对二极管箝位型三电平逆变器的中点电位偏移与中点电位波动问题进行了研究． 通过对电压矢量与中点电位关系的分析，建立了系统在无差拍控制下的数学模型． 在无差拍控制下，结合虚拟矢量调制，经综合判断，对中点电位进行调节． 仿真与实验结果表明:与传统方法相比，该方法可以缩短消除中点偏移所需的时间，调节中点电位的能力不受调制度大小的影响，同时该方法可以消除低频的中点电位震荡．

In this paper an exploration is performed into midpoint potential migration of NPC three-level inverter and the midpoint potential fluctuation． On the basis of the analysis of the voltage vectors and the midpoint potential，a mathematical model is constructed under the deadbeat control framework． In order to keep the ability to fix the drifted midpoint potential，the virtual voltage vector method is employed． In the proposed algorithm，the vectors applied to modify the midpoint potential are evaluated accordingly． Compared with the conventional algorithm，the time needed to fix the midpoint potential is decreased in this proposed algorithm，and the ability to fix the midpoint potential is in-sensitive to the modulation index． Moreover，the proposed algorithm can eliminate the oscillation of the midpoint po-tential． The validity of the proposed algorithm is verified by the simulation and experiments．