Evaluation and Comparison between Multilevel Converters for Variable Speed Operation of Pumped Storage Power Plants with Full-size Converters

This paper compares the full-size converter topologies for the converter fed synchronous machines which can enable the fixed speed pumped storage power plant to variable speed operation. Three converter topologies: Neutral Point Clamped (NPC), Active NPC and Modular Multilevel Converter (MMC) topologies have been selected as suitable solution for this application. The characteristics of these topologies have been evaluated based on the startup torque required in pump mode, flexibility in fast transition from generating to pumping mode, number of semiconductor and passive components required and the efficiency of the converter. The review of the topologies shows that MMC can provide startup torque of about 35% whereas ANPC can yield about 60% of rated torque.