Publisher Copyright: © 2022 IEEE.

Low switching frequency modulation techniques such as Selective Harmonic Elimination - Pulse Width Modulation (SHE-PWM) or Optimal Pulse Pattern (OPP) are commonly used in medium voltage - high power multilevel converters to improve their efficiency. These techniques require solving non-linear equations in order to calculate the firing angles. These equations can be solved by meta-heuristic optimization algorithms, which depend on a set of hyperparameters that must be properly adjusted to ensure their effectiveness. This paper presents a methodology to tune different meta-heuristic algorithms to fairly compare them and select the best algorithm to solve SHE-PWM/OPP formulation. The methodology is applied considering different meta-heuristic algorithms such as genetic algorithm, differential evolution, harmony search and simulated annealing. It has been validated in SHE-PWM and OPP techniques with different number of firing angles.

Medium-voltage high-power converters are usually modulated using low switching frequency techniques such as Selective Harmonic Elimination - Pulse Width Modulation (SHE-PWM) in order to improve their efficiency. To calculate the firing angles, SHE-PWM transcendental equations are usually solved by offline calculation methods, whose computational burden depends on the number of firing angles or eliminated harmonics and the required accuracy in the solutions. Consequently, with the aim of reducing this computational burden, this paper presents an analysis that estimates the maximum accuracy required in the calculated SHE-PWM solutions considering the main non-idealities of the converter. In this sense, a systematic methodology to evaluate the error in the harmonic amplitudes due to control and dead time effects has been developed, providing an optimal error tolerance for the calculation methods that solve the SHE-PWM problem.

Selective harmonic elimination (SHE) - pulse with modulation (PWM), when applied to multilevel converters (MCs), can be optimized in case a half-wave (HW) symmetry is implemented. This kind of symmetry is able to provide a wide variety of solutions. This paper proposes a novel method, based on optimization algorithms, which provides a universal formulation of the SHE-PWM problem with HW symmetry, in such a way that different equation systems are not required to find a solution when different switching patterns are considered. In this way, the proposed technique is able to search simultaneously both the switching patterns and their associated firing angles that solve the SHE-PWM problem, without using predefined waveforms. Therefore, the search process is significantly simplified and the flexibility to find solutions with different waveforms, throughout the reference modulation index, ma, range, is increased. Different sets of solutions provided by this method have been presented and simulation results, obtained from a five-level modular multilevel converter (MMC), have proved the validity of the new proposed technique.