Effective Utilization of Parallel Connected Megawatt Three-Level Back-to-Back Power Converters in Variable Speed Pumped Storage Units

Three level neutral-point-clamped (3L-NPC) megawatt back-to-back power converters configuration is desirable in large variable speed pumped storage power units (VSPSPU). For such configurations, reliability and efficiency are prominent. This paper proposes a methodology for effective utilization of parallel-connected back-to-back power converters for a 250 MW VSPSPU. The control strategy for active and reactive powers during part load operation in VSPSPU are formulated. This paper also focuses on converter losses at wide variation in power delivery. The proposed system and its control strategy decrease the losses in power converters and increase the annual power generation of the system. The effectiveness of proposed method is explained on a real-scale of 250 MW Doubly fed induction machine (DFIM) and validated a downscaled 2.2 kW DFIM laboratory prototype.