Sliding mode control of an autonomous parallel fuel cell-ultracapacitor power source

J.MORE; PULESTON P.F.; C.KUNUSCH; J. RIERA

Campinas

Congreso; 5th International Workshop on Hydrogen and Fuel Cells, WICaC 2010; 2010

CENEH y LH2 - UNICAMP

Nowadays, hydrogen fuel cell (FC) based systems emerge as one promising renewable alternative to fossil fuel systems in automotive and residential applications. However, their output dynamic response is relatively slow, mostly due to water and reactant gases dynamics. To overcome this limitation, FC-supercapacitors (SCs) topologies can be used. The latter is capable of managing very fast power variations, presenting in addition high power density, long lifecycle and good charge/discharge efficiency. In this work, a FC\SCs-based autonomous hybrid system for residential applications is considered. The FC and SCs are connected in parallel, through two separate DC/DC converters, to a DC bus.  Under steady state conditions, the FC must deliver the load power requirement, while maintaining the SCs voltage regulated to the desired value. Under sudden load variations, the FC current rate must be limited to assure a safe transition to the new point of operation. During this current rate limitation mode, the SCs must deliver or absorb the power difference. To this end, a sliding mode strategy is proposed to satisfy to control objectives. The main one is the robust regulation of the DC bus voltage, even in the presence of system uncertainties and disturbances, such as load changes and FC voltage variations. Additionally, a second control objective is attained, namely to guarantee the adequate level of charge in the SCs, once the FC reaches the new steady state operation point. In this way, the system can meet the load power demand, even under sudden changes, and it can also satisfy a power demand higher than the nominal FC power, during short periods. The proposed control strategy is evaluated exhaustively by computer simulation considering fast load variations. The results presented in this work, corresponds to the first stage of a R&D collaboration project for the design and development of a novel FC\SCs-based autonomous hybrid system. In the next phase, the proposed controllers will be implemented and experimentally validated in the ACES´s Fuel Cells Laboratory at the Institut de Robòtica i Informàtica Industrial, CSIC-Technical University of Catalonia (UPC).