Actuator nonidealities, such as backlash, dead zone, and others, present in a number of industrial systems, are known to severely degrade system performance. Providing nonconservative closed-loop robust performance guarantees for these systems in a consistent manner has been an open problem. For example, in boiler/turbine units, the turbine valve position actuation for manipulating steam flow rate is characterized by a small mismatch between the turbine valve command and the actual valve position, producing a small steady-state regulation error in the plant outputs. The standard linear H ∞ controller designed to provide zero steady-state error regulation drives this error to zero, producing the undesirable oscillations in the control signals and the plant outputs. This paper develops a nonsmooth H ∞ output regulator theory addressing this problem and applies this theory to the experimentally validated boiler/turbine model with actuator dead zone. The simulation results showing a considerable performance improvement are given.
Backlash and Coulomb friction occurring in systems with mechanical transmissions produce undesired inaccuracies, oscillations, and instability thereby degrading the system performance. In this paper, we made a comparative analysis of a nonsmooth H∞ controller [1] vs. a linear H∞ controller applied to a two-mass drive system with flexible shaft including backlash and Coulomb friction using measurements of the motor. The numerical results show the effectiveness of the nonsmooth H∞ synthesis, whereas the linear H∞-controller does not attenuate the undesirable oscillations in the control signals and the plant outputs.
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