CN110925197A - Scroll machine, axial back pressure dynamic control method thereof and storage medium - Google Patents

Scroll machine, axial back pressure dynamic control method thereof and storage medium Download PDF

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Publication number
CN110925197A
CN110925197A CN201911241902.3A CN201911241902A CN110925197A CN 110925197 A CN110925197 A CN 110925197A CN 201911241902 A CN201911241902 A CN 201911241902A CN 110925197 A CN110925197 A CN 110925197A
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force
axial
scroll
electromagnetic
control
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CN110925197B (en
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蔡炯炯
程楷一
曹阳
吴萱俊
瞿晓
刘峰
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Zhejiang Lover Health Science and Technology Development Co Ltd
Zhejiang University of Science and Technology ZUST
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Zhejiang University of Science and Technology ZUST
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
    • F04C18/02—Rotary-piston pumps specially adapted for elastic fluids of arcuate-engagement type, i.e. with circular translatory movement of co-operating members, each member having the same number of teeth or tooth-equivalents
    • F04C18/0207—Rotary-piston pumps specially adapted for elastic fluids of arcuate-engagement type, i.e. with circular translatory movement of co-operating members, each member having the same number of teeth or tooth-equivalents both members having co-operating elements in spiral form
    • F04C18/0215—Rotary-piston pumps specially adapted for elastic fluids of arcuate-engagement type, i.e. with circular translatory movement of co-operating members, each member having the same number of teeth or tooth-equivalents both members having co-operating elements in spiral form where only one member is moving
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C28/00—Control of, monitoring of, or safety arrangements for, pumps or pumping installations specially adapted for elastic fluids
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C28/00—Control of, monitoring of, or safety arrangements for, pumps or pumping installations specially adapted for elastic fluids
    • F04C28/28—Safety arrangements; Monitoring
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
    • F04C29/0021—Systems for the equilibration of forces acting on the pump
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C2270/00—Control; Monitoring or safety arrangements
    • F04C2270/04—Force
    • F04C2270/044—Force axial
    • F04C2270/0445—Controlled or regulated

Abstract

The invention provides a scroll machine, an axial back pressure dynamic control method thereof and a storage medium, wherein the method comprises the following steps: determining the advance step number which enables the force evaluation index to be overall optimal by adopting an iteration method under the stable operation state of the scroll machine; setting a rotation speed increment, acquiring optimal advanced steps corresponding to different rotation speeds, and generating a rotation speed-advanced step curve; detecting the exhaust pressure and the rotation angle value at the current moment, and combining an axial gas separation force-rotation angle-exhaust pressure curve to obtain the axial gas separation force at the current moment; determining the current rotating speed according to the current rotating angle value, and determining the advance step number N by combining a rotating speed-advance step number curve0(ii) a Combined with axial air at the current momentThe body separating force is N for advancing the moving scroll disk0PID advance control of (1). The method can accurately control the external back pressure of the movable scroll disk, thereby balancing the gas separating force in the movable scroll disk.

Description

Scroll machine, axial back pressure dynamic control method thereof and storage medium
Technical Field
The invention relates to a control technology of axial gas separation force of a scroll machine, in particular to a scroll machine, an axial back pressure dynamic control method and a storage medium thereof.
Background
The scroll machine is a fluid machine for realizing gas compression by means of volume change, and the internal structure of the scroll machine mainly comprises a fixed scroll, a movable scroll, a bracket, an eccentric shaft and an anti-rotation mechanism, wherein the movable scroll and the fixed scroll are eccentrically arranged, and along with the rotation of the movable scroll under the drive of the eccentric shaft, gas between the movable scroll and the fixed scroll is gathered towards the middle part or is diffused towards the periphery, so that the functions of a compressor or an expander are realized.
For other compressor/expander, the scroll machine has that gas leakage volume is few, small, light in weight, sustainable operating time is long, and complete machine noise advantage such as low, but because the movable scroll dish of scroll machine becomes upper and lower lock structure cooperation with quiet scroll dish between, the contact elasticity between the two is decided by the assembly, the tension can lead to gas leakage, the tension can lead to wearing and tearing in work earlier stage, it is serious to generate heat, work efficiency is low, contact surface still can become loose gradually after the long time, can arouse to reveal etc. and arouse bad consequence, therefore, in the current scroll machine structure, will move the scroll dish and set up to the floating condition, move promptly and float along the axial between quiet scroll dish and support at rotatory in-process. When the movable scroll rotates at a high speed, it is subjected to a large axial gas separating force which varies with the rotation angle of the main shaft and the gas pressure, and for this reason, the axial gas separating force is generally balanced by adding an axial gas separating force control mechanism to the scroll machine. Currently, the commonly used axial gas separation force control mechanism is as follows:
1) the spring back pressure scheme is as follows: the structure is relatively convenient to implement, but the pressure is not adjustable, and the spring and the scroll plate rub under high pressure, so that the service life of materials is greatly challenged, and the problems of friction loss on the working surface of the spring and the like are also brought;
2) the thrust bearing scheme is as follows: namely, a thrust bearing is arranged on the back of the vortex disc to realize mechanical positioning; the structure is adopted to fix the axial position of the scroll disk, the automatic compensation of the axial clearance can not be realized, the balance between sealing and small pressure is difficult to obtain, and a proper thrust bearing is difficult to find in many occasions (such as the field of high-pressure machines);
3) gas back pressure cavity scheme: certain gas pressure is applied to the back surface of the scroll disc, the pressure in the back pressure cavity changes along with the rotation angle according to a rule similar to the change of gas in the cavity, although the structure can offset the outward axial pressure of gas in the cavity with larger amplitude, the resultant force of the gas and the cavity still has residue with larger specific gravity, and the resultant force is related to the rotation angle, so that the problem of larger friction or leakage still exists, and the stable rotation of the scroll disc is not facilitated;
4) double-vortex body vortex plate scheme: the two sides of the circular plate of the movable scroll are provided with an upper scroll body and a lower scroll body which have the same geometric parameters of scroll profiles, and correspondingly, two fixed scroll bodies are matched with the upper scroll body and the lower scroll body. In the scroll compressor with the structure, the axial gas separating forces borne by the upper scroll body and the lower scroll body of the movable scroll disk are equal in magnitude and opposite in direction, so that the axial gas separating forces borne by the movable scroll disk are automatically and completely balanced, but in the structure, the axial gas separating forces borne by the two movable scroll disks of the double scroll bodies can be skillfully counteracted with each other from the theoretical point of view; after offset, in the practical implementation process, the assembly precision of the contact surfaces of the fixed scroll and the movable scroll is difficult to control, the contact is tight, the abrasion and the heat dissipation are more, and the contact is loose and easy to leak. If the installation is fixed, the state of the contact surface is difficult to adjust due to abrasion change after long-time work; if the device is mounted in an axial floating mode, the device can be realized only by axial floating of the fixed scroll, back pressure control is also needed, and the back pressure of the two scrolls increases the complexity.
Chinese patent publication No. CN110005611A discloses an electromagnetic mechanism of a scroll machine and a corresponding control method, in the scheme, an axial electromagnetic force is generated by dynamically controlling the electromagnetic mechanism to counteract an axial separating force (axial gas separating force) of a movable scroll, which realizes control of axial back pressure of the scroll machine to a certain extent, so that the sealing performance is improved while a low contact force is maintained in the operation process of the scroll machine. In the practical application process, however, the axial gas separation force of the scroll compressor is periodically and dynamically changed, the electromagnetic force required for balancing the axial separation force has nonlinear characteristics under high dynamic change, and particularly becomes gradually non-negligible along with the increase of the rotation frequency of the main shaft under the influence of hysteresis factors, so that obvious hysteresis is brought, the axial force control system adopts force feedback control, the sampling of electromagnetic pressure is periodic sampling, namely the system has the characteristic of a typical discrete system, and the running track of the system always generates a hysteresis error of a plurality of sampling steps; this problem is particularly acute when the scroll machine is rotating at elevated or high speeds.
Based on the above problems, how to accurately control the external back pressure and balance the internal gas separation force is a major technical difficulty of high-performance axial sealing.
Disclosure of Invention
In order to solve the above technical problems, a first object of the present invention is to provide a dynamic control method of axial back pressure of a scroll machine, which can precisely control the external back pressure of an orbiting scroll to balance the internal gas separating force thereof.
A second object of the present invention is to provide a scroll machine which controls an axial electromagnetic control force between an orbiting scroll and a fixed scroll by controlling an axial back pressure using the above method.
A third object of the present invention is to provide a storage medium storing a computer program for executing the steps of the above-described dynamic axial back pressure control method.
In view of the above, one aspect of the present invention provides an axial back pressure dynamic control method for a scroll machine using an electromagnetic mechanism to counteract axial gas separation force, the control method comprising the steps of:
sampling actual electromagnetic control force at the current rotating speed at equal time intervals in a stable running state of the scroll machine, comparing the actual electromagnetic control force with target electromagnetic control force at each sampling moment at the current rotating speed to obtain a total difference value between the actual electromagnetic control force and the target electromagnetic control force in a single sampling period, and determining the optimal advance step number which enables the total difference value to be minimum by adopting an iteration method; setting a rotation speed increment, acquiring optimal advanced steps corresponding to different rotation speeds, and generating a rotation speed-advanced step curve;
detecting the exhaust pressure and the rotation angle value at the current moment, and combining an axial gas separation force-rotation angle-exhaust pressure curve to obtain the axial gas separation force at the current moment; determining the current rotating speed according to the current rotating angle value, and determining the advance step number N by combining a rotating speed-advance step number curve0(ii) a The advance step number of the movable scroll disk is N by combining the axial gas separating force at the current moment0PID advance control of (1).
Preferably, the specific method for judging whether the scroll machine is in the stable operation state is as follows: and detecting the actual electromagnetic control force at the current moment, comparing the actual electromagnetic control force with the target electromagnetic control force at the current moment to obtain a control error, and determining that the scroll machine is in a stable operation state when the control errors in the last three periods are all lower than 5%.
Preferably, the specific method for determining the optimal advance step number by using an iterative method to minimize the overall difference between the actual electromagnetic control force f (k) and the target electromagnetic control force fa (k) is as follows:
inputting electromagnetic control force F (k) ═ Fa (k + N) to the movable scroll disk at the moment k, and judging that the value of N is N when the total difference between the actual electromagnetic control force and the target electromagnetic control force reaches the minimum according to the PID advanced prediction balance optimization performance index0；
Wherein N is the advance step number, and the sampling times (total tracking step number) in a single period is set to be k0(in the digital control system, a period actually consists of a plurality of sampling points, and the total tracking point number can be defined as the total tracking step number), the value range of the advance step number N is: n is an element of [0, k ]0]。
Preferably, the PID advanced prediction balance optimization performance index minErr is:
Figure BDA0002306483200000031
wherein k is the current sampling time, F (i) is the actual electromagnetic control force corresponding to the time i, and Fa (i) is the target electromagnetic control force at the time i.
Preferably, the total step number in a single period is set as x, the angle of each step is set as y, and the value range of k in the single period is k epsilon [0, x/y-1 ].
Preferably, the specific method of "determining the current rotation speed according to the current rotation angle value" includes:
Figure BDA0002306483200000032
where V is the rotation speed, theta (k) is the rotation angle value at the moment of k, and theta0The initial angle value is r, the radius of the movable scroll disk is r, and the time consumed by the rotation angle theta (k) is t.
Preferably, the step number of advancing the movable scroll is N in combination with the axial gas separating force at the current moment0The specific method of PID control of (1) is as follows: if the target electromagnetic control force corresponding to the current time k is fa (k), the electromagnetic control force F (k) actually output to the movable scroll by the electromagnetic mechanism at the time k is F (k)a(k+N0)。
In another aspect of the present invention, there is provided a scroll machine comprising an orbiting scroll and a fixed scroll, and further comprising an axial force electromagnetic control mechanism which employs the axial back pressure dynamic control method as described above to offset an axial gas separating force between the orbiting scroll and the fixed scroll.
Preferably, the axial force electromagnetic control mechanism comprises a control part, a detection part and an electromagnetic assembly; wherein:
the electromagnetic assembly is arranged between the movable scroll disk and the fixed scroll disk and used for generating electromagnetic control force to offset axial gas separation force between the movable scroll disk and the fixed scroll disk;
the detection part includes: the pressure detection part comprises an electromagnetic control force detection part and an exhaust pressure detection part which is arranged at an exhaust port extension pipeline of the scroll machine and used for detecting the pressure of an exhaust port of the scroll machine; the rotation angle detection piece is arranged at a driving shaft of the scroll machine and used for detecting rotation angle information of the movable scroll;
the control part is respectively connected with the detection part and the control execution part, and correspondingly adjusts the current in the electromagnetic assembly according to the detection result of the detection part, so that the axial electromagnetic force counteracts the axial gas separation force between the movable scroll and the fixed scroll.
In still another aspect of the present invention, a storage medium is provided, and the storage medium stores a computer program, and the computer program is processed and executed to implement the steps of the above-mentioned dynamic axial back pressure control method.
Compared with the prior art, the invention has the beneficial effects that:
on the aspect of dynamic electromagnetic force control, an advanced PID tracking method, an advanced step number determining method, an establishment method of an advance N database at different frequencies, and a method for adaptively adjusting the advance according to the advance database and real-time speed information are provided, so that the electromagnetic mechanism can realize the fast lag-free tracking of dynamic electromagnetic force at different rotating speeds, and high dynamic performance is realized.
By adopting a force closed loop-based scroll machine axial back pressure control strategy and combining a self-adaptive lead advanced tracking PID dynamic electromagnetic force control method, an actual electromagnetic air gap does not need to be calculated, a complex electromagnetic mathematical model does not need to be established, accurate high dynamic back pressure can be obtained through electromagnetic suction, exhaust port pressure, angle and speed information, high-performance axial gas separation force balance is realized, and high-performance axial near-zero friction dynamic contact sealing is realized between scrolls of the scroll machine.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a flow chart of a method of dynamic control of axial backpressure in an embodiment of the present invention;
FIG. 2 is a schematic diagram of the structure of the electromagnetic mechanism and the balance of the axial gas separation force and the axial electromagnetic control force in the embodiment of the present invention;
FIG. 3 is a flowchart of the "rotational speed-advance step number" curve acquisition in the embodiment of the present invention;
fig. 4 is a flowchart of advanced control of the axial electromagnetic control force of the electromagnetic mechanism in the embodiment of the invention;
FIG. 5 is a graph of axial separation force, vent pressure and angle of rotation for an embodiment of the present invention;
FIG. 6(a) is a graph of conventional PID tracking at a frequency of 50 Hz;
FIG. 6(b) is a graph of the optimum predictive advanced tracking control at a frequency of 50Hz in an embodiment of the present invention;
FIG. 6(c) is an iterative optimization curve of the number of system steps at different frequencies according to an embodiment of the present invention;
FIG. 7 is a flow chart of a PID closed-loop algorithm in an embodiment of the invention.
Wherein, 1, a static vortex disk bottom plate; 2. a first iron core; 3. an electromagnetic coil; 4. a second iron core; 5. a compression chamber; 6. a static scroll pan; 7. a movable scroll pan; 8. an electromagnetic control force detecting member.
Detailed Description
The invention is further described with reference to the following figures and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, 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.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
An axial back pressure dynamic control method is suitable for a scroll machine which adopts an electromagnetic mechanism to counteract axial gas separation force, and as shown in fig. 1, the control method comprises the following steps:
s1: sampling actual electromagnetic control force at the current rotating speed at equal time intervals in a stable running state of the scroll machine, comparing the actual electromagnetic control force with target electromagnetic control force at each sampling moment at the current rotating speed to obtain a total difference value between the actual electromagnetic control force and the target electromagnetic control force in a single sampling period, and determining the optimal advance step number which enables the total difference value to be minimum by adopting an iteration method; setting a rotation speed increment, acquiring optimal advanced steps corresponding to different rotation speeds, and generating a rotation speed-advanced step curve;
as a preferred embodiment, the specific method for judging whether the scroll machine is in the stable operation state is as follows: and detecting the actual electromagnetic control force at the current moment, comparing the actual electromagnetic control force with the target electromagnetic control force at the current moment to obtain a control error, and determining that the scroll machine is in a stable operation state when the control errors in the last three periods are all lower than 5%.
As a preferred embodiment, the specific method for determining the optimal advance step number by using an iterative method to minimize the overall difference between the actual electromagnetic control force f (k) and the target electromagnetic control force fa (k) is as follows:
inputting electromagnetic control force F (k) ═ Fa (k + N) to the movable scroll at the time k (namely, as shown in fig. 7, in the PID closed-loop control algorithm implemented specifically at the time k, the expected target before the closed loop is Fa (k + N) advanced by N steps), and judging that the value of N is N when the total difference between the actual electromagnetic control force and the target electromagnetic control force reaches the minimum value according to the PID advanced prediction balance optimization performance index0；
Wherein N is the current advance step number, and the total tracking step number in a single period (actually, in the digital control system, one period is composed of a plurality of points, and the total tracking point number can be defined as the total tracking step number) is set as k0The value range of the advance step number N is: n is an element of [0, k ]0]。
As a preferred embodiment, the PID look-ahead balance optimization performance index minErr is:
Figure BDA0002306483200000061
wherein k is the current sampling time, F (i) is the actual electromagnetic control force corresponding to the time i, and Fa (i) is the target electromagnetic control force at the time i.
S2: detecting the exhaust pressure and the turning angle value at the current moment, and obtaining the axial gas separation force at the current moment by combining an 'axial gas separation force-turning angle-exhaust pressure' curve (the obtaining method of the curve is disclosed in patent application with the publication number of CN110005611A, and the patent application of the name of an electromagnetic mechanism of a scroll machine and a control method thereof has description, and the description is not repeated herein); determining the current rotating speed according to the current rotating angle value, and determining the advance step number N by combining a rotating speed-advance step number curve0(ii) a The advance step number of the movable scroll disk is N by combining the axial gas separating force at the current moment0PID advance control of (1).
As a preferred embodiment, the specific method of "determining the current rotation speed according to the current rotation angle value" includes:
Figure BDA0002306483200000062
where V is the rotation speed, theta (k) is the rotation angle value at the moment of k, and theta0The initial angle value is r, the radius of the movable scroll disk is r, and the time consumed by the rotation angle theta (k) is t.
In a preferred embodiment, the step number of advancing the movable scroll is N in combination with the axial gas separating force at the current moment0The specific method of PID control of (1) is as follows: if the target electromagnetic control force corresponding to the current time k is fa (k), the electromagnetic control force F (k) actually output to the movable scroll by the electromagnetic mechanism at the time k is F (k)a(k+N0)。
It should be noted that, in some preferred embodiments, step S1 is completed in an off-line state, and step S2 is executed in an on-line control process, and the above control process may be performed continuously in an on-line state (i.e., the scroll machine is in an on-line operation state, and the dynamic control and adjustment of the axial back pressure are performed according to the continuous circulation of the program flow), or may be performed at intervals in an interrupted manner (i.e., the dynamic control and adjustment of the axial back pressure are performed at intervals in the on-line operation state of the scroll machine).
The present invention will be described below by taking the structure shown in fig. 2 as an example, and it should be noted that the control method shown in this embodiment can be applied to the electromagnetic mechanism with the structure shown in fig. 2, and can also be applied to other electromagnetic mechanisms with different topology forms of force closed-loop feedback.
The structure shown in fig. 2 adopts an annular electromagnet installed on a fixed scroll to realize a dynamic electromagnetic force structure for balancing gas separation force, and the sectional schematic diagram is as follows:
the scroll machine comprises an orbiting scroll and a fixed scroll, and particularly, further comprises an axial force electromagnetic control mechanism which adopts the axial back pressure dynamic control method to counteract the axial gas separating force between the orbiting scroll and the fixed scroll.
As a preferred embodiment, the axial force electromagnetic control mechanism comprises a control part, a detection part and an electromagnetic assembly; preferably:
as shown in fig. 2, a fixed scroll 6 is disposed on a fixed scroll base plate 1, and an electromagnetic assembly is disposed between the orbiting scroll and the fixed scroll, the electromagnetic assembly including an electromagnetic coil 3, a first iron core 2, and a second iron core 4, specifically: the first iron core 2 is arranged between the movable scroll 7 and the fixed scroll 6, the electromagnetic coil 3 is arranged between the first iron core 2 and the movable scroll 7, the second iron core 4 is arranged at the edge of the movable scroll 7, and the first iron core 2 is opposite to the second iron core 4, so that the electromagnetic force F (namely, axial control force) between the first iron core 2 and the second iron core 4 can be adjusted by adjusting the current direction and the current magnitude in the electromagnetic coil to counteract the axial gas separation force Fa1-Fa3 generated in the compression cavity 5 between the movable scroll 7 and the fixed scroll 7;
the detection part includes: a pressure detecting member including an electromagnetic control force detecting member 8 as shown in fig. 2, and an exhaust pressure detecting member (not shown) provided at an exhaust port extending line of the scroll machine for detecting an exhaust pressure at an exhaust port of the scroll machine, and a rotation angle detecting member (not shown) provided at a drive shaft of the scroll machine for detecting rotation angle information of the movable scroll; it should be noted that the detected electromagnetic control force of the electromagnetic control force detecting member 8 includes an electromagnetic attraction force and an electromagnetic pressure.
The control part is respectively connected with the detection part and the control execution part, and correspondingly adjusts the current in the electromagnetic assembly according to the detection result of the detection part, so that the axial electromagnetic force counteracts the axial gas separation force between the movable scroll and the fixed scroll.
In practical applications, taking a scroll machine as an example, a certain degree of delay due to core hysteresis exists in an axial force electromagnetic balance system, and the delay is particularly significant when the speed or frequency is fast, which causes a serious influence on dynamic tracking performance, and conventional PID cannot eliminate the delay, so that the present embodiment aims to provide an advanced prediction PID control method to eliminate a control error caused by the delay. According to the dynamic control method for axial backpressure, firstly, the optimal advance step number N is calculated0Optimal number of steps in advance for the system N0The selection of (2) requires a criterion to complete the determination of the optimal value of the number of steps in advance of the system.
In the performance evaluation method of the optimal system minimum variance in the embodiment, in an operation period of the scroll machine, the system continuously samples the magnitude of the electromagnetic attraction force f (k) at the time k, and compares the magnitude with the target electromagnetic attraction force fa (k), and the performance index minErr of the advanced prediction balance optimization of the PID is:
Figure BDA0002306483200000081
the value of the advanced step number N of the system is continuously iterated and optimized in the threshold, and the most suitable value of the advanced prediction step number N of the system is determined by taking the minErr value as the basis, and the specific iteration mode is as shown in fig. 3:
as shown in fig. 3, the initialization rotational speed V0And a sampling step number N, in order to clarify the corresponding position relation at different moments, determining the corresponding initial position when k is 0, and determining the system under a certain working conditionThreshold N for maximum number of early stepsmax(if the total tracking step number is 360, the value range is 0-359, which is related to the maximum delay time and frequency of the target compressor); when the system starts to operate, the system performs PID operation according to the error between the feedback quantity at the k moment and the target value and stores the error in a period of the rotation angle of the main shaft of the scroll, wherein the k value range in a single sampling period is 0-359 (in the embodiment, the total tracking step number is illustrated as 360, and the actual total tracking step number can be selected in a compromise mode according to the requirements of control precision and rapidity);
according to a formula (1), the optimized performance index of the PID controller is tracked in advance, whether the system is in a stable state or not is judged according to the difference between the error values of the system in the last three times which cannot exceed 5%, the current index is stored when the system is stable, and the number N of the advance steps of the system is increased by one in an iteration mode, wherein the value range of N is 0-359. When the system finishes the iterative search of the system error minErr values under different rotating speeds, the error minimum value is found, the N value corresponding to the value is determined as the optimal advance step number, and the rotation speed increment V is usedΔFinding out N values corresponding to different rotating speeds V and generating a corresponding speed-optimal advance step number curve (N)maxSet according to actual requirements).
Meaning of the three Loop variables in FIG. 3 (flow sheet from Top to bottom)
(1) Analyzing the tracking error at different time k in one period under the condition of fixed rotating speed, and judging whether the tracking error is stable or not (each fixed N, k value is from 0 to kmaxValue cycling);
(2) under the condition of fixed rotating speed, selecting the optimal sampling step number from different sampling step number N values (each fixed rotating speed N, N value optimizing parameter can be from 0 to NmaxValue cycle finding);
(3) scanning different rotation speeds in order to select the corresponding optimal advance step number N under the condition of different rotation speeds0。
During the execution of the process, the speed-optimal advanced step number curve and related parameters can be stored in a system memory, and when the system is started, whether the optimal advanced step number N matched with the current working condition exists or not is searched from the processor memory firstly0When N is present0If existing, the current N can be called directly0The value is subjected to advanced prediction PID operation, so that the system operation speed is improved.
As shown in fig. 4, the dynamic control method for axial back pressure according to the present embodiment performs the advance tracking of the curved surface as a whole, and the advance tracking step number N changes when the rotation speed changes, and fig. 4 illustrates how to calculate the rotation speed and find the corresponding optimal advance step number N in the "speed-N value" table0Then the axial separation force f tracked at the moment k is obtainedp[θ(k+N)]The following describes the steps of the dynamic control method for axial back pressure in detail with reference to fig. 4:
initializing relevant parameters, and if the total step number in a single period is x and the angle of each step is y, determining that the value range of k in the single period is k belongs to [0, x/y-1]](ii) a If the total step number n in each period is set to be 360 degrees, the angle of each step is 1 degree, and the value range of k in a single period is k epsilon [0, 359 ∈](ii) a Determining the angle corresponding to the scroll machine when k is 0 as the initial angle theta0Refreshing the curve family F (theta, p); because the relationship among the axial separating force, the pressure of the exhaust port and the rotation angle of the scroll machine is shown in a curved surface relationship chart 5 under the actual working condition, the gas pressure needs to be measured firstly, a curve family needs to be searched or interpolated, and a target tracking curve under the current gas pressure, namely a relationship curve between the axial separating force and the rotation angle, is determined; by measuring the angle theta (k) at the moment k, the rotated angle theta (k) -theta at the moment k is determined0According to the formula:
Figure BDA0002306483200000091
the rotation speed is calculated, the corresponding N value is found from the speed-N value table, and the angle theta of each step length is calculated△According to the formula θ (k + N) — (k + N) · θ△Determining the position of the target corner tracked in advance, and finding the axial gas pressure f from the relation curve of the axial separating force and the cornerp[θ(k+N)]I.e. the axial separation force at time k needs to be of magnitude fp[θ(k+N)]The electromagnetic force is balanced, the PID is operated to lead the advanced tracking curve to achieve the aim of accurate tracking, and the PWM duty ratio is modified in real time to update the curve family.
Wherein, the meaning of the circulation loop in fig. 4: in thatIn the debugging process, the updated initial angle theta is judged0Whether there is a change, if it can be adjusted manually or implemented programmatically. It should be noted that, in fig. 4, "setting an initial value of a PWM module parameter, and setting parameters such as a PID module interrupt time" may include: the system preset parameters are directly adopted, and can be changed on line.
The key parameters of the simulation experiment platform are shown in the following table 1:
Figure BDA0002306483200000092
Figure BDA0002306483200000101
TABLE 1 simulation experiment platform Key parameters
Respectively adopting a conventional PID controller and a PID controller with self-adaptive advanced steps to track an axial balance force curve between a movable vortex disk and a fixed vortex disk of a scroll compressor, as shown in figure 7, a PID closed-loop algorithm flow chart in the embodiment of the invention is to add an advanced compensation link e on the basis of a traditional PID servo control systemNkUsing the force F required for the target position at time k + Na(k + N) to track the control quantity F at time ka(k) And the transfer function PID (k) of the PID model, the transfer function F of the driving circuit model1Circuit(k) Transfer function F of electromagnet model2EleDevice(k) And the feedback quantity F (k) forms a closed-loop control system, and the stable tracking of the axial balance force curve between the movable scroll and the fixed scroll of the scroll compressor is realized through the continuous iterative optimization of the system.
When the target curve frequency is 50Hz, the curve tracking capability under the conventional PID control is shown in the following figure 6(a), and it can be seen that the system has a phenomenon of obvious phase lag. When the system steps advance the tracking algorithm control intervention, the system is optimized to the optimal position as shown in fig. 6 (b). Fig. 6(c) is an iterative optimization curve for finding the optimal advance step number under different frequencies, when the gas pressure is 16Mpa and the system rotation frequency is 50Hz, the optimal advance step number N of the controlled variable obtained through algorithm calculation is 20, because the error minErr is the minimum at this time, which is about 3.2%. When the target curve frequency is different, the required optimal advance step number is changed, for example, when the target curve frequency is 30Hz, the system optimal advance step number N is changed to 17, and the error minErr is minimum at about 2%.
As can be seen from fig. 6(a) and 6(b), the system curve tracking effect can be effectively improved by using the advance tracking control, and as can be seen from fig. 6(c), in addition to the difference in the optimum advance, the system control error evaluation ratio also changes when the frequency changes.
The embodiment also provides a scroll machine, which comprises an orbiting scroll and a fixed scroll, and further comprises an axial force electromagnetic control mechanism, wherein the axial force electromagnetic control mechanism adopts the axial back pressure dynamic control method to counteract the axial gas separating force between the orbiting scroll and the fixed scroll.
As a preferred technical solution, the axial force electromagnetic control mechanism includes a control part, a detection part and an electromagnetic assembly; wherein:
a detecting part including a pressure detecting part including an electromagnetic control force detecting part as shown in 8 of fig. 2 and an exhaust pressure detecting part (not shown) provided at an exhaust port extension pipe of the scroll machine for detecting an exhaust pressure of an exhaust port of the scroll machine, and a rotation angle detecting part provided at a drive shaft of the scroll machine for detecting rotation angle information of the movable scroll;
the electromagnetic assembly comprises a first magnetic circuit iron core fixed on the movable scroll disk and a second magnetic circuit iron core fixed on the fixed scroll disk, and the excitation coil is fixed between the two iron cores;
the control part is respectively connected with the detection part and the electromagnetic assembly, and correspondingly adjusts the current in the electromagnetic assembly according to the detection result of the detection part, so that the axial electromagnetic force counteracts the axial gas separation force between the movable scroll and the fixed scroll.
On the aspect of dynamic electromagnetic force control, an advanced PID tracking method, an advanced step number determining method, an establishment method of an advance N database at different frequencies, and a method for adaptively adjusting the advance according to the advance database and real-time speed information are provided, so that the electromagnetic mechanism can realize the fast lag-free tracking of dynamic electromagnetic force at different rotating speeds, and high dynamic performance is realized. By adopting a force closed loop-based scroll machine axial back pressure control strategy and combining a self-adaptive lead advanced tracking PID dynamic electromagnetic force control method, an actual electromagnetic air gap does not need to be calculated, a complex electromagnetic mathematical model does not need to be established, accurate high dynamic back pressure can be obtained through electromagnetic suction, exhaust port pressure, angle and speed information, high-performance axial gas separation force balance is realized, and high-performance axial near-zero friction dynamic contact sealing is realized between scrolls of the scroll machine.
Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and not to be construed as limiting the present invention, and those skilled in the art can make changes, modifications, substitutions and alterations to the above embodiments without departing from the principle and spirit of the present invention, and any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention still fall within the technical scope of the present invention.

Claims (10)

1. The axial back pressure dynamic control method is suitable for a vortex machine which adopts an electromagnetic mechanism to offset axial gas separation force, and is characterized by comprising the following steps:
sampling actual electromagnetic control force at the current rotating speed at equal time intervals in a stable running state of the scroll machine, comparing the actual electromagnetic control force with target electromagnetic control force at each sampling moment at the current rotating speed to obtain a total difference value between the actual electromagnetic control force and the target electromagnetic control force in a single sampling period, and determining the optimal advance step number which enables the total difference value to be minimum by adopting an iteration method; setting a rotation speed increment, acquiring optimal advanced steps corresponding to different rotation speeds, and generating a rotation speed-advanced step curve;
detecting the exhaust pressure and the rotation angle value at the current moment, and combining an axial gas separation force-rotation angle-exhaust pressure curve to obtain the axial gas separation force at the current moment; determining the current rotating speed according to the current rotating angle value, and determining the advance step number N by combining a rotating speed-advance step number curve0(ii) a The advance step number of the movable scroll disk is N by combining the axial gas separating force at the current moment0PID advance control of (1).
2. The dynamic control method for axial back pressure according to claim 1, wherein the specific method for determining whether the scroll machine is in a stable operation state is as follows: and detecting the actual electromagnetic control force at the current moment, comparing the actual electromagnetic control force with the target electromagnetic control force at the current moment to obtain a control error, and determining that the scroll machine is in a stable operation state when the control errors in the last three periods are all lower than 5%.
3. The dynamic control method for axial back pressure according to claim 1, characterized in that the specific method for determining the optimal number of advance steps by using an iterative method to minimize the overall difference between the actual electromagnetic control force f (k) and the target electromagnetic control force fa (k) is:
inputting electromagnetic control force F (k) ═ Fa (k + N) to the movable scroll disk at the moment k, and judging that the value of N is N when the total difference between the actual electromagnetic control force and the target electromagnetic control force reaches the minimum according to the PID advanced prediction balance optimization performance index0；
Wherein N is the advance step number, and the sampling times in a single period are set to be k0The value range of the advance step number N is: n is an element of [0, k ]0]。
4. The dynamic control method of axial backpressure of claim 3, wherein the PID lead predictive balance optimization performance index minErr is:
Figure FDA0002306483190000011
wherein k is the current sampling time, F (i) is the actual electromagnetic control force corresponding to the time i, and Fa (i) is the target electromagnetic control force at the time i.
5. The dynamic control method for axial backpressure of claim 4, wherein the total number of steps in a single period is x, and the angle of each step is y, so that the value range of k in the single period is k e [0, x/y-1 ].
6. The dynamic control method for axial back pressure according to claim 1, wherein the specific method of "determining the current rotation speed according to the current rotation angle value" is as follows:
Figure FDA0002306483190000021
where V is the rotation speed, theta (k) is the rotation angle value at the moment of k, and theta0The initial angle value is r, the radius of the movable scroll disk is r, and the time consumed by the rotation angle theta (k) is t.
7. The method for dynamically controlling axial backpressure of claim 1, wherein the step number of advancing the orbiting scroll in combination with the axial gas separating force at the present time is N0The specific method of PID control of (1) is as follows: if the target electromagnetic control force corresponding to the current time k is fa (k), the electromagnetic control force F (k) actually output to the movable scroll by the electromagnetic mechanism at the time k is F (k)a(k+N0)。
8. A scroll machine comprising an orbiting scroll and a non-orbiting scroll, further comprising an axial force electromagnetic control mechanism for canceling an axial gas separating force between the orbiting scroll and the non-orbiting scroll by using the axial back pressure dynamic control method as claimed in any one of claims 1 to 7.
9. The scroll machine according to claim 8, wherein said axial force electromagnetic control mechanism comprises a control member, a detection member and an electromagnetic assembly; wherein:
the electromagnetic assembly is arranged between the movable scroll disk and the fixed scroll disk and used for generating electromagnetic control force to offset axial gas separation force between the movable scroll disk and the fixed scroll disk;
the detection part includes: the pressure detection part comprises an electromagnetic control force detection part and an exhaust pressure detection part which is arranged at an exhaust port extension pipeline of the scroll machine and used for detecting the pressure of an exhaust port of the scroll machine; the rotation angle detection piece is arranged at a driving shaft of the scroll machine and used for detecting rotation angle information of the movable scroll;
the control part is respectively connected with the detection part and the control execution part, and correspondingly adjusts the current in the electromagnetic assembly according to the detection result of the detection part, so that the axial electromagnetic force counteracts the axial gas separation force between the movable scroll and the fixed scroll.
10. A storage medium, characterized in that a computer program is stored which, when being processed and executed, carries out the steps of the method for dynamic control of axial back pressure according to any one of claims 1 to 7.
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