A low-temperature scroll condensing unit control method and system

Abstract

The present application relates to the field of refrigeration, in particular to a low-temperature scroll condensing unit control method and system, comprising: the frequency fluctuation characteristics of the variable frequency compressor before and after changing are recorded as F0 and F1, the target compressor is started and the frequency fluctuation characteristics F2 is obtained; the difference between F2 and F0 is recorded as the load disturbance of the target compressor; all the fixed frequency compressors running before the target compressor is started are recorded as the reference compressor set, and the difference between F1 and F0 is recorded as the cooperative disturbance index; the load disturbance of the variable frequency compressor is obtained according to the difference between the cooperative disturbance index of the reference compressor set and the load disturbance of the target compressor; and the starting time of the fixed frequency compressor is determined according to the load disturbance of the running fixed frequency compressor and the load disturbance of the variable frequency compressor. The present application makes the variable frequency compressor and the fixed frequency compressor in the condensing unit work reasonably and cooperatively, and ensures the long-term stable operation of the condensing unit.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of refrigeration technology, in particular to a low-temperature scroll condensing unit control method and system. BACKGROUND

[0002] The low-temperature scroll condensing unit is a high-efficiency and compact refrigeration system, which is widely used in the field of low-temperature refrigeration (such as cold storage, chemical industry, pharmaceutical freezing, etc.). The scroll condensing unit realizes efficient and flexible output of refrigeration capacity by connecting multiple scroll compressors in parallel and sharing condensers, evaporators and other components. Many units also use frequency conversion technology to realize more precise, energy-saving and stepless regulation of energy adjustment by adjusting the speed of the compressor.

[0003] However, when the condensing unit works in parallel, with long-time operation, the parallel units will have problems and disturbances such as vibration wear and oil return imbalance. Such disturbances will affect the parallel operation of the compressors, for example, when using a PID algorithm to control the operation of the compressors under different working loads, the disturbances will cause the condensing unit to work unstably, and even cause more serious vibration wear and oil return problems, further causing the compressors in the condensing unit to be unable to work stably for a long time. SUMMARY

[0004] To solve the above problems, the present application provides a low-temperature scroll condensing unit control method and system.

[0005] The low-temperature scroll condensing unit control method and system of the present application adopts the following technical scheme:

[0006] An embodiment of the present application provides a low-temperature scroll condensing unit control method, which comprises the following steps:

[0007] The condensing unit comprises a variable frequency compressor and a plurality of fixed frequency compressors, and the frequency of the variable frequency compressor is controlled by a PID algorithm;

[0008] Whenever the working load of the condensing unit changes: the frequency fluctuation characteristics of the variable frequency compressor when running at the working load before the change are denoted as F0, the frequency fluctuation characteristics of the variable frequency compressor when running at the working load after the change are denoted as F1; a fixed frequency compressor is randomly denoted as a target compressor, after starting the target compressor, the frequency fluctuation characteristics F2 of the variable frequency compressor under the working load after the change are reacquired; the difference between F2 and F0 is denoted as the load disturbance corresponding to the target compressor; all fixed frequency compressors running before the target compressor is started are denoted as a reference compressor set, and the difference between F1 and F0 is denoted as a cooperative disturbance index of the reference compressor set;

[0009] When the working load of the condensing unit changes several times: for all the reference compressor sets obtained after each working load change, the load interference of the variable frequency compressor is obtained according to the difference between the cooperative interference index of the reference compressor set and the load interference of the target compressor in the reference compressor set.

[0010] When the working load of the condensing unit changes again, the starting time of the non-started fixed frequency compressor is determined according to the load interference of the running fixed frequency compressor and the load interference of the variable frequency compressor.

[0011] Preferably, the frequency fluctuation feature comprises the following specific steps:

[0012] When the variable frequency compressor is running at any working load under the control of the PID algorithm, a first frequency sequence composed of the frequencies of the variable frequency compressor in a preset time period before the time is obtained, the frequency spectrum distribution of the first frequency sequence is obtained by using the Fourier transform algorithm, and the average of the amplitudes of all frequencies in the frequency spectrum distribution is taken as the frequency fluctuation feature.

[0013] Preferably, the load interference of the variable frequency compressor is obtained according to the difference between the cooperative interference index of the reference compressor set and the load interference of the target compressor in the reference compressor set, comprising the following specific steps:

[0014] Among all the fixed frequency compressors contained in each reference compressor set, the fixed frequency compressors without corresponding load interference are marked as non-reference compressors; all the reference compressor sets are divided into several groups, each group contains several reference compressor sets, the different reference compressor sets in the same group have the same non-reference compressors; all the groups also contain a group composed of a target set, wherein the target set refers to a reference compressor set containing all fixed frequency compressors corresponding to load interference;

[0015] The load interference of the target compressor is corrected by using the cooperative interference indexes of all the reference compressor sets in all the groups; the load interference of the variable frequency compressor is calculated by using the difference between the cooperative interference index of the target set and the corrected load interference.

[0016] Preferably, the load interference of the target compressor is corrected by using the cooperative interference indexes of all the reference compressor sets in all the groups, comprising the following specific steps:

[0017] Initialize a frequency fluctuation interference x;

[0018] For any one group, subtract all load disturbances in each reference compressor set in the group from the frequency variation disturbance x respectively, and the result is recorded as the first difference, sum all first differences in each reference compressor set, and the difference between the cooperative disturbance index of each reference compressor set in the group and the sum result is recorded as the first estimated disturbance index of each reference compressor set;

[0019] Obtain the skewness of the first estimated disturbance index of all reference compressor sets in any one group, and the mean of the skewness obtained from all groups is recorded as a target value; use a stochastic gradient descent algorithm to optimize x so that the target value is minimized; subtract the frequency variation disturbance x when the target skewness is minimized from the load disturbance of any one target compressor to obtain the corrected load disturbance of the target compressor.

[0020] Preferably, the difference between the cooperative disturbance index of the target set and the corrected load disturbance is used to calculate the load disturbance of the variable frequency compressor, which includes the following specific steps:

[0021] The sum of the corrected load disturbances of all target compressors in the target set is recorded as A1, and the difference between the cooperative disturbance index of the target set and A1 is recorded as the estimated disturbance index of the variable frequency compressor under the target set; the mean of all estimated disturbance indexes of the target set is recorded as the load disturbance of the variable frequency compressor.

[0022] Preferably, the specific acquisition steps of the time corresponding to the operating load are as follows:

[0023] When at any operating load, every time a time elapses, a frequency sequence of a variable frequency compressor is recorded, the mean of all frequency sequences obtained at several times before the current time is obtained, and the maximum difference of all means is recorded as the stability index of the current time; when the stability index is less than a first preset threshold, it is determined that the frequency of the variable frequency compressor at the current time is in dynamic stability, and is regarded as the time when the variable frequency compressor operates at the operating load, and is also regarded as the start time of the target compressor.

[0024] Preferably, when the operating load of the condensing unit changes again, the start time of the non-started fixed frequency compressor is determined according to the load disturbance of the fixed frequency compressor being operated and the load disturbance of the variable frequency compressor, which includes the following specific steps:

[0025] When the operating load of the condensing unit changes again, for the stability index of the current time, when the stability index is less than a second threshold, it is determined that the frequency of the variable frequency compressor at the current time is in dynamic stability, and is regarded as the time when the variable frequency compressor operates at the operating load, and at the same time, a non-started fixed frequency compressor is randomly selected again for starting;

[0026] The second threshold value is positively related to the sum of the load interference of all fixed-frequency compressors and the load interference of the variable-frequency compressor.

[0027] Preferably, the second threshold value is positively related to the sum of the load interference of all fixed-frequency compressors and the load interference of the variable-frequency compressor, and the specific formula is as follows: ;

[0028] wherein, the second threshold value is represented by T2, the first preset threshold value is represented by T1.

[0029] wherein, w represents a dynamic threshold coefficient, ;

[0030] wherein, m1 represents the sum of the corrected load interference of all fixed-frequency compressors, and m2 represents the load interference of the variable-frequency compressor; N represents the number of fixed-frequency compressors and variable-frequency compressors in the condensing unit.

[0031] Preferably, when the working load of the condensing unit changes, and it is determined that the frequency of the variable-frequency compressor is in dynamic stability at the current time, the average frequency of the frequency sequence at the current time is represented as T1; for the upper limit value and the lower limit value of the frequency interval of the variable-frequency compressor, when the average frequency T1 is less than or equal to 90% of the upper limit threshold value and greater than or equal to 110% of the lower limit value, the fixed-frequency compressor is not started.

[0032] Another embodiment of the present application provides a low-temperature scroll condensing unit control system, which comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor executes the steps of the above-mentioned low-temperature scroll condensing unit control method when executing the computer program.

[0033] The technical scheme of the present application has the following beneficial effects:

[0034] The condensing unit of the present application comprises one variable-frequency compressor and several fixed-frequency compressors, and the frequency of the variable-frequency compressor is controlled by a PID algorithm; and when the working load of the condensing unit changes, the fixed-frequency compressor is started, so as to realize the cooperative control of the variable-frequency compressor and the fixed-frequency compressor in the condensing unit, and achieve the purpose of stepless regulation and energy regulation of the condensing unit.

[0035] Further, the present application records the difference between F2 and F0 as the load interference of the target compressor; records all the fixed-frequency compressors running before the target compressor starts as the reference compressor set, and records the difference between F1 and F0 as the coordinated interference index of the reference compressor set; after the working load of the condensing unit changes several times: for the reference compressor set obtained after all the working load changes, the load interference of the variable-frequency compressor is obtained according to the difference between the coordinated interference index of the reference compressor set and the load interference of the target compressor in the reference compressor set. In this process, the influence of the vibration wear and other interferences of the fixed-frequency compressor and the variable-frequency compressor on the PID control process is reliably evaluated. Based on this, when the working load of the condensing unit changes again, the starting time of the fixed-frequency compressor that has not started is determined according to the load interference of the fixed-frequency compressor running and the load interference of the variable-frequency compressor. This process further avoids the problem of inappropriate starting time of the fixed-frequency compressor by eliminating the interference of the fixed-frequency compressor and the variable-frequency compressor on the PID control process, so that the variable-frequency compressor and the fixed-frequency compressor in the condensing unit work reasonably and cooperatively, and the long-term stable operation of the condensing unit is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

[0037] Figure 1 A step flow chart of a low-temperature scroll condensing unit control method provided by an embodiment of the present application;

[0038] Figure 2 A frequency change diagram of a variable-frequency compressor after the working load changes provided by an embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following describes a low-temperature scroll condensing unit control method and system according to the present application, its specific implementation, structure, features and effects in detail, as shown in the drawings and the preferred embodiments. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0040] 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 application belongs.

[0041] The low-temperature scroll condensing unit control method and system provided by the present application will be described in detail below with reference to the accompanying drawings.

[0042] Embodiment one:

[0043] Please refer to Figure 1 , which shows a step flow chart of a low-temperature scroll condensing unit control method provided by an embodiment of the present application, which comprises the following steps:

[0044] Step S101, the condensing unit contains a variable frequency compressor and several fixed frequency compressors, the frequency of the variable frequency compressor is controlled by the PID algorithm.

[0045] The low-temperature scroll condensing unit in this embodiment contains a variable frequency compressor and several fixed frequency compressors; the frequency of the variable frequency compressor is adjustable for stepless adjustment of the cooling capacity output; the frequency of the fixed frequency compressor is fixed, and this embodiment changes the cooling capacity output by starting or stopping some fixed frequency compressors; in other embodiments, some fixed frequency compressors can also be used as backups to deal with the problem of emergency failure of the compressor.

[0046] As an example, this embodiment contains 10 fixed frequency compressors, and the frequency (rotational speed) is 50Hz; the frequency range of the variable frequency compressor is 14-160Hz.

[0047] The working load of the condensing unit is mainly determined by the external environment temperature and the target temperature of the cold storage. Among them, the target temperature of the cold storage means that in order to meet the needs of production or storage, the temperature of the cold storage needs to be maintained at the target temperature. In some embodiments, the external environment temperature and the target temperature of the cold storage are used as the working load. In this embodiment, the influence of short-term fluctuations of the external environment temperature on the work of the condensing unit is ignored, and only the target temperature of the cold storage is used as the working load.

[0048] This embodiment needs to control the condensing unit, specifically to control the frequency of the compressor in the condensing unit, so that the output temperature of the condensing unit at the current external environment temperature is equal to the target temperature of the cold storage.

[0049] The method for controlling the frequency of the compressor in the condensing unit in this embodiment is: for the fixed-frequency compressor, the frequency control of the compressor is realized by controlling its start-stop state; for the variable-frequency compressor, the frequency of the variable-frequency compressor is adjusted in real time according to the difference between the actual temperature and the target temperature by using the PID algorithm, so that the actual temperature of the cold storage approaches the target temperature and is dynamically stabilized at (or equal to) the target temperature, and the frequency of the variable-frequency compressor is also dynamically stabilized.

[0050] In this embodiment, the sampling frequency in the PID algorithm is once per second, that is, the frequency of the variable-frequency compressor is adjusted once per second by the PID algorithm, and in addition, the control parameters of the PID algorithm are manually set before the variable-frequency compressor is shipped. The specific principle of the PID algorithm is known, and this embodiment is not specifically limited.

[0051] In particular, when the frequency of the variable-frequency compressor is greater than the maximum value (i.e., the upper limit value) of the frequency range of the variable-frequency compressor or less than the minimum value (i.e., the lower limit value) of the frequency range of the variable-frequency compressor, it indicates that the variable-frequency compressor is operating at an over frequency or a low frequency, and at this time the variable-frequency compressor works at the upper limit value or the lower limit value.

[0052] In this embodiment, when the frequency of the variable-frequency compressor is dynamically stabilized, it is considered that the variable-frequency compressor is working at the corresponding working load.

[0053] As an example, the method for determining whether the frequency of the variable-frequency compressor is dynamically stabilized is:

[0054] In this embodiment, every second is considered as a time. When at any working load, from switching to the working load, every time a time interval occurs, a time sequence composed of the frequencies of the variable-frequency compressor in the previous several time intervals (for example, 10 time intervals including the current time) is obtained, which is simply denoted as the frequency sequence of each time, and the mean value of the frequency sequence is obtained. The mean values of all frequency sequences obtained before the current time and 5 time intervals (including the current time) are obtained, and the maximum and minimum values in these mean values are denoted as max and min, respectively. (max-min) / q0 is denoted as the stability index of the current time. When the stability index is less than a first preset threshold th1, it is determined that the current time is dynamically stabilized, otherwise it is not dynamically stabilized. In this embodiment, q0 represents a normalization coefficient for removing dimensions and orders of magnitude, and in this embodiment q0 is set to the medium frequency of the variable-frequency compressor (for example, 85 Hz), and th1=0.3 is taken as an example in this embodiment.

[0055] It should be noted that when it is determined that the current time is in dynamic stability, it is no longer necessary to continue to determine whether the subsequent time is in dynamic stability, so as to reduce the amount of calculation. When switching to other workloads, it is necessary to re-determine whether the current time is in dynamic stability.

[0056] It should also be noted that when it is determined that the current time is not in dynamic stability, it is necessary to continue to determine whether the stability index of the next time is less than the first preset threshold th1 until the stability index is less than the first preset threshold th1, and then execute the subsequent steps. In particular, if there is no stability index less than the first preset threshold th1 for two consecutive minutes since switching to the workload, then it is directly determined in this embodiment that the stability index less than the first preset threshold th1 occurs after two minutes, so as to continue to implement the subsequent steps.

[0057] In step S102, when the work load of the condensing unit changes, the frequency fluctuation characteristics of the variable frequency compressor when operating at the work load before the change are denoted as F0, and the frequency fluctuation characteristics of the variable frequency compressor when operating at the work load after the change are denoted as F1.

[0058] When the work load of the condensing unit changes, the work load before the change is denoted as P0, and the work load after the change is denoted as P1. If the work load of the condensing unit does not change, then the subsequent steps are not implemented, and the work process of the condensing unit remains unchanged until the work load of the condensing unit changes, and then the subsequent steps are implemented.

[0059] The change in the work load of the condensing unit includes the change in the external environment temperature and the change in the target temperature of the cold room. In this embodiment, the change in the target temperature of the cold room is taken as an example for description (for example, the target temperature of the cold room is re-set).

[0060] It should be noted that when the variable frequency compressor operates at a certain load, there will be some interference, which causes the frequency of the variable frequency compressor under PID algorithm control to fluctuate greatly when it is dynamically changed. These interferences include the interference caused by the variable frequency compressor itself and the interference caused by other fixed frequency compressors. For example, the interference caused by unstable problems such as long-term running wear and vibration of the variable frequency compressor or the fixed frequency compressor, and the interference caused by unbalanced compressor oil return. In addition, for the variable frequency compressor, too large or too small frequency will cause problems such as prominent noise, overheating and wear of parts, and difficult oil return, which will also interfere with the PID algorithm control process. In this embodiment, the frequency fluctuation characteristics of the variable frequency compressor are used to describe the interference of the variable frequency compressor when the frequency is changed in the PID control process.

[0061] The frequency fluctuation characteristic F0 of the variable frequency compressor is obtained when the variable frequency compressor works under the working load P0, and the frequency fluctuation characteristic F1 of the variable frequency compressor is obtained when the variable frequency compressor works under the working load P1. The greater the frequency fluctuation characteristic is, the more unstable the frequency of the variable frequency compressor controlled by the PID algorithm is, which will further aggravate the vibration and wear of the variable frequency compressor, and is not conducive to the balance of the power grid, and even affects the stable operation of other fixed frequency compressors. The smaller the frequency fluctuation characteristic is, the more stable the frequency of the variable frequency compressor controlled by the PID algorithm is, and even remains unchanged, which is conducive to the stable operation of the condensing unit.

[0062] As an optional example, the method for obtaining the frequency fluctuation characteristic of the variable frequency compressor is as follows:

[0063] When it is determined that the frequency of the variable frequency compressor is in dynamic stability (i.e., works under the corresponding working load), the frequencies at a plurality of time points before the time point are obtained (for example, the frequencies at 15 time points before the time point are obtained), and these frequencies are recorded as a first frequency sequence.

[0064] The standard deviation of the first frequency is taken as the frequency fluctuation characteristic.

[0065] As a preferred example, the method for obtaining the frequency fluctuation characteristic of the variable frequency compressor is as follows:

[0066] The frequency spectrum distribution of the first frequency sequence is obtained by using the Fourier transform algorithm, the frequency spectrum distribution contains the amplitudes of different frequencies, and the amplitude of each frequency represents the strength of an interference signal introduced in the first frequency sequence. The mean value of the amplitudes of all frequencies is taken as the frequency fluctuation characteristic; when the first frequency sequence introduces more interference, the amplitudes corresponding to various frequencies in the frequency spectrum distribution are larger, that is, the frequency fluctuation characteristic is larger.

[0067] It should be noted that, in order to avoid the frequency fluctuation characteristic obtained by all the above examples being equal to 0 (i.e., the values in the first frequency sequence are all equal), which will affect the subsequent calculation process, a Gaussian noise with a standard deviation of 3 Hz is added to the first frequency sequence when the standard deviation of the first frequency sequence is less than 3 Hz.

[0068] In step S103, a fixed frequency compressor is randomly recorded as a target compressor, and after the target compressor is started, the frequency fluctuation characteristic F2 of the variable frequency compressor under the changed working load is re-obtained.

[0069] The average frequency T1 of the variable frequency compressor working under the working load P1 is obtained, and the method for obtaining the average frequency T1 is as follows: the time point when the frequency of the variable frequency compressor is determined to be in dynamic stability is obtained, and the frequency sequence at the time point is obtained, and the mean value of the frequency sequence is recorded as T1.

[0070] For the upper limit value and the lower limit value of the frequency interval of the variable frequency compressor, when the average frequency T1 is greater than 90% of the upper limit threshold, it indicates that the condensing unit cannot continue to work at the working load P1 by controlling the variable frequency compressor, at which time the fixed frequency compressor needs to be started. When the average frequency T1 is less than 110% of the lower limit value, it also indicates that the condensing unit cannot continue to work at the working load P1 by controlling the variable frequency compressor, at which time the fixed frequency compressor needs to be stopped. When the average frequency T1 is less than or equal to 90% of the upper limit threshold and greater than or equal to 110% of the lower limit value, it indicates that the condensing unit can work at the working load P1 by controlling the variable frequency compressor, at which time the embodiment ends, and the implementation is restarted from step S102.

[0071] As shown in FIG. 6, it illustrates the change of the frequency of the variable frequency compressor under the PID control before and after the working load of the condensing unit changes and before and after the target compressor is started. Figure 2

[0072] Next, the embodiment is described by taking the case that the average frequency T1 is greater than 90% of the upper limit threshold.

[0073] A fixed frequency compressor that is not started is randomly recorded as a target compressor. After the target compressor is started, the frequency of the variable frequency compressor is still controlled by the PID algorithm, and the variable frequency compressor continues to work at the working load P1. In this process, the variable frequency compressor works at the working load P1 (i.e., the variable frequency compressor reaches dynamic stability at the working load P1), and the purpose of stepless adjustment of the cooling capacity output of the condensing unit is achieved by starting the fixed frequency compressor.

[0074] It should be noted that the frequency dynamic fluctuation of the variable frequency compressor when it is stably working before the target compressor is started is different from the frequency dynamic fluctuation after the target compressor is started. The frequency fluctuation characteristics of the variable frequency compressor when it works at the working load P1 after the target compressor is started are recorded as F2.

[0075] Step S104, the difference between F2 and F0 is recorded as the load interference of the target compressor; the difference between F1 and F0 is recorded as the cooperative interference index of the reference fixed frequency compressor.

[0076] (F2-F0) / F0 is recorded as the load interference of the target compressor, and F0 is taken as the denominator for the purpose of removing the dimension and order of magnitude of the load interference. The load interference describes the change amplitude of the dynamic fluctuation of the frequency of the variable frequency compressor caused by the introduction of the target compressor when the working load changes. The greater the load interference, the more serious the influence of the interference caused by the access of the target compressor on the PID regulation process when the target compressor is used to assist the variable frequency compressor to respond to the load interference change (i.e., more system noise is introduced in the PID algorithm).

[0077] ​Particularly, in the embodiment, when the load disturbance is less than 0.05, the load disturbance is equal to 0, which means that the PID control process of the variable frequency compressor is not disturbed by the PID control process of the fixed frequency compressor with similar or same load.

[0078] Further, all the fixed frequency compressors running before the target compressor is started are obtained, and the fixed frequency compressors are recorded as a reference compressor set of the target compressor.

[0079] The (F1-F0) / F0 is recorded as a cooperative disturbance index of the reference compressor set, and the cooperative disturbance index represents the disturbance introduced by the PID control process of the variable frequency compressor when the variable frequency compressor is used independently to cope with the change of the load disturbance. The cooperative disturbance index is greater, which means that the PID control process of the variable frequency compressor is seriously disturbed when all the fixed frequency compressors and the variable frequency compressor work cooperatively.

[0080] Particularly, in the embodiment, when the cooperative disturbance index is less than 0.05, the cooperative disturbance index is equal to 0.

[0081] So far, the steps S102 to S104 are performed, and the load disturbance of the target compressor and the cooperative disturbance index of the reference compressor set corresponding to the target compressor are obtained each time the working load of the condensing unit changes. With the long-term operation of the condensing unit, the working load changes over time, and the load disturbance of the target compressor and the cooperative disturbance index of the reference compressor set obtained each time are stored in the database (for example, a MySql database).

[0082] In step S105, after the working load of the condensing unit changes for several times, the load disturbance of the variable frequency compressor is obtained according to the difference between the cooperative disturbance index of the reference compressor set and the load disturbance of the target compressor in the reference compressor set.

[0083] When the working load of the condensing unit changes for several times (for example, 50 times), the load disturbance and the cooperative disturbance index stored in the database are used for further control of the condensing unit in the embodiment.

[0084] Specifically, the load disturbance of all the target compressors and all the reference compressor sets are read from the database. The load disturbance of the variable frequency compressor is obtained according to the difference between the cooperative disturbance index of all the reference compressor sets and the load disturbance of the target compressor.

[0085] The load disturbance of the variable frequency compressor describes the disturbance of the PID algorithm control process caused by the vibration wear and other factors of the variable frequency compressor itself when working.

[0086] As an optional example, the method for obtaining the load interference of the variable frequency compressor comprises:

[0087] For all target compressors stored in the database, each target compressor corresponds to a load interference. In particular, when the same target compressor corresponds to multiple load interferences, the average of these load interferences is regarded as the load interference of the target compressor and participates in subsequent calculations.

[0088] For any reference compressor set stored in the database, the reference compressor set contains several fixed frequency compressors. Some of these fixed frequency compressors may have worked as target compressors in step S103 to assist the variable frequency compressor, and these fixed frequency compressors have corresponding load interferences stored in the database. Some of these fixed frequency compressors may not have worked as target compressors in step S103 to assist the variable frequency compressor, and these fixed frequency compressors do not have corresponding load interferences stored in the database.

[0089] If all fixed frequency compressors contained in the reference compressor set are target compressors (i.e., all have worked as target compressors to assist the variable frequency compressor) or all correspond to load interferences, the reference compressor set is recorded as a target set.

[0090] The sum of the load interferences of all target compressors in the target set is recorded as A1, and the difference between the cooperative interference index of the target set and A1 is recorded as the estimated interference index of the variable frequency compressor under the target set.

[0091] The average of the estimated interference indexes of all target sets is recorded as the load interference of the variable frequency compressor.

[0092] In particular, if there is no target set, the embodiment ends, and the implementation is restarted from step S102.

[0093] As a preferred example, the method for obtaining the load interference of the variable frequency compressor comprises:

[0094] In the optional example, the estimated interference indicators of all target sets are not the same, one reason is the inevitable Gaussian error in the PID control process and the condensing unit working process, and the other reason includes that when obtaining the load interference of the fixed-frequency compressor, the error caused by the frequency change of the variable-frequency compressor is not considered. Specifically, after the working load changes and the target compressor works, the frequency of the variable-frequency compressor is different from and changes from the frequency before the working load changes, and when the variable-frequency compressor works at different frequencies, the vibration wear and oil return state are different, which changes the frequency fluctuation characteristics (i.e. interferes with the PID control process), so that the load interference of the fixed-frequency compressor has an error. Specifically, the load interference obtained in step S104 contains the interference caused by the frequency change of the variable-frequency compressor, which cannot be used to describe the interference of the fixed-frequency compressor on the PID control process of the variable-frequency compressor, so the load interference obtained in S104 needs to be corrected to ensure the accuracy of the load interference of the variable-frequency compressor. In addition, in the optional example, only the load interference in the target set stored in the database can be used, and the reference compressor set outside the target set cannot be used to directly or indirectly participate in the acquisition of the load interference of the variable-frequency compressor, resulting in a lack of big data support for the load interference of the variable-frequency compressor.

[0095] In the preferred example:

[0096] (1) For all reference compressor sets and all target sets therein, mark the fixed-frequency compressors in each other reference compressor set without corresponding load interference as non-referenced compressors. In the other reference compressor set, the reference compressor set containing the same non-referenced compressors is divided into a group; that is, each group contains several reference compressor sets, and each reference compressor set in these reference compressor sets contains all non-referenced compressors that are exactly the same as all non-referenced compressors contained in other reference compressor sets.

[0097] (2) Initialize a frequency variation interference x to describe the interference of the frequency change of the variable-frequency compressor on the PID control as a whole.

[0098] All target sets are also considered as a group. For any group and for each reference compressor set in the group that has a corresponding load interference of the fixed-frequency compressor, the load interference of these fixed-frequency compressors is subtracted by the frequency variation interference x to obtain the first difference of the fixed-frequency compressor, and the sum of the first differences of these fixed-frequency compressors is obtained. The difference between the cooperative interference indicator of each reference compressor set in the group and the sum is recorded as the first estimated interference indicator of each reference compressor set.

[0099] Wherein the first difference represents the correction result of the load disturbance obtained based on the initialized x.

[0100] (3) Obtain the skewness of the first estimated interference index of all reference compressor sets in any one group. The calculation method of the skewness of data is known, and this embodiment will not be described in detail.

[0101] The average of the skewness obtained by all groups is recorded as the target value.

[0102] At this point, a target value related to the frequency variation interference x is obtained, and the random gradient descent algorithm is used to optimize x to minimize the target value.

[0103] In the above process, the first estimated interference index of all reference compressor sets in any one group describes the load interference distribution of the variable frequency compressor after removing the frequency change of the variable frequency compressor from the PID control interference, and when the target skewness is minimum, it indicates that the load interference distribution of the variable frequency compressor after removing the frequency change of the variable frequency compressor from the PID control interference is close to Gaussian distribution, and further indicates that the frequency variation interference x at the minimum target skewness can accurately describe the frequency change of the variable frequency compressor from the overall PID control interference.

[0104] (5) The load interference of all target compressors in the database is respectively subtracted by the frequency variation interference x at the minimum target skewness, to obtain the corrected load interference. Specifically, when the corrected load interference is less than 0.05, the corrected load interference is equal to 0.

[0105] Then, the corrected load interference is used to obtain the load interference of the variable frequency compressor according to the method of the above optional example, including:

[0106] The sum of the corrected load interference of all target compressors in the target set is recorded as A1, and the difference between the cooperative interference index of the target set and A1 is recorded as the estimated interference index of the variable frequency compressor under the target set. The average of the estimated interference indexes of all target sets is recorded as the load interference of the variable frequency compressor.

[0107] It should be noted that in the above process, in each reference compressor set in the same group, there can be an un-referenced compressor, which makes each first estimated interference index describe the load interference under the joint action of the un-referenced compressor and the variable frequency compressor, and cannot directly describe the load interference of the variable frequency compressor; but since the same group has the same un-referenced compressor, the first estimated interference indexes obtained by all reference compressor sets in the same group (i.e. the first estimated interference indexes obtained after removing the frequency variation interference x) can describe the load interference distribution of the variable frequency compressor after removing the interference of the frequency variation of the variable frequency compressor on the PID control. Different groups have different un-referenced compressors, so the load interference distribution of the variable frequency compressor described by the first estimated interference indexes obtained by all reference compressor sets in different groups is different, so the embodiment optimizes the first estimated interference indexes obtained by each group respectively, so that the first estimated interference indexes obtained by each group all show the characteristics of Gaussian distribution, fully utilizes the data stored in the database (i.e. fully combines the working conditions of all compressors in the history working process), so that the frequency variation interference x at the minimum target skewness can further accurately describe the interference of the frequency variation of the variable frequency compressor on the PID control as a whole, and then the load interference of the fixed frequency compressor is corrected, and the accuracy of the load interference of the variable frequency compressor is also ensured.

[0108] In particular, when the number of first estimated interference indexes obtained by each group is less than 3, it means that the group data is invalid, and the group does not participate in the implementation of the preferred example.

[0109] Step S106, when the working load of the condensing unit changes again, the starting time of the un-started fixed frequency compressor is determined according to the load interference of the running fixed frequency compressor and the load interference of the variable frequency compressor.

[0110] When the working load changes again, the PID algorithm will continue to control the frequency of the variable frequency compressor, so that the frequency of the compressor reaches dynamic stability, and when the dynamic stability is reached, the purpose of stepless adjustment of the cooling capacity output of the condensing unit is achieved by starting and stopping the fixed frequency compressor.

[0111] Wherein, as described in step S101, the present embodiment determines whether it is at the time point of frequency dynamic stability according to the size of the stability index. However, with the long-term use of the condensing unit, the fixed-frequency compressor and the variable-frequency compressor in the condensing unit inevitably have problems such as vibration, noise, and oil return difficulty, which will interfere with the PID algorithm control process, for example, increase the system noise in the PID control process, cause the frequency of the variable-frequency compressor to have a large fluctuation amplitude and uncertainty, and make it difficult to accurately determine whether the frequency reaches dynamic balance, so that the time point of step S101 dynamic balance is delayed or advanced, or in other words, it is difficult to obtain the dynamic balance opportunity in time, thereby causing the start-stop opportunity of the fixed-frequency compressor to be inappropriate; when the start-stop opportunity of the fixed-frequency compressor is inappropriate, on the one hand, it may cause the variable-frequency compressor to run unstably in a high-frequency or low-frequency state for a long time, causing the vibration and wear of the variable-frequency compressor to be more serious. On the other hand, it may cause the start-stop state of the fixed-frequency compressor to be judged incorrectly, causing the fixed-frequency compressor to be started or stopped by mistake, which is not conducive to fully exerting the performance of the variable-frequency compressor and saving energy consumption.

[0112] In the present embodiment, the problem of inappropriate start-stop opportunity of the fixed-frequency compressor is further avoided by eliminating the load interference of the fixed-frequency compressor and the load interference of the variable-frequency compressor, so that the variable-frequency compressor and the fixed-frequency compressor in the condensing unit work reasonably and cooperatively, and the long-term stable operation of the condensing unit is ensured.

[0113] Specifically:

[0114] When the working load changes again, the variable-frequency compressor adjusts the frequency under the control of the PID algorithm, and the stability index at the current time is obtained according to the frequency sequence (the same as step S101). When the stability index is less than the second threshold th2, it is determined that the frequency reaches dynamic stability, and at this time the fixed-frequency compressor is started or stopped according to the method of step S103.

[0115] Wherein th2 is positively correlated with the sum of the load interference of all the fixed-frequency compressors running at the current time and the load interference of the variable-frequency compressor. The greater the interference of the running fixed-frequency compressor and the variable-frequency compressor to the PID algorithm, the greater th2 is.

[0116] In this process, the start-stop opportunity of the fixed-frequency compressor is determined based on the interference of the running fixed-frequency compressor and the variable-frequency compressor to the PID algorithm, which ensures the rationality of the cooperative work of the fixed-frequency compressor and the variable-frequency compressor in the condensing unit, and ensures that the condensing unit has the stepless adjustment of cold output function while ensuring the efficient operation of the condensing unit.

[0117] As an example, the calculation formula of th2 is:

[0118]

[0119] wherein w represents a dynamic threshold coefficient;

[0120]

[0121] wherein m1 represents the sum of the modified load disturbances of all the running fixed-frequency compressors, m2 represents the load disturbance of the variable-frequency compressor. N represents the number of all the compressors (including the fixed-frequency compressors and the variable-frequency compressors) in the condensing unit.

[0122] At this point, the step ends.

[0123] Then the step S102 is re-implemented to realize the cooperative control of all the compressors in the condensing unit.

[0124] At this point, the embodiment ends.

[0125] Embodiment Two:

[0126] The above embodiment describes the case that the average frequency T1 is greater than 90% of the upper threshold value in the step S103 to the step S104. The embodiment describes the case that the average frequency T1 is less than 110% of the lower threshold value. The difference between the embodiment and the embodiment one is that:

[0127] In the step S103, when the average frequency T1 is less than 110% of the lower threshold value, a running fixed-frequency compressor is randomly selected, which is also recorded as the target compressor. Then, the frequency of the variable-frequency compressor is still controlled by the PID algorithm after the target compressor is stopped, and the variable-frequency compressor continues to work at the working load P0.

[0128] Since the target compressor is stopped, the disturbance of the PID control process is equivalent to being reduced. Therefore, in the step S104, (F0-F2) / F2 is recorded as the load disturbance of the target compressor. Moreover, the load disturbance of the target compressor obtained in the embodiment and the cooperative disturbance index of the reference compressor set corresponding to the target compressor are stored in the database whenever the working load of the condensing unit changes.

[0129] In the step S105, the data (such as the load disturbance and the cooperative disturbance index) in the database includes the data obtained in the embodiment one and the data obtained in the embodiment.

[0130] Embodiment Three:

[0131] The embodiment provides a low-temperature scroll condensing unit control system, which comprises a memory, a processor, and a computer program stored in the memory and executable on the processor. The processor executes the computer program to perform all the methods in the above embodiments.

[0132] The above merely provides the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of controlling a low-temperature scroll condensing unit, the method comprising: The method comprises the following steps: The condensing unit comprises a variable frequency compressor and several fixed frequency compressors, and the frequency of the variable frequency compressor is controlled by a PID algorithm; Whenever the working load of the condensing unit changes: the frequency fluctuation characteristics of the variable frequency compressor when running at the working load before the change are recorded as F0, the frequency fluctuation characteristics of the variable frequency compressor when running at the working load after the change are recorded as F1; a fixed frequency compressor is randomly recorded as a target compressor, after starting the target compressor, the frequency fluctuation characteristics F2 of the variable frequency compressor at the working load after the change are re-acquired; the difference between F2 and F0 is recorded as the load interference corresponding to the target compressor; all fixed frequency compressors running before the target compressor is started are recorded as a reference compressor set, and the difference between F1 and F0 is recorded as the cooperative interference index of the reference compressor set; After the working load of the condensing unit changes several times: for all the reference compressor sets obtained after the working load changes, the load interference of the variable frequency compressor is obtained according to the difference between the cooperative interference index of the reference compressor set and the load interference of the target compressor in the reference compressor set; When the working load of the condensing unit changes again, the starting time of the fixed frequency compressors that are not started is determined according to the load interference of the fixed frequency compressors that are running and the load interference of the variable frequency compressor.

2. The control method of claim 1, wherein, The frequency fluctuation characteristics comprise the following specific steps: When the variable frequency compressor is running at any working load under the control of the PID algorithm, a first frequency sequence composed of the frequencies of the variable frequency compressor in a preset time period before the time is acquired, the frequency spectrum distribution of the first frequency sequence is acquired by using a Fourier transform algorithm, and the average of the amplitudes of all frequencies in the frequency spectrum distribution is taken as the frequency fluctuation characteristics.

3. The control method of claim 1, wherein, The load interference of the variable frequency compressor obtained according to the difference between the cooperative interference index of the reference compressor set and the load interference of the target compressor in the reference compressor set comprises the following specific steps: In all the fixed frequency compressors contained in each reference compressor set, the fixed frequency compressors without corresponding load interference are marked as non-reference compressors; All the reference compressor sets are divided into several groups, each group contains several reference compressor sets, and the different reference compressor sets in the same group have the same non-reference compressors; All the groups also contain a group composed of a target set, and the target set refers to: a reference compressor set containing all the fixed frequency compressors corresponding to the load interference; The load interference of the target compressor is corrected by using the cooperative interference indexes of all the reference compressor sets in all the groups, and the load interference of the variable frequency compressor is calculated by using the difference between the cooperative interference index of the target set and the corrected load interference.

4. The control method of claim 3, wherein, The specific steps of correcting the load interference of the target compressor by using the cooperative interference indexes of all the reference compressor sets in all the groups comprise the following steps: Initialize a frequency fluctuation interference x; For any one group, subtract all load disturbances in each reference compressor set in the group from the frequency variation disturbance x respectively, and the result is recorded as the first difference. Sum all first differences in each reference compressor set, and the difference between the cooperative disturbance index of each reference compressor set in the group and the sum is recorded as the first estimated disturbance index of each reference compressor set; Obtain the skewness of the first estimated disturbance index of all reference compressor sets in any one group. The mean of the skewness obtained from all groups is recorded as the target value. Use the stochastic gradient descent algorithm to optimize x so that the target value is minimized. Subtract the frequency variation disturbance x when the target skewness is minimized from the load disturbance of any one target compressor to obtain the corrected load disturbance of the target compressor.

5. The control method of claim 3, wherein, The specific steps of calculating the load disturbance of the variable frequency compressor by using the difference between the cooperative disturbance index of the target set and the corrected load disturbance include the following: The sum of the corrected load disturbances of all target compressors in the target set is recorded as A1. The difference between the cooperative disturbance index of the target set and A1 is recorded as the estimated disturbance index of the variable frequency compressor under the target set. The mean of the estimated disturbance index of all target sets is recorded as the load disturbance of the variable frequency compressor.

6. The control method of a low-temperature scroll condensing unit according to claim 1, wherein, The specific steps of obtaining the time corresponding to the operation under the working load are as follows: When under any working load, every time a time elapses, the frequency sequence of a variable frequency compressor is recorded. The mean of all frequency sequences obtained at a number of times before the current time is obtained. The maximum difference of all means is recorded as the stability index of the current time. When the stability index is less than a first preset threshold, it is determined that the frequency of the variable frequency compressor at the current time is in dynamic stability, and it is considered that the variable frequency compressor is operating under the working load. It is also considered as the starting time of the target compressor.

7. The control method of claim 6, wherein, The specific steps of determining the starting time of the non-started fixed frequency compressor according to the load disturbance of the running fixed frequency compressor and the load disturbance of the variable frequency compressor when the working load of the condensing unit changes again include the following: When the working load of the condensing unit changes again, for the stability index of the current time, when the stability index is less than a second threshold, it is determined that the frequency of the variable frequency compressor at the current time is in dynamic stability, and it is considered that the variable frequency compressor is operating under the working load. At the same time, a non-started fixed frequency compressor is randomly selected for starting again. The second threshold is positively correlated with the sum of the load disturbances of all running fixed frequency compressors at the current time and the load disturbance of the variable frequency compressor.

8. The control method of claim 7, wherein, The second threshold value is positively related to the sum of the load disturbances of all the fixed-frequency compressors running at the current time and the load disturbance of the variable-frequency compressor, and the specific formula is as follows: ; wherein, represents a second threshold value, represents a first preset threshold value; wherein w denotes a dynamic threshold coefficient, ; Wherein, m1 represents the sum of the corrected load disturbances of all running fixed frequency compressors at the current time, m2 represents the load disturbance of the variable frequency compressor; N represents the number of fixed frequency compressors and variable frequency compressors in the condensing unit.

9. The control method of claim 6, wherein, When the working load of the condensing unit changes, and it is determined that the frequency of the variable frequency compressor at the current time is in dynamic stability, the average frequency of the frequency sequence at the current time is represented as T1; for the upper limit value and the lower limit value of the frequency interval of the variable frequency compressor, when the average frequency T1 is less than or equal to 90% of the upper limit threshold value, greater than or equal to 110% of the lower limit value, the fixed frequency compressor is not started.

10. A low temperature scroll condensing unit control system, the system comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein, The processor executes the computer program to perform the steps of the low-temperature scroll condensing unit control method of any one of claims 1-9.

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