Switching Policies for Mold Level Control in Continuous Casting Plants

Abstract

The problem of controlling the liquid level in the mold of a continuous casting process is considered. Essentially, the system operates in two different modes: (a) one in which the system is affected only by small-amplitude high-frequency disturbances, and (b) one in which the system is affected by a comparatively large disturbance related to an abrupt unclogging phenomenon. To cope with the first situation, the control system must exhibit a narrow bandwidth, whereas the second situation requires a much larger bandwidth. The two conflicting requirements lead naturally to the design of two distinct controllers and a switching rule that activates either controller according to the operating condition. Due to the time-varying nature of the resulting control system, the controllers should be properly realized to guarantee stability; to this purpose, a recent result on switching systems [15] is invoked. Since the sudden switching between controllers can cause controller and actuator output bumps, a soft switching policy that still ensures stability is also proposed. Simulations and laboratory experiments carried out on an electronic analogue of the process show the effectiveness of the suggested control schemes.

Variable-structure control of casting processes

“…The proposed control techniques have been tested successfully using Matlab R . The numerical simulations have been validated by means of an electronic analogue of the casting process that has confirmed the obtained results [13].…”

“…Theorem 5.1: [13] With reference to the classic feedback control structure of Figure 5, let P:{A, B, C} denote a minimal realization of the strictly-proper transfer function P (s), and let K i :{Â i ,B i ,Ĉ i ,D i }, i = 1, 2, denote the realizations of the two alternatively-functioning controllers that ensure the closed-loop stability of the switching system. Then, for any function α(t) taking values in the interval [0, 1], the controller realization (7) guarantees closed-loop stability.…”

Robust linear parameter‐varying control of induction motors

“…The control of IMs is a rather difficult task because their behavior is highly nonlinear. However, by considering the rotor speed as a varying parameter, the nonlinear state–space equations describing the motor dynamics can be embedded into an LPV model , which allows us to profit by some recent results on switching and LPV control .…”

“…Quite interestingly, in , it has been pointed out that the IM nonlinear state–space equations can be embedded into a quadratically stable linear parameter‐varying (LPV) model by considering the rotor speed as a varying parameter. This fact allows us to exploit some recent results on switching and LPV control . In particular, a control scheme is suggested that is guaranteed stable for any function ω ( t ) such that , with ω max arbitrary.…”

An Adaptive Liquid Level Controller Using Multi Sensor Data Fusion

“…Switching type of liquid level controller for casting plant is reported in [9]. A control algorithm for the modelled beer fermentation process in a multi-stage process is discussed in [10].…”