Variable speed pumped storage units have obvious advantages in efficiency and adaptability under various operation conditions compared with traditional fixed-speed pumped storage units. Since the full-power converter is the key equipment in variable speed pumped storage units, it is of great significance to study the application of various inverter topologies in large capacity variable speed pumped storage units. Taking a 100-MW-scale variable speed pumped storage unit as an example, based on the existing devices, an evaluation index system is constructed from the aspects of cost, loss, volume, etc., and entropy method is used to weight the indexes. Four topologies are compared and analyzed in the design of the high-power variable speed pumped storage units with access voltage of 13.8 kV, including back-to-back three-level neutral point clamped (NPC) converter, back-to-back five-level stacked multicell converter (SMC), back-to-back modular multilevel converter (MMC) and modular multilevel matrix converter (M3C). The results show that the cost of back-to-back MMC is the lowest, the overall efficiency of M3C is the highest, and the occupation space of M3C is the smallest. In summary, back-to-back MMC and M3C are two preferred solutions for the full power converter of 100-MW-scale variable speed pumped storage units.