The Prescribed Fixed Structure Intelligent Robust Control of an Electrohydraulic Servo System

Abstract

The paper is focused to design a robust and a simple fixed structure ${\mathbf{H}}_{\infty }$ control synthesis for an Electrohydraulic Servo System (EHSS) and comparing its performance with the conventional ${\mathbf{H}}_{\infty }$ controller and the classical proportional integral derivative (PID) controller. The precise position tracking of the piston load of EHSS system using classical PID controller is a difficult task due to some non-linear properties of EHSS and the dynamic behaviour of its parameters. The conventional ${\mathbf{H}}_{\infty }$ controllers also have constraints on gain ( ${\mathbf{H}}_{\infty }$ norm) for typical design requirement such as the speed of response, higher order, complex structure, control bandwidth, and robust stability. To overcome the above limitations, the proposed synthesis is formulated in the MATLAB. The proposed synthesis has fixed order and fixed structure and is also a linear robust controller. The control parameters of proposed synthesis are tuned using Genetic Algorithm optimization in MATLAB. Another advantage of this design is to use higher order complex shaping fillers to shape the close loop sensitivity $\mathbf{S}\left(\mathbf{s}\right)$ and complementary sensitivity $\mathbf{T}\left(\mathbf{s}\right)$ for the desired robust performance, without effecting the structure fixed of proposed synthesis. The order of the proposed controller is not affected by using the higher order complex weights transfer functions ${\mathbf{W}}_{\mathbf{s}}\left(\mathbf{s}\right)$ and ${\mathbf{W}}_{\mathbf{T}}\left(\mathbf{s}\right)$ on sensitivity and complementary sensitivity, respectively, whereas the structure of the conventional ${\mathbf{H}}_{\infty }$ controller becomes more complex due to higher order shaping weights. Model of the Electrohydraulic Servo System is validated experimentally, and results of proposed robust synthesis are compared with conventional ${\mathbf{H}}_{\infty }$ controller and the classical PID.