Research on Three-level SPWM and SVPWM modulation algorithms and their midpoint voltage control

Based on the mathematical structure of NPC converter, this paper analyzes two modulation algorithms commonly used in three-level converters: SPWM modulation algorithm and SVPWM modulation algorithm. It uses a midpoint potential fluctuation suppression method and compares the effects of the two modulation algorithms. The fluctuation of midpoint potential is a common problem in NPC converters. The article analyzes the principle of midpoint potential fluctuation for the two modulation algorithms. SPWM controls the midpoint voltage fluctuation according to the control period and SVPWM suppresses the midpoint voltage fluctuation by adjusting the positive and negative small vector action time. The simulation verifies that SVPWM performs better than SPWM and the fluctuation becomes smaller after adding midpoint voltage control.