Energy management strategy based on health state for a PEMFC/Lithium-ion batteries hybrid power system

The traditional energy management strategies (EMSs) for fuel cell/battery hybrid vehicle systems frequently neglect the degradation issues of power sources. The health-conscious EMS can take active control over the operation, thus mitigating the detrimental effects of degradation. Here, we will discuss an EMS that takes into account both proton exchange membrane fuel cell (PEMFC) and lithium-ion battery (LIB) degradation. To develop the desired strategy, performance degradation models for two power sources are constructed. It is the first time that the aggregation of platinum particles is taken into account in the water content model and used as the degradation index of PEMFC. The model's accuracy is checked by comparing the voltage drop when the model outputs steadily with data from experiments. Meanwhile, the optimal range of water content is deter-mined based on the analysis of the impact of water content on the stack voltage degradation. This provides a benchmark for the health control of PEMFC in EMS. Then, accurate knowledge of battery SoC can contribute to the rational management of LIBs. An improved UKF (unscented Kalman filter) algorithm is utilized to jointly estimate the SoC and model parameters of the battery and is compared with other methods. It can be found that the proposed joint estimation method has more precise SoC estimation results than the EKF (extended Kalman filter) and the traditional UKF approaches. This provides a reliable basis for the regulation of LIBs in EMS. Finally, taking PEMFC water content, battery SoC, and the required power as inputs, a rule-based health -conscious EMS is developed. The power response curve obtained from the HIL (hardware-in-the-loop) simulation platform shows that the proposed EMS can meet different load demand changes. In addition, during the test, the water content in the stack is kept in the range of 14-18.5, and the battery SoC is kept in the range of 0.6-0.8. Both of them are within the established benchmark range of energy source health, indicating that the EMS suggested in this paper can effectively reduce fuel cell and LIB attenuation, and meet the power demand.