Generation of 24-Sided Polygonal Voltage Space Vector Structure with Reduced Hardware Complexity for Induction Motor Drives

This paper presents new scheme with reduced hardware complexity for generation of a 24-sided polygonal voltage space vector structure in induction motor drives with open-end stator windings. For variable speed operation of drives, pulse width modulation (PWM) technique such as voltage space vector PWM is used. Conventional hexagonal voltage space vector PWM produces low order harmonics in the inverter output voltages when operated in the over-modulation region. These low order harmonics produce torque pulsations in the motor in addition to the increase in losses. 24-sided polygonal voltage space vector based switching scheme eliminates (or highly suppresses) low order harmonics in over-modulation operation as well as increases the linear modulation range. However, the hardware requirement for generation of 24-sided voltage space vector structure is substantially higher compared to that of hexagonal voltage space vector structure. The virtual vector based scheme proposed in this paper can generate 24-sided polygonal voltage space vector structure in a dual inverter fed open-end winding induction motor with a single DC source with substantial reduction in the hardware requirement. The switching scheme eliminates common mode voltage from motor windings thereby preventing circulation of common mode current even when both inverters share a common DC link. Extensive simulation studies were carried out to validate the proposed schemes. It is then experimentally verified on a laboratory prototype using TMS320F28069M digital signal controller for implementation of the control scheme.