Applied Energy Symposium 2019: Low carbon cities and urban energy systems
October 16-18, 2019, Xiamen, China
Paper ID: 0017
THERMAL MANAGEMENT OF HYBRID ENERGY STORAGE SYSTEMS BASED ON
SPATIAL ARRANGEMENT
Nzeba Kalala Antoinette*, M.S. Masaki, Farshad Barzegar, Xiaohua Xia
Department of Electrical, Electronic, and Computer Engineering, University of Pretoria, Pretoria 0002, South Africa
ABSTRACT
Temperature has a significant impact on the
performance and ageing of electrochemical storages,
especially the battery. It is therefore of paramount
importance to understand and control their thermal
stress for increased longevity. This paper presents the
preliminary findings on a thermo-electric management
of a battery-supercapacitor hybrid system considering
the spatial layout of storage cells. The structural
arrangement aims to improve the cooling characteristics
of battery cells by means of heat transfer with the
supercapacitor cells placed nearby. The simulation
results show that the arrangement of cells and the
operating mode of the battery-supercapacitor hybrid
system has a considerable influence on the thermal
behavior of both battery and supercapacitor cells.
Keywords: Hybrid energy storage system, Thermal
management, Structural arrangement, Battery,
Supercapacitor
1. INTRODUCTION
Nowadays, renewable energy sources (RES) and clean
energy transport systems are increasingly being
developed because of energy crisis and environment
pollution facing the planet [1]. In this context, energy
storage systems (ESS) such as battery, flywheel,
supercapacitor (SC), superconducting magnetic energy
storage, fuel cell and pumped hydro have gain in
importance for intermittent renewable and electric
transportation systems [2] – [5].
Considering their high energy density, flexibility and
reliability, batteries are among the most popular energy
storage systems in industrial applications. Nonetheless,
their low power density dwells the main weakness of
batteries. In an attempt to mitigate the effects of the low
power density of batteries, control models including
minimizing the battery aging factor [2, 3], and penalizing
the charge and discharge operations [4] have been
developed. In the absence of alternative power source,
batteries must supply fast-varying and peak current
demands despite the implementation of mitigating
strategies. Thus, the combination of two or several
energy storage technologies into a hybrid energy storage
system (HESS) has been seen as a cost effective solution
to offset the weaknesses of the battery-alone storage
system. Battery-SC HESS is currently one of the most
encountered association because of the maturity of the
two technologies and the high specific power and wide
operating temperature range of SC that balance the
corresponding limitations of the battery [7] – [9].
However, the performance and the lifetime of both
battery and SC are frequently affected by the
temperature rise under certain operating and
environmental conditions [6, 10, 11]. A proper thermal
management of ESS is therefore of critical importance for
both economic and safety reasons.
In practice, the use of cooling systems and the
control of heat generated by the ESS are the two main
methods found in the literature on thermal management
[1], [7] – [12]. The former improves heat transfer inside
and around the storage device by modifying the heat
transfer resistance [1, 11, 12]. The disadvantage of
cooling systems such as ventilation system and pumps is
their significant power consumption. The second method
has a direct impact on the heat generated by the ESS and
can be achieved through a reduction of current-induced
heat generation of ESS [7, 8, 9]. In this category, one
approach consists in the use of SC as battery current
fluctuation filter, with battery thermal management as a
spinoff effect [8, 9].
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The literature study shows that thermal
management of battery-SC HESS was seldom
investigated in the past. A battery thermal management
using a SC have been presented in [7]. In this control
strategy, the battery is disconnected whenever its
temperature exceeds a specific threshold. During this
period, the SC is operated as energy buffer to supply the
load. The battery is re-connected in parallel with the SC
as soon as its temperature returns below the threshold.
While the battery thermal behavior is modelled and
analyzed,
the
non-consideration
of
thermal
characteristics of the SC and possible heat transfer
between the storage devices constitutes a major
drawback of the proposed controller.
To the best of our knowledge, there have been few
previous attempts to use the spatial configuration of
battery-SC hybrid system in terms of thermal
management during charge/discharge. This paper
presents the preliminary findings on a thermo-electric
management of a battery-SC HESS considering the
spatial configuration of storage cells. The structural
arrangement aims to improve the cooling characteristics
of battery cells by means of heat transfer with the SC
cells placed nearby. The thermoelectric models of
battery and SC are described in the section 2, the thermal
management strategy is outlined in the section 3 and the
section 4 concludes this paper.
generation model and a simple model of heat transfer
within and outside the system [6, 10, 14]. The total heat
generation encompasses the heat generation due to
ohmic losses and entropy change while the heat transfer
could occur by conduction, convection and radiation
phenomena. Considering the low contribution of heat
generated due to entropy change under large load
current, only the ohmic heat generated is considered in
this study.
Figure 3 shows the lumped parameters model that
describes the battery and SC thermal behavior under the
following assumptions: (1) the distribution of heat
generated, heat transfer and temperature is uniform; (2)
the core of ESS cell is composed of opaque component;
(3) the convection inside the core neglected [6, 10]. The
model parameters are the ESS internal and shell thermal
capacitance, denoted by Ci and Cs, respectively, and the
thermal resistance between the ESS core and shell, and
between the ESS shell and the ambience, denoted by Rcs and Rs-a respectively. Qi is the ESS heat generated; and
Ta is the ambient temperature. Ti and Ts are the ESS
internal and shell temperature, respectively. The
following expressions describe the thermal equivalent
circuit in Fig. 3.
Qi  Ci
Ti  Ts
2.
THERMOELECTRIC MODELLING OF HESS
The layout diagram of an HESS consisted of a battery
cell and a SC cell is shown in Fig. 1. The thermoelectric
models of battery and SC cells combine their respective
electrical and thermal models.
Rc  s
dTi

Ti  Ts
dt
 Cs
,
(1)
Rc  s
dTs
dt

Ts  Ta
.
(2)
Rs  a
Charge/Discharge Current
2.1 Electrical models
Among the various electrical models of battery and
SC, the second order equivalent circuit models shown in
Fig. 2 are adopted in this work. These models have a
relatively simple structure, as well as an acceptable
accuracy in terms of the description of the dynamic
behavior of HESS [6, 10, 13]. In these models shown in
Fig. 2, Rs and Ri are the series resistance of SC and
battery, respectively; C is the SC capacitance; and OCV is
the battery open circuit voltage function of its state of
charge (SOC). The two RC networks aim to capture both
short-term and long-term dynamics of ESS.
Switch Control
S1
S2
2.2 Thermal models
The thermal model of both battery and SC is based
on the energy conservative law describing the
temperature dynamics of a system using the heat
Battery Cell
Supercapacitor Cell
Fig 1 System layout diagram.
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3.
C1
C2
R1
R2
+
C1
C2
R1
R2
+
Rs
Ri
C
OCV = f(SOC)
-
(a)
-
(b)
Fig 2 (a) Dynamic electric model of SC (b) Second order
equivalent circuit model of battery.
Rc-s
Ti
Qi
Ts
Rs-a
Ta
Cs
Ci
Fig 3 Thermal model of ESS.
In order to illustrate the effect of thermal interaction
between a battery cell and a SC cell disposed side by side
as illustrated in Fig. 4(a), the thermal model of the entire
system is designed as shown in Fig. 4(b). Here, the
subscripts b and s denote battery and SC, respectively.
The thermal resistance Rbs exhibits that the presence of
heat transfer from the battery to SC or reversely,
depending on temperature gradient between the two
cells.
The heat generated is computed as the total power
dissipated in the battery as well as SC cells, as follows:
Qib  (Vb  OCV )  I b ,
(3)
Qis  (VS  U C )  I S ,
(4)
where Vb and Vs are battery and SC terminal voltage,
respectively, Uc is the SC capacitance voltage, Ib and Is are
the current value flowing through battery and SC,
respectively.
THERMAL ANALYSIS STRATEGY
By assuming that, the SC is fully charged initially and
able to supply the discharge current for the entire
simulation duration, the evolution of internal and shell
temperatures of both the battery and SC as a function of
time are collected for the following operating conditions
by means of switch control:
 S1 = 1 and S2 = 0: the battery in standalone mode
 S1 = 0 and S2 = 1: the supercapacitor in standalone
mode
 S1 = 1 and S2 = 1:the battery and SC in parallel mode
 S1 and S2 set sequentially to 1 and 0 or 0 and 1,
respectively: the switching mode.
During standalone and parallel modes, the thermal
behaviors of both battery and SC are analyzed when the
two devices are relatively far from each other, i.e., Rbs
→∞, and when they are relatively close to each other,
0<Rbs<∞.
The results from the two cases are thus compared to
illustrate the influence of the spatial configuration of
battery and supercapacitor cells in a hybrid system.
3.1 Case Study
The HESS consists of a prismatic battery cell with a
nominal capacity of 30 Ah and a prismatic SC cell with a
nominal capacity of 3000F. The height, width and
thickness of the two cells are 182, 100, and 32 mm,
respectively [10]. The electrical and thermal parameters
of the battery cell are taken from [10], while the
electrical and thermal parameters of the SC cell are taken
from [13] and [15], respectively. Table 1 gives a summary
of these parameters. The thermal resistance Rbs is
computed considering the thermal conductivity of air,
which is equal to 0.03 [15]. The space between the two
cells and their initial temperature are set to 1 mm and
20oC, respectively. Figure 5 (a) and Fig. 5 (b) gives
respectively the curve of the charge/discharge current
applied to the HESS and the operating sequence of
battery and SC during switching mode.
Rbc-s
Tsb
Tib
Rbs
Qib
Cib
Rsc-s
Tis
Rss-a
Rbs-a
SC
Tss
Qis
Csb
Ta
Ta
Css
Cis
Bat
(a)
(b)
Fig 4 (a) Structural arrangement of ESS (b) Thermal model of HESS.
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Table 1. Battery and SC parameters.
Battery Cell
Supercapacitor Cell
Value
Parameter (unit)
Value
Ri (Ω)
[R1 (Ω), C1 (F)]
[R2 (Ω), C2 (F)]
0.0135
[0.008, 1875]
[0.006, 100000]
Rs (mΩ)
[R1’ (mΩ), C1’ (F)]
[R2’ (mΩ), C2’ (F)]
0.8216
[0.3146, 627]
[0.3883, 1843]
[Cib (J/K), Csb (J/K)]
[Rbc-s (K/W), Rbs-a (K/W)]
[287.77, 30.8]
[0.5776, 0.8333]
[Cis (J/K), Css (J/K)]
[Rsc-s (K/W), Rss-a (K/W)]
[580 , 30.8]
[2.6, 0.8333]
(A)
Parameter (unit)
(a)
(b)
Fig 5 (a) Charge/Discharge current (b) Operating sequence of battery and SC in switching mode.
3.2 Simulation results and discussions
(oC)
(oC)
The above proposed thermal management strategy
is implemented and simulated in the MATLAB/Simulink
environment. Figure 6 (a) shows the comparison of Tib
obtained in the standalone mode, the separate mode
with thermal connection to SC, and the switching mode.
It is observed that the thermal connection allows the
heat transfer from the battery (hottest device) to the SC
(coldest device), which results in a decreased battery
internal temperature. This can also be seen from the
comparison of Tsb for the same three cases as illustrated
in Fig. 6 (b). It is important to notice that the higher
temperature difference between Tib and Tis as well as the
(a)
(b)
Fig 6 (a) Battery internal temperatures (b) Battery shell temperatures.
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(oC)
(oC)
(a)
(b)
(oC)
(oC)
Fig 7 Influence of the distance between the two cells (a) Battery internal temperatures (b) Battery shell temperatures.
(a)
(b)
Fig 8 (a) SC internal temperature in switch mode and internal and shell temperatures in standalone mode (b) Battery internal
temperatures in parallel mode (Is = 0.3I).
smaller spacing between the two ESS will result in more
heat transfer from battery to SC.
Figure 7 (a) and Fig.7 (b) give respectively Tib and Tsb
for three different distances between the two cells.
Figure 8 (a) gives Tis and Tss for SC in the standalone
mode without any thermal connection to the battery and
Tis in the switching mode. In the latter, the increase in Tis
is seen during battery operating periods because Qis is
zero in this case and thus the more heat is transferred
from battery to SC.
In order to illustrate the influence of the structural
configuration of HESS when SC is used for load
fluctuation filter, Tib is obtained when there is no thermal
connection and when the latter is considered. It is found
that besides the decrease of Tib with SC filtering, the
spatial arrangement proposed in this work allows the
further reduction of Tib as shown in Fig. 8 (b).
4.
CONCLUSION
A thermal management strategy based on the spatial
arrangement for a battery-SC hybrid system was
presented in this paper. The considered configuration of
battery and SC cells into HESS may achieve an effective
thermal management of battery and SC. The simulation
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results show that the thermal connection between the
two cells allows the heat transfer from the battery
(hottest device) to the SC (coldest cell). It is further
noteworthy that the higher temperature difference
between Tib and Tis as well as the smaller spacing
between the two ESS will result in more heat transfer
from battery to SC. Therefore, the temperature of the
battery cell is reduced and its lifetime as well as its safety
will be increased.
ACKNOWLEDGEMENT
The authors gratefully acknowledge the support for
this work provided by the Organization for Women in
Science for Developing World (OWSD).
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