Maximizing Output Voltage of Three-Phase Nine-Leg Multilevel STATCOM by Minimum Infinity Norm Optimization

Power converters based on classic three-phase three-leg voltage source inverters (VSIs) that provide a multilevel output voltage are an interesting alternative to multilevel converters that suffer from complexity and higher costs. However, the multiple degrees of freedom of these systems pose a challenge to their optimal control. In this article, the minimum infinity norm algorithm is proposed and implemented for triple three-leg VSI static synchronous compensators (STATCOM) connected to a three-phase power grid. It is shown that the method provides optimal utilization of the dc-link voltage and allows to increase the output voltage by 39% compared to the minimum <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\boldsymbol{l}_{\mathbf{2}}$</tex-math></inline-formula> norm method and by 16% compared to the phase-disposition pulse width modulation (PD-PWM) while keeping total harmonic distortion (THD) below 0.5%. In addition, the algorithm has been optimized for real-time systems, resulting in a very fast algorithm with a worst-case complexity of 39 scalar–scalar multiplications and no division.