新能源并网系统短路比指标分析及临界短路比计算方法

Short Circuit Ratio Index Analysis and Critical Short Circuit Ratio Calculation of Renewable Energy Grid-connected System

短路比作为评估新能源并网系统电压支撑强度的重要指标,其准确性与实用性之间存在矛盾,且由于构建方法众多导致临界短路比计算不统一。该文对新能源并网系统的短路比指标进行分析,并提出临界短路比计算方法,实现对系统电压支撑强度的评估。首先,建立新能源并网系统的等效分析模型,依据叠加定理分析新能源接入对节点电压的影响,推导交流系统短路容量以及计及多馈入相互影响的新能源等效并网容量;进一步,提出两个等价短路比指标:依据短路比的容量比概念,提出基于容量计算的短路比指标SCR-S,以及通过分析短路比与节点电压之间的关系,提出基于电压计算的短路比指标SCR-U,通过解析推导SCR-U与SCR-S完全等价关系,SCR-U形式及解析表达更加简单。其次,基于最大传输功率提出临界短路比数值的理论算法,进一步求解临界短路比的极值,建议将临界短路比极值2作为划分新能源并网系统强弱的标准,当SCR-U小于2时,系统为弱系统。然后,结合SCR-U及临界短路比提出系统电压支撑强度评估方法,当SCR-U小于临界短路比时,系统处于P-V特性不稳定区域。最后,通过算例验证了采用SCR-U及临界短路比极值对电压支撑强度进行评估的准确性与合理性。

There is a contradiction between the accuracy and practicability of the short circuit ratio(SCR) for system strength evaluation of renewable energy systems, and numerous construction methods lead to inconsistent values of the critical short circuit ratio(CSCR). This paper analyzed the SCR index and proposed the CSCR calculation method. Firstly,the short circuit capacity of AC system and the equivalent grid-connected capacity of the renewable energy were derived.Secondly, the SCR-S calculated by the capacity was proposed according to the SCR concept, and the SCR-U calculated by the voltage was proposed by the relationship between the SCR and the node voltage. And then, the CSCR was solved according to the maximum transmission power. It was recommended that the CSCR extreme value 2 serve as the basis to divide the system strength. Finally, the simulations verified the accuracy and rationality of the system strength evaluation according to SCR-S, SCR-U and CSCR.