Control of a fast switching hydraulic valve

Pulse-width modulated switching control of hydraulic actuation systems has the potential to very significantly improve their energy efficiency. To realise this type of digital hydraulic system, valves capable of quickly switching large flow rates need to be developed. The majority of proposed designs utilize ’bang-bang’ configurations to achieve this, however, the valve described in this paper uses a combination of State Variable Feedback (SVF) and Iterative Learning Control (ILC) to provide position control of the valve spool. This resulted in a measured switching time of 0.5ms for a 55 L/min flow rate at 10 bar pressure drop. The ILC used a low-pass filter to ensure long-term stability and reduce controller effort as a result of high-frequency, unmodelled behaviour, as in most published studies. The ILC has been extended in this paper to ensure stability with both modelled and unmodelled saturation in the control and actuation system by modifying the learning gain. This approach could be used to protect against other non-linear behaviours in the future. The research demonstrates that utilising advanced control methods can help to achieve the very high valve dynamic performance required for future high-efficiency digital hydraulics.