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Three-level neutral-point clamped (NPC) active-front-end three-phase (3LAFE) converters can be applied to high-power medium voltage applications, with four-quadrant unity-power-factor operation, allowing a broad range for power conversion systems, such as decentralized energy distribution and utilization. Switching losses and network interaction limit the operation of 3LAFE high-power converters, especially when GTO-converters are used. This is why low switching frequency and reduced harmonic distortion are the main goals when using optimum pattern pulsewidth modulation (PWM) where the selective harmonic elimination modulation method (SHEPWM) is used. This paper introduces a simple strategy to choose a good operating point for two 3LAFE converters in a 12-pulse configuration based on the behavior of noneliminated harmonics by SHE method. This strategy allows accomplishing the meeting of the IEEE Std. 519-92 and jointly, the minimization or elimination of harmonics filters. A complete characterization is given as a base of SHE method and for noneliminated harmonics behavior, as well as the full explanation of the optimization strategy. Experimental results show the strategy effectiveness for reducing harmonic distortion and meeting IEEE Std. 519-92.