Controller design for active magnetic bearing system supporting a gyroscope for wave energy conversion

A transition towards renewable energy sources is needed to reduce emissions and the growing reliance on fossil fuels. Sea waves represent one of the most promising sources of renewable energy. The Inertial Sea Wave Energy Converter (ISWEC) is a floating device devoted to the conversion of waves kinetic energy into electric energy. This conversion is performed by exploiting the gyroscopic moment provided by a spinning rotor. An ISWEC prototype has already been deployed. The current rotor is mounted on roller bearings which are the main source of power losses due to friction and heating. This thesis is carried out in the context of replacing the mechanical bearings with active magnetic bearings with the purpose of reducing energy losses. The system is composed of 32 axial electromagnets and 4 radial electromagnets which control the rotor position and orientation. The aim of this work is to design a control algorithm for driving the electromagnets. A first rotor dynamic model of the system was determined through a set of kinematic-dynamic equations. The model was implemented and tested in Simulink. Several modes of allocating the axial forces were developed and evaluated on the basis of ohmic losses and computational load. Once the most suitable distribution was defined, the Simulink model was improved by including the actuators dynamics. The first developed control strategy consists of 5 parallel PIDs tasked with controlling the 5 degrees of freedom. Later, the control strategy was enhanced by adding a feedforward action. The two strategies were evaluated by comparing the obtained results.