Research Journal of Applied Sciences, Engineering and Technology 4(15): 2555-2563, 2012 ISSN: 2040-7467 © Maxwell Scientific Organization, 2012 Submitted: March 30, 2012 Accepted: April 17, 2012 Published: August 01, 2012 LMI-Based Method of Robust Fault Detection H4 Filter for Anti-Pinch of Pure Electric Vehicles 1 Xiaogang Yu, 1Changyun Miao, 2Haijing Yang, 1Hongqiang Li, 1Fangshu Liu, 1 Yongqiang Meng and 2Hong Chen 1 School of Electronics and Information Engineering, Tianjin Polytechnic University, Tianjin 300387, China 2 Library, Tianjin University of Technology, Tianjin 300384, China 3 China Automotive Technology and Research Center, Tianjin 300162, China Abstract: In order to effectively solve the risk of safety on power window, this study introduces the LMI-based method of designing robust fault detection H4 filter for anti-pinch window control system. For detecting the pinched condition, the pinch torque is considered as a fault to design a residual generator. By comparing the residual signal with the pre-designed threshold, the occurrence of pinch can be detected. The main contribution consisted of the formulation of the multi-objective optimization H4 and H- problem as H4 optimization problem by using the residual error instead of residual. The solution of the optimization problem is solved via LMI technique. Based on MATLAB, the results show that the algorithm can detect the fault after it occurs 70 ms. In addition, simulation results show that the proposed algorithm has high sensitivity to fault and strong robustness to uncertainties. Keywords: Anti-pinch window, H4 filter, LMI, pure electric vehicle, robust fault detection INTRODUCTION In the automotive industry, electronic systems used to provide the rapid increase in customer comfort with a variety of vehicles, but also put forward new requirements for the vehicles, such as power windows (Ma et al., 2008). Power windows automatically rise and fall brings convenient operation and security issues. It is often possible hurt part of the body located in the path of the window (Lee et al., 2008). Numerous of accidents caused by power window without safety precaution have been reported. Therefore, an anti-pinch window control system, which can effectively solve the security risks and will not affect the vehicle's comfort and working normal has been paid much attention. The conventional methods to detect pinching conditions are generally divided into two categories: The differential type pinch estimator based on the assumptions that the sharp decline of velocity in the pinch condition and the window move at a constant speed in smooth operating conditions. However, this algorithm is inadequate in reality, because the window frames friction torque through the full range of vehicles closed panel is usually different characteristics. The amount of computation required in this pinch estimator is small, but its performance could be degraded in the presence of measurement noises. On the other hand, the absolute pinch estimated response time advantage by changes in the motor control current to compensate for the pinch torque and angular velocity (Buja et al., 1995; SyedAhmad and Wells, 1993). However, it cannot guarantee the robustness of abnormal vibration under real driving conditions. Furthermore, this approach requires additional current sensor to avoid false positives (Syed-Ahmad and Wells, 1993), which cannot be a universal solution, because the detection of the pinching condition depends entirely on the engineer's inspired to determine current restrictions. One type which recognizes a pinched condition from a detected change in window velocity is proposed and the other type recognizes a pinched condition when the applied motor torque exceeds a predetermined limit which requires an additional current sensor to avoid false alarm (Zhang and Wang, 2011; Angelo et al., 2006; Henry and Zolghadri, 2005). It might not be a general solution because its performance relies on the validity of a current limit. Using the change of motor control current to detect the pinched condition compensate the low response time of the pinch torque as well as the window velocity (Doh and Ryoo, 2008). All the changes of the DC motor are detected by sensors like Hall sensors and current sensors in the above references. These methods are poor on timeliness. The detection of current amplitude method is proposed, which describes the anti-pinch measures without sensors, but often makes error detection (Yang et al., 2005). Correspondindg Author: Hongqiang Li, School of Electronics and Information Engineering, Tianjin Polytechnic University, Tianjin 300387, China 2555 Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 Model based fault detection has received much attention in the last years, especially the design of fault detection observer. The problem is treated in different ways, for example, unknown input observer (Isermann, 2005), H4/H2 filter (Adil et al., 2010), multiple-observer (Niaki and Seyed, 2009) and LMI approaches. The main methods of model based (MBD)fault detection are as follows: The first method: utilize a reference model which will be used to describe the ideal residual r. The reference model should achieve both robustness and detection performance which is as follows: rf(s) = Trf(s) f(s) + Trd(s) d(s) Trf, Trd are the transfer functions of fault and disturbance. rf(s) is the residual, f(s) is the fault and d(s) is the disturbance. In fact the realistic model is different from the reference model, so the optimization problem used here to synthesize the residual generator is formulated as a robust H4 filtering problem. The second method: provide some performance index that will transfer the fault diagnosis to an optimization question. The frequently-used performance indices are as follows: min J / J / L min J / J / L min J J L Trd ( s) x Ax Bu B f f Bd d y Cx Du D f f Dd d (1) where x is the state, u is the control input, y is the measurement, d is the unknown finite energy disturbance (including modeling error signal, external signal and noise signal), f represents the faults input. A, B, C, D, Bd, Dd, Bf, Df are known matrices with appropriate dimensions (Zheng and Wu, 2009). The residual generator (or namely fault detection observer) takes the form: x Ax Bu H ( y y ) y Cx Du r y y (2) Obviously, the design of a robust fault detection observer, i.e., determination of the observer gain matrix H. Using (1) and (2), we can obtain the following form: e ( A HC)e ( B f HD f ) f ( Bd HDd )d r Ce D f f Dd d (3) Note that the dynamics of the residual signal r depends on not only d and f, but also the state e. We can express the (3) in the form of transfer function: Trf ( s) Trd ( s) Problem statements: Consider the linear time-invariant system of the following form: Trf ( s) Trd ( s) METHODOLOGY i (Trf ( jw)) r(s) = Trd(s) d(s) + Trf(s) f(s) w [0, ) The ||T||4 is the maximum singular value of the transfer function matrix, ||T||- is the minimum singular value of the transfer function matrix; Trf, Trd are the transfers of fault and disturbance. Fi(Trf(jw)) is the nonzero singular value of the Trf. In the second method the H- is not a norm, which is not easy to optimized. So in this study the formulation of the multi-objective optimization H4 and H- problem as H4 optimization problem by using the residual error instead of residual. By optimizing the performance index, the gap between the reference signal and the fault signal is reduced. As the result, the residual signal has high sensitivity to fault and strong robustness to uncertainties. Next the detail devise of robust fault detection observer based on first method will be discussed. (4) Trd, Trf are the transfer functions from d, f to r respectively. Generating a residual signal which has best sensitivity to the fault and robustness to the disturbance is the purpose of the fault detection. In order to achieve the best features of the residual, the following condition (5), (6) are represented: H Trd H Trf sup (Trd ( j )) 0 inf (Trf ( j )) 0 (5) (6) Condition (5) represents the worse-case criterion for the effect of disturbances on the residual r, condition (6) stands for the worse-case criterion for the sensitivity of r to fault. Clearly, these two criteria capture the most significant features of fault detection observer. 2556 Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 Since in condition (6) H- is not a system norm, for static fault detection observer, we introduce reference residual model WF(s) to describe the desired behavior for the residual vector r and define the rF as the reference residual: rf(s) = WF(s) f(s). Fig. 1: Reference residual model in fault detection The criterion is: f WF ( S ) r rf J w sup w wL2 , w 0 sup Tzw ( s) w wL2 w 2 2 sup 2 wL2 , w 0 Tzw ( s) 2 re 2 w 2 Trf ( s) Trd ( s)WF ( s) Trf ( s)] So Trd(s), WF(s)-Trf(s) are as smaller as possible, one gets: f By the triangle inequality, the following is obtained: WF ( s) So, Trf ( s) f (11) f , 0d which meets the request of the index in (5) and (6). The above process can be depicted by Fig. 1. So the minimum singular value of the original maximum problem, namely the H- index, is changed into a H4 model matching problem. Next the fault detection observer estimation for anti-pinch window based on reference residual model will be discussed. (10) d , f (0, ] WF ( s) Trf ( s) WF ( s) 0 WF ( s) (9) d WF ( s) Trf ( s) In Eq. (10), the left reduces the effect of d to residual, the later makes the fault approaching the reference signal, which ensures the sensitivity. So designing the following formularies: (8) J<( Minimize J is minimizing the infinite norm of Eq. (8), which meet: Trd ( s) Trf ( s) From the above equations, the following relation is obtained: (7) where w = [uT fT dT], re = r!rf. The optimization criterion Jw is the worst-case distance between the residual r and the ideal residual rf, normed by the size of the inputs. The Jw is the gain from w to the re: Tzw ( s) Analytical model of fault detection algorithm: Modeling of DC motor for fault detection estimation: The fault detection is based on analytical model. We firstly estimate the accurate state-space model for the antipinch control system. As shown in the Fig. 2, the DC motor system to drive window can be linearized. The nomenclature of the linearized motor is given: w(angular velocity speed), u(driving voltage), Fig. 2: Linearized motor model 2557 Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 x Ax Bu I(armature current), Tm(rotational torque), Td(disturbance torque), Tc(control torque), Lm(armature inductance), Rm(armature resistance), J(moment inertia), B(viscous friction coefficient), Ke(back electromotive force coefficient) and Kt(torque coefficient). From Fig. 2, the transfer function from the rotational torque to the angular velocity is given by: ( s) Tm Tm = Tc-Td = Tc-Tp-Tw-Tv Since the vibration torque varies along the road condition, it is difficult to define the velocity as a finite mathematic model. To solve this problem we classified it into energy bounded disturbance. The motor angular velocity speed can be rewritten as: B 1 1 Tc (Tp Tw ) uv J J J Because of the electrical dynamics of the motor is faster than the mechanical one, the control torque can be approximated as follow: Tc A 1 Js B The disturbance torque is classified into vibration torque Tv, pinch torque Tp and load torque Tw, so the rotational torque can be written as follow: y = Cx+Du Ke Kt 1 K (Tp Tw ) uv t u JRm J JRm The Tp and Tw can be modeled as a single state for the estimator design: T = Tp+Tw C C 0 1 , B 0 Kt JR m 0 , C [1 0 0], D [0] 0 Armature resistance test: The test is operated under motor stall and the result is 0.85 S. EMF coefficient test: Because of the inductor presence the voltage of the armature reaches the stable value after an adjustment time which reflects the inductor. We can know the adjustment time is 1.2 ms from the waveform of the voltage changes, so the inductance is 0.649 mH. The stable value of the angular velocity speed is 99.7 rad/s and the EMF coefficient can be obtained from linear approximation between the voltage and the angular velocity speed. Moreover, Ke is equal to Kt. (3) Moment inertia test. Put the step voltage signal on the motor and measure the corresponding speed curve, the Tn can be obtained as 9.3 × 10G3 s under the 5% deviation of the adjustment time. Based on the formula J = Ke*Kt*Tn/Rm, the moment inertia is 1.586× 10G4 kgAm2. The motor parameters are given in Table 1. The matrices of the model can be designed as follow: Since uncertain motor parametric uncertainty causes the bias error in the model estimate, the previous result using the torque estimate only is not suitable to the realistic condition. To solve the problem, the torque rate is augmented as an additional state and seen as a rank disturbance: 893109 107.530 6305170 . . 0 0 0 1 , B 0 , C [1 0 0], D [0], A 0 0 0 0 893109 893109 . . Bd 0 , B f 0 , Dd [0.05], D f [1] 0 0 T uTD So we can have the state-space model for the design of pinch estimator. 1 J 0 0 Design parameters for the model system: The main uncertain factors of the anti-pinch window control system are the vibration torque uv, model uncertain uTD and the disturbance from traction torque when the window lifts, these factors can be attributed as the finite energy disturbance d. Bd, Dd are the distribution matrices of the unknown finite energy disturbance According to the test, the window height is 435 mm, rising time is 5 s, so the average rate of increase is 87 mm/s. The anti-pinch resign is 4-200 mm, so the fault detection is achieved after the window lifts 2.7 s. Bf, Df are the distribution matrices of the possible fault. The parameters of the DC can be got by experiments, the process is: Kt (u Ke ) Rm The viscous friction coefficient B has less influence on the torque, so it can be neglect. Choose the angular velocity speed as a single state the motor control torque speed can be reorganize as: Ke Kt JRm 0 0 Fault detection observer estimation for anti-pinch window: Assume we select the reference residual model is the following form (Zhong et al., 2007): 2558 Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 Table 1: Nominal value of the motor parameters Motor parameters Rm Lm Ke Kt Tn J Vc The following three conditions hold: Value 0.8500[S] 0.6490[mH] 0.1204[V•s/rad] 0.1204[V•s/rad] 9.3×10-3[s] 1.586×10-4[kg•m2] 12[V] x F (t ) AF x F (t ) BF f (t ) rF (t ) C F x F (t ) DF f (t ) C C C The coefficient matrix of the reference model can be solved as follow: (12) AF ( R X ) 1 M T 1 BF ( R X ) K T CF N D T F ~ Choose x [eT x F T ]T , using (3) and (12), the following form can be obtained: ~~ ~ x (t ) Ax (t ) ~~ re (t ) Cx (t ) ~ Bw(t ) ~ Dw(t ) Lemma 2 transfers the existence condition of fault detection filter into a solvability problem of linear matrix inequalities. Equation (14) is a linear matrix inequalities about scalar (, so it can be optimized as a variable ( by solving the following optimization problem to get H4 filter: (13) For more resolve, two lemmas are given as following: Lemma 1: Given a system as follow: min constra int s : formula (14) x(t ) Ax (t ) Bw(t ) z (t ) Cx (t ) Dw(t ) A is asymptotically stable, ||T(s)||4<(, if and only if there exists a matrix P = PT>0 satisfying: Trd E14 E22 E23 E24 * * I * 0 I * * * E11 = RA+ATR!ZC!CTZT E12 = RA!ZC+ATX!CTY+M, E13 = Rbd!ZDd, E14 = RBf!ZDf, E15 = CT!N, E22 = ATX + XA!CTY!YTC, E23 = XBd!YDd, E24 = XBf !YTDf+K, E45 = DfT!TT WF 14633 . CF = [0.6386 - 0.0154 0.0013], DF = [0.8655], E15 C T DdT 0 E45 I X-R > 0 0.0575, Trf 0.0001 0.000 0.000 AF 0.00029 0.0921 0.0225 0.0009 0.0335 0.0998 Lemma 2: For system (1), given (>0, if there exists positive definite matrix R and X, the matrix K, M, N, T, Y and Z, which satisfy the following LMI: E13 7.3967 0.0494 H 0.0164 , BF 0.6203 0.4900 0.0201 The system asymptotically stable and satisfy ||Tzw(s)||4<(, Tzw is the transfer function of w to r. E12 (15) Using the LMI toolbox in MATLAB, the index, the observer gain and the coefficient matrix of the reference model can be got: PA A T P PB CT T 1I D 0 B P C D 1 I E11 * * * * For system (1), there exists a H4 filter. The observer gain H = R-1Z. The system (13) asymptotically stable and satisfy ||re||2 < (||w||2, namely the index J<(. (14) Design of threshold: The basic method of the fault detection is to construct an optimal fault detection observer to acquire a residual. By comparing the residual evaluation value with a threshold, the occurrence of pinch can be detected. So we first decide the threshold based on the normal states of the window. From Eq. (4) we know the feature of residual is: r(s) = Trd(s)d(s)+Trf(s)f(s) When no fault occurs, there is also a certain load torque in window control system. So according to the 2559 600 550 500 450 400 350 300 250 200 150 100 0.0 Pinch angular velocity Normal angular velocity 6 Torque rate (Nm/s) Angular velocity (deg/s) Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 0.5 24 1.0 1.5 2.0 2.5 3.0 3.5 Time [sec] 4.0 4.5 2 0 -2 -6 0.0 5.0 Residual 12 4.5 5.0 -0.4 -0.6 -0.8 8 -1.0 4 -1.2 1.5 2.0 2.5 3.0 3.5 4.0 Time [sec] 1.5 2.0 2.5 3.0 3.5 4.0 Time [sec] 0 -0.2 16 1.0 1.0 0.2 Pinch torque Normal torque 0.5 0.5 Fig. 5: Pinch torque rate 20 Torque (Nm) 4 -4 Fig. 3: Pinch angular velocity 0 0.0 Pinch torque rate Normal torque rate 4.5 -1.4 -1.6 0.0 5.0 0.5 1.0 1.5 2.0 2.5 3.0 Time [sec] 3.5 4.0 4.5 Fig. 4: Pinch torque Fig. 7: Normal residual signal theory of fault detection, with the absence of fault and the input voltage is a constant value case, Truu(s) + Trdd(s) = 0. The Eq. (16) can be obtained in the normal state: r ( s) Trf ( s) f ( s) (16) Solving the steady-state value of residual signal in normal and taking the averag value of it as Jr. Because the residual strikes in a certain range, we select threshold for the average of 20% margin, namely the threshold meets (Jr!Jth)/Jr = 20%. SIMULATION AND RESULT ANALYSIS MATLAB simulation results: When the fault occurs, the angular velocity, torque and torque rate change as follow Fig. 3 to 5, we can see at the pinch condition 2.7 s, the rate changes dramatically. So by considering the torque rate as criterion of pinch detection, the system could improve the reliability of pinch detection even in the presence of disturbance. Using Simulation toolbox to build the robust fault diagnosis system model of anti-pinch window, the input is angular velocity and output is residual signal, shown in Fig. 6. The model bases on the residual generator. The Fig. 7 shows the normal residual when the window lifts without fault. After 0.2 s the residual reaches the steady-state value, taking the average of the residual signal between 0.2~4.5 s. Based on the former analysis we design the threshold as 0.8*-1.03823 (the average value) = !0.8306. When the force from the external obstacles is large, the residual signal is shown as Fig. 8. After the pinch occurs at 2.7 s, it can be detected with 70 ms timely in the margin 20% as the Fig. 8 shown, which meets the requirements that the residual has high sensitivity to fault. When the force from the external obstacles is small, the residual signal is shown as Fig. 9. The anti-pinch Fig. 6: Simulink model of anti-pinch window 2560 Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 Residual Threshold Pinch detection -0.4 Pinch occurs X: 2.77 Y: -0.7988 -0.8 -1.0 -0.4 -0.6 Pinch occurs X: 2.78 Y: -0.7964 -0.8 -1.0 -1.2 -1.2 -1.4 -1.6 0.0 Pinch detection -0.2 Residual Residual -0.6 Residual Threshold 0.2 0 0.5 1.0 1.5 2.0 2.5 3.0 Time [sec] 3.5 4.0 -1.4 -1.6 0.0 4.5 0.5 1.0 1.5 2.0 2.5 3.0 Time [sec] 3.5 4.0 4.5 Fig. 8: Fault residual signal with large obstacles Fig. 9: Fault residual signal with small obstacles condition can also be detected with 80 ms timely in the margin 20%. So we consider the proposed algorithm detects the pinched condition relatively fast in spite of the disturbance and noise, which meets our requirements that the residual has strong robustness to uncertainties. Co-simulation results on CANoe-MATLAB: The CAN bus technology has been widely applied in the pure electric vehicles system at present (Duan et al., 2010). We verify the anti-pinch algorithm in realistic window system by using CANoe-MATLB interface connected with Simulation node LFD_ECU MATLAB/Simulink CANoe CANopen network Motor CANoe/ MATLAB interface Left rear view mirror Right rear view mirror Door Lock CANcaseXL USB 2.0 Interface card Control switch CAN Bus Fig. 10: The co-simulation of anti-pinch window 2561 Control algorithm Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 1.2 current and the angular velocity is considered as a fault to generate a residual which can be effectively detected and guarantee the robustness in the method. By CANoeMatlab interface we realize the Co-simulation of the real (CAN) hardware in a networked environment and the function of anti-pinch. The simulation results show the observer can detect the fault after it occurs 0.16 s and the bus load rate is 3.49%. All of these valid the proposed method can be used for anti-pinch detection on pure electric vehicles. Pinch detection 1.0 Residual 0.8 0.6 0.4 Pinch occurs 0.2 0.0 -0.2 -0.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Time [sec] ACKNOWLEDGMENT 5.0 Fig. 11: Residual of pinch condition MATLB/Simulink which has power modeling functions and CANoe which has perfect functions of bus simulation. CANoe-MATLAB interface can be operated in two different modes: one is offline mode, the other is Hardware-in-the-Loop (HIL) mode. The whole system simulation process is based on HIL mode as shown in Fig. 10. In HIL mode, CANoe runs as MATLAB/Simulink subsidiary mode. When the time starts running simulink model, CANoe will automatically open the bus monitor and display bus message value and signal value. With the Simulink Real-Time Workshop we can target CANoe and produce a Windows DLL which can be loaded in CANoe's simulation environment. One DLL must be generated per node. With this approach it is possible to test and verify a design with real (CAN) hardware in a networked environment. The simulation can be used as a simulation of the remainder of the bus in a real-time environment. Several Electronic Control Units (ECUs) can be simulated simultaneously the remaining bus in real time. The simulation results are as follows. Figure 11 shows the residual signal in co-simulation. We can see the results are similar as the MATLAB Simulation results. The residual changes dramatically under the pinch condition which exceeds the threshold as former results. CONCLUSION In this study, the pinch torque rate detection algorithm based on H4 filter fault detection is proposed. A performance index which includes both robustness against disturbances and sensitivity against fault is used. By using some results of H-infinity optimization, the H4 filter design problem is formulated as an H-infinity optimization problem. By using the LMI toolbox of MATALB, we get the indices, the observer gain and the coefficient matrix of the reference model. The designed observer considers both robustness against disturbances and sensitivity to fault. The simulation results show the observer can detect the fault after it occurs 70 ms. Compared with the former methods mentioned in the instruction, we can see torque rate not the motor control This study was supported by the National High Technology Research and Development Program of China (863 Program) (Grant No. 2001AA501310) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (No. 20101201120001)”. REFERENCES Adil, A., D. Mohamed and B. Mohamed, 2010. Design of robust H-reduced-order unknown-input filter for a class of uncertain linear neutral systems. IEEE T. Automat. Contr., 55(1): 6-19. Angelo, C., G. Bossio, J. Solsona, G.O. Garcia and M.I. Valla, 2006. Mechanican sensor-less speed con control of permanent magent AC motors driving an unkonwn load. IEEE T Ind. Electron., 53(2): 406-414. Buja, G.S., R. Menis and M.I. Valla, 1995. Disturbance torque estimation in a sensorless DC drive. IEEE T Ind. Electron ., 42(4): 351-357. Duan, J., H. Deng and Y. Yu, 2010. Co-Simulation of SBW and FlexRay Bus Based on CANoe_MATLAB. Proceedings of the 2010 IEEE International Conference on Automation and Logistics, Hong Kong and Macau, August, pp: 16-20. Doh, T. and J. Ryoo, 2008. Robust stability condition and analysis on steady-state tracking erors of repetitive control systems. Int. J. Cont. Autom., 6(6): 960-967. Henry, D. and A. Zolghadri, 2005. Design and analysis of robust residual generators for systems under feedback control. Automatica, 41(2): 251-264. Isermann, R., 2005. Model-based fault detection and diagnosis-status and application. Annu. Rev. Cont., 29: 71-85. Lee, Hye-Jin, R. Won-sang, Y. Tae-Sung and P. Jin-Bae, 2008. Practical pinch torque detection algorithm for anti-pinch window control system application. IEEE T. Ind. Electron., 55: 1376-1384. Ma, W., S. Zhang and H. Wang, 2008. The design of antipinch car window using Hall sensor. Automot. Eng., 35(12): 1256-1260. Niaki, S. and A. Taghi, 2009. Decision-making in detecting and diagnosing faults of multivariate statistical quality control systems. Int. J. Adv. Manuf. Tech., 42(8): 713-724. 2562 Res. J. Appl. Sci. Eng. Technol., 4(15): 2555-2563, 2012 Syed-Ahmad, N. and F.M. Wells, 1993. Torque estimation and compensation for speed control of a DC motor using an adaptive approach. Proceedings of the 36th Midwest Symposium on Circuits and Systems, pp: 68-71. Yang, H., J. Mathew and L. Ma, 2005. Fault diagnosis of element bearing using basis pursuit. Mech. Syst. Signal., 19: 341-356. Zhang, X.Z. and Y.N. Wang, 2011. A novel positionsensorless control method for brushless DC motor. Energ. Convers. Manage., 52(3): 1669-1676. Zheng, Q. and F. Wu, 2009. Nonlinear H- infinity control designs with axisym metric spacecraft control. J. Guid. Contr. Dynam., 32(3): 850-859. Zhong, M., S.X. Ding, J. Lam and W. Haibo, 2007. An LMI approach to design robust fault detection filter for uncertain LTI systems. Automatica, 39: 543-550. 2563