Multi-level space-vector PWM algorithm for seven-phase open-end winding drives

Open-end winding variable speed drives with dual-inverter supply have been extensively investigated for various applications in the past, based on a three-phase machine configuration. This topology is relatively simple for practical realisation. It offers a higher number of switching states without the need for capacitor voltage balancing algorithms, when compared to the equivalent standard multi-level converter in single-sided supply mode. The extension of the idea to multi-phase machines is however not straightforward. The main reason is that inclusion of a multi-phase machine leads to exponential increase in the number of possible switching states, so that the design of a suitable space vector modulator (SVM) represents a considerable challenge. This paper considers for the first time a seven-phase open-end winding topology. A relatively simple SVM algorithm, based on already developed seven-phase two-level drive SVM method, is used for operation of both inverters. The proposed modulation technique is straightforward to implement and is capable of generating pure sinusoidal output voltages, without any low-order harmonic components. The method generates up to 25-level load phase voltage and therefore offers superior harmonic performance when compared to the two-level seven-phase topology in single-sided supply mode. The developed scheme is verified by simulation, using a seven-phase induction machine operated under V/f control.