A double-fold line hysteresis implementation method based on rate limiting

Abstract

The application discloses a kind of double fold line hysteresis implementation methods based on rate limiting, the application is by judging the change direction of input signal, dynamically select corresponding rising fold line function or falling fold line function as the input of rate limiter, and the rising rate and falling rate of rate limiting function block are configured simultaneously: when rising direction, set as rising unlimited speed, falling rate is 0;When falling direction, set as rising rate is 0, falling unlimited speed.Rate limiting function block output is the control signal with double fold line hysteresis characteristics.The application overcomes the defects that traditional MAX / MIN implementation method is poor in interpretability and not easy to understand, and the logic is clear, easy to configure on DCS or PLC platform, especially suitable for the control of feedwater pump minimum flow recirculation valve, can effectively eliminate the frequent action of valve caused by measurement error and flow fluctuation.Simulation verification shows that the output effect of the application and the traditional method is completely consistent.

Description

Technical Field

[0001] This invention relates to the field of industrial process control technology, specifically to a method and control system for implementing double-segmented hysteresis based on rate limiting, which is particularly suitable for controlling the minimum flow recirculation valve of a feedwater pump. Background Technology

[0002] In industrial control systems, bi-segmented hysteresis is a commonly used nonlinear control strategy. The basic characteristics of this strategy are: when the input signal changes in an upward direction, the output signal changes according to a first upward-sloping piecewise linear function F2(x); when the input signal changes in a downward direction, the output signal changes according to a second downward-sloping piecewise linear function F1(x). A hysteresis gap exists between F1(x) and F2(x), within which changes in the input signal do not alter the magnitude of the output signal, thus forming a bi-segmented hysteresis relationship with directional memory characteristics.

[0003] For the input / output characteristics of the dual-segmented hysteresis function, please refer to the appendix of the instruction manual. Figure 1 And Table 1. Table 1 gives a typical example of a bilinear hysteresis mapping, where F1(x) and F2(x) correspond to different output values ​​when the input signal varies in the range of 0 to 110, and there is a clear hysteresis gap between them.

[0004] In existing technologies, the mainstream logic configuration implementation method for dual-segmented hysteresis function is as shown in the appendix to the manual. Figure 2 As shown, this method typically employs a combination of maximum value (MAX) and minimum value (MIN) function blocks. While its logical structure is relatively simple and widely used in engineering, it suffers from poor interpretability, difficulty in understanding and maintenance. Engineers struggle to intuitively grasp the formation mechanism of the hysteresis gap and the direction switching logic from the function block connections, hindering the debugging, optimization, and troubleshooting of control strategies.

[0005] In the control application of the minimum flow recirculation valve for feedwater pumps, the bilinear hysteresis strategy is of great significance. During operation, when the feedwater flow rate falls below the pump's minimum safe flow rate, the corresponding recirculation path needs to be opened through the recirculation valve to ensure that the flow rate within the pump does not fall below the minimum requirement. Due to errors in flow measurement and normal fluctuations in feedwater flow, if the recirculation valve control strategy is overly sensitive to changes in input flow, it will lead to frequent valve operation, affecting the stability of boiler feedwater flow and hindering the stable operation of automatic feedwater control. It will also increase valve mechanical wear and failure rate. The hysteresis gap in the bilinear hysteresis characteristic effectively filters out the effects of small flow fluctuations and measurement errors, avoiding unnecessary frequent adjustments to the recirculation valve, thereby improving the operational stability of the feedwater system and reducing valve failure rate. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the poor interpretability of the existing bi-segmented hysteresis implementation method when using MAX / MIN function block combination. In order to solve the above problem, a bi-segmented hysteresis implementation method based on rate limiting is provided.

[0007] The object of this invention is achieved in the following manner: A rate-limited bisegmented hysteresis implementation method includes the following steps: A bi-segmented hysteresis mapping relationship is established between the input signal and the output signal, wherein when the input signal changes in the rising direction, the output signal changes according to the first piecewise linear function F2(x), and when the input signal changes in the falling direction, the output signal changes according to the second piecewise linear function F1(x). There is a hysteresis gap region between F1(x) and F2(x), and changes in the input signal within the hysteresis gap region do not change the output signal. Determine the direction of change of the input signal; According to the direction of change of the input signal, the input signal of the rate limiting function block is selected by the first selection function block. When the input signal is rising, F2(x) is selected as the input of the rate limiting function block, and when the input signal is falling, F1(x) is selected as the input of the rate limiting function block. According to the direction of change of the input signal, the rising rate and falling rate of the rate limiting function block are set by the second selection function block and the third selection function block respectively. When the input signal is rising, the rising rate is set to an unlimited value and the falling rate is set to zero. When the input signal is falling, the rising rate is set to zero and the falling rate is set to an unlimited value. The signal selected by the first selection function block is input to the rate limiting function block, and the rate limiting function block outputs the double-segmented hysteresis control result.

[0008] The unlimited speed value is a preset, sufficiently large positive or negative number, used to indicate that the rate limiting function block does not limit the rate of signal change in that direction.

[0009] The direction of change of the input signal is determined by a derivative function block or a differential function block. The upward or downward direction is determined by the sign of the output. When the output is zero or the absolute value is less than a preset threshold, the direction determination result of the previous moment is maintained.

[0010] The method is applied to the control of the minimum flow recirculation valve of the water pump in an industrial control system, and utilizes the hysteresis clearance characteristic to eliminate the influence of flow measurement error and water flow fluctuation on the control of the recirculation valve.

[0011] The determination of the direction of change of the input signal, the first selection function block, the second selection function block, the third selection function block, and the rate limiting function block are implemented in a function block configuration manner on the distributed control system (DCS) platform.

[0012] The first piecewise linear function F2(x) is the output characteristic curve corresponding to the rising direction of the input signal, and the second piecewise linear function F1(x) is the output characteristic curve corresponding to the falling direction of the input signal. F1(x) and F2(x) have a hysteresis gap formed by horizontal offset within the same input interval.

[0013] The direction of change of the input signal is determined by differentiation.

[0014] The rate limiting function block is a standard function block in industrial control systems that has rise rate and fall rate limiting parameters.

[0015] The beneficial effects of this invention are as follows: This invention utilizes the inherent unidirectional rate limiting characteristic of the rate limiting function block, combined with the differentiation judgment and selection function block, to realize a dual-segmented hysteresis control strategy. When the input increases, the rate limiting function block only allows the output to track rapidly along the F2(x) direction and prohibits reverse changes; when the input decreases or remains constant, the rate limiting function block only allows the output to track rapidly along the F1(x) direction and prohibits reverse changes, thus naturally forming a hysteresis gap within the rate limiting framework, with a clear and intuitive logical meaning. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the input and output characteristics of the double-segmented hysteresis function of the present invention.

[0017] Figure 2 This is a schematic diagram of the traditional mainstream configuration method for implementing bilinear hysteresis using MAX / MIN function blocks in the existing technology.

[0018] Figure 3 This is a functional block configuration diagram of the bi-segmented hysteresis implementation method based on rate limiting according to the present invention.

[0019] Figure 4 This is one of the schematic diagrams showing the comparison results of the method of the present invention and existing traditional methods using MATLAB simulation.

[0020] Figure 5 This is the second schematic diagram showing the comparison between the method of this invention and existing traditional methods using MATLAB simulation. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same technical meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0023] A rate-limited bisegmented hysteresis implementation method includes the following steps: A bi-segmented hysteresis mapping relationship is established between the input signal and the output signal, wherein when the input signal changes in the rising direction, the output signal changes according to the first piecewise linear function F2(x), and when the input signal changes in the falling direction, the output signal changes according to the second piecewise linear function F1(x). There is a hysteresis gap region between F1(x) and F2(x), and changes in the input signal within the hysteresis gap region do not change the output signal. Determine the direction of change of the input signal; According to the direction of change of the input signal, the input signal of the rate limiting function block is selected by the first selection function block. When the input signal is rising, F2(x) is selected as the input of the rate limiting function block, and when the input signal is falling, F1(x) is selected as the input of the rate limiting function block. According to the direction of change of the input signal, the rising rate and falling rate of the rate limiting function block are set by the second selection function block and the third selection function block respectively. When the input signal is rising, the rising rate is set to an unlimited value and the falling rate is set to zero. When the input signal is falling, the rising rate is set to zero and the falling rate is set to an unlimited value. The signal selected by the first selection function block is input to the rate limiting function block, and the rate limiting function block outputs the double-segmented hysteresis control result.

[0024] The unlimited speed value is a preset, sufficiently large positive or negative number, used to indicate that the rate limiting function block does not limit the rate of signal change in that direction.

[0025] The direction of change of the input signal is determined by a derivative function block or a differential function block. The upward or downward direction is determined by the sign of the output. When the output is zero or the absolute value is less than a preset threshold, the direction determination result of the previous moment is maintained.

[0026] The method is applied to the control of the minimum flow recirculation valve of the water pump in an industrial control system. It utilizes the hysteresis clearance characteristic to eliminate the influence of flow measurement errors and water flow fluctuations on the control of the recirculation valve, thereby reducing the frequent adjustment of the recirculation valve and improving the stability of the water supply system.

[0027] The determination of the direction of change of the input signal, the first selection function block, the second selection function block, the third selection function block, and the rate limiting function block are implemented in a function block configuration manner on the distributed control system (DCS) platform.

[0028] The first piecewise linear function F2(x) is the output characteristic curve corresponding to the rising direction of the input signal, and the second piecewise linear function F1(x) is the output characteristic curve corresponding to the falling direction of the input signal. F1(x) and F2(x) have a hysteresis gap formed by horizontal offset within the same input interval.

[0029] The direction of change of the input signal is determined by differentiation.

[0030] The rate limiting function block is a standard function block in industrial control systems that has rise rate and fall rate limiting parameters.

[0031] This embodiment provides a method for implementing bi-segmented hysteresis based on rate limiting. Its overall functional block configuration structure is shown in the appendix to the specification. Figure 3 As shown.

[0032] First, based on actual control requirements, it is confirmed that there is a double-segmented hysteresis characteristic between the input and output signals, and the rising segmented function F2(x) and the falling segmented function F1(x) are determined. Taking the control of the minimum flow recirculation valve of the feedwater pump as an example, the input signal is the feedwater flow rate or a related calculated quantity, and the output signal is the recirculation valve opening command. F1(x) and F2(x) can be obtained through table lookup, piecewise linear interpolation, or other commonly used engineering methods.

[0033] The typical bi-segmented hysteresis mapping parameters used in this embodiment are shown in Table 1.

[0034]

[0035] As shown in Table 1 and appendix Figure 1 As shown, when the input rises from 0 to 40, the output remains at 0 along F2(x); when the input continues to rise to 70, the output rises to 60 along F2(x); when the input rises to 90 or above, the output reaches 100 along F2(x). When the input falls from 110, the output remains at 100 along F1(x); when the input falls to 70, the output still remains at 100; when the input falls to 40, the output falls to 40 along F1(x); when the input falls to 20 or below, the output falls to 0 along F1(x). Within the gap region between F1(x) and F2(x), input changes do not cause output changes, forming a hysteresis characteristic.

[0036] The implementation steps of this embodiment are as follows: Step S1: Perform differentiation on the input signal x. A differential function block is used to differentiate the input signal in real time, obtaining the input rate of change dx / dt. When dx / dt is greater than zero, the input signal is considered to be rising; when dx / dt is less than zero, the input signal is considered to be falling; when dx / dt is equal to zero, the input signal is considered to be remaining constant.

[0037] Step S2: Based on the direction of input change, select the input of the rate limiting function block through the first selection function block SWITCH1. When the input is increasing, SWITCH1 selects F2(x) as the input signal of the rate limiting function block; when the input is decreasing or remains constant, SWITCH1 selects F1(x) as the input signal of the rate limiting function block.

[0038] Step S3: Based on the direction of input change, set the rising rate and falling rate of the rate limiting function block through the second selection function block SWITCH2 and the third selection function block SWITCH3 respectively.

[0039] As input is increasing: SWITCH2 selects the rise rate parameter as 999 (meaning no rate limit, i.e., allowing the output to quickly track F2(x)); SWITCH3 selects the descent rate parameter as 0 (which disables output descent, thus creating a hysteresis gap between F2(x) and F1(x)).

[0040] When the input is decreasing or remaining constant: SWITCH2 selects the rise rate parameter as 0 (meaning that the output rise is disabled); SWITCH3 selects the descent rate parameter as -999 (meaning no rate limit, i.e., allowing the output to quickly track F1(x)).

[0041] Step S4: The signal selected by SWITCH1 is sent to the rate limiting function block. The rate limiting function block limits the output according to the set rise rate and fall rate, and finally outputs the double-segmented hysteresis control result y.

[0042] The detailed connection relationships of the above configuration logic are shown in the appendix of the instruction manual. Figure 3 As shown. Among them, the differentiation function block is used to determine the input direction; the three selection function blocks SWITCH1, SWITCH2, and SWITCH3 respectively control the input source and bidirectional rate parameter of the rate limiting function block; the rate limiting function block is the core execution unit, which realizes the bi-segmented hysteresis characteristic through a unidirectional rate limiting mechanism.

[0043] It should be noted that the use of 999 and -999 for the unlimited speed value in this embodiment is merely a common practice in engineering implementation, representing a sufficiently large speed limit to approximate infinity. In actual DCS configuration, other sufficiently large positive or negative numbers can be selected according to the parameter range of the platform function blocks, as long as the "unlimited speed" control effect can be achieved. This invention does not impose any limitations on this.

[0044] Example

[0045] Based on Example 1, this embodiment applies the double-segmented hysteresis implementation method to the control loop of the minimum flow recirculation valve of the feedwater pump.

[0046] During the operation of the feedwater pump, the feedwater flow signal at the pump inlet is acquired or calculated in real time and used as the input signal x for the dual-segmented hysteresis control. Based on the pump's minimum flow protection requirements, the segmented parameters F1(x) and F2(x) are pre-tuned so that the recirculation valve opens according to a predetermined pattern when the flow rate is below the safety threshold and closes according to another pattern after the flow rate returns to normal, with an appropriate hysteresis gap between the two.

[0047] The output signal y obtained by the method described in Example 1 is used as a control command for the opening of the recirculation valve and sent to the valve positioner or electric actuator. Due to the existence of the hysteresis clearance, when the feedwater flow fluctuates within a small range or when there is noise in the flow measurement value, the output signal will not change frequently, thereby avoiding repeated opening and closing of the recirculation valve. This not only benefits the stable operation of the boiler feedwater automatic control but also significantly reduces the number of valve operations, extends valve service life, and reduces the failure rate.

[0048] This embodiment provides a rate-limited dual-segmented hysteresis control system, which corresponds in structure and function to the method described in Embodiment 1, including: The derivative function block, connected to the input signal terminal, is used to output the result of determining the direction of change of the input signal; The first selection function block SWITCH1 has its selection terminal connected to the output of the derivative function block, its first input terminal connected to the calculation result of F1(x), its second input terminal connected to the calculation result of F2(x), and its output terminal connected to the signal input terminal of the rate limiting function block. The second selection function block SWITCH2 has its selection terminal connected to the output of the derivative function block, which is used to provide the rise rate parameter to the rate limiting function block. The third selection function block SWITCH3 has its selection terminal connected to the output of the derivative function block, which is used to provide the descent rate parameter to the rate limiting function block. The rate limiting function block receives the signal output from SWITCH1 and the rate parameters output from SWITCH2 and SWITCH3, and outputs the result of the bilinear hysteresis control.

[0049] When the input signal is rising, SWITCH1 selects F2(x), SWITCH2 outputs an unlimited speed value, and SWITCH3 outputs zero; when the input signal is falling or remains constant, SWITCH1 selects F1(x), SWITCH2 outputs zero, and SWITCH3 outputs an unlimited speed value.

[0050] This embodiment performs simulation verification on the technical solutions described in Embodiments 1 to 3.

[0051] On the Hollysys DCS platform, according to the attached... Figure 3 Function block configuration is performed, and an equivalent simulation model is built using MATLAB. The method of this invention is compared with the existing mainstream method using MAX / MIN function blocks (as shown in the appendix). Figure 2 As shown, a comparative simulation was performed under the same input signal conditions.

[0052] Simulation results show that the output curves of the two methods completely overlap under various operating conditions, including rising, falling, and fluctuating input signals, as indicated in the instruction manual. Figure 4 and attached Figure 5 As shown, this proves that the rate-limited bisegmented hysteresis implementation method of this invention is functionally equivalent to the existing mainstream methods, can accurately reproduce the bisegmented hysteresis characteristics, and meets the requirements of engineering applications.

[0053] In summary, this invention determines the input direction by differentiation, dynamically switches the piecewise linear function and rate limiting parameter using the selection function block, and achieves dual piecewise linear hysteresis control by leveraging the unidirectional speed limiting characteristic of the rate limiting function block. It has the advantages of clear logic, ease of understanding, and reliable performance, and can be widely applied in the field of industrial process control, especially suitable for applications such as minimum flow recirculation valves for water pumps where high requirements are placed on control stability and valve life.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for implementing bi-segmented hysteresis based on rate limiting, characterized in that: Includes the following steps: A bi-segmented hysteresis mapping relationship is established between the input signal and the output signal, wherein when the input signal changes in the rising direction, the output signal changes according to the first piecewise linear function F2(x), and when the input signal changes in the falling direction, the output signal changes according to the second piecewise linear function F1(x). There is a hysteresis gap region between F1(x) and F2(x), and changes in the input signal within the hysteresis gap region do not change the output signal. Determine the direction of change of the input signal; According to the direction of change of the input signal, the input signal of the rate limiting function block is selected by the first selection function block. When the input signal is rising, F2(x) is selected as the input of the rate limiting function block, and when the input signal is falling, F1(x) is selected as the input of the rate limiting function block. According to the direction of change of the input signal, the rising rate and falling rate of the rate limiting function block are set by the second selection function block and the third selection function block respectively. When the input signal is rising, the rising rate is set to an unlimited value and the falling rate is set to zero. When the input signal is falling, the rising rate is set to zero and the falling rate is set to an unlimited value. The signal selected by the first selection function block is input to the rate limiting function block, and the rate limiting function block outputs the double-segmented hysteresis control result.

2. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The unlimited speed value is a preset, sufficiently large positive or negative number, used to indicate that the rate limiting function block does not limit the rate of signal change in that direction.

3. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The direction of change of the input signal is determined by a derivative function block or a differential function block. The upward or downward direction is determined by the sign of the output. When the output is zero or the absolute value is less than a preset threshold, the direction determination result of the previous moment is maintained.

4. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The method is applied to the control of the minimum flow recirculation valve of the water pump in an industrial control system, and utilizes the hysteresis clearance characteristic to eliminate the influence of flow measurement error and water flow fluctuation on the control of the recirculation valve.

5. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The determination of the direction of change of the input signal, the first selection function block, the second selection function block, the third selection function block, and the rate limiting function block are implemented in a function block configuration manner on the distributed control system (DCS) platform.

6. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The first piecewise linear function F2(x) is the output characteristic curve corresponding to the rising direction of the input signal, and the second piecewise linear function F1(x) is the output characteristic curve corresponding to the falling direction of the input signal. F1(x) and F2(x) have a hysteresis gap formed by horizontal offset within the same input interval.

7. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The direction of change of the input signal is determined by differentiation.

8. The method for implementing bi-segmented hysteresis based on rate limiting according to claim 1, characterized in that: The rate limiting function block is a standard function block in industrial control systems that has rise rate and fall rate limiting parameters.

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