Modified DC-bus voltage balancing algorithm based three-level neutral point clamped PMSM drive with low power factor

A modified DC-link voltage balancing scheme is proposed, which keeps the two DC-link capacitor voltage differences at a desired level for wider load variation and for low power factor. Moreover, the proposed control strategy uses a reduced number of switching sequences compared to conventional DC-link voltage balancing strategy, which helps to reduce the switching losses. Effects of low power factor on the DC-link voltage balancing is also studied and a numerical expression is derived for an optimum power factor angle, above which conventional balancing strategies results in capacitor voltage difference. Detailed simulation studies are carried out in Matlab/Simulink with a 6.0 kW surface permanent magnet synchronous machine (SPMSM) used for electric vehicle propulsion applications. Experimental studies are also carried out with a 6.0 kW SPMSM drive. Both the simulation and experimental results show the effectiveness of the proposed system.