This paper presents analysis on determiniton of optimum reference signal for natural sampled pulse width modulation (PWM) technique applied in three phase three level diode clamped dc/ac power converter structure. Using Fourier analysis method, analytical expression of the mean square value of converter line-to-line output current harmonics is derived. Next, a signal that must be injected to the original sinusoidal reference to minimize this converter output current harmonics is determined. Minimization method shows that the optimum injected signal is one fourth of the third harmonic to that for conventional three phase two level dc/ac power converter structure