Robust Servo Control of a High Friction Industrial Turbine Gas Valve by Indirectly Using the Standard$mu$-Synthesis Tools

The current mu-synthesis tools are not directly suitable for industrial turbine fuel and water control because they lead to high-order controllers with physically meaningless states. The production valve example here is the Woodward GS6 Turbine Gas Metering Valve that has a single-phase permanent magnet motor coupled by a shaft to an inertia disc and a gas metering shoe with a high level of dry (nonlinear) friction and flow forces. The embedded TI-DSP-2407 processor that runs the position controller in the 1 ms loop rate practically limits the maximum controller order to seven. This paper describes how an industrial seventh-order 2-degrees of freedom (DOF) controller was designed by indirectly using the standard tools available in the mu-Toolbox. Step, limit cycle, and frequency response measurements show that the new design compares favorably well with the standard production controller. However, the key advantages were that the first design downloaded into the controller did not require retuning, the design process was higher level, and the measure of "robustness" was in terms of the physical description of plant uncertainties