Gas Turbine Diagnostics: Signal Processing and Fault Isolation
References 1. Volponi, A. Gas Turbines Power, , pp. Fasching, W. Glenny, D. Signal Process. Power, 19, pp. Power, 18, pp. Power Energy,, pp. Merrington, G. Ogaji, S.
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Navy Gas Turbine Systems. In a more specific form of the present invention, the improved control system employs a continuously updated engine model to simulate engine performance and to generate signals which represent estimates of the various engine parameters for the particular engine operation. The model is comprised of control system logic hardware whose performance is analogous to a set of mathematical equations which define the interrelationships between the various engine performance parameters, typically rotational velocities, pressures and temperatures of the various components, as a function of the various controlled parameters, typically fuel flow and geometry.
The model generated estimate signals are compared with the corresponding actual engine parameter sensor signals and difference signals are produced. As long as the difference signals are within specific tolerance limits, they are utilized to update the model. If one or more of the difference signals exceeds the tolerance limits, the particular signal or signals are inhibited from updating the model and a sensor failure indication may be provided to the engine operator.
The model is then updated by the remaining uninhibited difference signals. Referring to FIG. Shown in dashed lines in FIG. The gas turbine engine may be of any type known in the art, for example including a turbojet, turboprop, turboshaft or turbofan, and a detailed description of its operation is not necessary for purposes of describing the present invention.
The control system 10 includes engine performance parameter sensor means 12, such as a plurality of sensors for measuring the actual values of the engine performance parameters.
Gas turbine diagnostics : signal processing and fault isolation
The performance parameters include the pressures and temperatures of various engine components as well as velocities of various parts of the engine. The sensed performance parameter values are utilized by the control system 10 to control various engine controlled mechanisms 14, typically fuel flow and engine geometry, in order to maintain a selected level of engine performance. In a typical prior art gas turbine engine control system, such as the one shown in solid lines in FIG. The control computational unit 26, which may be of the analog or digital type, utilizes the sensor signals to generate control signals which are transmitted to actuator means 28 such as of the electromechanical and electrohydraulic type.
The actuators in turn operate to modify the controlled mechanisms in order to maintain a selected level of engine performance. Although, under normal operating conditions, such a control system is adequate for controlling a gas turbine engine, the failure or malfunctioning of an engine parameter sensor or its associated transmitting or receiving circuitry could result in a loss of control of one or more controlled parameters and a corresponding degradation in engine performance.
Gas turbine gas path diagnostics: A review | MATEC Web of Conferences
The present invention, in one form, operates to overcome the effects of sensor failure or malfunction by interposing a digital computer shown generally, in dashed lines, as 18 between the output of the engine parameter sensors 12 and 16 and the control computational unit The computer hardware may be of a type well known in the art and comprises a machine having a cycle time which is fast enough to provide real time operation. Depending upon the type of sensors and digital computer being employed, it may be necessary to employ signal processing amplifiers and analog to digital converters neither of which are shown in order to condition the sensor output signals to be compatible with the input requirements of the digital computer.
The amplifiers and converters may be of any suitable type well known in the art and a detailed description of their operation is not necessary for purposes of describing the present invention. The computer memory 24 comprises known hardware which includes an engine model program which simulates the performance of the gas turbine engine. The model is comprised of a set of mathematical equations which define the interrelationships between the various engine performance parameters as a function of the various engine controlled parameters.
The equations utilized to construct the model of this particular embodiment of the invention are shown below.
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It was necessary to introduce a number of constants K1-K67 for purposes of scaling, unit correction and to achieve the best possible mathematical fit for certain non-linear functions. In addition to the above-described exemplary equations, a section of the computer memory 24 is provided with stored data items from sensor means 12 and 16 which represent the current, real time internal status of the engine. As will be discussed below, these stored data items are retrieved and processed to develop estimate signals which correspond to the appropriate actual engine performance and actual engine controlled parameters.
After an initial start-up period during which values for both the engine performance parameters and the engine controlled parameters are preset into the engine model, the model continuously receives signals from the engine parameter sensors in means 12 and 16 as well as the control signals from the control computational unit The engine model utilizes these signals in conjunction with the mathematical equations and the data items to calculate signals representing estimates of the engine parameters sensor signals. The estimate signals thus provided are then transmitted to the control computational unit 26 in lieu of the actual engine parameter sensor signals.
The control computational unit 26 utilizes the estimate signals to generate control signals which are transmitted to the actuators A computer printout representative of a fortran language computer program which implements the engine model is shown below. The right hand marginal notations indicate the portions of the program in which the above-identified equations are actually implemented. Some of the equations are identified as being implemented in several places within the program due to the use of iterative calculations and subcalculations and in some cases, the subcalculations are identified as being utilized in several equations as indicated.
In addition to the above-described model, in one form of the present invention the computer memory 24 includes a logic program for both model updating and failure detection and indication. Referring now to the operational flow diagram of FIG. Each resulting difference signal is then utilized to update the engine model by changing all of the stored data items which are affected by the engine parameter which corresponds to the difference signal.
In order to provide improved accuracy, the magnitude of the change produced by a particular difference signal to each stored data item is weighted so as to be proportional to the degree of control that the engine parameter corresponding to the difference signal has over the particular data item as compared with the degree of control that the other engine parameters have over that data item. In order to determine whether a particular engine parameter sensor in means 12 and 16 or its associated transmission and interconnection circuitry is functioning properly, each difference signal is compared with a set of specific tolerance limits.
The tolerance limits may be predetermined stored values or may be continuously calculated as a function of current engine operational characteristics. For those difference signals which exceed the tolerance limits, corrective action is taken to insure that a significant degradation of engine performance does not occur.
Such corrective action includes immediately inhibiting the out-of-tolerance difference signals from being utilized to update the engine model. The model is updated, however, by the remaining uninhibited difference signals as described above and continues to generate estimate signals for all of the engine parameters. Thus, if an improper sensor signal resulted from a transient or some other temporary condition and a proper signal is subsequently received, the difference signal associated with the particular sensor is no longer inhibited and is again utilized to update the engine model.
In addition to inhibiting an out-of-tolerance difference signal from updating the model, an indication that a particular engine performance parameter sensor is providing an improper signal may be provided to the engine operator. Such an indication may take the form of a light or any other suitable indicator not shown which is known in the art. A computer printout representative of a fortran language computer program which implements the above-discussed logic program is shown below.
From the foregoing description it can be seen that the present invention provides an improved gas turbine engine control system which maintains engine operation without any significant degradation even though one or more engine parameter sensors are providing improper signals. This represents a significant improvement over prior art control systems in which the loss of a single sensor signal could lead to a drastic reduction in engine performance and perhaps necessitate completely shutting down the engine.
It will be obvious to one skilled in the art that changes can be made to the above-described invention without departing from the broad inventive concepts thereof. For example, although the invention has been illustrated in connection with add-on hardware for use with an existing control system, when used with an existing control system which already employs a digital computer, the invention could be programmed into the existing computer without the addition of separate computer hardware.
Alternatively, this invention could be employed in a system in which the sensor signals are transmitted directly to the control computational unit unless an improper signal is detected by the invention, in which case the engine model would supply an estimate signal only for that sensor.
It is to be understood, therefore, that this invention is not limited to the particular embodiment disclosed, but it is intended to cover all modifications which are within the spirit and scope of the invention as claimed. An improved gas turbine engine control system maintains a selected level of engine performance despite the failure or abnormal operation of one or more engine parameter sensors. The control system employs a continuously updated engine model which simulates engine performance and generates signals representing real time estimates of the engine parameter sensor signals.
The estimate signals are transmitted to a control computational unit which utilizes them in lieu of the actual engine parameter sensor signals to control the operation of the engine. The estimate signals are also compared with the corresponding actual engine parameter sensor signals and the resulting difference signals are utilized to update the engine model. If a particular difference signal exceeds specific tolerance limits, the difference signal is inhibited from updating the model and a sensor failure indication is provided to the engine operator.
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Field of the Invention This invention relates to gas turbine engine control systems and more particularly to an apparatus in a gas turbine control system for detecting the failure of an engine parameter sensor and taking corrective action. Description of the Prior Art Gas turbine engine control systems, particularly for use in controlling aircraft engines, generally include a number of sensors which measure various engine parameters.
SUMMARY OF THE INVENTION These and other objects, which will hereinafter become apparent, are accomplished by the improved control system of the present invention which includes means for sensing actual engine performance and controlled parameters, control computational means, actuator means and further includes failure indication and corrective action means for receiving signals from the sensor means and from the control computational means and for generating signals representing real time estimates of the engine performance parameters and the controlled parameters while the engine is in operation.
SPC1 In addition to the above-described model, in one form of the present invention the computer memory 24 includes a logic program for both model updating and failure detection and indication. SPC2 From the foregoing description it can be seen that the present invention provides an improved gas turbine engine control system which maintains engine operation without any significant degradation even though one or more engine parameter sensors are providing improper signals. What is claimed is: 1. An improved gas turbine engine control system including: sensor means for sensing actual engine performance parameters and actual engine controlled parameters, control computational means for generating control signals, actuator means for receiving said control signals and for modifying the controlled parameters in order to maintain a selected level of engine performance wherein the improvement comprises: failure indication and corrective action means disposed between said sensor means and said control computational means for receiving signals from said sensor means, for receiving said control signals, and for generating signals representing real time estimates of said actual engine performance parameters and of said actual engine controlled parameters while said engine is in operation, said estimate signals being transmitted to said engine control computational means in lieu of said actual engine performance and actual controlled parameter sensor signals.
The control system of claim 1 wherein said failure indication and corrective action means operates as follows: performing a simulation of the performance of the gas turbine engine as an engine model including the interrelationships between the engine performance parameters and the engine controlled parameters and generating said estimate signals;.
The control system of claim 2 wherein the magnitude of the change to said engine model produced by each difference signal is proportional to the degree of control that the engine parameter corresponding to the difference signal has over said engine model as compared with the degree of control that remaining engine parameters have over said engine model. The control system of claim 3 wherein said tolerance limits are predetermined fixed values. The control system of claim 3 wherein said tolerance limits are calculated. The control system of claim 4 or 5 wherein said second comparison also provides an indication to an engine operator when any of said difference signals exceeds said tolerance limits.
The control system of claim 6 wherein said failure detection and corrective action means is comprised of a programmed digital computer.