The present paper investigates the complete regulation strategy for a large double-fed asynchronous motor-generator equipped with a 3-level VSI cascade for applications mainly in the field of pumped storage plant. For the present application, the specific problem of the DC link capacitors voltage balancing is investigated. Also a sensorless method for the determination of the rotor angle is proposed and verified in practice. Measurements of the system performed on a laboratory low power system are discussed and compared to simulations.