Start-up and synchronization of a variable speed pump-turbine unit in pumping mode

This paper presents the start-up and synchronization procedures of a variable-speed pump-turbine unit of 250 MW in pumping mode. These procedures applied to a doubly-fed induction motor-generator with three-level voltage source inverters VSI cascade in the rotor side, can be achieved without any supplementary equipment. The control strategy used in the start-up procedure and based on a stator flux oriented control, is described in details as well as different steps in order to reach the minimal speed required for synchronization. The controls of the amplitude, frequency and phase of the stator voltage related to the synchronization procedure are presented. Simulated results confirm the validity of the proposed approach.