中文摘要：

三电平中点钳位(3 L-NPC)半桥拓扑输入端为电容串联结构，由于电路的非理想因素，存在电容电压不均衡问题。文中根据推导出的3 L-NPC半桥等效电路，从时域角度详细分析了电容压差与电容电流的关系，表明3 L-NPC具有自平衡特性，且其自平衡电流主要来自于负载电流的直流分量。基于此总结出2类均压控制策略：第1类，采用传统比例-积分或比例-谐振等调节器，加入特定变量反馈，以恢复3 L-NPC 自平衡特性；第2类，采用不破坏3 L-NPC 自平衡特性的调节器。根据第2类均压控制思想，提出了采用准谐振调节器的均压控制策略，可简化系统控制，降低系统成本。此外还给出了具备自平衡特性的双环控制方案，改善了系统的响应速度。仿真与实验结果证明了理论分析的正确性。

英文摘要：

The input terminal of three-level neutral point clamped(3L-NPC)topology is a structure of series capacitors.Owing to non-ideal factors in the circuit,there exists the problem of capacitor voltage unbalance.Based on the equivalent circuit of the 3L-NPC derived,the relation between the capacitor voltage difference and the capacitor current is analyzed in detail. Theoretical analysis indicates that 3L-NPC possesses the feature of capacitor voltage natural balance,whose natural balance current mainly depends on the direct current(DC)component of the output current.Two types of the voltage balance control strategy are proposed based on the analysis:type one,that capacitor voltage difference feed-forward or DC component of modulation wave feedback is utilized with the proportion-integration (PI) regulator or proportion-resonant (PR) regulator to ensure the natural balance;type two,particular regulators are employed without damaging the natural balance.Based on type two,the quasi-resonant regulator is proposed which can balance the capacitor voltage and simplify the system control at low cost.Moreover,in order to improve the dynamic response performance,a double-loop control scheme is proposed.The theoretical analysis is verified by both simulation and experimental results.