CN1269050C - Control architecture for foundation fieldbus to reduce bus traffic - Google Patents
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Abstract
The invention discloses a control structure for reducing bus communication traffic of a foundation fieldbus, which comprises two devices, wherein a device 1 comprises an analog input function block connected with a sensor; the device 2 comprises a control function block and an analog quantity output function block, wherein the analog quantity output function block is connected with an actuator; in the device 1, a predictive control function block and a control function block are added, wherein the parameters of the control function block are identical to the parameters of the control function block in the device 2; a prediction function block which is completely the same as the prediction function block in the device 1 is additionally arranged in the device 2; the parameter connections between the various functional blocks in the device 1 and the device 2 are configured using common configuration software. The invention can reduce the communication burden of the bus network, thereby improving the real-time performance and the certainty of the data communication of the bus network; and the alarm is given to wrong sampling data, the function of a second sensor is realized, and the stability of the control system is improved.
Description
Technical field
The present invention relates to fieldbus (FOUNDATION Filedbus, be called for short FF) technology, specifically a kind of control structure that is used for the minimizing bus traffic of foundation fieldbus belongs to a kind of in the foundation fieldbus FFB (Flexible Function Block).
Background technology
Functional block is one of most characteristic technology of foundation fieldbus.It is the software logic processing unit of core with the data structure that functional block is one, finishes an independence and complete control function.The control system of FF logically can be considered as being made up of the several function piece.The functional block that constitutes control system can be in same equipment, also can be dispersed in a plurality of equipment, carry out configuration by configuration software after, control algolithm is finished in cooperation.Can comprise a plurality of functional blocks in the field apparatus, these functional blocks can be the functional blocks of the standard of fieldbus foundation (Fieldbus Foundation) definition, also can be the FFB of developer according to specific control requirements definition.
Functional block can be divided into input function piece (for example analog quantity input function piece AI), three kinds of control (calculating) functional block (for example control function piece PID) and output function pieces (for example analog quantity output function piece AO).The equipment at input function piece place links to each other with sensor, and the equipment at output function piece place links to each other with actuator, and the control function piece may reside in any equipment.In the typical closed-loop control system, in each control cycle, the input function piece is undertaken sending sampled value to the control function piece after filtering and the linearization by the current controlled physical quantity of sensor.The control function piece calculates controlled quentity controlled variable, by the output function piece controlled quentity controlled variable is sent to actuator and finishes control.
In the prior art, finish each control cycle, control system all needs once to communicate by letter by bus network at least.Frequent bus communication must take the more network bandwidth, has influenced the real-time and the determinacy of control system, and especially under the communication mechanism of Ethernet fieldbus carrier sense/collision avoidance, this problem is more outstanding.On the other hand, in existing control system, be difficult to the fast detecting sensor or (with) fault that occurs of actuator; Fault occurred even detect sensor, control system will enter safe condition, stop the control to controlled device.This must cause damage to production, even dangerous situation occurs.
Summary of the invention
In order to overcome because frequent communication and sensor or (with) instability and the potential safety hazard of the control system that actuator failures caused, the invention provides a kind of solution based on prediction, it is a kind of control structure that is used for the minimizing bus traffic of foundation fieldbus, it is predicted controlled physical quantity according to transport function, controlled quentity controlled variable and the sampled value of controlled device, thereby reduce the traffic of bus network, and the duty of sensor in the control system and actuator monitored, improve the stability and the security of control system.
To achieve these goals, technical scheme of the present invention is: comprise two equipment, wherein comprise an analog quantity input function piece in first equipment, link to each other with sensor; Comprise the second control function piece, analog quantity output function piece in second equipment, described analog quantity output function piece links to each other with actuator; In first equipment, increase by the first forecast function piece and the first control function piece, wherein the parameter of the second control function piece is just the same in the parameter of the first control function piece and second equipment, and role's mark of functional block is set to sensor one side in the first forecast function piece; In second equipment, set up one with first equipment in the identical second forecast function piece of the first forecast function piece, and role's mark of its functional block is set to actuator one side; It is as follows to use general configuration software to dispose in first equipment and second equipment between each functional block the connection of parameter: in first equipment, the output parameter of analog quantity input function piece links to each other with the input parameter sampled value of the first forecast function piece, the output parameter of the first control function piece links to each other with the input parameter controlled quentity controlled variable of the first forecast function piece, the output parameter of the first forecast function piece simultaneously with first equipment in the input parameter of the first control function piece link to each other with the input parameter sampled value of the second forecast function piece in second equipment; In second equipment, the output parameter of the second control function piece links to each other with the input parameter controlled quentity controlled variable of the second forecast function piece and the output parameter of analog quantity output function piece simultaneously, the output parameter of the second forecast function piece links to each other with the input parameter of the second control function piece, and the input parameter sampled value of the second forecast function piece links to each other with the output parameter of the first forecast function piece in first equipment;
Wherein by general configuration software, dispose the scheduling of functional block in first equipment, at first be that analog quantity input function piece is carried out, whether need to send by the next sampled value of analog quantity input function block transfer to second equipment by the decision of forecast function piece then by bus, whether need to send and report to the police, be that the first control function piece is carried out at last; Wherein dispose the scheduling of functional block in second equipment, decide the first control function piece to carry out by whether receiving the sampled value that the first forecast function piece sends from first equipment, calculate the controlled quentity controlled variable of this control cycle, and controlled quentity controlled variable sent to analog quantity output function piece, send to the second forecast function piece in second equipment simultaneously; Be that analog quantity output function piece is carried out at last, conversion sent to actuator after the controlled quentity controlled variable that second equipment, the second control function piece is sent was carried out range conversion, put on the controlled device;
Wherein the execution of the forecast function piece in sensor one side first equipment flow process is as follows: the first forecast function piece at first calculates predicted value, and calculate the absolute value of deviation between the sampled value that this predicted value and analog quantity input function piece send, and judge with reference to the limits of error whether the precision of predicted value reaches requirement: if the absolute value of deviation is less than the limits of error between predicted value and the sampled value, replace sampled value with predicted value, and the sampled value (being predicted value) that is replaced sent in the first control function piece, finish the implementation of the first forecast function piece; If the absolute value of deviation is greater than the limits of error between predicted value and the sampled value, need recomputate the prediction correction, then sampled value is sent in the second forecast function piece in second equipment by bus network, judge sensor according to alarm threshold value or/and whether the duty of actuator is normal again: if the absolute value of deviation is less than alarm threshold value between predicted value and the sampled value, sampled value is sent in the first control function piece, finish the implementation of the first forecast function piece; If the absolute value of deviation is greater than alarm threshold value between predicted value and the sampled value, send warning reminding field engineer maintenance, sampled value is sent in the first control function piece then, finish the implementation of the first forecast function piece;
Wherein the execution of the second forecast function piece in actuator one side second equipment flow process is as follows: the second forecast function piece at first calculates predicted value, judge whether to receive the sampled value that the first forecast function piece from first equipment sends then, if do not receive the sampled value that the first forecast function piece from first equipment sends, predicted value is sent in the second control function piece in second equipment, finish the implementation of the second forecast function piece; If receive the sampled value that the first forecast function piece from first equipment sends, recomputate the prediction correction, calculate the absolute value of deviation between the sampled value that predicted value and the first forecast function piece from first equipment send then, and judge sensor or/and whether the duty of actuator is normal: if the absolute value of deviation is less than alarm threshold value between predicted value and the sampled value with reference to alarm threshold value, the sampled value of will the first forecast function piece from first equipment sending sends in the second control function piece, finishes the implementation of the second forecast function piece; If the absolute value of deviation is greater than alarm threshold value between predicted value and the sampled value, need decide implementation after this according to the value of prediction duration: if the prediction duration is greater than 0, to predict that duration subtracts 1, then predicted value is sent in the second control function piece in second equipment, finish the implementation of the second forecast function piece; If the prediction duration equals 0, the sampled value of will the first forecast function piece from first equipment sending sends in the second control function piece in second equipment, finishes the implementation of the second forecast function piece.
The present invention has following advantage:
1. alleviate the bus network communication burden.The present invention reduces the communications burden of bus network by the prediction to controlled physical quantity, thereby has improved the real-time and the determinacy of control system, and especially under the communication mechanism of Ethernet fieldbus carrier sense/collision avoidance, this advantage is obvious especially.
2. rationally utilize device resource.The redundant computation that the present invention predicts same controlled physical quantity by the PREDICTIVE CONTROL functional block in two equipment alleviates communications burden, not only can not influence the equipment operate as normal, and rational and effective has been utilized and has been dispersed in idling-resource in each equipment and computing power in the field bus control system.
3. improve the stability and the security of control system.The scope whether the present invention exceeds limits of error MAX_ERR defined by the deviation between comparison prediction value and the sampled value judge control system sensor or (with) duty of actuator, play the effect of second sensor, thereby improve the stability and the security of control system, avoid causing danger.
4. reduce the loss that causes because of sensor fault.The present invention can use predicted value to proceed control in the control cycle of prediction duration defined, thereby reduce the loss that pauses production is caused because of control, for slip-stick artist's examination and repair system is raced against time when the control system sensor break down.
Description of drawings
Fig. 1 is a typical closed-loop control system structural drawing in the prior art.
Fig. 2 is a control system structure diagram of the present invention.
Fig. 3 is control principle figure among Fig. 2
Fig. 4 is the graph of a relation of actual sample value of the present invention and predicted value.
Fig. 5 is a forecast function block structural diagram among Fig. 2.
Fig. 6 is the flowchart of the present invention's forecast function piece in first equipment.
Fig. 7 is the flowchart of the present invention forecast function piece PC in second equipment.
Fig. 8 is the one embodiment of the invention structural representation.
Fig. 9 is one embodiment of the invention control design sketch.
Embodiment
Below in conjunction with accompanying drawing the present invention is described in further detail.
As shown in Figure 1, typical foundation fieldbus control system is by analog quantity input function piece (Analog Input in the prior art, abbreviation AI), analog quantity output function piece (Analog Output, be called for short AO) and three kinds of functional blocks compositions of control function piece (Proportional Integral Derivative is called for short PID).In each control cycle, analog quantity input function piece AI is undertaken after filtering and the linearization by the current controlled physical quantity of sensor, and sampled value is sent to control function piece PID.Control function piece PID calculates controlled quentity controlled variable, by analog quantity output function piece AO controlled quentity controlled variable is sent to actuator and finishes control.In an equipment, except can having the control function piece, can also have input function piece or output function piece, but can not have input function piece and output function piece simultaneously.Therefore, finish each control cycle, all need at least once to communicate by letter by bus network, frequent bus communication, must take the more network bandwidth, influenced the real-time and the determinacy of control system, especially under the communication mechanism of Ethernet carrier sense/collision avoidance, this problem is more outstanding.On the other hand, if the sensor in the system or (with) actuator breaks down and do not detected by system, must have a negative impact to production, even cause dangerous situation.Even so, break down even detected sensor, traditional control system will enter safe condition, stop the control to controlled device, equally also will cause damage to production.
As shown in Figure 2, the present invention includes two equipment, wherein comprise an analog quantity input function piece AI in first equipment, link to each other with sensor; Comprise the second control function piece PID2, analog quantity output function piece AO in second equipment, described analog quantity output function piece AO links to each other with actuator; In first equipment, increase by the first forecast function piece PC1 and the first control function piece PID1, wherein the parameter of the second control function piece PID2 is just the same in the parameter of the first control function piece PID1 and second equipment, and role's mark of functional block is set to sensor one side among the first forecast function piece PC1; In second equipment, set up one with first equipment in the identical second forecast function piece PC2 of the first forecast function piece PC1, and role's mark of its functional block is set to actuator one side; By general configuration software, the scheduling process that disposes functional block in first equipment is as follows: at first be that analog quantity input function piece AI carries out, will obtain the sampled value SAMPLE in this cycle by sensor and send to the first forecast function piece PC1; Be that the first forecast function piece PC1 carries out then, describe G according to transport function
1, controlled quentity controlled variable in the past and sampled value in the past calculate predicted value, and compare with sampled value SAMPLE that analog quantity input function piece AI sends, determining this control cycle to adopt predicted value still is that sampled value SAMPLE controls, whether need to send sampled value SAMPLE to second equipment, whether need to send and report to the police by bus; Be that the first control function piece PID1 carries out at last, calculate the controlled quentity controlled variable CONTROL of this control cycle, and this controlled quentity controlled variable CONTROL is sent to the first forecast function piece PC1, be used to calculate the predicted value of next control cycle; The scheduling process that disposes functional block in second equipment is as follows: at first be that the second forecast function piece PC2 carries out, describe G according to transport function
1, controlled quentity controlled variable in the past and sampled value in the past calculate predicted value, and to decide this control cycle to adopt predicted value still be that sampled value SAMPLE controls by whether receiving the first forecast function piece PC1 sends from first equipment sampled value SAMPLE; Be that the second control function piece PID2 carries out then, calculate the controlled quentity controlled variable CONTROL of this control cycle, send to analog quantity output function piece AO, this controlled quentity controlled variable CONTROL also will send to the second forecast function piece PC2 in second equipment simultaneously, is used to calculate the predicted value of next control cycle; Be that analog quantity output function piece AO carries out at last, the controlled quentity controlled variable CONTROL that the second control function piece PID2 is sent carries out the range conversion and sends to actuator, puts on the controlled device.
As shown in Figure 3, it is as follows to use general configuration software to dispose in first equipment and second equipment between each functional block the connection of parameter: in first equipment, the output parameter OUT of analog quantity input function piece AI links to each other with the input parameter sampled value SAMPLE of the first forecast function piece PC1, the output parameter OUT of the first control function piece PID1 links to each other with the input parameter controlled quentity controlled variable CONTROL of the first forecast function piece PC1, the output parameter OUT of the first forecast function piece PC1 simultaneously with first equipment in the input parameter IN of the first control function piece PID1 link to each other with the input parameter sampled value SAMPLE of the second forecast function piece PC2 in second equipment; In second equipment, the output parameter OUT of the second control function piece PID2 links to each other with the input parameter controlled quentity controlled variable CONTROL of the second forecast function piece PC2 and the output parameter OUT of analog quantity output function piece AO simultaneously, the output parameter OUT of the second forecast function piece PC2 links to each other with the input parameter IN of the second control function piece PID2, and the input parameter sampled value SAMPLE of the second forecast function piece PC2 links to each other with the output parameter OUT of the first forecast function piece PC1 in first equipment.
As shown in Figure 4, the slip-stick artist describes G to the controlled device transport function
1And have certain gap between the actual controlled device transport function G, the precision of forecast function piece PC predicted value depends on to a great extent describes G to the controlled device transport function
1Accuracy.If to the identification out of true of controlled device, promptly actual controlled device transport function G and controlled device transport function are described G
1There is bigger deviation, then identical controlled quentity controlled variable CONTROL acts on these two models, the sampled value that is produced must be different with predicted value, that is to say no matter adopt which kind of prediction algorithm, and all will there be bigger deviation in the predicted value that obtains with actual sample value.Therefore, in order to obtain accurate predicted value, be vital to the accurate description of controlled device transport function G.But, for the field engineer, relatively more difficult to the accurate identification of controlled device.In addition, controlled device is controlled the influence of site environment, and drift also can appear in its model.Therefore need to adopt certain correction algorithm to improve the precision of predicted value.
As shown in Figure 5, the structure of forecast function piece PC comprises following content: the SAMPLE parameter receives actual sample value; The CONTROL parameter receives the controlled quentity controlled variable of last one-period that is sent by control function piece PID; This controlled quentity controlled variable CONTROL acts on the controlled device transport function and describes G
1On, just can obtain predicted value.Predicted value and sampled value SAMPLE compare, if the deviation between them surpasses alarm threshold value MAX_DEV, then think when front sensor or (with) the actuator working state abnormal, forecast function piece PC sends warning.MAX_ERR is the limits of error between predicted value and the actual sample value SAMPLE.When absolute value of the bias between predicted value and the actual sample value SAMPLE surpasses limits of error MAX_ERR, this difference is saved in the array of a regular length (for example 5), and overrides time data the earliest in this array; In the next performance period, the mean value of getting data in this array is as correction, with the predicted value addition that directly calculates as final predicting the outcome; The purpose of doing like this is that the same controlled quentity controlled variable CONTROL of manual compensation acts on model controlled device transport function and describes G
1And the actual controlled device transport function of model G goes up the deviation between the resulting output, thereby improves precision of prediction; Forecast function piece PC adopts this simple method, not only effectively raise precision of prediction, and the execution time of functional block has also obtained better controlled, make that adding forecast function piece PC in control system can't cause too big computation burden to equipment, thereby also can not influence the real-time of control system.
As shown in Figure 6, the execution of the first forecast function piece PC1 in sensor one side apparatus (i.e. first equipment) flow process is as follows: the first forecast function piece PC1 at first calculates predicted value, and predicted value is to describe G according to transport function
1, in the past controlled quentity controlled variable and in the past sampled value calculate, add the prediction correction to improve the precision of predicted value; Calculate the absolute value ERROR of deviation between the sampled value SAMPLE that this predicted value and analog quantity input function piece AI send then, and judge with reference to limits of error MAX_ERR whether the precision of predicted value reaches requirement: if the absolute value ERROR of deviation is less than limits of error MAX_ERR between predicted value and the sampled value, the precision that predicted value is described meets the demands, replace sampled value SAMPLE with predicted value, and the sampled value SAMPLE (being predicted value) that is replaced sent among the first control function piece PID1, finish the implementation of the first forecast function piece PC1, do not need in this case to send sampled value SAMPLE by bus network; If the absolute value ERROR of deviation is greater than limits of error MAX_ERR between predicted value and the sampled value SAMPLE, the precision that predicted value is described can not meet the demands, can not replace sampled value SAMPLE, need recomputate the prediction correction, to improve accuracy of predicting next time, then sampled value SAMPLE is sent among the second forecast function piece PC2 in second equipment by bus network, need in this case to send sampled value SAMPLE by bus network; Next according to alarm threshold value MAX_DEV judge sensor or (and) whether the duty of actuator normal: if the absolute value ERROR of deviation is less than alarm threshold value MAX_DEV between predicted value and the sampled value SAMPLE, illustrate that sensor and actuator are working properly, do not need to send and report to the police, sampled value SAMPLE is sent among the first control function piece PID1, finish the implementation of the first forecast function piece PC1; If the absolute value ERROR of deviation is greater than alarm threshold value MAX_DEV between predicted value and the sampled value SAMPLE, illustrate sensor or (with) actuator work is undesired, need to send warning reminding field engineer maintenance, sampled value SAMPLE is sent among the first control function piece PID1 then, finish the implementation of the first forecast function piece PC1.
As shown in Figure 7, the second forecast function piece PC2 implementation in actuator one side apparatus (i.e. second equipment) is as follows: the second forecast function piece PC2 at first calculates predicted value, and predicted value is to describe G according to transport function
1, in the past controlled quentity controlled variable and in the past sampled value calculate, add the prediction correction to improve the precision of predicted value; Judge whether to receive the sampled value SAMPLE that the first forecast function piece PC1 from first equipment sends then, if do not receive the sampled value SAMPLE that the first forecast function piece PC1 from first equipment sends, the precision that predicted value is described meets the demands, predicted value is sent among the second control function piece PID2 in second equipment, finish the implementation of the second forecast function piece PC2; If receive the sampled value SAMPLE that the first forecast function piece PC1 from first equipment sends, the precision that predicted value is described can not meet the demands, need recomputate the prediction correction, to improve accuracy of predicting next time, calculate the absolute value ERROR of deviation between the sampled value SAMPLE that predicted value and the first forecast function piece PC1 from first equipment send then, and judge sensor or/and whether the duty of actuator is normal: if the absolute value ERROR of deviation is less than alarm threshold value MAX_DEV between predicted value and the sampled value SAMPLE with reference to alarm threshold value MAX_ERR, illustrate that sensor and actuator are working properly, the sampled value SAMPLE that will the first forecast function piece PC1 from first equipment sends sends among the second control function piece PID2, finishes the implementation of the second forecast function piece PC2; If the absolute value ERROR of deviation is greater than alarm threshold value MAX_DEV between predicted value and the sampled value SAMPLE, need decide implementation after this according to the value of prediction duration: if the prediction duration is greater than 0, explanation uses predicted value to control in the control cycle of prediction duration defined, to predict that duration subtracts 1, then predicted value is sent among the second control function piece PID2 in second equipment, finish the implementation of the second forecast function piece PC2; If the prediction duration equals 0, the control cycle of distrusting predicted value or having reached prediction duration defined is described, the sampled value SAMPLE that will the first forecast function piece PC1 from first equipment sends sends among the second control function piece PID2 in second equipment, finishes the implementation of the second forecast function piece PC2.
Comprise following parameter among the forecast function piece PC:
---the controlled device transport function is described G
1
---controlled quentity controlled variable CONTROL;
---sampled value SAMPLE;
---predicted value;
---limits of error MAX_ERR, the deviation between predicted value and the actual sample value SAMPLE just thinks that predicted value has enough precision, can replace sampled value SAMPLE within this scope;
---alarm threshold value MAX_DEV, the deviation between predicted value and actual sample value SAMPLE exceeds this scope, just thinks that sensor or actuator break down, and needs to send to report to the police;
---the prediction duration, at this moment between in can use predicted value to control;
---the prediction correction, predicted value is revised, improve precision of prediction;
---role's mark of functional block, control the executive mode of current forecast function piece PC;
Wherein: described predicted value is to describe G according to the controlled device transport function
1, in the past sampled value and in the past controlled quentity controlled variable calculate; What the limits of error and alarm threshold value MAX_DEV all adopted is absolute value, and big I is set by the field engineer; The prediction correction is to obtain according to predictor calculation in the past; The prediction duration can be set by the field engineer, and numerical value is the multiple of control cycle; When being marked at the control system configuration, the role of functional block sets by the field engineer;
The description of described controlled device transport function is a series of interior containing parameters, and these parameters have been portrayed the characteristic of controlled device, and its numerical value is set according to concrete controlled device by the field engineer.In process control, most of controlled device all is single order or inertial element and the integral element that can be approximated to be single order, has only a spot of second order oscillation element, and the general type of these controlled device transport functions is
Only need enlargement factor K, time constant T
1, T
2And T
3These four parameters just can be described the transport function of this form.For first order inertial loop, the form of its transport function is
The transport function of describing this class needs the field engineer that K and T are set
2Two parameters, and with T
1Be set to 0, T
3Be set to 1; For single order integral element, the form of its transport function is
The transport function of describing this class needs the field engineer that K and T are set
2Two parameters, and with T
1And T
3Be set to 0; For the second order oscillation element, the form of its transport function is
The transport function of describing this class needs the field engineer that K, T are set
1, T
2And T
3Four parameters.The field engineer is by these four described transport functions of parameter, may have deviation with the transport function of actual controlled device, and for sake of convenience, the description of the controlled device transport function that the slip-stick artist is set is designated as G
1, the transport function of actual controlled device is designated as G.Identical controlled quentity controlled variable CONTROL acts on the description G of controlled device transport function
1On, just obtain predicted value, act on the transport function G of actual controlled device, just obtain sampled value SAMPLE;
Described controlled quentity controlled variable CONTROL is an input parameter, receives the controlled quentity controlled variable that is calculated by control function piece PID.This controlled quentity controlled variable is the controlled quentity controlled variable of a last control cycle to controlled device, and AO carries out putting on the controlled device by actuator after the range conversion through analog quantity output function piece.Controlled quentity controlled variable CONTROL is one of necessary condition of calculating predicted value, and controlled quentity controlled variable CONTROL acts on the description G of controlled device transport function
1On, just obtain predicted value.For first-order system, the predicted value of calculating this control cycle needs the controlled quentity controlled variable of last control cycle; For second-order system, the predicted value of calculating this control cycle needs the controlled quentity controlled variable of preceding two control cycles, therefore the controlled quentity controlled variable of front second control cycle need be preserved;
Described sampled value SAMPLE is an input parameter, receives by analog quantity input function piece AI and transmits the actual sample value of a next last control cycle to controlled physical quantity.According to the deviation between actual sample value SAMPLE and the predicted value that calculates, and with reference to the numerical value that limits of error MAX_ERR sets, deciding within this control cycle with sampled value SAMPLE still is that predicted value is controlled.If the deviation between actual sample value SAMPLE and the predicted value is within limits of error MAX_ERR scope, then the predicted value of sampled value SAMPLE replaces.Sampled value SAMPLE is one of necessary condition of calculating predicted value, and for first-order system, the predicted value of calculating this control cycle needs the sampled value of last control cycle; For second-order system, the predicted value of calculating this control cycle needs the sampled value of preceding two control cycles, therefore the sampled value of front second control cycle need be preserved;
Described predicted value is an interior containing parameter, calculates according to description, controlled quentity controlled variable CONTROL and the sampled value SAMPLE of controlled device transport function.The computing method of predicted value are: consider zero-order holder, to the description G of controlled device transport function
1Carry out transform, and be converted to difference equation.For first-order system, the form of difference equation is Y (k)=α U (k-1)+bY (k-1), wherein Y (k) is the predicted value in calculative cycle, U (k-1) is the controlled quentity controlled variable of a last control cycle, Y (k-1) is the sampled value of a last control cycle, and constant a and b describe G according to the transport function of controlled device
1In parameter K, T
1, T
2And T
3Calculate; For second-order system, the form of difference equation is Y (k)=α
1U (k-1)+α
2U (k-2)+b
1Y (k-1)+b
2Y (k-2), wherein Y (k) is the predicted value in calculative cycle, and U (k-1) and U (k-2) they are respectively the controlled quentity controlled variables of last one, two control cycles, and Y (k-1) and Y (k-2) they are respectively the sampled values of last one, two control cycles, constant a
1, a
2, b
1And b
2Be parameter K, the T in describing according to the transport function of controlled device
1, T
2And T
3Calculate.The predicted value that calculates by difference equation, SAMPLE compares with actual sample value, if the deviation between them is within limits of error scope, then replace sampled value SAMPLE with predicted value, controlled device is controlled also conduct calculate the foundation of next period forecasting value, and do not need to send sampled value SAMPLE by bus communication; If the absolute value of deviation is greater than the limits of error between them, then abandon this predicted value, use sampled value SAMPLE to control and calculate next period forecasting value, and need send sampled value SAMPLE by bus communication.Predicted value is also used as second sensor, and principle of work is: in normal control procedure, the deviation between predicted value and the sampled value SAMPLE is not too large.When the sensor of control system breaks down, can't collect correct sampled value SAMPLE, perhaps the actuator when control system breaks down, and when controlled quentity controlled variable CONTROL can't correctly be applied on the controlled device, bigger deviation can appear in predicted value and sampled value SAMPLE.If the absolute value of this deviation greater than alarm threshold value MAX_DEV, then think control system sensor or (with) actuator breaks down, and needs to send to report to the police, and reminds the slip-stick artist that system is overhauled.According to field condition and security requirement, actuator is working properly if fault has appearred in sensor, can also continue to control with predicted value within the prediction duration, for maintenance is raced against time, reduces the loss;
Described limits of error MAX_ERR is an interior containing parameter, and its numerical value is an absolute value, is set according to the control needs by the field engineer, as the standard of judging precision of prediction.If the absolute value of deviation is less than limits of error MAX_ERR between actual sample value SAMPLE and the predicted value, think that then predicted value has reached needed precision, can replace actual sample value SAMPLE; If the absolute value of deviation is greater than limits of error MAX_ERR between actual sample value SAMPLE and the predicted value, think that then predicted value does not reach needed precision, need finish control and prediction with actual sample value SAMPLE;
Described alarm threshold value MAX_DEV is an interior containing parameter, and its numerical value is an absolute value, is set according to needed safety coefficient by the field engineer, as the standard of judging when front sensor and actuator duty.Under the normal duty of control system, the deviation between actual sample value SAMPLE and the predicted value can not surpass alarm threshold value MAX_DEV.If the deviation between actual sample value SAMPLE and the predicted value surpasses alarm threshold value MAX_DEV, then think sensor or (with) the actuator working state abnormal, need to send and report to the police, remind the field engineer to overhaul, avoid causing bigger loss and produce dangerous;
Described prediction duration is an interior containing parameter, and its numerical value is the multiple of control cycle, is set according to the precision of needed safety coefficient and predicted value by the field engineer.The absolute value of deviation is greater than alarm threshold value MAX_DEV between actual sample value SAMPLE and predicted value, and detect the working sensor state when undesired, the loss that produces because control pauses in order to reduce, in the control cycle of prediction duration defined, control system adopts predicted value to replace actual sample value SAMPLE to proceed control, for the slip-stick artist races against time to the maintenance of system.The prediction duration is the reflection to the trusting degree of predicted value, and the size of its numerical value depends on the precision of predicted value to a great extent;
Described prediction correction is a read-only parameter, calculates according in the past predicted value and sampled value.Because the controlled device transport function that the field engineer sets is described G
1May there be bigger error with actual controlled device transport function G, makes identical controlled quentity controlled variable CONTROL act on the controlled device transport function and describe G
1And have bigger deviation between predicted value that obtains respectively on the transport function G of actual controlled device and the sampled value, and in order to reduce this deviation, on the predicted value that calculates, increase a correction, make predicted value more near sampled value SAMPLE.The computing method of prediction correction are: when absolute value of the bias between predicted value and the actual sample value SAMPLE surpasses the limits of error, this difference is saved in the array of a regular length (for example 5), and overriding time data the earliest in this array, the mean value of getting data in this array is as the prediction correction.The prediction correction improves the precision of predicted value, reduces the deviation between predicted value and the sampled value SAMPLE, thereby reduces the bus network communication amount, and improves the degree of confidence of second sensor, increases the prediction duration;
Role's mark of described functional block is an interior containing parameter, indicates the executive mode of current functional block and being born in control system of task.Forecast function piece PC in connecting the equipment of sensor with the equipment that is being connected actuator in executive mode be different.Forecast function piece PC in the equipment that connects sensor calculates predicted value, and compares with sampled value SAMPLE in the process of implementation.If absolute value of the bias is less than limits of error MAX_ERR between predicted value and the sampled value SAMPLE, then replaces sampled value SAMPLE, and do not need to send sampled value SAMPLE by bus with predicted value; If absolute value of the bias is greater than limits of error MAX_ERR between predicted value and the sampled value SAMPLE, then needs to send sampled value SAMPLE, and recomputate correction by bus.If this deviation greater than alarm threshold value MAX_DEV, then think sensor or (with) actuator work is undesired, need to send to report to the police.Forecast function piece PC in connecting the equipment of sensor calculates predicted value in the process of implementation, and the sampled value SAMPLE that judges whether to receive the forecast function piece PC in the comfortable equipment that connects sensor to send.If receive sampled value SAMPLE, illustrate that current predicted value is accurate inadequately, abandon current predicted value, sampled value SAMPLE is sent to actuator control, recomputate correction simultaneously; If do not receive sampled value SAMPLE, illustrate that current predicted value has enough precision, replace sampled value SAMPLE to control with predicted value.
Replenish experiment condition and result:
As shown in Figure 8, experiment condition condition and experimental result are as follows: that sensor 1 adopts is thermal resistance sensor PT100, and by the analog quantity input function piece AI in first equipment it being sampled obtains sampled value SAMPLE; The silicon-controlled voltage regulation module changes 4～20mA Current Control amount CONTROL that analog quantity output function piece AO in second equipment exports into 0～200V DC voltage controlled quentity controlled variable as actuator, the brightness of bulb 3 controlled, and then the temperature of control lamp box 2.Experiment records controlled device (present embodiment is the temperature of lamp box 2) transport function and describes G
1In enlargement factor K=4.47, time constant T
2=525 seconds.The control cycle that experiment is adopted is 1 second, and test result is as shown in table 1.From table 1, can see, when limits of error MAX_ERR is 0.2 ℃ (overhead control range 40 ℃ 5/1000ths), utilize forecast function piece PC of the present invention can save traffic more than 3/4ths; Even when limits of error MAX_ERR is 0.08 ℃ (overhead control range 40 ℃ 5/1000ths), also can save the traffic more than 1/3rd.Therefore, the effect that adopts forecast function piece PC of the present invention to save traffic is very tangible.
Table 1 test result
| The control cycle number | Allow maximum error MAX_ERR | Do not send number of times | Do not send number of times number percent |
| 7608 7324 | 0.2℃ 0.08℃ | 5889 2461 | 77.4％ 33.6％ |
As shown in Figure 9, be under the condition of 0.2 ℃ (overhead control range 40 ℃ 5/1000ths) at limits of error MAX_ERR, the working control effect curve of drawing with opc server that utilizes the present invention that lamp box temperature shown in Figure 8 is controlled.From the control effect curve, the present invention has increased forecast function piece PC, can't influence the stability and the control effect of control system.As can see from Figure 9, even in control, used a large amount of predicted values to control, still can reach very satisfied control effect.
The present invention can use in foundation fieldbus H1 equipment, also can use in Fast Ethernet (HSE) equipment.
Claims (5)
1. a control structure that is used for the minimizing bus traffic of foundation fieldbus comprises two equipment, wherein comprises an analog quantity input function piece (AI) in first equipment, links to each other with sensor; Comprise the second control function piece (PID2), analog quantity output function piece (AO) in second equipment, described analog quantity output function piece (AO) links to each other with actuator; It is characterized in that: in first equipment, increase by the first forecast function piece (PC1) and the first control function piece (PID1), wherein the parameter of the second control function piece (PID2) is just the same in the parameter of the first control function piece (PID1) and second equipment, and role's mark of functional block is set to sensor one side in the first forecast function piece (PC1); In second equipment, set up one with first equipment in the identical second forecast function piece (PC2) of the first forecast function piece (PC1), and role's mark of its functional block is set to actuator one side; It is as follows to use general configuration software to dispose in first equipment and second equipment between each functional block the connection of parameter: in first equipment, the output parameter (OUT) of analog quantity input function piece (AI) links to each other with the input parameter sampled value (SAMPLE) of the first forecast function piece (PC1), the output parameter (OUT) of the first control function piece (PID1) links to each other with the input parameter controlled quentity controlled variable (CONTROL) of the first forecast function piece (PC1), the output parameter (OUT) of the first forecast function piece (PC1) simultaneously with first equipment in the input parameter (IN) of the first control function piece (PID1) link to each other with the input parameter sampled value (SAMPLE) of the second forecast function piece (PC2) in second equipment; In second equipment, the output parameter (OUT) of the second control function piece (PID2) links to each other with the input parameter controlled quentity controlled variable (CONTROL) of the second forecast function piece (PC2) and the output parameter (OUT) of analog quantity output function piece (AO) simultaneously, the output parameter (OUT) of the second forecast function piece (PC2) links to each other with the input parameter (IN) of the second control function piece (PID2), and the input parameter sampled value (SAMPLE) of the second forecast function piece (PC2) links to each other with the output parameter (OUT) of the first forecast function piece (PC1) in first equipment.
2. according to the described control structure that is used for the minimizing bus traffic of foundation fieldbus of claim 1, it is characterized in that: wherein by general configuration software, dispose the scheduling of functional block in first equipment, at first be that analog quantity input function piece (AI) is carried out, whether need to send the sampled value (SAMPLE) that sends by analog quantity input function piece (AI) to second equipment by the decision of forecast function piece then by bus, whether need to send and report to the police, be that the first control function piece (PID1) is carried out at last.
3. according to the described control structure that is used for the minimizing bus traffic of foundation fieldbus of claim 1, it is characterized in that: the scheduling of wherein disposing functional block in second equipment, decide the first control function piece (PID1) to carry out by whether receiving the sampled value (SAMPLE) that the first forecast function piece (PC1) sends from first equipment, calculate the controlled quentity controlled variable (CONTROL) of this control cycle, and controlled quentity controlled variable (CONTROL) sent to analog quantity output function piece (AO), send to the second forecast function piece (PC2) in second equipment simultaneously; Be that analog quantity output function piece (AO) is carried out at last, conversion sent to actuator after the controlled quentity controlled variable (CONTROL) that second equipment, the second control function piece (PID2) is sent was carried out range conversion, put on the controlled device.
4. according to the described control structure that is used for the minimizing bus traffic of foundation fieldbus of claim 1, it is characterized in that: wherein the execution of the first forecast function piece (PC1) in sensor one side first equipment flow process is as follows: the first forecast function piece (PC1) at first calculates predicted value, and calculate the absolute value (ERROR) of deviation between the sampled value (SAMPLE) that this predicted value and analog quantity input function piece (AI) send, and judge with reference to the limits of error (MAX_ERR) whether the precision of predicted value reaches requirement: if the absolute value of deviation (ERROR) is less than the limits of error (MAX_ERR) between predicted value and the sampled value, replace sampled value (SAMPLE) with predicted value, and the sampled value (SAMPLE) (being predicted value) that is replaced sent in the first control function piece (PID1), finish the implementation of the first forecast function piece (PC1); If the absolute value (ERROR) of deviation is greater than the limits of error (MAX) ERR between predicted value and the sampled value (SAMPLE)), need recomputate the prediction correction, then sampled value (SAMPLE) is sent in the second forecast function piece (PC2) in second equipment by bus network, judge sensor or/and whether the duty of actuator is normal according to alarm threshold value (MAX_DEV) again: if the absolute value (ERROR) of deviation is less than alarm threshold value (MAX_DEV) between predicted value and the sampled value (SAMPLE), sampled value (SAMPLE) is sent in the first control function piece (PID1), finish the implementation of the first forecast function piece (PC1); If the absolute value (ERROR) of deviation is greater than alarm threshold value (MAX_DEV) between predicted value and the sampled value (SAMPLE), send warning reminding field engineer maintenance, then sampled value (SAMPLE) is sent in the first control function piece (PID1), finish the implementation of the first forecast function piece (PC1).
5. according to the described control structure that is used for the minimizing bus traffic of foundation fieldbus of claim 1, it is characterized in that: wherein the execution of the second forecast function piece (PC2) in actuator one side second equipment flow process is as follows: the second forecast function piece (PC2) at first calculates predicted value, judge whether to receive the sampled value (SAMPLE) that the first forecast function piece (PC1) from first equipment sends then, if do not receive the sampled value (SAMPLE) that the first forecast function piece (PC1) from first equipment sends, predicted value is sent in the second control function piece (PID2) in second equipment, finish the implementation of the second forecast function piece (PC2); If receive the sampled value (SAMPLE) that the first forecast function piece (PC1) from first equipment sends, recomputate the prediction correction, calculate the absolute value (ERROR) of deviation between the sampled value (SAMPLE) that predicted value and the first forecast function piece (PC1) from first equipment send then, and judge sensor or/and whether the duty of actuator is normal: if the absolute value (ERROR) of deviation is less than alarm threshold value (MAX_DEV) between predicted value and the sampled value (SAMPLE) with reference to alarm threshold value (MAX_ERR), the sampled value (SAMPLE) of will the first forecast function piece (PC1) from first equipment sending sends in the second control function piece (PID2), finishes the implementation of the second forecast function piece (PC2); If the absolute value (ERROR) of deviation is greater than alarm threshold value (MAX_DEV) between predicted value and the sampled value (SAMPLE), need decide implementation after this according to the value of prediction duration: if the prediction duration is greater than 0, to predict that duration subtracts 1, then predicted value is sent in the second control function piece (PID2) in second equipment, finish the implementation of the second forecast function piece (PC2); If the prediction duration equals 0, the sampled value (SAMPLE) of will the first forecast function piece (PC1) from first equipment sending sends in the second control function piece (PID2) in second equipment, finishes the implementation of the second forecast function piece (PC2).
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| CN101753543B (en) * | 2008-12-19 | 2012-07-04 | 中国科学院沈阳自动化研究所 | FF (foundation field) bus frame type recognizer |
| US8937555B2 (en) * | 2011-05-31 | 2015-01-20 | General Electric Company | Systems and methods to overlay behaviors on foundation fieldbus alerts |
| US8868732B2 (en) * | 2011-05-31 | 2014-10-21 | General Electric Company | Systems and methods for facilitating communication with foundation fieldbus linking devices |
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