<p>Five-level converters are a mainstream choice in medium voltage high power applications, where the common mode voltage (CMV) problem should be carefully considered. Even though many studies have been carried out to reduce CMV, they mainly focus on the CMV problem under high switching frequency (SF) modulation or for two- and three-level converters. However, the CMV problem becomes very tricky under low SF modulation like selective harmonic elimination pulse width modulation (SHE-PWM), since there is a lack of control degrees of freedom to regulate the switching angles after the constraint equations have been calculated. Thus, an optimal PWM strategy with CMV reduction is proposed for five-level converters in this paper. First, the effects on the distribution characteristics of switching angles and the corresponding CMV are analyzed by actively adjusting the amplitude of the 3rd harmonic. Then, the optimal 3rd harmonic with CMV reduction capability is determined by taking the solvability range, the continuity of the switching angles, and the CMV as indicators. Finally, a modified constraint equation is constructed based on the optimal 3rd harmonic. Thus, the CMV is effectively reduced under optimal PWM, which is verified by experimental results.</p>