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In case of high-speed maglev trains, the propulsion force of their linear synchronous motor (LSM) is an essential performance element since the LSM is responsible for both the propulsion and levitation of the train. A large thrust force ripple causes vibration, noise and severe levitation disturbance during the train operation. Because of these reasons, efforts must be made to reduce the thrust ripple of the LSM for propulsion and levitation. In this study, a method to decrease the thrust force ripple that causes the noise, vibration, and levitation disturbance generated during the high-speed operation of the 700 km/h ultra-high-speed tube train's LSM was investigated. In this method, the module phase set shift (MPSS) was applied. If the MPSS method is applied, the position of each field magnet module of the LSM changes as much as MPSS value relative to the reference load angle. To precisely calculate the total thrust force that occurs due to the position changes, thrust force mapping (TFM) method was applied to each field magnet module, and the generated total thrust force of the LSM were accurately obtained. Through this study, a method of reducing the thrust force ripple without considerable reduction of the LSM's average thrust force was presented.