ABNORMALITY DIAGNOSING METHOD AND ABNORMALITY DIAGNOSING SYSTEM

Abstract

An abnormality diagnosing method includes a model generation step of generating a simulation model of a monitoring target, an operation start step of starting an operation of the monitoring target, a measurement step of measuring an internal state quantity in the operating state of the monitoring target and extracting a measured value, a prediction step of inputting into the simulation model same control input value used in the operating state of the monitoring target and calculating a predicted value of the internal state quantity of the monitoring target, a Mahalanobis distance calculation step of calculating a Mahalanobis distance from a difference between the measured value and the predicted value, and an abnormality diagnosis step of diagnosing whether the operating state of the monitoring target is abnormal based on the Mahalanobis distance.

Claims

1. An abnormality diagnosing method of diagnosing an abnormality of a monitoring target having an operating state that includes a non-steady state, the abnormality diagnosing method comprising: generating a simulation model of the monitoring target; measuring an internal state quantity in the operating state of the monitoring target and extracting a measured value; inputting into the simulation model same control input value used in the operating state of the monitoring target and calculating a predicted value of the internal state quantity of the monitoring target; calculating a Mahalanobis distance from a difference between the measured value and the predicted value; and diagnosing whether the operating state of the monitoring target is abnormal based on the Mahalanobis distance.

2. The abnormality diagnosing method according to claim 1, further comprising calculating an error vector that includes the difference and an integral value of the difference as components thereof.

3. The abnormality diagnosing method according to claim 2, wherein the calculating of the predicted value is made based on a measured value that was measured immediate previously in a time series.

4. An abnormality diagnosing system for diagnosing an abnormality of a monitoring target having an operating state that includes a non-steady state, the abnormality diagnosing system comprising: a simulation model that simulates the monitoring target; a measuring unit configured to measure an internal state quantity in the operating state of the monitoring target; a diagnosing device that calculates a Mahalanobis distance from a difference between a predicted value calculated by the simulation model and a measured value extracted by the measuring unit and diagnoses whether the operating state of the monitoring target is abnormal based on the Mahalanobis distance; and a controlling unit configured to transmit same control input value to at least the monitoring target and the simulation model.

5. The abnormality diagnosing system according to claim 4, wherein the diagnosing device calculates the Mahalanobis distance based on an error vector that includes the difference and an integral value of the difference as components thereof.

6. The abnormality diagnosing system according to claim 5, wherein the simulation model calculates the predicted value based on a measured value that was measured immediate previously in a time series.

7. The abnormality diagnosing system according to claim 4, wherein the monitoring target is an engine for reusable spacecraft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is an overall structural schematic diagram of an abnormality diagnosing system according to the present disclosure.

[0016] FIG. 2 is a flowchart of an abnormality diagnosing method according to the present disclosure.

[0017] FIGS. 3A and 3B are drawings for explaining a Mahalanobis distance calculation step, where FIG. 3A shows an error vector and FIG. 3B shows an example of a calculation method of a predicted value.

[0018] FIGS. 4A and 4B are drawings for explaining an abnormality diagnosis step, where FIG. 4A is a conceptual diagram of a Mahalanobis distance and FIG. 4B is a conceptual diagram of an abnormality diagnosis.

[0019] FIGS. 5A to 5C are explanatory drawings to verify the efficacy when the present disclosure is applied to an engine for reusable spacecraft, where a result of the abnormality diagnosis based on a control input value is shown in FIG. 5A, the same based on simulated data of a measured value is shown in FIG. 5B, and the same based on the Mahalanobis distance is shown in FIG. 5C.

DESCRIPTION OF THE EMBODIMENTS

[0020] Exemplary embodiments according to the present disclosure are explained below by using the accompanying drawings. FIG. 1 is an overall structural schematic diagram of an abnormality diagnosing system according to the present disclosure. FIG. 2 is a flowchart of an abnormality diagnosing method according to the present disclosure. FIGS. 3A and 3B are drawings for explaining a Mahalanobis distance calculation step, where FIG. 3A shows an error vector and FIG. 3B shows an example of a calculation method of a predicted value. FIGS. 4A and 4B are drawings for explaining an abnormality diagnosis step, where FIG. 4A is a conceptual diagram of a Mahalanobis distance and FIG. 4B is a conceptual diagram of an abnormality diagnosis.

[0021] An abnormality diagnosing system 1 according to one embodiment of the present disclosure is, as shown in FIG. 1, an abnormality diagnosing system for diagnosing a monitoring target 2 having an operating state that includes a non-steady state. The abnormality diagnosing system 1 includes a simulation model 3 that simulates the monitoring target 2, a measuring unit 4 that measures a predetermined internal state quantity in the operating state of the monitoring target 2, a diagnosing device 5 that calculates a Mahalanobis distance MD from a difference (x̂−x) between a predicted value x calculated by the simulation model 3 and a measured value x̂ (̂ (circumflex or hat) on x. Same holds true in the below explanation.) extracted from the measuring unit 4, and that diagnoses whether the operating state of the monitoring target 2 is abnormal based on the Mahalanobis distance MD, and a controlling unit 6 that transmits the same control input value u to both the monitoring target 2 and the simulation model 3.

[0022] The monitoring target 2 is, for example, an engine for reusable spacecraft. However, the monitoring target 2 is not limited to the engine for reusable spacecraft and can be any other internal-combustion engine such as a jet engine, various plants such as a gas turbine power plant, a nuclear power plant, a thermal power plant, a chemical plant, and the like. Particularly, it is desirable that the monitoring target 2 has a steady state that is a stable operating state and a non-steady state that is a transient unstable operating state before reaching the steady state.

[0023] The simulation model 3 is a model that allows an estimation of the internal state quantity of the monitoring target 2. The simulation model 3 is generated, for example, by applying a numerical simulation technique. In generating the simulation model, a recurrence relation expression (ARMA) can be used in consideration of a real-time process. When the monitoring target 2 is, for example, the engine for reusable spacecraft, as the internal state quantity, for example, a combustion pressure Pc, a regenerative cooling outlet temperature Tjmf, a fuel pump rotation frequency Nf, an oxidant pump rotation frequency No, a fuel pump outlet pressure Pdf, an oxidant pump outlet pressure Pdo, and the like, can be selected. Accordingly, the simulation model that allows calculation of these internal state quantities is generated. The simulation model 3 can be one simulation model that simulates the entire monitoring target 2 or can be constituted by a plurality of simulation models each of which calculates a different internal state quantity.

[0024] The measuring unit 4 is installed in the monitoring target 2. The measuring unit 4 is, for example, a sensor that measures one or more of the internal state quantities such as the combustion pressure Pc, the regenerative cooling outlet temperature Tjmf, the fuel pump rotation frequency Nf, the oxidant pump rotation frequency No, the fuel pump outlet pressure Pdf, and the oxidant pump outlet pressure Pdo. The measuring unit 4 is, for example, a pressure gauge, a thermometer, a rotary encoder, and the like. However, the measuring unit 4 is not limited to these devices, and can be selected appropriately based on the type of the monitoring target 2 and/or the internal state quantity to be measured.

[0025] The controlling unit 6 is a device that transmits to the monitoring target 2 the control input value u necessary to operate the monitoring target 2. The operating state of the monitoring target 2 can be an actual operation or can be a test operation. Moreover, the controlling unit 6 transmits also to the simulation model 3 the control input value u necessary to operate the monitoring target 2. The simulation model 3 calculates an internal state quantity based on this control input value u, and also calculates a predicted value x for each of the internal state quantities. It is allowable to measure an output value y of the monitoring target 2 that is operated by using the control input value u, and extract the output value y to the outside.

[0026] The diagnosing device 5 is a device that receives data of the measured value x̂ measured by the measuring unit 4 and data of the predicted value x calculated by the simulation model 3, and performs an abnormality diagnosis of the monitoring target 2 by using the received data. The diagnosing device 5 performs a process based on, for example, the flowchart shown in FIG. 2. A diagnosis result and diagnosis data can be output from the diagnosing device 5 to the outside by various methods such as displaying on a monitor, printing on a paper, outputting in the form of data.

[0027] As shown in FIG. 2, the flowchart has the following steps: a model generation step (Step 1) of generating the simulation model 3 of the monitoring target 2, an operation start step (Step 2) of starting the operation of the monitoring target 2, a measurement step (Step 3) of measuring the internal state quantity in the operating state of the monitoring target 2 and extracting the measured value x̂, a prediction step (Step 4) of inputting into the simulation model 3 the same control input value u used in the operating state of the monitoring target 2 and calculating the predicted value x of the internal state quantity of the monitoring target 2, a Mahalanobis distance calculation step (Step 5) of calculating the Mahalanobis distance MD from the difference (x̂−x) between the measured value x̂ and the predicted value x, and an abnormality diagnosis step (Step 6) of diagnosing whether the operating state of the monitoring target 2 is abnormal based on the Mahalanobis distance MD.

[0028] The diagnosing device 5 performs the Mahalanobis distance calculation step (Step 5) and the abnormality diagnosis step (Step 6). In the abnormality diagnosing method according to the present embodiment, whether the obtained data (measured value x̂) is abnormal is diagnosed based on multivariable analysis that uses the Mahalanobis distance. A correlation among a plurality of variables can be processed at one time by using the Mahalanobis distance. That is, because it is not necessary to separately perform the diagnosis per variable to decide whether the variable is abnormal, the abnormality diagnosis can be made simple and fast.

[0029] The Mahalanobis distance calculation step (Step 5), as shown in FIG. 2, can include a difference calculation step (Step 51) of calculating the difference (x̂−x) between the measured value x̂ and the predicted value x, an error vector calculation step (Step 52) of calculating an error vector ε having the difference (x̂−x) and an integral value Σε of an error as components thereof, and a Mahalanobis distance computation step (Step 53) of calculating the Mahalanobis distance MD based on the error vector ε.

[0030] The error vector ε can be expressed in the manner shown in FIG. 3A. When an error vector that changes with time is calculated continuously, the integral value Σε, which constitutes a component of the error vector ε, can be calculated as a so-called integral value. To calculate the error vector ε per a certain period of time (span), the integral value Σε can be calculated as a grand total of the difference (x̂−x). In this manner, a cumulative error evaluation sensitivity in the same direction can be prevented from becoming weak by use of the integral value Σε of the error (difference).

[0031] When the combustion pressure Pc, the regenerative cooling outlet temperature Tjmf, the fuel pump rotation frequency Nf, the oxidant pump rotation frequency No, the fuel pump outlet pressure Pdf, and the oxidant pump outlet pressure Pdo are selected as the internal state quantity, for example, the error vector ε can be written as a matrix of (ΔPc, ΔTjmf, ΔNf, ΔNo, ΔPdf, ΔPdo, ΣΔPc, ΣΔTjmf, ΣΔNf, ΣΔNo, ΣΔPdf, ΣΔPdo) as shown in FIG. 3A. In this example, because the error vector ε includes 12 variables, the error vector ε is contained in a vector space R.sup.12 formed by these variables.

[0032] The prediction step (Step 4) includes an inputting step (Step 41) of inputting into the simulation model 3 the same control input value u as the operation of the monitoring target 2, and a predicted value calculation step (Step 42) of calculating the predicted value x of the internal state quantity based on the control input value u. At the predicted value calculation step Step 42 (prediction step (Step 4)), as shown in FIG. 3B, it is allowable to calculate a predicted value xn based on a measured value x.sub.n−1̂ that was measured immediate previously in the time series (i.e. a last value previously measured in the time series). That is, the predicted value xn is calculated based on the measured value x.sub.n−1̂, and a predicted value x.sub.n+1 is calculated based on a measured value x.sub.n̂. With this method, the accumulation of the error can be inhibited, the accuracy of predicted value x.sub.n can be improved, and therefore, the accuracy of the abnormality diagnosis can be improved.

[0033] At the Mahalanobis distance computation step (Step 53), to calculate the Mahalanobis distance MD from the error vector ε, at first, the error vector ε is standardized by using Expression 1 to convert the error vector into a state so that the error vector ε does not depend on a physical quantity unit. To standardize the error vector ε, an entire average value vector during the operation period

ε  [Equation 1]

and a deviation

σε  [Equation 2]

are used.

[00001]$\begin{array}{cc}\left[\mathrm{Equation}.Math..Math.3\right]& \\ {\mathrm{.Math.}}_n^{″}=\left(\frac{{\mathrm{.Math.}}_{n.Math..Math.1}-\stackrel{\_}{{\mathrm{.Math.}}_{n.Math..Math.1}}}{{\mathrm{\sigma .Math.}}_{n.Math..Math.1}},\frac{{\mathrm{.Math.}}_{n.Math..Math.2}-\stackrel{\_}{{\mathrm{.Math.}}_{n.Math..Math.2}}}{{\mathrm{\sigma .Math.}}_{n.Math..Math.2}},\mathrm{.Math.}.Math.,\frac{{\mathrm{.Math.}}_{n.Math..Math.12}-\stackrel{\_}{{\mathrm{.Math.}}_{n.Math..Math.12}}}{{\mathrm{\sigma .Math.}}_{n.Math..Math.12}}\right)& \left(\mathrm{Expression}.Math..Math.1\right)\end{array}$

where

[00002]$\left[\mathrm{Equation}.Math..Math.4\right]$$\stackrel{\_}{{\mathrm{.Math.}}_{n.Math..Math.1}}=\frac{1}{N}.Math.\underset{n=1}{\overset{N}{.Math.}}.Math.{\mathrm{.Math.}}_n,{\mathrm{\sigma .Math.}}_n=\sqrt{\frac{{\Sigma \left({\mathrm{.Math.}}_n-\stackrel{\_}{{\mathrm{.Math.}}_n}\right)}^2}{N}}$

The error vector εn″ standardized based on Expression 1 is expressed as εn and used in the subsequent calculation.

[0034] Then, the Mahalanobis distance MD is calculated by using Expression 2. Here, ε.sup.T indicates a transposed matrix of the error vector ε, and dim(ε) indicates a dimension of the error vector ε. Moreover, a covariance matrix can be derived, for example, from the accumulated data of the past that is diagnosed as being normal.

[Equation 5]

MD.sub.n=√{square root over (ε.sub.n.sup.−1ε.sub.n.sup.T/dim(ε))}  (Expression 2)

where

  [Equation 6]

is the covariance matrix.

[0035] By calculating the Mahalanobis distance MD and connecting equidistant points, for example, a correlation among the internal state quantities shown in FIG. 4A can be calculated. The error becomes large as one goes away from a center of a substantially elliptical region shown in this drawing. Therefore, it can be diagnosed that there is an abnormality when the value is outside of this region. The correlation shown in FIG. 4A represents a correlation between only two variables, i.e., internal state quantities D1 and D2, to promote an intuitive understanding. From this correlation, it can be understood that a permissible value of the error is large along the major axis of this substantially elliptical region, and a permissible value of the error is small along the minor axis of this substantially elliptical region. Although not shown in this drawing, a 12-dimensional correlation is obtained when the 12 variables are used as mentioned above.

[0036] At the abnormality diagnosis step Step 6, for example, as shown in FIG. 4B, the Mahalanobis distance MD is calculated, with respect to the error (difference) that changes over time, each time the diagnosis is performed. Moreover, a determination is made as to whether the error (difference) is within the Mahalanobis distance MD each time the Mahalanobis distance MD is calculated. For example, a Mahalanobis distance MD1 at time t1, a Mahalanobis distance MD2 at time t2, a Mahalanobis distance MD3 at time t3, a Mahalanobis distance MD4 at time t4, and a Mahalanobis distance MD5 at time t5 change from time to time based on the environmental conditions, the operating conditions, and the like at a given time. The graph of FIG. 4B is shown to promote an intuitive understanding of the abnormality diagnosing method according to the present embodiment.

[0037] In the abnormality diagnosing method and the abnormality diagnosing system 1 according to the present embodiment, the simulation model 3 that simulates the internal state of the monitoring target 2 is generated, and whether the monitoring target 2 is abnormal is diagnosed by using the difference (x̂−x) between the measured value x̂ obtained by the monitoring target 2 and the predicted value x calculated by the simulation model 3. Accordingly, the predicted value x that suits with the environmental conditions and/or the operating conditions at the time the abnormality diagnosis is made can be calculated by the simulation model 3. Moreover, because the difference has been used, the measured value x̂ obtained by the monitoring target 2 can be replaced with a variation value of a normal value. Accordingly, even if the operating state of the monitoring target 2 is the non-steady state, the dynamic change thereof can be followed and an action can be taken, and the abnormality diagnosis of the monitoring target 2 can be performed not only in the steady state but also in the non-steady state.

[0038] FIG. 5A to FIG. 5C are explanatory drawings to verify the efficacy when the present disclosure is applied to the engine for reusable spacecraft, and a result of the abnormality diagnosis based on a control input value is shown in FIG. 5A, the same based on simulated data of the measured value is shown in FIG. 5B, and the same based on the Mahalanobis distance is shown in FIG. 5C. In FIG. 5A and FIG. 5B, a thrust value is shown by a continuous line, a fuel value is shown by a dotted line, an oxidant value is shown by an alternate long and short dash line, and a combustion pressure value is shown by a two-dot chain line. In FIG. 5A, a portion of the thrust curve that protrudes up (substantially trapezoidal portion) simulates the non-steady state.

[0039] The amount of the fuel and the oxidant are controlled to obtain the thrust shown in FIG. 5A. Here, to verify the efficacy of the abnormality diagnosis performed by using the Mahalanobis distance MD, as shown in FIG. 5B, by setting an offset value (portion a in the drawing) with respect to the normal measured value, simulated data of the measured value that intentionally includes an abnormal value has been generated. When the Mahalanobis distance calculation step Step 5 is performed by using the simulated data of the measured value and the predicted value calculated by the simulation model 3, a result shown in FIG. 5C is obtained.

[0040] In FIG. 5C, a continuous line shows a change of the Mahalanobis distance MD over time, and black dots show points in time at which diagnosed as being abnormal. It can be understood from this verification result that the Mahalanobis distances MD of the parts corresponding to the offset portions in which the abnormal values were intentionally set have been diagnosed as being abnormal. Accordingly, it can be confirmed that the abnormality diagnosing method and the abnormality diagnosing system 1 according to the present embodiment are able to perform the abnormality diagnosis when the operating state includes the non-steady state.

[0041] The present disclosure is not limited to the above embodiments, and it can be implemented by making various changes in a range that do not deviate from the gist of the present disclosure.