g-th ambient temperature rise time is calculated as the trend difference value at the g-th ambient temperature rise time. The mean of the trend difference values ​​at all ambient temperature rise times is calculated and recorded as the fourth mean. The ratio of the third mean to the fourth mean is taken as the cooling loss of the chiller unit caused by the ambient temperature during the i-th target monitoring period.

[0093] It should be noted that if the chiller compressor is in a high-temperature environment, heat convection may occur during the chiller's heat dissipation process, leading to cooling losses. Specifically, a smaller trend difference value indicates that both the cutting temperature and ambient temperature are rising, potentially causing the compressor to be in a state of heat collision, resulting in cooling losses. Therefore, a larger ratio indicates that when the heat generated during machining rises, it may be in a high-temperature environment, thus affecting the chiller's cooling capacity and further increasing cooling losses.

[0094] The normalized value of the product of the chiller's cooling loss caused by ambient temperature during the i-th target monitoring period and the chiller's energy consumption during the i-th target monitoring period is used as the control coefficient of the variable frequency drive control system during the i-th target monitoring period.

[0095] It should be noted that in this embodiment, the norm() linear normalization function is used to normalize the above product, normalizing the data values ​​to the [0,1] interval. The greater the cooling loss and energy consumption, the greater the need to regulate the operating rate of the compressor in the chiller unit.

[0096] Step S006: Adjust the compressor operating speed of the chiller unit according to the control coefficient and the compressor speed.

[0097] Preferably, in one embodiment of the present invention, the method for obtaining the regulated compressor operating speed includes:

[0098] The preset judgment threshold is 0.5, and this will be used as an example for explanation.

[0099] If the current monitoring period is the target monitoring period, the compressor speed at the current moment is calculated as the product of the control coefficient of the variable frequency drive control system during the current monitoring period. If the control coefficient of the variable frequency drive control system during the current monitoring period is greater than the preset judgment threshold, the sum of the compressor speed at the current moment and the product is taken as the compressor operating speed after control. If the control coefficient of the variable frequency drive control system during the current monitoring period is less than or equal to the preset judgment threshold, the difference between the compressor speed at the current moment and the product is taken as the compressor operating speed after control.

[0100] It should be noted that: if the current monitoring period is not the target monitoring period, the demand for chiller units during CNC machine tool processing is low, and there is no need to adjust the compressor speed. When the control coefficient is greater than the preset judgment threshold, the CNC machine tool is considered to be in a high-load state. At this time, the compressor should run at a higher speed to meet the cooling demand, that is, increase the controlled compressor speed to meet the cooling demand during actual processing. When the control coefficient is less than or equal to the preset judgment threshold, the CNC machine tool is considered to be in a low-load state. At this time, the compressor speed can be reduced by adjusting the control coefficient to reduce energy consumption, that is, reduce the controlled compressor speed. Therefore, by combining real-time monitoring and frequency conversion control methods with the obtained compressor speed control coefficient, energy-saving control of the chiller unit can be effectively carried out, effectively reducing the energy consumption of the chiller unit.

[0101] The present invention also provides an energy-saving control system for a chiller unit, including a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the computer program stored in the memory to implement the steps of the aforementioned energy-saving control method for a chiller unit.

[0102] This invention is now complete.

[0103] In summary, in this embodiment of the invention, the CNC machine tool machining process is divided into several monitoring periods. Based on the changes in cutting force, cutting temperature, and machine tool vibration data within each monitoring period, the demand for chiller units during the CNC machine tool machining process is determined to identify target monitoring periods. Based on the changes in cutting temperature and the difference between the inlet and outlet water temperatures of the chiller unit within the target monitoring period, the cooling effect of the chiller unit during the target monitoring period is determined. Combining the time interval between the rise in cutting temperature and the change in compressor speed, the energy consumption of the chiller unit during the target monitoring period is determined. Furthermore, considering the changes in cutting temperature and ambient temperature, the control coefficient of the variable frequency drive control system is determined for the target monitoring period, thereby regulating the compressor operating speed of the chiller unit. This invention achieves the purpose of energy-saving control of the chiller unit by obtaining the control coefficient for energy-saving control of the chiller unit in the variable frequency control system and regulating the operating speed of the chiller unit compressor.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An energy-saving control method for a chiller unit, characterized in that, The method includes the following steps: During CNC machine tool processing, the cutting force, cutting temperature, machine tool vibration data, chiller inlet water temperature, chiller outlet water temperature, compressor speed, ambient temperature, and the time when the compressor speed changes at each moment are acquired. The CNC machine tool machining process is divided into several monitoring periods. Based on the changes in cutting force, cutting temperature, and machine tool vibration data during the monitoring periods, the demand for chiller units during the CNC machine tool machining process is determined. Based on the magnitude of the demand, target monitoring periods are selected; based on the rise and change of cutting temperature and the difference between the inlet and outlet water temperatures of the chiller unit during the target monitoring period, the cooling effect of the chiller unit during the target monitoring period is determined. Based on the cooling effect, and combined with the time interval between the rise in cutting temperature and the change in compressor speed, the energy consumption of the chiller unit during the target monitoring period is determined. Based on the energy consumption and the changes in cutting temperature and ambient temperature, the control coefficient of the variable frequency drive control system during the target monitoring period is determined. The operating speed of the chiller unit's compressor is adjusted based on the aforementioned control coefficient and the compressor speed.

2. The energy-saving control method for a chiller unit according to claim 1, characterized in that, The specific steps involved in determining the demand for chiller units during CNC machine tool processing within the monitoring period are as follows: During the t-th monitoring period, the information entropy of all extreme values ​​of the cutting force at all times is obtained. The average of the absolute values ​​of the differences between all adjacent extreme values ​​of the machine tool vibration data at all times is taken as the first average. The average of the time intervals between all adjacent extreme values ​​of the machine tool vibration data at all times is taken as the second average. The product of the ratio of the first average to the second average and the information entropy is taken as the instantaneous state of the CNC machine tool during the t-th monitoring period. Obtain the mean square error between cutting force and cutting temperature at all times within the t-th monitoring period, and record the ratio of the instantaneous state to the mean square error as the demand of the chiller unit during the CNC machine tool machining process within the t-th monitoring period.

3. The energy-saving control method for a chiller unit according to claim 1, characterized in that, The specific steps for selecting the target monitoring period based on the magnitude of demand are as follows: In all monitoring periods, the monitoring periods are sorted in ascending order of the demand for chiller units during CNC machine tool processing to obtain a monitoring period sequence; In the monitoring time period sequence, the maximum value of the absolute difference of the demand of the chiller unit during the CNC machine tool processing in all adjacent monitoring time periods is obtained, and the monitoring time period sequence is divided into the left segment and the right segment of the monitoring time period sequence from the middle of the adjacent monitoring time period corresponding to the maximum value. Each monitoring period in the right segment of the monitoring period sequence is designated as the target monitoring period.

4. The energy-saving control method for a chiller unit according to claim 1, characterized in that, The specific steps for determining the cooling effect of the chiller unit during the target monitoring period are as follows: During the i-th target monitoring period, the difference between the cutting temperature at time j and the cutting temperature at time j-1 is taken as the cutting temperature trend at time j. The time when the cutting temperature trend is positive is recorded as the cutting temperature rise time. The absolute value of the difference between the inlet and outlet water temperatures of the chiller unit at the x-th cutting temperature rise time is calculated. The ratio of the cutting temperature trend at the x-th cutting temperature rise time to the absolute value of the difference is recorded as the first ratio at the x-th cutting temperature rise time. The inverse proportional value of the mean of the first ratios at all cutting temperature rise times is taken as the cooling effect of the chiller unit during the i-th target monitoring period.

5. The energy-saving control method for a chiller unit according to claim 1, characterized in that, The specific steps for determining the energy consumption of the chiller unit during the target monitoring period are as follows: Record the moment when the compressor speed changes each time as the speed adjustment moment; Obtain the first corresponding speed adjustment time after the x-th cutting temperature rise time in the i-th target monitoring period; Based on the time interval between the cutting temperature rise time and the response speed adjustment time, the response delay of the chiller unit control system in the i-th target monitoring period is determined; The ratio of the response delay to the cooling effect of the chiller unit during the i-th target monitoring period is taken as the energy consumption of the chiller unit during the i-th target monitoring period.

6. The energy-saving control method for a chiller unit according to claim 5, characterized in that, The specific steps for determining the response delay of the chiller unit control system during the i-th target monitoring period based on the time interval between the cutting temperature rise time and the corresponding speed adjustment time are as follows: During the i-th target monitoring period, the time interval between the x-th cutting temperature rise time and the corresponding speed adjustment time during the x-th cutting temperature rise time is obtained as the response duration of the x-th cutting temperature rise time. The average of the response durations of all cutting temperature rise times is used as the response delay of the chiller unit control system during the i-th target monitoring period.

7. The energy-saving control method for a chiller unit according to claim 4, characterized in that, The specific steps for determining the control coefficient of the variable frequency drive control system during the target monitoring period are as follows: During the i-th target monitoring period, the difference between the ambient temperature at time y and the ambient temperature at time y-1 is taken as the ambient temperature trend at time y. The time when the ambient temperature trend is positive is recorded as the ambient temperature rise time. The mean of the ambient temperature at all times is calculated as the third mean. The absolute value of the difference between the ambient temperature trend and the cutting temperature trend at the g-th ambient temperature rise time is calculated as the trend difference value at the g-th ambient temperature rise time. The mean of the trend difference values ​​at all ambient temperature rise times is calculated as the fourth mean. The ratio of the third mean to the fourth mean is taken as the cooling loss of the chiller unit caused by the ambient temperature during the i-th target monitoring period. Based on the cooling loss and energy consumption of the chiller caused by the ambient temperature during the i-th target monitoring period, the control coefficient of the variable frequency drive control system during the i-th target monitoring period is determined.

8. The energy-saving control method for a chiller unit according to claim 7, characterized in that, The specific steps for determining the control coefficient of the variable frequency drive control system during the i-th target monitoring period based on the cooling loss and energy consumption of the chiller caused by the ambient temperature are as follows: The normalized value of the product of the chiller's cooling loss caused by ambient temperature during the i-th target monitoring period and the chiller's energy consumption during the i-th target monitoring period is used as the control coefficient of the variable frequency drive control system during the i-th target monitoring period.

9. The energy-saving control method for a chiller unit according to claim 1, characterized in that, The specific steps for regulating the compressor operating speed of the chiller unit based on the regulation coefficient and the compressor speed are as follows: If the current monitoring period is the target monitoring period, the compressor speed at the current moment is calculated as the product of the variable frequency drive control system's regulation coefficient during the current monitoring period. If the regulation coefficient of the variable frequency drive control system during the current monitoring period is greater than a preset judgment threshold, the sum of the compressor speed at the current moment and the product is taken as the regulated compressor operating speed. If the regulation coefficient of the variable frequency drive control system during the current monitoring period is less than or equal to the preset judgment threshold, the difference between the compressor speed at the current moment and the product is taken as the regulated compressor operating speed.

10. An energy-saving control system for a chiller unit, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is executed by the processor, it implements the steps of the energy-saving control method for a chiller unit as described in any one of claims 1-9.

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