A pumped storage power plant with double-fed induction machine and cascaded frequency converter

The paper presents a variable speed drive for pump-storage plant applications. A reversible turbine is energized by a double-fed induction machine (DFIM) exited on the rotor side with a cascaded frequency converter made up of M single-phase cells. The DFIM is started up as a synchronous machine by means of a CSI on the stator side and a VSI on the rotor side. An emphasis is placed on the control system aimed at the plant active and reactive power regulation. In order to balance out currents of the transformer secondary windings feeding single-phase active rectifiers, a phase disposition PWM strategy has been modified by introducing a consecutive cycling step-wise displacement of triangular wave offsets within a saw tooth period consisting of M triangle wave periods. The paper concludes by analyzing start-up responses and performance characteristics of the system in sub- and over-synchronous modes of operation.