PID (Proportion Integration Differentiation) control method and device of one-inlet two-outlet system

Abstract

The invention discloses a PID control method and device for a one-inlet two-outlet system, and the method comprises the steps: calculating a control increment based on a PID controller, the PID controller is used for controlling at least two paths of control outputs based on one measurement input, the two paths of control outputs correspond to a first output quantity and a second output quantity respectively, wherein the steady-state gain of the first output quantity is greater than or equal to the second output quantity; determining a center value based on a preset upper adjustment limit and a preset lower adjustment limit of the second output quantity; determining a coefficient K based on a preset upper adjustment limit, a preset lower adjustment limit, the center value and the direction of the control increment of the second output quantity; and respectively calculating and obtaining a first output quantity and a second output quantity based on the coefficient K. Through an intuitive and linear solution, the adjustment requirements of the system on the first output quantity and the second output quantity when large disturbance exists or does not exist are met; and the requirements that the first output quantity participates in adjustment and the second output quantity runs near the central value of the adjustable interval after the large disturbance is eliminated are met.

Description

Technical Field

[0001] The present invention relates to the field of automatic control technology, and in particular to a PID control method and device for a one-input and two-output system. Background Art

[0002] In the field of industrial control, in order to achieve precise control of process indicators, a one-input and two-output process control system is often configured, and the following process control requirements are proposed:

[0003] (1) For example, a large-diameter valve is combined with a small-diameter valve, or a large-flow speed-regulating pump is combined with a small-flow speed-regulating pump;

[0004] (2) When a large disturbance occurs, use large-diameter valves or large-flow speed-regulating pumps to adjust the response in time;

[0005] (3) After the large disturbance disappears, large-diameter valves or large-flow speed regulating pumps are required to participate in regulation as little as possible, and small-diameter valves or small-flow speed regulating pumps are mainly used to achieve fine regulation;

[0006] (4) In the absence of large disturbances, small-diameter valves or small-flow speed-regulating pumps are required to operate as close to the center value of the adjustable range as possible to improve response characteristics and control accuracy.

[0007] This demand is common in the industrial field, and if it can be well solved, it will have broader significance.

[0008] At present, the following solutions are generally adopted to meet the above process control requirements:

[0009] (1) MVb refers to the control output of a large-diameter control valve or a large-flux speed-regulating pump, and MVs refers to the control output of a small-diameter control valve or a small-flux speed-regulating pump;

[0010] (2) PIDb is a PID controller that uses MVb as output; PIDs is a PID controller that uses MVs as output;

[0011] (3) Switching rules are formulated based on the values ​​of ERR, MVb, MVs, etc. to achieve control switching between PIDb and PIDs when different deviations, MVb, and MVs values ​​are met, so as to realize the above-mentioned process control requirements.

[0012] Then the disadvantages of the above scheme are as follows:

[0013] (1) The switching rules are complex, the relationship between the control scheme and the process requirements is not intuitive and linear, and on-site debugging and maintenance are difficult;

[0014] (2) There are usually jumps in the control switching process, resulting in poor control accuracy.

[0015] Use Figure 1and Figure 2 Conventional split-range control as shown does not meet the process control needs. Summary of the invention

[0016] In order to overcome the deficiencies of the above technologies, the present invention provides a PID control method and device for a one-input and two-output system. Through an intuitive and linear solution, it not only meets the system's regulation requirements for MVb and MVs with and without large disturbances, but also meets the requirements that after the large disturbance is eliminated, MVb participates less in the regulation and MVs runs near the center value of the adjustable range.

[0017] The technical solution adopted by the present invention to overcome the technical problems is:

[0018] The first aspect of the present invention provides a PID control method for a one-input and two-output system, wherein the one-input and two-output system at least includes a PID controller, and the PID control method includes: calculating a control increment based on the PID controller, wherein the PID controller is used to control at least two control outputs based on a measurement input, wherein the two control outputs correspond to a first output quantity and a second output quantity respectively, wherein the steady-state gain of the first output quantity is greater than or equal to the second output quantity; determining a center value based on a preset upper adjustment limit and a preset lower adjustment limit of the second output quantity; determining a coefficient K based on the preset upper adjustment limit, the preset lower adjustment limit, the center value and the control increment of the second output quantity, including: if the second output quantity MVs is greater than the center value, determining the coefficient K based on the preset upper adjustment limit and the center value of the second control output quantity using formula (1), if the control increment is less than 0, the coefficient K is equal to 1, if the second output quantity MVs is less than or equal to the center value, determining the coefficient K based on the preset lower adjustment limit and the center value of the second control output quantity using formula (2), if the control increment is greater than 0, the coefficient K is equal to 1, wherein MVs is the second output quantity,

[0019] K = ((preset upper limit of adjustment - center value) - (MVs - center value)) / (preset upper limit of adjustment - center value) (1)

[0020] K = ((center value - preset adjustment lower limit) - (center value - MVs)) / (center value - preset adjustment lower limit) (2)

[0021] Based on the coefficient K, the first output quantity and the second output quantity are respectively calculated and obtained.

[0022] The coefficient is used to achieve linear switching of the two MVs in the one-input and two-output system to avoid output jumps. Only one PID controller is used to achieve one-input and two-output system control, and the parameters are easier to adjust.

[0023] Furthermore, the determining coefficient K based on the preset upper adjustment limit, the preset lower adjustment limit, the center value and the control increment of the second output quantity also includes limiting the coefficient K so that the coefficient K is not greater than 1.0 and not less than 0.0.

[0024] Further, the first output quantity and the second output quantity are calculated and obtained based on the coefficient K, specifically including: calculating the first output quantity and the second output quantity based on formula (3) and formula (4) respectively,

[0025] MVb′=MVb+(1.0-K)*△MV (3)

[0026] MVs′=MVs+K*magnification*△MV (4)

[0027] Among them, MVb is the current first output, MVb′ is the first output to be output, MVs is the current second output, MVs′ is the second output to be output, the amplification factor is the steady-state gain of MVb / the steady-state gain of MVs, and △MV is the control increment.

[0028] Furthermore, it also includes sequentially judging the state of controlling the current second output and the state of controlling the first output, thereby calculating the second output and the first output in sequence, wherein calculating the second output specifically includes: if the state of controlling the second output is manual, then no operation is performed on the second output; if the state of controlling the second output is automatic, then judging the state of controlling the first output, and if the state of controlling the first output is automatic, then calculating the second output based on the formula (4); if the state of controlling the first output is manual, then calculating the second output based on the formula (5), MVs′=MVs+amplification factor*△MV(5), and limiting the second output based on a preset upper adjustment limit and a preset lower adjustment limit.

[0029] Furthermore, it also includes sequentially determining the state of controlling the current second output and the state of controlling the first output, thereby sequentially calculating the second output and the first output,

[0030] The step of calculating the first output quantity specifically includes:

[0031] If the state of controlling the first output quantity is manual, the first output quantity is not operated;

[0032] If the state of controlling the first output is automatic, then the state of controlling the second output is determined.

[0033] If the state of controlling the second output is automatic, the first output is calculated based on the formula (3);

[0034] If the state of controlling the second output is manual, the first output is calculated based on formula (6):

[0035] MVb′=MVb+ΔMV (6).

[0036] Furthermore, it also includes replacing the central value with a preset value, where the preset value is any value within the range of a preset lower adjustment limit and a preset upper adjustment limit.

[0037] The coefficient K is related to the relative position of MVs and the center value of the adjustable interval and the direction of △MV change. The further MVs deviates from the center value, the smaller the coefficient. If the direction of △MV change makes MVs approach the center value of the adjustable interval, the coefficient K is set to 1.0. When MVs approaches the upper or lower limit of the adjustable interval, the adjustment of MVs becomes slower and slower, while the adjustment of MVb becomes faster and faster; when MVs approaches the center value of the adjustable interval, MVs adjusts at full speed and MVb remains unchanged.

[0038] Another aspect of the present invention also proposes a PID control device for a one-input and two-output system, which is used to run the above-mentioned PID control method for a one-input and two-output system, including: a PID module, a coefficient calculation module and a linear switching module, wherein the PID module controls at least two control outputs according to a measurement input, and obtains a control increment based on PID parameters and control deviation calculation; the coefficient calculation module is used to calculate a center value, and determine a coefficient K based on a preset upper limit, a preset lower limit, an adjustable range center value and a control increment; the linear switching module is used to switch the control of a first output quantity and a second output quantity based on the coefficient K.

[0039] The beneficial effects of the present invention are:

[0040] 1. Use coefficients and magnifications to implement a PID controller to simultaneously control two MVs in a one-input and two-output system;

[0041] 2. Use the coefficient to achieve linear switching between two MVs in a one-input and two-output system to avoid output jumps;

[0042] 3. Only one PID controller is needed to realize one-input and two-output system control, and the parameters are easier to adjust;

[0043] 4. It not only meets the system's regulation needs for MVb and MVs with and without large disturbances, but also meets the requirements that after the large disturbance is eliminated, MVb participates less in the regulation and MVs runs near the center value of the adjustable range. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of a conventional control scheme of a dual-valve co-directional engineering according to an embodiment of the present invention;

[0045] Figure 2 It is a schematic diagram of a conventional control scheme of dual-valve reverse engineering according to an embodiment of the present invention;

[0046] Figure 3 A schematic flow chart of a PID control method for a one-input and two-output system according to an embodiment of the present invention;

[0047] Figure 4 It is a schematic diagram of the corresponding relationship between the coefficient K and the operating position of MVs;

[0048] Figure 5 A control logic diagram of a PID control method for a one-input and two-output system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0049] First, some abbreviations and key terms mentioned in the present invention are explained.

[0050] PV: refers to the measured value of the process production, including temperature, pressure, flow, liquid level, analysis and other types, which can be used to measure process control indicators;

[0051] SV: refers to the set value of the process control index;

[0052] MV: Control output, which is the operable value of the process. For example, by adjusting the pump speed, valve opening, current intensity, etc., the material balance or energy balance of the process can be changed to make the PV value approach the SV value.

[0053] One-inlet-two-outlet system refers to a system where one PV corresponds to two MVs, for example, the reactor temperature (one PV) is controlled by the opening of the two-way cooling water valve (MV), the reactor pressure is controlled by two discharge pumps, and the inlet and outlet valves are combined to control the liquid level of the water storage tank, etc.

[0054] Steady-state gain: Assuming that other MVs remain unchanged, the final change in PV (absolute value) caused by a unit change in a single MV is defined as the steady-state gain of the MV;

[0055] MVb: In the above one-input and two-output system, the MV with a larger steady-state gain is called MVb;

[0056] MVs: In the above one-input and two-output system, the MV with smaller steady-state gain is called MVs;

[0057] Amplification factor: In the above one-input two-output system, amplification factor = steady-state gain of MVb / steady-state gain of MVs;

[0058] ERR: Deviation between PV and SV;

[0059] PID controller: A control algorithm that continuously corrects MV by performing proportional, integral, and differential operations on ERR or PV to make the PV value approach the SV value. PID controllers are widely used in the industrial field.

[0060] △MV: Control increment, calculated periodically by the PID controller. When the MV is in automatic control, △MV is used to continuously correct the MV output; when the MV is in manual control, the MV is manually set by the operator and is not affected by △MV.

[0061] Large-diameter valves and small-diameter valves: The difference in the nominal diameter of the valves. Large-diameter valves can achieve large flow regulation, while small-diameter valves can achieve small flow regulation;

[0062] Large-flow speed-regulating pump and small-flow speed-regulating pump: The large-flow speed-regulating pump has the function of speed regulation, can handle a large amount of fluid, and has the characteristics of large flow, high pressure and great energy saving effect; the small-flow speed-regulating pump has the function of speed regulation, the flow is relatively small, and can accurately control the flow and pressure, which is suitable for low flow and high precision occasions.

[0063] In order to facilitate those skilled in the art to better understand the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The following is only exemplary and does not limit the protection scope of the present invention.

[0064] like Figure 3 As shown, the control method of a PID control system of a one-input and two-output system described in this embodiment specifically includes:

[0065] S1, calculating a control increment based on a PID controller, the PID controller is used to control at least two control outputs based on a measurement input, the two control outputs correspond to a first output quantity and a second output quantity, respectively, wherein a steady-state gain of the first output quantity is greater than or equal to the second output quantity.

[0066] Set up a PID controller and calculate the deviation ERR between PV and SV through PID to obtain the control increment △MV.

[0067] It should be noted that a conventional PID controller uses PID parameters and control deviation to calculate the control increment △MV and then calculates the output. The PID controller described in this application uses PID parameters and control deviation to calculate the control increment △MV, then calculates the distribution coefficient K, and then calculates the output.

[0068] It should be noted that if the steady-state gain of the first output is greater than or equal to the steady-state gain of the second output, the second output can be fully utilized to achieve fine tuning. In some practical applications, the steady-state gain of the first output may also be less than the steady-state gain of the second output, to achieve certain process purposes unknown to the inventor.

[0069] S2, determining a central value based on a preset upper adjustment limit and a preset lower adjustment limit of the second output amount.

[0070] The middle position between the preset upper adjustment limit and the preset lower adjustment limit of MVs is called the center value of the adjustable range.

[0071] The method also includes replacing the central value with a preset value, wherein the preset value is any value within the range of a preset lower adjustment limit and a preset upper adjustment limit.

[0072] In some embodiments, the central value can be replaced by any other value of the second output MVs in the adjustable range to obtain other targeted benefits. For example, if the economic operation point of MVs is 20%, the central value can be replaced by 20%. The adjustable range is the range between the preset upper limit and the preset lower limit of MVs.

[0073] S3, determining a coefficient K based on a preset upper adjustment limit, a preset lower adjustment limit, a center value of an adjustable range and a control increment of the second output.

[0074] If the second output is greater than the center value, the coefficient K is determined based on the preset upper limit of the second output and the center value, as shown in formula (1). If the control increment is less than 0, the coefficient K is equal to 1.

[0075] K = (preset upper limit of adjustment - center value) - (MVs - center value)) / (preset upper limit of adjustment - center value) (1)

[0076] like Figure 4 As shown in the figure, the corresponding relationship between coefficient K and the running position of MVs is shown. When MVs approaches the upper limit, the k value gradually approaches 0 from 1.0, so that the action amplitude of MVs gradually weakens and the action amplitude of MVb gradually increases; when MVs approaches the center value, MVs moves at full speed according to the amplitude of △MV, while MVb does not move at all, realizing the running preference of MVs approaching the center value, prompting MVs to gradually return to the vicinity of the center value when the system is stable.

[0077] If the second output is less than or equal to the center value, the coefficient K is determined based on the preset lower limit of the second output and the direction of the center value, as shown in formula (2). If the control increment is greater than 0, the coefficient K is equal to 1. Figure 4 As shown in the figure, when MVs approaches the lower limit, the k value gradually approaches 0 from 1.0, so that the movement amplitude of MVs gradually weakens and the movement amplitude of MVb gradually increases; when MVs approaches the center value, MVs moves at full speed according to the amplitude of △MV, while MVb does not move at all, realizing the operation preference of MVs tending to the center value, prompting MVs to gradually return to near the center value when the system is stable.

[0078] K = ((center value - preset lower limit of adjustment) - (center value - MVs)) / (center value - preset lower limit of adjustment) (2).

[0079] S4, based on the coefficient K, respectively calculate and obtain the first output quantity and the second output quantity.

[0080] like Figure 5As shown, the first output quantity and the second output quantity are calculated and obtained by the coefficient K, and the state of controlling the first output quantity and the state of controlling the second output quantity are firstly judged.

[0081] In one embodiment of the present invention, a large pump is used to control the first output amount, and a small pump is used to control the state of the second output amount.

[0082] S41, judging the working status of the small pump and the large pump in turn.

[0083] like Figure 5 As shown, if the small pump is in manual state, the process jumps to S43 to judge the working states of the large pump and the small pump in turn.

[0084] If the small pump is in automatic state, continue to judge the working state of the large pump. If the working state of the large pump is automatic, calculate the second output based on formula (3). If the working state of the large pump is manual, calculate the second output based on formula (4).

[0085] MVs′=MVs+K*magnification*△MV (3)

[0086] MVs′=MVs+magnification*△MV (4)

[0087] S42, limiting the second output according to a preset lower adjustment limit and a preset upper adjustment limit.

[0088] S43, judging the working status of the large pump and the small pump in turn.

[0089] If the large pump is in manual mode, the calculation of the first output will not be performed directly;

[0090] If the large pump is in automatic state, the working state of the small pump is determined. If the small pump is in automatic state, the first output is calculated based on formula (5). If the small pump is in manual state, the second output is calculated based on formula (6).

[0091] MVb′=MVb+(1.0-K)*△MV (5)

[0092] MVb′=MVb+△MV (6)

[0093] In another embodiment of the present invention, the PID control method of a one-input two-output system proposed in the present invention can also be used for a one-input multiple-output system, and the coefficient K can be calculated through other related parameters. For example, a heating furnace can dynamically allocate the power output of multiple heating devices according to the temperature distribution of the furnace body while maintaining the overall heating amount.

[0094] In another embodiment, the present invention proposes a PID control device for a one-input and two-output system, comprising: a PID module, a coefficient calculation module and a linear switching module, wherein the PID module controls at least two control outputs according to a measurement input, and obtains a control increment based on PID parameters and control deviations; the coefficient calculation module is used to calculate a center value, and determine a coefficient K based on a preset upper limit, a preset lower limit, a center value of an adjustable range and a control increment; the linear switching module is used to switch control between a first output quantity and a second output quantity based on the coefficient K.

[0095] The present invention proposes a PID control method and device for a one-input and two-output system, which uses coefficients and magnification factors to realize a PID controller to simultaneously control two MVs of the one-input and two-output system, wherein the coefficient K is related to the relative position of MVs and the center value of the adjustable interval and the direction of change of △MV. The more MVs deviate from the center value, the smaller the coefficient. The direction of change of △MV makes MVs tend to the center value of the adjustable interval, and the coefficient K is set to 1.0. Therefore, when MVs tend to the upper or lower limit of the adjustable interval, the adjustment of MVs becomes slower and slower, while the adjustment of MVb becomes faster and faster; when MVs tend to the center value of the adjustable interval, MVs is adjusted at full speed, and MVb remains unchanged. It not only meets the system's adjustment requirements for MVb and MVs when there is or is not a large disturbance; it also meets the requirements that MVb participates less in the adjustment after the large disturbance is eliminated, and MVs runs near the center value of the adjustable interval. After field verification, the PID control method and device for a one-input and two-output system proposed by the present invention have achieved very good technical effects.

[0096] It should be noted that: in other embodiments, the steps of the corresponding method are not necessarily performed in the order shown and described in this specification. In some other embodiments, the steps included in the method may be more or less than those described in this specification. In addition, a single step described in this specification may be decomposed into multiple steps for description in other embodiments; and multiple steps described in this specification may be combined into a single step for description in other embodiments.

[0097] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The system and system embodiment described above are only illustrative, and some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

Claims

1. A PID control method for a one-input and two-output system, characterized in that: The one-input and two-output system at least includes a PID controller, and the PID control method includes: Calculating a control increment based on a PID controller, the PID controller being used to control at least two control outputs based on a measurement input, the two control outputs corresponding to a first output quantity and a second output quantity, respectively, wherein a steady-state gain of the first output quantity is greater than or equal to the second output quantity; determining a center value based on a preset upper adjustment limit and a preset lower adjustment limit of the second output; The coefficient K is determined based on a preset upper adjustment limit, a preset lower adjustment limit, a center value and a control increment of the second output, including: If the second output MVs is greater than the center value, the coefficient K is determined by using formula (1) based on the preset upper limit of the second control output and the center value. If the control increment is less than 0, the coefficient K is equal to 1. If the second output MVs is less than or equal to the center value, the coefficient K is determined by using formula (2) based on the preset lower limit of the second control output and the center value. If the control increment is greater than 0, the coefficient K is equal to 1. K = ((preset adjustment upper limit - center value) - (MVs - center value)) / (preset adjustment upper limit - center value) (1) K = ((center value - preset adjustment lower limit) - (center value - MVs)) / (center value - preset adjustment lower limit) (2) Based on the coefficient K, the first output and the second output are calculated and obtained respectively.

2. The PID control method of a one-input two-output system according to claim 1, characterized in that: Specifically, it includes: the preset upper adjustment limit, the preset lower adjustment limit, the center value and the control increment determination coefficient K based on the second output quantity, and also includes, The coefficient K is limited so that the coefficient K is not greater than 1.0 and not less than 0.

0.

3. The method of a PID control system of a one-input two-output system according to claim 2, characterized in that: The first output quantity and the second output quantity are calculated and obtained based on the coefficient K, specifically including: calculating the first output quantity and the second output quantity based on formula (3) and formula (4) respectively, MVb′=MVb+(1.0-K)*△MV (3) MVs′=MVs+K*magnification*△MV (4) Among them, MVb is the current first output, MVb′ is the first output to be output, MVs is the current second output, MVs′ is the second output to be output, the amplification factor is the steady-state gain of MVb / the steady-state gain of MVs, and △MV is the control increment.

4. The PID control method of a one-input two-output system according to claim 3 is characterized in that: The method further includes sequentially determining a state of controlling the current second output and a state of controlling the first output, thereby sequentially calculating the second output and the first output. The calculating of the second output quantity specifically includes: If the state of controlling the second output is manual, the second output is not operated; If the state of controlling the second output is automatic, then the state of controlling the first output is determined. If the state of controlling the first output is automatic, the second output is calculated based on the formula (4); If the state of controlling the first output is manual, the second output is calculated based on formula (5): MVs′=MVs+magnification*△MV (5) The second output amount is limited based on a preset upper adjustment limit and a preset lower adjustment limit.

5. The PID control method of a one-input two-output system according to claim 4, characterized in that: The method further includes sequentially determining a state of controlling the current second output and a state of controlling the first output, thereby sequentially calculating the second output and the first output. The step of calculating the first output quantity specifically includes: If the state of controlling the first output quantity is manual, the first output quantity is not operated; If the state of controlling the first output is automatic, then the state of controlling the second output is determined. If the state of controlling the second output is automatic, the first output is calculated based on the formula (3); If the state of controlling the second output is manual, the first output is calculated based on formula (6): MVb′=MVb+ΔMV (6).

6. The PID control method of a one-input two-output system according to claim 1, characterized in that: The method also includes replacing the central value with a preset value, where the preset value is any value within a range of a preset lower adjustment limit and a preset upper adjustment limit.

7. A PID control device for a one-input and two-output system, used for running a PID control method for a one-input and two-output system according to any one of claims 1 to 6, characterized in that: include: PID module, coefficient calculation module and linear switching module, The PID module controls at least two control outputs according to a measurement input, and calculates a control increment based on a PID parameter and a control deviation; The coefficient calculation module is used to calculate the center value and determine the coefficient K based on the preset upper limit of adjustment, the preset lower limit of adjustment, the center value of the adjustable range and the control increment; The linear switching module is used for switching and controlling the first output quantity and the second output quantity based on the coefficient K.

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