Identification modeling of micro thrust cold gas propulsion system

Cold gas propulsion system is the most widely used propulsion technology for Drag-free spacecraft at home and abroad. The flow output is generated by feedback-loop control of valve opening of piezoelectric proportional valve, and then the micro flow is converted into micro thrust. Due to the inherent nonlinear characteristics of piezoelectric actuator in piezoelectric proportional valve, such as hysteresis, creep, temperature drift, as well as the mechanical structure of valve body, fluid flow, there are nonlinear factors, resulting in a nonlinear relationship between the output flow rate of the system and the driving voltage. Therefore, in order to realize control compensation, the nonlinear link in the system should be analyzed first, a reasonable mathematical model should be established. This paper analyses the structure of each link of the system and determines the nonlinear factor of the system. And analyze the reason why the existing model is not suitable for the whole model of piezoelectric proportional valve. Combined with the analysis of the theoretical model, an improved BW model is proposed: the linear ARX model is combined with the BW hysteresis component model. The order information of the linear component is determined through the system structure identification, and the unknown parameters in the model are identified by the genetic algorithm, and the curve mean absolute error of fitting is 0.2643 mg/s, and the goodness of fit is 97%. Furthermore, the proposed soft measurement method of valve core displacement can reconstruct the displacement output of valve core without adding displacement sensor, which is used for the design of feedback-loop controller. The system model established in this paper has guiding significance for the controller design of the cold gas propulsion system, the structural improvement of the piezoelectric proportional valve and the nonlinear compensation.