The growing relevance of voltage source converters (VSCs), and the deep impact they have on the development and maintenance of the electrical grid, increase the necessity of further research on how to deal with nonideal grid conditions from the VSCs control. This paper is aimed to summarize the basic techniques and schemes that might be required for a grid-connected VSC to work under these conditions: grid synchronization schemes, sequence decomposition, current reference generation, and current controllers. At the same time, some alternative schemes that improves the basic ones are cited. Modelling and the two typical current controllers design and tuning under stationary and synchronous reference frames are also exhibited. Given the importance of the current control stage in the VSC behaviour, five control schemes, designed to track negative sequence currents, are shown and tested in simulation and experiments. According to the experiments, it is shown that the standard proportional-resonant controller achieves the best performance in negative sequence tracking due to the robustness of its non-ideal version, the improved implementation thanks to the delta operator, and the non-dependence on grid-synchronization schemes. Alternatively, one approach based on dual synchronous reference frame is also highlighted for easiness of implementation and good performance.

中文翻译：

---

电网跟随电压源换流器：在不平衡电压条件下运行的基本方案和电流控制技术

电压源换流器 (VSC) 的日益增长的相关性以及它们对电网发展和维护的深远影响，增加了进一步研究如何从 VSC 控制中处理非理想电网条件的必要性。本文旨在总结并网 VSC 在这些条件下工作可能需要的基本技术和方案：电网同步方案、序列分解、电流参考生成和电流控制器。同时，还列举了一些改进基本方案的替代方案。还展示了在静止和同步参考系下的建模和两个典型的电流控制器设计和调整。鉴于当前控制阶段在 VSC 行为中的重要性，五种控制方案，设计用于跟踪负序电流，在模拟和实验中显示和测试。根据实验表明，标准比例谐振控制器由于其非理想版本的鲁棒性、delta 算子的改进实现以及不依赖于网格，在负序跟踪中实现了最佳性能-同步方案。或者，为了易于实现和良好的性能，还强调了一种基于双同步参考系的方法。由于 delta 运算符的改进实现，并且不依赖于网格同步方案。或者，为了易于实现和良好的性能，还强调了一种基于双同步参考系的方法。由于 delta 运算符的改进实现，并且不依赖于网格同步方案。或者，为了易于实现和良好的性能，还强调了一种基于双同步参考系的方法。