并网逆变器超高次谐波产生与传播机理分析

超高次谐波是新能源发电技术中不可忽略的新型电能质量问题,并网逆变器作为典型超高次谐波源受到广泛关注。为揭示超高次谐波产生与传播机理特性,文中首先对正弦脉冲宽度调制(sinusoidal pulse width modulation,SPWM)下的逆变器超高次谐波产生机理进行分析,发现逆变器产生的超高次谐波主要分布在开关频率整数倍附近,且可以等效为电压源,同时对造成该电压源变化的影响因素进行理论分析。然后,建立包含逆变器、滤波器以及网侧阻抗的超高次电路模型,并推导超高次谐波发射电流的数学表达式,在此基础上通过控制变量法探究多逆变器并联时容量和台数对超高次谐波传播特性的影响。最后,在Simulink中进行仿真实验。结果表明,并网逆变器超高次谐波主要受直流侧电压与调制比影响,多逆变器并联运行时超高次谐波的发射强度与容量成正比,验证了文中对并网逆变器超高次谐波理论分析的正确性。

Analysis of generation and propagation mechanism of supraharmonic in grid-connected inverter

Supraharmonics are a new power quality problem that can not be ignored in new energy power generation technology. As a typical supraharmonic source,the grid-connected inverter has received extensive attentions. To reveal the characteristics of its generation and propagation mechanism,the mechanism of supraharmonic generation in sinusoidal pulse width modulation (SPWM) inverters is analyzed firstly. It is found that the supraharmonics generated are mainly distributed around integer multiples of the switching frequency,and can be equivalent to a voltage source. At the same time,the influencing factors that cause changes in the voltage source are theoretically analyzed. Then,a supraharmonic circuit model including inverter,filter and grid side impedance is established,and the mathematical expression of supraharmonic emission current is derived. On this basis,the influence of capacity and number of inverters on supraharmonic propagation characteristics when multiple inverters are connected in parallel is explored through the control variates. Finally,the simulation experiment is carried out in Simulink. The results show that supraharmonics in the grid-connected inverter are mainly affected by the DC side voltage and modulation ratio,and the emission intensity of supraharmonics is proportional to the capacity when multiple inverters operate in parallel. The correctness of the theoretical analysis of supraharmonics in the grid-connected inverter is verified in this paper.