Electronically controlled capacitive energy storage element for DC grids

A major and very important challenge in dc grid development is maintaining continuous converter operation under dc faults. This paper proposes a novel capacitive energy storage device which improves security of dc grids by avoiding terminal blocking. The device provides current from the capacitor bank during dc faults, reducing fault current contribution and voltage drop of dc grid converters. Moreover, the device also helps in balancing pole voltages which is of particular significance during pole-to-ground faults in symmetrical monopole systems. Other benefits like improved transient grid stability are also demonstrated. Device’s design and performance is assessed using theoretical analysis and verified on a three-terminal offshore dc grid model in PSCAD. The cost of the device’s electronics is minimized and the total cost and weight estimation are also shown.