Permanent magnet synchronous motor for passenger ship propulsion

A special permanent magnet synchronous motor for ship propulsion in the power range between 50 and 250 kW is presented. It is fed by a PWM-voltage source inverter with field oriented control. A motor feature is the very low stator inductance. It leads to low reactive power and high maximum torque, but on the other hand it produces large current ripples and therefore harmonic losses up to 10 % of the electrical input power. Two methods are investigated to reduce the stator current ripples and therefore the harmonic power content. The first method is the increase of the inverter switching frequency. An increase from 4 kHz to 9 kHz reduces the harmonic power content from 6,3 % to 1,5 %. A more simple way is a three-phase inverter output inductance. An inductance of 0,1 mH also reduces the harmonic power content to 1,5 %.