Enabled by the Internet of Things technology, effective control and management of critical assets, such as energy storage in electric power systems is of great interest. This article proposes a two-stage energy management framework to minimize the degradation and equivalent hydrogen consumption of electric-hydrogen hybrid energy storage systems in the context of islanded microgrids. The first stage minimizes the system degradation by optimizing the start-stop states of the hydrogen components, including the electrolyzer and the fuel cell. The logic variables associated with the start-stop states and the component reference power are optimized in the first stage. The second stage minimizes the system equivalent hydrogen consumption while minimizing the deviation of the component power with respect to the component reference power determined in the first stage. The objective function of the second stage introduces two weights to measure the contributions of the battery and the hydrogen components to the system equivalent hydrogen consumption, which are defined based on the two virtual forces related to the battery state of charge (SOC) and the hydrogen storage tank state of hydrogen charge (SOHC). Offline and real-time simulations demonstrate the effectiveness of the framework in properly allocating the net load power to the battery and the hydrogen components to optimize the two objectives. Furthermore, the effects of the virtual forces on the SOC, SOHC, and system equivalent hydrogen consumption are investigated.

As an energy storage technology, supercapacitors feature a high power density. In particular, supercapacitors can be charged or discharged by a relatively large pulse current for a limited period of time. This paper takes advantage of this characteristic and develops a dual-mode fast charger for supercapacitors that employs both continuous and fine-tuned pulse currents. Based on the conventional forward converter, the proposed charger introduces an energy storage capacitor and a branch resistor to tune the rising and falling edges of the pulse current, respectively. Consequently, the transitions between the continuous and pulse current modes are significantly accelerated, which ultimately shortens the supercapacitor charging time. A prototype is built and tested using a 3 V/6 F supercapacitor. To charge the supercapacitor from 2 to 2.5 V, the proposed charger takes 0.87 and 1 s when it is configured to operate in the dual-mode and the continuous current mode only, respectively, which leads to a 13% reduction in the charging time. Moreover, compared to the forward converter, the pulse characteristics of the proposed charger are significantly improved in that the pulse rising and falling times are dramatically reduced: 2.1 versus$147~\mu $s and 7.2 versus$103~\mu $s, respectively.

This paper proposes a reconfigurable cell balancing circuit for supercapacitors by incorporating a CLLC converter and coupling each supercapacitor with a bank of six switches. When the supercapacitors are not exchanging energy with external sources or loads, static balancing can be achieved by properly configuring the switches to divide the supercapacitors into two groups based on their voltages. Each group is connected to one port of the CLLC converter and bidirectional power flows between the two groups can be implemented to balance the supercapacitors. If the supercapacitors are being charged or discharged, dynamic balancing can be implemented by bypassing certain supercapacitors with excessively high (during charging) or low (during discharging) voltages. Simulation results verify the static and dynamic balancing schemes.

Due to the compatibility considerations, it is not attractive for the commercial wireless charger to modify the Qi-standard coils for charging multiple loads. This paper would explore the potential of a power relay module (PX) to address this issue. The multiple-coil PX would enhance the effective coupling when the standard coupler fails. In this paper, different types of PXs are developed for various applications, including a two-coil PX using series compensation, a two-coil PX using high-order compensation, and a three-coil PX using high-order compensation. Their power and efficiency characteristics are analyzed in a uniform manner, and the benefits of different PXs are justified through a planar charger and a bowl-shape charger in the experiment. The implemented bowl-shape charger is able to offer one fast-charging channel for a single device (30 W) and one multiple-load channel for at most four devices (each 10 W) simultaneously. The peak efficiency is 88% when the overall delivered power of PX is 70W.

To improve the efficiency of hybrid energy storage systems composed of fuel cells and supercapacitors used in high-power applications such as electrified transportation systems and renewable energy systems, the interfacing power converters need to be carefully designed. This paper proposes an active clamping current-fed three port converter for an application scenario in which modular converters are required to aggregate distributed energy storage resources. The converter topology is conceived to implement four operation modes: single input dual output, dual input single output, and two scenarios of single input single output. These operation modes are combinations of three types of power flows: fuel cell to load, fuel cell to supercapacitor, and supercapacitor to load. Simulation results verify the functionality of the proposed converter.

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.

As the penetration of electric vehicles (EVs) increases, how to power them becomes an even challenging problem. Among others, swapping depleted batteries at a battery swapping station (BSS) is a possible solution as a swapping service may be conveniently completed within minutes. This paper proposes a joint optimization framework to maximize the sum of the BSS revenue and the benefits of the EV owners by introducing tiered pricing incentives including rewards and penalties. Depending on the grid state, the BSS encourages the EV owner to swap a battery with an optimal state of charge that can be beneficial to either the BSS or the EV owner (or even both of them). By conducting a case study, this paper shows that the EV owners can be rewarded or penalized and their benefits can be optimized when the tiered pricing scheme is in effect. Moreover, the BSS can utilize the batteries in stock to boost its capability of shaving the peak of the power grid.

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.

This paper examines the applicability of Peukert’s law to supercapacitor modules and analyzes the underlying supercapacitor physics. Peukert’s law is an empirical relationship originally developed to describe the dependence of the lead-acid battery charge capacity on the discharge current. Recent studies show that Peukert’s law can also be used to characterize the charge delivery capability of supercapacitor cells. Given the relatively low voltage and current ratings of supercapacitor cells, they are usually connected in parallel and/or series in high-power energy storage systems. This paper extends the study of Peukert’s law for supercapacitor cells to supercapacitor modules. After verifying the applicability of Peukert’s law to supercapacitor parallel and series modules, this paper investigates the dependence of the supercapacitor module Peukert constant on voltage and reveals the physical mechanisms accounting for the dependence.

This paper proposes to consolidate a piezoelectric roadway energy harvesting system and a dynamic wireless charging system to improve the energy autonomy of electric vehicles. A conceptual design of the integrated system is presented and the benefits of the integrated system in enhancing the vehicle energy autonomy are analyzed. By comparing the typical power densities of the energy harvesting and wireless charging systems, this paper shows that the vehicle energy dependence on the power grid can be reduced by approximately 20%. To exploit the benefits of the integrated system, this paper outlines multiple open research and development issues.

This paper studies the supercapacitor energy delivery capability during a constant power discharge process, which refers to the amount of energy delivered by a supercapacitor when a constant power load is applied. Extensive constant power discharge experiments are conducted using three supercapacitor samples with different rated capacitances from different manufacturers. The relationship between the delivered energy and the discharge power is examined. In the upper bound case corresponding to a fully charged supercapacitor, the delivered energy increases when the discharge power decreases if the discharge power is above a certain threshold, i.e., Peukert's law applies. When the discharge power is below the threshold, this law does not apply anymore. In the lower bound case corresponding to a partially charged supercapacitor, the delivered energy peaks at a particular discharge power. These relationships are due to the combined effects of three aspects of supercapacitor physics: porous electrode structure, charge redistribution, and self-discharge. This paper also compares the bounds of the delivered energy and shows that the difference is significant.