Various modulation schemes have already been developed for conventional three‐phase buck‐type converters such as sinusoidal pulse‐width modulation and space vector modulation (SVM). However, SVM is not applicable to boost‐type converters. This study proposes a new concept on sinusoidal modulation for both buck and boost‐type three‐phase DC–AC converters. A novel optimised modulation technique is introduced by using basic equations of conventional buck and boost. By solving the optimisation problem, pulse widths will be obtained for a given modulation index. The significant point is that the optimisation problem should not be solved for every modulation index because the answer of the optimisation problem obeys a certain pattern. Also, this method has a positive effect on reducing losses, especially in boost‐converters. Analysis and simulations are first introduced for three‐phase boost‐converters, and then is extended to a buck converter. Furthermore, practical verification takes place on two implemented 1 kVA boost and buck‐converters in order to confirm the proposed technique as well as theoretical analysis and simulations. The experiments and simulations both verify the suggested optimised modulation technique.