Stabilization of Passive Self-Bearing Motor Through D-axis Current Injection

Robert, Adrien [UCL] Van Verdeghem, Joachim [UCL] Dehez, Bruno [UCL]

Self-bearing machines use rotor magnetic levitation to suppress friction and reach high rotation speeds. Recent studies have proposed the integration of electrodynamic suspension in these machines in order to achieve fully passive levitation, improving their compactness and reliability. However, the latter do not take into account the impact that ferromagnetic materials can have on the dynamic behaviour of these machines, through the generation of axial and angular dependence of the winding inductance coefficients. In this context, this paper presents an electromechanical model which describes the dynamics of an electrodynamic thrust self-bearing machine, taking into account the reluctant force and torque arising from the variation of the inductance coefficients. Based on the latter, quasi-static expressions of the current and the electomagnetic force are first derived and analyzed. It is then applied to a case study to highlight the impact of these additional force components on the rotor axial and angular dynamics, and shows that d-axis current injection can significantly improve the suspension force.