High dynamic digital control for a hydraulic cylinder drive

The control of hydraulic cylinders with digital hydraulic valves is often based on modulation principles like pulse-width modulation, pulse-code modulation, or pulse–frequency control. In many cases the dynamic drive performance using such control strategies is far below the natural dynamics of the system, since closed-loop controllers demand a certain phase margin for stability. However, some drive applications require a high dynamic response, which cannot be realized with common closed-loop concepts. In this article the design of a bang–bang feedforward control with regard to the dynamics of a hydraulic cylinder drive in accordance with the theory of optimal control is presented. The control achieves the maximum physical dynamic response and no remaining oscillations after the movement, which forms the basis of a high dynamic three-level position control for hydraulic drives. Furthermore, the influence of valve dynamics and pipe line dynamics with regard to the design of the digital valve control are considered by simulations.