| A dynamic loading system for pump controlled motor and valve controlled motor which are commonly used in hydraulic system of construction machinery is built in this paper. The dynamic loading system is classified as electro- hydraulic proportional relief valve loading system and electro- hydraulic proportional throttle valve loading system according to the different loading control elements. The composition and working principle of proportional loading system are described on the basis of the working principle of electro- hydraulic proportional valve. Then, the limit of excitation signal of the electro- hydraulic proportional loading system is calculated. The mathematical model of the proportional loading system is established. The design and experimental research of system identification are completed. The linear quadratic optimal control strategy is applied to the system and the simulation analysis is conducted.The output torque of electro-hydraulic proportional loading system is controlled by input control signal, so the key focus of the study is the relationship between the output torque and the input control signal. Firstly, mathematical models of electro-hydraulic proportional relief valve and proportional throttle valve loading system are derived on the basis of theoretical modeling and analysis of electro-hydraulic proportional loading system. Then, the scheme of system identification is designed, including the selection of an input signal(also known as the excitation signal), the selection of data acquisition node, pretreatment of the original data and the selection of identification model. The hardware is built and software flow chart of the system identification test is designed. Programs of the control signal generator are finished. The experiment of system identification is designed in view of the hardware and software of system identification test, including the design of the experiment scheme, the choice of sampling time and the length of the data and the main experimental steps. The original experimental data is obtained by carrying on the dynamic test. The test data of output torque and input control signal is drawn through the experiment. The data is analysed and processed using System Identification Toolbox. The unknown parameters of the system model are identified on the basis of a priori knowledge of the mathematical model derived from theoretical modeling using ARMAX model and transfer function model of the system identification research respectively. The residual correlations are analysed and the accurate mathematical model of the system are selected relatively in consideration of the goodness of fit and dynamic response of the model.The performance of mathematical model which is derived from system identification is analysed. The rising time of the electro-hydraulic proportional load ing system is too long. The overshoot is too excessive and the oscillation is too intense. The overall performance of the system can not meet the functional requirements. Firstly, the basic content of linear quadratic optimal control theory is described. The linear quadratic optimal controller is applied to the electro-hydraulic proportional loading system. The overall performance of the system has been greatly improved after correction. |
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