Pulse width modulated sliding mode control of an electrohydraulic system

Sliding mode control is a robust control technique which is able to provide a desired dynamic behaviour in spite of disturbances and uncertainties under matching conditions. In recent years, because of simplicity and robustness, sliding mode control has become popular and various sliding mode control techniques have been developed. At the same time, it is drawing considerable interest in the world to digitally control electrohydraulic systems with lower cost valves instead of servovalves. It is found that, unlike pneumatic systems, a comprehensive and updated study on hydraulic systems with on/off cartridge valves with sliding mode control is not available in open literature. It is also seen that even the most prominent study using this technique was implemented using valves, computer and electronic components of its time and using a preliminary version of a control method. Thus, with this study, using current technological components and a more developed control technique, it was tried to approach an output quality of a servovalve with pulse width modulated sliding mode control utilizing low cost solenoid operated on/off cartridge valves for position control of an electrohydraulic system. In order to prove the usability degree of the technique, a large number of simulations and experiments were carried out with servovalve and cartridge valves and obtained results were compared with each others. It is concluded that, to a certain output quality level, several systems in industry can be controlled with this technique with low cost valves; advantages and disadvantages of the technique and some suggestions for further studies are presented. Keywords: electrohydraulic system, cartridge valve, servovalve, pulse width modulation, sliding mode control, modelling, simulation, experiment