Abstract: The power-off protection mechanism of the maglev system is particularly important in the field of aerospace.When a high speed running magnetic bearing disengages from active control due to a sudden power-off, the permanent magnet synchro-nous machine (PMSM) in the levitation system must immediately switch to an energy feedback power supply mode to main-tain levitation stability. This process, however, induces transient inrush currents far exceeding rated values through electro-magnetic coupling, leading to risks such as power device breakdown and motor winding insulation damage. To suppress the inrush current, The paper proposes an inrush current suppression strategy based on feeding voltage trajectory planning. By establishing a feeding mathematical model of PMSM driven by a neutral point clamped (NPC) converter, the mechanism of inrush-current generation is analyzed, and a segmented given voltage method based on trajectory planning is designed. Ex-perimental results confirm that the proposed strategy achieves 42% and 47% reductions in no-load and loaded inrush currents within a controllable switching time. Compared with conventional “ramp”- and “S”-curves trajectory planning strategy, the proposed segmented given method based on trajectory planning achieves a better balance between the target voltage response speed and inrush current magnitude suppression, which are the two constraints of each other.

Key words: Permanent Magnet Synchronous Motor, Three-level Converter, Operation Mode Switching, Inrush Current, power-off energy feedback