This paper deals with a fixed-frequency variable-speed motor/generator with 3-level VSI (Voltage Source Inverter) cascade. The 3-level VSI is applied to a DASM (Doubly-fed ASynchronous Machine) for large pump storage plants. The extension to 3 levels is the original part of this paper. The whole system behavior has been simulated using the “SIMSEN” simulation software. This paper focuses on the simulation results and also on the comparison with the 12-pulse cyclo-converter topology.