Multi-stack Fuel Cell System Research Articles

Fuzzy logic-based energy management system for grid-connected residential DC microgrids with multi-stack fuel cell systems: A multi-objective approach

Hybrid energy storage systems (HESS) are considered for use in renewable residential DC microgrids. This architecture is shown as a technically feasible solution to deal with the stochasticity of renewable energy sources, however, the complexity of its design and management increases inexorably. To address this problem, this paper proposes a fuzzy logic-based energy management system (EMS) for use in grid-connected residential DC microgrids with HESS. It is a hydrogen-based HESS, composed of batteries and multi-stack fuel cell system. The proposed EMS is based on a multivariable and multistage fuzzy logic controller, specially designed to cope with a multi-objective problem whose solution increases the microgrid performance in terms of efficiency, operating costs, and lifespan of the HESS. The proposed EMS considers the power balance in the microgrid and its prediction, the performance and degradation of its subsystems, as well as the main electricity grid costs. This article assesses the performance of the developed EMS with respect to three reference EMSs present in the literature: the widely used dual-band hysteresis and two based on multi-objective model predictive control. Simulation results show an increase in the performance of the microgrid from a technical and economic point of view.

Stacks multi-objective allocation optimization for multi-stack fuel cell systems

For a multi-stack fuel cell system (MFCS), the optimal stacks allocation result with a single optimization index cannot meet the MFCS requirements under various operating conditions. In this work, an MFCS stacks multi-objective allocation optimization method is proposed. A multi-objective optimization model of MFCS stacks allocation with boundary conditions is established to obtain the optimal MFCS stacks allocation scheme. The minimum life-cycle cost (LCC) is selected as an optimization objective to investigate the mathematical modeling process of the stacks optimization allocation problem. The different optimization indexes, application scenarios, stack unit cost trends, hydrogen and stack retail prices, stack characteristics, and hydrogen unit usage cost weights have an impact on the minimum LCC-based MFCS stacks allocation results. As a result, compared to the conventional equal allocation MFCS, the minimum LCC-based stacks allocation MFCS could save 0.06 kg per 100 km of hydrogen for a 240 kW MFCS under the C-WTVC driving cycle. Finally, the multi-objective optimization method for determining the optimal MFCS stacks allocation scheme is discussed.

Online energy management strategy considering fuel cell fault for multi-stack fuel cell hybrid vehicle based on multi-agent reinforcement learning

Because of the high-power demand of fuel cell hybrid vehicles, a multi-stack fuel cell system (MFCS) composed of multiple low-power fuel cell stacks (FCSs) instead of a high-power one has become a satisfactory solution. This is due to the modularity of MFCS, which is more reliable and durable. However, the hybrid power system (MHPSS) of an MFCS hybrid electric vehicle possesses not only MFCS, but also batteries to improve the dynamic performance of MHPSS. Due to the difference in characteristics of MFCS and battery, the energy management strategy (EMS) of MHPSS is the key of ensuring its safe and efficient operation. However, most of the existing MHPSS EMSs are complicated in design and complex to compute online. Besides, they also do not consider the robustness of EMS, that is, EMS has the ability to guarantee the safe operation of MHPSS when the MFCS fails. To solve the above problems, this paper proposes an EMS based on independent Q-learning (IQL) which is an algorithm of multi-agent reinforcement learning to maintain battery state of charge (SOC) and minimize hydrogen consumption. The proposed EMS is not only simple in design, but also can guarantee the normal operation of the MHPSS when the MFCS fails, and can be transplanted to execute online on a microcontroller unit or a field programmable gate array. The various parts of the MHPSS model are first built, then the IQL strategy (IQLS) is trained offline in the established model environment, and finally, the IQLS is ported to the hardware-in-the-loop platform for validation. In order to verify the effectiveness of the proposed EMS, the solution of dimensionality-reduced DP is also used to calculate the fuel economy. Through the experimental verification under different initial SOC and driving cycles, it can be seen that the IQLS proposed in this paper can achieve the goal of maintaining battery SOC and minimizing hydrogen consumption, and also has good generalization ability and safe operation ability under fault conditions.

Minimum hydrogen consumption power allocation strategy for the multi-stack fuel cell (MFC) system based on a discrete approach

In high-powered application scenarios, a multi-stack fuel cell system (MFCS) could have advantages such as higher robustness, lifetime, and reliability than a single-stack fuel cell system. In particular, MFCS could maintain a high efficiency and increase system redundancy by power configuration between subsystems. In order to reduce the operational expenses for systems, a reasonable power management strategy is necessary to minimize the hydrogen consumption of MFCS. First, the power-hydrogen consumption curve of the single-stack fuel cell system is discretized from experimental measurements. Next, the discrete data are reassembled by the inverse derivation of the dynamic programming method to produce a minimum solution for the hydrogen consumption in the output power range. It is found that the strategy varies depending on activated state On or Off. Finally, two power allocation strategies are developed and modeled in a lookup-table block considering the activated state. The optimal stack output power strategy is analyzed with four stacks. The results indicate that the hydrogen consumption is smaller and more efficient than the other allocation strategies. It can respond to the load demand with a high efficiency sooner than the average strategy.

Design and energy consumption research of an integrated air supply device for multi-stack fuel cell systems

The multi-stack fuel cell system (MFCS) could be widely used in high-power application scenarios because of its higher efficiency, stronger robustness and longer life. For a specific application scenario, an integrated air supply device is designed to meet the air demand of each fuel cell stack by maintaining the air pressure in the buffer. Under different buffer pressure control strategies (for example, constant pressure control and hybrid control), the maximum electrical power and electrical power consumption of the integrated air supply device for the MFCS are analyzed. The results show that compared with the single-stack scheme, the integrated air supply device can significantly reduce the maximum electric power and the electric power consumption. Using the 140 kW, 210 kW, and 280 kW MFCS as examples, with the increase of the power level of the fuel cell system, the benefits of the designed integrated air supply device become increasingly apparent.

Comparison of Different Topologies of Thermal Management Subsystems in Multi-Stack Fuel Cell Systems

The performance of a fuel cell stack is affected by the operating temperature of the stack. The thermal management subsystem of a multi-stack fuel cell system (MFCS) is particularly significant for the operating temperature control of each stack in the MFCS. To study the influence of different topologies of a MFCS thermal management subsystem, this paper proposes and establishes two different topologies. Firstly, the integrated topology is proposed. Secondly, seven component models, namely the mixer, thermostat, radiator, tank, pump, bypass value, and proton exchange membrane fuel cell stack temperature models, are described in detail. Finally, the performance of the two topologies of the MFCS thermal management subsystem under two working conditions, steady (200 A) and variable (China heavy-duty commercial test cycle, C-WTVC), is compared. Furthermore, there are two evaluating indicators, including the stability duration and deviation of the operating temperatures of the single stack in the MFCS. Results show that when the MFCS operates under steady working conditions, the integrated topology is superior in operating temperature control accuracy (ΔT<0.5 K), while the distributed topology is superior in the adjustment process (t ≤ 100 s). Moreover, when the MFCS operates under variable working conditions, the distributed topology is superior in operating temperature control accuracy.

Post-prognostics decision-making strategy for load allocation on a stochastically deteriorating multi-stack fuel cell system

This work proposes a load allocation decision strategy based on deterioration prognostics information for multi-stack fuel cell systems. The fuel cell deterioration is characterized by the overall resistance value, as it carries the key aging information of a fuel cell. The fuel cell deterioration dynamics is then modeled as an increasing stochastic process whose trend is a function of the fuel cell output power. Combining system deterioration and fuel cell consumption, a multi-objective optimization (MOO) based decision-making strategy is proposed to manage the operation of a multi-stack fuel cell system. Based on this algorithm, the optimal operating power load is computed for each stack. Finally, the performance of the proposed approach is compared to the case without post-prognostics decision for a three-stack fuel cell system. The simulation results show that the proposed post-prognostics decision-making strategy can manage fuel cell system operating in real time by scheduling the optimal load allocation among stacks.

Online identification of optimal efficiency of multi-stack fuel cells(MFCS)

With the development of fuel cells, the demand for high-power fuel cells has gradually increased, but the multi-stack fuel cell system(MFCS) has received wide attention due to the existing technical barriers. The optimal efficiency of the multi-stack fuel cell system is the target, and the power distribution point of the multi-stack fuel cell is obtained by combining the KKT condition. Equipped with the recursive gradient correction method, the online identification of the optimal efficiency of the system is realized. The results are compared with the average distribution and Daisy-chain methods, and the online identification algorithm results in the highest optimal efficiency and the lowest hydrogen consumption. It was validated on two 1kW air-cooled fuel cell systems.

Performance evaluation of a solid oxide fuel cell multi-stack combined heat and power system with two power distribution strategies

Solid oxide fuel cell (SOFC) combined heat and power (CHP) system is a promising candidate for future energy conversion systems. Large power SOFC-CHP system needs multi-stack fuel cell (MFC) to solve the problems of thermal stress and system stability because MFC systems can achieve better performances for maximum power output and average efficiency than single stack fuel cell systems. This study develops an energy management strategy (EMS) for a SOFC multi-stack CHP system coupled with a methane reformer. SOFC multi-stacks are connected in parallel and verified by the published results. The effect of pressure and temperature on the overall multi-stack CHP system electrical efficiency and heat power is investigated with chain and adaptive EMS. The results show that as temperature and pressure increase, the system power increases. The temperature is more effective for the multi-stack system peak efficiency. Up to 11% of electrical system efficiency can be improved when the temperature rises from 700 °C (973 K) to 900 °C (1173 K). However, higher pressure reduces the peak efficiency by 1.5%. Both temperature and pressure can enlarge the output power range. The proposed model can serve as an effective solution for optimizing the SOFC multi-stack CHP system running on methane.

A review on proton exchange membrane multi-stack fuel cell systems: architecture, performance, and power management

To achieve carbon emission reduction and energy structure upgrading, the proton exchange membrane (PEM) multi-stack fuel cell system (MFCS) is an option to meet high-power demands in application scenarios. However, several barriers of the PEM MFCS have not been solved. This paper is aimed to summarize existing information and propose future R&D potentials. Firstly, detailed R&D activities and advances related to PEM MFCSs are reviewed including applications and design principle, architectures (fluidic, electrical, and thermal), power management strategy (PMS), water and thermal management, degraded mode operation, lifetime, efficiency, and hydrogen consumption. Among them, applications and design principle include application scenarios and influencing factors. Moreover, the architecture determination for MFCSs is the core issue, directly affecting the PMS, water and thermal management, degraded mode operation, lifetime, efficiency, and hydrogen consumption. It is noted that a MFCS is better than a single fuel cell system (SFCS) in fields of the lifetime, efficiency, and hydrogen consumption. Furthermore, the synergy between internal combustion engines (ICEs) and MFCSs is proposed to be applied for the MFCS R&D. Secondly, scientific challenges and prospects are presented, including effects of the load power-sharing on the lifetime and efficiency, comparisons of the performance, efficiency and lifetime, and control issues. Finally, the difference of several aspects is discussed, including the architecture, redundancy, lifetime, and PMS between a PEM MFCS and a PEM SFCS.

Numerical Analysis of 0-40 Kw Multistack Fuel Cell System with Series-Type Configuration and Active Hydrogen Recovery

Numerical Analysis of 0-40 Kw Multistack Fuel Cell System with Series-Type Configuration and Active Hydrogen Recovery

Scenario-oriented stacks allocation optimization for multi-stack fuel cell systems

The multi-stack fuel cell system (MFCS) could have advantages (e.g. higher efficiency, stronger robustness, longer lifetime, etc.) versus the single-stack fuel cell system (SFCS) in high-powered application scenarios. For an application scenario with its probability distribution of electrical power demands, the optimization problem of stacks allocation is generally proposed for the MFCS under constraint conditions of the probability distribution and characteristics (e.g. specific efficiency curves) of a set of available stacks. As a special case, a decision model of MFCS stacks allocation and related power management for the application of heavy-duty commercial vehicles is established with an integrated optimization index of efficiency and remaining useful life (RUL) and co-solved by iterative and heuristic algorithms. The optimal stacks allocation schemes for three stacks to five stacks is obtained. The optimal stacks output powers scheme is analyzed with three stacks. Finally, the solution results are investigated and analyzed through change the impact factors of efficiency weights, application scenarios, the efficiency, and RUL characteristics of available stacks.

Hardware-in-the-loop real-time validation of fuel cell electric vehicle power system based on multi-stack fuel cell construction

This paper proposed a Fuel Cell Electric Vehicle (FCEV) power system model which was validated by Hardware-in-the-Loop (HIL) real-time emulation. Multi-stack Fuel Cell (MFC) system was used to increase the system redundancy. Nickel-metal Hydride (NiMH) battery pack (BAT) was selected as the secondary energy source. Dual-input single-output Boost converters were connected with MFC system to satisfy the voltage requirement of DC bus. Bi-directional Buck-Boost converter was connected with BAT and then both discharging and charging modes were controlled. Close loop control strategies were developed for converters to assure their stabilities. Rule-based Energy Management Strategy (REMS) was proposed to distribute the required power among Proton Membrane Exchange Fuel Cells (PEMFCs) and BAT. The proposed model was evaluated by HIL real-time emulation, using the Supplemental Federal Test Procedure US06 (SFTP-US06) driving cycle. MicroLabBox, in which real-time processor and Field Programmable Gate Array (FPGA) were embedded, was selected as the HIL real-time validation platform. The MFC system, BAT model, REMS and low-level controllers were executed by real-time processor while the converter general models were built in FPGA. According to the results, the proposed model and method effectively driven MFC system operating in high efficiency region and successfully kept BAT State of Charge (SOC) in the desired range.

Increment-oriented online power distribution strategy for multi-stack proton exchange membrane fuel cell systems aimed at collaborative performance enhancement

The multi-stack fuel cell system based on proton exchange membrane fuel cell has gained increasing attraction in high-power transportation applications. However, the real-time coordinated optimization among multiple fuel cell systems still remains a promising problem. To achieve the online collaborative performance enhancement between fuel economy and durability for the parallel multi-stack architecture, an increment-oriented power distribution strategy is proposed in this paper. It is inspired by the quadratic polynomial formulation derived from the hydrogen consumption analysis of integrated fuel cell system. The quantitative correlation between the fuel economy and durability is obtained with analytical power increments. To improve the strategy applicability with fault tolerance, iterative high-order sliding-mode differentiation procedure is utilized in the initial condition determination. Besides, performance-dominated power limits are considered in the global switching sequence calculation. The effectiveness and practicability of the proposed strategy are verified by two designed scenario cases with one-cycle short-term and life-cycle long-term evaluations. Detailed simulation results demonstrate that the proposed strategy can guarantee fault tolerance operation and collaborative performance enhancement for multi-stack fuel cell systems with minimum hydrogen consumption and maximum service life compared with other advanced strategies. • The hydrogen consumption characteristics for PEM fuel cell system is analyzed. • An increment-oriented power distribution strategy for MFCS is proposed. • Coupling between fuel economy and durability for MFCS is characterized. • Fault tolerance performance of the proposed strategy are investigated. • Collaborative performance between fuel economy and durability is improved.

Experimental study of the dynamic and transient characteristics of sub-health fuel cell multi-stack systems without DC/DC

Multi-stack fuel cell systems without DC/DC converters can greatly reduce cost, efficiency loss, and particularly appropriate for weight-constrained applications. In this study, two sub-health fuel cell stacks with poor consistency were applied to study the dynamic and transient characteristics, power adaptive allocation and output stability in no-DC/DC series and parallel architectures. The results show voltage difference, voltage overshoot rate and undershoot rate in the series system are positively correlated with current loads, and the poor performance stack is more serious. In the parallel structure, the output currents are unequal and the current difference goes up with the increase of loads. Furthermore, extremely current overshoot and backflow phenomenon were observed at the moment of one fuel cell suddenly turned on. Unexpectedly, the transient backflow current flows through the same point when it rebounds and the poor consistency fuel cell stacks have similar transient current. The terrific result is the fuel cells run steadily and less than 50 ms transient process in both structures. The results not only indicate the proposed architectures are feasible and provide a foundation research for no-DC/DC multi-stack systems management, but also lay a novel reference for the improvement and verification of the fuel cell transient mathematical model.

A Grid-Tied Fuel Cell Multilevel Inverter with Low Harmonic Distortions

As a result of global energy demand increase, concerns over global warming, and rapid exhaustion of fossil fuels, there is a growing interest in energy system dependence on clean and sustainable energy resources. Attractive power technologies include photovoltaic panels, wind turbines, and biomass power. Fuel cells are also clean energy units that substitute power generators based on fossil fuels. They are employed in various applications, including transportation, stationary power, and small portable power. Fuel cell connections to utility grids require that the power conditioning units, interfacing the fuel cells and the grids, operate accordingly (by complying with the grid requirements). This study aims to model a centralised, single-stage grid-tied three-level diode clamped inverter interfacing a multi-stack fuel cell system. The inverter is expected to produce harmonic distortions of less than 0.5% and achieve an efficiency of 85%. Besides the grid, the system consists of a 1.54 MW/1400 V DC proton exchange membrane fuel cell, a 1.3 MW three-level diode clamped inverter with a nominal voltage of 600 V, and an inductance-capacitance-inductance (LCL) filter. Two case studies based on the load conditions are considered to assess the developed system’s performance further. In case 1, the fuel cell system generates enough power to fully meet this load and exports the excess to the grid. In the other case, a load of 2.5 MW was connected at the grid-tied fuel cell inverter’s output terminals. The system imports the grid’s power to meet the 2.5 MW load since the fuel cell can only produce 1.54 MW. It is demonstrated that the system can supply and also receive power from the grid. The results show the developed system’s good performance with a low total harmonic distortion of about 0.12% for the voltage and 0.07% for the current. The results also reveal that the fuel cell inverter voltage and the frequency at the point of common coupling comply with the grid requirements.

Integration of a Multi-Stack Fuel Cell System in Microgrids: A Solution Based on Model Predictive Control

This paper proposes a multi-objective model predictive control (MPC) designed for the power management of a multi-stack fuel cell (FC) system integrated into a renewable sources-based microgrid. The main advantage of MPC is the fact that it allows the current timeslot to be optimized while taking future timeslots into account. The multi-objective function solves the problem related to the power dispatch at time that includes criteria to reduce the multi-stack FC degradation, operating and maintenance costs, as well as hydrogen consumption. Regarding the scientific literature, the novelty of this paper lies in the proposal of a generalized MPC controller for a multi-stack FC that can be used independently of the number of stacks that make it up. Although all the stacks that make up the modular FC system are identical, their levels of degradation, in general, will not be. Thus, over time, each stack can present a different behavior. Therefore, the power control strategy cannot be based on an equal distribution according to the nominal power of each stack. On the contrary, the control algorithm should take advantage of the characteristics of the multi-stack FC concept, distributing operation across all the stacks regarding their capacity to produce power/energy, and optimizing the overall performance.

A Power Allocation Method for Multistack PEMFC System Considering Fuel Cell Performance Consistency

The purpose of this work is to design a power allocation method (PAM) for multistack fuel cell system (MFCS). Due to the limitations of technology, large-scale application of proton exchange membrane fuel cell (PEMFC) in the field of rail transportation has not been implemented. Therefore, this study presents an MFCS to promote the use of PEMFCs in the high-power energy market. During the operation of the MFCS, since the output power of the FC varies dynamically with different operation conditions, the performance of each stack is usually inconsistent. A method for evaluating the degree of performance degradation (DOPD) of stacks is presented in this study. In addition, a fuel cell (FC) semiempirical model is also adopted to simulate the effects of aging on the stacks’ performance. In order to maintain the uniform performance of stacks and enhance the lifespan of the MFCS, a PAM that considers the DOPD of each stack is presented. Besides, in order to facilitate system expansion, this article proposes a virtual droop control method to realize power splitting among the stacks. Also, a voltage control strategy is presented to compensate for the bus voltage drop caused by the droop control. The effectiveness and practicability of the presented PAM and MFCS are verified on the hardware-in-the-loop test bench constructed by RT-LAB.

A method to study the intake consistency of the dual-stack polymer electrolyte membrane fuel cell system under dynamic operating conditions

The Polymer Electrolyte Membrane Fuel Cell (PEMFC) system is considered as one of the most potential power plant on vehicle. However, the efficiency of the high power fuel cell stack has restricted the high power system which is developed for the full power fuel cell vehicle. The multi-stack system integrated by several fuel cell stacks is a solution aimed for high power level system. However, the inconsistency of the stacks flow distribution restricts the performance uniformity of each stacks and the efficiency of the multi-stack fuel cell system. In this paper, a dual-stack polymer electrolyte membrane fuel cell system was setup, and its intake manifold was established. A porous medium was applied to replace the complex flow field structure inside the fuel cells to simulate the pressure drop of the gas through the stack. According to the operating conditions of the vehicle, variable conditions are designed to carry out simulation experiments for the first time. The results show that there is not a significant effect of the changing load’s range on the instantaneous uniformity. However, the initial value of the changing load has a great influence on the instantaneous uniformity. In addition, the settling time of the loading process is much shorter than that of the load shedding process. The equivalent model of porous media proposed provides a new method to model the fuel cell stack, which is very useful in the fuel cell pipe system design and system dynamic response analysis. The uniformity simulation result provides the directions for the fuel cell control strategy design and optimization, and the references for gas intake manifold design.

Heat management methodology for enhanced global efficiency in hybrid electric vehicles

The transportation impact on pollution and global climate change, has forced the automotive sector to search for more ecological solutions. Owing to the different properties of Fuel Cell (FC), real potential for reducing vehicles’ emissions has been witnessed. The optimization of FC integration within Electric Vehicles (EVs) is one of the original solutions. This paper presents an innovating solution of multi-stack Fuel Cell Electrical Vehicle (FCEV) in terms of efficiency, durability and ecological impact on environment. The main objective is to illustrate the interest of using the multi-stack FC system on the global autonomy, cycling, and efficiency enhancement, besides optimizing its operation performance.