Digital fluid power transmissions (DFPTs) are a promising alternative to drivetrains based on gearboxes and power electronics. One application is offshore wind turbines where the characteristics of high reliability and robustness of hydraulic systems are highly desirable.

A DFPT consists of a digital displacement pump and motor connected to shared pressure lines, thereby forming the transmission. The decision to update the displacement of such machines occurs at a number of fixed shaft positions, why for variable-speed operation, the control rates of the machines are both asynchronous and non-uniform creating a multirate control problem.

To obtain a linear control model, all dynamics are transformed to the spatial-domain. A new multirate modelling technique is hereafter derived by combining two existing multirate methods. From this multirate technique, the DFPT is linearly modelled and applicability of conventional control and analysis tools are evaluated.

Based on this thesis’ results, it is concluded that multirate modelling and control of a DFPT is possible both in the time-domain and spatial-domain, but that the time-domain implementation of a spatialdomain control law is not straight forward.