In this paper, a new application of optimal servomechanism (OSM) controller is explained and applied to the sine-wave pulse width modulation (PWM) converters. It is desired to find an optimal fixed structure controller (OFSC) in an ac PWM converter for online exact asymptotic output regulation and current and voltage harmonics elimination. Straightforward design method for controller, optimal dynamic performances, dynamical input and output harmonics elimination, and output regulation are occurred by simple optimal fixed structure controllers. The proposed method is applied to an ac PWM three-phase converter. Various simulation results illustrate that the OFSC has good dynamical performances and robustness properties.