Implementation on a microcontroller of a space vector modulation technique for NPC inverters

The recent improvements in semiconductor technology made rather interesting the employment of the new high current-high voltage IGBTs in the inverters used in traction drives. At first, their utilization was limited to the drives for trams or regional trains, but now they are also becoming attractive for high-speed traction locomotives. For these applications, however, neutral point clamped (NPC) inverters must be used, to reduce the maximum drop voltage on the IGBTs. Authors have already been analyzed the problems connected to the development of modulation techniques useful for NPC inverter and, in a recent paper, they presented a first proposal of an interesting space vector modulation technique based on a six hexagons subdivision of the three-phase plane. The proposed technique preserves the advantages of the SVM used in traditional two-level inverters: to this aim, all the commutations can happen only between adjacent states so that, during each modulation interval, only three commutations occur. In present paper, the proposed approach is further improved, taking into consideration the problems connected to the movement from a hexagon to the next one, in such a way to preserve the previously mentioned adjacencies. Finally, the paper describes the procedure used for implementing the modulation procedure on a modern microcontroller.