Harmonic and Imbalance Compensation in Grid-Forming VSC

The massive integration of distributed energy resources is strongly linked to the development of voltage source converters responsible for connecting them to the grid. These will have to provide a series of services that facilitate their integration into the future distribution network. Among them, it is important to highlight the need to improve the wave quality of the voltages which can be distorted by the increase of nonlinear and unbalanced loads in the system. This paper presents a control strategy for grid-forming voltage source converter able to compensate harmonics and imbalances of the voltages at the point of common coupling. The objective of the controller is to generate a balanced three-phase voltage with a given amplitude and frequency for any type of load or generation connected to the power converter. The proposed control algorithm works over the rotating axes adding resonant structure tuned at the specific harmonic to be eliminated in the outer voltage control loop. Moreover, a systematic methodology is presented to compute the gains of the controller. A laboratory testbed with different type of loads is used to validate the proposed algorithm. The experimental results demonstrate the effectiveness of the proposal by achieving low levels of harmonic distortion and imbalances in steady-state.