Rapid growth of electric vehicles has increased the demand for fast charging infrastructure, posing new challenges to grid stability and energy management. Meanwhile, the reuse of second-life batteries (SLBs) offers a sustainable approach to battery retirement, mitigating environmental impact and reducing costs. This paper presents a comprehensive framework for modeling and controlling SLBs in DC fast charging stations. A second-order RC equivalent circuit model is developed to characterize the performance of fresh and aged battery modules, and is further scaled to represent full battery packs. Buck-boost DC/DC converters are designed to regulate the DC bus voltage for multiple battery packs with different states of health (SoH), employing dual PI control loops for current and voltage. To enhance transient performance, a disturbance compensation loop is incorporated. In addition, a current allocation strategy based on real-time SoH estimation is proposed to reduce stress on weaker packs and promote more uniform degradation. The simulation results verify the effectiveness of the proposed approach in improving voltage stability and extending battery lifetime, highlighting the feasibility of SLB deployment in fast charging applications.

The precision and stability of droop control are easily affected by the difference of feeder impedance values and hardware filters in islanded inverter-based microgrids with distributed generations. To improve the performance of the conventional droop control, a distributed hierarchical control framework is introduced in this paper for reactive power sharing. Due to limited communication and transmission delays, an improved discrete consensus algorithm is proposed to reduce the overshoot and convergence error. Moreover, according to Lyapunov's second theorem, an event-triggered mechanism is adopted to control time instants of iteration calculation for each agent, and therefore to save communication resources. The proposed control scheme is extended to applications for the case of time-varying communication delays to compensate iteration error and negative effect due to delays in a distributed multi-agent system. To verify the feasibility and superiority of the proposed control scheme, simulations are implemented in MATLAB/Simulink. Several case studies and their results show that the proposed method can improve the convergence speed and the dynamic stability.

Electric vehicles powered by hybrid energy storage systems composed of fuel cells and supercapacitors are of great interest. To further improve the efficiency of such hybrid systems, better energy management strategies need to be developed. This paper proposes an adaptive power allocation method with real-time monitoring and optimization for fuel cell/supercapacitor hybrid energy storage systems used in electric vehicles. This method utilizes a low-pass filter to distribute power between fuel cells and supercapacitors. The cut-off frequency of the filter is obtained by splitting the load current spectrum according to the supercapacitor state of charge (SOC). The DC-link voltage fluctuation and the supercapacitor SOC are monitored in a real-time fashion. Consequently, a real-time optimization scheme is developed to reduce the dependence of the proposed algorithm on its initial parameters and enhance the adaptivity of the proposed algorithm. To validate the effectiveness of the proposed method, a Simulink model is developed and two standard drive cycles (i.e., NYCC and US06) are selected. Simulation results show that the DC-link voltage fluctuation drops significantly and the supercapacitor SOC can be effectively controlled.

Fuel cell powered ferries with fast refueling time and high energy density are of great interest as they help reduce carbon emissions. This paper considers the sizing and management of fuel cell based powertrains and performs a case study using the real-world data of a city ferry, i.e., Älvsnabben 4. An optimization problem is formulated to minimize the sum of the hydrogen cost and the component costs. Various components of the powertrain are examined: electric machine, fuel cell, and energy buffer. In particular, the fuel cell degradation and the cycle life characteristics of different energy buffer technologies including lithium-ion battery, supercapacitor, and lithium-ion capacitor are taken into account. Results show that the total cost of the hybrid system composed of fuel cell and supercapacitor is the lowest due to the long cycle life and high power density of the supercapacitor technology. Moreover, since the hydrogen cost is the major contributor to the total cost, the variation of the hydrogen unit price can significantly impact the total cost.