Construction method of Fourier equation for three-level selected harmonic elimination pulse width modulation

The invention belongs to the field of variable frequency modulation of alternating current inverters. In order to ensure that selected harmonic elimination pulse width modulation achieves an expected harmonic elimination effect, the technical scheme adopted by the invention is that a construction method of a Fourier equation for three-level selected harmonic elimination pulse width modulation comprises the following steps: 1, deriving a midpoint voltage fluctuation equation and carrying out quantitative analysis on voltages at the two ends of a support capacitor; 2, through analyzing a midpoint voltage expression, knowing and controlling a moderate amount of triple frequency harmonic waves contained in output phase voltage to restrain midpoint voltage fluctuation; 3, reconstructing the Fourier equation as shown in the specification; Udc is direct current side voltage; N is the number of switch angles within 1/4 period; g=2,4,6,8,10; ak is an unknown switch angle. The construction method is mainly used for the variable frequency modulation of the alternating current inverters.