STATCOM & Gray Wolf Optimization for Hybrid Renewable Energy Systems

Results in Engineering 25 (2025) 104405
Available online 6 March 2025
2590-1230/© 2025 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Addressing power quality challenges in hybrid renewable energy systems
through STATCOM devices and advanced gray wolf optimization technique
Muhammed F. Alwaeli
*
, Sadjad Galvani , Vahid Talavat
Faculty of Electrical and Computer Engineering, Urmia University, Urmia, Iran
ARTICLE INFO
Keywords:
Hybrid energy resource systems (HRES)
STATCOM
Grey wolf optimization (GWO)
Power quality (PQ)
Voltage stability
Reactive power regulation
ABSTRACT
This research proposes an intelligent technique designed to optimize the power quality of grid-connected hybrid
power systems that use both solar photovoltaic and wind energy. Regrettably, these hybrid systems are liable to
the damaging environmental results of weather gusts, which could lessen average system efciency. Moreover,
several faults, such as three-phase faults and voltage uctuations on the point of common coupling (PCC), can
adversely affect system balance. To address those challenges, Static Synchronous Compensators (STATCOMs) are
employed to enhance the integration of renewable energy sources (RESs) by providing vital reactive energy
support. This examination additionally highlights the importance of advanced optimization techniques for tuning
controllers, given the complexity of hybrid systems. The proposed observation indicates the application of a grey
wolf optimization (GWO) primarily based on the multi-objective function. This algorithm acts to improve control
parameters, thus increasing the system’s reliability. The developed strategy is presented in several processes.
Scenario 1 shows the system’s capability to stabilise at 1 pu during voltage and current swell and sag. Scenario 2
highlights effective reactive power generation during renewable energy source penetration, while Scenario 3
demonstrates improved power quality with unbalanced non-linear loads. Lastly, Scenario 4 conrms that PCC
stability is maintained between 0.92 and 0.97 pu during three-phase faults. Through tests, simulation results
conrm the improvement of both current, voltage and Total Harmonic Distortion (THD) and reveal the efciency
of the proposed controller in supporting fast dynamic response. Thus, the activity of the proposed system has
been veried through tests with the GWO strategy.
Abbreviations
PCC Point Of Common Coupling
DVR Dynamic Voltage Restorers
FACTS Flexible AC Transmission Systems
FC Fuel Cell
GA Genetic Algorithms
GWO Grey Wolf Optimization
HRES Hybrid Energy Resource Systems
ITAE Integral Time Absolute Error
MPPT Maximum Power Point Tracking
PI Proportional Integral
PLL Phase Locked Loop
PMSG Permanent Magnet Synchronous Generator
PQ Power Quality
PSO Particle Swarm Optimization
PV Photovoltaic
PWM Pulse Width Modulation
RES Renewable Energy Sources
STATCOM Static Synchronous Compensator
THD Total Harmonic Distortion
UPFC Unied Power Flow Controller
UPQC Unied Power Quality Conditioner
VSC Voltage Source Converter
WECS Wind Energy Conversion Systems
1. Introduction
The increasing global demand for electrical energy has driven the
widespread integration of renewable energy sources (RES) into power
systems. Among the various RES technologies, wind energy conversion
systems (WECS) and photovoltaic systems have seen particularly rapid
growth in recent years due to signicant advantages [1]. However, the
incorporation of these variable RES into electrical grids presents new
* Corresponding author.
E-mail address: [email protected] (M.F. Alwaeli).
Contents lists available at ScienceDirect
Results in Engineering
journal homepage: www.sciencedirect.com/journal/results-in-engineering
https://doi.org/10.1016/j.rineng.2025.104405
Received 16 November 2024; Received in revised form 18 January 2025; Accepted 17 February 2025

Results in Engineering 25 (2025) 104405
2
challenges, especially regarding voltage stability and power quality.
Various hybrid energy resources (HRESs), including fuel cells (FCs),
wind energy, photovoltaic energy, and biomass, have been integrated
into conventional power networks [2]. Regardless of being an AC or DC
source, each renewable energy source possesses distinct characteristics
that differentiate the source from others [3]. Yet when hybrid power
setups merge wind energy conversion systems (WECSs) with PV systems,
difculties frequently arise in providing reactive power during fault
occurrences. These setups may undergo voltage uctuations at the point
of common coupling (PCC) where the connection with the grid occurs,
which can negatively impact system stability, power factor, and overall
power quality [4,5]. Poor management of these uctuations could result
in disconnections of energy sources (RESs), from the grid as stipulated
by regulations such as the IRENA grid code [6].
To provide the necessary reactive power support during faults,
exible AC transmission systems (FACTS) devices are employed [7]. By
boosting reactive power, these devices improve the link between RESs
and the power system. FACTS devices can be classied as series, shunt,
or a combination of both, each with unique characteristics and appli-
cations [8]. Series FACTS devices, such as dynamic voltage restorers
(DVRs), grow transmission line capacity and regulate line reactances.
Shunt devices, just like static VAR compensators (SVCs) and static syn-
chronous compensators (STATCOMs), inject or absorb reactive power
during voltage sags or swells, respectively [9]. Compound devices, such
as the Unied Power Flow Controller (UPFC) and Unied Power Quality
Conditioner (UPQC), combine the functionalities of series and shunt
[10].
Despite the simplicity and distinctness of classical PI controllers,
performance in improving hybrid systems relies upon the appropriate
tuning of parameters. Hybrid systems, characterised by way of nonlin-
earity, complexity, and uncertainty because of the presence of diverse
power electronic devices, require advanced optimisation methods for
effective controller parameter tuning [11]. Modern optimization tech-
niques, such as genetic algorithms (GA), particle swarm optimization
(PSO), and grey wolf optimisation (GWO), have been proposed for the
most fullling controller tuning, outperforming conventional techniques
[12].
1.1. Literature survey
The integration of renewable energy sources (RESs) into electric
grids is essential to full growing energy demands and deal with envi-
ronmental issues [13,14]. Hybrid energy systems, combining RESs like
wind and photovoltaic systems, provide an option to meet energy de-
mands [15]. Challenges along with wind gusts and faults disconnecting
RESs highlight the need for powerful control strategies. The Static
Synchronous Compensator (STATCOM) plays an important role in
enhancing stability in hybrid systems. This literature assessment section
aims to explore current studies on STATCOM applications, optimization
strategies for PI controllers, and the importance of Flexible AC Trans-
mission Systems (FACTS) devices in advancing energy storage technol-
ogy for energy systems applications.
O. Ibitoye’s analysis addresses the technical demanding situations
related to integrating renewable energy sources (RES) into power dis-
tribution systems, focusing on the issues of variability and unpredict-
ability. The research emphasizes the need for green management
Table 1
Analysis of Previous Contributions.
References Impacts of
STATCOM
Enhancing System
Reliability and
Flexibility
Voltage Stability Frequency
Stability
Control Methods
(Algorithm Use)
Positive Causes Negative Causes
[21] Mehta,
P., Bhatt,
P., Pandya,
V.
Improved voltage
stability and energy
loss minimisation
Enhances system
reliability by
minimizing energy
losses
Enhances voltage
stability signicantly
Not addressed Optimal placement
techniques (Heuristic
optimization
techniques)
Improved control
features
Complexity in optimal
placement
[22] Murali,
D., et al.
Comparison of
FACTS devices for
power system
stability
enhancement
Enhances system
reliability through
robust control and
Improves voltage
regulation
Voltage regulation
via STATCOM
Improves
frequency
stability
marginally
Flexible PI control Flexible control
features
Implementation
complexity
[23]
Mahdad,
B., Srairi,
K.
Multi-objective
optimal reactive
power ow using
STATCOM
Enhances system by
improving power
quality by reactive
power compensation
Signicant
enhancement in
voltage stability
Frequency
stability is
maintained
Multi-objective
optimization (PSO)
Multi-objective
optimization
Potential for improper
optimization
[24] Y. M.
Esmail
et al.
Mitigating power
quality
disturbances
PQ improvement
investigations
Effective voltage
regulation
LC lter to
mitigate the
unwanted high-
freq.
PI controllers
-STATCOM
(fuzzy logic control
strategy-UPQC)
The study
emphasises need
for the FACTS
less cost-effective for
the same kVAR
[25] Rabiee,
A.,
Soroudi, A.
Corrective voltage
control scheme
considering
demand response
Improves system
exibility with
demand response
Improves voltage
stability under
variable conditions
Maintains
frequency
stability
Stochastic
optimisation
algorithms
Effective under
varying
conditions
Complexity in demand
response integration
[26] J.
Bhukya
and V.
Mahajan
Contribution to
power quality using
reactive power
support
Systems can better
manage uctuations
in renewable energy
generation
Maintain voltage
levels during
disturbances
The critical
Low-Frequency
Oscillations
(LFOs)
Power Oscillation
Damping (POD) and
Power System
Stabilizers (PSS).
(Genetic Algorithm
(GA))
Improved
damping of low-
Fre. oscillations
and system
stability
The need for precise
tuning, which can lead
to instability if not
managed properly
[27] R. S.
Camargo,
A. E. A.
Amorim
The SDC-CHB
STATCOM
enhances fault ride-
through
capabilities in wind
farms
Increases the
reliability and
exibility of power
systems
The SDC-CHB
topology improves
voltage proles
While
primarily
focused on
voltage
stability
Employs Model
Predictive Control
(MPC) to optimize
reactive power
injection
leads to
improved power
quality
Include potential short
circuits in capacitors if
not properly managed
[28] M. M.
Mahmoud
et al.
Improves dynamic
performance during
grid disturbances
STATCOM
contributes to the
overall reliability
During transient
events,
outperforming xed
capacitors and
maintaining voltage
Not addressed Including PI
controllers
leads to
improved fault
ride-through
capabilities
Potential drawbacks
include the complexity
of control systems
M.F. Alwaeli et al.

Results in Engineering 25 (2025) 104405
3
strategies to handle these challenges, making sure of balance and reli-
ability in strong distribution networks with high-RES penetration [16,
17,18]. According to Sinsel et al., the uctuating nature of these energy
sources can result in massive imbalances in power supply and demand.
Accurate forecasting techniques are emphasized as crucial to mitigate
these effects, although modern strategies nevertheless struggle with
excessive stages of uncertainty [19].
STATCOM is relatively effective in improving voltage stability inside
hybrid systems. According to S. Sharma, STATCOM offers rapid-acting
reactive power compensation, which helps hold voltage levels inside
proper limits regardless of uctuations in RES output. The study dem-
onstrates that STATCOM can dynamically add reactive power injection,
thereby stabilizing voltage for the duration of sudden changes in load or
generation [20].
Table 1
1.2. Contribution
The study’s objective was to enhance the performance of a Static
Synchronous Compensator (STATCOM) within renewable-based hybrid
systems by proposing a scheduling method for PI controllers through the
application of metaheuristic optimization strategies. The Grey Wolf
Optimization Algorithm was utilized for this purpose. The aim was to
enhance the system’s dynamic performance during faults and RES
uctuations.
1. The study centred on improving the dynamic performance of hybrid
systems primarily based on renewable energy, especially wind en-
ergy conversion systems (WECS) and photovoltaic (PV) systems.
2. The research proposed scheduling of proportional integral (PI) con-
trollers for a Static Synchronous Compensator (STATCOM) in the use
of a metaheuristic optimizer, Gray Wolf Optimization (GWO).
3. By the use of the proposed controlled STATCOM, the paper validated
that the (GWO) become greater effective in optimizing the controller
parameters for the STATCOM.
4. The outcomes conrmed that proposed control of the STATCOM
stepped forward the system’s reactive power for the duration of
abnormal operating conditions, which leads to progressed dynamic
efciency of a grid-connected hybrid power system.
5. The study highlighted the signicance of using current optimization
strategies for tuning controller parameters in complex and uncertain
systems like hybrid renewable power systems.
1.3. Layout of the paper
This work describes the implementation of two optimised controllers
for STATCOM, the goal of which is to adjust the integration of PMSG-
based wind turbines and solar systems into the electrical grid. STAT-
COM, placed at the factor of common coupling, efcaciously regulates
uctuating voltages for the duration of grid disturbances by replacing
reactive power with the system, thereby enhancing typical performance
and commitment to grid requirements. The tuning of PI controllers for
the STATCOM device is performed with the use of GWO, incorporating
each qualitative and quantitative analysis while considering the dy-
namic overall performance of the system.
2. Proposed HRES System Structure with a Description
Traditional generating sources cannot meet the required power de-
mand in the current modern power system, which raises issues about
power reliability and enhanced protection [29]. The most advanced
system is the Hybrid Renewable Energy Sources (HRES) system, which
can improve system reliability as well as performance. In a
grid-connected context, power quality issues arise from HRES adaption
and need to be reduced to maintain the dependability and adaptability
of the system [30]. One of the most widely used xes for PQ problems
such as disruption, interference, sell, and voltage sag is the Reality de-
vice. In order to account for power quality problems, including voltage
swell, voltage sag, voltage interference, and voltage disturbances,
STATCOM is therefore incorporated in the HRES in this article [31]. PQ
issues are less common when the STATCOM system is in place. The fact
that the STATCOM system works with both reactive and real power
control theory gives rise to its name. Nonlinear loads and imbalanced
loads, when connected to a grid-interfaced HRES system, are the cause
of an increase in PQ issues [16]. The classication and identication of
each disturbance are conducted according to standards; the IEC and
IEEE possess multiple PQ standards to facilitate power quality unifor-
mity [32,33], as delineated in Table 2.
The suggested structure involves linking the wind turbine system and
variable load to the power systems via a power transformer, incorpo-
rating STATCOM, as illustrated in Fig. 1. The WT system employs PMSG
because of its advantages over other types. This section presents the
modelling of wind turbines and photovoltaic systems to assist in ana-
lysing the behaviour of the investigated hybrid renewable energy sys-
tem. Connecting the HRES to the SG leads to signicant issues,
particularly voltage uctuations and harmonics, which will be validated
subsequently.
2.1. Wind System
This investigation will examine the impact of STATCOM on HRES;
hence, climate alterations, including variations in wind velocity, will be
Table 2
Power Quality IEEE Standards.
Technical Hitches Period Amplitude
Dip 0.5-30 cycle 0.1 pu-0.9 pu
Swell 0.5-30 cycle 1.1 pu-1.9 pu
Fluctuation Discontinuous o.1-0.9%
Under Voltage >60 s 0.8 pu-0.9 pu
Over Voltage >60 s 1.1 pu-1.2 pu
Interruption 0.5 cycle-30 s >0.1 pu
Nose Steady-state 0-1%
DC offset Steady-state 0-0.1%
Harmonics Steady-state 0-20%
Fig. 1. Conguration of power system under study.
Fig. 2. General wind turbine PMSG system
M.F. Alwaeli et al.

Results in Engineering 25 (2025) 104405
4
considered a form of system disturbance [34]. The Permanent Magnet
Synchronous Generator (PMSG) [35] is the optimal generator for ap-
plications requiring variable speed [36]. The PMSG and wind turbine
specications are (80 kw, base wind speed 12m/s, rated mechanical
speed 3000 RPM, Pole pair 26). The wind energy conversion systems
(WECS) schematic is illustrated in Fig. 2 [37].
2.2. PV System
In the last twenty years, there has been a signicant increase in the
production of electricity from solar systems [38]. This results from the
rising efciency of solar cells and lower prices of photovoltaic systems.
The current produced by a photovoltaic cell is contingent upon sun
irradiance and temperature [36]. The power produced, current and
terminal voltage of the designed PV panel are calculated using Equation
(1) [39,40].
PPV(t) = NPV (t) ∗ IPV(t) ∗ VPV (t)(1)
A schematic diagram of the grid-connected solar PV that has been
built with MPPT is shown in Fig. 3.
The API-P250 module (Maximum Power 250 Wp, Vmpp 31.2 V,
Impp 8.03 A) is used in this research with a maximum power point
tracking (MPPT) approach based on the Perturb-and-Observe (P&O)
technique proposed. The optimal power extraction from the solar system
may not consistently occur due to uctuations in both load and envi-
ronmental circumstances [41]. Consequently, MPPT and VSC control
will be relied upon to achieve the highest production and provide a
dependable connection with the HRES.
3. Modeling and Control Strategy of the Developed STATCOM
System
Improving the quality of voltage and reducing other PQ disruptions
in the power system by utilizing Static Synchronous Compensator
(STATCOM) devices to supply Q to the PCC with a rapid response [42].
The STATCOM used consists of a 25kV/1.25kV coupling transformer, a
voltage-sourced PWM inverter, LC-damped lters connected, a
10000-microfarad capacitor, a voltage regulator, and anti-aliasing lters
used for voltage and current acquisition.
Fig. 4. illustrates the STATCOM-equipped system. Shunt controllers
utilize control techniques to adjust active (P) and reactive (Q) power in
the power system [43] by either absorbing or generating reactive power
(Q) by way of the use of modulation index (m) and the ring angle (
α ) to
the pulse width modulation (PWM) on the voltage source converter
(VSC) [34], which lters and injects the requisite power by optimizing
the gain parameters for the STATCOM controller. The controller utilizes
a GWO strategy programmed to determine the requisite values for
executing the control operation under PQ conditions [44].
3.1. Mathematical Model of the STATCOM
Mathematical modeling of a STATCOM involves developing equa-
tions that describe its behavior, control strategy, and interaction with
the power system. A STATCOM typically consists of a Voltage Source
Converter (VSC), a DC capacitor and an interfacing inductor. In an
HRES, voltage uctuations are predominantly observed at the feeder
Fig. 3. Layout diagram of a grid-connected solar PV system.
Fig. 4. Proposed hybrid system with the architecture of STATCOM
Fig. 5. A single-line diagram of a STATCOM illustrates Q and V terminals.
M.F. Alwaeli et al.

Results in Engineering 25 (2025) 104405
5
load terminal. Consequently, the built STATCOM is integrated into the
microgrid with the bus containing essential loads. Fig. 5. illustrates the
schematic conguration of the reactive power compensating STATCOM
linked to the power system.
The voltage method can be described using a simple circuit including
two AC sources, V1 ∠λ and V2 ∠0, as shown in Fig. 5. linked by a
reactance-dominated impedance line (Z). Therefore, equation (2) rep-
resents the energy transfer between the two sources [45].
P=(V1V2)sin λ
Z,Q=V1(V1−V2cosλ)
Z(2)
The active power transferred is proportional to λ, as the angle re-
mains small throughout typical system operation. The reactive power
transmitted varies proportionally with the voltage magnitude differen-
tial at both ends.
3.2. Voltage Source Converter (VSC) Model
The VSC can be described by its AC side dynamics. Assuming a three-
phase balanced system, the equations in the dq-reference frame [46]
(synchronously rotating frame) are given by:
vd=Ldid
dt +Rid−wLiq+vcd (3)
vq=Ldiq
dt +Riq−wLid+vcq (4)
where: vd are the d and q components of the AC side voltage, vq are the
d and q components of the AC side current, vcd, vcqare the d and q
components of the converter voltage, R and L are the resistance and
inductance of the interfacing inductor, and
ω is the angular frequency of
the system.
3.3. DC Side Model
The measured DC-link voltage V
dc
is directly compared to the
reference DC-link voltage V
dc.ref
, and the resultant error signal is input to
the PI controller [47,44]. The DC side dynamics are governed by the
energy balance equation:
Fig. 6. STATCOM controller
Fig. 7. Conguration of STATCOM controller-based GWO
Fig. 8. Distribution of data points with outliers and error stability
Fig. 9. The curves of the objective function convergence (GWO) algorithm
M.F. Alwaeli et al.