Optimal control method and device for variable frequency screw chiller and air conditioning unit

Abstract

The present application discloses an optimization control method, device and air conditioning unit for a variable frequency screw chiller. The control method for the variable frequency screw chiller includes the following steps: obtaining the actual water temperature and the user's set water temperature; determining the adjustment mode of the compressor and performing water temperature control according to the difference between the actual water temperature and the set water temperature; obtaining the current operating parameters of the compressor when performing water temperature control, and controlling the compressor to execute the corresponding operating strategy to avoid unfavorable operating conditions according to the comparison results of the current operating parameters and the set operating parameters. By intelligently determining the best operating strategy and avoiding unfavorable operating conditions, the control method automatically optimizes according to the current cooling demand, so that the screw compressor can be controlled by frequency conversion without changing the internal structure of the compressor, without affecting the adjustable range of the compressor.

Description

Technical Field

[0001] The present application relates to the technical field of air conditioning, and in particular to an optimization control method and device for a variable frequency screw chiller and an air conditioning unit. Background Art

[0002] Compared with fixed-frequency screw compressors, variable-frequency screw compressors have the advantages of more energy saving and smoother and more accurate water temperature regulation, but the compressor needs to be specially designed to achieve variable-frequency control. When energy-saving transformation is carried out on the units that have been put into use, since the compressor does not have a variable-frequency design, it is impossible to achieve energy-saving control of the compressor by changing the control method. In addition, conventional fixed-frequency compressors use variable-frequency control methods to avoid the compressor's poor operating points by sacrificing the unit's adjustable range, and its adjustable range becomes narrower, which to a certain extent limits the energy-saving effect of variable-frequency screw compressors and the accuracy of water temperature adjustable control. Summary of the invention

[0003] The purpose of the present application is to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes an optimization control method for a variable frequency screw chiller, which can control the screw compressor through variable frequency without changing the internal structure of the compressor, intelligently determine the best operating strategy and avoid unfavorable operating conditions without affecting the energy adjustment range of the compressor, and automatically optimize the control according to the current cooling demand.

[0004] The application also proposes a control device.

[0005] The present application also proposes an air conditioning unit including the above control device.

[0006] The present application also proposes a storage medium for storing the optimization control method of the variable frequency screw chiller.

[0007] According to the first aspect of the present application, the optimal control method for a variable frequency screw chiller comprises the following steps:

[0008] Get the actual water temperature and the user's set water temperature;

[0009] According to the difference between the actual water temperature and the set water temperature, determine the adjustment mode of the compressor and perform water temperature control;

[0010] When performing water temperature control, the current operating parameters of the compressor are obtained, and based on the comparison results between the current operating parameters and the set operating parameters, the compressor is controlled to execute a corresponding operating strategy to avoid unfavorable operating conditions.

[0011] The optimization control method for a variable frequency screw chiller according to the first aspect of the present application has at least the following beneficial effects: by intelligently determining the best operating strategy and avoiding unfavorable operating conditions, the optimal control method is automatically optimized according to the current cooling demand, thereby enabling the screw compressor to be controlled by variable frequency without changing the internal structure of the compressor and without affecting the energy adjustment range of the compressor.

[0012] According to the optimization control method of the variable frequency screw chiller described in the first aspect of the present application, the method for determining the adjustment mode of the compressor according to the temperature difference between the actual water temperature and the set water temperature includes:

[0013] Set the water temperature to T Wset , the actual water temperature is set as T, and the temperature interval is divided based on the set water temperature, where the temperature interval includes the load increase area, frequency increase area, slide valve holding area, frequency holding area, load reduction area, frequency reduction area and shutdown area. The frequency increase area is closer to the frequency holding area than the load increase area, and the frequency reduction area is closer to the frequency holding area than the load reduction area. D and A are constants;

[0014] When T ≥ T Wset When +D / 2(℃), the actual water temperature is in the load increase area and frequency increase area;

[0015] When T Wset +0.2≤T<T Wset +D / 2(℃), the actual water temperature is in the frequency increasing area and the slide valve holding area;

[0016] When T Wset -0.2(℃)≤T<T Wset +0.2(℃), the actual water temperature is in the slide valve holding area and frequency holding area;

[0017] When T Wset -D / 2(℃)≤T<T Wset When -0.2(℃), the actual water temperature is in the slide valve holding area and frequency reduction area;

[0018] When T Wset -D / 2-A(℃)≤T<T Wset -D / 2(℃), the actual water temperature is in the load reduction and frequency reduction areas;

[0019] When T<T Wset -D / 2-A(℃), the actual water temperature is in the shutdown area;

[0020] The adjustment mode of the compressor is determined according to the temperature range in which the actual water temperature is located and the water temperature is controlled.

[0021] According to the optimization control method of the variable frequency screw chiller described in the first aspect of the present application, the method for determining the adjustment mode of the compressor includes:

[0022] When the actual water temperature is in the load increase area and frequency increase area, the load increase of the compressor is achieved by simultaneously controlling the compressor slide valve load increase and the compressor operating frequency increase;

[0023] When the actual water temperature is in the frequency increasing area and the slide valve holding area, the compressor slide valve maintains the current position, and the motor speed of the compressor is controlled by frequency control, thereby realizing the load control of the compressor;

[0024] When the actual water temperature is in the slide valve holding area and the frequency holding area, the operating frequency and slide valve control of the compressor remain unchanged at the current state;

[0025] When the actual water temperature is in the slide valve holding area and the frequency reduction area, the compressor slide valve maintains the current position, and the motor speed of the compressor is controlled by frequency control, thereby realizing the load control of the compressor;

[0026] When the actual water temperature is in the load reduction area and the frequency reduction area, the load reduction of the compressor is achieved by simultaneously controlling the compressor slide valve to reduce the load and the compressor operating frequency to reduce the load;

[0027] When the actual water temperature is in the shutdown zone, the compressor slide valve does not move and the operating frequency of the compressor returns to zero.

[0028] According to the optimization control method of the variable frequency screw chiller described in the first aspect of the present application, the method for determining the adjustment mode of the compressor and performing water temperature control includes:

[0029] When the actual water temperature is in the load increase area and frequency increase area, the load increase signal is continuously output for a1 seconds every interval of n*t seconds, where n is a positive integer, to increase the load of the compressor slide valve, and the frequency increase signal is output every interval of t seconds to increase the frequency of the compressor;

[0030] When the actual water temperature is in the frequency increase zone and the slide valve holding zone, the slide valve maintains the current position and outputs a frequency increase signal every t seconds to increase the operating frequency of the compressor;

[0031] When the actual water temperature is in the slide valve holding area and the frequency holding area, the slide valve maintains the current position and the operating frequency of the compressor remains unchanged;

[0032] When the actual water temperature is in the slide valve holding area and the frequency reduction area, the slide valve maintains the current position and outputs a frequency reduction signal every t seconds to reduce the frequency of the compressor;

[0033] When the actual water temperature is in the load reduction area and the frequency reduction area, the load reduction signal is continuously output for a2 seconds at each interval of n*t seconds, where n is a positive integer, to reduce the load of the compressor slide valve, and the frequency reduction signal is output at each interval of t seconds to reduce the frequency of the compressor;

[0034] When the actual water temperature is in the shutdown zone, the slide valve does not move and the operating frequency of the compressor returns to zero.

[0035] According to the optimization control method for a variable frequency screw chiller described in the first aspect of the present application, the operating parameters include an average current change rate. According to the comparison result between the average current change rate Q of the current unit and the set change rate A, the compressor executes a corresponding operating strategy to avoid an unfavorable operating condition point, including:

[0036] When the actual water temperature is in the load increase area, set the change rate A1 to 13%, A2 = A1-1%, when the average current change rate Q> change rate A1, the compressor outputs 0.2 seconds of load reduction every 10 seconds, and the frequency is increased by 7HZ until the average current change rate Q≤change rate A2;

[0037] When the actual water temperature is in the frequency increase zone, set the change rate A1 to 10%, A2 = A1-0.8%, when the average current change rate Q> change rate A1, the compressor outputs 0.2 seconds of load reduction every 15 seconds, and the frequency is increased by 5HZ until the average current change rate Q≤change rate A2;

[0038] When the actual water temperature is in the slide valve holding area and the frequency holding area, set the change rate A1 to 5%, A2 = A1-0.5%, when the average current change rate Q> change rate A1, the compressor outputs 0.3 seconds of load increase at intervals of 25 seconds, and the frequency is reduced by 3HZ until the average current change rate Q≤change rate A2;

[0039] When the actual water temperature is in the frequency reduction zone, set the change rate A1 to 10%, A2 = A1-0.8%, when the average current change rate Q> change rate A1, the compressor outputs 0.1 second load increase every 15 seconds, and the frequency is reduced by 5HZ until the average current change rate Q≤ change rate A2;

[0040] When the actual water temperature is in the load reduction zone, set the change rate A1 to 12%, A2 = A1-1%, when the average current change rate Q> change rate A1, the compressor outputs 0.1 second load increase every 10 seconds, and the frequency is reduced by 6HZ until the average current change rate Q≤change rate A2.

[0041] According to the optimization control method for a variable frequency screw chiller described in the first aspect of the present application, the operating parameters include an instantaneous COP change rate. According to the comparison result between the instantaneous COP change rate P of the current unit and the set change rate B, the compressor executes a corresponding operating strategy to avoid an unfavorable operating condition point, including:

[0042] When the actual water temperature is in the load-increasing zone, the change rate B1 is set to 1.5%, B2 = B1-1%, and when the instantaneous COP change rate P> change rate B1, the compressor outputs a 0.1 second load reduction at intervals of 10 seconds, and the frequency is increased by 3HZ until the instantaneous COP change rate P ≤ change rate B2;

[0043] When the actual water temperature is in the frequency increase zone, set the change rate B1 to 0.7%, B2 = B1-0.8%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load reduction every 15 seconds, and the frequency is increased by 2HZ until the instantaneous COP change rate P≤ change rate B2;

[0044] When the actual water temperature is in the slide valve holding area and the frequency holding area, set the change rate B1 to 0.5%, B2 = B1-0.5%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load increase at intervals of 25 seconds, and the frequency decreases by 1HZ until the instantaneous COP change rate P ≤ change rate B2;

[0045] When the actual water temperature is in the frequency reduction zone, set the change rate B1 to 0.7%, B2 = B1-0.8%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load increase every 15 seconds, and the frequency is reduced by 3HZ until the instantaneous COP change rate P ≤ change rate B2;

[0046] When the actual water temperature is in the load reduction zone, set the change rate B1 to 1.5%, B2 = B1-1%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load increase at intervals of 10 seconds, and the frequency is reduced by 6HZ until the instantaneous COP change rate P ≤ change rate B2.

[0047] According to the optimization control method of the variable frequency screw chiller described in the first aspect of the present application, the operating parameters include the pipeline vibration value, and according to the comparison result of the current unit pipeline vibration value Z and the set vibration value C, the compressor executes the corresponding operating strategy to avoid the unfavorable operating condition point, including:

[0048] When the actual water temperature is in the load-increasing zone, the change rate C1 is set to 2, C2 = C1-1%, and when the pipeline vibration value Z> the set vibration value C1, the compressor outputs a 1-second load reduction at intervals of 10 seconds, and the frequency is increased by 3HZ until the pipeline vibration value Z≤the set vibration value C2;

[0049] When the actual water temperature is in the frequency increase zone, the change rate C1 is set to 1.5, C2 = C1-0.8%, when the pipeline vibration value Z> the set vibration value C1, the compressor outputs 0.5 seconds of load reduction every 15 seconds, and the frequency is increased by 2HZ until the pipeline vibration value Z≤the set vibration value C2;

[0050] When the actual water temperature is in the slide valve holding area and the frequency holding area, the change rate C1 is set to 1, C2 = C1-0.5%, when the pipeline vibration value Z> the set vibration value C1, the compressor outputs 0.3 seconds of load increase at intervals of 25 seconds, and the frequency is reduced by 1HZ until the pipeline vibration value Z≤the set vibration value C2;

[0051] When the actual water temperature is in the frequency reduction zone, the change rate C1 is set to 1.5, C2 = C1-0.8%, when the pipeline vibration value Z> the set vibration value C1, the compressor outputs 0.1 second load increase every 15 seconds, and the frequency is reduced by 3HZ until the pipeline vibration value Z≤the set vibration value C2;

[0052] When the actual water temperature is in the load reduction zone, the change rate C1 is set to 2, C2 = C1-1%. When the pipeline vibration value Z> the set vibration value C1, the compressor outputs a 0.2 second load increase at intervals of 10 seconds, and the frequency is reduced by 6HZ until the pipeline vibration value Z≤the set vibration value C2.

[0053] According to the second aspect of the present application, the control device described in the embodiment includes:

[0054] An acquisition module is used to obtain the actual water temperature and the user's set water temperature;

[0055] The regulating module is used to set the water temperature difference according to the actual water temperature, determine the regulating mode of the compressor and perform water temperature control;

[0056] The control module is used to obtain the current operating parameters of the compressor, and control the compressor to execute a corresponding operating strategy to avoid an unfavorable operating condition point according to a comparison result between the current operating parameters and the set operating parameters.

[0057] An air conditioning unit according to an embodiment of the third aspect of the present application includes: a control device as described in the embodiment of the second aspect of the present application.

[0058] According to the storage medium of the fourth aspect embodiment of the present application, includes: at least one instruction is stored in the storage medium, and the instruction is loaded and executed by the processor to implement the operation performed by the optimization control method of the variable frequency screw chiller in the first aspect embodiment.

[0059] It is not difficult to understand that the control device in the embodiment of the second aspect of the present application, the air-conditioning unit in the embodiment of the third aspect of the present application, and the storage medium in the embodiment of the fourth aspect of the present application all have the technical effects of the optimal control method of the variable frequency screw chiller in the embodiment of the first aspect, and therefore will not be elaborated upon.

[0060] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present application is further described below with reference to the accompanying drawings and embodiments;

[0062] Figure 1 A system schematic diagram of an embodiment of the present application;

[0063] Figure 2 This is a control flow chart of an embodiment of the present application. DETAILED DESCRIPTION

[0064] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0065] In the description of the present application, it should be understood that descriptions involving orientation, such as up, down, front, back, left, right, etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0066] In the description of this application, "several" means one or more, "more" means at least two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0067] In the description of this application, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in this application after combining the specific content of the technical solution.

[0068] It is understandable that the energy-saving control of central air conditioners has attracted much attention in the industry. Compared with traditional fixed-frequency screw compressors, variable-frequency screw compressors have the advantages of more energy-saving in partial load operation and more stable and accurate water temperature regulation. The variable-frequency screw chillers in related technologies are mainly realized in the following two ways:

[0069] The first method is to change the internal design of the compressor, including: 1. Use a screw specially designed for frequency conversion. Compared with conventional fixed-frequency compressors, its rotor specifications are small, and the bearings and structural components are designed with frequency conversion. 2. Through the lengthened design of the adjustable slide valve, the slide valve can cover the rotor cavity throughout the entire stroke. The compressor controls the speed of the compressor motor through frequency conversion, thereby achieving adjustable control. 3. By adding a compressor slide valve indicator, the position of the slide valve is controlled by controlling the internal and external pressures of the compressor to achieve variable pressure ratio frequency control. The above three methods all require changing the internal structure of the compressor to achieve variable frequency control of the compressor.

[0070] The second method includes: the fixed-frequency compressor is directly driven by the frequency converter, and the control method is usually to change the motor speed by increasing / decreasing the frequency, thereby increasing / decreasing the compressor exhaust volume. The frequency or slide valve can be further adjusted in stages through priority frequency control or priority slide valve control. However, the frequency change and slide valve position of this control method are responsible for different stages of energy regulation. During the frequency change process, low frequency leads to an increase in the leakage rate between rotors, a decrease in motor efficiency, and an increase in the risk of shaft seal leakage; the slide valve unloading process still causes obvious performance degradation. During the entire energy regulation process, the internal and external pressure ratio of the compressor cannot be matched, the motor efficiency is low, and the operating conditions of the compressor deviate from the design optimum, so the performance is relatively poor. Similarly, when the slide valve is reduced to the maximum bypass volume (that is, the slide valve is at the lowest load position), the frequency control will also cause the problem of internal and external pressure ratio not matching and internal leakage increasing.

[0071] The above two forms of variable frequency control methods have the following disadvantages:

[0072] 1. The compressor needs to be specially designed to achieve variable frequency control. When the energy-saving transformation of the units that have been put into use is carried out, since the compressor does not have a variable frequency design, it is impossible to achieve energy-saving control of the compressor by changing the control method.

[0073] 2. Conventional fixed-frequency compressors use variable frequency control methods to avoid poor operating points of the compressor by sacrificing the adjustable range of the unit. The adjustable range becomes narrower, which to a certain extent limits the energy-saving effect of the variable frequency screw compressor and the accuracy of water temperature adjustable control.

[0074] Reference Figure 1 to Figure 2 The optimization control method of the variable frequency screw chiller of the first aspect of the present application comprises the following steps:

[0075] Acquire the actual water temperature and the user's set water temperature; in some embodiments, the water temperature control object can be the outlet water temperature or the inlet water temperature, which can be adaptively adjusted according to usage requirements;

[0076] According to the difference between the actual water temperature and the set water temperature, determine the adjustment mode of the compressor and perform water temperature control;

[0077] When performing water temperature control, the current operating parameters of the compressor are obtained. According to the comparison results between the current operating parameters and the set operating parameters, the compressor is controlled to execute the corresponding operating strategy to avoid the unfavorable operating condition point.

[0078] It is understandable that this variable frequency screw chiller follows the water temperature control operation strategy under normal conditions. When the comparison result between the current operating parameters of the compressor and the set operating parameters reaches the preset conditions, it means that the number of effective sealing teeth of the variable frequency compressor is reduced when running under low load, and the internal and external leakage of the rotor is greatly increased, which leads to a sharp drop in the isentropic efficiency and volumetric efficiency of the compressor, and the operating efficiency is low. In some embodiments, it is usually manifested as an increase in operating current, abnormal vibration of the pipeline, and a decrease in instantaneous COP. At this time, the automatic optimization control condition is entered, and the compressor executes the corresponding operation strategy including but not limited to controlling the load increase or load reduction of the compressor slide valve, the increase or decrease of the compressor operating frequency, etc., until the automatic optimization control condition is exited and the adjustment mode controlled by water temperature is restored.

[0079] Reference Figure 1 to Figure 2 The optimal control method for the variable frequency screw chiller of the first aspect of the present application intelligently determines the optimal operating strategy and avoids unfavorable operating conditions, and automatically optimizes the control method according to the current cooling demand, so that the screw compressor 1 can be controlled by variable frequency without changing the internal structure of the compressor, without affecting the energy adjustment range of the compressor.

[0080] In some embodiments of the present application, the method for determining the adjustment mode of the compressor according to the temperature difference between the actual water temperature and the set water temperature includes:

[0081] Set the water temperature to T Wset , the actual water temperature is set as T, and the temperature interval is divided based on the set water temperature, where the temperature interval includes the load increase area, frequency increase area, slide valve holding area, frequency holding area, load reduction area, frequency reduction area and shutdown area. The frequency increase area is closer to the frequency holding area than the load increase area, and the frequency reduction area is closer to the frequency holding area than the load reduction area. D and A are constants;

[0082] When T ≥ T Wset When +D / 2(℃), the actual water temperature is in the load increase area and frequency increase area;

[0083] When T Wset +0.2≤T<T Wset +D / 2(℃), the actual water temperature is in the frequency increasing area and the slide valve holding area;

[0084] When T Wset -0.2(℃)≤T<T Wset +0.2(℃), the actual water temperature is in the slide valve holding area and frequency holding area;

[0085] When T Wset -D / 2(℃)≤T<T Wset When -0.2(℃), the actual water temperature is in the slide valve holding area and frequency reduction area;

[0086] When T Wset -D / 2-A(℃)≤T<T Wset -D / 2(℃), the actual water temperature is in the load reduction and frequency reduction areas;

[0087] When T<T Wset -D / 2-A(℃), the actual water temperature is in the shutdown area;

[0088] The adjustment mode of the compressor is determined according to the temperature range in which the actual water temperature is located and the water temperature is controlled.

[0089] It can be understood that by dividing the temperature range, the control strategy of the variable frequency screw chiller is optimized, and the corresponding control mode is set according to different ranges, so as to meet the use needs while reducing energy consumption.

[0090] In some embodiments of the present application, the method for determining the adjustment mode of the compressor includes:

[0091] When the actual water temperature is in the load increase area and frequency increase area, the load increase of the compressor is achieved by simultaneously controlling the compressor slide valve load increase and the compressor operating frequency increase;

[0092] When the actual water temperature is in the frequency increasing area and the slide valve holding area, the compressor slide valve maintains the current position, and the motor speed of the compressor is controlled by frequency control, thereby realizing the load control of the compressor;

[0093] When the actual water temperature is in the slide valve holding area and the frequency holding area, the operating frequency and slide valve control of the compressor remain unchanged at the current state;

[0094] When the actual water temperature is in the slide valve holding area and the frequency reduction area, the compressor slide valve maintains the current position, and the motor speed of the compressor is controlled by frequency control, thereby realizing the load control of the compressor;

[0095] When the actual water temperature is in the load reduction area and the frequency reduction area, the load reduction of the compressor is achieved by simultaneously controlling the compressor slide valve to reduce the load and the compressor operating frequency to reduce the load;

[0096] When the actual water temperature is in the shutdown zone, the compressor slide valve does not move and the operating frequency of the compressor returns to zero.

[0097] It can be understood that by adjusting the frequency or slide valve in stages through priority frequency control and / or priority slide valve control, in conjunction with the automatic optimization control method, it is possible not only to change the motor speed by increasing / decreasing the frequency, thereby increasing / decreasing the compressor exhaust volume, but also to avoid as much as possible the increase in rotor leakage rate, decrease in motor efficiency, and increase in shaft seal leakage risk due to low frequency during the frequency change process; the slide valve unloading process still causes obvious performance degradation.

[0098] In some embodiments of the present application, the method for determining the adjustment mode of the compressor and performing water temperature control includes:

[0099] When the actual water temperature is in the load increase area and frequency increase area, the load increase signal is continuously output for a1 seconds every interval of n*t seconds, where n is a positive integer, to increase the load of the compressor slide valve, and the frequency increase signal is output every interval of t seconds to increase the frequency of the compressor;

[0100] When the actual water temperature is in the frequency increase zone and the slide valve holding zone, the slide valve maintains the current position and outputs a frequency increase signal every t seconds to increase the operating frequency of the compressor;

[0101] When the actual water temperature is in the slide valve holding area and the frequency holding area, the slide valve maintains the current position and the operating frequency of the compressor remains unchanged;

[0102] When the actual water temperature is in the slide valve holding area and the frequency reduction area, the slide valve maintains the current position and outputs a frequency reduction signal every t seconds to reduce the frequency of the compressor;

[0103] When the actual water temperature is in the load reduction area and the frequency reduction area, the load reduction signal is continuously output for a2 seconds at each interval of n*t seconds, where n is a positive integer, to reduce the load of the compressor slide valve, and the frequency reduction signal is output at each interval of t seconds to reduce the frequency of the compressor;

[0104] When the actual water temperature is in the shutdown zone, the slide valve does not move and the operating frequency of the compressor returns to zero.

[0105] It is understandable that when the unit is just started, due to the high inlet water temperature of the evaporator 4, the user sets the water temperature T Wset =7℃, at this time the water temperature of evaporator 4 is T≥T Wset+D / 2(℃), the water temperature is in the load increase area and frequency increase area. According to the water temperature control in Table 1, the adjustable period of frequency control is t (the default is 9 seconds, which can be set), and the adjustable period of slide valve control is n*t seconds (n is a positive integer, which can be set). The frequency control has a shorter period than the slide valve control, and can control the change of water temperature more finely. Furthermore, the frequency increase control method is to perform PID control based on the difference between the water temperature and the set water temperature. PID control is a common technical knowledge and will not be described here. The load increase control method is: every interval of the adjustable period n*t seconds, continuously output a1 second load increase solenoid valve opening signal. By simultaneously controlling the slide valve load increase of the compressor and the frequency increase of the compressor, the load of the compressor can be quickly increased.

[0106] As the load of the unit increases, the water temperature gradually decreases, and the water temperature of the evaporator 4 is close to the user set temperature T Wset The difference decreases, and the water temperature T of the evaporator 4 Wset +0.2≤T<T Wset +D / 2(℃), the water temperature is in the frequency increase area and the slide valve holding area. At this time, the frequency control can be adjusted for a period of t (9 seconds by default, which can be set). The compressor slide valve maintains the current position (the load increase and load reduction solenoid valves do not work). The compressor motor speed is controlled only by frequency control, thereby achieving the load control of the compressor. At this time, the frequency increase control method is to perform PID control based on the difference between the water temperature and the set water temperature.

[0107] When the water temperature is further reduced, the water temperature of the evaporator 4 is equal to the user set temperature T Wset The difference decreases, and the water temperature T of the evaporator 4 Wset -0.2(℃)≤T<T Wset +0.2(℃), the water temperature is in the slide valve holding area and the frequency holding area, then the frequency and slide valve control of the compressor remain unchanged in the current state.

[0108] When the water temperature drops further, the water temperature of the evaporator 4 is lower than the user set temperature T Wset At this time, the water temperature of evaporator 4 is T Wset -D / 2(℃)≤T<T Wset -0.2 (℃), the water temperature is in the slide valve holding area and the frequency reduction area. At this time, the adjustable period of frequency control is t (the default is 9 seconds, which can be set). The compressor slide valve maintains the current position (the load increase and load reduction solenoid valves do not work). The motor speed of the compressor is controlled only by frequency control, thereby realizing the load control of the compressor. At this time, the frequency reduction control method is to perform PID control based on the difference between the water temperature and the set water temperature.

[0109] When the water temperature drops further, the water temperature of the evaporator 4 is lower than the user set temperature T Wset At this time, the water temperature of evaporator 4 is T Wset -D / 2-A(℃)≤T<TWset -D / 2(℃), the water temperature is in the load reduction area and the frequency reduction area. At this time, the adjustable period of frequency control is t (the default is 9 seconds, which can be set), and the adjustable period of slide valve control is n*t seconds (n is a positive integer, which can be set). Compared with the slide valve control period, the frequency control has a shorter period and can control the change of water temperature more finely. Furthermore, the frequency reduction control method is to perform PID control based on the difference between the water temperature and the set water temperature. PID control is a common technical knowledge and will not be described here. The load reduction control method is: every interval of the adjustable period n*t seconds, continuously output the load reduction solenoid valve opening signal. By simultaneously controlling the load reduction of the compressor slide valve and the frequency reduction of the compressor, the load of the compressor can be quickly reduced.

[0110] When the water temperature drops further, the water temperature of the evaporator 4 is much lower than the user set temperature T Wset At this time, the water temperature of the evaporator 4 is T<T Wset -D / 2-A(℃), the unit enters the shutdown process, the adjustable slide valve does not move, and the compressor operating frequency returns to zero.

[0111]

[0112] Table 1

[0113] It is understandable that when the variable frequency compressor is running under low load, the number of effective sealing teeth is reduced, and the internal and external leakage of the rotor is greatly increased, which leads to a sharp drop in the isentropic efficiency and volumetric efficiency of the compressor, and low operating efficiency. It is usually manifested as an increase in operating current, abnormal vibration of the pipeline, and a decrease in instantaneous COP. The current detection device 8 monitors the input current of the variable frequency chiller, and the vibration detection device detects the vibration value of individual pipelines, instantaneous COP, etc., which can effectively avoid bad operating points. Combining the water temperature frequency control and the slide valve control method can effectively reduce the impact of fluctuations on water temperature control.

[0114] It should be noted that the automatic optimization control: during the entire water temperature control cycle (including the load increase area, frequency increase area, maintenance area, load reduction area, frequency reduction area), at least one of the following conditions is met:

[0115] ① The current average change rate of the unit's operating current Q> the change rate A, (can be set) the average change rate of current

[0116]

[0117] ② The current instantaneous COP change rate P> change rate B;

[0118] ③The current pipeline vibration value Z>the set value C;

[0119] When the above ①, ② or ③ are met, the corresponding action is performed according to the area where the current water temperature is located, as shown in Table 2 below.

[0120] In some embodiments of the present application, the operating parameters include an average current change rate. According to the comparison result of the average current change rate Q of the current unit and the set change rate A, the compressor executes a corresponding operating strategy to avoid an undesirable operating condition point, including:

[0121] When the actual water temperature is in the load increase area, set the change rate A1 to 13%, A2 = A1-1%, when the average current change rate Q> change rate A1, the compressor outputs 0.2 seconds of load reduction every 10 seconds, and the frequency is increased by 7HZ until the average current change rate Q≤change rate A2;

[0122] When the actual water temperature is in the frequency increase zone, set the change rate A1 to 10%, A2 = A1-0.8%, when the average current change rate Q> change rate A1, the compressor outputs 0.2 seconds of load reduction every 15 seconds, and the frequency is increased by 5HZ until the average current change rate Q≤change rate A2;

[0123] When the actual water temperature is in the slide valve holding area and the frequency holding area, set the change rate A1 to 5%, A2 = A1-0.5%, when the average current change rate Q> change rate A1, the compressor outputs 0.3 seconds of load increase at intervals of 25 seconds, and the frequency is reduced by 3HZ until the average current change rate Q≤change rate A2;

[0124] When the actual water temperature is in the frequency reduction zone, set the change rate A1 to 10%, A2 = A1-0.8%, when the average current change rate Q> change rate A1, the compressor outputs 0.1 second load increase every 15 seconds, and the frequency is reduced by 5HZ until the average current change rate Q≤ change rate A2;

[0125] When the actual water temperature is in the load reduction zone, set the change rate A1 to 12%, A2 = A1-1%, when the average current change rate Q> change rate A1, the compressor outputs 0.1 second load increase every 10 seconds, and the frequency is reduced by 6HZ until the average current change rate Q≤change rate A2.

[0126] In some embodiments of the present application, the operating parameters include an instantaneous COP change rate. According to the comparison result of the instantaneous COP change rate P of the current unit and the set change rate B, the compressor executes a corresponding operating strategy to avoid an undesirable operating condition point, including:

[0127] When the actual water temperature is in the load-increasing zone, the change rate B1 is set to 1.5%, B2 = B1-1%, and when the instantaneous COP change rate P> change rate B1, the compressor outputs a 0.1 second load reduction at intervals of 10 seconds, and the frequency is increased by 3HZ until the instantaneous COP change rate P ≤ change rate B2;

[0128] When the actual water temperature is in the frequency increase zone, set the change rate B1 to 0.7%, B2 = B1-0.8%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load reduction every 15 seconds, and the frequency is increased by 2HZ until the instantaneous COP change rate P≤ change rate B2;

[0129] When the actual water temperature is in the slide valve holding area and the frequency holding area, set the change rate B1 to 0.5%, B2 = B1-0.5%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load increase at intervals of 25 seconds, and the frequency decreases by 1HZ until the instantaneous COP change rate P ≤ change rate B2;

[0130] When the actual water temperature is in the frequency reduction zone, set the change rate B1 to 0.7%, B2 = B1-0.8%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load increase every 15 seconds, and the frequency is reduced by 3HZ until the instantaneous COP change rate P ≤ change rate B2;

[0131] When the actual water temperature is in the load reduction zone, set the change rate B1 to 1.5%, B2 = B1-1%, when the instantaneous COP change rate P> change rate B1, the compressor outputs 0.1 second load increase at intervals of 10 seconds, and the frequency is reduced by 6HZ until the instantaneous COP change rate P ≤ change rate B2.

[0132] In some embodiments of the present application, the operating parameters include a pipeline vibration value. According to the comparison result between the current unit pipeline vibration value Z and the set vibration value C, the compressor executes a corresponding operating strategy to avoid an undesirable operating condition point, including:

[0133] When the actual water temperature is in the load-increasing zone, the change rate C1 is set to 2, C2 = C1-1%, and when the pipeline vibration value Z> the set vibration value C1, the compressor outputs a 1-second load reduction at intervals of 10 seconds, and the frequency is increased by 3HZ until the pipeline vibration value Z≤the set vibration value C2;

[0134] When the actual water temperature is in the frequency increase zone, the change rate C1 is set to 1.5, C2 = C1-0.8%, when the pipeline vibration value Z> the set vibration value C1, the compressor outputs 0.5 seconds of load reduction every 15 seconds, and the frequency is increased by 2HZ until the pipeline vibration value Z≤the set vibration value C2;

[0135] When the actual water temperature is in the slide valve holding area and the frequency holding area, the change rate C1 is set to 1, C2 = C1-0.5%, when the pipeline vibration value Z> the set vibration value C1, the compressor outputs 0.3 seconds of load increase at intervals of 25 seconds, and the frequency is reduced by 1HZ until the pipeline vibration value Z≤the set vibration value C2;

[0136] When the actual water temperature is in the frequency reduction zone, the change rate C1 is set to 1.5, C2 = C1-0.8%, when the pipeline vibration value Z> the set vibration value C1, the compressor outputs 0.1 second load increase every 15 seconds, and the frequency is reduced by 3HZ until the pipeline vibration value Z≤the set vibration value C2;

[0137] When the actual water temperature is in the load reduction zone, the change rate C1 is set to 2, C2 = C1-1%. When the pipeline vibration value Z> the set vibration value C1, the compressor outputs a 0.2 second load increase at intervals of 10 seconds, and the frequency is reduced by 6HZ until the pipeline vibration value Z≤the set vibration value C2.

[0138]

[0139] Table 2

[0140] Reference Figure 1 to Figure 2 The control device of the second aspect of the present application may be a control device configured to execute the optimization control method of the variable frequency screw chiller of the first aspect of the present application, and the control device includes:

[0141] An acquisition module is used to obtain the actual water temperature and the user's set water temperature;

[0142] The regulating module is used to set the water temperature difference according to the actual water temperature, determine the regulating mode of the compressor and perform water temperature control;

[0143] The control module is used to obtain the current operating parameters of the compressor, and control the compressor to execute a corresponding operating strategy to avoid an unfavorable operating condition point based on the comparison result between the current operating parameters and the set operating parameters.

[0144] In some embodiments, the conventional refrigeration cycle principle is the reverse Carnot cycle principle, and the inlet water temperature of the evaporator 4 is detected by the temperature sensor 5, and the inlet water temperature and the user-set water temperature are determined, and divided into the load increase area, frequency increase area, slide valve holding area, holding area (frequency holding area and slide valve holding area), frequency reduction area, load reduction area, and shutdown area according to the following setting method. From the area division diagram, it can be seen that the frequency increase area and the frequency reduction area are closer to the holding area than the load increase area. By intelligently determining the best operating strategy and avoiding the bad operating condition point, the optimal control is automatically sought according to the current cooling demand.

[0145] Reference Figure 1 to Figure 2The air conditioning unit of the third embodiment of the present application includes the control device of the second embodiment of the present application, and also includes a screw compressor 1, a condenser 2 (which can be any one of air cooling, water cooling, and evaporative cooling) and an evaporator 4, and further includes a cut-off device 3, a temperature sensor 5, a pressure sensor 6, a refrigerant pipeline 7, a current detection device 8, and a vibration detection device 9, wherein the control device includes at least one of a frequency conversion control unit 10 or an intelligent control unit 11. Further, the current detection device 8 can be replaced by the current output detection function of the frequency conversion control unit 10.

[0146] Reference Figure 1 to Figure 2 The storage medium of the fourth aspect embodiment of the present application includes: at least one instruction is stored in the storage medium, and the instruction is loaded and executed by the processor to implement the operations performed by the optimal control method of the variable frequency screw chiller in the first aspect embodiment of the present application, through variable frequency energy-saving control, intelligent determination of the optimal operating strategy and avoidance of adverse operating conditions, and automatic optimal control according to the current cooling demand.

[0147] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0148] The embodiments of the present application are described in detail above in conjunction with the accompanying drawings, but the present application is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present application.

Claims

1. A method for optimizing the control of a variable frequency screw chiller, characterized in that: The following steps are involved: Get the actual water temperature and the user's set water temperature; According to the difference between the actual water temperature and the set water temperature, determine the adjustment mode of the compressor and perform water temperature control; When performing water temperature control, the current operating parameters of the compressor are obtained, and according to the comparison result between the current operating parameters and the set operating parameters, the compressor is controlled to execute a corresponding operating strategy to avoid an unfavorable operating condition point; The current operating parameters of the compressor include the average current change rate, the instantaneous COP change rate or the pipeline vibration value; Methods for determining the adjustment mode of the compressor according to the temperature difference between the actual water temperature and the set water temperature include: Set the water temperature to T Wset , the actual water temperature is set as T, and the temperature interval is divided based on the set water temperature, where the temperature interval includes the load increase area, frequency increase area, slide valve holding area, frequency holding area, load reduction area, frequency reduction area and shutdown area. The frequency increase area is closer to the frequency holding area than the load increase area, and the frequency reduction area is closer to the frequency holding area than the load reduction area. D and A are constants; When T ≥ T Wset When +D / 2(℃), the actual water temperature is in the load increase area and frequency increase area; When T Wset +0.2≤T<T Wset +D / 2(℃), the actual water temperature is in the frequency increasing area and the slide valve holding area; When T Wset -0.2(℃)≤T<T Wset +0.2(℃), the actual water temperature is in the slide valve holding area and frequency holding area; When T Wset -D / 2(℃)≤T<T Wset When -0.2(℃), the actual water temperature is in the slide valve holding area and frequency reduction area; When T Wset -D / 2-A(℃)≤T<T Wset -D / 2(℃), the actual water temperature is in the load reduction and frequency reduction areas; When T<T Wset -D / 2-A(℃), the actual water temperature is in the shutdown area; The adjustment mode of the compressor is determined according to the temperature range in which the actual water temperature is located and the water temperature is controlled.

2. The optimization control method for a variable frequency screw chiller according to claim 1, characterized in that: Methods for determining how the compressor should be adjusted include: When the actual water temperature is in the load increase area and frequency increase area, the load increase of the compressor is achieved by simultaneously controlling the compressor slide valve load increase and the compressor operating frequency increase; When the actual water temperature is in the frequency increasing area and the slide valve holding area, the compressor slide valve maintains the current position, and the motor speed of the compressor is controlled by frequency control, thereby realizing the load control of the compressor; When the actual water temperature is in the slide valve holding area and the frequency holding area, the operating frequency and slide valve control of the compressor remain unchanged at the current state; When the actual water temperature is in the slide valve holding area and the frequency reduction area, the compressor slide valve maintains the current position, and the motor speed of the compressor is controlled by frequency control, thereby realizing the load control of the compressor; When the actual water temperature is in the load reduction area and the frequency reduction area, the load reduction of the compressor is achieved by simultaneously controlling the compressor slide valve to reduce the load and the compressor operating frequency to reduce the load; When the actual water temperature is in the shutdown zone, the compressor slide valve does not move and the operating frequency of the compressor returns to zero.

3. The optimization control method for a variable frequency screw chiller according to claim 2, characterized in that: Methods for determining the compressor adjustment method and performing water temperature control include: When the actual water temperature is in the load increase area and frequency increase area, the load increase signal is continuously output for a1 seconds every interval of n*t seconds, where n is a positive integer, to increase the load of the compressor slide valve, and the frequency increase signal is output every interval of t seconds to increase the frequency of the compressor; When the actual water temperature is in the frequency increase zone and the slide valve holding zone, the slide valve maintains the current position and outputs a frequency increase signal every t seconds to increase the operating frequency of the compressor; When the actual water temperature is in the slide valve holding area and the frequency holding area, the slide valve maintains the current position and the operating frequency of the compressor remains unchanged; When the actual water temperature is in the slide valve holding area and the frequency reduction area, the slide valve maintains the current position and outputs a frequency reduction signal every t seconds to reduce the frequency of the compressor; When the actual water temperature is in the load reduction area and the frequency reduction area, the load reduction signal is continuously output for a2 seconds at each interval of n*t seconds, where n is a positive integer, to reduce the load of the compressor slide valve, and the frequency reduction signal is output at each interval of t seconds to reduce the frequency of the compressor; When the actual water temperature is in the shutdown zone, the slide valve does not move and the operating frequency of the compressor returns to zero.

4. The optimization control method for a variable frequency screw chiller according to claim 1, characterized in that: The operating parameters include the average current change rate. According to the comparison result of the current average current change rate Q of the unit and the set change rate A, the compressor executes the corresponding operating strategy to avoid the unfavorable operating condition point.

5. The optimization control method for a variable frequency screw chiller according to claim 1, characterized in that: The operating parameters include an instantaneous COP change rate. According to the comparison result between the instantaneous COP change rate P of the current unit and the set change rate B, the compressor executes a corresponding operating strategy to avoid an unfavorable operating condition point.

6. The optimization control method for a variable frequency screw chiller according to claim 1, characterized in that: The operating parameters include pipeline vibration values. According to the comparison result between the current unit pipeline vibration value Z and the set vibration value C, the compressor executes a corresponding operating strategy to avoid an unfavorable operating condition point.

7. A control device, characterized in that: The control device is configured to be able to execute the optimization control method for a variable frequency screw chiller according to any one of claims 1 to 6, and the control device comprises: An acquisition module is used to obtain the actual water temperature and the user's set water temperature; The regulating module is used to set the water temperature difference according to the actual water temperature, determine the regulating mode of the compressor and perform water temperature control; The control module is used to obtain the current operating parameters of the compressor, and control the compressor to execute a corresponding operating strategy to avoid an unfavorable operating condition point according to a comparison result between the current operating parameters and the set operating parameters.

8. An air conditioning unit, characterized in that: include: A control device as claimed in claim 7.

9. A storage medium, characterized in that: include: The storage medium stores at least one instruction, which is loaded and executed by the processor to implement the operation performed by the optimization control method for a variable frequency screw chiller according to any one of claims 1 to 6.

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