This paper introduces a method for three-level inverter operating at low switching frequency and presents a novel current harmonic optimum pulsewidth modulation strategy. Combining the selected harmonic elimination PWM (SHEPWM) with the current harmonic minimum PWM (CHMPWM), the switching angles can not only eliminate the selected harmonic but also reduce the current harmonic. The three-level inverter output voltage is analyzed using fourier series and the expression of the total harmonic current distortion(THD
) rate is calculated. The THD
is regarded as the objective function, with the voltage fundamental amplitude is equal to the reference voltage amplitude and the other harmonic amplitude is zero as nonlinear constraints. Then the switching angle is solved by calculating the THD
. After researching its basic principle and the solution of the switching angle, results of the switching angle at 280Hz switching frequency are verified by using MATLAB software.