Sensor Fault Detection and Diagnosis Simulation of a Helicopter Engine in an Intelligent Control Framework

Transcription

1 NASA Tehnial Memrandum Army Researh Labratry Tehnial Reprt ARL-TR-637 Sensr Fault Detetin and Diagnsis Simulatin f a Helipter Engine in an Intelligent ntrl Framewrk Jnathan Litt Vehile Prpulsin Diretrate U.S. Army Researh Labratry Lewis Researh enter leveland, hi Mehmet Kurtkaya and Ahmet Duyar Flrida Atlanti University Ba Ratn, Flrida Prepared fr the 1994 nferene f Military, Gvernment, and Aerspae Simulatin spnsred by the Siety fr mputer Simulatin San Dieg, alifrnia, April 11-13,1994 U.S. ARMY Natinal Aernautis and Spae Administratin RESEARH LABRATRY

2 SENSR FAULT DETETIN AND DIAGNSIS SIMULATIN F A HELIPTER ENGINE IN AN INTELLIGENT NTRL FRAMEWRK Jnathan Litt Mehmet Kurtkaya and Ahmet Duyar Vehile Prpulsin Diretrate Mehanial Engineering Department Army Researh Labratry Flrida Atlanti University Lewis Researh enter Ba Ratn, FL leveland, H ABSTRAT This paper presents an appliatin f a fault detetin and diagnsis sheme fr the sensr faults f a helipter engine. The sheme utilizes a mdel-based apprah with real time identifiatin and hypthesis testing whih an prvide early detetin, islatin, and diagnsis f failures. It is an integral part f a prpsed intelligent ntrl system with health mnitring apabilities. The intelligent ntrl system will allw fr ammdatin f faults, redue maintenane st, and inrease system availability. The sheme mpares the measured utputs f the engine with the expeted utputs f an engine whse sensr suite is funtining nrmally. If the differenes between the real and expeted utputs exeed threshld values, a fault is deteted. The islatin f sensr failures is amplished thrugh a fault parameter islatin tehnique where parameters whih mdel the faulty press are alulated n-line with a real-time multivariable parameter estimatin algrithm. The fault parameters and their patterns an then be analyzed fr diagnsti and ammdatin purpses. The sheme is applied t the detetin and diagnsis f sensr faults f a T7 turbshaft engine. Sensr failures are indued in a T7 nnlinear perfrmane simulatin and data btained are used with the sheme t detet, islate, and estimate the magnitude f the faults. INTRDUTIN n-line fault detetin and diagnsis is an area with great ptential fr high payff, espeially in the battlefield envirnment. The ability t detet and islate a fault as it happens allws a deisin t be made immediately abut the viability f the system and the likelihd f mpleting the missin. In a situatin where the unavailability f a system may have muh direr nsequenes than merely the lss f sme infrmatin r apability, every pssible piee f data helps in gaining the advantage. Sensr malfuntins are partiularly perniius beause they might ause a missin t be terminated when all systems are atually funtining prperly. Prime examples f this me frm the Spae Shuttle where numerus sensr failures ver the years have aused subsystem shutdwns and abrted launhes at great expense as well as psing ptential danger t the astrnauts.

3 It is well knwn that the variables in mplex systems are ften rrelated and that this infrmatin an be used t detet and islate inrret sensr readings. This tehnique allws sensr failures t be islated, and it allws lst r inrret values t be revered using the remaining valid measurements (DeLaat and Merrill 1984, Gu and Nurre 1991). A prpsed intelligent ntrl system ntains the sensr fault detetin, islatin, and ammdatin sheme rdinated with mplementary shemes fr the atuatrs and mpnents (Figure 1). If the differenes between the estimated and sensed system utputs exeed sme threshld values, the fault detetin lgi will initiate a parameter estimatin algrithm whih determines the type and magnitude f the failure. This is ahieved thrugh the use f fault parameters, variables defined t nvert the mdel frm that f the fully funtining system t that f an impaired ne as their values mve ff nminal. ne the fault is islated, the ntrl system will ammdate it if pssible (Litt 199). The test bed fr this researh is the T7 turbshaft engine, whih is used in pairs in the army's Blakhawk and Apahe helipters. It is a 16 hrsepwer-lass mdular tw-spl engine nsisting f a gas generatr and a free pwer turbine (Figure 2). In the simplified mdel used here there is ne input: fuel flw, W f. There are fur measured utput variables: gas generatr speed, N g, interturbine gas temperature, T 45, interturbine gas pressure, P 45, and pwer turbine trque utput, Q PT. Shuld any f the sensrs fail, the engine wuld appear t be malfuntining and, if the faulty measurement were fed bak thrugh the ntrl system, the engine wuld perate ff the design pint. SENSR FAULT DETETIN AND ISLATIN The Sensr Fault Detetin and Islatin sheme is develped using a fault mdel. A simplified linear perturbatin mdel has been develped whih swithes between several pint mdels fr full envelpe verage (Duyar, Gu, and Litt 1992). The simplified mdel at an perating pint is f the standard frm x(k + i) = Ax(k) + Bu(k) m y(k) = x(k) The variables in these pint mdels are all nrmalized with their zer values rrespnding t the perating pint. We assume that the (A, B, ) realizatin f the system is in a-annial frm (Eldem and Duyar 1993). Lak f spae preludes a thrugh presentatin here, but, very briefly, = [ s H- 1 ] (2) A =A + KH v J where Kis a deadbeat bserver gain (Kwakernaak and Sivan 1972), and A is nilptent, i.e. A ' l =Q fr sme n>. There are several ther requirements whih are listed in the referenes.

4 The mdel is reated by substituting the equatin fr A frm (2) int (1), evlving (1) thrugh time frm t k, and rearranging, thus y(k) = A k x(p) + A?[KH i B] i=l y(k-i) u(k-i) (3) The fat that A is nilptent is imprtant beause it allws (3) t be simplified t y(k) = A^IKH i B] j=i y(k-i) u(k-i) (4) when k>ix. ne in this frm, the unknwn parameters an be identified using a least squares tehnique. This way the initial mdel is develped. The sensr fault mdel is built n tp f (1) in the frm x(k + l) =Ax(k) + Bu(k) 1 y s (k) = F s x(k) + / rf ] (5) where y s (k) is the set f nrmalized sensr readings at time k. In the ase where all sensrs are fully funtinal, F s is the identity matrix and^, is the zer vetr, thus reduing (5) t (1). The diagnal matrix F s aunts fr hanges in sensr gain while a nn-zer f s represents bias errrs. Substituting and rearranging as befre yjt = F s A k x() - ^FSA^KHF; 1^ + ^F^A^KHF; 1 : B] i=l i=l u(k-i) + f«(6) Using the nilpteny f A t simplify (6) we get y&> = fs ~ Y,*. 4>*n*?f* + EF* A i-l KHF: 1 : B yfl-ti u(k-i) i=l i=l (7) when k>/i. ne a failure is deteted, an n-line estimatin tehnique alulates values fr the fault parameters, f^ and F s. As lng as F s is nnsingular, the value f the parameters alng with sme simple lgi prvides an assessment f the type and magnitude f the errr. In the ase where F s

5 bemes singular, implying that the gain f a sensr beame zer, a lgial hek an be used t determine whih sensr has failed. SIMULATIN SETUP A full nnlinear simulatin f the T7 turbshaft engine subjeted t a lad (Ballin 1988) is used in the simulatin test bed t represent the engine in questin (Kurtkaya 1992). The fault detetin and hypthesis testing mdules run in parallel with the nnlinear simulatin as shwn in Figure 1. The time step used is 6 ms. All prgrams are written in FRTRAN and are embedded in Mdel-, a ntrl analysis and simulatin pakage. Past ntrller utputs tgether with the sensr readings are fed thrugh the fault detetin mdel desribed by (7) and the resulting estimate f the set f sensed variables is mpared t thse reeived frm the simulatin at the urrent time step. The differenes, r residuals, are heked against threshld values whih, when exeeded, ativate the fault detetin sheme. Initially, the system is assumed t be funtining nrmally, thus the value fr F s is identity and/^ is the zer vetr implying n multipliative sensr gain errr and n sensr bias, respetively. The fault detetin sheme ntains mdels apprpriate fr eah type f failure, i.e. atuatr, mpnent, and sensr. Just as the sensr fault parameters are assiated with the matrix as shwn in (5), the atuatr fault parameters are assiated with the B matrix f (1) and the mpnent fault parameters are assiated with the A matrix (Duyar et al. 1991). Fault mdels similar t (7) are derived fr the atuatr and mpnent failures. When the residual exeeds the ativatin threshld, an n-line parameter estimatin sheme is initiated whih alulates the fault parameters, e.g. F s and^ in the sensr ase. It is imprtant t run the parameter estimatin sheme using data frm the impaired system s that the results are nt skewed by pre-failure infrmatin. Therefre, the parameter estimatin mdule begins lleting data nly after the ativatin threshld is exeeded. A reursive least squares tehnique with a frgetting fatr f.98 is used t mpute the value f the fault parameters. The mdels f the atuatr, mpnent, and sensr failures are develped in parallel and the three sets f fault parameters are mputed simultaneusly. At eah time step the resulting fault parameters are passed t the hypthesis testing mdule, atually a battery f simple lgial heks, whih determines what fault urred using the identified parameters. The lgi assumes that nly ne failure urs at a time. The result is heked by nfirming that the seleted mdel using the identified fault parameters prdues a smaller sum f the squared errrs (residuals) ver a fixed time than d the ther estimated mdels using their fault parameters. In this ase a mving windw f five data pints was used fr summing the squares f the residuals befre mparing the mdels, resulting in a delay f at least.3 sends (5 samples X.6 sends/sample) befre the errr is islated and its magnitude estimated. This data length is seleted t prdue reliable results in relatively few samples.

6 RESULTS Testing was perfrmed at the 96% pwer level. Results fr tw types f faults are presented: gas generatr speed sensr bias, and multipliative gain errr f the gas generatr speed sensr. Fr the first ase, a sensr bias f 1.8% f nminal was intrdued t the nnlinear simulatin's gas generatr speed sensr's utput at the start f the run. As sn as the bias was added, the misinfrmatin, whih was fed bak fr ntrl purpses, disrupted all f the ther utput variables and aused the engine t perate ff f the design pint. The fault parameters were first mputed after the impaired system was sampled twie, i.e..12 sends after the threshld was exeeded. Figure 3 shws hw the fault parameters rrespnding t the multipliative sensr gain nverged immediately t their rret values f 1. as determined thrugh reursive least squares, indiating n sensr gain failure. Figure 4, n the ther hand, shws that the bias n the N g sensr nverged t apprximately.18 while the ther bias values stayed within the nrmal expeted variatin arund zer. Figure 5 shws the results f the hypthesis testing using the fault parameters determined fr eah type f failure. The sums f the squared errrs ver a five sample mving windw fr eah type f failure were mputed beginning with the sample after the fault parameters had been first estimated, i.e..18 sends after the threshld was exeeded. It an be seen that the sensr fault parameters prvided a muh better math t the simulated failure than either the atuatr r mpnent faults parameters did. Fr the send ase, the riginal unity gain f the N g sensr was saled by a multipliative gain f.1 at the start f the run. Figure 6 shws the multipliative gain fault parameters as determined by the reursive least squares tehnique frm past data. It tk signifiantly lnger t nverge than the previus example did but eventually the parameter rrespnding t the N g sensr's gain nverged t abut.1 while the ther three hvered near 1.. Figure 7 displays the estimated values f the bias parameters, whih, after sme initial hunting, nverged t apprximately.. The maximum time it takes t ahieve a gd identifiatin depends upn hw quikly the fault parameters nverge, whih an vary frm almst instantaneusly t several sends as demnstrated by the examples. In general, hwever, with the mbinatin f lgi used t examine the fault parameters and the windwed residual infrmatin, it is usually pssible t identify a failure and estimate its magnitude in a shrt perid f time. NLUSINS A sheme t detet, islate, identify and estimate the type and magnitude f sensr faults in a T7 turbshaft engine has been develped and demnstrated. It is an integral part f a prpsed Intelligent ntrl System. The injetin f a fault aused the residual t exeed the threshld value and trigger the identifiatin sheme. ne running, the sheme prdued aurate results, usually in under a send. The identified fault parameters an be used in the state equatin t anel the bias r eliminate the inrret gain, thereby ammdating the sensr faults and allwing the lsed lp system t run as if unimpaired.

7 PppFRENES Ballin, M. G.~1988. "A High Fidelity Real-Time Simulatin f a Small Turbshaft Engine." NASA Tehnial Memrandum DeLaat J. D.; W.. Merrill "A Real-Time Implementatin f an Advaned Sensr Failure Detetin, Islatin, and Ammdatin Algrithm." NASA Tehnial Memrandum Duyar A.; Z. Gu; and J. S. Litt "A Simplified Dynami Mdel f the T7 Turbshaft Engine." NASA Tehnial Memrandum Duyar A T.-H. Gu; W. Merrill; and J. Musgrave "Implementatin f a Mdel Based Fault Detetin and Diagnsis Tehnique fr Atuatin Faults f the Spae Shuttle Main Engine." NASA Tehnial Memrandum Eldem, V.; and A. Duyar "Parametrizatin f Multivariable Systems Using utput Injetins: Alpha annial Frms," Autmatia 29, N. 4: Gu, T. -H.; J. Nurre "Sensr Failure Detetin and Revery by Neural Netwrks." NASA Tehnial Memrandum Kurtkaya, M. H "Fault Detetin and Diagnsis f the T7 Helipter Engine." Master's Thesis, Mehanial Engineering Department, Flrida Atlanti University, Ba Ratn, FL. Kwakernaak, H., and R. Sivan Linear ptimal ntrl Systems. Wiley-Intersiene, New Yrk, NY, 527. Litt, J "An Expert System t Perfrm n-line ntrller Restruturing fr Abrupt Mdel hanges." NASA Tehnial Memrandum 1369.

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15 REPRT DUMENTATIN PAGE Frm Apprved MB N Publi reprting burden fr this lletin f infrmatin is estimated t average 1 hur per respnse, inluding the time fr reviewing instrutins, searhing existing data sures, gathering and maintaining the data needed, and mpleting and reviewing the lletin f infrmatin. Send mments regarding this burden estimate r any ther aspet f this lletin f infrmatin. Inluding suggestins fr reduing this burden, t Washingtn Headquarters Servies, Diretrate fr Infrmatin peratins and Reprts, 1215 Jeffersn Davis Highway Suite 124, Arlingtn, VA , and t the ffie f Management and Budget, Paperwrk Redutin Prjet (74-188), Washingtn, D AGENY USE NLY (Leave blank) 2. REPRT DATE Nvember TITLE AND SUBTITLE Sensr Fault Detetin and Diagnsis Simulatin f a Helipter Engine in an Intelligent ntrl Framewrk 6. AUTHR(S) Jnathan Litt, Mehmet Kurtkaya, and Ahmet Duyar REPRT TYPE AND DATES VERED Tehnial Memrandum S. FUNDING NUMBERS WU X 1L16112AH45 7. PERFRMING RGANIZATIN NAME(S) AND ADDRESS(ES) NASA Lewis Researh enter leveland, hi and Vehile Prpulsin Diretrate U.S. Awiy Researh Labratry leveland, hi SPNSRING/MNITRING AGENY NAME(S) AND ADDRESS(ES) Natinal Aernautis and Spae Administratin Washingtn, D and U.S. Army Researh Labratry Adelphi, Maryland PERFRMING RGANIZATIN REPRT NUMBER E SPNSRING/MNITRING AGENY REPRT NUMBER NASA TM ARL-TR SUPPLEMENTARY NTES Prepared fr the 1994 nferene f Military, Gvernment, and Aerspae Simulatin spnsred by the Siety fr mputer Simulatin, San Dieg, alifrnia, April 11 13, Jnathan S. Litt, Vehile Prpulsin Diretrate, U.S. Army Researh Labratry, NASA Lewis Researh enter, Mehmet Kurtkaya and Ahmet Duyar, Flrida Atlanti University, Mehanial Engineering Department, Ba Ratn, Flrida (wrk funded by NASA Grant NAG3-1198). Respnsible persn, Jnathan S. Liu, rganizatin de 255, (216) a. DISTRIBUTIN/AVAILABILITY STATEMENT 12b. DISTRIBUTIN DE Unlassified -Unlimited Subjet ategry ABSTRAT (Maximum 2 wrds) This paper presents an appliatin f a fault detetin and diagnsis sheme fr the sensr faults f a helipter engine. The sheme utilizes a mdel-based apprah with real time identifiatin and hypthesis testing whih an prvide early detetin, islatin, and diagnsis f failures. It is an integral part f a prpsed intelligent ntrl system with health mnitring apabilities. The intelligent ntrl system will allw fr ammdatin f faults, redue maintenane st, and inrease system availability. The sheme mpares the measured utputs f the engine with the expeted utputs f an engine whse sensr suite is funtining nrmally. If the differenes between the real and expeted utputs exeed threshld values, a fault is deteted. The islatin f sensr failures is amplished thrugh a fault parameter islatin tehnique where parameters whih mdel the faulty press are alulated n-line with a real-time multivariable parameter estimatin algrithm. The fault parameters and their patterns an then be analyzed fr diagnsti and ammdatin purpses. The sheme is applied t the detetin and diagnsis f sensr faults f a T7 turbshaft engine. Sensr failures are indued in a T7 nnlinear perfrmane simulatin and data btained are used with the sheme t detet, islate, and estimate the magnitude f the faults. 14. SUBJET TERMS Fault detetin; Sensrs; T7 engine; ntrl systems 17. SEURITY LASSIFIATIN FREPRT Unlassified 18. SEURITY LASSIFIATIN F THIS PAGE Unlassified 19. SEURITY LASSIFIATIN F ABSTRAT Unlassified 15. NUMBER F PAGES PRIE DE A3 2. LIMITATIN F ABSTRAT NSN Standard Frm 298 (Rev. 2-89) Presribed by ANSI Std. Z