Dimensioning of DC Capacitor for Voltage Source Converter

Grid-forming voltage source converter (GFM-VSC) can significantly improve the stability of renewable energy generation system connected with power gird. However, in photovoltaic power generation applications, the fluctuation and randomness of the irradiation can lead to the DC voltage fluctuation of GFM-VSC. When a sudden drop of irradiation occurs, DC voltage of converter would also drop significantly, leading to undervoltage problems and shutdown accidents. As an energy storage element, the DC capacitor can support the power imbalance between AC and DC sides of the converter, suppressing DC voltage fluctuation. This paper presents a DC capacitor dimensioning method for GFM-VSC. Through the transient modeling of DC voltage of the converter. the relationship between irradiance and DC voltage fluctuation is built. Then a dimensioning method is proposed. Capacitors selected by this method can avoid DC undervoltage and improve the DC voltage stability. Examples and simulations verify the effectiveness of the proposed method.