Improved Grid-Side Current Control of LCL-Filtered Grid-Tied Inverters Under Weak Grid Conditions

Three-phase voltage source inverters are key parts to integrate renewable energy resources into the electrical grid. In order to achieve an acceptable attenuation of current harmonics in grid tied inverters and meet grid interconnection recommendations, an inductor-capacitor-inductor (LCL) type filter is commonly used as an interface between the inverter and the grid. However, this filter exhibits a resonant peak that should be properly damped to ensure system stability. Moreover, grid impedance variations, mainly under weak grid conditions, may shift the resonance frequency which compromises the controller design. This paper proposes a systematic approach to actively damp the LCL filter resonance using the notch filter-based control. An adaptive approach is also considered to improve the control performance under grid impedance variations. Computer simulations results are presented to demonstrate the effectiveness and robustness of the proposed control method.