Overmodulation Techniques of Asymmetrical Six-Phase Machine With Optimum Harmonic Voltage Injection

Abstract

Overmodulation techniques of asymmetrical six-phase machine achieve higher dc-bus utilization by applying voltage in the nonenergy transfer plane. This results into unwanted current and associated copper loss. Existing overmodulation technique minimizes this voltage from space-vector perspective with predefined set of four active vectors. To find the best technique, one needs to perform the above minimization problem with all possible sets of active vectors with which higher voltage gain can be attained. Therefore, this requires evaluation of large number of cases. This article formulates the above minimization problem in terms of average voltage vectors of two three-phase inverters, where active vectors need not to be specified beforehand and, thus, the analysis is more general. Sixteen possible techniques with different set of active vectors are derived following the above analysis, which attain minimum voltage injection in the nonenergy transfer plane. This article also identifies one of these 16 techniques, which can be implemented without involving complex six-dimensional transformation. The above technique is validated through experiments on six-phase induction motor and simulations in MATLAB at 3.5-kW power level.