Embedded Sliding Mode Controller Applied to Control Valves with High Friction
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Embedded Sliding Mode Controller Applied to Control Valves with High Friction Matheus C. Hidalgo1,2 · Claudio Garcia1 · Bruno A. Angélico1 · Eduardo A. Tannuri3 Received: 5 September 2018 / Revised: 23 June 2019 / Accepted: 9 July 2019 © Brazilian Society for Automatics–SBA 2019
Abstract Friction is one of the most frequent causes of oscillations in process control loops. Normally, the first step in resolving this problem should be to stop the process and to perform valve maintenance. However, it is not always possible to do it, because it can lead to a loss of production and some processes are not simple to halt, e.g. a nuclear power plant or an oil refinery. Therefore, it is important to find other ways to solve this problem. Lately, many academic works have proposed the use of the integrative sliding mode controller to reduce the friction effect in control loops. This paper proposes to discretize this controller and to implement it in a microcontroller, acting as a control valve positioner. The experiments were conducted in a hardware-in-the-loop simulation environment running in real time. Tests are performed under various conditions, and the results are compared to a widely used friction compensation algorithm and a control disable technique. The results show that the implementation of the sliding mode controller in digital positioners is an interesting alternative for friction compensation in control valves in the industry. Keywords Control valves · Friction compensation · Nonlinear control · Sliding mode control · Embedded controller
1 Introduction Kayihan and Doyle (2000) proposed the use of some nonlinear controllers to regulate the control valve stem position, emphasizing cases in which the valve has high friction. They performed tests considering a simulated valve. In the work of Baeza and Garcia (2018), nonlinear controllers were tested with a real valve for stem position control, but without a master control loop, for instance, a temperature or flow control loop. Among all the controllers designed in Baeza and Garcia (2018), the integrative sliding mode controller (ISMC) produced the best results, reducing the valve stem posi-
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Matheus C. Hidalgo [email protected]
1
Department of Telecommunications and Control Engineering, Escola Politécnica - University of São Paulo, São Paulo, Brazil
2
Present Address: Av. Prof. Luciano Gualberto, 380, São Paulo, SP, Brazil
3
Department of Mechatronics Engineering and Mechanical Systems, Escola Politécnica - University of São Paulo, São Paulo, Brazil
tion variability when compared to a PID controller actuating through an I/P (current to pressure) converter. Furthermore, in the work of Hidalgo and Garcia (2017), the ISMC was tested in a real flow control loop in two situations: The first one was controlling the flow of the plant using the valve as a control element. This implementation can be named ISMC under external topology, because it is normally implemented in a distributed control system (DCS) level, i.e., externally to the field. The second
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