Neutral-point Balance Control Strategy of Three-level NPC Inverter Based on Proportional Resonant Algorithm

To solve the inherent neutral-point voltage fluctuation problem of neutral-point clamped three-level inverter (NPC), a neutral-point voltage balance control strategy based on Proportional Resonant (PR) algorithm is proposed. Firstly, the topology and Space Vector Pulse Width Modulation (SVPWM) of NPC three-level inverter are introduced briefly. Secondly, the influence of space vector on neutral-point voltage is analyzed in detail. Then, according to the negative relationship between the positive and negative small vectors on the neutral-point voltage, the DC side neutral-point voltage deviation is introduced into the PR closed-loop control, and the action time of the positive and negative small vectors is dynamically adjusted. This method effectively reduces the neutral-point voltage fluctuation and at the same time reduces the harmonic distortion rate of the output voltage. Finally, the feasibility and effectiveness of the proposed method are verified by simulation.