Method to quantify closed loop position control health

A monitoring system includes a processor configured to calculate a first distance of a first signal, wherein the first distance represents changes in magnitude of the first signal over a period of time, and wherein the first signal is associated with a desired signal output of a feedback loop system. The processor is configured to receive a second signal from an output of the feedback loop system. The processor is configured to calculate a second distance of the second signal, wherein the second distance represents changes in magnitude of the second signal over the period of time. The processor is configured to determine a first difference between the first distance and the second distance. The processor is configured to provide an error signal indicating an error if the difference exceeds a threshold value.

BACKGROUND

The subject matter disclosed herein relates to feedback, and more particularly, to assessing health of a feedback signal.

Feedback signals may be used with control systems in a variety of industries, such as in automotive or power generation industries. In the power generation industry, various engines, such as gas, steam, or diesel engines, may use one or more feedback signals to control a variety of electric or hydraulic actuators, such as lever arms, vane angles, or the like. Frequently, feedback in control systems is desirable to determine and/or control a difference between an actual signal and a reference signal. For example, electrical power output from a gas engine may be fed back and used as an input to compare the power generated to the desired power generated.

A feedback signal that does not accurately represent the output signal can cause a variety of operational problems for closed loop control. For example, if the feedback signal is unstable, erratic, or noisy, the difference between the feedback signal and the reference signal may be inaccurate as well, thereby causing incorrect adjustments by the system receiving the feedback signal. For the foregoing reasons, it may be beneficial to improve assessment of feedback signals.

BRIEF DESCRIPTION

In a first embodiment, a monitoring system includes a processor configured to calculate a first distance of a first signal, wherein the first distance represents changes in magnitude of the first signal over a period of time, and wherein the first signal is associated with a desired signal output of a feedback loop system, receive a second signal from an output of the feedback loop system, calculate a second distance of the second signal, wherein the second distance represents changes in magnitude of the second signal over the period of time, determine a first difference between the first distance and the second distance, and provide an error signal indicating an error if the difference exceeds a threshold value.

In a second embodiment, a non-transitory computer readable medium comprising instructions configured to be executed by a processor of a control system, wherein the instructions comprise instructions configured to cause the processor to calculate a first distance of a first signal, wherein the first distance represents changes in magnitude of the first signal over a period of time, and wherein the first signal is associated with a desired signal output of a feedback loop system, receive a second signal from an output of the feedback loop system, calculate a second distance of the second signal, wherein the second distance represents changes in magnitude of the second signal over the period of time, determine a first difference between the first distance and the second distance, and provide an error signal indicating an error if the difference exceeds a threshold value.

In a third embodiment, a method, comprising calculating a first distance of a first signal, wherein the first distance represents changes in magnitude of the first signal over a period of time, and wherein the first signal is associated with a desired signal output of a feedback loop system, receiving a second signal from an output of the feedback loop system, calculating a second distance of the second signal, wherein the second distance represents changes in magnitude of the second signal over the period of time, determining a first difference between the first distance and the second distance, and providing an error signal indicating an error if the difference exceeds a threshold value.

DETAILED DESCRIPTION

The system and method described below are related to assessing a health of a feedback signal. For example, many negative feedback control systems use an output signal as an input, called a feedback signal, to compare to a reference signal representing the desired output. Using the difference between the reference signal and the feedback signal, the control system can reduce an error between the feedback signal and the reference signal.

However, if the feedback signal is unstable, erratic, and/or noisy, the feedback signal can cause problems in the control process, because the feedback signal cannot be relied upon. For example, if the feedback signal is more erratic than the reference signal, then the feedback signal may be experiencing significant noise or a regulator that regulates an operational parameter of the feedback signal may be unstable. As another example, if the feedback signal changes over time less than the reference signal, it may indicate feedback system failure, such as actuator driver issues, because the feedback signal reflects the operation of actuators. Further, if multiple feedback signals are used (e.g., for redundancy), then it can be difficult identifying which of the feedback signals should be used and which of the signals are unhealthy. As such, it may be beneficial to have ways of determining health of a feedback signal

The system and method described herein can determine an amount of noise or a degree of erraticism in a feedback signal as compared to a reference signal. For example, a processor of a monitoring system may calculate travel of a reference signal and travel of a feedback signal over a time period. As used herein, the distance traveled of a signal may be a length of a line that represents the signal between a first point in time and a second point in time. That is, as the magnitude of the signal changes over a given period of time more frequently, the length of the respective signal will increase, and, in the same manner, the distance traveled by the signal will also increase. As such, the distance traveled may indicate an amount of changes in magnitude over a period of time. The processor may determine a difference between the reference travel and the feedback travel. Then, the processor may provide an alert for erratic behavior of the feedback signal when the difference exceeds a threshold value.

Turning to the figures,FIG. 1is an example of a control system10that is configured to receive a reference signal12. For example, the reference signal12may be a demand signal for a variable stator vane (VSV-DMD), a bleed valve, or a vane lever arm that generates desired vane angles, pressures, voltages, currents, or other output of the control system10. The reference signal12may be compared with one or more feedback signals that indicate the output of the system returned as an input. For example, the system may have a variable stator vane A feedback signal14(VSV-A) that provides a representation of an output16of the control system10. A comparator18may generate an error signal20by comparing the reference signal12with the VSV-A feedback signal14. The error signal20may then be received by a process controller22, such as a proportional-integral-derivative (PID) controller, to generate an output signal16based on the error signal20. The process controller22(e.g., PID controller) reduces the error signal20over time based on feedback data provided to the PID controller by adjusting one or more actuators.

It should be appreciated that these examples, such as variable stator vanes, bleed valves, or lever arms, are merely illustrative and are discussed merely to simplify explanation and to provide context for examples discussed herein. That is, while variable state vane angles are used as an example, the present approaches may be used in any suitable electronically and/or hydraulically actuated device that uses a feedback signal with a reference signal or demand signal, such as in control systems for gas, steam, or diesel engine or other control systems.

As described in detail below, the comparator18may be part of a monitoring system24. The monitoring system24may be part of a feedback controller that generates the error signal20by comparing the reference signal12with the first feedback signal14. As another example, the process controller22and the monitoring system24may be integrated into one system. In other embodiments, the monitoring system24of the present disclosure may be apart from the system.

The control system10may include more than one feedback signal for redundancy, such as a variable stator vane B feedback signal30(VSV-B). If the first feedback loop stops sending signals, then the control system10may rely on the second feedback loop. Similarly, if the second feedback loop stops sending signals, then the control system10may rely on the first feedback loop. However, it is often difficult to discern which signals can be relied upon due to a lack of information regarding whether each signal is providing accurate information and whether a portion of each signal includes noise or other interference factors. Moreover, it may be difficult to determine which input to believe in systems having two or more feedback signals.

For example, one indication that a feedback signal may be unreliable is when the signal exhibits erratic behavior.FIG. 2is a graph40of the feedback signals14and30and the reference signal12received by the monitoring system24. While the graph40may be shown on a display of the monitoring system24, the graph40is meant to be illustrative and the signals may instead be processed by the monitoring system24without displaying the data. As shown in the graph40, the VSV-DMD reference signal12indicates the desired output16of the system. The VSV-A feedback signal14is a healthy signal that accurately reflects the measured output of the control system10. In this example, VSV-A feedback signal14and VSV-B feedback signal30are monitoring the same output signal similar to the feedback signals ofFIG. 1. However, the VSV-B feedback signal30is an example of an unreliable signal exhibiting erratic behavior. That is, the VSV-B feedback signal30fluctuates due to noise or other interference factors. As such, the VSV-B feedback signal30does not accurately reflect the measured output of the control system10.

Erratic behavior may be characterized by rapid increases and/or decreases in the signal over a period of time. For example, between time42and time44, the VSV-B feedback signal30increases and/or decreases several times in amplitude as compared to the VSV-A feedback signal14, which primarily increases smoothly. As such, as will be described in detail with respect toFIG. 4below, the VSV-B feedback signal30may be characterized as traveling a further distance than the VSV-A feedback signal14and/or the VSV-DMD reference signal12. That is, a length of the line that represents the VSV-B feedback signal30between time42and time44may be determined and compared to a length of the line that represents the length of the VSV-A feedback signal14. Since the VSV-B feedback signal30has more changes over the period of time, the length of the VSV-B feedback signal30may be significantly larger than the lengths of the VSV-A feedback signal14and/or the VSV-DMD reference signal12. This greater distance traveled by the VSV-B feedback signal30may indicate erratic behavior.

With this in mind, the monitoring system24may determine a distance of one or more feedback signals traveled over a given period of time to determine whether the signal can be relied upon.FIG. 3is a block diagram of a monitoring system24that monitors feedback and reference signals of an electronically or hydraulically actuated device of a control system. The monitoring system24may determine whether one or more of the feedback signals14and30are unstable, erratic, and/or noisy.

The monitoring system24may include a processor54or multiple processors, memory56, and inputs/outputs (i.e., I/O)58. The processor54may be operatively coupled to the memory56to execute instructions for carrying out the presently disclosed techniques. These instructions may be encoded in programs or code stored in a tangible non-transitory computer-readable medium, such as the memory56and/or other storage. The processor54may be a general purpose processor (e.g., processor of a desktop/laptop computer), system-on-chip (SoC) device, or application-specific integrated circuit, or some other processor configuration. The memory56, in the embodiment, includes a computer readable medium, such as, without limitation, a hard disk drive, a solid state drive, diskette, flash drive, a compact disc, a digital video disc, random access memory (RAM), and/or any suitable storage device that enables the processor54to store, retrieve, and/or execute instructions and/or data. The memory56may include one or more local and/or remote storage devices. The system24may include a wide variety of inputs/outputs58(i.e. I/O). For instance, the I/O58may include inputs for the VSV-A, VSV-B, and VSV-DMD signals12,14, and30.

Instructions for the process described below may be stored in the memory56of the system24and executed as instructions by the processor54(e.g., running code). While the process described below may include instructions executed by the processor54as an example, the monitoring system24may include hardware to perform one or more of the processes. The processor54of the system24may access the VSV-A, VSV-B, and VSV-DMD signals12,14, and30. The monitoring system24may include distance calculation component60, timer component62, and comparison component64. As used herein, the distance calculation component60, the timer component62, and the comparison component64may be understood to refer to computing software, firmware, hardware (e.g., circuitry), or various combinations thereof. The distance calculation component60, the timer component62, and the comparison component64may include software implemented on hardware, firmware, or recorded on a processor readable storage medium, such as the memory56. For example, referring toFIG. 2, the system24may use the timer component62to track time (e.g., between time42and time44). The processor54may then enable the distance calculation component60to determine a distance traveled by one or more signals over the time period between time42and time44. The processor54may then compare the distance traveled by the one or more signals with one another, via the comparison component64, over the time period monitored by the timer component62. The processor54may then generate an output signal66indicating erratic behavior of one or more of the feedback signals14and30when the compared values exceed a threshold. The output signal66may be sent to alarm circuitry, the feedback controller, the process controller22, or the like. If the output signal66is sent to an alarm, for instance, an operator may use the output signal66to identify the erratic feedback signal for further testing. As another example, if the output signal66includes a command signal to control use of the feedback signal, the feedback controller may receive the command signal and rely on other feedback signals when there is redundancy.

To determine the distances traveled by signals, the processor54may determine the amount the VSV-B feedback signal30changes over a time segment.FIG. 4is a diagram of the distance calculation component60and the comparison component64. While the VSV-B feedback signal30is used here as an example, the VSV-A feedback signal14as well as the reference signal12may undergo a similar process. Initially, the processor54may, for example, verify a status of the VSV-B feedback signal30by determining whether measured values of the feedback signal are zero or approximately zero. If the feedback signal is zero or approximately zero, the processor54may provide a signal indicating that the VSV-B feedback signal30is invalid. The distance calculation component60may store a measured value76of an amplitude of the feedback signal30(e.g., in the memory56). The distance calculation component60may then compare a measured value78of the amplitude of the feedback signal with the previous measured value76. The distance calculation component60may then determine an absolute value80to determine a positive net change between the recent measured value78and the previous measured value76. In other words, the distance calculation component60may determine an absolute value of a difference between a measured value and a previous measured value over a time segment to calculate the reference distance and/or the feedback distance. The distance calculation component60may then determine an integral82and/or sum the net changes with respect to time (e.g., over more than one time segment) to determine a distance of the VSV-B feedback signal30. That is, the feedback distance and/or the reference distance indicates an amount the feedback signal and/or the reference signal change over a period of time.

The comparison component64may then compare the distance of the VSV-B signal30with one or more other distance measurements, such as the distance of the VSV-DMD signal12, to determine a compared distance value88. The comparison component64may determine whether the compared distance value88is greater than (90) a threshold value, then the VSV-B feedback signal30may be associated with erratic behavior. As such, the processor54may then generate the output signal66.

To determine if a signal is exhibiting erratic behavior, measured values of the signals may be taken at various times.FIG. 5is a portion100of the graph40between time42and time44ofFIG. 2used below to explain how distance may be calculated in accordance with the distance calculation and comparison components and/or instructions ofFIG. 4. The portion100shows the erratic behavior of VSV-B feedback signal30, as well as the VSV-A feedback signal14and the VSV-DMD reference signal12. As noted above, the process described herein is simply meant as an example of how distance may be calculated, and any suitable method may be used to determine distances of signals.

The timing component62may begin tracking a time period at time42over which distances are determined. The time period may be a preset time period. The processor54may then determine measured values102,104, and106for each of the signals30,12, and14respectively. The measured values102,104, and106may be stored (e.g., in the memory56) to be used to compare later values. After a time segment110, at time108, the processor54may determine measured values112,114, and116. The processor54may then subtract the measured value112from the previous measured value102, subtract the measured value114from the previous measured value104, and subtract the measured value116from the previous measured value106and take the absolute value80of the differences, as inFIG. 4. Note that the absolute value of the difference between the VSV-B feedback signal30values is larger than the difference between the VSV-A14and VSV-DMD reference signal12values as the VSV-B feedback signal30changes more than the VSV-A feedback signal14and the VSV-DMD reference signal12over the time segment110. The processor54may then include the absolute values80in, for example, the integral82and/or a sum.

After the next time segment118, the processor54may perform a similar step at time120with respect to measured values122,124, and126compared to values112,114, and116respectively. The absolute value of the compared values may again be included in the sum and/or integral82ofFIG. 4to find the distance traveled. Again, note that the distance of these VSV-B feedback signal30values is larger than the distance of the VSV-A feedback signal14and VSV-DMD reference signal12values. As this occurs over the period of time between time42and44, the distance of the VSV-B feedback signal30may become significantly larger than the distance of the VSV-A feedback signal14and VSV-DMD reference signal12to where the difference (88) between the distance of the VSV-B feedback signal30and the VSV-DMD reference signal12and/or the VSV-A feedback signal14is greater than a threshold value (90). After the period of time between time42and44, the timer62may be reset for further monitoring.

One or more processes may be stored in the memory56of the system24and executed as instructions by the processor54(e.g., running code) to indicate when signals are exhibiting erratic behavior.FIG. 6is an example of a process136that may be performed by the processor54in accordance with an embodiment of the disclosure. The process136may begin by the processor54starting a timer to begin a time period (block138). Over the time period, the processor54may access the feedback signal (block140) to determine measured values, such as measured value102, at various points in time. The processor54may also access the reference signal (block142) to determine measured values, such as measured value104, at various points in time. The processor54may then use these measured values to calculate distance of the feedback and reference signals over a time period (block144). For example, as explained with respect toFIG. 4, the processor54may determine a second measured value112for the VSV-B feedback signal30. The processor54may then find a difference between the measured value102and the measured value112. The processor54may determine an absolute value of the difference and include the absolute value80in a summation or integral82to determine a distance traveled, as shown inFIG. 4. At the end of the time period, the processor54may then compare distance of the feedback signal with the reference signal (block146). For example, as shown inFIG. 4, if the compared distances are greater than a threshold value90, then the compared distances may indicate that the feedback signal is exhibiting erratic behavior. Depending on the compared distances, the processor54may generate an output signal66to indicate that a signal is exhibiting erratic behavior.

This written description uses examples to enable a person of ordinary skill in the art to practice the disclosure, including the best mode, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.