一种具有中点电位平衡能力的两级三电平逆变器

三电平逆变器开关管应力小，开关损耗低，输出谐波小，因而在大、中功率开关电源中有广泛的应用前景，但其存在着母线电容中点偏移的固有问题，而传统中点电位平衡算法在负载参数变化时存在着不可控区域。采用双输出三电平Boost变换器作为前级，可以在保证宽范围输入电压的同时，对母线电容中点电位进行平衡。分析了传统中点电位平衡算法在负载功率不平衡时的失效问题，在此基础上利用前级三电平Boost变换器解决逆变器的中点偏移问题，给出了变换器平衡母线电容中点电位的一种控制方法，并与传统算法的效果进行对比，最后进行了仿真和实验验证。实验结果证明该方法能够很好的解决负载功率不平衡时三电平逆变器直流母线电容的中点偏移问题。

A Two-Stage Three-Level Inverter With Neutral-point Potential Balance

Three-level inverter is widely used in medium & high distributed generation system for the advantages of lower switch voltage stress, lower switching power loss and smaller output harmonic. However, the problem of the neutral point voltage drift exists inherently and traditional voltage balance algorithm has uncontrollable areas when load parameters changed. By using the front-end dual output three-level Boost converter, the bus capacitor voltage can be balanced while wide range input voltage is ensured. The paper analyzes the failure of traditional algorithm when load power is unbalanced. Then a three-level Boost converter is used to solve the neutral point drift problem of the inverter. A method to balance the voltage of the divided capacitors is proposed and is compared with traditional algorithm. Simulation and experiment is also completed in this paper. The results of both simulation and experiment verify that the method can well solve the neutral point drift problem of the inverter with unbalanced load power.