Research On Cascaded Pressure Control For Atmospheric Pressure Simulation System

The atmospheric pressure simulator(APS) is a vital device for the Hardware-in-the-loop(HIIL) simulation for aircrafts, which can generate corresponding pressure signal. High precision and quick response are demanded for the APS. The thesis propose a new construction of pressure control which is called cascaded pressure control method based on the analysis of nonlinearity at different control pressure point and strong asymmetry of charging and discharging at lower pressure. The advantage of adopting cascaded pressure control compared with common-used single-stage pressure control is that the asymmetry can be distinctly weakened. The positive pressure source of second control stage is provided by the output pressure of first control stage, this is the reason why cascaded pressure control method can weaken the asymmetry. A nonlinearity compensation strategy is presented to improve control performance based on the cascaded pressure control construction. The main research in this thesis is shown as below:1. The mathematic models of subsystems of the single-stage pressure control system are built based on the pneumatic technology and theory. And the simulation is conducted to analyze characteristics by digital simulation tool. The simulation result reveals the strong asymmetry at lower pressure point. A new pressure control construction is proposed to weaken the asymmetry in the next chapter.2. The nonlinearity influenced by varied working pressure points and asymmetry at lower pressure point of the system are analyzed. A new control construction ——cascaded control construction is proposed to solve the nonlinearity and asymmetry. The positive pressure source of target control stage is provided by the output pressure of compensation stage to create the best working condition for target loop, and complete nonlinearity compensation strategy for target control loop is adopted to realize the consistency of control performance at large working pressure points.3. The mathematic models and simulation models are built. Simulation results are compared between common used uncompensated construction and new proposed cascaded construction. It shows that asymmetry is remarkably reduced through cascaded construction. Also the comparison between PID controller and nonlinearity compensation strategy is conducted to show better control consistency though nonlinearity compensation.4. Experiment platform is established to conduct corresponding experiments to prove proposed control strategy. The experiment result indicate that asymmetry at lower pressure point is well conquered by adopting cascaded pressure control construction. The proposed nonlinear compensation method can improve control performance and ensure the adaption of control parameters.The innovation work in this thesis is mainly concentrated on cascaded control construction. This proposed control construction can provide a reference method to conquer the asymmetry and nonlinearity of pneumatic servo control system.