虚拟同步发电机与交流电网交互特性及振荡抑制研究

Nowadays, an increasing number of renewable energies are integrated into the utility grid through current source inverters. However, with this kind of grid interfaces, it is impossible for the renewable sources to take part in the grid’s primary frequency/voltage regulation process. What’s worse, in some extreme cases, they may have negative interactions with the grid and excite oscillations, which would bring complete shut-down of the utility grid. To address this problem, in this project, a new type of power electronic interface, namely virtual synchronous generator (VSG), is pushing ahead and deeply studied. Several efforts have been made to improve the performance of VSG connected to the grid. Firstly, in order to improve the power quality of VSG, an improved control strategy for non-ideal grid conditions will be proposed and studied. Then, the positive and negative sequence impedance model of VSG is going to be established, and some key parameters which have direct influence on the output impedance will be explored. Afterwards, the impedance stability criterion for voltage source inverter system like VSG will be deeply studies, and the analysis of interaction and coupling mechanism between VSG and the power grid is carried out, aiming to obtain some theoretical solution. Finally, interaction between VSG and current source type devices or reactive power like STATCOM is elaborated, and the oscillation conditions, mechanism and corresponding countermeasure for such interconnected system are carefully explored. In conclusion, the interaction between VSG and AC power grid and system oscillation mechanism are analyzed by the means of impedance model for the first time in this project, and the research result may leads to better understand of VSG and provide an optional grid friendly way for renewable energy generation system.

基于电力电子装置的可再生能源规模化接入给电网带来了诸多问题和挑战。研究电网友好型的新型电力电子变换装置，解决现有并网装置无法参与系统调频/调压、易与电网发生交互振荡等问题，已迫在眉睫。本项目主要针对虚拟同步发电机(VSG)的控制策略及其与交流电网交互作用和振荡机理与对策开展研究，包括：①研究非理想电网条件下VSG的控制策略，改善输出电能质量；②建立VSG正负序阻抗模型，探索关键参数对其输出阻抗的影响规律；③研究适用于VSG等电压源型并网系统的阻抗稳定性判据，分析装置与电网之间的交互作用和耦合机理，给出理论性解决方案；④研究VSG与电流源型并网装置或STATCOM等无功电源之间的交互作用，探索此类互联系统的振荡发生条件、机理与对策。本项目首次以阻抗角度对VSG的阻抗模型及其与交流电网的交互作用及振荡机理开展研究，预期成果将有助于完善VSG的理论体系，为新能源的规模化友好接入提供一种新的途径。

虚拟同步发电机（VSG）因具备良好的电网支撑能力和调频调压能力，是实现分布式电源大规模接入电网的一种有效方案。本项目围绕VSG与交流电网交互机理及其振荡抑制问题，重点开展了非理想电网条件下VSG控制策略研究，VSG等电压源型并网装置的阻抗建模方法，并网装置与电网耦合机理剖析，以及VSG与电流源型并网装置或无功电源之间交互作用等四个方面的研究。1）针对并网模式下电网电压不对称且含有背景谐波、离网模式下负载三相不平衡及从并网过渡到离网模式时并网装置无法稳定运行的三种非理想情况，提出了相应的解决办法，改善了并网装置的输出电能质量，保证了并网装置的可靠运行。2）以VSG和下垂控制逆变器（DCI）两种典型的电压源型并网装置为例，采用谐波线性化方法建立了其正负序阻抗模型，给出了系统参数的优化设计和定向调整方法，探究了关键参数对阻抗特性的影响规律。3）基于并网装置的阻抗模型，分析了并网装置与电网的交互特性，利用奈奎斯特稳定判据对VSG和DCI在弱电网下的稳定性问题进行了讨论，揭示了VSG等电压源型并网系统耦合机理以及振荡规律，进而提出采用“虚拟电感+低通滤波器”的方法提高DCI在弱电网下的稳定性；提出通过调整控制环路参数，重塑阻抗特性的方法达到抑制VSG与弱电网交互系统振荡的目的。4）针对VSG与电流源型并网装置以及STATCOM等无功电源构成的交互系统，通过建立各部分的阻抗模型，探究了系统发生振荡的条件并给出了相应的解决措施。仿真及实验结果验证了理论分析的正确性。本项目为分布式新能源友好接入电网提供了理论基础，对并网装置自身及其与交流电网构成的交互系统的安全稳定运行具有重要意义。