Fuel Cell Hybrid Power Source Research Articles

Optimal Sizing of Fuel Cell Hybrid Power Sources with Reliability Consideration

This paper addresses the issue of optimal sizing reliability applied to a fuel cell/battery hybrid system. This specific problem raises the global problem of strong coupling between hardware and control parameters. To tackle this matter, the proposed methodology uses nested optimization loops. Furthermore, to increase the optimal design relevance, a reliability assessment of the optimal sizing set is introduced. This new paradigm enables showing the early impact of the reliability criteria on design choices regarding energetic performance index. It leads to a smart design methodology permitting to avoid complexity and save computing time. It considerably helps design engineers set up the best hybridization rate and enables practicing tradeoffs, including reliability aspects in the early design stages.

Air Flow Real‐time Optimization Strategy for Fuel Cell Hybrid Power Sources with Fuel Flow Based on Load‐following

AbstractThe Fuel_LF‐RTO strategy is real‐time optimization (RTO) strategy proposed here to find the optimal values of fueling for the polymer electrolyte membrane fuel cell hybrid power sources under unknown load profile, which is the case of fuel cell vehicle. The proposed optimization strategy is based on global extremum seeking (GES) algorithm and load‐following (LF) control for air and fuel flows. The results show the performance obtained with Fuel_LF‐RTO strategy in comparison with the Static Feed‐Forward strategy. The performance was estimated for constant and variable load. The FC system efficiency and the fuel consumption efficiency for maximum load of 8 kW can increase with up to 1.88% and 11.26 W lpm−1 in comparison with the sFF RTO strategy. Also, the fuel economy is 27.36 L during the 8 kW/12 s constant load cycle, which means an economy of 136.8 lpm. This performance is highlighted for constant load in range 2 to 8 kW, which represents 0.33% and 1.25% from nominal power of the 6 kW FC stack used in this study. Also, the performance was estimate for variable load considering the fuel economy, which can be up to 21.86 l during the 6.25 kW/12 s pulsed load cycle.

Real-time optimization strategy for fuel cell hybrid power sources with load-following control of the fuel or air flow

This paper analyses two Real-Time Optimization (RTO) strategies for Proton Exchange Membrane Fuel Cell (PEMFC) system which is used as main energy source for Fuel Cell Hybrid Power Source (FCHPS) of the FC vehicle (FCV). In this study the optimization function was defined as mix of the FC net power and the Fuel Consumption Efficiency by using two weighting coefficients. The Global Extremum Seeking (GES) algorithm is proposed here as RTO method for multimodal optimization surfaces having many peaks on the plateau around the optimal point that is the Global Maximum Point (GMP). One of the fueling rates is Load-Following (LF) controlled in order to adapt the FC net power to load demand and assure the charge-sustaining mode for the battery. The GES algorithm will establish the optimal duty cycle for the Boost converter, so the proposed strategies will be called the Boost-GES-RTO strategies with Air-LF and Fuel-LF, respectively. The Static Feed-Forward (sFF) control strategy will be used as reference for constant and variable load profile. The gaps in performance indicators were estimated for both Boost-GES-RTO strategies. For example, the gaps in FC system efficiency and fuel economy could be up to 1.61% and 142 lpm, and 2.65 and 114 lpm for the Boost-GES-RTO strategies with Air-LF and Fuel-LF. The performance of Boost-GES-RTO strategies was also shown by estimating the fuel economy for 6 kW FCHPS under variable load profile.

Performances analysis of WT-DFIG with PV and fuel cell hybrid power sources system associated with hydrogen storage hybrid energy system

This paper highlights the modeling and the simulation of a micro-grid renewable power system. It comprises wind turbine (WT) doubly fed induction generators (DFIGs), photovoltaic generator (PV), a proton exchange membrane (PEM) fuel cell (FC) generator, a water electrolyzer used for long-term storage, a Hydrogen tank, and a battery bank (BB) utilized for short-term storage. Based on the given configuration and the different characteristics of the main components in the micro-grid, an overall control and a power management strategy are proposed for this system. This strategy consists in charging the BBs and producing hydrogen from the water electrolyzer in the case of excess power from the WT-DFIGs and PV generators. Therefore, the FC and the BBs will be used as a backup generator to supply the demand required power, when the WT-DFIGs and the PV energy are deficient. The effectiveness of this contribution is verified through computer simulations, where very satisfactory results are obtained.

Energy control strategies for the Fuel Cell Hybrid Power Source under unknown load profile

Four new energy control strategies are proposed here for the Fuel Cell Hybrid Power Source (FCHPS) used in stationary and mobile FC application (such as the FC backup source for a smart-house and FC vehicle, respectively) based on the Load Following (LF) control and Maximum Efficiency Point Tracking (MEPT) control of the fueling rates. The LF control approach is used to design simple strategies of the Energy Management Unit (EMU) that will assure a charge-sustaining mode for the batteries stack of the Energy Storage System (ESS). If a fueling rate is controlled based on the LF strategy, then the other is controlled based on MEPT strategy in order to maximize the FC net power available. The advantages of the proposed EMU strategies during an unknown load cycle are comparatively shown.

Nonlinear control of fuel cell hybrid power sources: Part II – Current control

In this paper is proposed a nonlinear current-mode control for the fuel cell/battery/ultracapacitor hybrid power sources (HPS) that improves the ripple factor of the fuel cell current. The nonlinear current control is analyzed and designed using a systematic approach. The design goal is to generate an anti-ripple via buck current controlled source in order to mitigate the inverter current ripple. All the results have been validated in several simulations. The simulation results successfully show that nonlinear current-mode control determines in the low frequency-domain better performances than other current-mode control techniques, such as the hysteretic current-mode controller or the peak current-mode controller. The current ripple factor is one of the used performance indicators.

Nonlinear control of fuel cell hybrid power sources: Part I – Voltage control

In this paper is proposed a nonlinear control for fuel cell/battery/ultracapacitor hybrid power sources (HPS) that improves the performance and durability of fuel cell. The nonlinear voltage control is analyzed and designed using a systematic approach. The design goal is to stabilize the HPS output voltage at a low voltage ripple that is also spread in a large frequencies band. All the results have been validated in several simulations. The simulation results successfully show that nonlinear voltage control performs good performances in the frequency-domain (a high spreading level of power spectrum) and in the time domain (a low level of output voltage ripple factor), too.

Development of integrated fuel cell hybrid power source for electric forklift

A hybrid drivetrain comprising a 16 kW polymer electrolyte membrane fuel cell system, ultracapacitor modules and a lead-acid battery was constructed and experimentally tested in a real counterweight forklift application. A scaled-down version of the hybrid system was assembled and tested in a controlled laboratory environment using a controllable resistive load. The control loops were operating in an in-house developed embedded system. The software is designed for building generic control applications, and the source code has been released as open source and made available on the internet. The hybrid drivetrain supplied the required 50 kW peak power in a typical forklift work cycle consisting of both loaded and unloaded driving, and lifting of a 2.4 tonne load. Load variations seen by the fuel cell were a fraction of the total current drawn by the forklift, with the average fuel cell power being 55% of nominal rating. A simple fuel cell hybrid model was also developed to further study the effects of energy storage dimensioning. Simulation results indicate that while a battery alone significantly reduces the load variations of the fuel cell, an ultracapacitor reduces them even further. Furthermore, a relatively small ultracapacitor is enough to achieve most of the potential benefit.

A new topology of fuel cell hybrid power source for efficient operation and high reliability

This paper analyzes a new fuel cell Hybrid Power Source (HPS) topology having the feature to mitigate the current ripple of the fuel cell inverter system. In the operation of the inverter system that is grid connected or supplies AC motors in vehicle application, the current ripple normally appears at the DC port of the fuel cell HPS. Consequently, if mitigation measures are not applied, this ripple is back propagated to the fuel cell stack. Other features of the proposed fuel cell HPS are the Maximum Power Point (MPP) tracking, high reliability in operation under sharp power pulses and improved energy efficiency in high power applications. This topology uses an inverter system directly powered from the appropriate fuel cell stack and a controlled buck current source as low power source used for ripple mitigation. The low frequency ripple mitigation is based on active control. The anti-ripple current is injected in HPS output node and this has the LF power spectrum almost the same with the inverter ripple. Consequently, the fuel cell current ripple is mitigated by the designed active control. The ripple mitigation performances are evaluated by indicators that are defined to measure the mitigation ratio of the low frequency harmonics. In this paper it is shown that good performances are obtained by using the hysteretic current control, but better if a dedicated nonlinear controller is used. Two ways to design the nonlinear control law are proposed. First is based on simulation trials that help to draw the characteristic of ripple mitigation ratio vs. fuel cell current ripple. The second is based on Fuzzy Logic Controller (FLC). The ripple factor is up to 1% in both cases.

Analysis of Differential Flatness-Based Control for a Fuel Cell Hybrid Power Source

This paper presents an innovative control law for distributed dc generation supplied by a fuel cell (FC) (main source) and supercapacitor (auxiliary source). This kind of system is a multiconverter structure and exhibits nonlinear behavior. The operation of a multiconverter structure can lead to interactions between the controls of the converters if they are designed separately. Typically, interactions between converters are studied using impedance criteria to investigate the stability of cascaded systems. In this paper, a nonlinear control algorithm based on the flatness properties of the system is proposed. Flatness provides a convenient framework for meeting a number of performance specifications for the hybrid power source. Using the flatness property, we propose simple solutions to hybrid energy management and stabilization problems. The design controller parameters are autonomous of the operating point; moreover, interactions between converters are taken into account by the controllers, and high dynamics in disturbance rejection is achieved. To validate the proposed method, a hardware system is realized with analog circuits, and digital estimation is accomplished with a dSPACE controller. Experimental results with small-scale devices (a polymer electrolyte membrane FC of 1200 W, 46 A and a supercapacitor module of 100 F, 500 A, and 32 V) in a laboratory corroborate the excellent control scheme during a motor-drive cycle.

Operating Characteristics of a Direct Methanol Fuel Cell and Li-ion Battery Hybrid Power Sources

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