Abstract
A hydraulic pressure servo system based on two high-speed on/off valves (HSV) is a discontinuous system due to the discrete flow of HSV when driven by pulse width modulation (PWM) signal. Pressure variation in the testing chamber is determined by the flow rate difference between the charging and discharging HSV. In this paper, a pressure controller consisting of a differential PWM (DPWM) scheme, asymmetric pressure difference compensation (APDC) and nonlinear adaptive control (NAC) is proposed to precisely control the pressure. The DPWM scheme is designed to improve the resolution of the net flow rate into the testing chamber. Furthermore, due to the strong asymmetry between the charging and the discharging process, the APDC method is proposed to design the two initial duty cycles of the DPWM signal which help to balance its charging and discharging ability under different working pressure points. Since the pressure system is a nonlinear, uncertain system due to oil compression and leakage, the NAC is designed to calculate the control duty cycle of the DPWM signal, which is used to overcome the unmodeled dynamic and parameter uncertainties. Comparative experiments indicate that the proposed controller can ensure good pressure tracking performance and enhance system robustness under different working pressure points and tracking frequencies.
Highlights
Electro-hydraulic servo systems (EHSS) have been widely used in the field of aircraft, such as in flight control subsystems [1], landing gear control subsystems [2], aircraft brake subsystems [3], and clutch pressure control systems for helicopters [4], because of their high power-weight ratio, high precision, and high-frequency response
A pressure controller consisting of a differential pulse width modulation (DPWM) scheme, asymmetric pressure difference compensation (APDC) and nonlinear adaptive control (NAC) is proposed
When the charging high speed on/off valve (HSV) is energized, the oil flows into the testing chamber from the power supply which leads to the pressure in the testing chamber to rise
Summary
Electro-hydraulic servo systems (EHSS) have been widely used in the field of aircraft, such as in flight control subsystems [1], landing gear control subsystems [2], aircraft brake subsystems [3], and clutch pressure control systems for helicopters [4], because of their high power-weight ratio, high precision, and high-frequency response. A novel seven-mode sliding controller was proposed to simultaneously improve the position accuracy of the actuator and reduce the switching number of the HSV. To improve the pressure tracking accuracy of a pneumatic servo system controlled by two fast-switching valves, Lin et al [21] proposed a novel hybrid control strategy in which a time interlaced modulation and seven new possible control modes were designed to reduce the overshoot, the steady-state error and the settling time. The overall aim of this research is to accurately track the dynamic pressure via the use of two HSVs. A pressure controller consisting of a differential pulse width modulation (DPWM) scheme, asymmetric pressure difference compensation (APDC) and nonlinear adaptive control (NAC) is proposed. Extensive comparative simulations and experiments indicate that pressure tracking accuracy was significantly improved by the proposed pressure controller
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