Fault-Tolerant Multi-Level Converter Architecture for Resilient Offshore Hydrogen Energy Storage Systems

Abstract

Abstract This paper proposes an offshore Hydrogen Energy Storage System (HESS) to interface with subsea oil and gas production systems and offshore renewable energy sources (like wind, floating solar, etc.). Such a HESS will provide a stable energy supply for an extended period, reducing the need for carbon-heavy backup systems such as diesel generators, thereby resulting in a much cleaner energy future. The proposed offshore architecture is modeled using a Hydrogen Energy Storage System (HESS) along with offshore renewables (primarily wind energy), subsea loads (such as drives for pumps, compressors, etc.), and a medium voltage DC (MVDC) grid. Each unit of the HESS is constructed using an electrolyzer to produce hydrogen from electricity, a hydrogen tank to store the fuel, and a fuel cell to transform hydrogen back into electrical energy. Each unit has separate converters to step up/down the voltage. These units are further interconnected through a multi-level cascaded bridge architecture to achieve a 6 kV output. The multi-level cascaded bridge architecture ensures the reliable operation of the system by re-balancing the energy storage electrically between the cascaded mode and protecting the system from any misshape that happens in the system. Suppose a fault occurs in one of the fuel cell units. In that case, the cascaded bridge architecture disconnects that unit from the system. It compensates for that unit by recovering the difference voltage from the other units to maintain the 6 kV DC output voltage.