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Journal ArticleDOI

Power and energy management of grid/PEMFC/battery/supercapacitor hybrid power sources for UPS applications

TL;DR: In this article, a hybrid power and energy source supplied by a proton exchange membrane fuel cell (PEMFC) as the main power source in an uninterruptible power supply (UPS) system is presented.
About: This article is published in International Journal of Electrical Power & Energy Systems.The article was published on 2015-05-01 and is currently open access. It has received 50 citations till now. The article focuses on the topics: Uninterruptible power supply & Hybrid power.

Summary (5 min read)

1. Introduction

  • An uninterruptible power supply (UPS) system based on traditional batteries only is hard to provide sufficient backup power to critical loads, especially when relatively long time supply is necessary.
  • Since the PEMFCs can provide electrical power with high energy density, high efficiency and no pollution, they are considered as a promising technology for UPS products.
  • As a result, fast load demand for the PEMFCs will lead to a high voltage drop in a short time, which is recognized as a fuel starvation and causes the degradation of FC.
  • The power control and energy management of hybrid power sources have already been studied recently.
  • Feroldi et al. [12] presented an energy management strategy for a sustainable hybrid system, which is based on wind-solar energy and bioethanol.

2. Modeling of hybrid power and energy system

  • Li the limiting current density at which the cell voltage will fall rapidly (A⋅cm-2); ni the internal current or parasitic current density that is wasted (A⋅cm-2); and i the PEMFC stack current density (A⋅cm-2).
  • According to the above voltage output equation, an equivalent circuit for electrochemical circuit model of PEMFC is obtained, as shown in Fig. 3, where C is the equivalent capacitor due to the double-layer charging effect (F); cV the voltage across the capacitor (V); actR the activation resistance (Ω); and concR the concentration resistance (Ω).

2.2. Power and energy model of PEMFC

  • The hydrogen and oxygen/air are fed to the PEMFC generating system at an appropriate rate according to the current and voltage drawn from the external load of UPS.
  • Air on the cathode side is often supplied with a higher stoichiometric flow rate because the cathode reaction is much slower than the anode reaction.
  • Three air fans with an optimal speed can supply varying amounts of air for the power and inside temperature demand.
  • According to the real-time current and voltage measurements of PEMFC stack based on the loads of UPS, the power (ranging from 12 to 330 W) can be firstly calculated.
  • The output power of the stack can be calculated by IVP StackStack = (3) where PStack is the output power (W), VStack the output voltage (V), and I the output current of the stack (A).

2.2.1. Hydrogen mass flow rate

  • According to the hydrogen mass flow controller designed by fuzzy logic control rules, the hydrogen flow rate varies between 0 and 4.7 SL/min at stoichiometric ratio of 1.2 and under the current variations of 0 to 9 A, while the air flow rate is supplied by the three fans.
  • The hydrogen flow rate can keep tracking the reference value given by power tracking controller.

2.2.2. Air mass flow rate

  • Because the PEMFC stack selected is an air-breathing and air-cooling FC, that is, air is passing through the cathode compartment in excess of oxygen exact stoichiometry, and the same air is used as a coolant.
  • With the increase of the load, the temperature of stack will go up as soon as possible to obtain a better performance.
  • In general, higher operating temperature is desirable due to decreased mass transport limitations and increased electrochemical reaction rates.

2.3. Modeling of SC

  • A SC is a type of electrochemical energy storage device, which is an electrochemical capacitor that has an unusually high energy density when compared to common capacitors, typically thousands times greater than that of a high capacity electrolytic capacitor.
  • It also has almost 90% of high cycle efficiency.
  • Due to the structure of a SC, the boundary conditions are shown in Fig.
  • In the similar manner, on the surface contacting with a current collector, ion flux is not allowed and the normal component of potential gradient in electrolyte is zero.

2.4. Modeling of lead-acid batteries

  • The lead-acid batteries or secondary batteries are a kind of electrochemical energy storage devices, known as the rechargeable batteries which store energy in the electrochemical form.
  • The use of high-capacity lithium-ion rechargeable batteries have been recommended in the various applications such as electric, hybrid electric vehicles and hybrid power systems including the backup power source.
  • Because it is extremely difficult to build and understand the dynamic modeling of a lead-acid battery, in this paper, a simple battery model is introduced.
  • The battery current BatI as function of the required battery power BatP , the internal resistance BatR and the OVC voltage 0E is [16].

3. Power Sizing of hybrid UPS system

  • In order to meet the demand of the technical reliability and calculate the life cycle costs of the system, the sizing of an UPS hybrid power system will be dealt with the aim of obtaining a cost efficiency system according to any defined hourly load profile and any defined backup time.
  • A solution is defined by PEMFC, SC and battery sizes and the energy management strategy.

3.1. Power sizing of PEMFC

  • A 300W single-phase high-frequency low-loss smart UPS has been designed, with nominal voltage of 36V; minimum supply voltage of 30V; efficiency of 0.9; maximum load of 270W; backup time of 24 hours for PEMFC; backup time of 15 s for SC; and backup time 20 min for battery.
  • The PEMFC size is the largest, the fuel cell capital cost is the highest, and the battery and SC requirements are the least restrictive.
  • Thus, in order to release a 24h continuous backup operation mode, according to its working voltage of 31.5-56.7V, a 300W (36V/8.4A) air-breathing air-cooling self-humidified PEMFC is employed to supply the main power source for UPS system.
  • Because the PEMFC stack is a new type of self-humidified, air-breathing and air-cooling together, some parameters are confidential to the manufacturer of the stack such as the anode volume, cathode volume and so on, the authors have done some experiments, but no simulations.
  • The basic experimental conditions of PEMFC are: hydrogen maximum input flow of 3.9 L/min; hydrogen pressure of 50-55kPa; number of cells of 63; effective area of 18 cm2; start up time of 10 s under the condition of constant voltage; and maximum stack temperature of 55°C.

3.2. Power sizing of lead-acid battery

  • Because the PEMFC is the main power source and lead-acid battery is used as the auxiliary power source in the UPS system, based on minimum cost profile, the sizing of battery is designed taking into account the PEMFC start-up time of 10 s and maintaining time of 10 min when PEMFC fails.
  • Based on the demand of UPS system, 3-cell Yuasa® NP deep cycle lead-acid batteries, with nominal voltage of 12 V, are selected.
  • On the other hand, according to the recommended calculation method of battery size required for constant power load conditions, calculating the battery capacity from the list is 4.46.
  • At present, the lead-acid battery has two types of products: deep cycle battery and gel battery.

4. Power and energy management strategy

  • The purpose of the UPS system with hybrid PEMFC/battery/SC power sources is to provide uninterruptible, reliable, and high-quality power of 24 hours to the loads.
  • The concept of multiple hybrid power sources is to ensure a sustainable power supply for their system.
  • On the other hand, the grid charges the batteries or SCs through the AC/DC recharger.
  • In Fig. 9, when the PEMFC starts up and the external load charges sharply, the batteries or SCs feeds the DC/AC inverter through the DC/DC converter, also known as 3) Battery/SC operating mode.
  • To overcome this issue, the rechargeable batteries or SCs can be employed as the auxiliary power source to respond fast to the external load and protect the PEMFC from degradation and damage.

5.1. Experimental setup

  • The UPS hybrid system with backup PEMFC and SC/battery provides the AC power source and controls the linear loads (e.g. lamp box and resistances) and nonlinear loads (i.e. PC), while the data-acquisition system measures and records the required information.
  • In the PEMFC generating and testing system, both hydrogen and air are regulated by two mass flow controllers (type: F-201C-GAS-22V and F-112AC-GAS-22V, Bronkhorst).
  • The temperature and humidity of air and hydrogen can be measured at the inlet by the hydrotransmitter (type: HD2008TV1, Delta OHM) as well as the pressure transmitter (type: AUS EX 1354X, Burkert) between the inlets of cathode and anode.
  • Fig. 17 shows a photo of the experimental setup.

5.2. Experimental validation

  • The experimental test and analysis have been carried out on the PEMFC generating system and intelligent network UPS hybrid system.
  • As mentioned and discussed above, the performances of the four operating modes of UPS hybrid system are measured with the load of a lamp box.

5.2.1. Utility grid operating mode

  • Based on the developed intelligent UPS system, the voltage-current and power-current performances of the UPS are tested under the conditions of the grid operating mode.
  • Fig. 18 shows the measured power, current curves of input and output and the efficiency profile for UPS without charging the battery and SC.
  • According to the measured value, the efficiency of UPS under the rated load of 270W is %85/)(/GridUPS == ACDCrtDCAC ηηη )(.
  • In grid operating mode, for a high frequency UPS system, its efficiency in the utility grid operating mode should be more than 90% under the rated load of 270W.

5.2.2. Bypass operating mode

  • Fig. 19 shows the measured power, current curves of input and output and the efficiency profile for UPS without charging the battery and SC.
  • According to the measured value, the efficiency of UPS in the bypass operating mode under the rated load of 270W is ( ) 98%UPS Bypassη =.
  • In the bypass operating mode, because the energy flows through the thyristor K0 and wire, the UPS has a loss of 2%.

5.2.3. Battery operating mode

  • Fig. 20 shows the measured input power and current curves of the battery and the output and the efficiency profile for UPS.
  • Mode According to the measured value, the efficiency of UPS under the rated load of 270W is %78//BatUPS == ACDCDCDC ηηη )(.
  • In battery operating mode, because DC/DCη is less than AC/DC(rt)η , UPS(Bat)η is less than UPS(Grid)η .

5.2.4. FC operating mode

  • Fig. 21 shows the measured input power and current curves of the PEMFC and the output and the efficiency profile for UPS without charging the battery and SC.
  • Mode According to the measured value, the efficiency of UPS in FC operating mode under the rated load of 270W is %72//FCUPS == ACDCDCDC ηηη )(.
  • In FC operating mode, as a result of using the current interrupting method to measure the resistance of membrane and improve the performance of the PEMFC, a part of energy has to be lost, UPS(FC)η is less than UPS(Bat)η .
  • If the current interrupting does not be applied in this mode, UPS(FC)η is almost the same as UPS(Bat)η .
  • Fig. 22 shows the voltages and currents waveform in the PEMFC operating mode, where the current interrupting method is used.

5.2.5. SC operating mode

  • Fig. 23 shows the measured input power and current curves of the SC and the output and the efficiency profile for UPS.
  • According to the measured value, the efficiency of UPS under the rated load of 270W is %82//SCUPS == ACDCDCDC ηηη )( In SC operating mode, because UPS(SC)η is more than UPS(Bat)η or UPS(FC)η , it indicates that the SC has better performance in UPS applications, as compared with the PEMFC or battery.
  • In sum, the efficiency of the hybrid PEMFC/battery/SC power sources in the UPS applications is that the efficiency of the PEMFC is less than those of the battery and SC, and the efficiency of SC is the highest.
  • And the total efficiency in UPS system needs deeply to improve.
  • The results can be the same as that in the automobile applications.

6. Conclusion

  • The power control and energy management strategies and efficiency considerations of four operating modes for an intelligent network UPS system with backup PEMFC, SC and battery power sources are proposed in this paper, to overcome the slow dynamics when PEMFC starts up or an external load changes suddenly leading to the fuel starvation and degradation of the stack.
  • Based on the designed UPS hybrid system, three stages of theoretical analysis and experimental test are conducted.
  • Firstly, the modeling and the power sizing of PEMFC, SC and battery are presented and calculated.
  • Then the proposed intelligent power control and energy management strategy of hybrid UPS system are implemented and examined.
  • The theoretical analyses and experimental validations indicate that the developed power and energy management strategies in the UPS system with back PEMFC/SC/battery power sources are suitable for portable, backup and emergency power, and vehicles applications, and can guide the optimal design of the UPS system with hybrid PEMFC/battery/SC power sources.

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Citations
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01 Jan 2019
TL;DR: This thesis aims at proposing suitable batterysupercapacitor HESS designs and control strategies that can effectively extend the battery service lifetime via mitigating its operation stress, thereby realizing the cost reduction on the installing construction and operating costs of the stand-alone photovoltaic (PV) power system.
Abstract: This thesis made a comprehensive study about the battery-supercapacitor hybrid energy storage systems for stand-alone photovoltaic power systems that aims to mitigate primary chemical battery operating stress by minimizing life-limiting factors such as high charging/discharging rate, fluctuating current and frequent charge-discharge transition. The results of this study demonstrate the effectiveness of extending the lifetime of the battery in such systems. The outcomes of this thesis could significantly contribute to energy researchers and industry practitioners to address the issues in rural electrification and to reduce the lead-time required in designing and implementing new hybrid energy storage solution from photovoltaic-battery power systems.

3 citations


Cites background from "Power and energy management of grid..."

  • ...Recently, the development of Battery-SC HESS for residential energy storage applications is beginning to generate positive outcomes, and it typically is connected to the power system via AC or DC coupling [199]–[204]....

    [...]

Journal ArticleDOI
TL;DR: An autonomous energy management strategy is proposed for multiple batteries, photovoltaic (PV) generators and fuel-cells (FCs) s in a promising future power system of more-electric aircraft (MEA), which provides a more comprehensive and generalized approach to coordinate those three types of power sources.

3 citations

Journal ArticleDOI
TL;DR: In this paper , a 50 kW class PEMFC and battery model were evaluated to find appropriate battery capacity for 50 kW-class vehicles, and fuel cell and battery EMS strategies were established in response to rapid load changes.

3 citations

Book ChapterDOI
01 Jan 2019
TL;DR: This chapter introduces a set of possible solutions so that uninterrupted power supply can be provided to emergency feeders and critical loads such as hospitals and communication systems.
Abstract: The major purpose of uninterruptible power supply (UPS) systems is to supply regulated sinusoidal voltage at constant frequency and amplitude. UPS systems are gaining much popularity as a means of providing clean and continuous electricity to critical loads during any disturbances in main grid. Modern equipment is sensitive to power fluctuation and requires back up power supply for optimal performance. This chapter introduces a set of possible solutions so that uninterrupted power supply can be provided to emergency feeders and critical loads such as hospitals and communication systems. Different network configurations can be applied to micro-grid system for obtaining an uninterrupted power supply. Various hybrid energy and modern UPS systems for micro-grid along with their control techniques have been elucidated. A comparative assessment of all UPS technologies on the basis of cost, performance, and efficiency of the system has been presented.

2 citations

Proceedings ArticleDOI
01 Feb 2020
TL;DR: In this article, Li-ion cells were modeled using the 2RC model implemented through the modified block in MATLAB/Simulink and the model parameters were extracted with a relaxation time of only six minutes.
Abstract: Lithium-ion (Li-ion) based batteries are now commonly used in many applications such as electric vehicles, utility-scale storage, and even consumer electronics. However, to maximize the power utilization and optimize runtime voltage-current (V-I) characteristics of these cells, it is imperative to accurately predict the behavior of these batteries for varying load profiles. In this work, we explicitly model Li-ion cells using the 2RC model implemented through the modified block in MATLAB/Simulink. The 2RC model parameters are extracted with a relaxation time of only six minutes. The model was tested (through measurements of six cells) for two Li-ion cell chemistries (NMC and LiFeP04) in three packages (18650, 32650, and 26650) and varying capacities (1500 mAh to 6000 mAh) with high accuracy. The root mean square error between experimental and modeled results ranges from 0.3 ‐ 0.7 % even with varying load profiles, which is key in the accurate performance modeling of these cells. This work will, therefore, be very useful in modeling Li-ion cells and battery pack for a wide variety of applications with diverse usage profiles.

2 citations


Cites background from "Power and energy management of grid..."

  • ...Such accurate modeling is essential for the modeling of Li-ion cells and battery packs for a wide variety of applications with diverse usage profiles [25-28]....

    [...]

References
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Book
09 Oct 2012
TL;DR: A comprehensive guide to PEM fuel cells can be found in this article, covering all aspects of PEM, from theory and fundamentals to practical applications, from design, electrochemistry, heat and mass transport.
Abstract: Demand for fuel cell technology is growing rapidly. Fuel cells are being commercialized to provide power to buildings like hospitals and schools, to replace batteries in portable electronic devices, and as replacements for internal combustion engines in vehicles. PEM (Proton Exchange Membrane) fuel cells are lighter, smaller, and more efficient than other types of fuel cell. As a result, over 80 per cent of fuel cells being produced today are PEM cells. This new edition of Dr. Barbir's groundbreaking book still lays the groundwork for engineers, technicians and students better than any other resource, covering fundamentals of design, electrochemistry, heat and mass transport, as well as providing the context of system design and applications. Yet it now also provides invaluable information on the latest advances in modeling, diagnostics, materials, and components, along with an updated chapter on the evolving applications areas wherein PEM cells are being deployed. This comprehensive guide covers all aspects of PEM fuel cells, from theory and fundamentals to practical applications. It provides solutions to heat and water management problems engineers must face when designing and implementing PEM fuel cells in systems. Hundreds of original illustrations, real-life engineering examples, and end-of-chapter problems help clarify, contextualize, and aid understanding.

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"Power and energy management of grid..." refers background in this paper

  • ...The air volumetric mass flow rate in SL/min is [14]...

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Journal ArticleDOI
30 Apr 2007
TL;DR: In this paper, the authors focused on the use of lithium-ion batteries and carbon/carbon ultracapacitors as the energy storage technologies most likely to be used in future vehicles.
Abstract: The application of batteries and ultracapacitors in electric energy storage units for battery powered (EV) and charge sustaining and plug-in hybrid-electric (HEV and PHEV) vehicles have been studied in detail. The use of IC engines and hydrogen fuel cells as the primary energy converters for the hybrid vehicles was considered. The study focused on the use of lithium-ion batteries and carbon/carbon ultracapacitors as the energy storage technologies most likely to be used in future vehicles. The key findings of the study are as follows. 1) The energy density and power density characteristics of both battery and ultracapacitor technologies are sufficient for the design of attractive EVs, HEVs, and PHEVs. 2) Charge sustaining, engine powered hybrid-electric vehicles (HEVs) can be designed using either batteries or ultracapacitors with fuel economy improvements of 50% and greater. 3) Plug-in hybrids (PHEVs) can be designed with effective all-electric ranges of 30-60 km using lithium-ion batteries that are relatively small. The effective fuel economy of the PHEVs can be very high (greater than 100 mpg) for long daily driving ranges (80-150 km) resulting in a large fraction (greater than 75%) of the energy to power the vehicle being grid electricity. 4) Mild hybrid-electric vehicles (MHEVs) can be designed using ultracapacitors having an energy storage capacity of 75-150 Wh. The fuel economy improvement with the ultracapacitors is 10%-15% higher than with the same weight of batteries due to the higher efficiency of the ultracapacitors and more efficient engine operation. 5) Hybrid-electric vehicles powered by hydrogen fuel cells can use either batteries or ultracapacitors for energy storage. Simulation results indicate the equivalent fuel economy of the fuel cell powered vehicles is 2-3 times higher than that of a gasoline fueled IC vehicle of the same weight and road load. Compared to an engine-powered HEV, the equivalent fuel economy of the hydrogen fuel cell vehicle would be 1.66-2.0 times higher

762 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a perfect energy source supplied by a polymer electrolyte membrane fuel cell (PEMFC) as a main power source and storage devices: battery and supercapacitor, for modern distributed generation system, particularly for future fuel cell vehicle applications.

523 citations


"Power and energy management of grid..." refers background in this paper

  • ...[6] proposed a perfect energy source supplied by a PEMFC as the main power source and storage devices: battery and SC, for modern distributed generation system, particularly for future fuel cell vehicle applications....

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Journal ArticleDOI
TL;DR: Experimental results in a laboratory authenticate that energy-storage devices can assist the FC to meet the vehicle power demand and help achieve better performance, as well as to substantiate the excellent control schemes during motor-drive cycles.
Abstract: This paper studies the impact of fuel-cell (FC) performance and control strategies on the benefits of hybridization. One of the main weak points of the FC is slow dynamics dominated by a temperature and fuel-delivery system (pumps, valves, and, in some cases, a hydrogen reformer). As a result, fast load demand will cause a high voltage drop in a short time, which is recognized as a fuel-starvation phenomenon. Therefore, to employ an FC in vehicle applications, the electrical system must have at least an auxiliary power source to improve system performance when electrical loads demand high energy in a short time. The possibilities of using a supercapacitor or a battery bank as an auxiliary source with an FC main source are presented in detail. The studies of two hybrid power systems for vehicle applications, i.e., FC/battery and FC/supercapacitor hybrid power sources, are explained. Experimental results with small-scale devices (a polymer electrolyte membrane FC of 500 W, 40 A, and 13 V; a lead-acid battery module of 33 Ah and 48 V; and a supercapacitor module of 292 F, 500 A, and 30 V) in a laboratory authenticate that energy-storage devices can assist the FC to meet the vehicle power demand and help achieve better performance, as well as to substantiate the excellent control schemes during motor-drive cycles.

285 citations


"Power and energy management of grid..." refers background in this paper

  • ...It should ensure the enough fuel and battery/SC capacity for providing the power needed by the external load [5]....

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Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of simulation models of energy sources for battery, hybrid, fuel cell and internal combustion vehicles and compare different drive train topologies for energy consumption and emissions as well as for performances.

261 citations


"Power and energy management of grid..." refers background in this paper

  • ...Bat I as function of the required battery power Bat P , the internal resistance Bat R and the OVC voltage 0 E is [16]...

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  • ...The voltage SC V and current SC I are [16] ( ) SC cell s C SC I R V N V − = 0 (12)...

    [...]

Frequently Asked Questions (17)
Q1. What have the authors contributed in "Power and energy management of grid/pemfc/battery/supercapacitor hybrid power sources for ups applications" ?

This paper presents a hybrid power and energy source supplied by a proton exchange membrane fuel cell ( PEMFC ) as the main power source in an uninterruptible power supply ( UPS ) system. 

Since using an air-breathing and self-humidified PEMFC in UPS system, and the PEMFC voltage heavily relies on the air stoichiometric flow rate, the role of the fans is very important to blow more air through the system. 

Since the PEMFCs can provide electrical power with high energy density, high efficiency and no pollution, they are considered as a promising technology for UPS products. 

For the nonlinear electrical response of a battery, the different common modes of discharge are constant current, constant load, and constant power. 

Because the open circuit voltage of lead-acid battery is a function of charge and the current, a simple equivalent circuit for a battery can thus be written as0( ) ( , ) loadV V Q V The authorQ IR= − = (31)where 0( )V Q is the open circuit voltage when 0I = ; ( , )V The authorQ the cell overpotential(relative to the equilibrium), which is a positive voltage loss for a positive (galvanic) current 0I > , and negative for a negative (electrolytic) current 0I < . 

To prevent the PEMFC shutting down when charging, the power control and energy management control unit firstly turns on K3 and K4, which lets the battery charge the SCs, and then turns on K2 and K4, which lets the PEMFC charge the SCs. 

In grid operating mode, for a high frequency UPS system, its efficiency in the utility grid operating mode should be more than 90% under the rated load of 270W. 

Theoutput power of the stack can be calculated byIVP StackStack = (3)where PStack is the output power (W), VStack the output voltage (V), and The authorthe output current of the stack (A). 

Because the PEMFCs are modular, UPS systems using them can be more readily sized to fit a wider variety of sites than thoseusing conventional generators [1] 

The theoretical analyses and experimental validations indicate that the developed power and energy management strategies in the UPS system with back PEMFC/SC/battery power sources are suitable for portable, backup and emergency power, and vehicles applications, and can guide the optimal design of the UPS system with hybrid PEMFC/battery/SC power sources. 

According to the real-time current and voltage measurements of PEMFC stack based on the loads of UPS, the power (ranging from 12 to 330 W) can be firstly calculated. 

Considering again a battery with open circuit voltage, which is 20 max( ) 1 QV t V Q = − , (34)and neglecting the internal resistance, then integrating equation (20), an implicit solution for( )Q t can be obtained as30 max max max1 3 Q QP V Q Q Q = − (35)Fig. 16 shows the discharging process diagrams of 3-cell lead-acid batteries when themain PEMFC fails, while the load of UPS is the rated power of 270W and the minimumdischarging voltage is 30V. 

The air volumetric mass flow rate in SL/min is [14]22 4 608.22 OAir ref O SFINMQ ×⋅××= (6)where MAir is the air mass (kg) and 2OS is the required air stoichiometric ratio, whichis calculated theoretically as follows and selected within 20~30 by experience. 

In this paper, in order to reduce the cost, improve the performance, and decrease the losses for the UPS system, a structure of grid/PEMFC/battery/SC hybrid power system is proposed in a high-frequency single-phase small-power UPS system as depicted in Fig. 

According to (7), (8), and (9), the required air stoichiometric ratio is222222 1)254.1(4N OO Opcell OOM rr MTc VFMS −+∆ −+ = (10)In the designed PEMFC generating system, the air mass flow rate guarantees the enough air supply for the stack, and the air supply and thermal controller keep the temperature of the stack in the range of the 46~55oC. 

Feroldi et al. [12] presented an energy management strategy for a sustainable hybrid system, which is based on wind-solar energy and bioethanol. 

2. In Fig. 2, the outputs of PEMFC, batteries and/or SCs are linked in parallel, and the outputs of power and energy are controlled intelligently by power switches K0-K6 (thyristors) through the energy management and power control system.