Suppression method of neutral point potential fluctuation for threelevel NPC inverter based on SHEPWM
                                               ZHOU You, HU Yaowei, CHENG Jingling, CHEN Guozhu
                                     (College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China)

Abstract: Aiming at the neutral point potential fluctuation of threelevel NPC inverter based on traditional selective harmonic elimination pulse width modulation (SHEPWM), the influence of the fundamental and 3order harmonic on the neutral point potential fluctuation was analyzed, the relationship between the neutral point potential and 3order harmonic content was established, an improved SHEPWM method based on the 3order harmonic quantitative control was presented, the solving equation of SHEPWM switching angle was reconstructed by introducing the controlling equation of 3order harmonic, and on the basis of this, the optimal 3order harmonic content was deduced for the purpose of maximally suppressing the neutral point potential fluctuation. The gridconnected 2 MW/3 kV inverter model was built on the Matlab / Simulink platform, and the voltage fluctuation suppression effect of the improved SHEPWM method was tested. The results indicate that the improved SHEPWM method based on the 3order harmonic optimal content control can effectively suppress the low frequency fluctuation of the neutral point potential, which is significant to improve the output performance and to reduce the DClink capacitance of threelevel NPC inverter.

Key words: selective harmonic elimination pulse width modulation (SHEPWM); neutral point potential fluctuation; threelevel NPC converter; 3order harmonic