This paper presents an analysis of the synchronization process of the high-power, two-speed synchronous motor out of over synchronous speed. A method of increasing the effectiveness of synchronization by applying a change system of polarization of the field circuit supply DC voltage is proposed. The process of synchronization from the stator supply voltage is also analyzed. The influence of the periodic reduction value of the supply voltages on the synchronization processes was also investigated. The proposed synchronization method can be applied during the synchronization processes of line start permanent magnet synchronous motors with a two-stage start-up.