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Journal ArticleDOI

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

01 May 2015-International Journal of Electrical Power & Energy Systems (Elsevier)-Vol. 67, pp 598-612

Abstract: 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. To prevent the PEMFC from fuel starvation and degradation and realize their seamless linking in the hybrid UPS system, the power and energy are balanced by the battery and/or supercapacitor (SC) as two alternative auxiliary power sources. Based on the modeling and sizing of hybrid power and energy components, the power and energy management strategies and efficiency measurements of four operating modes in UPS system are proposed. To evaluate the proposed strategies, an experimental setup is implemented by a data acquisition system, a PEMFC generating system, and a UPS system including AC/DC rectifier, DC/AC inverter, DC/DC converter, AC/DC recharger and its intelligent control unit. Experimental results with the characteristics of a 300 W self-humidified air-breathing of PEMFC, 3-cell 12 V/5 Ah of batteries, and two 16-cell 120 F/2.7 V of SCs in parallel corroborate the excellent management strategies in the four operating modes of UPS system, which provides the basis for the optimal design of the UPS system with hybrid PEMFC/battery/SC power sources.
Topics: Uninterruptible power supply (60%), Hybrid power (60%), Energy source (56%), Battery (electricity) (53%), Lead–acid battery (51%)

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1
Power and energy management of
grid/PEMFC/battery/supercapacitor hybrid power sources
for UPS applications
Yuedong Zhan
a, *
, Youguang Guo
b
, Jianguo Zhu
b
and Li Li
a
a
Department of Automation, Kunming University of Science and Technology
Kunming, 650500, China
b
School of Electrical, Mechanical and Mechatronic Systems, University of
Technology, Sydney
PO Box 123, Broadway, NSW 2007, Australia
(Emails: ydzhan@163.com, youguang.guo-1@uts.edu.au, Jianguo.zhu@uts.edu.au)
*Corresponding author: Tel.: +86 871 5623806; Fax: +86 871 5916643, Email
address: ydzhan@163.com (Yuedong Zhan)
ABSTRACT
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. To prevent the PEMFC from fuel starvation and degradation and
realize their seamless linking in the hybrid UPS system, the power and energy are
balanced by the battery and/or supercapacitor (SC) as two alternative auxiliary power
sources. Based on the modeling and sizing of hybrid power and energy components, the
power and energy management strategies and efficiency measurements of four
operating modes in UPS system are proposed. To evaluate the proposed strategies, an

2
experimental setup is implemented by a data acquisition system, a PEMFC generating
system, and an UPS system including AC/DC rectifier, DC/AC inverter, DC/DC
converter, AC/DC recharger and its intelligent control unit. Experimental results with
the characteristics of a 300W self-humidified air-breathing of PEMFC, 3-cell 12V/5Ah
of batteries, and two 16-cell 120F/2.7V of SCs in parallel corroborate the excellent
management strategies in the four operating modes of UPS system, which provides the
basis for the optimal design of the UPS system with hybrid PEMFC/battery/SC power
sources.
Keywords: Power and energy management; Proton exchange membrane fuel cell
(PEMFC); Lead-acid battery; Supercapacitor (SC); Uninterruptible power supply (UPS)
system
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. Other energy sources and storage technologies, such as a
proton exchange membrane fuel cells (PEMFC) and liquid-fed direct methanol fuel cell
(DMFC), have been investigated to replace the batteries. 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. Hence, compared with
other energy storage devices, such as battery and supercapacitor (SC), the PEMFCs can
offer longer continuous run-time of 24 hours and greater durability in harsh outdoor
environments under a wide range of temperature conditions. Compared with
conventional internal combustion generators, the PEMFCs are quieter and have low or
zero emissions depending on fuel source. Because the PEMFCs are modular, UPS
systems using them can be more readily sized to fit a wider variety of sites than those

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using conventional generators [1].
The PEMFCs are emerging as an economically viable option for providing UPS
systems, which play a very important role as the backup and emergency power supply
for important applications, particularly for computers, medical/life support systems,
communication systems, office equipment, hospital instruments, industrial controls and
integrated data center to supply uninterruptible and reliable power with constant voltage
and frequency in case of power failure [2, 3]. For instance, US Department of Energy
(DOE) funded 18 fuel cell (FC) backup power systems at 10 installation sites will help
accelerate the deployment of clean technology at Federal government facilities and
provide valuable data and feedback for FCs [4].
When the utility grid power source is interrupted, the hydrogen will be supplied to the
PEMFCs stack in a UPS system. One of the main weak points of the PEMFCs, however,
is slow dynamic characteristics administrated by the fuel transport system, such as the
air and water pumps, control valves, pressure devices, mass flow devices, and a
hydrogen reformer. During the start-up of PEMFCs stack, or a sudden change of
external load, the hydrogen cannot be fed in time, and the stack may take a few seconds
to reach the required output voltage. 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. So, to overcome this issue, a PEMFC should be used as
the main power source in the UPS and vehicles applications. And at least a rechargeable
battery or a SC must be employed as an auxiliary power source to improve the
performance and prevent the PEMFC stack from degradation when the external loads
demand a high energy in a short time. It should ensure the enough fuel and battery/SC
capacity for providing the power needed by the external load [5].

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The power control and energy management of hybrid power sources have already been
studied recently. For instant, Thounthong et al. [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. Zhang et al. [7] proposed a seamless transfer control strategy by using a
power management unit, which was suitable for FC-UPS. García et al. [8] presented a
comparative study performed in order to select the most suitable control strategy for
high-power electric vehicles powered by FC, battery and SC, in which each energy
source uses a DC/DC converter to control the source power and adapt the output voltage
to the common DC bus voltage, from where the vehicle loads are supplied. Torreglosa
et al. [9] evaluated a hybrid power-train based on FC, battery and SC for a tramway,
which currently operates in the city of Zaragoza, Spain. Kyriakarakos et al. [10, 11]
presented an agent system for the multi-generation micro-grid topology which also
included the fuzzy logic and gray prediction algorithms for better management
respectively. Feroldi et al. [12] presented an energy management strategy for a
sustainable hybrid system, which is based on wind-solar energy and bioethanol.
The major topology of parallel structures for a PEMFC/battery/SC hybrid power
sources UPS system is shown in Fig. 1, in which the three DC/DC converters in
parallel is widely used. 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. 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 K
0
-K
6
(thyristors) through the energy
management and power control system.

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Fig. 1. Traditional structure of PEM fuel cell/battery/SC hybrid power source
Fig. 2. Proposed structure of grid/fuel cell/battery/SC hybrid power source in UPS
2. Modeling of hybrid power and energy system
2.1. Voltage model of PEMFC

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References
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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

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Abstract: This paper proposes 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. The energy in hybrid system is balanced by the dc bus voltage regulation. A supercapacitor module, as a high dynamic and high power density device, functions for supplying energy to regulate a dc bus voltage. A battery module, as a high energy density device, operates for supplying energy to a supercapacitor bank to keep it charged. A FC, as a slowest dynamic source in this system, functions to supply energy to a battery bank in order to keep it charged. Therefore, there are three voltage control loops: dc bus voltage regulated by a supercapacitor bank, supercapacitor voltage regulated by a battery bank, and battery voltage regulated by a FC. To authenticate the proposed control algorithm, a hardware system in our laboratory is realized by analog circuits and numerical calculation by dSPACE. Experimental results with small-scale devices (a PEMFC: 500-W, 50-A; a battery bank: 68-Ah, 24-V; and a supercapacitor bank: 292-F, 30-V, 500-A) corroborate the excellent control principle during motor drive cycle.

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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.

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Abstract: Resulting from a Ph.D. research a Vehicle Simulation Programme (VSP) is proposed and continuously developed. It allows simulating the behaviour of electric, hybrid, fuel cell and internal combustion vehicles while driving any reference cycle [Simulation software for comparison and design of electric, hybrid electric and internal combustion vehicles with respect to energy, emissions and performances, Ph.D. Thesis, Department Electrical Engineering, Vrije Universiteit Brussel, Belgium, April 2000]. The goal of the simulation programme is to study power flows in vehicle drive trains and the corresponding component losses, as well as to compare different drive train topologies. This comparison can be realised for energy consumption and emissions as well as for performances (acceleration, range, maximum slope, etc.). The software package and its validation are described in [J. Automot. Eng., SAE IEE 215 (9) (2001) 1043L]. Different hybrid and electric drive trains are implemented in the software [Views on hybrid drive train power management strategies, in: Proceedings of the EVS-17, Montreal, Canada, October 2000]. The models used for the energy sources like fuel cells, batteries, ultracapacitors, flywheels and engine-generator units will be discussed in this paper in three stages: first their functionality and characteristics are described, next the way these characteristics can be implemented in a simulation model will be explained and finally some calculation results will illustrate the approach. This paper is aimed to give an overview of simulation models of energy sources for battery, hybrid and fuel cell electric vehicles. Innovative is the extreme modularity and exchangeability of different components functioning as energy sources. The unique iteration algorithm of the simulation programme allows to accurately simulate drive train maximum performances as well as all kind of power management strategies in different types of hybrid drive trains [IEEE Trans. Veh. Technol., submitted for publication].

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