Control of fuel cell and electrolyzer based hydrogen storage system with ultra-capacitor for voltage stability and enhanced transient stability of a DC micro grid

In a DC micro grid, the energy can be stored in the form of hydrogen using electrolyzer and fuel cell combination for a long-term storage. Though the round trip efficiency of such system is very low, it can store relatively high amount of energy for a long term. In this paper, a hydrogen storage system is implemented to respond to a continuous mismatch between generation and load. It is also used to control the DC bus voltage. The proposed strategy controls the power flow through the electrolyzer, fuel cell, and ultra-capacitor to regulate the DC bus voltage. With the proposed strategy, the number of sensing elements required is less. The strategy also optimizes the performance by adjusting the rate of change power for fuel cell and electrolyzer by using the low pass filter without deteriorating the quality of DC bus voltage. Ultra-capacitor feeds the high-frequency power requirement of the grid using a fuzzy logic controller, which minimizes the fluctuations in the DC bus voltage. The proposed strategy is simple, gives superior performance and operates the fuel cell and electrolyzer with optimized dynamics. It also smoothens out the fluctuations due to suddenly changing Solar PV power.