新能源发电正负序调控下多变流器并网系统小信号稳定性建模与分析

新能源大规模开发利用是我国能源战略的重要组成部分，其中负序电流控制是实现新能源可靠并网和消纳的关键技术之一，如何评估负序电流控制为新能源发电系统带来的失稳风险是亟需解决的技术难题。具备正负序电流控制时，新能源发电并网变流器呈现较强的非线性周期时变特征，因此本项目提出利用线性周期时变(LTP)理论揭示正负序调控下新能源发电系统的小信号稳定机理。首先，建立新能源发电正负序调控下多变流器并网系统LTP状态空间模型和无穷阶谐波状态空间(HSS)模型，以满足系统稳定性判定和稳定性主导因素分析的需要；其次，提出无穷阶HSS模型合理截断的理论依据，改进LTP系统稳定机理分析方法，进而研究正负序控制对系统稳定性及相互作用机理的影响规律；最后，基于稳定机理分析结果，提出优化控制设计方案和参数优化机制，以提升各类工况下的系统稳定性。本项目成果为新能源发电作为主力电源下的现代电力系统安全稳定运行提供理论支撑。

Large-scale development and utilization of renewable energy is an important part of energy strategy in China, and the negative sequence current control is one of the key technologies to achieve reliable grid connection and consumption of renewable energy. Therefore, how to evaluate the instability risk caused by negative sequence current control for renewable power generation systems is an urgent technical problem to be solved. With positive and negative sequence current control, the grid-connected converters of renewable power generation present strong nonlinear periodic time-varying characteristics. Therefore, this project proposes to use linear periodic time-varying (LTP) theory to reveal the small-signal stability mechanism of renewable power systems under positive and negative sequence control. Firstly, the LTP state-space model and infinite order harmonic state space (HSS) model of multiple grid-connected-converter system under positive and negative sequence control of renewable energy power generation are established to meet the needs of system stability judgment and stability dominant factor analysis. Secondly, the theoretical basis of reasonable truncation for infinite order HSS model is proposed, which improves the stability mechanism analysis method of LTP system, then the influence of positive and negative sequence control on the stability and the interaction mechanism is analyzed. Finally, based on the analysis results of the stability mechanism, the optimal control design scheme and parameter optimization mechanism are proposed to improve the system stability under various grid conditions. The achievements of this project provide theoretical support for the safe and stable operation of modern power systems with renewable power generation as the main power source.