基于VSC的功率双向交直流互联系统直流侧阻抗特性分析及重塑

Analysis and Reshaping of DC-side Impedance Characteristic in VSCs-based Bidirectional Power AC/DC Interconnected System

基于电压源型换流器(voltage source converter,VSC)的交直流互联系统因其接入灵活、电能转换高效得到越来越广泛的研究和应用。但高比例新能源接入、高比例电力电子化的特征会带来稳定性问题,系统的不同功率流向也会造成系统直流侧稳定性的差异。为研究与提升基于VSC的交直流互联系统的直流侧稳定性,该文综合考虑功率双向流动、锁相环(phase-locked loop,PLL)、电压和电流控制环以及电网阻抗等影响因素,建立VSC的直流侧导纳模型,通过解析分析VSC直流侧导纳特性,揭示系统失稳风险来源,并提出基于二阶微分环节的直流电压前馈控制方法重塑VSC直流侧阻抗,以提升交直流互联系统的稳定性。最后,在控制硬件在环(control-hardware-in-loop,CHIL)实验平台中构建基于VSC的交直流互联系统,通过实验验证对交直流互联系统直流侧阻抗特性分析的正确性及所提出阻抗重塑策略的有效性。

Voltage source converters(VSCs)-based AC/DC interconnected systems are increasingly studied and utilized due to their flexible access and efficient power conversion.However,the high proportion of renewable energy access and power electronics can cause stability issues,and the different power flow directions of the system can result in varying DC-side stability.In this paper,a DC-side admittance model of VSC is comprehensively established,taking into account factors such as bidirectional power flow,phase-locked loop(PLL),voltage and current control,and grid impedance.The DC-side admittance characteristics of VSC are analytically analyzed to reveal the origin of instability risk in the system.A DC voltage feedforward control method based on second-order differential loop is proposed to reshape the DC-side impedance of VSC for improving the stability of AC/DC interconnected system.Finally,a VSCs-based AC/DC interconnected system is constructed and emulated on the control-hardware-in-loop(CHIL)experimental platform to verify the accuracy of the analysis on the DC-side impedance characteristics and the effectiveness of the proposed impedance reshaping strategy.