Study On The Dynamic Loading Of Electro-hydraulic Position System With Pulse Width Modulation

Electro-hydraulic position system with pulse width modulation refers to the position system controlled by pulse width modulation proportional valve. Pulse width modulation proportional valve, consisting of main valve and the pilot hydraulic bridge from the high speed on-off valves controlled by the pulse width modulation (PWM) signal, has been widely used in the fields of engineering vehicle steering system with its strong anti-pollution ability, low cost, and convenient computer interface etc. Electro-hydraulic dynamic loading system is the system used to simulate all kinds of loads acting on the loaded object (such as aircraft rudder) under laboratory conditions, in this way can we study the influence of control system performance by these loads. Electro-hydraulic dynamic loading system has redundant power (or torque) during the loading process, which seriously affect static and dynamic quality of the dynamic loading system. When the loaded object is as electro-hydraulic position system with pulse width modulation, due to the effects modulation frequency of PWM signal of and duty cycle, and seriously dead features of the proportional valve and other nonlinearity factors, which make it more difficult to the establishment of the mathematical model of the location system, the analysis and improvement of the system accuracy and response characteristics, and the inhibition of redundant power (or torque) of the loaded system and other issues.This paper used the electro-hydraulic position system with the pulse width modulation as the research object, which ignored the elastic condition caused by the flexible structure of the load connection and fixed place, and established the mathematical model of electro-hydraulic position system controlled by the proportional valve with the pulse-width modulated. On this basis, this paper established the mathematical model of a valve-controlled hydraulic motor loading process, which can be dynamically loaded for the position system. This paper analyzed the impact of modulation frequency of PWM signal of and duty cycle to the control accuracy of the electro-hydraulic position system, the mechanism of the extra torque generated and the factors affecting the size of the extra torque.For the extra torque characteristics, static and dynamic load characteristics with disturbance, and static and dynamic load characteristics without disturbance of electro-hydraulic position system dynamically loaded with pulse width modulation, this paper has researched the size of load torque, movement amplitude of the loaded system, and the impact of frequency to load performance of electro-hydraulic dynamic loading system using of AMESim software. This paper analyzed the method that used P-Q servo valves and double valve parallel structures and based on the use of the structural invariance principle, designed excess force compensation controller to compensate the extra force. Compensation control scheme of a single-loaded servo valve structure based on pressure feedback is proposed, which resolved the problem that the high quality of the speed signal is difficult to obtain, and effectively inhibited excess force of the dynamic loading. On the basis, this paper established the hardware-in-the-loop simulation experiment scheme of dynamic load of electro-hydraulic position system with pulse width modulation based on xPC Target.Study shows that the pulse width modulation proportional valve have the dead zone when the duty ratio is small, and the duty ratio close to1appear saturation phenomenon, which seriously affect control accuracy of electro-hydraulic position system with the pulse width modulation; In the paper for the research object, electro-hydraulic position system with pulse width modulation surplus torque is the largest, at the beginning of the work, and when the motion frequency increases to5Hz extra torque increases to97N·m. Based on pressure feedback compensation control scheme of the simulation analysis show that the load torque on the phase advance1°～2°or so, the tracking error is5.8%under the condition of torque load50N-m, and9.5%under the condition of load torque100N-m. the tracking performance index can meet the double tenth performance index of the dynamic loading system.