Performance Evaluation and Improvement of Symmetrical Six-Phase Drives Under Two Open Legs With Star and Hexagon Connections

It has recently been shown that, in symmetrical six-phase drives under an open converter leg (OCL), hexagon connection yields smaller stator copper loss (SCL) for given torque, and much larger maximum achievable torque (MAT), than star. The superiority of hexagon is even greater when compared with two deltas or stars. However, for hexagon only the case of a single OCL was studied. This paper addresses the postfault performance of symmetrical six-phase drives under two OCLs, for star and hexagon connections. It is proved that hexagon is also preferable over star for two OCLs (in some conditions with even greater advantage than for one OCL), and that the MAT and SCL are the best when there is a healthy leg between both OCLs. In view of the latter, a method is proposed to improve the performance by altering the connection between the converter and machine terminals. Experimental results are provided.