Fractal-based low computation space phasor generation scheme for a four-level inverter using an open-end winding induction motor

Abstract

In this study, a space vector-based pulse width modulation scheme for an inverter with even number of levels is proposed. An approach based on fractal theory which utilises the self-similarity of the triangular sectors is employed in the present work, to find the sector and the inverter switching vectors. The space vector locations and associated computations are performed in a 60° coordinate system. Representation in a 60° framework avoids fractional arithmetic, thereby reducing computational complexity compared with the methods based on a Cartesian coordinate system. The duration of the switching vectors is determined after mapping the instantaneous reference space vector to an equivalent two-level inverter. The scheme is experimentally verified by using a four-level inverter configuration. four-level inversion is achieved with a dual inverter fed induction motor in the open-end winding configuration. The individual inverters are supplied with asymmetric DC link voltages. The switching vectors for the two inverters are automatically generated without using look-up tables. The scheme is implemented and tested with a 2-HP open-end winding induction motor drive.