Space Vector Pulse Density Modulation Scheme for Zero Sequence Voltage Elimination in Dual Inverter fed Open End Winding Induction Motor Drive

Existence of zero sequence voltage induces flow of bearing current, causing motor bearing failure, motor winding insulation breakdown and electromagnetic interference in induction motor drive. A space vector based pulse density modulation scheme to eliminate zero sequence voltage in an induction motor drive is presented in this paper. The scheme operates by switching only those vectors of five level inverter which do not generate zero sequence voltage, resulting in a 300 tilted three level space vector diagram. In the proposed work, sub-hexagon containing the reference vector is mapped to inner three level vector space. The mapped reference vector is vector quantized in the sigma delta modulator to obtain switching vectors of inner three level sub-hexagon. Actual switching vectors are calculated by the process of reverse mapping. Proposed scheme operates efficiently in both linear as well as over-modulation region. The scheme includes additional benefits such as absence of minimum pulse width problem, non requirement of complex duty ratio calculations and better harmonic performance, which pertains to space vector based pulse density modulation. The scheme is experimentally verified with 5 HP dual inverter fed open end winding induction motor drive and the results obtained validates the scheme.