Flatness-Based High Frequency Control of a Hydraulic Actuator

This paper presents the design and implementation of a nonlinear feedforward control algorithm for a hydraulic actuator driven by a multistage servo valve. Combined with a conventional feedback control algorithm, high frequencies can be achieved even for large-scale strokes. In addition to the desired trajectory, the feedforward controller accepts the predicted dynamic load on the hydraulic actuator as an input. The performance of the control concept as well as the advantages of the load input are verified in simulations and experiments. Being exemplarily used for realizing a crankshaft-less test stand for free piston engines, the control algorithm is potentially suitable for further applications using hydraulic actuators in high frequency domain.