This paper proposes a unified energy management scheme for a renewable grid-integrated hybrid energy storage system incorporating battery and supercapacitor technologies. The scheme effectively addresses the intermittent nature of renewable energy sources and the unpredictability in load demands by dynamically regulating the DC link voltage, facilitating real power transfer, and enhancing power quality. Validation through simulations and experiments confirms the scheme's effectiveness in improving energy management and extending battery life.

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10.1109/TIE.2015.2455063, IEEE Transactions on Industrial Electronics
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 1
Dynamic Energy Management of Renewable Grid
Integrated Hybrid Energy Storage System
Narsa Reddy Tummuru, Student Member, IEEE, Mahesh K. Mishra, Senior Member, IEEE,
and S. Srinivas, Member, IEEE
Abstract—In this paper, a unified energy management scheme
is proposed for renewable grid integrated system with battery-
supercapacitor hybrid storage. The intermittent nature of renew-
able energy resources coupled with the unpredictable changes in
the load, demands high power and high energy density storage
systems to coexist in todays microgrid environment. The proposed
scheme dynamically changes modes of renewable integrated
system based on availability of renewable energy resources (RES)
power and changes in load as well. The participation of battery-
supercapacitor storage to handle sudden/average changes in
power surges results in fast DC link voltage regulation, effective
energy management and reduced current stress on battery.
In addition, the proposed energy management scheme enables
the real power transfer along with ancillary services such as
current harmonics mitigation, reactive power support and power
factor improvement at the point of common coupling (PCC).
The proposed scheme is validated through both simulation and
experimental studies.
Index Terms—Battery, power quality features, renewable grid
integration, supercapacitor, voltage source inverter.
I. INTRODUCTION
Energy storage systems (ESSs) are gaining more attention in
the modern electric grid due to the rapid growth of renewable
grid integration. ESSs support the renewable energy producers
and also system operators by providing many services such
as energy time frame shifting, ancillary features, capacity
firming, intermittency handling, transmission congestion relief
and power quality improvements [1], [2].
Battery energy storage systems are considered to be the
most basic and popular amongst distributed network ESSs due
to their easy implementation and geographical independence
as compared to other storage technologies [2], [3]. However,
batteries have low power densities to meet the required power
capabilities [4], [5]. Battery-supercapacitor based hybrid en-
ergy storage systems (HESS) combine the benefits of each
energy storage devices (ESDs) and used to extend battery
life expectancy by diverting transient battery current to the
supercapacitor units [4]. Many battery-supercapacitor hybrids
are popular in renewable grid integrated microgrid systems
Manuscript received December 31, 2014; revised April 17, 2015 and June
04, 2015; accepted June 17, 2015.
Copyright (c) 2015 IEEE. Personal use of this material is permitted.
However, permission to use this material for any other purposes must be
obtained from the IEEE by sending a request to pubs-permissions@ieee.org.
This work is supported by the Department of Science and Technology
(DST), India, under the project grant DST/TM/SERI/2k10/47(G).
The authors are with the Department of Electrical Engineering, Indian
Institute of Technology Madras, Chennai 600 036, India. (e-mail: narasai-
itm@gmail.com; mahesh@ee.iitm.ac.in; srsrini12@ee.iitm.ac.in).
[6]–[13], in hybrid electric vehicle applications [14], [15] and
in the UPS applications [16].
In light of microgrid applications, various studies have
been reported in the literature for energy management in
a hybrid energy storage system [5]–[13]. In [5], an energy
management scheme for a PV based power system with hybrid
energy storage units is proposed. It is shown that, the EMS
chooses the operating mode of three sources based on their
states and determines the reference power for each of the
individual source. In [6], a renewable grid integrated hybrid
energy management scheme was reported with main focus on
high battery state of charge and overcharge limits. In [11],
an effective power management strategy was proposed for
the renewable grid integrated system with battery ESS and
it is demonstrated that the power management scheme (PMS)
provides fast DC link voltage regulation compared with AC
line current regulation method reported in [17]. However, the
battery current and voltage undergo sudden changes during
renewable/load variation, which affects battery life span in the
long term [18].
In [12], a model predictive based power management
scheme was proposed for supercapacitor-battery hybrid in
a DC microgrid environment. The main advantage of this
scheme is that, it provides a uniform approach to design a
control system that ensures the operation of the supercapacitor-
battery hybrid within predefined limits. However, the DC
link voltage is assumed to be constant throughout the work.
Moreover, the classical model predictive control (MPC) that
relies on a discrete model of the control system and a cost
function makes it computationally intensive. A control strategy
is devised in [19] to balance the power flow in a DC microgrid
environment under renewable side variations and load as well.
However, this scheme does not allow to divert transient powers
to the supercapacitor units.
In [13], a low complexity control system for a hybrid
battery-supercapacitor DC power source was proposed. The
key feature of this scheme is that it is less complex and
hence easier to implement. Moreover, it provides comparable
performance with the work reported in [12]. In [14], battery-
supercapacitor hybrid for vehicle applications was proposed
using neural network (NN). The NN was trained using various
sets of data and the optimal current was computed for a
specified load. However, the optimality depends on how many
sets of data have been used to train the NN. In [20], it is shown
that the supercapacitor-battery hybrid can achieve a longer
run-time and higher power capability compared to a battery-
alone under a pulsed load condition. However, the DC link

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10.1109/TIE.2015.2455063, IEEE Transactions on Industrial Electronics
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 2
voltage regulation is not achieved due to the direct connection
of battery and supercapacitor units to the DC bus.
The effective regulation of the DC link voltage is one of
the important aspect that determines the performance of the
renewable grid integrated system [21]. Only few works have
been reported on control of renewable grid integrated system
with battery-supercapacitor units as the ESDs [5], [6]. The
DC link voltage can be subjected to transient conditions due
to following reasons; (i) unpredictable changes of renewable
power/load at the DC link, (ii) oscillations in the instantaneous
power on the AC side and (iii) energy management priorities
defined in control algorithms. The main concerns in the
hybrid microgrid environment under large changes in the DC
link voltage include, (a) the operating point shifting from
maximum power point (MPP) on the renewable sources side,
(b) inability to achieve effective power management at the DC
link and (c) degradation of compensation performance of the
grid side VSC. Therefore, fast acting DC link voltage based
energy management schemes are necessary to ensure good
performance of the renewable grid integrated system.
Power quality is another important aspect that needs to
be addressed for renewable grid integrated hybrid system. In
addition to the above, the energy management schemes should
achieve the main function of real power transfer along with
the additional power quality features such as current harmonic
compensation, reactive power support and unity power factor
operation at the point of common coupling. These combined
features, need to be addressed in detail on the grid interactive
hybrid energy storage system.
Keeping in view of above perspective and issues, a simple
unified energy management scheme is proposed in this paper
for a renewable grid integrated system with supercapacitor-
battery as the energy storage elements. The main features
obtained from the proposed scheme are: (i) fast regulation of
the DC link voltage under unpredictable changes of renewable
power and also for sudden load changes, (ii) effective power
flow management at the DC link along with additional power
quality features at the point of common coupling, (iii) reduces
the sudden current stress on the battery unit, and therefore,
extends its life span, (iv) allows inherent current limits for
both supercapacitor and battery units and (iv) computationally
less intensive. The proposed energy management scheme is
discussed in detail and all the features listed above are clearly
demonstrated using digital simulations and are verified by
experimental studies.
In this paper, system configuration and proposed energy
management scheme are described in Section II. In Section III,
current control structures of various power converters such as
supercapacitor, battery, RES and grid side VSC are presented.
Some of the results and discussion are described in Section
IV. Finally, concluding remarks are presented in Section V.
II. SYSTEM CONFIGURATION AND PROPOSED ENERGY
MANAGEMENT SCHEME
The grid interactive hybrid microgrid system considered in
this paper is shown in Fig. 1. The emulated RES system
is connected with the high gain DC-DC converter in order
Ls2
D1
L1
D2
S
RL
vpv
Do
C1
Co
+
vc1
+
+
vo
Emulated
PV system
RES converter
Lb
vB
S1b
S2b
Cdb
Cb
Lsc
S1s
S2s
Cdsc
Csc
Supercapacitor
Battery
+
Lf
S1
S4
Cdi
S3
S2
vg
RLac
Non-linear load
Utility grid
Cf
vsc
DC bus
Microgrid converter
Powers description
Rnl Lnl
Cdc
pres
pef
psc
pB
pg
pl
vdc
Transformer
vdc
Fig. 1. Renewable grid interactive hybrid energy storage system.
to mimic the unpredictable changes in the renewable energy
source. Batteries and supercapacitors are used as ESDs to meet
the requisite the power flow in the microgrid environment. The
bidirectional buck-boost DC-DC converter topologies are used
to control the power flow between the ESDs and utility grid.
The VSC is mainly employed for real power exchange from
RES to the utility grid. In addition to the above, the converter
also provides additional services like current harmonic miti-
gation, reactive power support and power factor improvement
at the point of common coupling (PCC).
The proposed energy management scheme mainly consists
of reference currents generation, power management algo-
rithm, current control and switching pulse generation for
various converter stages as shown in Fig. 2. The average and
transient power references are generated using low pass filter
and rate limiter. The average reference currents of battery unit
and utility grid are generated from the low pass filter. The
supercapacitor reference current is generated by subtracting
average current from the effective current requirement and also
a term proportional to the DC link voltage error is added to
the supercapacitor current control loop in order to improve the
DC link voltage dynamics under disturbances.
The power management algorithm (PMA) decides the mode
of operation of the system based on the changes in renewable
energy resources power and also load. In each power mode,
based on the SoC status of ESDs, four operational objec-
tives are formulated and then PMA generates the appropriate
reference quantities for various power converter stages. The
reference quantities obtained from the PMA are tracked by the
current control stages and the control signals from the current
control stages are used to generate the switching pulses for
various power converters (i.e., VSC, battery, supercapacitor
and RES converter). In Fig. 2, MAF represents moving average
filter [22].
A. Generation of Reference Currents
The effective power requirement to balance the power
flow at the DC link is divided into three components; (i)
average power component (p̄ef ), which varies mainly based
on the average renewable power change and/or average load
requirement, (ii) oscillatory power component (p̃ef ), which
appears in the DC link due to the oscillatory component of
AC power and (iii) transient power component (p0
ef ), which is

3. 0278-0046 (c) 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See
http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI
10.1109/TIE.2015.2455063, IEEE Transactions on Industrial Electronics
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 3
vdc
vdc,r
Voltage
controller
vg
Low pass
filter
Rate
limiter
G’
λ
1-λ
iB,r
Synchronization
ig,r
1
s
1
3600CS
SoCsco
isc
Low pass
filter
1
s
1
3600CN
SoCbo
Low pass
filter
Power
management
scheme
[PMA]
pdcl
PH isc,r
MAF
vg
iacl
vres
ires pH
iB
S1-S4
Reference
currents
tracking
ires ig
iB
isc
Switching
pulses
generation
S1b-S2b
S1s-S2s
Sres
Mode selector i*
B,r
i*
g,r
i*
sc,r
ires,r
pacl
pres
δsc
δB
δvsc
δres
SoCB
SoCsc
ief
Fig. 2. Proposed energy management scheme for grid interactive system.
mainly due to the sudden changes in renewable power and/or
also load. Using these power components, the power balance
at the DC link for a grid interactive hybrid energy storage
system (GIHESS) shown in Fig. 1 can be written as follows,
pres(t)+pB(t)+psc(t)+pg(t)−pl(t) = p̄ef (t)+p̃ef (t)+p0
ef (t)
(1)
where pres(t), pB(t), psc(t) and pg(t) are the RES, battery
unit, supercapacitor unit and utility grid powers respectively.
The power pl(t)=pdcl(t) + pacl(t) is the combination of both
DC and AC load powers. Based on (1), the net power needed
to regulate the DC link voltage (vdc) is given by (2),
pef = p̄ef + p̃ef (t) + p0
ef = vdc ief (2)
where pef is effective power flow from various sources/sinks
such as RES, HESS and utility grid to maintain the power
balance at the DC link. From (2), the effective current demand
corresponding to the above three powers at the DC link is
given as follows,
ief =
p̄ef
vdc
+
p̃ef
vdc
+
p0
ef
vdc
= īef + ĩef + i0
ef (3)
This effective current (ief ) at the DC link is derived from the
voltage control loop and it is given in (4),
ief = īef + ĩef + i0
ef = Kpvd ve + Kivd
Z
ve dt (4)
where ve = vdc,r −vdc, Kpvd and Kivd are the proportional and
integral constants of the voltage control loop. The separation of
the above three currents are essential at the DC link in order
to achieve effective performance from the proposed energy
management scheme. The average component of the effective
current (īef ) is extracted as follows,
īef (s) =
s
1 + Tl s
ief (s) (5)
where fl=1/Tl is the cutoff frequency of the low pass filter.
The other two components of ief are collectively derived as
follows,
ĩef + i0
ef =
1 −
s
1 + Tl s
ief (s). (6)
The average component of effective current (īef ) is shared
by the RES, HESS and utility grid. The supercapacitor sup-
plies the transient and oscillatory components of the effective
current.
B. Power Management Algorithm
The proposed PMA decides the operating mode of the
system as shown in Fig. 3. It has the following features (i)
always limits the battery and supercapacitor SoCs within their
higher (H) and lower (L) limits as specified, (ii) provides
seamless mode transfer, (iii) allows battery and supercapacitor
currents to be within limits, (iv) reduced current stress on bat-
tery units and hence extends its lifespan. Based on renewable
power availability and load power requirement, three modes
are identified in the system as follows,
1) Deficit power mode (DPM) (PH 0)
2) Excess power mode (EPM) (PH 0) and
3) Floating power mode (FPM) (PH = 0)
where PH=Pres−Pl. In each power mode, the four operational
objectives are defined based on the SoC status of the ESDs.
1) Deficit Power Mode: In this mode, the deficit average
power demand at the DC link is shared by the RES, utility
grid and battery until the battery SoC reaches to its lower
limit. The supercapacitor continues to supply oscillatory and
transient power components of the pef (t) until it reaches its
lower SoC limit. The operational objectives which are defined
for DPM are discussed as follows,
Step-1:The expressions for SoCB and SoCsc are computed
using Coulomb counting method [23] as mentioned below,
SoCB = SoCbo −
1
3600 CN
Z
iB dt,
SoCsc = SoCsco −
1
3600 CS
Z
isc dt,
(7)
where iB, isc, SoCbo, SoCsco, CN and CS are the battery,
supercapacitor currents, initial SoCs of battery and superca-
pacitor units, nominal capacity of battery and supercapacitor
respectively.
Step-2: If SoCBL and SoCscL then discharge both the
battery and supercapacitors using following relations.
i∗
B,r = λ īef , i∗
g,r = (1 − λ) īef , i∗
sc,r = ĩef + i0
ef (8)
where i∗
B,r, i∗
g,r, i∗
sc,r and λ are the battery, grid, superca-
pacitor reference currents and average power sharing constant
respectively. The value of λ can be changed based on SoC
status of battery. A four level logic is used to select the value
of λ and is given in Table I,
Step-3: If SoCBL and SoCscL then make the battery
idle or charge from grid and discharge the supercapacitor to

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This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 4
TABLE I
LOGIC OF SHARING CONSTANT λ IN DEFICIT POWER MODE
SoCB(t) λ 1 − λ
Level-1 0.7 SoCB H 1 0
Level-2 0.5 SoCB 0.7 0.6 0.4
Level-3 0.1 SoCB 0.5 0.3 0.7
Level-4 SoCB L 0 1
supply transient and oscillatory powers as per the following,
i∗
B,r
∼
= 0 or
PB,r
vB
, i∗
g,r = īef , i∗
sc,r = ĩef + i0
ef (9)
Step-4: If SoCBL and SoCscL then discharge the
battery and make the supercapacitor idle or charge from grid
as per the following,
i∗
B,r = λ īef , i∗
g,r = (1 − λ) īef , i∗
sc,r
∼
= 0 or Psc,r
s
Csc
2 Esc,r
(10)
Step-5: If SoCBL and SoCscL then make both battery
and supercapacitor idle or charge with rated power from utility
as per the following,
i∗
B,r
∼
= 0 or
PB,r
vB
, i∗
g,r = īef , i∗
sc,r
∼
= 0 or Psc,r
s
Csc
2 Esc,r
(11)
where PB,r, Psc,r, vB, Csc and Esc,r are the battery, superca-
pacitor reference (rated) powers, battery voltage, capacitance
of supercapacitor and rated supercapacitor energy respectively.
2) Excess Power Mode: In this mode, the excess power is
used to charge the ESDs, until they reach to the higher limit of
SoCs. Once, the ESDs are fully charged, then the remaining
excess power can be injected into the utility grid through the
VSC. The operational objectives defined in this mode are given
in Table II, where ig,r = il − ires − iB,r − isc,r.
3) Floating Power Mode: In this mode, the power from
the RES is more or less equal to the load demand. The
battery and supercapacitor units charge from the utility grid
until they reach to the higher SoC limits. Once, the energy
storage devices are fully charged, the battery becomes idle
and the supercapacitor supplies the oscillatory and transient
components. The operational objectives defined for this mode
are given in Table II. Further, the Ploss and iloss terms are used
in Fig. 3 and Table II to represent the losses in the system.
The term P̂H in Fig. 3 represents the oscillatory and transient
components of power changes.
III. CURRENT CONTROL
A. Supercapacitor, Battery and RES Converter Control
The supercapacitor control loop mainly consists of reference
current generation (isc,r), PMA and the current control part
as shown in Fig. 4. The reference transient and oscillatory
components of ief are extracted through the reference current
generation block. The computation of above two components
are given as follows,
isc,r(t) = ief (t) −
1
Tsc
Z to
to−Tsc
ief (t) dt + G
0
(vdc,r − vdc)
(12)
Start
Pres(k),SoCB(k),SoCsc(k),Pac(k) and Pdcl(k)
is
PH0
y
PH=Pacl(k)+Pdcl-Pres(k)
n
SoCscH
is
n
SoCBH
is
y
SoCBH
is
n P*
sc(k)=P^
H, P*
B(k)=0
Pgrid(k)=Ploss
P*
sc(k)=-Pscr, P*
B(k)=0
Pgrid(k)=Pscr+Ploss
P*
sc(k)=P^
H, P*
B(k)=-PBr
Pgrid(k)=PBr+Ploss
P*
sc(k)=-Pscr, P*
B(k)=-PBr
Pgrid(k)=PBr+Pscr+Ploss
End
Generate the reference currents for
Battery/supercapacitor/VSC
0
y
n
y
Deficit mode
Excess mode
SoCscL
is
SoCBL
is y
n
n
P*
sc(k)=0, P*
B(k)=P^
H+λP-
H
Pgrid(k)=(1-λ)P-
H+Ploss
SoCBL
is
y yP*
sc(k)=P^
H, P*
B(k)=λP-
H
Pgrid(k)=(1-λ)P-
H+Ploss
n P*
sc(k)=P^
H, P*
B(k)=0
Pgrid(k)=P-
H+Ploss
P*
sc(k)=0, P*
B(k)=0
Pgrid(k)=P^
H+λP-
H+Ploss
D
A
B
C
C
D
n
SoCBH
is
SoCscH
is
y
P*
sc(k)=-Pscr, P*
B(k)=-PBr
Pgrid(k)=Ploss
y
P*
sc(k)=-Pscr, P*
B(k)=0
Pgrid(k)=Ploss
SoCBH
is
n
P*
sc(k)=0, P*
B(k)=0
Pgrid(k)=Ploss-P^
H-P-
H
P*
sc(k)=0, P*
B(k)=-PBr
Pgrid(k)=Ploss
n n
y
A
y
B
Deficit mode
Excess mode
Floating mode
Continue
?
y
n
Fig. 3. Proposed power management algorithm.
The reference current computed in (12) is given to the PMA as
one of the input variable and the PMA decides the operating
mode of the supercapacitor pack based on the other input
variables (SoCB, SoCsc, PH). Therefore, the supercapacitor
reference current (i∗
sc,r) is computed as follows,
i∗
sc,r(t) = fsc(PMA) isc,r(t) (13)
where to, Tsc, fsc(PMA) and G
0
are the arbitrary time in-
stant, supercapacitor average block window length, objectives
defined in PMA for supercapacitor control and gain of the DC
link voltage error respectively. The reference current of super-
capacitor (i∗
sc,r) from PMA is used for deriving the switching
pulses through the current control loop. The modulating signal
i*
sc,r
G’
vdc
vdc,r
δsc
PWM
S
1s
S
2s
isc
Current
controller
PMA
LPF
Voltage
control
vdc,r
vdc
i*
B,r
λ selection
δB
PWM
S
1b
S
2b
iB
Current
controller
PMA
SoCB
RTL
isc,r
δres
PWM
S
res
Current
controller
ires
ires,r
iB,r
Fig. 4. Control of supercapacitor, battery and RES converters.

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http://www.ieee.org/publications_standards/publications/rights/index.html for more information.
This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI
10.1109/TIE.2015.2455063, IEEE Transactions on Industrial Electronics
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 5
TABLE II
THE OPERATIONAL OBJECTIVES IN EXCESS AND FLOATING POWER MODES
Modes Excess Power Mode Floating Power Mode
SoCBH SoCscH i∗
B,r=
PB,r
vB
, i∗
g,r=ig,r, i∗
sc,r=Psc,r
q
Csc
2 Esc,r
i∗
B,r=
PB,r
vB
, i∗
g,r=i∗
B,r + i∗
sc,r, i∗
sc,r=Psc,r
q
Csc
2 Esc,r
SoCBH SoCscH i∗
B,r=
PB,r
vB
, i∗
g,r=ig,r + isc,r, i∗
sc,r=ĩef + i0
ef or 0 i∗
B,r=
PB,r
vB
, i∗
g,r=i∗
B,r, i∗
sc,r=ĩef + i0
ef
SoCBH SoCscH i∗
B,r
∼
= 0, i∗
g,r=−ig,r + iB,r, i∗
sc,r=Psc,r
q
Csc
2 Esc,r
i∗
B,r
∼
= 0, i∗
g,r=i∗
sc,r, i∗
sc,r=Psc,r
q
Csc
2 Esc,r
SoCBH SoCscH i∗
B,r
∼
= 0, i∗
g,r=−(ires,r − il), i∗
sc,r=ĩef + i0
ef or 0 i∗
B,r
∼
= 0, i∗
g,r=iloss, i∗
sc,r=ĩef + i0
ef
vdc
vdc,r
LPF
Voltage
control Mode
selector
RTL 1-λ
PLL
PH
vg Sin wt
ig
ig,r Current
controller
s1 s4
..
To supercapacitor
Fig. 5. VSC control structure.
(δsc) of supercapacitor converter is obtained as follows,
δsc = Kp,sc isc,e(t) +
Ki,sc
Tsc
Z t
t−Tsc
isc,e(t) dt (14)
where isc,e, Kp,sc and Ki,sc are the supercapacitor error
current, proportional and integral constants of supercapacitor
current control PI regulator respectively.
The battery control consists of reference current generation
(i∗
B,r), rate limiter function (fRT L), PMA and the average
power sharing constant (λ) selection based on SoCB in the
deficit power mode as shown in Fig. 4. The battery reference
current and modulating signal (δB) for battery converter are
given as follows,
i∗
B,r(t) = fB(PMA) λ
1
T
Z to
to−TB
ief (t) dt
fRT L(t)
(15)
where to, fB(PMA) and TB are the arbitrary time instant,
objectives defined in PMA for battery unit control and battery
average block window length respectively.
δB = Kp,B iB,e(t) +
Ki,B
TB
Z t
t−TB
iB,e(t) dt (16)
where iB,e, Kp,B and Ki,B are the battery error current,
proportional and integral constants of battery current control
PI regulator respectively.
The reference current for the RES converter is selected in
such a way that the system could operate in all three possible
modes as defined in Section II. The chosen RES reference
current (ires,r) is then compared with the actual current of
the high gain converter and controlled through the PI current
controller as shown in Fig. 4. The modulating signal (δres) for
the RES converter is given as follows,
δres = Kp,res ires,e(t) +
Ki,res
Tres
Z t
t−Tres
ires,e(t) dt (17)
where ires,e, Tres, Kp,res and Ki,res are the RES error
current, RES average block window length, proportional and
integral constants of RES converter current control PI regulator
respectively.
B. VSC Current Control
The VSC control mainly consists of reference current gen-
eration, computation of voltage template and current control
part as shown in Fig. 5. The reference current for the VSC is
generated based on the bidirectional power flow (inverter or
rectifier) from the AC grid to the DC link or vice versa. In
EPM, the excess power is primarily used to charge the batteries
and supercapacitors. Once the energy storage devices reach to
their high SoC limits, then the remaining excess power is
injected into the utility grid via VSC. In this mode, the VSC
operates as inverter.
In DPM, the deficit load power is shared by the grid and
battery based on its SoC status. In this mode, if the battery
is fully discharged then the VSC operates as rectifier in order
to supply deficit load power from the utility grid and also to
charge the ESDs. The reference current for the VSC to meet
the aforementioned objectives are given as follows,
ig,r =
(1 − λ) ief (t) fRT L(t) sin(wt) if PH0 (deficit)
ief sin(wt) if PH0 (excess)
where w is the grid angular frequency. The hysteresis current
control is used to track the reference and actual grid current
as shown in Fig. 5.
TABLE III
SYSTEM PARAMETERS FOR SIMULATION AND EXPERIMENTAL STUDIES
Supercapacitor pack parameters Values
Terminal voltage (Vsc) 16.2 V
Max. peak current (Ip) 200 A
Capacitance/pack (Csc) 58 F
Max. continuous current (Imc) 19 A
Battery pack specifications Values
Ah capacity 14 Ah
Terminal voltage (VB) 12 V
No. of batteries in series 4
Battery converter parameters Lb = 1 mH, Cb = 220 µF
Cdb = 220 µF
Supercapacitor converter parameters Lsc = 1 mH, Cdsc = 220 µF
VSC parameters Lf = 5 mH, Cf = 15 µF,
Cdi = 1000 µF
High gain RES converter parameters L1 = 2 mH, Co = 220 µF,
C1 = 110 µF, L1 = 1 mH
Parameters of PI controller’s Values
Supercapacitor Kp,sc=0.4, Ki,sc=100
Battery Kp,B=0.15, Ki,B=12.5
RES converter Kp,res=3, Ki,res=0.1
DC link voltage Kpvd=0.1, Kivd=10
AC and DC load parameters RL = 50 Ω, RLac = 20 Ω and
1-Φ bridge rectifier with
Rnl = 20 Ω, Lnl = 1 mH
Utility and DC link parameters Vg = 230 V, 50 Hz, Vdc = 80 V

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 6
State-4
State-3
47
47.8
30.32
30.36
60
80
100
-400
0
400
-15
0
15
1 2 3 4 5 6 7 8 9 10
vB (V)
vsc (V)
vdc (V)
ivsc (A)
t1
t3
to t2
SoCBL SoCscL SoCBL SoCscL SoCBL SoCscL SoCBL SoCscL
Sudden change
Soft change
pdcl
pB
pacl
pvsc
psc
pg
pres
Current
Powers
(W)
(b)
(c)
(d)
State-1 State-2
v
B
v
sc
v
dc
Time (s)
(a)
Fig. 6. Performance under deficit power mode: (a) DC link voltage, (b)
Battery and supercapacitor voltages, (c) VSC current and (d) Powers.
IV. RESULTS AND DISCUSSION
A. Simulation Studies
Detailed simulation studies are carried out using MAT-
LAB/Simulink software in order to verify the validity of the
proposed energy management scheme. The system parameters
used for the simulation study are presented in Table III.
The steady state and dynamic performance of the proposed
energy management scheme are presented in this section under
various operating modes. Four sub-states are possible in each
power mode based on SoC status of energy storage devices.
1) Performance under deficit power mode: Based on the
SoC status of the energy storage devices, four sub-states
are identified in this power mode (i.e., State-1: SoCBL
and SoCscL; State-2: SoCBL and SoCscL; State-3:
SoCBL and SoCscL; State-4: SoCBL and SoCscL).
In State-1, the battery shares the deficit load power with
the utility grid until the SoCBL as shown in Fig. 6(d). The
supercapacitor pack supplies the sudden change in the DC load
power at t=1 sec. As a result, fast DC link voltage regulation
and the smooth change in the battery current are achieved as
shown in Figs. 6(a) and (d).
In State-2, at t=t1 the battery SoCBL (made intentionally)
and this condition forces the battery reference power to zero
as shown in Fig. 6(d). Therefore, the grid supplies total deficit
load power under steady state and the transient change in
power at t=t1 is absorbed by the supercapacitor packs. As
a result, the soft change in the VSC current is achieved as
shown in Fig. 6(c).
In State-3, at t=t2, the supercapacitor SoCscL and battery
SoCBL (made intentionally to test the control scheme). The
battery and utility grid share the deficit load power until the
1 1.1 1.2
-2
0
2
ivsc (A)
DC load change
Current
(a)
-10
0
15
-5
0
10
-60
0
60
5.9 5.94 5.98 6.02 6.06 6.1
-100
0
400
Time (s)
ig (A)
vg (V)
ivsc (A)
iacl (A)
pdcl
pB
pacl
pvsc
psc
pg
pres
Current
Current
Powers
(W)
(b)
(c)
(d)
(e)
t1
Fig. 7. Performance under deficit power mode: (a) Zoomed view of Fig.
6(c), (b)-(d) Power quality features and (e) Corresponding changes in system
powers.
SoCBL as shown in Fig. 6(d).
In State-4, both energy storage device SoCs are made less
than lower limit (L) at t=t3. As a result, the total deficit load
power is supplied by the utility grid alone as shown in Fig.
6(d). The corresponding dynamics in DC link voltage, battery
and supercapacitor voltages are illustrated in Figs. 6(a) and
(b).
Fig. 7(a) shows the VSC current under DC load changes.
At t=1 s, the DC load current is increased. As a result, the
VSC draws the power from utility grid to support the increased
DC demand. Figs. 7(b)-(d) show the power quality features of
the proposed approach. The non-linear part of the AC load is
increased at t1 instant and as a consequence, the VSC supplies
the harmonic components required by the load as shown in
Fig. 7(c). Therefore, the grid current remains constant and the
unity power factor is achieved on the grid side as illustrated
in Fig. 7(d). The corresponding changes in the system powers
are shown in Fig. 7(e).
2) Performance under seamless transfer of modes : The
dynamic performance of the proposed energy management
scheme under different modes based on the RES power
variation is shown in Fig. 8. An emulated RES current pattern
as shown in Fig. 8(a) is applied to the high gain RES converter
in order to test the effectiveness of proposed scheme. As a
result, the system changes dynamically from one mode to
another based on RES power availability and load conditions
as shown in Figs. 8(b)-(e). The transient power surges during
sudden changes of RES and/or load are supplied/absorbed
by the supercapacitor packs and the excess average power
at the DC link is used to charge the energy storage devices

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 7
TABLE IV
OPERATION OF PROPOSED ENERGY MANAGEMENT SCHEME UNDER RES AND LOAD POWER CHANGES
Modes DPM EPM DPM
Time Instants t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12
Emulated RES Power (W) 100 100 180 264 264 360 269 269 120 160 160 80
SoCB L L L L L H L L L L L L
SoCsc L L L L L H L L L L L L
Battery Status DCR DCR DCR DCR DCR CR Idle DCR DCR DCR DCR DCR
Supercapacitor Status CR DCR CR CR DCR CR DCR CR DCR Idle CR DCR
Utility Grid SHL SHL SHL SHL SHL CRG SHL SHL SHL SHL SHL SHL
Load Power (W) 175 303 303 303 328 328 328 328 328 328 328 328
iB (A)
ivsc (A)
ig (A)
isc (A)
0
5
10
-4
0
4
ires (A)
idcl (A)
-5
0
5
-2
0
2
Current
Current
Current
Current
75
80
85
vdc (V)
v
dc
t1 t2 t3 t4 t5
to t7 t8 t9 t10 t11 t12
(a)
(b)
(c)
(d)
(e)
Soft change sudden change
1 2 3 4 5 6 7 8 9 10
Time (s)
DPM EPM DPM
t13
t6
Fig. 8. Performance under seamless change of modes: (a) RES and DC load
currents, (b) Battery and supercapacitor currents, (c) DC link voltage, (d) Grid
current and (e) VSC current.
or injecting into utility grid based on SoC status of energy
storage devices.
From to-t6 instants, the ires is made less than the load
demand. As a result, the system operates in DPM and the
battery and utility share the deficit load power. The ires is
made greater than the load demand during t6-t7 instants. As
Battery units
RES converter
Bidirectional converters
DC
load
DSO
Variac
VSC
Transducers
PCC
AC filter
AC load
P
V
s
u
p
p
l
y
DC filter
Supercapacitors
Fig. 9. Experimental setup of grid interactive hybrid energy storage system.
a consequence, the system operates in EPM and mostly the
excess power is used to charge the ESDs. From t7-t13 instants,
again the ires is made less than the load demand. As a result,
the system operates in DPM as shown in Fig. 8. During
transition between the modes, the smooth variations in the
battery, grid and VSC currents are observed as shown in Figs.
8(b)-(e).
Various operational modes shown in Fig. 8 are summarized
in Table IV(where SHL:Sharing the load, CRG:Charging from
grid, CR:Charging, DCR:Discharging). From these results it
can be observed that, the dynamics in the DC link voltage
is significantly reduced due to the high power density su-
percapacitor packs and its effective control on the DC link
voltage as shown in Fig. 8(c). The reduced dynamics in the
DC link voltage cause less current stress on the battery pack,
and therefore, with the proposed hybrid energy management
scheme the life span of the battery pack can be extended.
B. Experimental Studies
The developed experimental setup of the renewable grid
integrated hybrid energy storage system is shown in Fig.
9. It consists of supply from the PV emulator, battery and
supercapacitor units, RES converter, bidirectional converters,
VSC and loads as shown in Fig. 9. The power level voltages
and currents from various power converters are converted to
low level voltage signals using LEM Hall effect voltage and
current transducers. The proposed energy management scheme
is implemented in real time dSPACE 1104 control board with
digital signal processor module in the PCI slot of the host
computer. The parameters used for experimental study are
given in Table III.
The proposed EMS operates in different power modes
based on the PH value. Fig. 10(a) shows the ESDs currents,
grid current and DC link voltage under PH0 (DPM) and
PH0 (EPM). In each power mode, the ESDs change their
states according to respective SoC0
s. Figs. 10(b)-(e) show the
waveforms of the proposed EMS under deficit power mode
(i.e., the zoomed view of Fig. 10(a) at ∆t1, ∆t2, ∆t3 and
∆t4 respectively). Figs. 10(b),(c) show the zoomed view of
Fig. 10(a) at ∆t1 and ∆t2 intervals under DC load changes.
The battery and utility grid share the deficit power and the
sudden change in the load at t2 and t3 instants are supplied or
absorbed by the supercapacitors. At t=t1 [Fig. 10(a)] instant,
SoCBL and as a result, the battery enters into the idle mode
as shown in Fig. 10(d). At t=t4 instant, the transient change
in the load is supplied by the supercapacitors and the utility
grid supplies the change in deficit load power.

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 8
DPM EPM DPM
ig
iB
vdc
isc
ig
iB
vdc
isc
iB
isc
200 V/div
5 A/div
50 s/div
200 V/div
5 A/div
1 s/div
5 A/div
500 ms/div
iB
isc
5 A/div
iB
isc 5 A/div
Δt1
Δt2
Δt3
Δt4
SoCBL SoCscL
SoCBL SoCscL
SoCBL SoCscL
SoCBL SoCscL
SoCBL SoCscL
SoCBL SoCscL
SoCBL SoCscL
(b)
(c)
(d)
(e)
(a)
t2
t3
t4
t1
500 ms/div
500 ms/div
Δt5 Δt6
Δt7
Fig. 10. Experimental results of proposed energy management scheme
under deficit power mode: (a) Performance under different modes with load
changes, (b)-(e) Zoomed view of Fig. 10(a) around ∆t1, ∆t2, ∆t3 and ∆t4
respectively.
In ∆t4 duration, both ESD SoC0
sL (made intentionally)
and hence, ESDs enter into idle mode. The change in load
and the deficit average power during this instant is supplied
by utility grid alone as shown in Figs. 10(a) and (e).
Similarly, the excess power mode performance of the pro-
posed EMS is illustrated in Fig. 11 under different conditions
of ESD SoC0
s and load changes. During ∆t5 [Fig. 10(a)], the
PH0, which makes the system to operate in excess power
mode and ESDs start charging with rated current at t5 as
shown Fig. 11(a). During ∆t6, the battery SoCBH at t6
instant and as a result, the battery becomes idle as shown
in Fig. 11(b). Part of the excess power is used to charge the
supercapacitor and remaining excess power is injected into the
grid. At t7 instant, both ESD SoC0
sH and this condition
makes both the ESDs to operate in idle mode as shown in
Fig. 11(c). In all above cases, fast DC link voltage regulation
is achieved due to the participation of supercapacitor packs.
The additional PQ features of proposed EMS under DPM
and EPM are shown in Fig. 12. The grid current contains
fundamental and harmonic components of the AC and DC load
ig
iB
vdc
isc
ig
iB
vdc
isc
200 V/div
5 A/div
500 ms/div
200 V/div
5 A/div
ig
iB
vdc
isc
200 V/div
5 A/div
SoCBH SoCscH
SoCBH SoCscH
SoCBH SoCscH
SoCBH SoCscH
SoCBH SoCscH
(a)
(b)
(c)
SoCBL SoCscL
t5
t6
t7
500 ms/div
500 ms/div
Fig. 11. Experimental results of proposed energy management scheme under
excess power mode: (a)-(c) Zoomed view of Fig. 10(a) around ∆t5, ∆t6 and
∆t7 respectively.
ig
vg
vdc
ivsc
ig
vg
vdc
ivsc
(a)
200 V/div
200 V/div
50 V/div
10 A/div
50 ms/div
100 V/div
10 A/div
20 ms/div
t1
(c)
vg
iB
ig
vdc 80 V/div
10 A/div
20 ms/div
30 V/div
(b)
DC load change
Fig. 12. Experimental results showing additional power quality features: (a)
vdc, vg, ig and ivsc without compensation. (b) vdc, vg, ig and ivsc with
compensation and DC load changes at t1 instant. (c) vdc, vg and ig under
EPM.
current when the VSC control is not activated as shown in Fig.
12(a). The VSC supplies/absorbs the real power to/from utility
grid in addition to the compensation of current harmonics
and reactive power. As a result, unity power factor and total
harmonic distortion (THD) below 5 % in the grid current are
achieved even under load changes at t1 instant as shown in
Figs. 12(b) and (c).
The RES current pattern shown in Fig. 13(a) is applied to
high gain RES converter and the system changes its mode of
operation dynamically. From t0 to t3 the PH0 and hence, the
system operates in DPM. At t3 instant the PH0 due to the
increase in RES power. As a consequence, the system operates

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 9
vsc
ires
vB
idcl
t3 t4
t1 t2 t5 t6 t7 t8 t9 t10 t11
2 A/div
20 V/div
10 V/div
50 s/div
ig
vdc
t3
t4
t1 t2 t5 t6 t7 t8 t9 t10 t11
200 V/div
5 A/div
50 s/div
isc
isc
iB
vdc
ig
isc
iB
vdc
ig
isc
iB
vdc
ig
200 V/div
5 A/div
200 ms/div
200 V/div
500 ms/div
5 A/div
200 V/div
200 ms/div
5 A/div
(a)
(b)
(c)
(d)
(e)
t11
t10
DPM EPM DPM EPM EPM
SoCBH SoCscH SoCBL SoCscL
SoCBH SoCscH
SoCBH SoCscH
SoCBH SoCscH
to
iB
Fig. 13. Experimental results showing seamless transfer between the modes
under RES and load power changes: (a) idcl, ires, vsc and vB. (b) vdc, ig,
iB and isc. (c)-(e) Zoomed view of Fig. 13(b) at t10, t11 and t9 instants
respectively.
ig
isc
vdc
iB
20 V/div
5 A/div
5 s/div
ig
isc
vdc
iB
20 V/div
5 A/div
7 s/div
diB
dt
(b)
(a)
diB
dt
Fig. 14. Experimental results (a) Performance with battery units alone and
(b) Performance with both ESDs.
in EPM. The zoomed view of some of the time instants (i.e.,
t11, t10 and t9) in Fig. 13(b) are shown in Figs. 13(c)-(e).
At t10 and t11 instants, the system changes its mode from
EPM to DPM and vice versa based on load power change. The
transients during the mode transfer are absorbed or supplied by
supercapacitors as shown in Figs. 13(c) and (d). The changes
TABLE V
PERFORMANCE COMPARISON BETWEEN THE VARIOUS SCHEMES
DPM with ires changes from 4.5 A to 7.5 A
EMSs/Parameters Without Scheme-I Proposed
S-Caps EMS
DC link voltage (vdc)
ts (s) 2.5 0.9 0.25
Mp (%) 12 5 5.3
ess 1.5 V 1 V 0.1 V
Battery current (iB)
diB
dt
15 (A/s) 2.1 (A/s) 1.4 (A/s)
iBp (A) 7 2 1.8
ts (s) 2.3 0.88 0.22
% THD ig 5.5% 5.3% 4.2%
Execution time tc (µs) – 95 75
at other time instants in Fig. 13(b) are similar to one explained
in Fig. 8 of simulation results.
The performance of the proposed EMS without and with
supercapacitor units as shown in Figs. 14(a) and (b) respec-
tively. The battery units experience high current rates diB
dt
under the changes in the load power and consequently, the DC
link voltage undergoes changes as shown in Fig. 14(a). In this
case, the battery units and utility grid share the transient as
well as average power requirement and therefore, the DC link
voltage takes higher time to settle down. Participation of su-
percapacitors control reduces the current stress on the battery
units. Moreover, the transient power is supplied/absorbed by
supercapacitor units and consequently, it ensures fast DC link
voltage regulation as illustrated in Fig. 14(b).
The performance of both the control schemes (proposed
scheme and scheme in [19] called as scheme-I) are given in
Table V. In this Table, ts, Mp, ess and iBp represent settling
time, peak overshoot, steady state error and peak battery cur-
rent respectively. The supercapacitor (S-Caps) unit takes a bit
higher time to balance the power flow at the DC link with the
use of scheme-I. As a result, the DC link voltage takes longer
time to settle compared to the proposed scheme. Moreover,
the proposed EMS takes less computational time compared
with the scheme-I. From these results, it is observed that the
proposed scheme provides better performance compared to
scheme-I.
V. CONCLUSION
A unified energy management scheme is proposed for a
renewable grid integrated system with a battery-supercapacitor
units as energy storage devices. It is shown that, the proposed
energy management scheme performs the main function of
bidirectional real power transfer along with additional power
quality features at the point of common coupling. The seam-
less transfer between the various modes, fast DC link voltage
regulation, effective energy management at the DC link and
inherent current limiting for battery and supercapacitor units
are the main features of the proposed scheme. In addition to
the above, the proposed approach also limits the battery and
supercapacitor SoCs within their higher and lower values.
Moreover, the proposed scheme provides better performance
compared to the scheme-I.
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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS 10
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Narsa Reddy Tummuru (S’12) received his Bach-
elor degree from Jawaharlal Nehru Technological
University, Hyderabad, India, in 2002 and Master
of Technology from Indian Institute of Technology
Delhi in 2006. Presently he is pursuing Ph.D. at
Indian Institute of Technology Madras, Chennai,
India.
His research interests are power electronic con-
verter applications in microgrid and renewable en-
ergy systems, power quality, and control of switch-
mode power converters.
Mahesh K. Mishra (S’00-M’02-SM’10) received
the B.Tech. degree in electrical engineering from the
College of Technology, Pantnagar, India, in 1991;
the M.E. degree in electrical engineering from the
University of Roorkee, Roorkee, India, in 1993; and
the Ph.D. degree in electrical engineering from the
Indian Institute of Technology, Kanpur, India, in
2002.
He has teaching and research experience of about
23 years. For about ten years, he was with the Elec-
trical Engineering Department, Visvesvaraya Na-
tional Institute of Technology, Nagpur, India. Currently He is a Professor in
the Electrical Engineering Department, Indian Institute of Technology Madras,
Chennai, India. His research interests include the areas of power distribution
systems, power electronic applications in microgrid, and renewable energy
systems. He is life member of the Indian Society of Technical Education.
S. Srinivas (M’11) received the B.E. degree in
electrical engineering from the University College of
Engineering, Osmania University, Hyderabad, India,
in 1996 and the M.Tech. degree in electrical en-
gineering with specialization in electrical machines
and industrial drives and the Ph.D. degree from the
National Institute of Technology Warangal (formerly
known as Regional Engineering College, Warangal),
Warangal, India, in 2002 and 2008, respectively.
From 1997 to 2008, he was with the Faculty of
Electrical Engineering, National Institute of Tech-
nology Warangal. Since 2008, he has been with the Department of Electrical
Engineering, Indian Institute of Technology Madras, Chennai, India, where
he is currently an Associate Professor. His research interests are multilevel
inverters, dc and ac drives, power electronic applications in renewable energy
systems and distributed energy systems.
Dr. Srinivas was recipient of the Best paper Award at the 2011 IEEE Power
Electronics, Drive Systems and Technologies Conference (PEDSTC) held at
Tehran, Iran and the Best Presenter Award at the 2010 Power Control and
Optimization (PCO) Global Conference held at Gold Coast, Australia.