Embedded Sliding Mode Controller Applied to Control Valves with High Friction

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.