The converter control functions to provide the capabilities similar to synchronous generators are referred to as grid forming converters (GFC). Identical to a synchronous machine, a grid forming converter is expected to behave as a voltage source behind an impedance beyond the control bandwidth. However, GFC's realization has been different, with some utilizes inner current and voltage controllers while others do not. This paper studies the impact of the inner loop on the grid forming converter's ability to behave as a voltage source behind an impedance. Three of the most popular GFC structures, 1) GFC with cascaded voltage and current control, 2) with inner current control, 3) with no inner loop, are chosen for the comparison. The analysis revealed that MW level GFC with inner loops could potentially go unstable under weak power system. Additionally, the GFC with cascaded control can only operate stably within a narrow range of network impedances. Furthermore, it is also shown that slow response behavior based on cascaded inner loop can impact on dynamic reactive and active power-sharing.

中文翻译：

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基于电压源行为的并网变流器典型控制实现的比较评估

提供类似于同步发电机的能力的变流器控制功能被称为并网变流器 (GFC)。与同步电机相同，电网形成转换器预期在超出控制带宽的阻抗后面充当电压源。但是，GFC 的实现方式有所不同，有些使用内部电流和电压控制器，有些则不使用。本文研究了内回路对电网形成转换器作为阻抗后面的电压源的能力的影响。选择三种最流行的 GFC 结构进行比较，1) 具有级联电压和电流控制的 GFC，2) 具有内部电流控制，3) 没有内部回路。分析表明，在弱电力系统下，具有内环的 MW 级 GFC 可能会变得不稳定。此外，具有级联控制的 GFC 只能在较窄的网络阻抗范围内稳定运行。此外，还表明基于级联内环的慢响应行为会影响动态无功和有功功率共享。