A carrier-based PWM strategy providing neutral-point voltage oscillation elimination for multi-phase neutral point clamped 3-level inverter

Abstract

General pulse width modulation (PWM) model for multi-phase neutral point (NP) clamped (NPC) 3-level inverter (3LI) is described. A novel PWM strategy for N -phase NPC 3LI with unconditional NP voltage balance is proposed as well as its carrier-based realization, in which PWM sequences are generated by comparing a single carrier wave with double modulation waves. The proposed PWM strategy is consistent with the principle of virtual space vector PWM (VSVPWM). However, the mechanism of NP voltage balance under the proposed PWM strategy is based on precisely calculating and executing level 1 action time of each phase, which may be influenced by some non-ideal factors. To avoid that, an active NP voltage control for the proposed PWM strategy is put forward. Then 3-phase and 5-phase NPC 3LIs are built as examples to verify the correctness of the proposed PWM strategy. Finally, the experimental results indicate that the proposed PWM strategy has better NP voltage control abilities.