Heliyon 11 (2025) e42334
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Heliyon
journal homepage: www.cell.com/heliyon
Review article
A review on topology and control strategies of high-power
inverters in large- scale photovoltaic power plants
Amirreza Azizi a , Mahdi Akhbari a,*, Saeed Danyali b , Zahra Tohidinejad b,
Mohammadamin Shirkhani b
a
b
Department of Electrical Engineering, Shahed University, Tehran, Iran
Department of Electrical Engineering, Ilam University, Ilam, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
High power inverters
Large-scale PV systems
Inverter topologies
Control methods
Modulation strategies
In recent years, there has been a substantial growth in renewable energy sources and among these
sources, solar energy is known as one of the best energies. The increasing adoption of solar energy
across various applications underscores its significance in the renewable energy landscape. The
integration of large-scale photovoltaic power plants into the primary power grid necessitates
efficient and reliable power conversion processes, particularly as there is a growing demand for
enhanced controllability and flexibility from the grid side. Power electronic converters, bolstered
by advancements in control and information technologies, play a pivotal role in facilitating largescale power generation from solar energy. High-power multilevel inverters have emerged as a
compelling solution for addressing the escalating energy requirements. This paper aims to delve
into the exploration of diverse structural configurations and technical hurdles encountered in
high-power multilevel inverter topologies, alongside the associated control systems and modu­
lation techniques tailored for application in large-scale photovoltaic power plants (LS-PV-PP)
systems. A comprehensive analysis of high-power multilevel inverter topologies within solar PV
systems is presented herein. Subsequently, an exhaustive examination of the control methods and
strategies employed in high-power multilevel inverter systems is conducted, with a comparative
evaluation against alternative approaches. Lastly, the paper delves into a discussion on prominent
modulation methods utilized in multilevel power inverters, assessing their performance charac­
teristics in various operational scenarios.
1. Introduction
1.1. Renewable energy and photovoltaic systems
The development and progress of large industrial entities, as well as broader societal advancements, are intricately intertwined
with the generation and distribution of energy resources. Consequently, the establishment of robust mechanisms for large-scale energy
generation is widely recognized as a pivotal determinant in fostering the evolution of contemporary societies. With the increasing
demand for electrical energy and growing environmental concerns associated with fossil fuels, the need for a fundamental shift to a
* Corresponding author.
E-mail addresses: amirreza.azizi@shahed.ac.ir (A. Azizi), akhbari@shahed.ac.ir (M. Akhbari), s.danyali@ilam.ac.ir (S. Danyali), z.tohidinejad@
ilam.ac.ir (Z. Tohidinejad), ma.shirkhani@ilam.ac.ir (M. Shirkhani).
https://doi.org/10.1016/j.heliyon.2025.e42334
Received 23 May 2024; Received in revised form 18 January 2025; Accepted 28 January 2025
Available online 28 January 2025
2405-8440/© 2025 The Authors.
Published by Elsevier Ltd.
This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Heliyon 11 (2025) e42334
A. Azizi et al.
sustainable solution is deemed essential. Increasing investments in renewable energy resources have become one of the key global
objectives due to climate change and environmental pollution [1,2]. With the aim of solving the existing challenges in the development
of sustainable energy generation, significant efforts have been made in recent decades to develop and replace Renewable Energy
Resources (RESs). In recent years, Distributed Energy Resources (DER) have witnessed substantial advancements with a primary
objective of enhancing grid reliability, transitioning away from conventional grid frameworks, facilitating the assimilation of
renewable energy sources, and conscientiously addressing environmental concerns [3]. Of these resources, PV systems have emerged
as a frontrunner in renewable energy generation networks by efficiently harnessing the sun’s radiant energy to generate electrical
power. The growing significance and adoption of PV systems underscore a pivotal shift towards sustainable energy practices within the
energy sector. Fig. 1 shows the general structure of a PV system and its main components including PV arrays, converters, loads and
their connections. By the year 2020, the global photovoltaic solar capacity had increased to more than 627 GW (GW), with projections
indicating a trajectory of substantial expansion exceeding current thresholds [4].
1.2. Importance of LS-PV-PP systems and high-power inverters
This growth trend in solar PV capacity underscores a promising outlook for the future development and adoption of photovoltaic
technologies worldwide.LS-PV-PPs are recognized as a sustainable and evolving solution for harnessing solar energy in high capacities.
One of the reasons for the widespread adoption of LS-PV-PP is the advancement in power electronic technology and the reduction in
the cost of components, modules, and cells, which has expedited the installation and deployment of a power plant within less than a
year [5]. LS-PV-PP systems are comprehensive and suitable solutions for meeting the short-term needs of multi-megawatt demands,
especially in off-grid regions. The design, installation, and commissioning of these systems take less than one year, while for a con­
ventional power plant, this period increases to four years. The structure of an LS-PV-PP is shown in Fig. 2. PV arrays are depicted, and
their modules are connected in series or parallel. In the structure of this system, the PV arrays are connected to DC/DC converters, and
their outputs are connected through a common bus with a voltage range of 400–700 V. Then, a central DC/AC inverter is connected to a
common DC link Subsequently, a central DC/AC converter is linked to a shared DC link, facilitating the transfer of AC power to the load
[6].
In order to efficiently and fully utilize the received energy from solar panels in LS-PV-PP, high-power inverters play an important
role in converting the received DC energy from the panels into AC power for supply the AC loads. In large-scale applications such as PV
power plants, "high-power" in medium voltage (MV) inverters is characterized by the use of multilevel inverters to enhance efficiency
and scalability. These high-power MV systems generally function within a power range of 0.4 MW–40 MW, and in certain applications,
can reach up to 100 MW. The typical voltage range for these systems spans from 2.3 kV to 13.8 kV. In the context of PV power plants,
the "high-power" classification for multilevel inverters usually applies to systems operating in the MW range, incorporating medium
voltage levels of 2.3–13.8 kV to optimize energy transmission efficiency and support reliable system performance [7]. The evolution of
semiconductor technologies has been very effective in the field of inverter challenges, especially the problems related to voltage
fluctuations. This development shows a great achievement and provides users with more control and flexibility in using inverters [8].
In the structure of LS-PV-PPs, the inverter is considered as the main component of the generation and transmission system, which can
control the generated power. In the common structure of LS-PV-PPs, a medium-voltage transformer is also utilized, resulting cost and
weight increases. On the other hand, due to the size and structure of this transformer, the system will be shut-down when a fault occurs
in either unit during the transfer to the central inverter.
1.3. Challenges in LS-PV-PP system design and operation
While multilevel inverters provide improved power quality and reduced harmonic distortion, challenges related to component
complexity, control demands, and thermal management remain. These challenges limit their adoption in large-scale applications,
where cost and reliability are crucial considerations. A multitude of factors require meticulous consideration when designing an LS-PVPP system. These include ensuring safe operational parameters, mitigating risks associated with overvoltage and overcurrent condi­
tions, implementing galvanic isolation measures, and minimizing power losses within semiconductor devices. A particularly signifi­
cant aspect of such systems involves the integration of efficient maximum power point tracking (MPPT) protocols tailored to the PV
Fig. 1. An integrated solar PV system.
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Fig. 2. The structure of a LS-PV-PP.
system. MPPT algorithms are critical in PV systems to ensure maximum energy extraction under varying environmental conditions. PV
modules have a specific point on their power-voltage (P-V) curve, the Maximum Power Point (MPP), where power output is highest.
Since MPP fluctuates with changes in sunlight and temperature, MPPT controllers dynamically adjust the system’s operating point in
real time to maintain optimal efficiency [9].
Working of the MPPT algorithms is an important element in PV systems to make sure maximum power extraction is done even
under different environmental conditions. The maximum power point is the specific point on the current-voltage (C-V) curve where the
module generates the highest current. Since MPP shifts with the radiation and temperature variations, MPPT controllers adapt the
operating point of the system from the optimal one in real time to keep the efficiency as high as possible and thus a decrease in MPP
loss. MPPT methods to enhance the PV systems are the most important ones grouped into four categories, namely, measurement-based,
calculation-based, intelligent schemes, and hybrid methods. Measurement-based algorithms are based on direct parameter mea­
surements with examples of the Open-Circuit Voltage (OCV) and the Short-Circuit Current (SCC) methods, which can be simple but
may lead to a loss of accuracy in case of partially shaded PVs. Calculation-based algorithms expect the MPP through mathematics
models, such as Perturb and Observe (P&O), which are simple but tend to oscillate around the MPP, and Incremental Conductance (IC),
which makes a precise calculation of the PV curve slope, what is best under dynamic weather conditions [10]. Intelligent schemes,
among which are Fuzzy Logic Control (FLC), Neural Networks (NN), and Particle Swarm Optimization (PSO), are AI techniques that
manage the nonlinear interaction between multiple PPS and the load to identify the global MPP, even if there is partial shading of the
module. Finally, hybrid methods, the conjoint ones, for instance, FLC and P&O, that balance both accuracy and speed, often are the
best in the utmost challenging conditions yet the need for higher costs and exertion of implementation are required [11].
Therefore, high-power inverters, which has been introduced as a new technology to meet high-power industrial needs, are
potentially used in LS-PV-PP systems to achieve these goals [12]. These converters are designed to receive high-voltage DC inputs from
PV panels and regulate them to deliver the necessary output of AC voltage with an appropriate frequency for seamless grid integration
via an advanced conversion system. High-power converters continuously adjust the voltage and current levels using MPPT algorithms
to maximize the output power and ensure its high efficiency. In addition to LS-PV-PPs, high-power inverters are used in various ap­
plications, including large electric motors, Flexible AC Transmission Systems (FACTS) devices and renewable energy (RE) converters
[13]. Also, these converters have recently been presented as a widely used technology to meet the needs and challenges in industries
such as electric drives and rolling mills [14]. One of the highly important advantages of these inverters compared to classic inverters is
the low voltage-stress and power losses, and improved power quality.
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1.4. High-Power Inverter’s innovations for LS-PV-PP applications
Because they provide us with a type of power converter that minimizes the destructive effects of harmonics in an integrated grid
with low power losses [15]. In addition to the mentioned features, high-power inverters provide advanced monitoring and control
capabilities. This feature allows operators to remotely monitor power plant performance, troubleshoot system errors more quickly, and
perform necessary repair and maintenance tasks with minimal cost and waste of time and energy, if needed. In addition, they support
seamless integration with grid management systems through internal communication interfaces, enhancing grid stability and control.
Efficiency and reliability are key features of high-power inverters. These converters are designed to continue operating under adverse
weather conditions, providing optimal performance and ensuring a high lifespan. These inverters, utilizing modern control systems,
robust protective features, and comprehensive fault detection mechanisms, can maintain satisfactory performance even in challenging
environments. They minimize losses and failures, optimizing energy generation [16,17].
The main contribution of this paper are as follows:
• Presenting a general review of renewable systems and the importance of power electronics in them
• Analysis of the application of high-power inverters in LS-PV-PP systems
• A complete review of the proposed structures of high-power inverters in LS-PV-PP systems in recent years and stating their ad­
vantages and disadvantages
• A review of the control methods used in high-power inverters
• A study of modulation methods in the structure of high-power inverters
The rest of the paper are organized as follows: the classification of high-power inverters is presented in section 2, The control
methods for high power inverters is introduced in section 3, modulation strategies of high-power inverters are discussed in section 4,
limitations of multilevel inverter technologies and future research suggestions is presented in section 6 and finally, conclusion is
discussed in section 7.
2. Classification of high-power inverters
The advent of high-power inverters has catalyzed a notable transformation in the progression of diverse advancements within the
Fig. 3. The classification of high-power inverters.
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realm of electrical power conversion across various energy sources. Furthermore, such inverters occupy a distinctive niche owing to
their specialized applications and inherent features. The following section evaluates the classification of high-power inverters and their
application in LS-PV-PP system applications. Hence, high-power inverters are finding increasing acceptance in LS-PV systems with the
capacity to handle high amounts of DC power and deliver grid-compatible AC power with a minimum of losses, providing stability.
Harmonic reduction, modular design, and flexibility in grid integration are three major features that make specific inverter topologies,
such as Multilevel Inverters (MLIs), well suitable for LS-PV-PP applications [18]. High-power inverters exhibit a diversity of classi­
fications contingent upon several parameters, encompassing topology, control methodologies, and modulation techniques. Fig. 3,
shows the classification of high-power converters based on topology type, which is determined based on key parameters such as circuit
structure and performance characteristics. This section will undertake an examination of the most prevalent and widely utilized types
of high-power inverters based on their topological configurations [19–22]:
2.1. Current source inverters (CSI)
The Current Source Inverter (CSI) topology employs a current source as its input. As depicted in Fig. 4, within the CSI configuration,
the circuit’s input is linked to a current source. Here, the DC input current undergoes conversion into high-frequency alternating
current at the output, achieved through a high-frequency switching circuit. The advantages associated with CSI inverters encompass
robust short-circuit protection and enhanced fault tolerance. These inverters find frequent application in scenarios demanding high
levels of fault tolerance, notably in drive systems and for speed control in high-power motors [23]. Despite their advantages, CSIs
typically demonstrate lower efficiency compared to voltage source inverters (VSIs), largely due to the need for multiple active
components, such as large inductors and capacitors, to ensure steady current flow. This regulation process increases the complexity of
control algorithms and introduces energy losses, making CSIs less suitable for large-scale applications where efficiency is critical [24].
This reliance on large inductors only increases operational costs and losses in terms of efficiency due to resistive heating and magnetic
hysteresis. Furthermore, the increased component count and related maintenance requirements raise initial and long-term costs, thus
placing a burden on remote PV installations, which need to be maintenance-free. Because of this, CSIs are seldom employed in
cost-conscious PV projects that emphasize efficiency and minimal maintenance [25].
2.2. Voltage source inverter (VSI)
The Voltage Source Inverter configuration, as depicted in Fig. 5, entails the circuit’s input being linked to a DC voltage source.
Operational functionalities are executed through high-frequency switching within this structure. Consequently, the DC input voltage
undergoes transformation into high-frequency AC output voltage. VSI inverters, due to their high reliability and simple structure,
provide a fast response and are used in applications such as motor drive systems and renewable energy systems [26]. Additionally, VSIs
require fewer protective components in comparison with CSIs; therefore, VSIs have simpler designs and require much less mainte­
nance. Still, scalability becomes the issue when power starts to deal with higher levels. Very large-scale PV systems may require
additional capacitors or protective circuitry to stabilize output voltage, especially when they are exposed to a high level of power [27].
2.2.1. Multilevel Inverter (MLI)
Multilevel Inverter topologies, as depicted in Fig. 6, are designed with the objective of mitigating the adverse impact of harmonics
within the output waveform. This is achieved through the incorporation of multiple levels of DC voltage sources within the circuit
structure. In MLIs, a combination of switches and capacitors is employed to generate staircase voltages, ultimately producing a si­
nusoidal waveform at the output of the inverter circuit. This topology offers several advantages, including enhanced output waveform
Fig. 4. The conventional topology of a CSI in a LS-PV-PP.
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Fig. 5. The conventional topology of a VSI in a LS-PV-PP.
Fig. 6. The conventional topology of a MLI.
quality, reduced stress on switches, and lower levels of electromagnetic interference (EMI). MLIs are commonly used in high-power
applications such as high-voltage transmission systems, electric vehicles, and integration of renewable energy sources.
As previously mentioned, high-power multilevel inverters play a crucial role in LS-PV-PPs by facilitating integration into the
primary power distribution grid. Multilevel inverters are designed with a modular structure comprising power electronic elements.
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Within the realm of LS-PV-PP systems, several prominent topologies find application, notable among which are the Neutral-PointClamped (NPC), Cascaded H-Bridge (CHB), and Flying Capacitor (FC) configurations. In these delineated topologies, the direct cur­
rent (DC) input interfaces with multiple Insulated Gate Bipolar Transistors (IGBTs), organized either in series or parallel configura­
tions. Such organization facilitates the attainment of specified output voltage levels in accordance with the intricacies of the circuit
design [28]. High-power Multilevel Inverters possess the capability to furnish voltage across a spectrum of levels, spanning from
kilovolts (KVs) to megavolts (MVs), contingent upon the specific needs of the user. Given the necessity for diverse voltage tiers within
the converter, discrete capacitors are mandated within each submodule to harbor energy reserves. Sustaining equilibrium in capacitor
voltage emerges as a pivotal imperative, crucial not only for the protracted reliability but also for the optimal functionality of the
converter [29].The necessity of reducing additional components in PV-connected inverter systems is unavoidable, and for this reason,
an optimization scheme has been proposed for an Switched-Capacitor Multilevel Inverter (SC-MLI). In their investigated scheme,
researchers have introduced a new topology with a 13-level AC output by increasing voltage levels to 6 and 3. In the presented scheme,
to enhance the degrees of freedom in levels and voltage magnitudes, a complementary structure of 9 levels with a voltage and degree of
freedom of 4 has also been suggested [30]. A new 9-level inverter based on grid-connected MLIs in PV systems has been proposed to
reduce frequency modulation and increase power transmission efficiency [31]. As shown in Fig. 7, A single-stage system has been
employed for extracting MPPT from PV arrays, which can be integrated with the distribution grid. To minimize power losses, the
simultaneous conduction of switches has been minimized, utilizing 8 switches in the circuit, including two bidirectional switches for
controlling reactive power flow. Switching losses are minimized, and system reliability is achieved by adjusting the DC bus voltage,
supported by a backup battery. One of the main objectives of the presented topology is to reduce leakage current and address chal­
lenges related to power quality. The power quality of the grid, for supplying nonlinear loads, is controlled through a minimum mean
square algorithm. The structure of this topology is designed by the management of two isolated DC sources in a 1:3 ratio through the
array of PV system, providing a high number of output voltage levels with a minimal number of components. This distinguishes it from
requiring additional clamp diodes and flying capacitors.
In the study [32], a novel inverter topology for grid-connected PV systems is presented. As shown in Fig. 8, Comprising six power
switches, one DC source, three capacitors, and one diode, this configuration represents a streamlined approach compared to preceding
topologies, thereby engendering heightened system efficiency and compactness. The fundamental design encompasses a trans­
formerless five-level inverter, leveraging Switched Capacitor (SC) technology to effectuate size reduction within the system. Notably,
at elevated frequencies, merely four power switches within this inverter operate, thereby mitigating switching losses. Furthermore, a
Common Ground (CG) structure is incorporated to curtail system leakage current effectively. The management of reactive power is
facilitated through the utilization of the Phase-Disposition Pulse Width Modulation (PD-PWM) technique, which instigates a
self-balancing mechanism for the voltage across switched capacitors. This modulation strategy is characterized by its simplicity and
efficacy. Additionally, a closed-loop control mechanism is instituted to uphold the equilibrium of the neutral point voltage on the DC
side, thereby ensuring the seamless operation of the system. In Ref. [33], a 9-level topology is proposed for a multilevel inverter,
introducing a novel compact design. The goal of the proposed method is to increase the output power at a large scale, add more
outputs, and enhance the topology. In the presented scheme, a DC source controls two switched capacitors with the aim of trans­
forming it into a single diode. By utilizing switched capacitors, the circuit becomes integrated, providing the capability of doubling the
output voltage to the grid.
Study [34] presents a single dc source-based double LDN high-resolution multilevel inverter topology that addresses practical
Fig. 7. Configuration of the proposed MLI topology in Ref. [31].
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Fig. 8. Configuration of the single-phase five-level grid-tied inverter in Ref. [32].
constraints of central inverter application, such as power quality, efficiency, reliability, and cost of implementation. The authors
propose a two-stage high-resolution multilevel inverter solution to double the inverter utilization and increase efficiency. They
demonstrate the reactive power handling and fault blocking capability of the system. With the aim of increasing the sinusoidal output
power in LS-PV-PPs, a new topology for a three-phase multilevel inverter has been proposed in Ref. [35]. In the proposed topology, the
DC-link capacitors and high-frequency transformer have been eliminated to deliver output power to the load in a trapezoidal waveform
instead of a sinusoidal waveform. The presented circuit design consists of two parallel inverters connected to DC sources, which are
introduced with an N-module inverter. Considering the widespread application of transformerless multilevel inverters in PV systems, a
topology for a 5-level Switched-Capacitor Bridge inverter based on switched capacitors has been proposed in order to reduce har­
monics and generate a multilevel output voltage. To reduce switching losses, the number of high-frequency switches has been reduced.
Additionally, as depicted in Fig. 9, a new control scheme has been introduced to control the injected active and reactive power into the
grid [36].
Authors in [37] have developed a novel five-level common ground type (5L-CGT) transformer-less inverter topology with double
voltage boosting, employing eight switches and two capacitors charged at the input voltage level The inverter functions initially as a
string inverter for low-power PV applications but demonstrates scalability to operate as a multi-level inverter with increased power
handling capacity, suitable for centralized applications. The paper provides a thorough mathematical analysis of the inverter’s
Fig. 9. Circuit configuration of the proposed transformerless MLI in Ref. [36].
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operation and component sizing. CHB inverters as shown in Fig. 10 are a type used for converting direct current to alternating current
at high power levels. This structure is composed of multiple H-bridge modules connected in a Cascade configuration to achieve the
desired output voltage and power level. Each H-bridge module in the Cascade configuration consists of four power electronic switches
(transistors or IGBTs) arranged in an organized H-shaped configuration [38]. The CHB topology is considered a suitable option for use
in LS-PV-PP systems due to its fundamental advantages, such as a reduced number of switches, lower DC source requirements, and
cost-effectiveness. These converters primarily generate an AC output waveform with the appropriate frequency and voltage range at
the circuit output by employing a suitable control method and determining the proper switching sequence and timing. This topology is
capable of operating at high power levels while maintaining precise control over the output waveform. Additionally, the use of
appropriate modulation techniques can enhance the quality of the generated AC waveform and significantly eliminate the adverse
effects of harmonic distortions [39].
In the study referenced by Ref. [40], a novel isolated bridge cells (I-BC) topology is introduced with the primary objective of
mitigating the inherent challenges associated with phase imbalance in three-phase systems, as well as streamlining the complexity
intrinsic to circuit structures. Within this proposed topology, a multilevel inverter undertakes power conversion operations at elevated
frequencies while interfacing with multiple high-power DC buses. Notably, the elimination of DC-link capacitors in the central section
obviates the necessity for balancing control measures therein. Moreover, the inverters are interconnected in parallel with PV cells,
facilitating power conversion in a singular-stage configuration. In the traditional structure of solar power plants, inverters and
low-frequency transformers are utilized as an interface between PV panels and the AC grid for power transmission. However, the use of
transformers leads to a decrease in efficiency, an increase in system bulk, and consequently, a rise in system costs. To address these
challenges, the adoption of transformerless inverters with CHB topology is suggested as a suitable solution. However, the absence of a
transformer and galvanic insulation between the grid and the inverter in this scenario results in leakage currents during high-frequency
power conversion and reducing system safety. For this reason, aiming to reduce leakage currents in CHB multilevel inverters in PV
systems connected to the grid, a three-phase transformerless topology has been proposed. As shown in Fig. 11, In each phase of the
circuit, six switches are employed, and gate pulses for all switches are applied using the pulse width modulation (PWM) technique,
such as sinusoidal triangular modulation. This ensures easy control and maintains the constancy of common-mode voltage (CMV),
resulting in a significant reduction in leakage currents [41].
Given the escalating adoption of multilevel inverters owing to their enhanced system efficiency and reduced frequency switching
within high-power LS-PV-PP systems, the imperative to address challenges in power converters becomes paramount. Consequently, in
Fig. 10. The conventional topology of an isolated 3-ϕ CHB-MLI for solar PV system.
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Fig. 11. PV fed 3-ϕ transformerless CHB inverter in [41].
order to bolster power quality, ensure optimal system performance under demanding conditions posed by linear and unbalanced loads,
and diminish frequency switching, thereby mitigating harmonics and reactive power, a novel three-level CHB hybrid inverter topology
has been proposed as detailed in Ref. [42]. This innovative topology incorporates a single-input–multiple-output single-ended pri­
mary-inductance converter (SIMO-SEPIC) inductive converter. Notably, the presented topology integrates a mixed second- and
third-order generalized integral (MSTOGI) control scheme to effectively manage active and reactive powers while synchronizing with
the grid. This control method helps eliminate DC offset, leading to the preservation of power quality in the grid current. The proposed
topology is capable of transmitting higher power, reducing the THD of the system, and accurately MPPT under various radiations and
dynamic load changes without oscillations. Additionally, in comparison to CHB inverters, this topology can generate a maximum
number of voltage output levels, with its voltage output waveform having nine levels, including four positive voltage levels, four
negative voltage levels, and one zero level, surpassing the symmetric source structure of CHB. According to Fig. 12, authors in Ref. [43]
presented the mechanism of active power backflow during low voltage ride through (LVRT) in three-phase CHB PV grid-connected
inverters. It deduces the quantitative relationship between active current and reactive current that needs to be injected under
different types of voltage faults and different degrees of voltage sags. The feasibility of suppressing active power backflow by
positive-sequence active power current injection is analyzed in detail, considering the relevant LVRT standard. The proposed method is
validated through simulation and experimental results, demonstrating its effectiveness in suppressing active power backflow during
LVRT.
In order to attain elevated output power levels, obviate the necessity for low-frequency transformers, generate multilevel output
voltage, and implement distributed MPPT, a novel three-phase topology has been introduced in Ref. [44] tailored for CHB-based
inverters. This innovative topology promises heightened efficiency and cost-effectiveness within LS-PV-PP systems by supplanting
centralized inverters. The proposed topology comprises diverse conversion units, wherein each unit integrates a direct AC-to-AC
conversion stage designed to generate low-frequency AC voltage from the medium-frequency AC voltage outputted by the trans­
former. This architectural arrangement engenders a reduction in the number of conversion stages within the novel topology, facilitated
through the sequential operation of the conversion units coupled with the utilization of zero-voltage switching (ZVS) and zero-current
switching (ZCS) techniques in each conversion stage. Relative to both centralized inverter topologies and conventional CHB
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Fig. 12. Circuit structure of ith module in 1-phase in proposed topology for high-power inverters in employed in LS-PV-PP [43].
configurations, the delineated topology showcases superior attributes deemed advantageous for deployment in LS-PV-PP systems. In
Ref. [45], a novel single-stage quasi-z-source (qZS) based power converter tailored for Photovoltaic applications is introduced. This
innovative converter design necessitates fewer passive components and power switching devices in contrast to prevailing seven-level
topologies employing impedance and quasi-impedance sources. Furthermore, the study proposes a modulation technique adept at
achieving the requisite voltage boosting levels utilizing the qZS networks, thereby facilitating the synthesis of seven levels within the
output voltage waveform. In CHB converters without transformers, leakage current occurs due to the lack of galvanic insulation,
resulting in increased losses, heavy harmonics, and electromagnetic interference. In Ref. [46], a new approach has been proposed to
eliminate this leakage current based on Highly Efficient and Reliable Inverter Concepts (HERIC). In the proposed method, by using a
suitable ac filter, the leakage current in each module is suppressed and can be extended to all voltage levels. To address the issues of
uncertainty, instability, and high cost in PV systems, a novel Cascaded H-Bridge -Multilevel Inverter (CHB-MLI) topology has been
proposed that achieves these objectives by eliminating additional components of DC/DC converters in the battery energy storage
systems (BESS) system. In the examined structure, a combined modulation scheme is considered, which prioritizes the placement of
each cascaded power cell in the circuit, and the proposed method utilizes this control algorithm for modulation index in MPPT to
enhance system stability [47]. The use of transformerless inverters has significant advantages and attractiveness. However, these
converter models lead to leakage currents through parasitic capacitors. In Ref. [48], a new topology has been presented while adhering
to the principle of reducing additional elements. As depicted in Fig. 13, By adding a blocking switch to the DC link in a 7-level CHB
inverter, the voltage across parasitic capacitors is kept constant, reducing leakage currents. In Ref. [49], a Modular Multilevel Con­
verter (MMC) with a CHB structure has been presented to address the challenges of unbalanced power distribution and complex control
in replacing transformer inverters for Line Frequency Transformers (LFT). Additionally, it enhances scalability and reliability against
short circuits through a simple and stable control scheme to a significant extent.
The high-power inverter with a NPC topology, also known as a three-level inverter, is a type of multilevel converter. In contrast to
traditional two-level inverters, which have two voltage levels (positive and negative), this inverter has an additional intermediate
voltage level known as the neutral point [50]. According to Fig. 14, in the NPC topology the neutral point is connected to the midpoint
of the DC bus by the use of a diode. By incorporating this additional voltage level, NPC inverters can generate a three-level output
waveform, resulting in reduced THD and improved output waveform quality compared to two-level inverters. The key advantage of
NPC inverters is the enhanced control of the output voltage, improved efficiency, and reduced voltage fluctuations across the circuit
switches [51]. The design of a PV connected Unified Power Quality Controller (UPQC) utilizing a NPC multilevel inverter aimed at
enhancing power quality is elucidated in Ref. [52]. The paper employs the Synchronous Reference Frame (SRF) theory to transform a
three-phase four-wire NPC multilevel inverter into a power quality conditioner. This approach leverages advanced control strategies to
mitigate power quality issues such as voltage sags, swells, and harmonics, thereby enhancing the overall performance and reliability of
the PV system. The study [53] introduces a novel voltage balancing converter designed for NPC inverters in grid-connected solar PV
systems. This converter effectively regulates the DC link capacitor voltage through the utilization of switched-capacitors and appro­
priate switching states. Furthermore, it demonstrates the capability to scale to higher voltage levels and boost the DC input voltage
11
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Fig. 13. Circuit configuration of the proposed single-phase seven-level CHB inverter topology for LS-PV-PP in Ref. [48].
Fig. 14. The conventional topology of a 3-ϕ NPC-MLI for solar PV system.
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without the need for magnetic components. The converter ensures self-balancing and possesses the capacity to boost the input voltage
to achieve the desired output voltage levels. The proposed converter is integrated into a grid-connected solar PV system featuring an
NPC inverter controlled by a vector control scheme. Notably, the voltage balancing converter is scalable and readily extendable to
operate at elevated voltage levels. Additionally [54], proposes a Boost Active Neutral Point Clamped (ANPC) configuration charac­
terized by diminished resource count, which engenders an output voltage of 11 levels leveraging merely 12 switches with blocking
voltage ratings lower than the peak value of the output voltages. Integral to this proposed Multilevel Inverter are four self-balanced
capacitors, instrumental in achieving a voltage boost of 2.5 in the output. These capacitors are efficiently charged and discharged
employing a straightforward logic governing parallel/series connection with the active power DC source. This innovative configu­
ration not only enhances voltage levels but also streamlines the complexity of the system architecture, thus presenting a viable solution
for advanced grid-connected solar PV systems. A three-phase three-level T-type NPC-MLI topology with transformerless PV grid
connected proficiency, aiming to mitigate CMV and switching-frequency leakage current in three-level inverters has been proposed in
Ref. [55]. The proposed TNP-MLI offers higher efficiency, lower breakdown voltage on the devices, smaller THD of output voltage,
good reliability, and long lifespan. In Ref. [56], a novel Five-Level quasi-Z-Source (qZS) based NPC inverter tailored for Photovoltaic
applications is introduced. This innovative topology boasts fewer switching devices and mitigated voltage stress in comparison to
prevailing NPC converters relying on impedance sources. The integrated circuit of the inverter comprises a dual quasi Z-source ar­
chitecture incorporating both a T-type arm and a diode-clamped arm, thus enhancing its performance and versatility within PV
systems.
The FC topology, which is similar to the NPC topology, is usually used to solve the challenges of traditional two-level inverters, such
as extreme voltage fluctuations on the switches. This topology uses several capacitors that are switched to achieve a stepped voltage
waveform, and as a result, the voltage stress on the power switches is reduced and the output efficiency is improved, which brings
benefits such as reducing switching losses, improving the quality of the output voltage. Fig. 15, shows the structure of an FC topology
and its main components and circuit connections. However, this structure still requires precise control algorithms in order to balance
the voltage of the capacitors to obtain an acceptable and suitable performance [57].
A new topology for a 5-level voltage source inverter (5L_VSI) is presented, which solves the complications caused by dc-link with a
simple structure and uses a control system without high complexity. The proposed structure as shown in Fig. 16, consists of only one FC
cell. It uses in its topology and compared to other structures, it has fewer elements to reduce cost and losses. On the other hand, a
simple PWM method is also used to balance the output voltage in the presented structure [58]. The study [59] introduces a novel
multilevel topology predicated on a flying capacitor topology. This topology is capable of operation in both symmetrical and asym­
metrical configurations of DC sources, yielding 9 and 25 levels of output voltage, respectively. Two distinct topologies have been
developed, each engineered with tailored parameters to achieve higher output voltage levels. advantages include the reduction in
device count, facilitation of negative polarity voltage generation without necessitating bridges, and the auxiliary H’s role in mini­
mizing the peak reverse voltage between switches. With the objective of enhancing power efficiency and simplifying the control system
complexity, a novel flying capacitor inverter topology has been proposed in Ref. [60]. This innovative topology streamlines the
requisite electrical components, featuring a seven-level multilevel inverter comprising power switches, capacitors, and drive circuits.
in Ref. [61] a single-phase flying capacitor multi-level inverter designed specifically for solar energy applications, employing Sinu­
soidal Pulse Width Modulation (SPWM) technique. The study delineates three distinct configurations of single-phase flying capacitor
multi-level inverters, namely three-level, five-level, and seven-level, elucidating their waveform patterns, output current, voltage
characteristics, and comparison of active and reactive power waveforms. The findings of this investigation suggest that higher-level
multi-level flying capacitor inverters exhibit superior performance metrics and reduced output noise levels, rendering them prefer­
able for the conversion of DC to AC in renewable energy applications. A novel transformerless five-level inverter, structured upon the
Fig. 15. The conventional topology of a 3-ϕ FC-MLI for solar PV system.
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Fig. 16. Circuit configuration of the Proposed 5L-VSI topology in [58].
FC topology, has been introduced for utilization in PV grid-connected systems [62]. This innovative design integrates seven switches
and three DC capacitors, leveraging a non-leakage current DC voltage source.
In [63], with the aim of optimal control of active and reactive powers in a grid-connected PV systems, a quasi-Z source inverters
(qZSI) has been designed. This inverter, compared to conventional single-stage voltage source inverters, has a single-stage power
conversion capability, leading to increased system reliability. It exhibits proper performance when the system load changes or when
the grid experiences disturbances and voltage reductions. The filter used in this design is selected based on commercial values, and
according to the calculations performed for the LCL filter, its resonance frequency is ten times the grid frequency and half of the
switching frequency. In order to reduce the size of inverter filters and minimize harmonic distortions, an enhanced impedance source
inverter with a parallel transformer structure has been introduced in Ref. [64]. The advantages of the proposed inverter include easy
maintenance and repair, improved output filter requirements, increased voltage gain through the addition of parallel inverters,
reduced EMI, and protection against short-circuit currents and circuit voltages. In order to reduce the circulating current in parallel
qZSI inverters in PV and BESS systems, a mathematical analysis of the performance of these inverters has been examined in Ref. [65].
During charging and discharging states, as well as under balanced and unbalanced loading conditions, the controller’s performance
presented between the PV and the battery is observed through its self-regulating mechanism, which establishes a two-way relationship
between neutral currents, output filters, and CMV. This leads to reduced losses and increased overall system efficiency. Through the LC
resonance circuit, it manages the power of the PV and battery systems. This single-stage structure reduces switching losses and,
considering the modified control scheme, decreases the circulating current. The study [66] explores a 3-level T-type inverter topology
predicated on the three-level T-type quasi-impedance source inverter (3L-T-type qZSI) for the provision and augmentation of injected
reactive power into the grid. This combined approach aims to injection reactive power to the grid, effectively functioning as a shunt
filter, while simultaneously addressing challenges associated with unbalanced currents and harmonics stemming from nonlinear loads
at the Point of Common Coupling (PCC). In Ref. [67], a novel single-stage five-level inverter, T-type in configuration, is introduced for
grid-connected PV generation applications. This innovative design, based on dual Z-source and an enhanced structure, circumvents the
cumbersome and costly two-stage conversion topologies prevalent in traditional systems. Furthermore, it tackles the challenge of
leakage current in PV systems through the implementation of a tailored PWM scheme and the effective utilization of passive filters.
Additionally, the study highlights the capability of the proposed power converter to support reactive power, a crucial aspect for PV
inverters. In Ref. [68], a three-level diode clamped active impedance source inverter (AIS-TLI) topology has been proposed based on
the three-level qZSI topology with minimal components and inherent advantages. In the presented structure, a higher modulation
index is provided to enhance the output waveform quality and require less inductance. AIS-TLI establishes a common ground between
input and output terminals and effectively eliminates leakage current in single-phase PV-fed systems. With the aim of addressing
common challenges such as frequency modulation, circuit complexity, and reliability in three-level T-type inverters powered by dual
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three-phase drives for high power applications, a control scheme based on predictive current control has been presented in Ref. [69] to
address potential errors. To obtain precise reference voltage for current control, Deadbeat control is first combined with current
prediction, and an optimized voltage vector is created for each three-phase three-level inverter based on the vector space division
method, reducing the complexity of control schemes in high-power systems, leading to a reduction in switching losses and smoother
power transmission. In Ref. [70], a zeta source inverter hybrid topology for power transfer in DGs has been proposed. The structure
under consideration is bridgeless and the secondary diodes are integrated into the paired diagonal switches. The aim of introducing
such a structure is to reduce the number of circuit elements, regulate reactive power injection into the grid, and reduce losses. In this
structure, a control scenario based on a dynamic model is also provided to address control challenges, where control parameters are
compared based on separate operation modes. As mentioned in previous cases, one of the challenges presents in 3-phase inverters in PV
systems is the problem of leakage current, which is solved using appropriate AC filters and changing switches. In Ref. [71], a topology
is presented in which, by increasing the switching frequency, in addition to controlling the leakage current, CMV noise and current
ripple are reduced. Many topologies of multi-level inverters used in LS-PV-PP were studied and the detail explanation as shown in the
following Table I.
Several studies have highlighted the advantages of multilevel inverters, yet they also reveal persistent challenges, including
increased power loss, thermal management difficulties, and the need for sophisticated control methods. Addressing these issues is
essential for enhancing inverter performance and scalability, particularly in high-power PV systems.
3. Control methods for high power inverters
Control methods in the high-power inverters are therefore necessary to attain stability, efficiency, and reliability in LS-PV-PPs; their
performance depends a lot on operational stability, scalability, and computational complexity [72].The design and implementation of
control systems hold significant importance in enhancing the operational efficiency of high-power inverters. The integration of various
control methods and algorithms within a cohesive framework is instrumental in achieving optimal functionality [73]. Control systems
include specific algorithms used to adjust main parameters such as voltage, current, and frequency in inverters to make them more
efficient and highly reliable. When discussing the operation of LS-PV-PP, the importance of control units in the structure of these power
plants becomes doubly significant, as these systems are responsible for monitoring, regulating, and optimizing various aspects of
power plant performance, ensuring reliability, and maintaining energy generation rates [74].One of the fundamental applications of
control systems in high-power inverters is to maintain precise and stable output voltage and frequency. This is crucial when the
inverter is connected to the main grid or other loads, as ensuring the stability of the output voltage and frequency is vital [75].
Adaptive and FLC control methodologies as shown in Fig. 17, in Ref. [76] further enhance the robustness of the system through
continuous re-tuning of the parameters of the system based on real-time measurements. These are quite effective in treating variations
in output power due to environmental changes or imbalances in the system, although their slower response times can make them less
suited to treating high-frequency disturbances [77,78].
Model predictive control (MPC) basically has some excellent capabilities: stable operation under dynamic conditions, balancing
flying capacitor voltages, and reduction of THD without any additional controllers. However, its dependency on precise system
modeling might bring instability in the presence of parameter variations or unmodeled dynamics [79]. One of the application of
control systems in high-power inverters is to increase the speed and accuracy in achieving MPPT. Control algorithms continuously
examine the input of the inverter and adjust its operational parameters to extract the maximum available power [80]. Another
essential factor is computational complexity. FCS-MPC gives high precision and fast dynamic response but becomes computationally
prohibitive in case of high-rise of control objectives, whereas traditionally used simple methods like Proportional-Integral (PI) and
Sliding Mode Controllers (SMC) are computationally simpler, in nonlinear or time-varying systems might be difficult to work out
without additional tuning or hybrid enhancements [81,82]. These all factors need to be weighed up based on the operational demands
while choosing appropriate control methods for LS-PV-PPs. Such systems operating under highly dynamic environments may give
priority to Model Predictive Control to ensure stability, while systems configured in a modular fashion might use a distributed control
despite its communication challenges.) In Ref. [83], a current control strategy has been proposed for a 7-level inverter topology
designed for high-power requirements. The control method is of the MPC type, aiming to establish balance in the output voltage of an
inverter topology of the FC type. It eliminates the need for additional controllers and modulations. The presented control technique not
only maintains voltage balance but also controls the output current of the inverter. In Ref. [84], a solution for controlling the output
voltage of high-power inverters in microgrids has been presented. The examined method utilizes an optimized model through a neural
network, employing a e gravity search algorithm (GSA) for a high-power inverter. In this approach, the output high-voltage is analyzed
and adjusted in series with the main grid using the proposed model and a PI controller. In the study [85], the authors introduced an
active power equalization control strategy premised on zero-sequence voltage compensation for three-phase common DC-bus cascaded
H-bridge multilevel inverters. This strategy aims to ensure uniform transmission of active power across all modules, irrespective of the
distribution of modules in each phase or the power factor of the inverter. By bolstering system modularity, this approach contributes to
the optimization of inverter performance and overall system efficiency. One of the inherent issues in high-power CHB inverters is the
imbalance in the output power, leading to instability and reduced current in grid-connected systems. Therefore, an adaptive control
technique has been proposed to regulate the output power in these converters. In the examined method, by calculating modulation and
comparing it with grid indices, the output power is adjusted, addressing the challenge of adapting the output power and the transfer
power of the converter, thus resolving modulation issues as well [86]. In Ref. [87], a new control algorithm has been proposed to
examine the capabilities of transferring and distributing reactive power in high-power inverters for LS-PV-PPs on GW scale. In the
proposed model, by examining weather conditions and the amount of solar radiation during different hours of the day, a droop control
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Table 1
Comparison of topologies for different high-power inverters employed in solar PV applications.
Reference
Description
Applications
Advantages
Disadvantages
Number of
power
switches
[30]
SC-MLI generates 13-level AC
output and 9-level AC via
modified switching.
a nine-level MLI-based gridconnected solar power transfer
unit to enhance power quality
and mitigate energy crises.
PV sources, fuel cells and
battery storage devices
Reduced Efficiency in
Practical Application
13
Failure to examine challenges
in practical tests
8
[32]
A switched-capacitor based
five-level transformerless
inverter for featuring voltage
self-balancing.
intended for grid- (PV)
systems.
Failure to mention potential
limitations including issues of
scalability and adaptation to
different environmental
conditions and load changes.
5
[33]
a single-source 9-level
multilevel inverter topology
using virtual DC sources
through switched capacitors
power stations, and
hybrid renewable energy
applications (e.g., WindPV, PV-Fuel Cell)
Lack of explicit discussion on
real-world integration
challenges in diverse
conditions.
9
[34]
a two-stage, single DC-sourcebased high-resolution
multilevel inverter
grid-connected solar
systems
Potential constraints due to
multiple floating capacitors.
12
[35]
a three-phase multilevel
inverter (MLI) designed for
photovoltaic applications
without the need for large DClink capacitors
a single-phase five-level
transformerless inverter using a
single switched-capacitor (SC)
for grid-tied PV systems
Primarily suitable for
solar systems and gridtied operations
Enhanced Output Voltage,
Modifying Switching Strategy,
-Self-Voltage Balancing
reduce device count and losses.
Improved efficiency and low
harmonic AC waveform.
Adaptable control for dynamic
load conditions Reactive power
control for grid quality.
Reduced number of switches and
components. Improved efficiency
with low Total Standing Voltage
(TSV) and Capacitance Factor
(CF). Addresses leakage current
and reactive power regulation.
Reduced size, weight, and cost
with a single DC supply.
Upgradeable to a 19-level
configuration with minimal
additions.
Reduced filter requirement due to
high-resolution output voltage,
Enhanced reactive power
injection capacity, Enhanced fault
blocking capability.
Increasing efficiency, sharing
power equally, reducing losses
reducing the destructive effects of
harmonics
Occurrence of conduction
losses at higher power levels
12
Possibility of Requiring
Complex Control Schemes
for Better Optimization
7
A five-level common ground
type (5L-CGT) transformer-less
inverter with double voltage
boosting using eight switches
and two capacitors.
a single-stage isolated cascade
PV inverter topology based on
multi-bus DC collection.
low-power PV
applications and
centralized inverter for
higher power handling.
use of capacitors for achieving
voltage boosting. And as a
result, there is a problem in the
converter.
8
require more complex control
strategies to maintain power
balance
16
[41]
three-phase transformerless
inverter topology with six
switches per phase
Grid-connected solar
photovoltaic systems.
Challenges with leakage
currents in the CHB MLI.
18
[42]
a trinary hybrid CHB multilevel
inverter and modified control
system
Grid-connected solar
power transfer
three-phase CDB-CHB PV gridconnected inverters during low
voltage ride-through (LVRT)
events.
three-phase topology for
medium-voltage cascaded
conversion systems in largescale PV plants
aimed at large-scale (PV)
power plants.
require careful attention to
switching losses, thermal
management, and protection
mechanisms
the issue of active power
backflow and its potential to
cause system shutdown.
8
[43]
Low Injected Grid Current THD
Enhances Power Quality.
Acceptable Power Loss and
Heat Distribution Among
Power Switches. Provide
Voltage Boosting Capability with
Single SC.
Reduced leakage current,
common ground structure, twice
voltage boosting, and quasi-soft
charging mechanism for
capacitors.
Reduced System Volume.
Eliminated Voltage-Balancing
Control. Eliminated SecondHarmonic Voltage Ripple.
Balanced Power Distribution.
Reduced leakage current
throughout operation.
Modulation strategy effectively
suppresses leakage current.
Simple and easily implementable
methodology.
Amplified Voltage Options.
Smoother Waveforms, Minimal
Distortion. Power Control
Perfected.
Understanding Active and
Reactive Currents in Various
Voltage Fault Conditions.
Increased stability.
Reduced dc wiring cost.
Distributed (MPPT). increased
efficiency.
Limited scalability
16
[31]
[36]
[37]
[40]
[44]
Grid connected PV
sources
Grid connected PV
sources
Grid-connected solar
photovoltaic systems.
designed for large-scale
PV plants
24
(continued on next page)
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A. Azizi et al.
Table 1 (continued )
Reference
Description
Applications
Advantages
Disadvantages
Number of
power
switches
[45]
a single-stage dual quasi-zsource 7-level inverter (DqZS7LI)
Designed for both
standalone and gridconnected PV systems.
Complexity of the Converter.
8
[46]
transformerless cascaded Hbridge (CHB) based PV systems
using High-Efficient and
Reliable Inverter Concept
(HERIC)
Single-phase PV inverter
utilizing Cascaded H-Bridge
(CHB) topology
CHB-based inverter with a
proposed CM model and
multicarrier pulsewidth
modulation strategy
CSI-based converter
applied to PV systems
Reduced Semiconductor
Switching Devices. Efficient
Performance for Standalone and
Grid-Connected Modes.
Minimized Leakage Current.
Reduces leakage current in
individual cells and the entire
system. easily extendable to CHB
inverters with varying voltage
levels.
Increasing stability. reducing
converter size. reducing costs.
Cannot eliminate leakage
current, posing safety risks in
PV systems.
12
Need for adequate modulation
index control in cases of deep
mismatch
Need for Redundancy States
10
[47]
[48]
[49]
[50]
Low Voltage (LV) grid
Transformerless PV
systems
Enhanced Leakage Current
Suppression. Compact System
Size.
High-power MV PV
systems
Eliminates the use of bulky linefrequency transformers.
Addresses challenges of CHB- and
MMC-based converters. High
scalability.
Neutral-point voltage balancing.
redundancy design challenges
8
Complexity of the Converter
8
solar photovoltaic
systems
DC link voltage balancing.
Complexity maintain power
balance
11
solar photovoltaic
systems
Reduced CMC and leakage
current, Elimination of shootthrough problem.
require careful grounding and
isolation measures
4
concerns related to voltage
ripple and lifespan by using
capacitors for voltage
balancing
complexity of the control
system
6
does not mention any potential
drawbacks or challenges
associated with implementing
this strategy
requires proper filter and
impedance component sizing.
12
complexity of control strategy
and parallel connection.
6
complexity of the analysis and
implementation.
Complexity in implementing
the control strategies.
12
complexity of its
implementation
4(for
single
phase)
complexity of the control
architecture
4(for
single
phase)
a single-phase NPC inverter
with one-leg clamping pulse
width modulation (OLC-PWM)
voltage balancing converter
tailored for grid-connected
solar PV systems utilizing NPC
MLIs
a transformer-less (TL) T-type
neutral point clamped (TNP)
multilevel inverter (TNP-MLI)
topology for grid-connected PV
power generation systems
a symmetric flying capacitor
(SFC) -MLI topology for gridconnected applications
high-power and
multilevel applications
medium voltage highpower grid-connected
systems
Low voltage rating of switches,
Multi-stage feedback control.
[58]
5-level voltage source inverter
High-power applications
[59]
Modulated Phase-Shifted Pulse
Width Modulation (PSPWM)
Strategy
Designed for PV systems
Simplified structure without DClink neutral points. Elimination of
isolated DC sources and complex
phase-shifting transformers.
Enhanced Output Voltage
Waveform Quality. Simplified
Modulation Process and Design.
[63]
quasi-Z source inverter (qZSI)
[64]
Parallel-configure.d improved
Z-source inverter (ZSI)
Large-scale gridconnected PV power
plants.
High-power solar and
wind power systems
[65]
Parallel operation of threephase quasi-Z-source inverter
3L-T-type quasi-impedance
source inverter (3L-T-type
qZSI) functionality assessment
Solar and battery energy
systems
Designed for PV systems
Three-level diode clamped
active impedance source
inverter (AIS-TLI) based on
qZSI
Fault-tolerant control for Ttype three-level inverter system
single-phase PVpowered systems
[53]
[55]
[57]
[66]
[68]
[69]
high-power, low
switching frequency
scenarios
Single-stage power conversion.
buck/boost capability. improved
reliability.
Immunity to open and short
circuits. resilience to
electromagnetic interference
noise. increased reliability.
Reduced switching losses.
Functions both as an active power
filter (APF) and for injecting
active/reactive power into the
grid.
Reduced components.
Integrates deadbeat control with
current prediction. ensuring
precise control.
13
8
6
9
(continued on next page)
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Heliyon 11 (2025) e42334
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Table 1 (continued )
Reference
Description
Applications
Advantages
Disadvantages
Number of
power
switches
[70]
Bridgeless Hybrid-Mode Zeta
Inverter
distributed energy
systems
Reduced number of active power
components. enhancing output
power transfer and reliability.
5
[71]
Silicon Carbide (SiC) Devices
and Inverter Filters
Grid-connected solar
photovoltaic systems.
Improved performance and
reduced inductor ripple with SiC
devices and increased switching
frequency.
Difficulty in control due to
distinct system dynamics
during discontinuous and
continuous conduction modes.
Increase in current ripple due
to DC-link referenced AC filter.
6
Fig. 17. Circulation chart of fuzzy logic control inference system [76].
has been presented for inverters to store reactive power in the specified grid. In study [88] a single-stage power conversion system for a
three-phase, seven-level multilevel inverter with clamped diodes has been proposed. This novel approach eliminates the need for an
intermediate dc-dc converter, leading to reduced complexity, size, and cost. To control the system, a multi-loop controller is employed,
encompassing an integral-proportional sliding mode controller (IP-SMC). The IP-SMC is responsible for optimizing the performance of
the grid-side parameters and the settling time of the dc link voltage under varying meteorological conditions. By integrating both
integral and proportional control actions, the proposed controller ensures robust power factor correction and MPPT for the PV system.
In study [89], an optimized control method has been proposed to increase the stability of high-power inverters. The presented control
system does not require additional equipment in the inverters. When the PV performs the momentary cessation (MC) operation, the
system prepares the DC-link capacitors and ensures stability in transient states by injecting active power. An optimized controller for
multiple parallel modular high-power inverters designed for wireless power transfer is presented in Ref. [90]. In the proposed control
system, the leakage current at the output, resulting from the control signals, is suppressed with a time delay in the inverters. Essen­
tially, an optimized PI controller adjusts the desired parameters by calculating the required time delay for suppressing the leakage
current with coordinated pole placements. Study [91] introduces a phased-shifted control strategy designed for high-power inverters
to regulate their output voltage. This control methodology finds application in an inverter integrated within a high-power Inductive
Power Transfer (IPT) system. The proposed approach entails the design of a virtual impedance-based dynamic model, which obviates
the need for a dedicated DC/DC power regulation section. Instead, the focus is directed solely towards inverter control, aimed at
mitigating the inherent complexities and control challenges associated with such inverters. Furthermore, to enhance the PV and BESS
and augment the Photovoltaic Hosting Capacity (PVHC) in PV-BESS hybrid systems, a novel method for controlling reactive power in
intelligent inverters within these grids has been delineated. In Ref. [92], a control method, considering the performance of the
high-power inverter in the system, proposes a model to minimize the voltage deviation (VD). The proposed controller utilizes an
intelligent-based swarm optimization algorithm (SMA) to optimize the examined factors. In Ref. [93], a LVRT control strategy for CHB
inverters is presented with the aim of suppressing reverse active current in high-power inverters in LS-PV-PP. In this strategy, by
extracting data from injecting active current and examining errors arising from this issue, a control scenario is adopted under various
conditions: single-phase short-circuit fault with ground, two-phase short-circuit fault with ground, and two-phase short-circuit fault
without ground. In Ref. [94], a control method is proposed with the aim of addressing the challenges of MPPT and input power to
high-power inverters connected to PV in shaded conditions. In the proposed method, a central controller is considered for the inverter
topology, which uses computational algorithms for power normalization, filtering, and data analysis to detect shaded points. The
analyzed data is then integrated into the inverter as control parameters, serving as an indicator to assess the performance of the in­
verter’s output power. In order to enhance the balanced output power in CHB inverters, an adaptive control method has been proposed
to address this requirement. The presented controller analyzes the injected power from the energy storage system modules based on
the maximum modulation index for all PV modules. This allows the modules to maintain the capability of proper charging and dis­
charging for power supply and storage systems, even in the case of moderate imbalance [95]. In the study [96], a MPC algorithm is
proposed for application in a PV system employing a multilevel inverter. This algorithm is specifically designed to achieve injection
from PV arrays utilizing NPC inverter topology, with a primary emphasis on MPPT. The core objectives of this algorithm include
ensuring voltage balance across DC link capacitors, reducing computational complexity relative to conventional methods, and
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Heliyon 11 (2025) e42334
A. Azizi et al.
imposing a focused SVM spectrum to enhance overall system performance. a MPC approach employing Finite Control Set (FCS) has
been devised for ANPC topology. The developed FCS-MPC framework achieves three distinct control objectives through the utilization
of a singular agent, thereby simplifying the coordination of weighting factors. This proposed control methodology enables the con­
verter to seamlessly transition between different operational modes even under faulty conditions, obviating the need for structural
modifications while ensuring continuous operation and component balance. Additionally, to mitigate the impact of parameter mis­
matches, an Extended Kalman Filter (EKF) is employed for online parameter estimation [97]. One of the new control methods in
high-power inverters that lack modulation stages is the MPC method. In Ref. [98], a control scenario is presented for a four-leg isolated
voltage source inverter (FLVSI) topology using the model predictive voltage control (MPVC) algorithm, which examines and predicts
15 switching states. The proposed algorithm eliminates complex delay calculations in system control by utilizing the two-stage pre­
diction horizon principle. The proposed method is compared with a Proportional–Integral–Derivative (PID) controller, and its ad­
vantages are identified. In Ref. [99], the authors have proposed an MPC control strategy along with Phase-Shifted (PS)-PWM to address
MPPT issues in CHB inverters due to variations in solar irradiance. The proposed scenario eliminates the power imbalance between the
phases and independently controls the inverters in each unit. High-power inverters of the type three - level neutral - point clamp (3L NPC) have widespread applications in high-output renewable energy sources. This model of inverters provides high power using
"lower-rank" switches. Therefore, aiming to reduce zero-sequence circulating current (ZSCC), maintain balance at the neutral point,
and reduce switching losses, a control method based on finite control set model predictive control (FCS-MPC) is proposed in Ref. [100].
In this method, as shown in Fig. 18, an L-3NPC topology is considered, utilizing a non-isolated DC-link in its structure.
Study [101] investigates the design of an FCS-MPC control in asymmetric cascaded H-bridge (ACHB) multilevel inverters. In the
modeling process, a detailed model is presented using discrete-time analysis to control the parameters of a 27-level chb inverter,
aiming to reduce instability in the network. In the proposed control method, the impact of variations in the examined system pa­
rameters on its dynamics is examined at high frequencies, and then the controller performs the operation of instability elimination. The
presence of transformers in multilevel inverters deployed in PV systems, besides increasing size and costs, provides insufficient effi­
ciency. In Ref. [102], a 5-level voltage source topology is presented, in which an MPC controller is utilized to control the current and
voltage of the capacitors. In the proposed method, two h-bridge cells are used to reduce losses in the switches, and the proposed
controller optimizes the charge and discharge current of the capacitors. One of the advanced and widely used control methods in
high-power inverters is deadbeat model predictive control (DB-MPC). This controller, with its high precision and straightforward
performance, addresses the challenge of efficiently managing multiple parameters simultaneously in converters. To overcome this
challenge, an optimized model of DB_MPC is introduced for a 9-level topology in an active neutral-point-clamped (ANPC) inverter. The
examined topology utilizes 9 switches and 2 diodes, and the proposed control method, without adding extra elements, focuses on
current control, stabilizing the FC’s performance, and maintaining balance in the dc-link. Additionally, the proposed DB_MPC enables
the inverter to operate with five faulty rows [103]. In Ref. [104], a FCB_MPC control scheme is proposed with the aim of overcoming
control challenges and addressing issues with modulators in DC voltages. The proposed scenario investigates a 5-level topology with 4
ports, establishing a connection between multiple PV arrays and batteries at different levels. The proposed scheme eliminates the need
for complex model-based calculations using the advantages of direct control, facilitating easy scalability to higher levels. In Ref. [105],
an MPC-based control scheme is proposed to compensate for power fluctuations and address dynamic challenges in the energy-stored
Fig. 18. Proposed FCS-MPC control block in [100].
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A. Azizi et al.
Table 2
Comparison of different control methods for high-power inverters systems in LS-PV-PP.
reference
Description
Advantages
Disadvantages
Implementation
Complexity
Stability
Flexibility
[83]
Model Predictive Control
(MPC) for Seven-Level Voltage
Source Inverter
Fewer active switches
and control complexity
high
high
high
[84]
Expanded Inverse Model
Control for BESS Inverter in
Stand-Alone Microgrid
Active Power Equalization
Control for Three-Phase CDBCHB PV Grid-Connected
Inverter
Power Adaptive Control for
Single-Phase CHB PV GridTied Inverter
Reactive Power Capability
Estimation & Self-Adaptive
Voltage Controller
Bidirectional Power Flow
Control and Hybrid Charging
Strategies for PV Inverters
Control Scheme for PV
Inverters during Momentary
Cessation Operation
MPMIs for High-Power WPT
with Master-Slave Control
High-Power Multi-Transmitter
IPT with Multi-Inverter
Balances flying capacitors without
PWM or PI controllers. Effective
control of load currents. Highquality voltage to the load.
Robust output voltage control of
BESS inverter.
Reliance on accurate
model representation
medium
high
low
Enhances system reliability and
redundancy.
Increased cost associated
with redundancy design
high
high
low
Enables normal operation even
with unbalanced output powers
among PV panels.
Accurate estimation considering
various factors. Enables improved
voltage control service for the grid.
Enables maximum PV power
utilization.
Involves complex control
strategies and
calculations
May need additional
equipment
high
high
low
medium
high
medium
Might require
sophisticated control
methods.
May require advanced
control techniques
High
high
medium
medium
high
medium
specific for WPT systems
high
high
high
Model complexity might
increase
medium
high
medium
Requires optimization
expertise for settings
medium
high
medium
Enhances Low Voltage Ride
Through (LVRT) capability in PV
systems.
Prevents overmodulation in the
higher-power H-bridge module.
Enables more efficient energy
harvesting.
Simpler control scheme.
Specific control strategies
for different fault
scenarios
Requires additional
components (battery
module)
medium
high
high
medium
high
medium
High computation time
and delay.
medium
high
medium
Fast dynamic response.
Potential operational
limitations in certain
conditions
medium
high
high
Reduces Total Harmonic Distortion
(THD). Mitigates ZSCC to near-zero
levels.
High efficiency due to optimal
modulation and high power main
H-bridge. Reduction in output filter
sizes due to high-quality waveform.
Low stress on switches due to low
on-state switches in the current
path.
Requires implementation
for specific 3L-NPC
parallel inverters
Requires a precise and
complex control strategy.
medium
high
medium
medium
high
low
The control technique’s
complexity for the
presented multilevel
inverter.
Requires careful tuning
and sensitivity to
parameter mismatch.
No modulator, requires
precise calibration
medium
high
high
medium
high
medium
medium
high
high
Poor dynamic response
during mode transition
with PI control
medium
high
high
[85]
[86]
[87]
[88]
[89]
[90]
[91]
[92]
[93]
[95]
[98]
[99]
[100]
[101]
[102]
[103]
[104]
[105]
Optimal Reactive Power
Control for PV and BESS Smart
Inverters
Optimized LVRT Control for
CHB Medium-Voltage PV
Inverters
Adaptive power control
strategy for single-phase CHB
PV inverter system
MPVC control technique used
for load voltage regulation in
FLVSI
PS-MPC strategy designed for
power balancing in CHB
converters using Phase-Shifted
Pulse-Width Modulation (PSPWM).
virtual voltage vectors model
predictive current control for
parallel 3L-NPC inverters
a control strategy using FCSMPC for a single-stage, singlesourced ACHB trinary inverter
topology
control of the PV multilevel
inverter topology at input and
control of the grid current at
the output.
an improved robust DB-MPC
method for a nine-level ANPCbased inverter.
a direct Model Predictive
Control for a multi-level NPC
inverter.
Model Predictive Control for a
Quasi-Z-Source Inverter (DMES-qZSI)
Improves transient stability of
synchronous generator connected
to the grid.
Achieves phase synchronization for
suppressing current circulation.
Utilizes multi-inverters to drive
multiple primary coils. facilitating
high power IPT.
Enhances PV Hosting Capacity
(PVHC).
High tracking quality with effective
FCs and NP balance in steady-state
and dynamic operations.
Simplified design with direct
control.
Single control loop for both modes.
20
Heliyon 11 (2025) e42334
A. Azizi et al.
quasi-Z-source inverter (ES-qZSI) topology. The suggested strategy analyzes, evaluates, and compares the MPPT for a grid consisting of
PV and batteries during different times of the day. In this proposed strategy, functional models of the system are predicted under
various daytime scenarios to enhance system performance. The different control methods and algorithms that have been used to
improve the performance of MLIs in LS-PV-PPs and have been reviewed in this article can be seen in Table II, more details:
4. Modulation strategies
Electrical energy conversion between different voltage, current, or frequency levels in power electronic converters is achieved
using semiconductor-based electronic switches. Control elements in electrical circuits operate in an active linear region. However,
semiconductor-based electronic switches function only in two states: fully on or fully off, simplifying their operation. Modulation
strategies are crucial in enhancing the performance of high-power inverters, particularly by reducing switching losses, minimizing
harmonic distortion, and ensuring compatibility with multilevel inverter architectures [106]. In high-power inverters, modulation
techniques are employed to switch the circuit between these states. Each topology of high-power converters employs specific mod­
ulation methods to enhance circuit performance. When examining various modulation techniques for power electronic converters,
parameters such as switching frequency, distortion, losses, and response speed must be carefully evaluated. Indeed, the output voltage
of a high-power inverter appears as a pure sinusoidal waveform with nominal distortion. The use of appropriate modulation methods
to control switches and generate required waveforms is a key aspect of controlling high-power inverters [107–109]. Pulse Width
Modulation (PWM) is a crucial strategy for generating switching pulses in high-power converter control. This method involves
comparing modulating signals with a carrier signal to generate switching pulses. By directly controlling the switching sequence in
inverters, this method is responsible for controlling the output waveforms of current and voltage. Inverter performance is determined
by managing and controlling switching losses and fluctuations, facilitating efficient operation according to the switching device’s
requirements. While the modulator generates output signals as a function of modulating and carrier signals, the modulator controller
executes algorithms tailored to the output parameter needs and utilizes physical measurements such as current, voltage, and phase
angle [110,111]. In high-power inverters, PWM modulation is determined based on the switching frequency. Essential Switching
Frequency (ESF) methods and High Switching Frequency (HSF) methods are among the modulation techniques used in controlling
these converters. The HSF method, in particular, is employed to generate thousands of switching signals per cycle due to its higher
carrier frequency, typically in the KHz range [112]. Sinusoidal Pulse Width Modulation (SPWM), a widely used technique, balances
simplicity and performance but suffers from high switching losses due to its elevated switching frequency, making it less suitable for
applications demanding high efficiency. Space Vector Pulse Width Modulation (SVPWM) optimizes switching sequences to reduce
transitions between states, thereby minimizing switching losses and making it a preferred choice for high-power applications. In terms
of harmonic distortion, Selective Harmonic Elimination (SHE) effectively suppresses specific low-order harmonics by solving nonlinear
equations to determine optimized switching angles, achieving superior harmonic performance compared to SPWM and SVPWM,
though its real-time implementation can be computationally demanding. Multilevel inverter topologies, such as CHB, NPC and FC,
benefit significantly from modulation strategies like SVPWM, which optimizes switching patterns across multiple levels to improve
system reliability and reduce common-mode voltage [113–115]. While SHE also offers superior harmonic suppression and waveform
quality for multilevel systems, their practical application requires sophisticated control systems to handle the increased complexity.
Fig. 19. (A) Block diagram of the SPWM generator scheme; (B) waveforms of the modulation and carrier signals; and (C) hexagon containing the
possible voltage vectors for SPWM [121].
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A. Azizi et al.
The choice of modulation strategy should align with specific application requirements, such as power quality, efficiency, and system
complexity; for instance, SVPWM is ideal for industrial settings prioritizing efficiency and low harmonic distortion, whereas SHE is
better suited for applications focused on eliminating specific harmonics [116]. This section explains conventional modulation methods
employed in high-power inverter systems, with a focus on their topological aspects [117–120]:
4.1. Sinusoidal pulse width modulation (SPWM)
Sinusoidal Pulse Width Modulation (SPWM) represents a fundamental technique employed in power electronics. In
SPWM, a sine wave known as the modulation signal (vm) is compared with two triangular waveforms serving as carrier signals (vc1 and
vc2) to produce PWM signals, as illustrated in Fig. 19A. To create switching signals for other phases, the modulation signals need to be
shifted by 120◦ relative to one another while still using the same carrier signals. The modulation signal’s frequency determines the
frequency of the output voltage, whereas the frequency of the carrier signals sets the switching frequency, as depicted in Fig. 19B.
Furthermore, the hexagonal representation of possible voltage vectors for SPWM is shown in Fig. 19C [121]. SPWM is widely utilized
for its ability to produce high-quality sinusoidal waveforms while effectively controlling harmonic content and achieving
desired output characteristics in power conversion applications.
4.2. Space vector PWM (SVPWM)
Among the array of PWM techniques previously discussed, wherein three-phase voltage references are modulated individually,
stands a distinct approach known as SVPWM. In contrast to conventional PWM techniques, SVPWM operates on the principle of space
vectors, representing three-phase voltage references as a vector Vabc in the complex plane. This voltage reference vector is subse­
quently modulated by output voltage vectors generated by the inverter. The adoption of SVPWM has become widespread across
numerous three-phase inverter applications due to its ability to produce fundamental output voltages approximately 15.5 % higher
than those achieved by conventional SPWM. Furthermore, SVPWM yields reduced harmonic distortion in load currents, mitigated
torque ripple in AC motors, and lower switching losses(Fig. 20) [122]. Its superior performance characteristics have rendered it a
preferred choice for modern power electronics applications.
4.3. Selective harmonic elimination (SHE) modulation
SHE is a new method used in high-power inverters for modulation. The application of this technique aims to suppress destructive
effects, such as excessive heat and grid disturbance. SHE modulation provides an effective solution for eliminating specific harmonics
from the voltage waveform output. The general structure for SHEPWM is shown in Fig. 21 [123]. This approach involves solving a set
of nonlinear equations, often referred to as the set of harmonic elimination equations, which relate the desired harmonic magnitudes to
the associated switching angles. Essentially, the SHE modulation technique encompasses a three-step process: identification of har­
monics, formulation of the set of harmonic elimination equations, and then utilizing numerical techniques to solve these equations and
achieve selective removal of the targeted harmonics.
4.4. High-Power Inverter’s modulation techniques for utilizing in LS-PV-PP
In reviewing various PWM techniques in LS-PV-PP high-power inverters, we find that these techniques focus on optimizing the
conversion of DC power from solar panels to AC power to inject an appropriate output power into the main grid. The three PWM
techniques commonly studied include SPWM, SHE PWM, and SVPWM. To enable precise control of high-power multilevel inverters, a
new approach is proposed in Ref. [124] for digital modulation of SPWM. This technique finds significant application in systems such as
solar pumping and motor drives, where it efficiently manages DC/AC inverter output voltage, minimizing distortion and low harmonic
components. The core concept involves converting a sampled, DC-biased sine wave signal into a repetitive pulse train. The widths of
these pulses fluctuate sinusoidally, thus giving rise to a digital SPWM. Different amplitude modulation indices, spanning from 0.5 to
1.3 (including over modulation), are implemented and analyzed in practical scenarios. Next research focuses on the development and
examination of single-stage photovoltaic generators (PVGs) integrated with CHB-MLI. The aim is to enhance the efficiency of the
multilevel inverter by presenting four MLI topologies: three, five, seven, and nine levels. These topologies effectively reduce voltage
drops and minimize THD in the output voltage and current by optimizing the inductance value of the L filter on the load side. To
regulate the suggested MLI circuits, we apply the Phase Opposition Disposition based on Sinusoidal pulse width modulation
(POD-SPWM) technique. In this approach, a modulating sine wave signal with a frequency of 50 Hz is compared to a carrier signal with
a frequency of 50 kHz to generate optimal switching combinations that yield a range of output voltage levels [125]. Conventional
methodologies applied to multilevel inverter circuits typically entailed a higher component count, thereby constraining the feasibility
of boost operation. To surmount this limitation, writers proposed a novel modified multilevel inverter PWM technique that facilitated
step-up operation while concurrently minimizing component complexity. In Ref. [126], writers expounded upon the development of
five-level, seven-level, and nine-level topologies rooted in this innovative approach. These topologies were propelled by a SPWM
technique, with particular attention directed towards devising a switching pattern conducive to capacitor equilibrium and optimizing
charging/discharging cycles throughout the operational trajectory. Reference [127] introduced the design of a symmetric multilevel
inverter aimed at generating a higher output voltage range with a fifteen-level output. An open-loop and closed-loop control system
has been employed to accommodate various operating load conditions, including resistive (R) and resistive-inductive (RL) loads. The
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A. Azizi et al.
Fig. 20. Block diagram of the control system with the SVPWM modulation for modular multilevel converter.[122]
Fig. 21. Flowchart for SHEPWM [123].
proposed solar-powered inverter (SFI), regulated by sinusoidal pulse width modulation, demonstrates a reduction in THD levels. In
multilevel inverters, practical application often faces challenges such as complex reference voltage synthesis, high CMV, and elevated
switching losses. Overcoming these obstacles while improving the performance of system requires an innovative approach to SVPWM.
To address this, a novel SVPWM scheme is proposed for PMSM vector control that is practical and independent of the level number
used in the multilevel inverter. This scheme simplifies computational complexity and enhances PMSM performance. Initially, the space
vector plane is subdivided, enabling direct determination of the coordinates and duty cycles of the nearest three vectors based on the
reference vector’s location. This process streamlines calculations and eliminates the need for iterative algorithms [128]. In the
investigation [129], an independent PV system was analyzed, comprising a DC-DC boost converter and a two-level three-phase Voltage
Source Inverter linked to a resistive-inductive load. The boost converter was integrated with incremental conductance (INC) control to
optimize power extraction from the PV panel. Regarding the regulation of the VSI output voltage, PWM emerged as a prevalent
technique. In efforts to enhance power quality, SHE-PWM and SVPWM methods were specifically employed and evaluated through
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A. Azizi et al.
simulations. To elucidate and compare the utilization of the DC bus in a three-level NPC inverter using the SVPWM and SHEPWM
techniques, a analysis was undertaken focusing on their performance in the linear region of the Modulation Index. The paper [130] also
presents an analogous relationship between the modulation indices in SPWM and SVPWM. Additionally, it is demonstrated that the
THD is lower in the SVPWM technique compared to the SPWM technique study [131] presented a hybrid approach combining artificial
neural network (ANN) and the Newton-Raphson algorithm (NR) for selective harmonic elimination in cascaded multilevel inverters
tailored for PV applications. This methodology leverages the SHE-PWM technique to optimize and mitigate harmonic distortion within
the inverter system, specifically targeting the reduction of THD. Additionally, the study incorporates the integration of a conventional
boost converter to elevate the PV voltage to an enhanced DC-link voltage, thereby fostering more efficient operational performance. To
provide a clearer understanding of the relative advantages and limitations of different modulation strategies for high-power PV sys­
tems, a comparative summary is presented in Table 3:
5. Current limitations of multilevel inverter technologies and future research suggestions
5.1. Component complexity and cost
Multilevel inverters require a greater number of components, including switches, capacitors, and diodes, to achieve higher voltage
levels and reduce harmonic distortion. However, this increase in component count leads to greater design complexity and higher
production costs [132]. In LS-PV-PP systems, where cost-effectiveness is critical, this complexity can pose significant barriers to
adoption. Additionally, the need for precise synchronization among components can complicate the design and increase maintenance
demands [133].
5.2. Efficiency and power loss
Although multilevel inverters effectively reduce harmonic distortion, they are not immune to power losses. Switching and con­
duction losses occur with each additional level, especially under high-power conditions typical of large-scale applications. These losses
can reduce the overall efficiency of PV systems, particularly when scaled to industrial levels. Minimizing these losses remains a
challenge, as it often requires a trade-off with increased complexity in control mechanisms or additional components [134].
5.3. Control and modulation complexity
To manage the multiple voltage levels and reduce switching losses, multilevel inverters often rely on advanced control techniques
such as MPC and SVPWM. These control methods, while effective in optimizing inverter performance, add computational demands and
can introduce latency, potentially impacting system reliability. For large-scale photovoltaic systems, implementing these control
systems at scale may require specialized hardware and software, increasing both the complexity and cost [135].
Given these limitations, our proposed future research directions focus on exploring innovative inverter topologies that can reduce
component count and complexity, developing control strategies that balance efficiency with simplicity, and enhancing thermal
management solutions for high-power applications. These directions are crucial for overcoming the identified challenges and enabling
the broader adoption of multilevel inverters in large-scale PV systems, where reliability, cost-efficiency, and performance are
paramount.
6. Conclusion
The critical role of multilevel inverters, particularly Voltage Source Inverters, in the efficient integration and transmission of solar
energy into the electrical grid is evident from the challenges and system application needs discussed. The analysis highlights the
necessity of a detailed examination of various inverter topologies to assess their performance in LS-PV-PP. Among the key issues
addressed, the paramount importance of maximizing solar energy generation to meet the escalating demand is evident. Achieving
these goals is fundamentally linked to the strategic selection and deployment of suitable inverter topologies within the system’s ar­
chitecture. Our comprehensive review of VSI topologies indicates distinct advantages inherent to each configuration. For instance, the
CHB topology demonstrates enhanced voltage tolerance, whereas NPC and FC topologies offer the benefit of eliminating the need for
individual DC sources for each module, a limitation observed in CHB configurations. Additionally, this paper provides an extensive
analysis of various control strategies utilized in high-power multilevel inverters, as outlined in our comparative tables. Among the
Table 3
Comparison of modulation strategies for high-power photovoltaic systems.
Modulation
Technique
Harmonic
Reduction
Energy
Efficiency
Complexity
Level
PV Suitability Notes
SPWM
SVPWM
Moderate
High
Moderate
High
Low
Moderate
SHE
High
High
High
Effective in simple PV systems with minimal harmonic requirements.
Suitable for large-scale PV systems that require efficient harmonic
control.
Ideal for PV applications in sensitive or highly regulated environments.
24
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A. Azizi et al.
control techniques reviewed, MPC is identified as particularly effective for these applications. Also, this review undertakes a thorough
exploration of modulation techniques applicable to high-power multilevel inverters. Looking forward, we anticipate advancements
that enhance system performance and reduce costs. This paper aims to serve as an indispensable resource for researchers and engi­
neers, guiding the selection of the most suitable converter topology for solar PV applications based on specific power requirements. For
the future researches, researchers can focus on several topics such as: Advanced Cooling Solutions, Hybrid Topology Optimization,
Artificial Intelligence in Control Strategies and Energy Storage Integration. This study highlights the pivotal role of advanced inverter
technologies in supporting the global transition to renewable energy and sustainable development. By addressing these areas, future
studies can contribute significantly to the evolution of inverter technologies, supporting the sustainable growth of solar energy
systems.
CRediT authorship contribution statement
Amirreza Azizi: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Software, Resources,
Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Mahdi Akhbari: Software,
Project administration, Methodology, Investigation, Formal analysis, Conceptualization. Saeed Danyali: Validation, Supervision,
Software, Resources, Methodology, Investigation, Data curation, Conceptualization. Zahra Tohidinejad: Supervision, Software, Re­
sources, Methodology, Investigation, Data curation, Conceptualization. Mohammadamin Shirkhani: Writing – review & editing,
Writing – original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investi­
gation, Formal analysis, Data curation, Conceptualization.
Data availability statement
No new data was generated for the research described in the article.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to
influence the work reported in this paper.
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