Abstract: In high-power traction drive systems, owing to the limit on switching losses and cooling conditions, the maximum value of switching frequency cannot be very high. Under such circumstances, we usually adopt multi-mode modulation strategies. The authors summarized the rules of space-vector-based generation of synchronized three-phase PWM waveforms with half-wave, quarter-wave and three-phase symmetries, and introduced five synchronized SVPWM strategies satisfying all the symmetries. On the base of analyzing five strategies, one complete set of multi-mode SVPWM modulation strategy is developed, which is suitable for the conditions of low switching frequency in high-power traction drive systems. At the same time, the rules for transitions between different modulation modes are proposed. Simulation and experiential results verify the validity and effectiveness of the proposed strategies and also realize the smooth transition between different modulation modes.