Associating PWM and balancing techniques for performance improvement of flying capacitor inverter

This paper aims at the reduction of the harmonic content in sinusoidal signals synthesized from flying capacitor multilevel inverters for AC electrical drive systems. In this sense, three distinct voltage-balancing techniques and pulse width modulation methods are jointly investigated. Among voltage-balancing techniques, a new method including restrictions of switching under charging/discharging and maximum current in the flying capacitors is presented. The strategies are analysed in a three-level inverter controlled by space-vector and carrier-based pulse width modulation (PWM). Regarding the carrier-wave strategy, specifically level shifted - phase disposition modulation (LSPWM - PDPWM), the authors propose a redundant switching states controller that enables the application of this technique to the flying capacitor topologies including an appropriate portion of the third harmonic component for greater utilization of the DC voltage bus. All techniques were validated using MatLab simulations and, in the SVPWM case, experimentally too. The results obtained have been comproved the main desired characteristics, namely output voltages and currents with low harmonic content, low computational complexity and ease of digital implementation.