Predictive Control Design Based on System Identification of an Electro-hydraulic Actuator Applied to Brazilian Sounding Rockets and Microsatellite Launchers

Abstract

This paper presents the modeling and control design to new hydraulic actuator being developed for thrust vector assembly applied to Brazilian rockets. Traditionally PID controllers are used for this issue but based on discrete models is proposed a new digital control for best performance. It is based on models obtained from closed-loop system identification of a Brazilian electro-hydraulic actuator using Nitrogen pressure-fed system applied to Sounding Rockets and Microsatellite Launcher (VLM). The vehicles are developed at the Aeronautics and Space Institute (DCTA/IAE) and a new actuator under test is being proposed using Helium gas to the Pressure-Fed-System. Traditionally the Nitrogen gas is used in low pressure operation to feed hydraulically the actuator and a new controller is being implemented to improve the system performance. Simulations developed in AMEsim and Matlab codes show best performance using Helium gas dealing on fast movements to the high pressure hydraulic cylinder, increasing the system bandwidth. The modeling of the hydraulic actuator is presented for linear and nonlinear analysis as well as their influences on system identification algorithms. The fluid flow through the internal pipes and spool are modeled using its nonlinear flow equation while the spool linear dynamics are obtained from Newton's law and the magnetforce from Biot-Savart law. Discrete models are obtained from system identification using experimental data from the hydraulic closed-loop operation while a digital controller is designed based on that discrete models and finally implemented in the loop. A real-time electronic system with digital-to-analog and analog-to-digital converters performs the digital control, using Labview programming environment. The linear and nonlinear dynamics associated to each subsystem are discussed and simplifications hypotheses are presented in order to obtain the Low Order Equivalent System (LOES) to the entire hydraulic actuator, as well as the influences on the predictive control strategy and linear system identification. According to results in time and frequency domain the performance attends the rocket design requirements.