In high voltage and high power applications, the neutral-point-clamped (NPC) three-level inverter is a widely used multi-level inverter. However, this type of inverter has neutral-point voltage fluctuations and common-mode voltage problems. To solve these two problems, this paper proposes an improved nearest three virtual vectors (NTV2) modulation. The zero vector, middle vector and large vector are used to redefine the virtual small vector and virtual middle vector. As a result, the maximum common-mode voltage generated by the virtual vector is Udc/6, which is 1/2 of the common-mode voltage generated by the traditional virtual vector. On this basis, it is possible to suppress the fluctuation of the midpoint voltage within a certain range by selecting the values of the distribution coefficient of virtual middle vector reasonably. Compared with the traditional nearest three virtual vectors method, the proposed method can effectively suppress the common-mode voltage and the neutral-point voltage fluctuations. The results of simulation and experiment show that the proposed method is correct and effective.%在高电压大功率应用场合中,中点钳位型(NPC)三电平逆变器是一种被广泛应用的多电平逆变器,但是该类型逆变器存在中点电压波动和共模电压问题.针对上述两个问题提出一种改进型虚拟空间矢量(NTV2)调制法,采用零矢量、中矢量和大矢量对虚拟小矢量和中矢量重新定义,使得到的虚拟矢量产生的共模电压最大值为Udc/6,是传统虚拟空间矢量法产生的共模电压幅值的1/2,从而实现对共模电压的抑制.在此基础上,通过合理选取虚拟中矢量分配系数的值,可以在一定范围内抑制中点电压的波动.与传统虚拟空间矢量法相比,所提方法能够有效地抑制共模电压和中点电压波动.仿真和实验验证了该方法的正确性和有效性.
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