Integration of Air-cooled Multi-stack Polymer Electrolyte Fuel Cell Systems into Renewable Microgrids

Currently, there is a growing interest in increasing the power range of air-cooled fuel cells (ACFCs), as they are cheaper, easier to use and maintain than water-cooled fuel cells (WCFCs). However, air-cooled stacks are only available up to medium power (<10 kW). Therefore, a good solution may be the development of ACFCs consisting of several stacks until the required power output is reached. This is the concept of air-cooled multi-stack fuel cell (AC-MSFC). The objective of this work is to develop a turnkey solution for the integration of AC-MSFCs in renewable microgrids, specifically those with high-voltage DC (HVDC) bus. This is challenging because the AC-MSFCs must operate in the microgrid as a single ACFC with adjustable power, depending on the number of stacks in operation. To achieve this, the necessary power converter (ACFCs operate at low voltages, so high conversion rates are required) and control loops must be developed. Unlike most designs in the literature, the proposed solution is compact, forming a system (AC-MSFCS) with a single input (hydrogen) and a single output (high voltage regulated power or voltage) that can be easily integrated into any microgrid and easily scalable depending on the power required. The developed AC-MSFCS integrates stacks, balance of plant, data acquisition and instrumentation, power converters and local controllers. In addition, a virtual instrument (VI)has been developed which, connected to the energy management system (EMS) of the microgrid, allows monitoring of the entire AC-MSFCS (operating temperature, purging, cell voltage monitoring for degradation evaluation, stacks operating point control and alarm and event management), as well as serving as a user interface. This allows the EMS to know the degradation of each stack and to carry out energy distribution strategies or specific maintenance actions, which improves efficiency, lifespan and, of course, saves costs. The experimental results have been excellent in terms of the correct operation of the developed AC-MSFCS. Likewise, the accumulated degradation of the stacks was quantified, showing cells with a degradation of >80%. The excellent electrical and thermal performance of the developed power converter was also validated, which allowed the correct and efficient supply of regulated power (average efficiency above 90%) to the HVDC bus, according to the power setpoint defined by the EMS of the microgrid.