A design procedure for an RLC damping branch applied at a voltage source inverter followed by an LCL output filter is carried out in this paper. The main purpose of the proposed methodology is to allow the system to operate properly in both grid-connected (GC) and islanded (IS) modes with smooth transitions between them. The usage of passive damping methods to smooth the resonating filters effects is well known. However, the design procedure of the damping branch is specific for either the GC or IS mode, and usually, the parameters tuned for an operation mode are unsuitable for the other one. Thereby, this paper contributes to presenting a methodology design of an RLC branch aimed to achieve damping effect for both operation modes, thus allowing the continuous operation with no hazardous transients during transitions. By means of the proposed approach, the passive elements are adequately designed in order to provide easy controller synthesis. Therefore, a two-loop control strategy is adopted where the inner loop controls the capacitor voltage and ensures the system stability for both operation modes; meanwhile, an additional outer loop controls the grid current for GC mode allowing active and reactive power flows. Experimental results for a 2-kW prototype are presented in order to validate the proposed design methodology and control strategy.

中文翻译：

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RLC 无源阻尼 LCL 单相电压源逆变器，能够在并网和孤岛模式下运行：设计和控制策略

本文介绍了一个应用在电压源逆变器和 LCL 输出滤波器上的 RLC 阻尼支路的设计程序。所提出方法的主要目的是使系统能够在并网 (GC) 和孤岛 (IS) 模式下正常运行，并在它们之间实现平滑过渡。使用被动阻尼方法来平滑谐振滤波器效果是众所周知的。然而，阻尼支路的设计程序是针对 GC 或 IS 模式的，通常，为一种操作模式调整的参数不适用于另一种模式。因此，本文有助于提出一种 RLC 分支的方法设计，旨在实现两种操作模式的阻尼效果，从而允许在过渡期间没有危险瞬变的连续操作。通过所提出的方法，无源元件被充分设计以提供简单的控制器综合。因此，采用双环控制策略，内环控制电容电压，保证两种运行模式下的系统稳定性；同时，一个额外的外环控制 GC 模式的电网电流，允许有功和无功功率流动。展示了 2 kW 原型的实验结果，以验证所提出的设计方法和控制策略。额外的外环控制 GC 模式的电网电流，允许有功和无功功率流动。展示了 2 kW 原型的实验结果，以验证所提出的设计方法和控制策略。额外的外环控制 GC 模式的电网电流，允许有功和无功功率流动。展示了 2 kW 原型的实验结果，以验证所提出的设计方法和控制策略。