Comparative research of harmonic suppression algorithm of the three-level NPC converter
The three-level NPC converter is an effective solution to medium-voltage and high-power electronic converters. Modulation strategy is one of research focus of the three-level NPC converter. There are many modulation strategies of the three-level NPC converter, among them, selective harmonic elimination PWM (SHEPWM) and selective harmonic mitigation PWM (SHMPWM) strategies are very useful technologies since they have the characteristics of low harmonics elimination or reduction. Nevertheless, the SHEPWM and the SHMPWM strategies have the disadvantages in solving non-linear transcendental equations. Here, non-linear transcendental equations solution of the SHEPWM and SHMPWM strategies are researched and compared. First, the homotopy algorithm is applied to the SHEPWM strategy. In the solution process, the initial value is obtained by the gravity centre coincidence method, and the numerical solution obtained by the homotopy algorithm is solved by the Newton iteration method to obtain the true solution. Second, the non-linear transcendental equations of the SHMPWM technique are established and optimised. Finally, simulation models of the three-level NPC converter using SPWM, SHEPWM, and SHMPWM strategies are built in MATLAB. The comparison and analysis of the three strategies are carried out to verify the effectiveness and superiority of SHEPWM and SHMPWM algorithms in harmonic suppression.
