A Flexible Compensation Strategy for Weak Grid-Tied Current Controlled Converters Under Unbalanced and Harmonic Conditions

In a weak grid environment, at renewable energy integration, the harmonics and unbalance issues are very frequent due to nonlinear loads. In this regard, achieving unbalance compensation involves two control targets, which are harmonics compensation and then unbalance compensation. Under nonlinear loads, in a weak grid environment, voltage compensation or current compensation alone not sufficient to improve power quality. To overcome the aforementioned drawback, a flexible compensation strategy is proposed for a current-controlled inverter connected to an unbalanced-distorted weak grid under nonlinear load conditions. The proposed compensation strategy uses harmonic components of nonlinear load current, and harmonic components of voltage are the feedback variables. This compensation strategy performs both voltage and nonlinear current compensation simultaneously with seamless interaction between voltage harmonic components and current harmonics components. The proposed compensation strategy achieves unbalance compensation and harmonics compensation simultaneously in a weak grid environment without stability issues. Further, to improve the performance of the proposed compensation strategy, individual phase compensation of the current controllers is included, and the effectiveness and superiority of the proposed strategy are validated through various test cases.