变虚拟空间矢量的三电平NPC变换器中点电位平衡控制策略

在多电平变换器研究领域,三电平中点钳位逆变器目前是一种研究比较广泛的一种拓扑结构,但是此拓扑结构容易造成中点电压偏移问题。基于理论上虚拟空间矢量的调制方法可以实现分压电容中点电压平衡控制,因此,为增强中点电压平衡的控制效果,提出调节虚拟中矢量中点电流和分配正、负小矢量作用时间的中点电压平衡控制方法。相对虚拟空间矢量脉宽调制算法和混合式调制算法来说,所采用的可变虚拟空间矢量控制算法简单、实用,能实现三电平NPC变换器中点电位平衡控制。

一种基于可变虚拟中矢量的三电平SVPWM调制策略

T型三电平拓扑因具有高效率、低谐波输出等优点而被广泛应用于电能变换器中,其电容中点电压控制的效果将直接影响变流器性能。文章分析了T型三电平主电路中点电压不平衡问题,提出了一种基于变虚拟空间矢量的调制策略,其利用正、负小矢量和中矢量合成的变虚拟中矢量参与空间矢量调制,有效控制了中点电压的偏移。仿真和实验结果验证了该T型三电平拓扑调制策略在地铁系统中应用的可行性与优越性。

A neutral-point potential balance control strategy for three-level inverter based on VSVPWM

The topology of diode neutral-point-clamped(NPC)three-level inverter is prone to neutral-point potential offset.When the sum of three-phase current is zero,the virtual space vector pulse width modulation(VSVPWM)scheme does not cause the neutral-point voltage offset,but it lacks the ability to balance the deviation.For this reason,a neutral-point potential control strategy combining virtual space vector modulation and loop width control is proposed.The neutral-point potential is balanced by introducing the distribution factor for the regions with redundant vectors.For other regions,the potential is controlled by selecting a suitable switching sequence.Meanwhile,the effect on the virtual vector modulation is reduced within the loop width by setting an appropriate loop width,thereby improving the balance effect.The simulation results show that the proposed method has a strong ability to control the offset and has excellent potential balance performance under the conditions of balanced load,unbalanced load and asymmetric capacitance parameters.