Electrohydrostatic actuator (EHA) is a new actuator for next generation aircraft actuation system. This actuator is essentially a nonlinear system; response speed and accuracy are the main consideration. We use sliding mode control for this nonlinear system in this paper. The variable structure filter (VSF) is introduced to obtain the unmeasured states. Derivation of the VSF gain based on the reaching law is presented in this paper. To improve the response speed and accuracy, a nonlinear function is introduced to construct the nonlinear sliding surface using the estimated states generated by VSF. Simulation results show that low settling time and quick response are obtained by using the nonlinear sliding surface. 1. Introduction Conventional aircraft hydraulic actuation systems are driven by the central hydraulic station. A major disadvantage of this arrangement is that the fuselage of the aircraft filled with hydraulic pipeline. The complicated pipelines increase the vulnerable areas and decrease the chances of survival in battlefield. The power by wire (PBW) technology is introduced to solve this problem. The central hydraulic station and the complicated pipelines can be removed by using this technology [1–3]. The key component is the so-called PBW actuators. The electrohydrostatic actuator (EHA) is an important one among these actuators. Architecture of the EHA can be illustrated by Figure 1. Figure 1: Schematic diagram of EHA. In Figure 1 the brushless dc motor (1) is controlled to provide energy for the bidirection hydraulic pump (2). Then the controlled pump drives the symmetrical cylinder (8) to a given position. The pressure measurement (7) is used to compensate the load disturbance. The controller uses position measurement (9) to construct position close-loop. The accumulator (4) is used to collect and store leakage oil. Another role of the accumulator is to guarantee the positive pressure in the return oil circuit. Check valve (3) is used to implement the logic judgment according to system pressures. Bypass valve (5) is used to isolate the actuator when system fails. (6) are safety valves. Mathematical model of the EHA is used to obtain the control laws. However design control laws to obtain desired performance of the controlled closed-loop system is a difficult task. The main reason for this problem is that the unknown disturbances, plant parameters variation, and unmodeled dynamics cannot be considered in the mathematical model. A robust control method is needed under these circumstances. One particular approach to robust controller design
References
[1]
B. Alan, “Actuator research complete,” NASA the Dryden X-Press, vol. 41, no. 1, 1999.
[2]
N. Robert, Performance of an Electro-Hydrostatic Actuator on the F-18 Systems Research Aircraft, 1997.
[3]
C. J. Stephen, D. J. Gavin, and D. David, “Flight test experience with an electromechanical actuator on the F-18 systems research aircraft,” NASA Report H-2425, 2000.
[4]
C. Edwards and S. K. Spurgeon, Sliding Mode Control: Theory and Applications, Taylor & Francis, London, UK, 1998.
[5]
Y. Shtessel, C. Edwards, L. Fridman, and A. Levant, Sliding Mode Control and Observation, Springer, New York, NY, USA, 2014.
[6]
S. R. Habibi and R. Burton, “The variable structure filter,” Journal of Dynamic Systems, Measurement and Control, vol. 125, no. 3, pp. 287–293, 2003.
[7]
S. Habibi, “The extended variable structure filter,” Journal of Dynamic Systems, Measurement and Control, vol. 128, no. 2, pp. 341–351, 2006.
[8]
S. Habibi, “The smooth variable structure filter,” Proceedings of the IEEE, vol. 95, no. 5, pp. 1026–1059, 2007.
[9]
S. Wang, Integrated control and estimation based on sliding mode control applied to electrohydraulic actuator [Ph.D. thesis], University of Saskatchewan, 2007.
[10]
V. I. Utkin, Sliding Modes in Control Optimization, Springer, New York, NY, USA, 1992.
[11]
W. B. Gao, Foundation of Variable Structure Control, China Press of Science and Technology, Beijing, China, 1990, (Chinese).
[12]
M. Thoma, Sliding Mode Control Using Novel Sliding Surfaces, Springer, Berlin, Germany, 2009.
[13]
B. M. Chen, T. H. Lee, and K. Peng, “Composite nonlinear feedback control for linear systems with input saturation: theory and an application,” IEEE Transactions on Automatic Control, vol. 48, no. 3, pp. 427–439, 2003.
[14]
Z. Lin, M. Pachter, and S. Banda, “Toward improvement of tracking performance: nonlinear feedback for linear systems,” International Journal of Control, vol. 70, no. 1, pp. 1–11, 1998.
[15]
M. C. Turner, I. Postlethwaite, and D. J. Walker, “Non-linear tracking control for multivariable constrained input linear systems,” International Journal of Control, vol. 73, no. 12, pp. 1160–1172, 2000.
[16]
V. I. Utkin, J. Guldner, and J. Shi, Sliding Mode Control in Electromechanical Systems, Taylor & Francis, London, UK, 2009.
[17]
W. Gao, Y. Wang, and A. Homaifa, “Discrete-time variable structure control systems,” IEEE Transactions on Industrial Electronics, vol. 42, no. 2, pp. 117–122, 1995.
[18]
W. Gao and J. C. Hung, “Variable structure control of nonlinear systems. A new approach,” IEEE Transactions on Industrial Electronics, vol. 40, no. 1, pp. 45–55, 1993.
[19]
J. Y. Hung, W. Gao, and J. C. Hung, “Variable structure control: a survey,” IEEE Transactions on Industrial Electronics, vol. 40, no. 1, pp. 2–22, 1993.
[20]
E. A. Misawa, “Discrete-time sliding mode control: the linear case,” Journal of Dynamic Systems, Measurement and Control, Transactions of the ASME, vol. 119, no. 4, pp. 819–821, 1997.
