Capacitor Voltage Balancing Strategy of NPC Three-level Dual-active Bridge Converter Based on Redundant Vector

Abstract

The neutral point clamped (NPC) three-level dual-active bridge (DAB) converter can be applied at higher voltage levels and in a wider operating range than the traditional DAB converter, and therefore it is more promising in future applications. However, the NPC DAB converter suffers from unbalanced capacitor voltage, which affects the operating characteristics. This paper analyzes the power transmission characteristics of the NPC DAB converter in the three-degree-of-freedom (3-DOF) control strategy, based on which power transmission can be effectively controlled. For the capacitor voltage imbalance problem, a capacitor voltage balancing strategy based on redundant vector is proposed. Compared to the traditional capacitor voltage balancing strategy, the proposed strategy can achieve faster capacitor voltage balance without affecting the transmission power. The proposed strategy was verified by simulation that it can well maintain the capacitor voltage at a balanced state for the converter subject to changes in the output voltage reference value, i.e. the capacitor voltage balancing can be realized within 0.000 4 s under the transient condition of only 1% fluctuation.

Keywords

• neutral point clamped (npc)
• dual-active bridge (dab) converter
• capacitor voltage balancing
• redundant vector
• power transmission characteristics