弱电网下考虑装置死区效应时的逆变器并网电能质量分析

Power Quality Analysis of Grid-connected LCL-type Inverter Considering Dead-time Effect under Weak Grid

弱电网接入下,逆变器-电网级联系统的阻抗不匹配易导致逆变器并网系统的稳定性能降低。为建立更准确的逆变器输出阻抗模型,以LCL型并网逆变器为例,将装置死区效应考虑到并网逆变器建模中。同时,考虑长线路对地分布电容的影响,建立弱电网下长线路分布参数模型并分析其输入阻抗幅频特性。基于此,采用基于奈奎斯特稳定判据的阻抗分析法分析并网系统稳定性并计算其稳定裕度,研究随着死区时间和长送出线线路长度的增加并网系统稳定裕度值的变化规律,并利用PSIM 9.0平台建立相关仿真模型,证明了理论分析的准确性和可行性。

In the weak grid-connected case,Impedance mismatch is likely to deteriorate the stability of the cascaded system of LCL-type inverter and grid,even making the system unstable. Taking the LCL-type inverter for an example,the dead-zone effect of inverter was considered to establish a more accurate model of the output impedance of inverter. Meanwhile,considering the influence of long line distribution capacitance,the distributed parameter model was established and the amplitude-frequency characteristics of input impedance were analyzed. Based on the above mentioned,the stability of grid-connected system was analyzed by impedance analysis method and its stability margin was calculated. The change law of the stability margin of the grid-connected system with the increase of dead-zone time and line length was also studied. Finally,based on the PSIM 9.0 platform,the simulation model was established,and the simulation results prove the accuracy and feasibility of the theoretical analysis.