In this paper a modelling of a hybrid actuator is proposed. The hybrid actuator consists of a piezo mechanical structure and a hydraulic ratio displacement. In particular, this hydraulic ratio displacement is modelled through a liquid spring model. The idea of this contribution is using the advantages of both: the high precision of the piezo and the force of the hydraulic part. Piezoelectric actuators (PEAs) are mostly used for precise positioning, despite their nonlinearities, such as saturations, hysteresis and creep. In control problems these kinds of nonlinearities must be taken into consideration. Particular attention is paid to a possible control strategy to track a periodic signal. Simulations and measured results are carried out for the suitability of the control approach.