A Power Ripple Suppression Method for Grid-Forming Converter under Imbalanced Grids

Grid-forming converter has been intensively discussed for the capability of active frequency and voltage magnitude regulation. However, due to the absence of closed-loop direct grid current tracking, it suffers from negative sequence grid voltage disturbances, causing significant double-frequency power oscillations. In this paper, a simple power ripple suppression method is proposed for voltage-controlled grid-forming converters, without using any sequence decomposition or complex signal processing. The proposed system consists of a double-frequency active power pulsation mitigation loop to produce an adjustment gain that couples with the instantaneous converter voltage signal, the fundamental component of this adjustment term is extracted and added to the reference voltage from traditional droop control loop. With only slight modifications, the active power pulsation can be effectively suppressed in various conditions. Extensive experimental results have obtained to validate the correctness of the proposed approach.