柔性直流输电系统高频稳定性分析及抑制策略(三):有源阻尼分频协调抑制策略

Time delay of MMC-HVDC is the essence for the negative damping effects of output impedance in high frequency ranges, which induces resonances at different high frequencies. To reveal the mechanism and solve the problems of such resonances, the positive-and negative sequence impedance models of MMC applied for high frequency region are established firstly. And then, the mechanism of negative damping effect has been elaborated as well as the inapplicability of single active damping controller for high frequency resonances suppression is analyzed. Secondly, the phase mathematical representation method of cosine function of impedance real part is used for the first time to reveal the mechanism of damping suppression strategy on how to change impedance characteristics and transfer the negative damping effect frequency regions. It is concluded that damping control cannot reshape the impedance of MMC into positive damping characteristics in high frequency range. Thirdly, an active damping with coordinated frequency division concept is proposed to address the suppression requirements of multiple high frequency resonance risk regions. The impact of this strategy on the phase characteristics of cosine function of impedance real part and the constraint relationships between parameters are analyzed. Finally, based on the demands for frequency division suppression in multiple high frequency regions, the analytical calculation method and expressions for the parameters’ selection ranges of the frequency division damping controller are presented. The parameters of damping controller suitable for multiple operating conditions of AC systems are given, and their effectiveness is verified through electromagnetic transient simulation models.