Multilevel inverter for low inductance permanent magnet synchronous motor

For ship propulsion a special permanent magnet synchronous motor with 46 kW rated power is constructed. The motor has a very low stator inductance. By feeding with a two-level PWM voltage source inverter large current ripples and therefore harmonic power losses up to 10 % of the electrical input power are produced. For this application a neutral-point-clamped three-level inverter is investigated. Without increasing the switching frequency the harmonic power content can be reduced by 5 %. Moreover, the three-level inverter can be equipped with 600 V-IGBT with lower conduction and switching losses. A detailed analysis shows the reduction of power semiconductor losses by 40 % compared to a two-level inverter.