Active Harmonic Filtering with Selective Overcurrent Limitation for Grid-Forming VSCs: Stability Analysis and Experimental Validation

The high penetration of renewable energy sources (RES) interfaced with power electronics together with new nonlinear loads pose new challenges in the grid operation. In fact, power systems with reduced inertia and high harmonic distortion will be common in a near future. Recently, the grid-forming operation of voltage source converters (VSCs) has emerged to address these challenges, mimicking the contribution of synchronous generators to the system inertia. In addition, these grid-connected VSCs can be used at the same time for reducing the harmonic distortion by applying active filtering techniques. However, these harmonic compensation algorithms can generate VSC overloading. This paper proposes a method for dynamically adjusting the individual virtual impedance of the filtered harmonics to prevent the power converter overcurrent. For this purpose, the value of each harmonic virtual impedance is modified according to a priority which can be set by the final user according to the established power quality standard. The paper includes a theoretical stability analysis of the controller and experimental results to validate the proposed algorithm.