Comparison Between A Three Level Inverter Synchronous Reluctance Machine and A Permanent Magnet Assisted Synchronous Reluctance Machine Drives

This paper is concerned with the use of a three level neutral point clamped (3L-NPC) inverter for a permanent magnet assisted synchronous reluctance machine (PMaSynRM). A comparison is conducted between a 3L-NPC inverter SynRM and PMaSynRM drives. The SynRM suffers from a poor power factor. Poor power factor translates to the need for a bigger inverter, moreover increases the challenge of balacing the two dc link capacitors of the three level 3L-NPC inverter. Using permanent magnets to assist the SynRM improves the power factor of the electric machine. This results in reduced burden of the 3L-NPC inverter dc link capacitors balancing algorithm. The inverter size can also be reduced to suit the size of the electrical machine. The three level inverter SynRM drive produced lower torque ripple of 0.7% as compared to the PMaSynRM drive. However the three level inverter PMaSynRM drive had a higher Root Mean Square (RMS) voltage for the same dc link voltage as compared to that of the SynRM drive. This would result in higher machine speed achieved as compared to the SynRM drive and ultimately higher constant power speed range which is desirable for traction applications. The neutral point voltage ripple between two drives was relatively the same with only a difference of 0.3%.