A superconducting magnetic levitation system for high speed and mass transportation is being developed in Japan. Various types of running tests have already been carried out on the Yamanashi Maglev Test Line. We developed a large capacity Pulse Width Modulation (PWM) inverter as a power conversion system to drive a Linear Synchronous Motor (LSM). To reduce the capacity of power conversion system, we installed a neutral point bias control system in the inverter for driving the LSM at the Yamanashi Maglev Test Line. This paper describes its test results.