With decarburization of the electrical grid, the penetration of renewable energy generators (REGs) is increasing. Consequently, the operating environment of the electrical grid is greatly altered and the existing protection system for the electrical grid cannot adapt to the new environment. In order to solve the existing protection problems, the equivalent model for calculating short-circuit current of the REGs should be built. The calculation model depends on the fault current characteristics of REGs that are different from the conventional generators (synchronous generators). The short-circuit current characteristics of REGs are related with the corresponding inverter control strategies. However, the strategies are diverse from manufacturer to manufacturer and are unknown to the public. As a result, it becomes difficult to reveal the fault current characteristics and realize fault current calculation without knowing the control strategies. In this paper, the focus is on the fault current characteristics and their calculation models of inverter-interfaced REGs (IIREGs). To reveal the relationship between the inverter’s control strategies and the IIREG’s short-circuit current characteristics, a coordinated control strategy for gird-tie inverter and DC-link chopper is proposed. The main factors affecting the transient and steady-state shortcircuit currents are analyzed and revealed for IIREGs. Further, the calculation model of the steady-state short-circuit current from IIREGs is established, which is independent of the specific inverter’s control strategies. Finally, based on the experimental test bench, both the fault ride through (FRT) capability and short-circuit current model of IIREG are verified. The results can be used for assessing and improving the relay protection strategies of the electrical grid with lots of IIREGs.

中文翻译：

---

计算逆变器接口可再生能源发电机故障电流的等效模型

随着电网脱碳，可再生能源发电机 (REG) 的渗透率正在增加。因此，电网的运行环境发生了很大的变化，现有的电网保护系统无法适应新的环境。为了解决现有的保护问题，应建立计算REG短路电流的等效模型。计算模型取决于 REG 不同于常规发电机（同步发电机）的故障电流特性。REG的短路电流特性与相应的逆变器控制策略有关。然而，这些策略因制造商而异，并且不为公众所知。因此，在不了解控制策略的情况下，很难揭示故障电流特性并实现故障电流计算。在本文中，重点是逆变器接口REG（IIREG）的故障电流特性及其计算模型。为了揭示逆变器控制策略与IIREG短路电流特性之间的关系，提出了并网逆变器和直流母线斩波器的协调控制策略。分析并揭示了影响 IIREG 瞬态和稳态短路电流的主要因素。进一步建立了IIREGs稳态短路电流的计算模型，该模型与具体逆变器的控制策略无关。最后，基于实验测试台，验证了 IIREG 的故障穿越 (FRT) 能力和短路电流模型。结果可用于评估和改进具有大量IIREG的电网的继电保护策略。