JP2021073629A - Control based on speed in controller to be updated non-periodically, method for controlling process, and process controller - Google Patents

Abstract

To control a process by using a process variable measurement value that is received at a low speed or non-periodically.SOLUTION: In order to generate a control signal on a computer processing device, the process includes using the computer processing device to generate integration feedback contribution for use in generating the control signal during each repetition of a control routine, using a repetition filter in order to determine a current integration feedback contribution value to the current repetition of the control routine from a precedent feedback integration feedback contribution value of the control routine and the value of the control signal during each of the plurality of repetitions, using the current integration feedback contribution during each controller repetition for receiving a new process response instruction, and not using the current integration feedback contribution in order to generate the control signal during controller repetition for not receiving a new process response instruction to the control signal.SELECTED DRAWING: Figure 4A

Description

The present patent relates to methods and system compensation for providing speed-based control in process control systems using aperiodic control or slow feedback process variable communication, more specifically in comparison with process dynamics. With respect to devices and methods configured to robustly control the process in performing control when receiving process variable feedback at a slow rate.

Process control systems, such as distributed or extensible process control systems such as those used in chemical, petroleum, or other processes, typically go through analog buses, digital buses, or a combination of analog and digital buses. Includes one or more process controllers that are communicably linked to each other to at least one host or operator workstation and to one or more field devices. Field devices that can be, for example, valves, valve positioners, switches, and transmitters (eg, temperature, pressure, and flow sensors) are functions within the process such as opening or closing valves and measuring process parameters. I do. The process controller receives a signal indicating process measurements and / or other information about the field device created by the field device and uses this information to perform a control routine to generate a control signal and control the control. The signal is sent over the bus to the field device to control the operation of the process. Information from field devices and controllers is typically available to one or more applications run by operator workstations. Allows the operator to perform any desired function on the process, such as checking the current state of the process or modifying the behavior of the process.

Some process control systems, such as the DeltaV® system sold by Emerson Process Management, use functional blocks called modules or groups of functional blocks located in controllers or different field devices. Perform control and / or monitoring operations. In these cases, the controller or other device may include and execute one or more functional blocks or modules, each of which is another functional block (either within the same device or within a different device). Receives input from and / or provides output to other functional blocks, such as measuring or detecting process parameters, monitoring devices, controlling devices, or performing proportional-integral-differential (PID) control routines. Perform some process operation, such as executing a control operation. Different functional blocks and modules within a process control system are generally configured to communicate with each other (eg, through a bus) to form one or more process control loops.

A process controller is typically defined for a process or contains different algorithms, subroutines for each of a number of different loops, such as flow control loops, temperature control loops, pressure control loops, etc. , Or are programmed to execute control loops (these are all control routines). Generally speaking, each such control loop controls one or more input blocks, such as analog input (AI) functional blocks, and a single output, such as proportional-integral-differential (PID) or fuzzy logic control blocks. Includes blocks and output blocks such as analog output (AO) functional blocks. Control routines, and functional blocks that perform such routines, are constructed according to a number of control techniques, including PID control, fuzzy logic control, and model-based techniques such as Smith Predictor or Model Prediction Control (MPC). There is.

To support routine execution, a typical industrial or process plant has a centralized control room communicatively connected to one or more process controllers and process I / O subsystems, process controllers and processes. The I / O subsystem is connected to one or more field devices. Traditionally, analog field devices are connected to the controller by two-wire or four-wire current loops for both signal transmission and power supply. An analog field device (eg, a sensor or transmitter) that transmits a signal to the control room modulates the current through the current loop so that the current is proportional to the detection process variable. On the other hand, an analog field device that performs an action under the control of a control room is controlled by the magnitude of the current passing through the loop.

With increasing data transfer volumes, one particularly important aspect of process control system design is that field devices are communicatively coupled to the process control system or controllers in the process plant and to other systems or devices. Includes styles. In general, the various communication channels, links, and routes that allow field devices to function within a process control system are commonly referred to collectively as input / output (I / O) communication networks. ..

The communication network topology and physical connections or routes used to implement an I / O communication network can be robust or sound in field device communication, especially when the network is subject to harmful environmental factors or harsh conditions. It can have a significant impact. These factors and conditions can compromise the integrity of communication between one or more field devices, controllers, and the like. Communication between the controller and the field device is particularly sensitive to any such disruption, as the monitoring application or control routine typically requires periodic updates of process variables for each iteration of the routine. is there. Therefore, impaired control communications can result in reduced efficiency and / or profitability of process control systems, and excessive wear or damage to equipment, as well as any number of potentially harmful failures.

The I / O communication networks used in process control systems to ensure robust communication have historically been hard-wired. Unfortunately, hard-wired networks introduce a number of complications, challenges, and limitations. For example, the quality of hard-wired networks can deteriorate over time. Further, hard-wired I / O communication networks, especially when the I / O communication network is associated with large industrial plants or facilities distributed over a large area, such as refineries or chemical plants that consume several acres of land. Is typically expensive to install. The required long wiring installation typically involves considerable labor, material, and cost, and may also introduce signal degradation resulting from wiring impedance and electromagnetic interference. For these and other reasons, hardwired I / O communication networks are generally difficult to reconfigure, modify, or update.

It has been proposed to use wireless I / O communication networks to mitigate some of the problems associated with hardwired I / O communication networks. For example, US Patent Application Publication No. 2003/0043052, entitled "Apparatus for Providing Redundant Wireless Access to Field Devices in a Distributed Control System," which is expressly incorporated herein by reference in its entirety. Discloses systems that utilize wireless communication to increase or supplement the use of.

Dependence on radio communications for control-related transmissions is traditionally limited due to reliability concerns, among other things. As explained above, modern surveillance applications and process controls rely on reliable data communication between the controller and field devices to achieve optimal control levels. In addition, typical controllers run control algorithms at high speed to quickly correct unwanted deviations in the process. Undesirable environmental factors or other adverse conditions can cause intermittent interference that interferes with or interferes with the high speed communications required to support such execution of monitoring and control algorithms. Fortunately, wireless networks have become much more robust over the last two decades, enabling the reliable use of wireless communications in several types of process control systems.

However, power consumption remains a complicating factor when using wireless communications in process control applications. Since the wireless field device is physically separated from the I / O network, the field device typically needs to provide its own power source. Therefore, the field device can be battery-powered, draw solar energy, or take out environmental energy such as vibration, heat, and pressure. For these devices, the energy consumed for data transmission can account for a significant portion of the total energy consumption. In fact, it is more during the process of establishing and maintaining a wireless communication connection than during other important operations performed by the field device, such as the steps taken to detect or detect the process variable being measured. It may consume a lot of power. Implemented a wireless process control system in which field devices such as sensors communicate with the controller in an aperiodic, slow, or intermittent manner to reduce the power consumption of the wireless process control system and thus extend battery life. It has been proposed to do. In one case, the field device may communicate with the controller or send a measurement of the process variable to the controller only when a significant change in the process variable is detected and leads to aperiodic communication with the controller. it can.

One control technique developed to handle aperiodic process variable measurement updates is the expected process response to control signals generated by the controller during infrequent or aperiodic measurement updates. Use a control system that provides and maintains instructions for. The expected process response can be developed by a mathematical model that calculates the expected process response for a control signal for a given measurement update. An example of this technique is described in US Pat. No. 7,587,252, entitled "Non-Periodic Control Communications in Wireless and Other Process Control Systems," the entire disclosure of which is expressly incorporated herein by reference. ing. Specifically, this patent, upon receiving an aperiodic process variable measurement update, generates an indication of the expected process response to the control signal until the arrival of the next aperiodic process variable measurement update. Discloses a control system with a filter that maintains the generated instructions of the expected process response. As another example, US Pat. No. 7,620,460, the name "Process Control With Unreliable Communications," whose entire disclosure is expressly incorporated herein by reference, is an expected response to a control signal. Provides instructions for, but includes filters that further modify the filter to generate more accurate indications of the expected process response by incorporating measurements of the time elapsed since the last aperiodic measurement update. , Disclosure the system.

However, in many control applications, the process control system may receive setpoint changes during process operation. In general, during the execution of a periodically updated control system (eg, a hard-wired control communication system), when a set point changes, a proportional action against an error between the set point and the measured process variable. A controller designed to do so immediately changes the controller output to drive process variables towards new steady-state values. However, in a radio control system that receives infrequent and aperiodic measurement updates, operating as described in both examples above, the measured process response reflected by each new measurement update is , Reflects the changes made in the controller output captured for the last reading update, in addition to the output changes caused by the setpoint changes made shortly after receiving the last reading update. In this case, calculating the controller reset component based on the controller output (as described in US Pat. No. 7,620,460) and the time since the last measurement update is the last measurement. It may overcompensate for changes that occur after the update. Therefore, the process response to a set point change may differ based on when the set point change took place after the last measurement update. As a result, when the controller generates a control signal after a setpoint change, it continues to rely on the previously generated (and now out of date) expected response instructions, so that the setpoint changes. On the other hand, it does not respond quickly or robustly. To solve this problem, the entire disclosure is explicitly incorporated by reference, US Patent Application Publication No. 2013/0184837, entitled "Compensating for System Changes in a Non-Periodically Updated Controller", any new process variable. A filter that is continuously updated in the feedback loop in the controller was used to track the behavior of the controlled variables during the time when no measurements were received, and the controller received new process variable measurements. Sometimes we use the output of this controller, but otherwise we disclose a system that uses the output of the most recent filter that received the measured values of the process variables and generated the control signal. .. In this system, the generated control signal responds better and operates better when the set point of the process variable changes during the time it takes to receive the measured value of the process variable.

In addition, when using battery-powered transmitters in wireless control systems, it is desirable to set up the system to maintain long battery life. For example, in order to obtain a battery life of 3-5 years using current transmitter and battery technology, it is generally necessary to use a communication update rate of 8 seconds or higher. However, in order to maintain control of the process, it is still important to have process feedback measurements received at a rate that is at least four times the rate associated with the process response time (ie, the inverse of the process response time). Therefore, using such a slow update rate limits the use of PID (proportional-integration-differential) -based radio control for processes with process response times of 30 seconds or more.

Furthermore, for wireless control, including position outputs provided to valves or other controlled elements that indicate the final position to move, such as those using the generation of 4-20 ma or digital signals. There are various types of PID algorithms that can be used to address. However, a speed-based control signal that directs a valve or other controlled element to move in a certain direction by a certain amount, for example by energizing a movable element over a certain amount of time. There are other PID algorithms to provide. Control signals based on such speeds are commonly used with electric motors and are also modulated to indicate the amount of time the valve must be energized (moveable elements to move over a certain period of time). The control signal is provided in the form of a pulse signal (having a pulse width). Speed-based controllers tend to generate changes in position signals rather than signals that indicate the actual position acquired by the movable element. Therefore, speed-based control algorithms tend to be used to provide incremental (increase / decrease) output to actuators, and thus can be used to control actuators that cannot provide position feedback. it can.

Control techniques allow for robust control of a process or control loop, with fast kinetics in terms of the rate at which measurements of controlled process variables are provided as feedback to the process controller. Specifically, the control technique can use a PID algorithm in the form of position or velocity to control the process so that the measured or feedback signal of the process variable is equal to or even the process response time. It is provided to the controller at longer time intervals. Specifically, the control technique can be used to provide robust control in processes that have a response time that is 2-4 times shorter than the feedback time interval. In such situations, for example, the feedback measurements of process variables are wirelessly, intermittently, or to the controller at time intervals that are shorter, closer to, or longer than the response time of the process. This can happen when using the provided wireless control.

The speed PID control routines disclosed are actuators that require position or incremental input to control using radio measurements when the actuator requires incremental input and no position feedback is available to the controller. Used in a number of different situations, such as to control by wired measurements when interfaced with, and to deal with conventional installations and new installations where wireless measurements are used for control. Can be done. In addition, the adjustment of the PID algorithm in the form of speed can be made based on process gain and kinetics, and is independent of the radio communication rate. Furthermore, the PID control routine in the form of speed automatically holds the last output position in the event of loss of communication and provides bumpless recovery when communication is reestablished.

In one case, the controller implementing the new control technique generally contains different structures in which the difference, proportional, integral, and derivative control signal components are generated and used to make a difference or move. The control signal is then transmitted to a controlled device, such as a valve, to control the operation of the controlled device, and thus the process. This difference or speed based control mode produces a control signal that works better than standard PID control in the presence of feedback measurements of slow process variables. Specifically, controllers using this control technique generate a proportional value of difference during each controller iteration, representing the difference between the previously calculated proportional control signal component and the newly calculated proportional control signal component. The proportional value of this difference is used as a reference for each new control signal from the controller. However, when a new process variable measurement signal is available in the controller, various other control signal components, such as the differential control signal component and / or the integral control signal component, are added to the proportional control signal component of the difference. , Or can be combined with the component. These two control signal components can also be based on the difference between the newly calculated value and the previously calculated value. Specifically, the new derivative can be calculated during controller iteration, at which point the newly received value of the process variable measurement can be utilized by the controller. Similarly, new integral components can be generated using a continuously updated filter, which generates new indications of the process's expected response to the iterations of each control routine of the controller. However, the output of the continuously updated filter is used to generate new integrating elements only when a new value of the process variable measurement is received. Otherwise, the integral control signal component is set to zero.

The speed-based PID control techniques disclosed herein use a form of difference to quickly respond to setpoint changes (even during the time that the feedback signal of the process variable is present at the controller input). Generates a matching control signal, but is still slower than the inverse of the response time of the controlled process (eg, 2-4 times slower), close to the inverse of the response time, or the inverse of the response time. It provides robust and stable control in the presence of slow-received (eg, intermittent) feedback signals, including feedback signals received at faster rates.

It is a block diagram of an exemplary, periodically updated hardwired process control system. FIG. 5 is a graph illustrating a process output response to a process input of an exemplary, periodically updated hardwired process control system, including process response time. FIG. 6 is a block diagram illustrating an embodiment of a radio process control system having a controller that receives slow or aperiodic feedback inputs. FIG. 6 is a block diagram of an exemplary controller that allows robust compensation for setpoint changes or feedforward disturbances in a periodically updated hardwired process control system. FIG. 5 is a graph illustrating the process output response of an exemplary controller of FIG. 4A as the controller responds to some setpoint changes. FIG. 5 is a block diagram of an exemplary controller that compensates for setpoint changes in a process control system that is updated aperiodically, where the controller compensates for delays in processes and / or measurements in the feedback signal. FIG. 3 is a block diagram of an exemplary controller that compensates for setpoint changes in an aperiodically updated process control system in which the process controller uses differential contributions or rate contributions to determine control signals. Process control that is updated aperiodically when the process controller receives additional controller input data provided by field devices, control elements, or other downstream devices and affects the response of process behavior. It is a block diagram of an exemplary controller that compensates for a change in a set point in a system. FIG. 3 is a block diagram of an exemplary controller in which a process controller compensates for setpoint changes in an aperiodically updated process control system that adapts to the use of either real or implicit controller input data for field devices. FIG. 3 is a block diagram of an exemplary speed-based PI controller that enables robust compensation for setpoint changes or feedforward disturbances in a process control system in response to process variable measurements received at low speed. FIG. 3 is a block diagram of an exemplary speed-based PID controller that enables robust compensation for setpoint changes or feedforward disturbances in a process control system in response to process variable measurements received at low speed. In a graph exemplifying the simulated process response of an exemplary prior art speed based PID controller in both wired and wireless configurations with a process response time of 8 seconds in response to setpoint changes in primary control variables. is there. In a graph illustrating the simulated process response of a speed-based PID controller according to the present invention in both wired and wireless configurations, which responds to setpoint changes in primary control variables and has a process response time of 8 seconds. is there. In a graph exemplifying a simulated process response of an exemplary prior art speed based PID controller in both wired and wireless configurations with a process response time of 3 seconds in response to setpoint changes in primary control variables. is there. In a graph illustrating the simulated process response of a speed-based PID controller according to the present invention in both wired and wireless configurations with a process response time of 3 seconds in response to a set point change in a primary control variable. is there. FIG. 5 is a graph illustrating a simulated process response of an exemplary prior art speed based PID controller in both wired and wireless configurations with a process response time of 8 seconds in response to disturbance changes. FIG. 5 is a graph illustrating a simulated process response of an exemplary speed-based PID controller according to the invention in both wired and wireless configurations, which respond to disturbance changes and have a process response time of 8 seconds. FIG. 5 is a graph illustrating a simulated process response of an exemplary prior art speed based PID controller in both wired and wireless configurations with a process response time of 3 seconds in response to disturbance changes. FIG. 5 is a graph illustrating a simulated process response of an exemplary speed-based PID controller according to the invention in both wired and wireless configurations with a process response time of 3 seconds in response to disturbance changes.

Control techniques can be used to control in a process loop where the process measurement feedback signal is received slowly or intermittently, especially the process measurement feedback signal, such as the inverse of the process response time. It is useful when receiving at a rate that is slower than the rate associated with the process kinetics being used, comparable to the rate, and slightly faster than the rate. This controller is, for example, in a slow and / or aperiodic manner, in particular, less than the process response rate of the controlled process dynamics (ie, the inverse of the process response time to the controlled process variable). It can be used in a controller that receives a process measurement signal as a feedback signal at a rate similar to or otherwise similar to the process response rate. In one case, the control technique combines a proportional contribution signal with one or more of a differential contribution signal and an integral contribution signal to generate a control signal for use in controlling a process device such as a valve. .. In one case where a speed-based PID algorithm is used, the controller generates a proportional contribution value from the difference between the set point and the feedback signal of the previously received process variable measurement. This error signal is then provided to the difference unit, which is multiplied by the gain signal to determine the change in this signal since the last run cycle of the controller. Further, the differential unit can receive the error signal and basically differentiate the error signal since the last measurement signal is received by the controller over time to perform the differential calculation with respect to the error signal. The derivative module or calculation output is also provided to the change detection unit or difference unit to determine the difference between the current output of the derivative calculation and the previous value used to calculate the control signal. Similarly, the integration calculation unit receives the difference of the control signal as a product of the proportional unit and the differential unit and integrates (for example, totals). The output of the adder is provided to the filter to filter the output of the adder to produce an integral contribution signal. However, this integral contribution is provided to the adder and sums this contribution with the output of the control signal only when a new feedback value is provided to the controller. That is, the integral contribution is set to zero for all controller iterations, except for those that have access to a new feedback signal in the controller.

Generally speaking, the continuously updated filter of the integral contribution unit in the controller repeats each control routine of the controller, even though it receives process variable measurement updates from the field device slowly or aperiodically. Generates instructions for the expected process response (also called feedback contribution). The continuously updated filter, in part, was generated earlier than the last control routine iteration and control routine execution period to generate the expected response indication during each control routine iteration. Use the expected response instructions. In addition, the integral output switch in the controller provides the output of the continuously updated filter to the control signal as a feedback contribution, such as an integral (also known as reset) contribution based on the latest measured indication. .. Generally speaking, the integral output switch is the last measurement update in the PID controller in the form of speed as an integral or reset contribution to the control signal during each iteration of the controller where the new measurement signal is not available. Provides an expected process response, or zero value, as caused by a filter that is continuously updated at the time received by the controller. When new measurement updates are available, the integral output switch responds to new indications of the expected process response generated by the continuously updated filter (based on the new measurement update instructions). It clamps and provides a new expected process response as an integral contribution of the control signal. As a result, the controller uses a continuously updated filter to determine the new expected response of the process during each controller iteration, and each new expected process response gives a new measurement on the controller. Even if the integration or reset component of the control signal changes only when it is available, it was done during the time between measurements updates and to the controller output during the expansion of the control signal. Reflects the effects of changes in set points or feed forwards.

FIG. 1 illustrates a process control system 10 that can be used to implement the control methods described. The process control system 10 can be connected to the data historian 12 and to one or more host workstations or computers 13 (which can be any type of personal computer, workstation, etc.), each of which has Includes a process controller 11 having a display screen 14. The controller 11 is also connected to field devices 15-22 via input / output (I / O) cards 26 and 28. The data historian 12 is any desired type of data acquisition unit having any desired type of memory for storing data and any desired or known software, hardware, or firmware. Can be done. In FIG. 1, the controller 11 is communicably connected to field devices 15-22 using a hardwired communication network and communication scheme.

In general, field devices 15-22 can be any type of device such as sensors, valves, transmitters, locators, etc., while I / O cards 26 and 28 can be any desired communication. Alternatively, it can be any type of I / O device that conforms to the controller protocol. The controller 11 includes a processor 23 that executes or supervises one or more process control routines (or any module, block, or subroutine thereof) stored in memory 24. Generally speaking, the controller 11 communicates with the devices 15-22, the host computer 13, and the data historian 12 to control the process in any desired manner. In addition, the controller 11 implements a control strategy or scheme using what is commonly referred to as a functional block, and each functional block implements a process control loop within the process control system 10 (with a link). An object or other part of the entire control routine (eg, a subroutine) that works with other functional blocks (via called communication). Functional blocks typically include input functions, PIDs, fuzzy logic controls that are associated with transmitters, sensors, or other process parameter measurement devices to perform some physical function within the process control system 10. It performs one of a control function associated with a control routine such as, or an output function that controls the operation of some devices such as valves. Of course, hybrid and other types of functional blocks exist and are available herein. Functional blocks can be stored and executed by the controller 11 or other device, as described below.

As illustrated in the disassembly block 30 of FIG. 1, controller 11 can include several single loop control routines, exemplified as control routines 32 and 34, and if desired, control loops. One or more advanced control loops, exemplified as 36, can be implemented. Each control loop is typically referred to as a control module. The single loop control routines 32 and 34 can be associated with a process control device such as a valve, a measurement device such as a temperature and pressure transmitter, or any other device within the process control system 10 as appropriate analog inputs ( Single-input / single-output fuzzy logic control blocks and single-input / single-output PID control blocks connected to AI) and analog output (AO) functional blocks, respectively, to provide single-loop control. Illustrated. The advanced control loop 36 is exemplified to include an advanced control block 38 having an input communicably connected to one or more AI functional blocks and an output communicably connected to one or more AO functional blocks. However, the inputs and outputs of the advanced control block 38 shall be connected to any other desired functional block or control element to receive other types of inputs and provide other types of control outputs. Can be done. Advanced control block 38 can implement any type of multiple input, multiple output control scheme, and also includes model predictive control (MPC) blocks, neural network modeling or control blocks, multivariable fuzzy logic control blocks, real-time optimizers. Blocks and the like can be constructed or included. The functional blocks illustrated in FIG. 1, including the advanced control block 38, can be executed by a stand-alone controller 11 or, in turn, one of workstations 13 or field devices 19-22. It will be appreciated that it can be located and executed within any other processing device or control element of the process control system, such as one. As an example, field devices 21 and 22 can be transmitters and valves, respectively, and can execute control elements for performing control routines, thus such as one or more functional blocks. , Processing components and other components for performing part of the control routine can be included. More specifically, as illustrated in FIG. 1, the field device 21 may have a memory 39A for storing the logic and data associated with the analog input block, while the field device 22 may have a memory 39A. An actuator with memory 39B for storing logic and data associated with a PID or other control block communicating with an analog output (AO) block can be included.

The graph in FIG. 2 is generally of control loops 32, 34, and 36 (and / or any control loop incorporating functional blocks present in field devices 21 and 22 or other devices). Illustrate a process output that is deployed in response to a process input in a process control system based on one or more implementations. The control routines being implemented are generally executed in a periodic fashion through a number of controller iterations, depending on the number of times the control routines are executed, as shown along the time axis by the thick arrow 40 in FIG. In conventional cases, each control routine iteration 40 is supported by updated process measurements indicated by thin arrows 42, provided, for example, by a transmitter or other field device. As illustrated in FIG. 2, there are typically a plurality of periodic process measurements 42 made and received by the control routine during each of the periodic control routine execution times 40. To avoid the limitations associated with synchronization of measurements and control execution, many known process control systems (or control loops) oversample process variable measurements by a factor of 2-10. Designed to. Such oversampling helps ensure that process variable measurements for use in the control scheme are up-to-date during the execution or iteration of each control routine. Also, in order to minimize control variability, in conventional designs, feedback-based control should be performed 4-10 times faster than process response time, and new process variable measurements are given to each controller. It is stipulated that it can be used at the time of repetition. Process response time, the process time constant (tau) (e.g., 63% of the process variable change), after performing step change 44 in the process input of a process delay or dead time (T _{D) (in} Figure 2 the lower It is represented by the process output response curve 43 in the graph of FIG. 2 so that it is the time associated with the addition of (shown by line 45). In any case, to meet these traditional design requirements, the process measurement update (indicated by arrow 42 in FIG. 2) is much higher than the control routine execution rate (indicated by arrow 40 in FIG. 2). Fast, thus much faster than process response time, or sampled at a higher rate and provided to the controller.

However, obtaining samples of frequently periodic measurements from a process can be done, for example, when the controller is operating in a process control environment where it receives measurements wirelessly from one or more field devices. It may not be practical or even impossible. Specifically, in these cases, if the controller can only receive slow process variable measurements or aperiodic process variable measurements (to save battery life on the wireless sensor / transmitter). There is. Moreover, in these cases, the time between aperiodic and even periodic process variable measurements may be longer than the control routine execution rate (indicated by arrow 40 in FIG. 2). FIG. 3 illustrates an exemplary radio process control system 10 capable of performing slow and / or aperiodic radio communication of process control data, or the use of process variable measurements on the controller 11.

The control system 10 of FIG. 3 is essentially similar to the control system 10 of FIG. 1 and the same elements are numbered the same. However, the control system 10 of FIG. 3 includes a number of field devices 60-64 and 71 that are wirelessly communicatively coupled to and potentially to the controller 11. As illustrated in FIG. 3, the wirelessly connected field device 60 is connected to the antenna 65 and cooperates to communicate wirelessly with the antenna 74, which in turn connects to the wireless I / O device 68. Be connected. Further, the field devices 61-64 are connected to a wired-to-wireless conversion unit 66, which is then gradually connected to the antenna 67. The field devices 61 to 64 wirelessly communicate with the antenna 73 connected to the further wireless I / O device 70 through the antenna 67. Also illustrated in FIG. 3, the field device 71 includes an antenna 72 that communicates with one or both of the antennas 73 and 74, thereby communicating with the I / O devices 68 and / or 70. The I / O devices 68 and 70 are then communicably connected to the controller 11 via a wired backplane connection (not shown in FIG. 3). In this case, the field devices 15-22 remain hardwired to the controller 11 via the I / O devices 26 and 28.

The process control system 10 of FIG. 3 is generally a radio of data measured, sensed, or calculated by other control elements such as transmitters 60-64 or field device 71, as described below. Use transmission. In the control system 10 of FIG. 3, new process variable measurements or other signal values are transmitted to controller 11 by devices 60-64 and 71 relative to slow speed or aperiodicity, such as when certain conditions are met. Is considered to be. For example, a new process variable measurement can be sent to the controller 11 when the process variable value changes by a predetermined amount with respect to the last process variable measurement sent by the device to the controller 11. These signals can also be transmitted periodically, but for typical process control systems such as wired process control signals, they are usually at a much slower rate. For example, a slow periodic feedback rate can be lower than the controller execution rate (the rate at which the controller generates a new control signal for use in creating the control signal), and is also described herein. Using the control techniques described, the process response rate or response time is lower than, comparable to, or similar to, such as a rate that is 2-4 times lower than the response rate of the controlled process dynamics. Can be a rate. Here, the process response rate is the reciprocal of the process response time. Of course, other methods of determining when to send process variable measurements in a periodic or aperiodic fashion can be implemented as well or instead.

As will be appreciated, transmitters 60-64 of FIG. 3 have their respective process variables (eg, flow rate, pressure) for use in one or more control loops or control routines, or in monitoring routines. , Temperature, or level signal) can be transmitted to the controller 11. Other wireless devices, such as the field device 71, may be configured to wirelessly receive process control signals and / or transmit other signals indicating any other process parameters. Generally speaking, as illustrated in FIG. 3, the controller 11 has a communication stack 80 running on a processor that processes incoming signals and to detect when incoming signals include measurement updates. It includes a module or routine 82 that runs on the processor and one or more control modules 84 that run on the processor to take control based on measurement updates. The detection routine 82 can generate a flag or other signal to indicate that the data provided via the communication stack 80 contains new process variable measurements or other types of updates. New data and update flags can then be provided to one or more of the control modules 84 (which can be functional blocks), as described in more detail below, and then the control modules. Is executed by the controller 11 at a predetermined periodic execution rate. Alternatively, or in addition, new data and update flags can be provided to one or more monitoring modules or applications running on the controller 11 or other parts of the control system 10.

The radio (or other) transmitter of FIG. 3 generally results in slow or periodic, irregular or otherwise frequent between field devices 60-64 and 71 and controller 11. Includes low data transmission. However, as mentioned above, the communication of measurements from field devices 15-22 to controller 11 is traditionally much faster than the execution rate of the controller, or at least faster than the dynamic rate of the process. It is constructed to be done in a cyclical fashion at a much faster rate, i.e. the reciprocal of the process response time (for the phenomenon of the controlled process). As a result, the controller 11 control routine is generally designed for periodic updates of process variable measurements used in the controller 11 feedback loop.

Suitable for slow, aperiodic, or otherwise unavailable measurement updates (and other unavailable communication transmissions) introduced, for example, by wireless communication between some of the field devices and the controller 11. To do so, controller 11 control and monitoring routines (s), as described below, make these updates, especially when using slow speeds, including aperiodic or aperiodic or intermittent updates. When is occurring less frequently than the execution rate of controller 11, further such updates are made at a rate similar to the process response rate (eg, the inverse of the process response time of the controlled process variable) (eg, 2). It can be rebuilt or modified to allow the process control system 10 to function properly when received at ~ 4x lower or similar rates, etc.). 4-10 show in more detail exemplary control schemes configured to operate using communications associated with slow and / or aperiodic control. For example, FIG. 4A schematically illustrates a position type process controller 100 coupled to process 101. The control scheme implemented by the controller 100, which can be the control element of the controller 11 of FIGS. 1 and 3, or a field device such as, for example, one of the wireless field devices of FIG. The functionality of the communication stack 80 illustrated and described in connection with FIG. 3, including the update detection module 82 and one or more of the control modules 84, and the movable elements of the control device. Generates a control signal indicating the position to move.

In the exemplary system of FIG. 4A, controller 100 is optionally from, for example, one of workstations 13 (FIGS. 1 and 3), within process control system 10, or communicating with said process control system. It operates to receive set point signals from other sources and generate one or more control signals 105 provided to process 101 from the output of controller 100. In addition to receiving the control signal 105, process 101 may be subject to disturbances, measured or unmeasured, outlined by arrow 104. Depending on the type of process control application, the setpoint signal can be changed at any time during the control of process 101, such as by the user, adjustment routine, and so on. Of course, the process control signal 105 can control the actuator associated with the valve, or any other field device to influence the response of the operation of process 101. The response of process 101 to a change in process control signal 105 is measured or detected by a transmitter, sensor, or other field device 106, eg, any one of transmitters 60-64 illustrated in FIG. Can be dealt with. The communication link between the transmitter 106 and the controller 100 can include a wireless connection and is illustrated in FIG. 4A using a dashed line.

In a simple embodiment, the controller 100 can implement a single input, single output closed loop control routine, such as a PI control routine, which is one form of a PID control routine. Therefore, the controller 100 includes several standard PI controller elements including the communication stack 80 and a control signal generator including an addition block 108, a proportional gain element 110, an additional addition block 112, and a high / low limiter 114. The control routine 100 also includes a direct feedback path that includes a filter 116 and an integral output switch that includes a selection block 118. The filter 116 is coupled to the output of the high and low limiter 114, and the switch block 118 is coupled to the output of the filter 116 to provide the additive block 112 with an integral or reset contribution or component of the control signal generated by the controller 100. ..

During the operation of the controller 100, the addition block 108 compares the set point signal with the process variable measurements received immediately before provided by the communication stack 80 in the controller 100 to generate an error signal. The proportional gain element 110 operates on the error signal in order to generate a proportional contribution or component of the control signal, for example, by multiplying _{the error signal by the proportional gain value K p.} The addition block 112 then combines the output of the gain element 110 (ie, the proportional contribution) with the components of the control signal produced by the integral or reset contribution, or the feedback path, in order to generate an essentially unrestricted control signal. To combine. The limiter block 114 then limits the output of the addition block 112 to a height limit in order to generate a control signal 105 transmitted to control the process 101.

Importantly, the filter 116 and the block or switch 118 in the feedback path of the controller 100 operate in the following manner to generate an integral or reset contribution component of the control signal. The filter 116 coupled to receive the output of the limiter 114 generates an indication of the expected process response to the control signal 105 based on the output value of the limiter 114 and the execution period or time of the control algorithm 100. The filter 116 provides this expected process response signal to the switch or block 118. Whenever the switch or block 118 receives a new process variable measurement, it samples and clamps the output of the filter 116 on the output of the switch or block 118 until it receives the next process variable output on the communication stack 80. To maintain. Therefore, the output of switch 118 remains the output of filter 116 sampled in the last measurement update.

The expected process response to changes in the output of adder 108, such as that produced by filter 116, can be approximated using a linear model, as described in more detail below. However, more generally, the expected process response can be generated using any suitable model of process 101, integrated into the model incorporated in the feedback path of controller 100, or integrated into the control signal. Not limited to the filter or model associated with determining the reset contribution. For example, a controller that utilizes the model to provide the expected process response can incorporate differential contributions such that control routine 100 executes the PID control scheme. Some examples incorporating exemplary types of differential contributions are described below in connection with FIGS. 6-8.

図４Ａに示されるように、コントローラ１００内でポジティブフィードバック経路を使用する１つの利点は、コントローラ出力が、高くまたは低く、すなわちリミッタ１１４によって制限されるときに、リセット寄与をワインドアップすることが自動的に防止されることである。 Before discussing the behavior of filter 116 in FIG. 4A in more detail, it is useful to note that a conventional PI controller can be run using a positive feedback network to determine the integral or reset contribution. is there. Mathematically, it can be seen that the transfer function for implementing conventional PIs is equivalent to the standard equation for unconstrained control, i.e. when the output is unconstrained. in particular:

As shown in FIG. 4A, one advantage of using a positive feedback path within controller 100 is that it automatically winds up the reset contribution when the controller output is high or low, i.e. limited by the limiter 114. It is to be prevented.

In any case, the control techniques described below allow the controller to use a positive feedback path to determine a reset or integral contribution when it receives an aperiodic update of a process variable. Nevertheless, it allows a robust controller response in the event of setpoint or feedforward changes that occur during the reception of new process variable measurements. Specifically, in order to provide robust setpoint changes to the operation of the controller, the filter 116 executes each or all of the controller 100, whether or not this output of the filter is provided to the addition block 112. In the meantime, it is configured to calculate new indications or values for the expected process response. As a result, the controller even if only the output of the filter 116 generated immediately after the controller 100 receives a new process measurement update from the communication stack 80 is used as an integral or reset contribution in the adder 112. During each execution cycle of the routine, the output of filter 116 is newly regenerated.

Specifically, a new indication of the expected response, such as generated by the filter 116, is the current controller output (ie, the control signal after the limiter 114), the last (ie, immediately preceding) controller execution cycle. Calculated during each controller execution cycle from the expected response indications generated by the filter 116 generated in and the controller execution period. As a result, the filter 116 is described herein to be continuously updated as it is executed to generate a new process response estimate during each controller execution cycle. An exemplary equation is provided below that can be performed by the continuously updated filter 116 to generate a new expected process response or filter during each controller execution cycle.

Here, the new filter output F _N is obtained by adding the _{current controller output value ON-1} and the current filter output value F _N-1 to the _{immediately preceding filter output F N-1} (that is, the current filter output value). You will notice that it is repeatedly determined by adding the damping component, which is determined by multiplying the difference between them by the reset time T _{Reset and a factor that depends on the controller execution period ΔT.} By using a filter that updates continuously in this fashion, the control routine 100 better determines the expected process response when calculating the integral control signal input when a new process variable measurement is received. It can be made more sensitive to changes in setpoints or to other feedforward disturbances that occur between the reception of two process variable measurements. More specifically, a change in the set point (without receiving a new process measurement) immediately results in a change in the error signal at the output of the adder 108, which changes the proportional contribution component of the control signal. Therefore, you will notice that it changes the control signal. As a result, the filter 116 immediately begins to generate a new expected response of the process to the altered control signal and therefore updates its output before the controller 100 receives the new process measurements. The filter then receives a new process measurement and the filter output sample is clamped to the input of adder 112 by switch 118 for use as an integral or reset contributor component of the control signal. 116, at least to some extent, repeats the expected process response that responded to or incorporated process 101's response to changes in the setpoint.

In the past, reset contribution filters used in controller feedback paths that are updated aperiodically, such as in the systems described in US Pat. Nos. 7,587,252 and 7,620,460, have been Only new indications of the expected response were calculated when new process variable measurements were available. As a result, the reset contribution filter compensates for setpoint changes or feedforward disturbances that occur during the reception of process variable measurements, as setpoint changes or feedforward disturbances are completely independent of any measurement updates. I didn't. For example, if a setpoint change or feedforward disturbance occurs between two measurement updates, the calculation of the new indication for the expected response is based on the time since the last measurement update and the current controller output 105. As a result, the expected process response of the controller could be distorted. As a result, filter 116 compensates for process (or control signal) temporal changes resulting from setpoint changes (or other feedforward disturbances) that occur between the reception of two process variable measurements on the controller. I couldn't get started.

However, as will be appreciated, the control routine 100 of FIG. 4A provides the expected process response by being based on the calculation of aperiodic measurements, while in addition a change in setpoint (or controller). To compensate for the changes caused by any measured disturbance) used as a feedforward input to 100, the expected response between the reception of the two measurements is determined. Therefore, the control techniques described above can be adapted to setpoint changes, feedforward actions against measured disturbances, etc. that can affect the expected process response, thus providing a more robust control response. To do.

As will be appreciated, the control technique exemplified in FIG. 4A indicates the expected response via a filter 116 (eg, a reset contribution filter) that is continuously updated for each execution of the control block or routine 100. Is calculated. Here, the controller 100 configures a filter 116 that is continuously updated to calculate new instructions for the expected response for each execution of the control block. However, in order to determine whether the output of the filter 116 should be used as an input to the addition block 112, the communication stack 80 and, in some embodiments, the update detection module 82 (FIG. 3) is new. When a process variable measurement is received, it processes incoming data from transmitter 106 to generate a new value flag for the integrated output switch 118. This new value flag informs switch 118 that it will sample and clamp the filter output value for this controller iteration for the input of adder 112.

Regardless of whether a new value flag is communicated, the continuously updated filter 116 continues to calculate the expected response indication for each iteration of the control routine. This new indication of the expected response is carried to the integral output switch 118 for each execution of the control block. In response to the presence of the new value flag, the integral output switch 118 allows the addition block 112 to pass a new indication of the expected response from the continuously updated filter 116 and that of the control block. Switch between maintaining the previously delivered signal to addition block 112 during the last run. More specifically, when a new value flag is communicated, the integral output switch 118 passes to the addition block 112 the indication calculated just before the expected response from the continuously updated filter 116. Make it possible. Conversely, in the absence of the new value flag, the integral output switch 118 retransmits the indication of the expected response from the last control block iteration to the addition block 112. In other words, the integral output switch 118 clamps to the new indication of the expected response each time a new value flag is communicated from the stack 80, but in the absence of the new value flag, of any expected response. The newly calculated instruction is also prevented from reaching the addition block 112.

This control technique allows the continuously updated filter 116 to continue modeling the expected process response, regardless of whether new measurements are communicated. If the control output changes as a result of a setpoint change or a feedforward action based on the measured disturbance, a continuously updated filter 116 is expected at each control routine iteration, regardless of the presence of the new value flag. Correctly reflect the expected process response by calculating new instructions for the response. However, new indications of the expected response (ie, reset contribution or integral component) are only incorporated into the controller's calculations when the new value flag is communicated (via the integral output switch 118).

Graph 200, illustrated in FIG. 4B, illustrates the simulated operation of controller 100 in FIG. 4A when driving the process output signal 202 to steady state values when controller 100 responds to some set point changes. Depict. In FIG. 4B, the process output signal 202 (illustrated by the thick line) during wireless operation of the process control system is shown in comparison with the set value signal 204 (shown by the thin line). As indicated by the arrows along the time axis at the bottom of the graph 200, when a set point change occurs, the controller 102 generates a control signal to drive the process output to create a new set value (ie, steady state). Respond to react to the state value). For example, as illustrated in Figure 4B, the change set point takes place at time T _1, which is evident from the fact that a significant change in to a lower value from a higher value is the magnitude of the setpoint signal 204 is there. In response, controller 102, in a smooth transition curve as exhibited by the output signal 202 between times T ₁ and time T _2, to drive the process variable associated with the set point or set point value for the new steady state .. Similarly, in Figure 4B, the second setpoint change takes place at time T _2, which is evident from the fact that a significant change in to a higher value from the lower value the magnitude of the setpoint signal 204 .. Accordingly, the controller 102 controls the set point or process variable associated with the set point value for the new steady state in a smooth transient curve as indicated by the output signal 202 between _{times T 2} and T _3. .. As a result, as can be seen in FIG. 4B, the controller 100 that implements the control routine described above allows compensation for setpoint changes in the aperiodic radio control system in a robust manner. Since the feedforward disturbance can be measured and included in the control action operation, the controller 100 that implements the control routine described above can also compensate for feedforward changes in the control output in the aperiodic radio control system. Can be.

The simple PI controller configuration of FIG. 4A uses the output of filter 116 directly as the reset contribution to the control signal, and in this case the reset contribution of the closed loop control routine (eg, continuously updated as presented above). It should be noted that the filter equation) can provide an accurate representation of the process response in determining whether the process exhibits steady-state behavior. However, other processes, such as waste-dominant processes, may require the incorporation of additional components into the controller of FIG. 4A to model the expected process response. For processes well represented by the primary model, process time constants can generally be used to determine the reset time of the PI (or PID) controller. More specifically, if the reset time is set equal to the process time constant, the reset contribution generally disables the proportional contribution so that the control routine 100 reflects the expected process response over time. To do. In the embodiment illustrated in FIG. 4A, the reset contribution can be achieved by a positive feedback network with a filter having the same time constant as the process time constant. Other models can be used, but positive feedback networks, filters, or models provide a convenient mechanism for determining the expected response of a process with known or approximate process time constants. For processes that require PID control, the differential contribution to the PID output, also known as the rate, can be recalculated and updated only when a new measurement is received. In such cases, the derivative calculation can use the elapsed time since the last new measurement. Other controller components can be used to control more complex processes using aperiodic reception of process measurements, but to provide robust control in response to setpoint changes. Some examples of controllers that can use the filtering techniques of are described below in conjunction with FIGS. 5-8.

With reference to FIG. 5, the alternative controller (or control element) 120, configured according to the control technique, is in many respects similar to the controller 100 illustrated in FIG. 4A, as described above. As a result, elements common to both controllers are identified by the same reference number. However, the controller 120 incorporates additional elements into the control routine, which determines the expected process response during the transmission of the measurements. In this case, the process 101 can be characterized by having a significant amount of wasted time, so that the wasted time unit or block 122 is included in the controller model for wasted time correction. The incorporation of the dead time unit 122 generally helps to reach a more accurate representation of the process response. More specifically, the dead time unit 122 can be implemented in any desired manner and can include or utilize methods common to Smith predictive means or other known control routines. However, in this situation, the continuously updated filter 116 and switch module 118 are the same as described above for controller 100 in FIG. 4A to provide robust control in response to setpoint changes. Works in style.

FIG. 6 depicts another alternative controller (or control element) 130, but differs from the controller 100 described above in FIG. 4A in that the derivative or rate contributing component is incorporated into the controller 130. The control routine performed by the controller 130 by incorporating differential contributions includes an additional feedback mechanism so that in some cases a proportional-integral-differential (PID) control scheme is implemented.

The control routine or technique of FIG. 6 includes a differential contribution composed in a manner similar to that described above in connection with the integral contribution of FIG. 4A, aperiodic or otherwise of process measurements. Adapts to updates that are not available. The differential contribution can be reconstructed based on the elapsed time since the last measurement update. In this manner, spikes in the differential contribution (and the resulting output signal) are avoided. More specifically, the differential contribution of FIG. 6 is determined by the differential block 132, which receives an error signal from the addition block 108 in parallel with the elements dedicated to proportional and integral contributions. Other PID configurations (eg, serial configurations) are also available, but proportional, integral, and differential contributions are combined in addition block 134, as shown in FIG.

To adapt to unreliable transmissions and, more generally, the availability of measurement updates, the differential contribution is last until the measurement update is received, as indicated by the new value flag from the communication stack 80. It is maintained at the value determined in. This technique allows a control routine to continue periodic execution according to the normal or established execution rate of the control routine. Upon receiving the updated measurement, the derivative block 132 can determine the derivative contribution according to the following equation, as illustrated in FIG.

This technique for determining differential contributions allows measurement updates to process variables (ie, control inputs) to be lost over one or more execution periods without producing output spikes. When the communication is reestablished, the term of the differential contribution equation (e _N- e _N-1 ) can generate the same value that was generated in the standard calculation of the differential contribution. However, for standard PID techniques, the divisor in determining the differential contribution is the execution period. In contrast, this control technique utilizes the elapsed time between two successfully received measurements. By using an elapsed time longer than the execution period, the control technique produces a smaller differential contribution than the standard PID technique and also reduces spiking.

To facilitate the determination of elapsed time, the communication stack 80 can provide the differential block 132 with the new value flag described above, as shown in FIG. Alternative examples can include or involve the detection of new measurements or updates based on their values. Process measurements can also be used in place of error in the calculation of proportional or derivative components. More generally, the communication stack 80 provides any software, hardware, to implement a communication interface with process 101, including any field device within process 101, process control elements outside the controller, and so on. Or it can include or involve firmware (or any combination thereof). However, in the controller 130 of FIG. 6, the continuously updated filter 116 and switch module 118 are described above with respect to the controller 100 of FIG. 4A to provide robust control in response to setpoint changes. It works the same as the one.

The actuators or other downstream elements controlled by the controller, described in connection with FIGS. 3, 4A, and 5-6, are particularly those of the controller or control element and the downstream actuator or other element. After a period of no communication in between, a control signal with sudden changes may still be received. The resulting control actions may, in some cases, be sudden enough to affect the operation of the plant, and such sudden changes can lead to inappropriate levels of instability. ..

The possibility of sudden control changes due to loss of communication between the controller and downstream elements is actually in place of the controller output during the last execution period when determining the feedback contribution (s) to the control signal. It can be dealt with by incorporating data downstream of. Generally speaking, such actual downstream data provides feedback instructions for the response to the control signal and therefore the downstream element (eg, process control module) or device (eg, actuator) that receives the control signal. ) Can be measured or calculated. Such data is provided in lieu of an implicit response to the control signal, such as the controller output from the last run. As shown in FIGS. 4A and 5-6, the continuously updated filter 116 receives the control signal 105 as an implicit indication of the downstream response. The use of such implicit data effectively assumes that a downstream element, such as an actuator, has received a communication of the control signal and therefore responds appropriately to the control signal. The actual feedback data also differs from other response instructions, such as measurements of controlled process variables.

FIG. 7 depicts an exemplary controller 140 that receives actuator position data from a downstream device or element that responds to a control signal. Downstream devices or elements often correspond to actuators and provide measurements of actuator position. More generally, downstream devices or elements can correspond to or include PID control blocks, control selectors, splitters, or any other device or element controlled by a control signal. In the exemplary case shown, actuator position data is provided as an indication of a response to a control signal. Therefore, the actuator position data is utilized by the controller 140 during the continuous execution period of the control routine, despite the lack of measured value updates for process variables. To this end, the continuously updated filter 116 can receive actuator position data via the communication stack 146, which establishes an interface for incoming feedback data. In this exemplary case, the feedback data includes two indications of the response to the control signal, the actuator position, and the process variables.

Similar to the previous embodiment, the continuously updated filter 116 is configured to adapt to the situation involved in the lack of measurement updates for process variables. The continuously updated filter 116 resembles that output during such a lack, despite the fact that only the filter output generated after receiving the new measurement flag is used by the adder 112. Recalculate to. However, upon receiving a measurement update, the continuously updated filter 116 no longer relies on control signal feedback to correct its output. Rather, the actual response data from the actuator is utilized as shown below.

The use of the actual indication of the response to the control signal is both during the period of periodic communication and during the period of aperiodic communication from the PID control element to the downstream element, eg, the actuator or after loss of communication of the control technique. It can help improve accuracy. However, the transmission of the actual response instructions typically requires additional communication between the field device and the controller when performed on different devices. Such communications can be wireless, as described above, and may therefore be susceptible to unreliable transmissions or power limits. Other reasons may also lead to the unavailability of feedback data.

As explained below, the control techniques discussed herein can also address situations in which such response instructions are not communicated in a periodic or timely manner. That is, the application of this control technique need not be limited to the lack of update of measured values of process variables. Rather, the control technique can be conveniently utilized to address situations involving the lack of other response instructions, such as the position of the actuator or the output of control elements downstream. Furthermore, the control technique involves loss of transmission from a controller (or control element) to a downstream element such as a field device (eg, actuator) or another control element (eg, cascade PID control, splitter, etc.). It can be used to deal with situations involving delays or other unavailability.

Radio or other unreliable transmission of additional data to the controller or control element (ie, response instructions or feedback of downstream elements), or additional data from the controller or control element (ie, control signal). It provides additional possibilities for communication problems and / or challenges. As explained above, feedback from downstream elements (eg, actuators) can be involved in determining integral contributions (or other control parameters or contributions). In this embodiment, the control routine relies on two feedback signals rather than the single process variable fed back in the embodiment described above. Moreover, if the control signal has never reached the downstream element, the process will not benefit from the control scheme. The transmission of any one of these signals can be delayed or lost, so the techniques described herein address both possibilities.

Lack of response instructions involved in filters or other control calculations can be addressed by maintaining instructions for the expected response (or other control signal component) until an update is received.

When the control signal does not reach the downstream element, the response instruction (ie, feedback) from the downstream element does not change. In such cases, the lack of value change of the controller (or control element) to maintain the indication of the expected response (or other control signal component) as well until the value change is received. You can trigger the logic.

The control technique can also be performed in situations where actual feedback data is not desired or available. The former case may be advantageous in situations where simplicity, such as using an implicit response to a control signal, is beneficial. For example, the communication of actual feedback data may be problematic or impractical. The latter case may involve actuators or other devices that are not configured to provide position measurement data, as described above. Older devices may not have such performance.

To adapt to such a device, a switch or other device can be provided to allow the control technique to use either implicit or actual response instructions. As illustrated in FIG. 8, controller 150 is coupled to switch 152 and thus receives both implicit and actual response instructions. In this case, the controller 150 can be identical to any of the controllers described above, as the implementation of the control scheme does not depend on knowing the type of response instruction. The switch 152 can be implemented with software, hardware, firmware, or any combination thereof. The control of the switch 152 can be independent of the implementation of the controller 150 and any control routine. Alternatively or additionally, the controller 150 can provide a control signal to configure the switch 152. Further, the switch 152 can be implemented as part of the controller itself and, in some cases, integrated as part of the communication stack or other part of the controller.

The practice of control methods, systems, and techniques is not limited to any one particular radio architecture or communication protocol. Suitable exemplary architectures and communication support schemes are described in US Patent Application No. 11 / 156,215, filed June 17, 2005, entitled "Willess Architecture and Support for Process Control Systems". The entire disclosure is incorporated herein by reference. In fact, modifications to the control routines are well suited for any situation where the control routines are carried out in a cyclical manner but without process variable measurements for each control iteration. Other exemplary situations include cases where sampled values are provided irregularly or rarely, for example by an analyzer or via a laboratory sample.

The implementation of this control technique is not limited to use with single input, single output PID control routines (including PI and PD routines), but rather a number of different multiple input and / or multiple output control schemes. It can also be applied to cascaded control schemes. More generally, the control technique is also an arbitrary closed-loop model-based control involving one or more process variables, one or more process inputs, or other control signals such as model predictive control (MPC). It can also be applied to routine situations.

FIG. 9 uses the principles described herein, but illustrates a further exemplary control system configured to have a controller 300 in the form of a speed-based controller. In the exemplary system of FIG. 9, the controller 300 is any communication from, for example, one of workstations 13 (FIGS. 1 and 3), within the process control system, or with the process control system. It operates to receive setpoint signals from other sources and generate one or more control signals 305 provided to process 301 from the output of controller 300. In addition to receiving the control signal 305, process 301 may be subject to disturbances, measured or unmeasured, outlined by arrow 304 in FIG. Depending on the type of process control application, the setpoint signal can be changed at any time during the control of process 301, such as by the user, adjustment routine, and so on. Of course, the process control signal 305 can control the actuator associated with the valve, or any other field device to influence the response of the operation of process 301. The response of process 301 to a change in process control signal 305 is measured or detected by a transmitter, sensor, or other field device 306, eg, any one of transmitters 60-64 illustrated in FIG. Can be dealt with. The communication link between the transmitter 306 and the controller 300 can include a wireless connection and is illustrated in FIG. 9 using a dashed line. However, this link can also be a wired communication link or another type of communication link. For the purposes of discussion, transmitter 306 is measuring a controlled process variable (ie, a controlled variable) or a proxy variable that correlates with a controlled process variable at a slow or intermittent update rate. It is regarded. This slow update rate can be periodic or aperiodic and is considered to be as large as the process dynamics process response rate associated with the controlled process variables. Therefore, process variable measurements are provided once per time interval that is longer than the process response time, once per time interval that is similar to the process response time, or once per time interval that is slightly shorter than the process response time. Therefore, in some cases, this update rate can be 1/2 to 1/4 of the process response rate (the reciprocal of the process response time).

In a simple embodiment illustrated in FIG. 9, the controller 300 can implement a single input, single output closed loop control routine such as a PI control routine, which is in one form of a PID control routine. is there. Therefore, the controller 300 includes several standard PI controller elements including the communication stack 380 and a control signal generator including an addition block 308, a proportional gain element 310, and an additional addition block 312. The control routine 300 also includes a direct integral feedback path that includes a filter 316 and an integral output switch that includes a selection block 318. However, in this case, the PI controller of FIG. 9 is configured to perform control calculations of position and difference with respect to the proportional and integral components of the control signal. Therefore, the controller 300 also has a differential block 320 placed in the proportional component calculation path, an adder 322 placed in the integral component calculation path, and a differentially calculated control component to generate the control signal 305. Also includes block 324 used for input to. Generally speaking, the block 324 scales the change in the position (speed) control signal when generated within the controller 300, or otherwise sends this signal to the control device in an analog. Or converted to a digital signal, instructing the control device to move in one direction or another direction by a certain amount over a particular period of time. The block 324 can, for example, transmit a pulse width modulated signal, a pulse signal, a digital signal indicating the turn-on time, or any other signal indicating the magnitude of the position change to the control device over time.

As illustrated in FIG. 9, the integrator filter 316 is coupled to the output of adder 322, which is then coupled to receive the output of adder 312, while block 318 of the switch is The integration or reset contribution or component of the control signal coupled to the output of the filter 316 and generated by the controller 300 is provided to the addition block 312.

During each iteration or operation of the controller 300, the addition block 308 adds a set point signal and a process variable measurement received just before provided from the communication stack 380 within the controller 300 to generate an error signal (e). Compare with. Proportional gain element or block 310, to produce a proportional contribution or component of the speed control signal, for example, by multiplying the proportional gain value K _p to the error signal e, which operates on the error signal e. The difference block 320 then determines the difference between the current output of the gain block 310 (generated during the last or previous controller iteration) and the previous value of the gain block 310 since the last controller iteration. Determine the change in the proportional gain value of. The addition block 312 then combines the output of the change unit 320 (ie, a proportional contribution based on speed) and the control signal generated by the integral feedback path to generate the speed control signal 326 provided to the output block 324. Combine with integral or reset contributions or components.

However, importantly, the adder 322, filter 316, and block or switch 318 in the integral feedback path of controller 300 operate in the following manner to generate an integral or reset contributory component of the control signal. Here, the adder 322 is coupled to receive the output of the adder 312 (ie, a speed-based control signal representing a change in the position of a movable control element) during each controller iteration. That value is summed with the previous output S of adder 322 (generated during the last iteration of controller 300), thereby actually producing a change in the change in the output signal over a particular period of time. Integrate or sum. A new output S of adder 322 is provided to the integrator filter 316, which produces an indication of the expected process response to the control signal 305, represented by R in FIG. The filter 316 provides this expected process response signal R to the switch or block 318. However, as shown in FIG. 9, the switch or block 318 samples and clamps the output of the filter 316 at the output of the switch or block 318 whenever a new process variable measurement is received, but otherwise. A zero (0.0) value is provided to the adder 312 as an integral control contribution during control iterations where no new process variable measurements are available. Therefore, the output of switch 318, which is provided as an integral control contribution to generate a new control signal during each controller iteration, can utilize new process variable measurements for use by the controller 300 during controller iteration. Only the output of the filter 316, and otherwise zero (0.0). Each time a new value flag generated by the communication stack 380 is set (indicating that a new process variable measurement is available on controller 300), adder 322 sets the output to zero and spans a new period. Start the addition. Thus, in practice, the adder 322 sums the changes in the control output signal over each controller iteration during the process variable measurement change and receives a new process variable measurement update on the controller 300 (during the controller iteration). Always reset after doing.

The expected process response to changes in the control signal, such as that produced by the filter 316, can be approximated using a linear model, as described in more detail below. However, more generally, the expected process response can be generated using any suitable model of process 301, integrated into the model incorporated in the feedback path of controller 300, or integrated into the control signal. Not limited to the filter or model associated with determining the reset contribution. For example, a controller that utilizes the model to provide the expected process response can incorporate differential contributions such that the control routine 300 executes the PID control scheme. An embodiment incorporating an exemplary differential contribution is described below in connection with FIG.

In any case, the control technique described below allows the controller 300 to use a positive feedback path to determine a reset or integral contribution when it receives a slow or aperiodic update of a process variable. However, it still allows a robust controller response in the event of a setpoint change or feedforward change that occurs during the reception of new process variable measurements. Specifically, the filter 316 has an expected process response during each or all execution of the controller 300, regardless of whether this output of the filter 316 was provided to the addition block 312 as an integral component of the control signal. It is configured to calculate a new instruction or value. As a result, only the output of the filter 316 generated immediately after (or during its execution cycle) the controller 300 receives a new process measurement update from the communication stack 380 is used as an integral or reset contribution for the adder 312. Even if this is the case, the output of the filter 316 is newly regenerated during each execution cycle of the controller routine.

Specifically, a new indication of the expected response R as produced by the filter 316 is the current adder output S (ie, the control output by the adder 312 since the last process variable measurement update. Calculated during each controller execution cycle from the total change of the signal), the indication of the expected response generated by the filter 316 generated during the last (ie, immediately preceding) controller execution cycle, and the controller execution period. Will be done. As a result, the filter 316 is described herein to be continuously updated as it is executed to generate a new process response estimate during each controller execution cycle. Illustrative equations that can be performed by the continuously updated filter 316 to generate a new expected process response or filter during each controller execution cycle are described below.

Here, the new filter output _RN is the sum of the previous filter output _RN-1 (that is, the current filter output value) and the current controller output value from the adder 322, and the current change _SN-1 . Notice that it is repeatedly determined by adding the attenuation component determined by multiplying the difference from the filter output value _RN-1 by the reset time T _{Reset and the coefficient depending on the controller execution period ΔT.} Will. By using a filter that updates continuously in this fashion, the control routine 300 better determines the expected process response when calculating the integral control signal input when a new process variable measurement is received. It can be made more sensitive to changes in setpoints or to other feedforward disturbances that occur between the reception of two process variable measurements. However, this calculation of the integral path prevents the control system from winding up in the presence of slow-received or intermittent process variable feedback measurements. More specifically, a change in the set point (without receiving a new process measurement) immediately results in a change in the error signal at the output of the adder 308, which provides a proportional contribution component of the speed control signal 326. You will notice that it changes and therefore changes the control signal 305. As a result, the adder 322 increases its output S by that amount, and then the filter 316 immediately begins to generate a new expected response of the process to the changed control signal, thus the controller 300 makes a new process measurement. Update the output before receiving the value. Filter 316 then when controller 100 receives a new process measurement and is clamped to the input of adder 312 by switch 318 so that a sample of the filter output is used as an integral or reset contributor to the control signal. Repeats, at least to some extent, the expected process response that responded to or incorporated process 301's response to a change in setpoint, based on a previously transmitted control signal 305. However, this integral is new so that the error signal e generated by the adder 308 can reflect changes in the process variables during the time it takes for the controller 300 to receive the process variable measurements. When the measured value is received, it is only added to the control signal 326. The integrator provided to the adder 312 is set to zero during controller iteration during the time it takes to receive the process variable measurements. This technique prevents or assists the control system 300 from winding up. In practice, the integrating elements generated by the filter 316 estimate the process response during the time it takes to receive subsequent process variable feedback (controller iteration), and the actual process variable response is as expected. In that case, when the controller 300 receives a new process variable measurement, the integration component sets the value generated in the proportional path to zero. If the expected response of the process differs from the actual process response during this time, the integral component changes the control signal 326 to move the actuator, thereby correcting the position of the actuator.

In the past, reset contribution filters used in controller feedback paths that are updated aperiodically, such as in the systems described in US Pat. Nos. 7,587,252 and 7,620,460, have been Only new indications of the expected response were calculated when new process variable measurements were available. As a result, the reset contribution filter compensates for setpoint changes or feedforward disturbances that occur during the reception of process variable measurements, as setpoint changes or feedforward disturbances are completely independent of any measurement updates. I didn't. For example, if a setpoint change or feedforward disturbance occurs between two measurement updates, the calculation of the new indication for the expected response is based on the time since the last measurement update and the current controller output 305. As a result, the expected process response of the controller could be distorted. As a result, the filter 316 compensates for process (or control signal) time changes resulting from setpoint changes (or other feedforward disturbances) that occur between the reception of two process variable measurements on the controller. I couldn't get started.

However, as will be appreciated, the control routine 300 of FIG. 9 provides the expected process response by being based on calculations performed on slow or aperiodic measurements, while adding. To compensate for changes caused by changes in setpoints (or any measured disturbance used as a feedforward input to controller 300), determine the expected response between the reception of the two measurements. To do. Therefore, the control techniques described above can be adapted to setpoint changes, feedforward actions against measured disturbances, etc. that can affect the expected process response, thus providing a more robust control response. To do. In addition, this control technique avoids windup in the controller so that when the feedback rate of the process variable measurements is equal to or even lower than the inverse of the process response time (ie, the feedback received by the controller). It can work effectively when the time between measurements is longer than the process response time).

As will be appreciated, the control technique illustrated in FIG. 9 indicates the expected response via a filter 316 (eg, a reset contribution filter) that is continuously updated for each execution of the control block or routine 300. Is calculated. Here, the controller 300 configures a filter 316 that is continuously updated to calculate new instructions for the expected response for each execution of the control block. However, if the output of the filter 316 should be used as an input to the adder block 312, then in the communication stack 380 and in some embodiments, the update detection module 82 (FIG. 3) is a new process variable measurement. Is received, it processes incoming data from transmitter 306 to generate new value flags for the integrated output switch 318 and adder 326. This new value flag informs switch 318 that it will sample and clamp the filter output value for this controller iteration for the input of adder 312. Alternatively, the switch 318 provides the adder 312 with a zero (0.0) value as the integral contribution value.

Regardless of whether a new value flag is communicated, the continuously updated filter 316 continues to calculate the expected response indication for each iteration of the control routine. This new indication of the expected response is delivered to the integral output switch 318 for each execution of the control block. Depending on the presence of the new value flag, the integral output switch 318 allows the addition block 312 to pass a new indication of the expected response from the continuously updated filter 316, or the addition block. Switch between maintaining a zero value when inputting to 312. More specifically, when a new value flag is communicated, the integral output switch 318 adds the indication immediately before or currently calculated from the expected response from the continuously updated filter 316 to the addition block 312. Allows you to pass to. Conversely, in the absence of a new value flag, the integral output switch 318 provides a zero value to the adder 312.

After or when the controller 300 receives a new process variable measurement and the adder 312 uses or uses the output R of the continuous filter 316, the time since the last communication is set to zero (0) and is continuous. Filter output R is set to zero. Similarly, the output of adder 322 is set to zero (0). Further, in these situations, the adder 312 subtracts the continuous filter output R from the output of block 320 in order to generate a new control signal 326, depending on the mode or order in which block 320 calculates the difference. can do.

This control technique allows the continuously updated filter 316 to continue modeling the expected process response, regardless of whether new measurements are communicated. If the control output changes as a result of a set point change or a feedforward action based on the measured disturbance, a continuously updated filter 316 is expected at each control routine iteration, regardless of the presence of the new value flag. Reflect the expected process response by calculating new instructions for the response. However, a new indication of the expected response (ie, reset contribution or integral component) is only incorporated into the calculation of the controller output signal when a new value flag is communicated (via the integral output switch 318). Prevents or reduces the controller from winding up in response to process variable measurements received at low speed by the controller 300.

The simple PI controller configuration of FIG. 9 uses the output of the filter 316 directly as the reset contribution to the control signal, and in this case the reset contribution of the closed loop control routine (eg, continuously updated as presented above). Note that the filter equation) can provide an accurate representation of the process response that determines whether the process exhibits steady-state behavior. However, other processes, such as waste time dominant processes, are illustrated in FIGS. 5 and 6 by including a waste time unit in the integral calculation path to model the expected process response. In addition, it may be necessary to incorporate additional components into the controller of FIG. For processes well represented by the primary model, process time constants can generally be used to determine the reset time of the PI (or PID) controller. More specifically, if the reset time is set equal to the process time constant, the reset contribution generally disables the proportional contribution so that the control routine 300 reflects the expected process response over time. To do. In the embodiment illustrated in FIG. 9, the reset contribution can be achieved by a positive feedback network with a filter having the same time constant as the process time constant. Other models can be used, but positive feedback networks, filters, or models provide a convenient mechanism for determining the expected response of a process with known or approximate process time constants. For processes that require PID control, the differential contribution to the PID output, also known as the rate, can be recalculated and updated only when a new measurement is received. In such cases, the derivative calculation can use the elapsed time since the last new measurement. Other controller components can be used to control more complex processes using aperiodic reception of process measurements, but to provide robust control in response to setpoint changes. An embodiment of a controller that can use the filtering technique of is described below in conjunction with FIG.

Specifically, FIG. 10 depicts an alternative controller (or control element) 400, but differs from the controller 300 described above in FIG. 9 in that a derivative or rate contributing component is incorporated into the controller 400. The control routine performed by the controller 400 by incorporating differential contributions includes an additional feedback mechanism so that in some cases a proportional-integral-differential (PID) control scheme is implemented.

The control routine or technique of FIG. 10 includes a differential contribution constructed in a manner similar to that described above in connection with the system of FIGS. 7 and 8, and is a slow, aperiodic process variable measurement. Adapt to updates that are not available otherwise. The differential contribution can be reconstructed based on the elapsed time since the last measurement update. In this manner, spikes in the differential contribution (and the resulting output signal) are avoided. More specifically, the differential contribution in the system of FIG. 10 is determined by the differential block 432, the fine fraction block (multiplied by a proportional gain K _p) in parallel with the proportional and integral contribution only elements from the gain block 310 receiving the error signal, and operable to generate a differential control component O _D, the fine fraction control components are then provided to change the block 433. Change block 433, the last controller repeatedly determines the change in the derivative control component O _D since, to provide the change in the adder 434, the adder, the change of the derivative control component on the output of the adder 312 Sum or add to generate changes in the control signal. In this case, the adder 322 of the integral contribution calculation path is connected to the output of the adder 434. However, the components of FIG. 10, also illustrated in FIG. 9, operate in the manner as described with respect to FIG. Here, the derivative block 432 (indicating that it has received a new value of the process variable measurements at the controller) only controller repeatedly in receiving a new value flag therein, only the operation to calculate the new differential component O _D You will find that you do. This operation actually keeps the output of change block 434 zero for all controller iterations while the controller 400 does not receive new process variable measurements or at that time.

Until unreliable transmission and, more generally, in order to accommodate unavailable for measurement update, the differential contribution O _D, as indicated by the new value flag from the communication stack 380, which receives the measurement update , Maintained at the last determined value. This technique allows a control routine to continue periodic execution according to the normal or established execution rate of the control routine. Upon receiving the updated measurement, the derivative block 432 can determine the derivative contribution according to the following equation, as illustrated in FIG.

Of course, if desired, the differential component calculation block 432, to receive the error signal, can be connected directly to the output of the adder 308, the differential gain term _the K _D, the differential gain with a proportional gain K _P Can be set to incorporate. This technique for determining differential contributions makes measurement updates to process variables (ie, control inputs) lost or unavailable over one or more execution sequence periods without producing output spikes. It can, which allows for bumpless recovery. When communication was reestablished, or when the controller received a new process variable measurement, the differential contribution equation term (e _N- e _N-1 ) was generated in the standard calculation of the differential contribution. It can generate the same value as the value. However, for standard PID techniques, the divisor in determining the differential contribution is the execution period. In contrast, this control technique utilizes the elapsed time between two successfully received measurements. By using an elapsed time longer than the execution period, the control technique produces a smaller differential contribution than the standard PID technique and also reduces spiking.

To facilitate the determination of elapsed time, the communication stack 80 can provide the differential block 432 with a new value flag as described above, as shown in FIG. Alternative examples can include or involve the detection of new measurements or updates based on their values. Process measurements can also be used in place of error in the calculation of proportional or derivative components. More generally, the communication stack 380 provides any software, hardware, to implement a communication interface with process 301, including any field device within process 301, process control elements outside the controller, and so on. Or it can include or involve firmware (or any combination thereof). However, in the controller 400 of FIG. 10, the continuously updated filter 316 and switch module 318 are described above with respect to the controller 300 of FIG. 9 in order to provide robust control in response to setpoint changes. It works the same as the one.

The practice of control methods, systems, and techniques described herein is not limited to any one particular radio architecture or communication protocol. Suitable exemplary architectures and communication support schemes are described in US Patent Application No. 11 / 156,215, filed June 17, 2005, entitled "Willess Architecture and Support for Process Control Systems". The entire disclosure is incorporated herein by reference. In fact, modifications to the control routines are well suited for any situation where the control routines are carried out in a cyclical manner but without process variable measurements for each control iteration. Other exemplary situations include cases where sampled values are provided irregularly or rarely, for example by an analyzer or via a laboratory sample.

The implementation of this control technique is not limited to use with single input, single output PID control routines (including PI and PD routines), but rather a number of different multiple input and / or multiple output control schemes. It can also be applied to cascaded control schemes. More generally, the control technique is also an arbitrary closed-loop model-based control involving one or more process variables, one or more process inputs, or other control signals such as model predictive control (MPC). It can also be applied to routine situations.

11 to 14 provide a graphical depiction (specifically, the operation of FIG. 10) of the simulated behavior of the control routines described herein, in which the process response time is controlled. A standard speed form of PID control algorithm was used to illustrate the effectiveness of this control routine in situations similar to or even shorter than the time between updates of process variable measurements. Compared with the conventional controller. The graphs of FIGS. 11-14 illustrate examples of simulated controls using only primary controls, although other types of controls such as override controls can be used. Generally speaking, each of the graphs of FIGS. 11A, 12A, 13A, and 14A illustrates the behavior of a standard prior art speed-based PID control algorithm, which is new. Both wired feedback configurations (whose behavior is illustrated on the left side of the graph) and wireless configurations (whose behavior is illustrated on the right side of the graph), where process variable measurements are available during each controller iteration. To use. However, FIGS. 11A and 13A illustrate control situations where the feedback rate or time between process variable measurements is 8 seconds and the process response time is 8 seconds, while FIGS. 12A and 14A show the process. Illustrates the operation of a prior art controller with a feedback rate or time between variable measurements of 8 seconds and a process response time of 3 seconds. Similarly, FIGS. 11 and 12 illustrate the operation of the controller in response to a set point change, while FIGS. 13 and 14 illustrate the operation of these same controllers in response to a disturbance change. For comparison, the graphs of FIGS. 11B, 12B, 13B, and 14B are the speeds described herein in the same process control situation as FIGS. 11A, 12A, 13A, and 14A, respectively. The operation of the PID algorithm based on is illustrated.

Generally speaking, the following parameters were used in the simulated control operations depicted in FIGS. 11-14, and these tests were performed on wired and wireless inputs as described above. On the other hand, it was performed for changes in set points and unmeasured disturbances. The control and process simulations used in the test were set up as follows.
Test for 8 second process response Primary process (same gain and kinetics)
Process gain = 1
Process time constant = 8 seconds Process waste time = 0 seconds PID adjustment for primary (lambda coefficient 1.0)
Proportional gain = 1
Integral gain = 7.5 repetitions / test for process response of 3 seconds Primary process (same gain and kinetics)
Process gain = 1
Process time constant = 3 seconds Process waste time = 0 seconds PID adjustment for primary (lambda coefficient 1.0)
Proportional gain = 1
Integral gain = 20 repetitions / minute Module execution rate 0.5 seconds for all tests Wireless communication update rate 8 seconds for all tests Periodic disturbance input Affects only primary measurement Gain = 1

As illustrated in FIGS. 11A and 13A, the speed-based PID control algorithms of the prior art have a wired configuration in which the process response time is equal to the interval between process variable measurements (both set to 8 seconds). Both wireless configurations operate somewhat satisfactorily in response to setpoint changes (FIG. 11A) and to disturbance changes (FIG. 13A). However, as indicated by the circled portion of the graphs 11A and 13A, this control technique causes significant variation in valve position during the response during radio control. As illustrated in FIGS. 11B and 13B, the control techniques described herein work somewhat well in these situations (setting point changes in FIG. 11B and disturbance changes in FIG. 13B) and are of wired configuration. Very similar in operation.

However, as illustrated in FIGS. 12A and 14A, the speed-based PID controllers of the prior art have set point changes and disturbance changes when the process response time is 3 seconds and the process variable update rate is 8 seconds. During wireless control in response to both, it does not work very well and actually becomes unstable. However, as illustrated in FIGS. 12B and 14B, current speed-based control routines still work very satisfactorily in these situations, with process variable measurement update interval times greater than process response times. It illustrates the effectiveness of the control routines currently described when they are large (long) and even significantly larger (eg, 2-4 times).

The term "field device" as used herein refers to a device or combination of devices (ie, a device that provides multiple functions, such as a hybrid transmitter / actuator), as well as any device that performs a function in a control system. Used broadly to include other devices (s). In any case, field devices include, for example, input devices (eg, devices such as sensors and devices that provide status, measurements, or other signals that indicate process control parameters such as temperature, pressure, flow rate), and controllers. And / or can include control operators or actuators that take action in response to commands received from other field devices such as valves, switches, flow control devices.

It should be noted that any control routine or module described herein can have a portion thereof that is implemented or executed in a distributed manner across multiple devices. As a result, the control routine or module can have parts implemented by different controllers, field devices (eg, smart field devices) or other devices, or other control elements, as desired. Similarly, the control routines or modules performed within the process control system described herein can take any form, including software, firmware, hardware, and the like. Any device or element involved in providing such functionality may have software, firmware, or hardware associated with it, placed on a controller, field device in a process control system, or any other. Regardless of whether it is located on a device (or a collection of devices), it is commonly referred to herein as a "control element." The control module can be, for example, any part or part of a process control system, including routines, blocks, or any element thereof stored on any computer readable medium. Such control modules, control routines, or any portion thereof (eg, blocks) shall be performed or performed by any element or device of a process control system, commonly referred to herein as a control element. Can be done. Control routines that can be modules or any part of a control procedure, such as a subroutine, part of a subroutine (such as a set of code), use object-oriented programming, or ladder logic, sequential functionality. It can be implemented in any desired software format using charts, functional block diagrams, or using any other software programming language or design paradigm. Similarly, control routines can be hard-coded into, for example, one or more EPROMs, EEPROMs, application specific integrated circuits (ASICs), or any other hardware or firmware element. Furthermore, control routines can be designed using graphical design tools, or any design tool, including any other type of software / hardware / firmware programming or design tool. Therefore, the controller 11 can be configured to carry out control strategies or control routines in any desired manner.

Alternatively or additionally, functional blocks can be stored in the field device itself or other control elements of the process control system and implemented by them, if the system utilizes fieldbus devices. obtain. A description of the control system is provided herein using a functional block control strategy, but control techniques and systems may also use other rules such as ladder logic, sequential functional charts, or any. It can also be implemented or designed using other desired programming languages or paradigms.

When performing, any of the software described herein stores in any computer-readable memory, such as a magnetic disk, laserdisc, or other storage medium, RAM or ROM of a computer or processor. be able to. Similarly, the software may use, for example, a computer-readable disk or other portable computer storage mechanism, or a communication channel such as a telephone line, the Internet, the Worldwide Web, any other local area network, or a wide area network. It can be delivered to a user, process plant, or operator workstation using any known or desired delivery method, including (delivery is to provide such software via a portable storage medium. Is considered to be the same as or compatible with). In addition, the software can be provided directly without modulation or encryption, or can be modulated and / or encrypted using any suitable modulated carrier and / or encryption technique before being transmitted over the communication channel. / Or can be encrypted.

As described above, the present invention has been described with reference to specific examples with the intention of merely exemplifying the present invention and not intending to limit the present invention. And it will become clear that control techniques can be changed, added, or deleted without departing from scope.

Claims (22)

A process controller that generates control signals to control process variables during each of a number of controller iterations of the process controller.
With a communication unit that receives a new value for the process variable, less than each of the many iterations of the process controller.
A proportional control component that generates a proportional control signal value during each of the iterations of the process controller.
A proportional control component, including a first adder that determines the difference between the set point value for the process variable and the value of the received process variable, and a proportional gain unit connected to the adder.
An integral control component that generates an integral control signal value during each of the iterations of the process controller.
During each iteration of the process controller, based on the previous values of the preliminary integral control component generated during the previous iteration of the process controller, and based on the control signal for the current iteration of the process controller. , The integral control component, including a iterative filter that determines the preliminary integral control component.
The switch, which is linked to the iterative filter that receives the preliminary integral control component and additional values, said during the process controller iteration associated with the reception of a new value of the process variable in the communication unit. As the integral control signal value, it operates to provide the preliminary integral control component generated by the repeat filter, and during controller iteration not associated with the reception of a new value of the process variable by the communication unit. With a switch that provides the further value as the integral control signal value.
A process controller comprising a second adder that sums the proportional control signal values and the integral control signal values during each process controller iteration to generate the control signals. The integral control component further comprises a third adder coupled to the repeat filter, the third adder providing the control signal to a previous controller repeat to generate a summed control signal value. The process controller according to claim 1, wherein the third adder sums and provides the summed control signal values as inputs to the repeat filter. The process controller according to claim 2, wherein the third adder resets the totaled control signal when the communication unit receives a new value of the process variable. The process controller according to claim 2 or 3, wherein when the third adder receives a new value of the process variable in the communication unit, the total control signal is reset to zero. The process controller according to any one of claims 2 to 4, wherein the proportional control component includes a difference unit connected to the proportional gain unit. The difference unit is connected between the proportional gain unit and the second adder, and the output of the proportional gain unit from the previous controller iteration and the output of the proportional gain unit in the current controller iteration. The process controller according to claim 5, wherein a difference value between the two is determined, and the difference value is provided to the second adder as the proportional control signal value. Claims 1 to 6 further include a control signal conversion unit coupled to the second adder that converts the control signal into a transmitted output control signal to control a device in the process. The process controller according to any one of the above. The differential gain unit further includes a differential control component that determines the differential control signal value, and the differential control component is connected to the first adder, the output of the differential gain unit from the previous controller iteration, and the above. The derivative that determines a further differential value from the output of the derivative gain unit in the current controller iteration and provides the derivative as the derivative control signal value to the second adder. The derivative control signal value having the integral control signal value and the proportional control signal, including the second difference unit connected to the gain unit, for the second adder to generate the control signal. The process controller according to any one of claims 1 to 7, wherein the values are summed. The process controller according to any one of claims 1 to 8, wherein the further value is an integral control signal value output by the switch in the previous controller iteration. A method of generating a speed-based process control signal between each of many iterations of a control routine.
Receiving new values of controlled process variables, less than each of the many iterations of the control routine, via a computer processing device.
A computer processing device was used to generate a difference-based integrated feedback contribution for use in generating the control signal during each of the numerous iterations of the control routine, summed up. To generate a control signal, sum the control signals generated during each iteration of the control routine since the last iteration of the control routine that received the new process variable value, and repeat the summed control signals. A number of said to provide to the filter and to determine the current integrated feedback contribution value for the current iteration of the control routine from the integrated feedback contribution value of the preceding iteration of the control routine and the summed control signal. Between each of the iterations, including using the iteration filter, and generating
Receiving a New Process Variable Value During each iteration, the current integrated feedback contribution value is used to generate the control signal for the current iteration of the control routine, and a new process variable value is received from the process. Do not use the current integrated feedback contribution value to generate the control signal during repetition and
A method of generating a speed-based process control signal, including the use of the control signal to control the process variable. A computer processing device is used to generate a proportional contribution based on the difference between each of the iterations of the control routine and between each of the iterations of the control routine to generate the control signal. The method of generating a speed-based process control signal according to claim 10, further comprising using the proportional contribution. The method of generating a speed-based process control signal according to claim 10 or 11, wherein the new process variable value is a measurement of a process parameter affected by the control signal. Determining the integral feedback contribution is the difference between the summed control signal for the current iteration of the control routine and the integral feedback contribution value of the preceding iteration of the control routine, as well as the reset time and. The method of generating a speed-based process control signal according to claim 10 or 11, comprising generating the current integrated feedback contribution value based on a product of a coefficient that depends on the controller execution period. Not using the current integrated feedback contribution value to generate the control signal during a iteration that does not receive a new process variable value from the process means that during an iteration that does not receive a new process variable value from the process. The method of generating a process control signal based on the speed according to any one of claims 10 to 13, which comprises using a fixed value as the current integrated feedback contribution to generate the control signal. .. The method of generating a speed-based process control signal according to claim 14, wherein the fixed value is zero. A speed-based process controller that generates control signals to control process variables during each of a number of controller iterations of the process controller.
With a communication unit that receives a new value for the process variable, less than each of the many iterations of the process controller.
An integral control component that generates an integral control signal value during each of the iterations of the process controller.
During each iteration of the process controller, based on the previous values of the preliminary integral control component generated during the previous iteration of the process controller, and based on the control signal for the current iteration of the process controller. , The integral control component, including a iterative filter that determines the preliminary integral control component.
The switch, which is linked to the iterative filter that receives the preliminary integral control component and additional values, said during the process controller iteration associated with the reception of a new value of the process variable in the communication unit. As the integral control signal value, it operates to provide the preliminary integral control component generated by the repeat filter, and during controller iteration not associated with the reception of a new value of the process variable by the communication unit. With a switch that provides the further value as the integral control signal value.
A speed, comprising a control signal generator, coupled to receive the integral control signal value to generate a control signal for use in controlling the process during each of the controller iterations. Based on the process controller. A proportional control component that generates a proportional control signal value during each of the iterations of the process controller.
Proportional control, including a first adder that determines the difference between a set point value for the process variable and a received value of the process variable, and a proportional gain unit connected to the first adder. With more ingredients,
16. The control signal generator comprises a second adder that sums the proportional control signal value and the integral control signal value during each process controller iteration to generate the control signal. Process controller based on the listed speed. The speed-based process controller of claim 17, wherein the proportional control component comprises a differential unit coupled to the proportional gain unit. The difference unit is connected between the proportional gain unit and the second adder, and the output of the proportional gain unit from the previous controller iteration and the output of the proportional gain unit in the current controller iteration. The speed-based process controller according to claim 18, wherein a difference value between the two is determined and the difference value is provided to the second adder as the proportional control signal value. The differential gain unit further includes a differential control component that determines the differential control signal value, and the differential control component is connected to the first adder, the output of the differential gain unit from the previous controller iteration, and the above. The derivative that determines a further difference value from the output of the derivative gain unit in the current controller iteration and provides the derivative value as the derivative control signal value to the second adder. The differential control signal value having the integral control signal value and the proportional control signal, including the second difference unit connected to the gain unit, for the second adder to generate the control signal. The speed-based process controller according to claim 17, which sums the values. The integral control component comprises an additional adder coupled to the repeat filter, which sums the control signals for previous controller iterations to generate a summed control signal value. The speed-based process controller according to any one of claims 16 to 20, wherein the additional adder provides the summed control signal values as inputs to the repeat filter. The speed-based process controller of claim 21, wherein the additional adder resets the summed control signal upon receiving a new value of the process variable in the communication unit.

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