NINAD - A_BESS_control_system_for_reducing_fuel-consumption_and_maintenance_costs_of_diesel-hybrid_mini-grids_with_high_penetration_of_renewables

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A BESS Control System for Reducing Fuel­
Consumption and Maintenance Costs of Diesel­
Hybrid Mini-Grids with High Penetration of 
Renewables 
Nayeem A. Ninad and Luiz A. C. Lopes 
Department of Electrical and Computer Engineering 
Concordia University 
Montreal, Quebec, Canada 
Email: {na_ahrued.lalopes}@encs.concordia.ca 
Abstract- Diesel hybrid mini-grids with high penetration of 
renewables have the potential for reduced operation costs and 
environmental impacts. However, the fluctuating characteristics 
of wind and Photovoltaics (PV) and the large variations of the 
frequently unbalanced mini-grid loads, result in additional 
challenges for optimizing the operation of the diesel genset(s). In 
such a case, a Battery Energy Storage System (BESS) can be very 
beneficial. This paper presents a control system of a BESS that 
allows it to operate in multiple modes. In the genset support 
mode, it balances the load, compensates for reactive power and 
forces the genset(s) to operate in a desired power range. In the 
grid forming mode, it supplies balanced voltages to highly 
unbalanced loads. Simulation results are provided. 
Keywords- diesel genset, mini-grid, renewabies, BESS, load 
unbalance, dq-control, grid forming, genset support. 
I. INTRODUCTION 
Traditionally, remote communities worldwide consist of 
autonomous power systems (mini-grids) supplied by diesel­
engine generator sets (gensets) [1]. This is a mature 
technology, but the optimization of the operation of the diesel 
system for reduced fuel consumption and maintenance costs is 
not an easy task. Remote communities are characterized by 
highly variable load profiles with the peak load as high as 5 to 
10 times the average load [2]. Normally the gensets are sized 
for the peak load condition of the mini-grid. Thus, they 
frequently operate at low load conditions, at low efficiency 
points and subject to carbon build up, what increases 
maintenance costs [3]. A minimum load of about 40% is 
recommended by genset manufacturers to prevent carbon 
build-up [3]. Often this is imposed by means of dump loads. 
The use of renewable energy sources (RESs) offers good 
potential for reducing fuel consumption in diesel based mini­
grids. However, due to its fluctuating characteristics, they 
further complicate the optimization of the operation of the 
gensets. In practice, a significant part of the renewable energy 
might need to be either curtailed or dissipated in dump loads to 
prevent operation of the genset under low load conditions [4]. 
The above mentioned issues can be mitigated with a battery 
energy storage system (BESS). In the grid support mode, it can 
978-1-4799-0482-2/13/$31.00 ©2013 IEEE 409 
provide minimum loading for the genset and supplement it 
under peak load conditions. In cases when the power demand 
from the genset is low, due to high supply of RESs and/or low 
load consumption, the genset can be shut-down and the BESS 
forms the grid, regulating voltage and frequency. 
Diesel-hybrid mini-grids with high penetration of RESs 
present some very particular characteristics. One issue that is 
frequently overlooked in small « 100 kVA) mini-grids, which 
usually present a low number of loads thus reducing the 
averaging effect, is load unbalance. Diesel gensets supplying 
unbalanced loads experience overheating in the synchronous 
generator and vibration in the shaft [5]. In fact, the ANSI 
standard specifies general-purpose multifunctional generator 
protective device with the maximum limit of 2% voltage 
unbalance and 10-20% current unbalance [5, 6]. If a BESS is 
used in a diesel-hybrid mini-grid, it can help minimize this 
problem and also provide additional ancillary services to 
reduce operating costs and increase power quality and 
reliability. It should be noted that autonomous power systems 
(mini-grids) are subject to some less stringent requirements 
than large interconnected systems. For instance, the European 
standard EN-51060 allows a wider range of frequency 
variation in non-interconnected systems, what can be used for 
additional control and energy management purposes [6]. 
Diesel-hybrid mini-grids with BESS, RESs and three-phase 
unbalanced loads have been discussed in the literature but 
mostly for the BESS supporting the genset [7, 8]. The BESS 
control logic was limited to load balancing and power factor 
correction in the genset support mode. The issue of light load 
operation of the genset, which leads to operation with low 
efficiency and increased maintenance costs, was not addressed. 
The operation of a BESS in the grid forming mode supplying 
balanced voltages to unbalanced loads was discussed in [9-11]. 
However, the impact of unbalanced renewable supply, 
commonly based on single-phase inverters, and the possibility 
of operating with variable frequency have not been considered. 
A common inverter control approach to provide balanced 
voltages to unbalanced loads is using dq control with 
symmetrical components to avoid the first and second order 
ripple components in the dq signals [9-11]. However, the 
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symmetrical components calculator (SCC) usually introduces a 
significant delay difficult to be compensated for in the control 
loops and most of them, are not suitable for variable frequency 
operation. SCC-Iess techniques have been proposed in the 
literature. One, based on sliding mode control, presented a 
slow transient response (> 3 line cycles) [12]. Another was 
only verified by simulation under steady-state conditions [13]. 
This paper deals with a multi-functional control system of a 
BESS for a variable frequency diesel-hybrid mini-grid with 
high penetration of RESs and highly unbalanced loads. In the 
grid support mode, it provides active power control of the 
genset for reducing fuel consumption and maintenance costs, 
on the top of load balancing and reactive power compensation. 
In the grid forming mode, it provides balanced voltages even 
when supplying power in two phases and absorbing in the 
other one, due to the presence of unbalanced loads and 
renewable generation. For fast dynamic response, it employs a 
per-phase, instead of three-phase, dq control scheme that does 
away with the need for a SCC [14]. 
II. DESCRIPTION OF THE SYSTEM 
The power circuit of the system under consideration is 
shown in Fig. 1. In the left-hand side, there is a three-phase 
diesel genset that operates with primary frequency control 
based on active power vs. frequency droop. It can be 
disconnected from the system in case of need or convenience. 
A three-phase BESS, based on a three-phase voltage source 
inverter (VSI) with an LC output filter, is connected in parallel 
to the genset at the point of common coupling (PCC). A three­
wire distribution system connects the diesel power plant and 
the BESS to loads and residential rooftop type PV systems. 
The latter are usually rated below 10 kW and are connected to 
the mini-grid by single-phase current controlled VSIs with 
maximum power point tracking (MPPT) capabilities. 
The BESS has two basic operation modes: Genset support, 
when the genset forms the grid, and grid forming, when the 
genset is off and the BESS regulates voltage and frequency. In 
T Va 
the first mode, it operates as a three-phase independently 
controlled current source. The injected currents have four main 
components: 1) The negative sequence current components 
(Jaben) of the load, so that the genset only supplies balance 
positive sequence current; 2) The reactive current components 
(Jabccap) of the output capacitors of the BESS; 3) the reactive 
current components (Jaber) of the load, so that the genset 
operates with unity power factor (UPF); and 4) The positive 
sequence active components of current (Jabcp) to inject/absorb 
the active power needed to force thegenset to operate within 
an ideal output power range. If the output power of the genset 
falls below a certain value (Pmin= 0.4 pU), the BESS absorbs 
active power to provide minimum loading for the genset. 
Conversely, the BESS will supply active power when the 
output power of the genset exceeds another value (Pmax = 0.9 
pu). The BESS does not deal any average active power when 
the genset operates in the ideal power range. 
In the second mode, the BESS forms the grid, what requires 
operation as a three-phase voltage source. One major challenge 
in this case is to provide balanced voltage to an unbalanced 
load. Appropriate control loops have to be used so as to 
guarantee that even under highly unbalanced output currents, 
the grid forming battery inverter can supply balanced voltages 
to the distribution grid. For defming the mode of operation of 
the BESS, and when a transition is needed, an Energy 
Management System (EMS), not discussed in this paper, 
should be used. For instance, if the genset operates under light 
load conditions and the BESS is fully charged while operating 
in the genset support mode, it could be advantageous to turn 
off the genset and have the BESS form the grid. 
III. OVERVIEW OF CONTROL CIRCUIT OF THE BESS 
The general block diagram of the control circuit of the 
BESS is shown in Fig. 2. It consists of a per-phase dq 
controller, a reference current generator module for the genset 
support mode, a PLL module and a "Mode Selection and 
Transition System (MSTS)" module. These components are 
discussed in the following sub-sections. 
Ia 
T Vb Ib 1---:-2"---40---"----1'--T"---""":O'------.,.--,---j Unbalanced 
T Ve Ie Load 
Diesel Genset loa lob loe 
-i -i -i PV Inverter . . ......... . . . . . . . .. ...... . . . : : 
. ......... . . . . . . . ......... . . . . . . . 
Unbalanced Distribution System 
BESS 
Fig. I - Circuit diagram of a three-phase three-wire diesel-hybrid mini-grid with battery inverter, single-phase RES and unbalanced load. 
410 
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I: 
I: 
I: 
I: 
IrejGenerator 
in Gensel 
. S1:'PP',!�/. A1'?d.� 
,'-"-"-"-' -"�' �Id�: __ -+� --�:�Id��----� 
Ea I Current 
Controller 
vsabC3 
E 
mode 
Vabc MSTS gs2f 
ill gf2' 
Vq L-__ ---.J fnvctrl 
Fig. 2 - Schematic diagram of the proposed control circuit for the BESS. 
A. The Per-Phase Cascaded DQ Control Block 
The BESS operates either as a controlled current source, for 
genset support, or as voltage source, fonning the grid. In such a 
case, it is convenient to employ a two loop cascaded control 
scheme with an inner current loop and an outer voltage loop. 
The key element for fast dynamic response is the frequency 
adaptive per-phase dq control block [15], that is used for the 
BESS with some modifications as shown in Fig. 3 and allows 
operation in both modes. The per-phase dq control strategy 
employs fictive axis emulation (F AE) in the inner current loop 
and frequency adaptive second order generalized integrator 
(SOGI) [16] in the outer voltage loop, to obtain the orthogonal 
components required for getting dq components from single­
phase quantities. As a result, the per-phase control strategy is 
fast and frequency adaptive, with zero error in steady-state. 
+ + + � 
�: 
Feed-forward (FF) loops are also used to compensate for 
the coupling between the dq equivalent circuits created by the 
presence of the LC filter. More details on this technique are 
presented in [15]. 
The three legs of the BESS are controlled independently 
from each other, as single-phase units with per-phase dq 
control. A switch controlled by the signal mode is used to 
select the reference current for the inner current loop, which 
can be either the output of the voltage control loop, when the 
BESS forms the grid, or an external signal coming from 
reference current generator (Idqext), when the BESS is 
supporting the genset. Besides, the input error of the voltage 
controller is also controlled by the signal mode, so that during 
genset support mode the output of the PI controller of the 
voltage loop is kept at zero which ensures minimal transition 
for the voltage during the mode transfer. 
The per-phase controller for phase "a" is shown in Fig. 3. 
The angular frequency (w) used in the SOGIs for orthogonal 
signal generation is provided by the PLL block. Besides, the 
sine and case terms required for the Park and inverse Park 
transformations are also obtained from the phase angle 
provided by the PLL block. Similar per-phase controllers also 
apply for phase "b" and phase "c" with the three e angles 1200 
apart. The reference voltages for the three phases have the 
same magnitude and are phase shifted by 1200 in the grid 
forming mode. Vq' is set at the peak value of the reference 
phase voltage as defined by the PLL block while V/ is set at 0 
V for the three per-phase controllers in the grid forming mode. 
B. Reference Current Generation in Genset Support Mode 
During the genset support mode, the reference current for 
the inner current loop is generated externally from the "1re/ 
Generator in Genset Support Mode" block as shown in Fig. 2. 
The generation of its four components is described below. 
1. Negative Sequence Component Extraction 
Any sets of unbalance voltages or currents can be 
expressed as three symmetrical components of positive, 
negative and zero sequence. In the absence of a neutral wire, 
like in the case considered in this paper, there are no zero 
sequence components. The negative sequence current 
components can be extracted as follows. Clark transformation 
is used for transforming the variables between the abc and the 
a.p frames, as shown in (1) and (2). 
V· q 
+ Vd 
Fig. 3 - Schematic diagram of the per-phase dq control block. 
411 
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[�:l=�[� -: -�Ej 
r�:L�[-� lXcJ -� 
o 
(1) 
(2) 
The positive and negative sequence a� components of the 
three-phase unbalanced signals can be obtained with (3). 
X+ a 0 0 Xa 
x+ 
= � 0 -1 0 Xp (3) p 
X- 0 0 -1 jXa a 
X- 0 0 jXp P 
In order to use (3) to obtain the positive and negative 
sequence components in a� frame, one needs to implement the 
j operator, that corresponds to a 90° phase shift. For that, one 
can use a SOGI [16] which is frequency adaptive, allowing 
operation under variable frequency conditions. In this case, the 
load currents (iabJ are fIrst converted into the a� frame (iaP) 
by (1), then (3) is used to extract the negative sequence 
components of the load current in a� frame (i;;p). Finally, (2) 
is applied to obtain the reference negative sequence current in 
abc frame (iabcn) which the BESS needs to inject for balancing 
the load. 
2. BESS Capacitor Current Compensation 
In the genset support mode, the BESS acts as a controlled 
current source. The purpose of the output capacitor is to reduce 
switching frequency harmonics mainly during the grid forming 
mode. The BESS can supply the reactive currents of the 
capacitors in the grid support mode. If Va and vp are the a� 
voltage components for 'a' phase, then the amplitude of the 
required reactive current of the capacitor is given by, 
�va2 +v/ 
III = -'-------'-Xc 
(4) 
Where, Xc is the capacitive reactance and it should be 
updated depending on the value of the angular frequency (w) . 
The three-phase instantaneous reference currents (iabccap) to 
compensate the capacitor current of the BESS will have the 
same amplitude and is generated using the cosine of the phase 
angle with abc phase sequence. 
3. Load Reactive Power Compensation 
The BESS should also supply the reactive power of the 
load, so that the genset operates with UPF. Note that in system 
with a small genset, it is advantageous touse all its apparent 
power for active power control. The total positive sequence 
reactive power of the load can be calculated as, 
(5) 
412 
Where the positive sequence a� components (v:p and i:p) 
of the pee voltage and the load currents are obtained using (1) 
and (3). 
The reactive power calculated from (5) is used to calculate 
the peak value of the reference reactive component of the 
current of the BESS for load reactive power compensation as, 
Q+ 2 I =--- (6) 
ar 
3 V+ 
Where, V+ is the peak value of the posItive sequence 
voltage components. The negative sign indicates that the BESS 
supplies reactive power while the load is consuming. The 
three-phase instantaneous reference reactive currents (iabcr) of 
the BESS for load reactive power compensation will have the 
same amplitude and is generated using the cosine of the phase 
angle with abc phase sequence. 
4. BESS' Active Component Current Calculation 
In order to avoid the carbon build-up phenomenon as well 
as low efficiency of the genset, it should typically run above a 
power capacity of Pm in = 0.4 pu. The BESS can absorb power 
to provide minimum loading for the genset and also supply 
extra power when the genset is about to operate at its 
maximum capacity ( Pmax = 0.9 pu). This logic can be 
implemented using the information of the mini-grid load power 
demand. The total positive sequence power of the load can be 
calculated from the positive sequence a� components (v:p and 
i:p) of the pee voltage and the load currents, as follows, 
P+ + .+ + .+ (7) = Vala +Vf31f3 
Then p+ is passed to a look-up table to determine the 
reference positive sequence power command for the BESS. 
The characteristics of the look-up table describing the 
relationship between the BESS positive sequence power 
(NESS) and the load positive sequence power (p+) is given by, 
(8) 
Therefore the peak value of the reference positive sequence 
active component of the current of the BESS is given by, 
I = P;ESS � 
ap 3 V+ (9) 
The instantaneous reference active currents (iabcP) of the 
BESS will have the same amplitude and is generated using the 
sine of the phase angle with abc phase sequence. 
C. Mode Selection & Transition System (MSTS) Module 
The Mode Selection & Transition System (MSTS) module 
is used to select and operate the BESS in the appropriate mode, 
genset support or grid forming, depending on the 
status/condition of the system. For instance, during daytime 
with high penetration of PV power generation, the genset can 
be turned off, and the BESS forms the grid, balancing active 
and reactive powers in the mini-grid. The MSTS module 
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generates four control signals: 1) mode signal, 2) gs2[ signal, 3) 
gj2s signal and 4) InvC/rl signal. 
The mode signal indicates the operating mode of the BESS 
in the mini-grid system. The BESS operates in the genset 
support mode when mode = 1, and in the grid forming mode 
when mode = O. The mode signal controls the genset breaker 
directly depending on the operating mode of the BESS. The 
genset breaker is open when the BESS forms the grid. The gs2[ 
and the gj2s signal can be used to perform planned transitions 
between the BESS operating modes. Finally, signal lnvclrl is 
used for controlling the breaker of the BESS, which is on when 
lnvc,rl = 1. In case of maintenance of the BESS, Invc'rI = 0 to 
disconnect the BESS from the mini-grid. 
The control signals generated by the MSTS module are 
used in the reference current generator module and the PLL 
module. The synchronization of the BESS with the genset and 
the disconnection process of the genset are coordinated by the 
PLL module based on the control signals gs2[and gj2s generated 
by the MSTS. Besides, the PLL module should be 
synchronized, depending on the signal mode, with the PCC 
voltage, in the genset support mode, or with the reference mini­
grid voltage in the grid forming mode. 
D. P LL Module 
The per-phase dq controller requires a phase angle and an 
angular frequency for the Park and inverse Park 
transformations during both modes, which are supplied by the 
PLL module. Besides, the external reference current generator 
also uses these signals to generate the reference current in the 
genset support mode. During the grid forming mode, the PLL 
module also provides the reference voltage signal for the per­
phase dq controllers. The angular frequency and magnitude of 
the PCC voltage provided by the PLL module are used as input 
signals in the MSTS module. In the genset support mode, the 
PCC voltage is the reference for phase angle and frequency 
while during the grid forming mode, the desired rated mini­
grid voltage is the reference signal which is generated 
internally in the PLL. More details about the PLL module can 
be found in [16]. 
IV. PERFORMANCE VERIFICATION 
The performance of the proposed control strategy for the 
BESS is verified by means of simulation using SIMULINK. 
The BESS operates with SPWM at 5 kHz from a 1000 V dc 
bus supplying 460 VL.L-60 Hz. Its output filter is given by L = 
3 mH, R = 0.1 nand C = 25 /IF. PI controllers were employed 
in both loops of the per-phase controllers. Tests of the 
proposed control strategy for the BESS operating in the two 
main modes are presented in the following subsections. 
A. BESS Supporting the Diesel Genset 
In this case, the genset forms the grid and the BESS 
balances the load, compensates the load reactive power and 
forces the genset to operate within an ideal power range: 0.4-
0.9pu. The genset is rated at 30 kW/460 V, 1800 RPM/60 Hz 
and presents a 5% droop characteristic (p vs. f and Q vs. E). 
Further details of the diesel genset model can be found in [17]. 
Table I shows the loads at different time instants. 
413 
TABLE T. MINI-GRID LOADS FOR THE BESS IN THE GENSET SUPPORT MODE 
No. Time(s) Load (A-B) Load (B-C) Load (C-A) 
1 0-17 6 kW 6 kW 6 kW 
2 17 -35 9 kW 6 kW 6 kW 
3 35 -52 12 kW 12 kW 9 kW 
4 52-70 9 kW &3 kVAR 6 kW 6 kW 
5 70-85 2.25 kW 2.25 kW 4.5 kW 
Fig. 4 shows key waveforms during load variations with the 
BESS in the genset support mode. As the load demand varies, 
the genset speed and mini-grid frequency vary as per the droop 
characteristics of the genset as shown in Fig. 4(a). During 
heavy load (#3) these quantities have the minimum value while 
during light load (#5), they have the maximum values. The 
magnitude of the peak value (of the positive sequence 
component) of the PCC voltage is not affected though the 
genset operates with Q-E droop characteristics. This happens 
because the reactive power demanded by the load is provided 
by the BESS. Fig. 4(b) shows the three-phase average or 
positive sequence real and reactive power of the genset, load 
and BESS in the genset support mode. The BESS supplies 
active power during load#3, when the load demand is higher 
than Pmax and absorbs active power when the load demand is 
lower than Pnlln as seen with load#5. Besides, when an 
inductive load (#4) is connected to the system, its reactive 
power is supplied entirely by the BESS. 
Shaft Speed (radls) 
Time[s) 
(a) 
50 �-
-:---::---:---:----:---::---:r=�� 40 
-10 '--__ --"---__ -'-__ ----L __ ---" ____ -'----__ -'-__ ----L __ ---'_ 
20 �--:---::---:---:�--:---::--�==�� 
� 15 
> :- 10 
� ;: � O r---+-�-r---+��----++--�--_+--�� 't � -5 " 
Time(s) 
(b) 
Fig. 4 -Waveforms for the genset support mode. (a) Diesel genset shaft 
speed, Mini-grid frequency and peak value of the positive sequence phase 
voltage; (b) Real and reactive power of the gensel, load and BESS. 
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Fig. 5 shows the steady-state waveforms of the PCC 
voltages, genset currents, load currents and the BESS outputcurrents in the genset support mode. Depending on the load 
demand, the BESS supplies/absorbs active power, performs 
load balancing by supplying the negative sequence currents 
and compensates the PF so that the genset operates with UPF. 
Due to all these actions, the PCC voltage is balanced and fixed 
at the rated value. Also, it ensures that the genset currents are 
balanced and limited to 48 A (peak) corresponding to a genset 
power of 27 kW (0.9 pu) while the load current in the three 
phases are in the range of 56 to 64 A (peak) for load#3. It also 
ensures the minimum current to be 21.3 A (peak) for the genset 
corresponding to the genset minimum power of 12 kW (0.4 
pU), while the load current in the three phases are in the range 
of 12 to 18 A (peak) for load#5. 
400� 
�,:::� -400 
�� �r:)(:*�----:-)E -·· ···�)(··· -�···:·) ··· r 'f")("'�"")("": "':'J" 
�" 
-
2� 
-50 
�l :l '�--:.:=::·-: .:- : :- .:- ::"":-::-:.-:: -:.-:: -: .·:;II""":.-::-:.-::-:.-::-::'t -:: -.: -:: ./ : :=:::- .:T,-.:- : :-'. 
-70 
�! : l '�-"-"-" -"'-:"- "" -"-"-"-"-"-""-"'-: .. -.. -.. -.. -.. -.. r!-.. -
.. 
-
.. 
-
... 
-: .. -.. ,!-.. -
.. ---,. 
-g � .955 51.965 51.975 51.985 51.995 52 
Time [sl 
(a) 
���� -400 
�o .�:�'- :: -:: _-:::-::-:.-.. ,... •. -.. -.. -.:-:: -:: -:: --r: __ -:::-::-.. - .. - .. -.. -.. ':: -:: -:: -:: -::--:::-:: ".- .. - .. '. 
4::�� 
J '2� -50 
j :!.-r-�-'-=E¥--'-:::::: ::=�.-+fB 
-gR.955 84.965 84.975 84.985 84.995 85 
Time [sl 
(b) 
Fig. 5 - Steady-state waveforms of the PCC voltages, genset currents, load 
currents and the BESS currents for: a) Load #3 and b) Load #5. 
414 
B. BESS Acting as Grid Forming Unit 
In the grid forming mode, the BESS is expected to provide 
balanced 460 V L-L at 60 Hz to the mini-grid even under severe 
load unbalance. The following conditions are simulated for 
testing the proposed control scheme: Initially the load is 
balanced with 7.5 kW (2.5kW/phase). At t = 0.2 s, the load 
demand increases to 5 kW between lines A and B. At t = 0.3 s, 
the load demand changes to 3 kW with PF = 0.8 lagging 
between lines C and A. Finally, at t = 0.4 s a single-phase PV 
inverter connected between lines B and C, starts supplying 3.5 
kW with UPF. The resulting three-phase load voltages and load 
currents are shown in Fig. 6 for the proposed control scheme. 
There one sees that the load voltages remain balanced for all 
cases. The proposed method presents a very fast response 
regulating the load voltages almost instantaneously even under 
highly unbalanced loads. 
Fig. 7 shows the reference and actual voltages and currents 
for the grid forming BESS in the dq frame. The deviations in 
the voltage signals are small and short. Variations in the 
reference current signals to compensate for voltage unbalances 
take place fast and only in the phases directly related to the 
load variations, while the others remain unaffected. 
t�_-:: 
-400;=====;:====�===�====�=� � ::� .. .... . .. j j : ........... -IN I 
� 
I,:� == :: 
-3�.1 0.2 0.3 0.4 0.5 Time[sl 
Fig. 6 - Waveforms of the output voltages and currents of the grid forming 
BESS for varying load conditions. 
V. CONCLUSION 
A Battery Energy Storage System (BESS) has the potential 
for reducing the fuel consumption and the maintenance costs of 
diesel hybrid mini-grids with high penetration of Renewable 
Energy Sources (RESs). For that, it should be able to support 
the grid forming genset or diesel power plant, by balancing the 
load and supplying/absorbing average active power so that the 
diesel genset(s) can operate in a high efficiency region. 
Besides, it should be able to allow the shut-down of the 
genset(s) and form the grid when the favorable conditions 
arise. The control system presented in this paper was capable to 
perform all this tasks as demonstrated by simulation. The main 
aspects of this paper were the actual configuration of the 
control circuit using per-phase dq control and the approach for 
controlling the active power absorbed/supplied by the BESS to 
force the genset to operate in a desired region supplying 
balanced currents. Also, the operation of the BESS in the grid 
forming mode, providing balanced voltages while supplying 
active power in two phases and absorbing in one. 
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� :�� [···············-I:················:l ............... -:: ................
• = :'/ 1 o 200 ............... , ................ , ............... ,................ ,d 
� 100 .............. .;. ............... � ............... ; ................ --V,q' 
� : : : v 
i 0 --'q 
1 ::: [::::::::::::::::11::::::::::::::::1-::::::::::::::::[1::::::::::::::::1 ::: 1 p:l 100 ............... , ................ , ............... ,................ bq 
j 0 : � : __ Vbq 
P-
� 
:�� [···············-I:················:: ............... 
_,: 
................ 1 = : 
ro
' l o 200 ............... , ................ , ............... ,................ 
ro 
o 100 ............... ; ................ � ............... ; ................ --V"l' 
� , , , 
� 0 : : : -- V"l 
P- 0.1 0.2 0.3 OA 0.5 0.6 
Time Is] 
(a) � 30,-------,-------,-------,--------,-------, 
� ---- Ia/ � 20 --------------- .. 
�' � ...... ..,.v.��� ......... ._H ____ I,d a 10· . . . . ... . . ........ , ... . . ... . . ... . . . 
____ 
, 
' � 0 ____ ___ _ aq 
" ---- I f _10 L-------L-------�-------L-------L------�� 
� 30,-------,-------,-------,--------,-----
,
- -" 
-- bd 
� 
'''''Mi� ---- � a 1 0 TJ' 
� _ l : [
·
�
·
�
··
�
·
�
·
�
··
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··
�'�������������=;-;=�:�:�'J 
� 30,-------,-------,-------,--------,====
-
,
--" 
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��It+I ............... if ---- I,d � 1 0�������H+��������� ---- �' " ---- � � _10 L-----��------�------�------��--�� 0.1 0.5 0.6 
Time Is] 
(b) 
Fig. 7 -Waveforms of the control loops of the grid forming BESS in dq 
frames, a) Reference & actual voltages; b) Reference & actual currents. 
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