PWM Algorithms for Multilevel Inverter Supplied Multiphase Variable-Speed Drives

Multiphase variable speed drives are nowadays regarded as serious contenders for various applications, due to the certain advantages that they possess when compared to threephase drives. On the other hand, the multilevel (predominantly three-level) voltage source inverter (VSI) has become an industrially accepted technology for medium-voltage three-phase drives. The logical next step is to integrate multilevel VSI and multiphase drive technologies, since benefits of each can then be combined. This paper will review recent advances in this area. Two different topologies of the multiphase supply will be considered and the emphasis will be placed on appropriate pulse width modulation (PWM) techniques that can be used in conjunction with the supply structure. The first topology utilises multilevel (three-level) VSI and the machine’s stator multiphase winding is star-connected with an isolated neutral point. In the second topology the winding is left open-ended and each side of the winding is connected to an isolated two-level VSI. This topology can also achieve three-level operation. Carrier-based and space vector based PWM strategies are considered and the obtainable performance is illustrated using experimental results.