Maximum power point tracking and space vector modulation control of quasi-z-source inverter for grid-connected photovoltaic systems

International Journal of Electrical and Computer Engineering (IJECE)
Vol. 14, No. 2, April 2024, pp. 1424~1436
ISSN: 2088-8708, DOI: 10.11591/ijece.v14i2.pp1424-1436  1424
Journal homepage: http://ijece.iaescore.com
Maximum power point tracking and space vector modulation
control of quasi-z-source inverter for grid-connected
photovoltaic systems
Essaid Jaoide1
, Faicel El Aamri2
, Mbarek Outazkrit1
, Abdelhadi Radouane1
, Azeddine Mouhsen1
1
Laboratory of Radiation-Matter and Instrumentation, Faculty of Science and Technology, University Hassan 1st
, Settat, Morocco
2
Laboratory of Materials Energy and System Control, Faculty of Science and Technology, Hassan II University, Mohammedia, Morocco
Article Info ABSTRACT
Article history:
Received Jul 25, 2023
Revised Sep 30, 2023
Accepted Oct 9, 2023
The quasi-Z-source inverter (qZSI) become one of the most promising
power electronic converters for photovoltaic (PV) applications, due to its
capability to perform a buck-boost conversion of the input voltage in a single
stage. The control strategy based maximum power point tracking (MPPT)
and proportional integral (PI) controller are well known in grid-connected
with traditional configuration but not in qZSI. This paper presents a control
strategy for qZSI grid-connected based on the MPPT algorithm and the
linear control by PI controllers. This is complemented by the capability to
efficiently transfer the harvested power to the grid, ensuring a unity power
factor. The proposed control strategy effectively separates the control
mechanisms for the direct current (DC) and alternating current (AC) sides by
utilizing the two control variables, the shoot-through duty ratio and the
modulation index. An adapted space vector modulation technique is then
utilized to generate the switching pulse width modulation (PWM) signals,
using these two control variables as inputs. The proposed approach was
tested and validated under MATLAB/Simulink and PLECS software.
Keywords:
DC-link voltage
Grid-connected photovoltaic
system
Maximum power point tracking
algorithm
Proportional integral controller
Quasi-z-source inverter
This is an open access article under the CC BY-SA license.
Corresponding Author:
Essaid Jaoide
Laboratory of Radiation-Matter and Instrumentation, Faculty of Science and Technology, University Hassan 1st
Settat, Morocco
Email: e.jaoide@uhp.ac.ma
1. INTRODUCTION
The substantial rise in energy requirements and the rapid depletion of fossil fuel reserves globally
has led to an increase in energy prices, as well as concerns regarding energy security and environmental
impacts. In this context, photovoltaic (PV) systems offer a clean and reliable alternative for the generation of
green energy. Indeed, the PV energy is rapidly becoming an essential component of power systems. The use
of PV systems has been historically confined to standalone configurations in a variety of applications.
However, the remarkable decrease in the cost of PV modules, the implementation of PV systems has
expanded beyond standalone configurations to include integration with grid-connected systems [1]. Over the
past decade, both government entities and private sectors have incentivized the power industry to embrace
the integration of PV solar energy into medium or low-voltage distribution grids, owing to the decline in cost
of power electronic devices and advancements in renewable energy technology.
As the utilization of solar PV systems continues to increase, it is imperative to examine and
understand the challenges that arise during the extraction of energy from these systems and its subsequent
integration into the electrical grid. In addition, the generation of solar PV energy requires processing through
a power electronics interface before it may be used. To address the issue of lower input voltage caused by

Int J Elec & Comp Eng ISSN: 2088-8708 
Maximum power point tracking and space vector modulation control of … (Essaid Jaoide)
1425
constraints in the PV strings connection, an inverter system applied with the PV source often incorporates a
DC-DC boost converter. This one is inserted in between to increase the voltage at the inverter’s DC-link,
enabling the connection to the grid and facilitating the maximum power point tracking (MPPT) operation
[2]–[5]. This additional stage leads to an increased volume and supplementary losses, consequently ending
with a decrease in the overall system efficiency [1], [2].
To overcome these limitations of dual stage conversion, the Z-source inverter (ZSI) has been
proposed [6]. In fact, the ZSI exhibits a distinctive configuration that enables it to achieve a significant
voltage buck-boost capability within a single stage. That is to say, providing an efficient means to manage
energy transfer between a power supply and a grid [2], [6].
Following the introduction of ZSI topology, a number of daughters topologies were subsequently
developed to enhance the inherent capabilities of the original topology [7], [8]. In the same hand, the most
promising topology is the quasi-Z source inverter (qZSI) which was introduced in 2008, due to its ability to
harvest the maximum power for PV systems [9]. In various research studies, the qZSI has been utilized in
conjunction with renewable energy sources, including PV systems [10], [11] and wind turbines [12].
The qZSI uses an L-C impedance network as shown in Figure 1, it allows the use of an extra-state
named the shoot-through (ST) state which is the mechanism used to boost the input voltage [2], [6].
Moreover, the implementation of the ST state can be achieved by simultaneous switching of the upper and
lower devices within a single phase-leg of the qZSI.
Three-phase qZSI have the capability to employ various conventional pulse width modulation
schemes or space vector modulation (SVM) schemes. However, it should be noted that the utilization of the
ST state cannot be feasible without adapting these methods to adhere to the operational principles of the
qZSI. In this context, many pulse width modulation (PWM) control methods tailored for qZSI have been
proposed in the literature [13]–[15].
The main objective of grid-connected PV applications is to invert the direct current (DC) power
generated by the PV generator into alternating current (AC) power that can be transmitted to the grid [1]. In
the case where a fixed topology is chosen for the grid-connected inverter, the control strategy plays a crucial
role in determining the overall performance of the system [1]. A well-designed control strategy can
significantly enhance the power quality of the grid-connected inverter and improving its overall
effectiveness. Therefore, the design of the control box claims to obtain the optimal power output from the PV
panels while maintaining the required power factor and minimizing the output total harmonic distortion
(THD). In order to achieve an effective qZSI performance control strategy, it is essential to develop a precise
dynamic model of the system. Various mathematical models were introduced in the literature to analyze and
optimize the performance of the overall system [2], [16]–[18]. Also, the feedback control strategies for qZSI
have been the subject of investigation in several recent scholarly works [17], [19]–[24].
Currently, the control methods employed for qZSI mainly comprise proportional integral [2], [11],
[12], proportional resonance control [17], [25], sliding mode control [21], predictive control [24], and various
other techniques [22], [23]. Based on the analysis of the existing literature, it can be inferred that the non-
linear control methods demonstrate superior dynamic response compared to proportional integral (PI)
controllers [2], [8]. Nevertheless, the complexity associated with these algorithms prevents their widespread
implementation, which encourage the need for continued exploration and investigation into linear control
approaches.
In this regard, for the linear control of qZSI for PV application, many closed-loop control schemes
have been reported in the literature to effectively regulate the DC-link voltage. Notable examples included
direct DC-link control, indirect DC-link control, dual-loop controls and unified control. These schemes
control have been widely studied and used to achieve accurate and reliable DC-link voltage control [8].
Associated with PV generator, several research works have shown that the qZSI inverter is able to
handle variations of the PV output voltage and to produce an output voltage adapted to the grid-connected
[2], [8], [10], [19], [26]. The studies reported in [10], [11], [22], [27] employs the MPPT algorithm to
generate the ST duty ratio, while the reference d-axis current on the grid side is obtained through the control
loop of the impedance network capacitor voltage. Other studies such as [12], [16], [24], [26] use the MPPT
algorithm to generate the d-axis current reference of the grid.
The principal objective of this work was to achieve the optimal utilization of power generated by PV
panels with employing a linear control strategy based on the MPPT algorithm and the PI-ZSVM (SVM
adapted to qZSI) technique. This paper exclusively focuses on the discussion of the grid-connected mode for
the qZSI, while the examination of standalone mode has been addressed in previous studies [28]. On the
other hand, it introduces a strategy for controlling separately both DC-link voltage and the AC-side current.
In the proposed control scheme, the peak DC-link voltage is indirectly estimated by considering the voltage
across the capacitors of the qZSI, the ST duty ratio is generated through a double loop control according to
the error signal of the DC-link voltage. Furthermore, the AC-side control ensures synchronization of injected
current and controls power transfer quality. The amplitude of the d-axis grid current reference is elaborated

 ISSN: 2088-8708
Int J Elec & Comp Eng, Vol. 14, No. 2, April 2024: 1424-1436
1426
through a PI controller in accordance with the error signal of the MPPT algorithm. The proposed control
scheme is simulated on the PLECS software and MATLAB/Simulink environment. Hence, the obtained
results show the effectiveness of the control scheme and controller proposed and examined in this work.
The present paper is organized as follows: the section 2 provides a comprehensive explanation of
the distinct elements comprising the control strategy proposed. Specifically, we have provided detailed
descriptions of the qZSI and its dynamic modeling, the adapted MPPT algorithm, grid synchronization, the
ZSVM technique, and the multiple control loops employed within the proposed control scheme. In section 3,
the simulation results are depicted and discussed. Finally, the conclusion and the perspectives of this work is
reported in section 4.
Figure 1. qZSI inverter structure
2. METHOD
2.1. qZSI modelling
The PV generator typically necessitates a two-stage power converter [2]–[5], which uses a DC-DC
boost converter and a bidirectional two-level voltage-source inverter (VSI) to regulate DC-link voltage, so as
to the power flow between the PV generator and the grid. This topology suffers from several constraints,
notably the decrease in its efficiency and the high cost [2], [7].
In this present study, the conventional two-stage power converter is substituted with a qZSI, which
comprises an impedance network and a two level VSI. Through the implementation of an efficient switching
control, the qZSI allows regulation of the active and reactive power exchanged with the grid, as well as the
DC-link voltage. Figure 2 presents the equivalent circuit of qZSI in its two operating states. The operating
principle of qZSI is based on an extra-state called shoot-through state. During this one, at least one arm of the
inverter is short-circuited. In fact, Figure 2(a) shows the equivalent circuit of the qZSI during this state. Out
of the shoot-through sequence, the qZSI works as a traditional inverter, the energy transfer is done towards
the load or the grid. The equivalent circuit of the qZSI during this state is shown in Figure 2(b). Note that the
shoot-through sequence does not affect the proper operation of the grid or the load.
(a) (b)
Figure 2. Equivalent circuit of qZSI, (a) in shoot-through state and (b) in non-shoot-through state
PV
To
grid
or
load
𝑉𝑑𝑐
𝑉𝐿1
+ −
𝑉𝐿2
+ −
𝐿1 𝐿2
𝑉𝐶1
+
−
+ −
𝑉𝐶2
𝑖𝐿1
𝑖𝐿2
𝑖𝐶2
𝑖𝐶1
D
+
−
𝑉𝑖𝑛
To grid
or load
𝑉𝑖𝑛
𝐿1 𝑟𝐿1
𝑉𝐿1
+ −
− +
𝑉𝐶2 +
−
𝐿2 𝑟𝐿2
𝑉𝐿2
+ −
𝐶1
𝑟𝐶1
𝑉𝐶1
+
−
𝑉𝑑𝑐
+
−
𝑖𝐿𝑜𝑎𝑑
𝑟𝐶2
𝐶2 𝐶2 𝑟𝐶2
𝑉𝑖𝑛
𝐿1 𝑟𝐿1
𝑉𝐿1
+ −
− +
𝑉𝐶2 +
−
𝐿2 𝑟𝐿2
𝑉𝐿2
+ −
𝐶1
𝑟𝐶1
𝑉𝐶1
+
−
𝑉𝑑𝑐
+
−
𝑖𝐿𝑜𝑎𝑑
𝑉𝐷1

1427
Henceforth, we shall adopt the nomenclature of the currents and voltages depicted in Figure 1 for all
subsequent analyses. We will also designate by: 𝑇𝐶 is switching cycle, 𝑇𝑆 is interval of the ST state, 𝑇𝑁𝑆 is
interval of the NST state, D =
TS
TC
is shoot-through duty ratio. During shoot-through interval, we can write:
𝑉𝑑𝑐 = 0, 𝑣𝐿1 = 𝑉𝐶2 + 𝑉𝑖𝑛, 𝑣𝐿2 = 𝑉𝐶1 (1)
At the non-shoot-through interval, we have:
𝑉𝑑𝑐 = 𝑉𝐶1 + 𝑉𝐶2, 𝑣𝐿1 = 𝑉𝑖𝑛 − 𝑉𝐶1, 𝑣𝐿2 = −𝑉𝐶2 (2)
During a single switching cycle in steady state, the mean voltage across the inductors is zero. Therefore,
using (1) and (2), we obtain:
𝑉𝐿1 = 𝑣𝐿1 = 𝐷(𝑉𝐶2 + 𝑉𝑖𝑛) + (1 − 𝐷)(𝑉𝐶1 − 𝑉𝑖𝑛) = 0 (3)
𝑉𝐿2 = 𝑣𝐿2 = 𝐷𝑉𝐶1 + (1 − 𝐷)(−𝑉𝐶2) = 0 (4)
Consequently, we can infer the subsequent expressions:
𝑉𝐶1 =
1−𝐷
1−2𝐷
𝑉𝑖𝑛 and 𝑉𝐶2 =
𝐷
1−2𝐷
𝑉𝑖𝑛 (5)
The peak input voltage of the inverter 𝑉𝑑𝑐 in the active state can be expressed as (6).
𝑉𝑑𝑐 = 𝑉𝐶1 + 𝑉𝐶2 =
1
1−2𝐷
𝑉𝑖𝑛 = 𝐵𝑉𝑖𝑛 (6)
Here, B represents the boost factor of the qZSI. In theory, the gain factor can be varied from one to infinity
by changing the duty cycle (D) between 0 and 0.5. But in practical situations, this factor is restricted by
external factors related to the modulation index of the AC side [2], [6], [9].
2.2. Proposed control strategy of qZSI PV grid-connected
The proposed structure of the qZSI PV grid-connected is illustrated in Figure 3. This one shows the
different components of the system and how they are interconnected. The role of the section is to provide a
detailed description of the various components comprising the proposed control scheme.
Figure 3. Structure and scheme control proposed for qZSI and PV grid-connected

 ISSN: 2088-8708
1428
2.2.1. MPPT algorithm
PV array characteristic is non-linear, which is why there is a maximum power point (MPP), and it
depends on environmental conditions. So, the operating point needs to be updated to follow weather
conditions. The mathematical model describing the PV modules can be referred to in [5]. The P-V curve of
the PV panel, as depicted in Figure 4, clearly illustrates that the output power is maximized at a single
operating terminal voltage, denoted as 𝑉
𝑚𝑝𝑝, which corresponds to the MPP.
The MPPT algorithm was proposed to keep the operating point at MPP in all conditions. In this
context, several MPPT techniques have been presented in the literature to optimize the power production of
PV systems [29]. Moreover, it is widely recognized that the basic P&O (perturb and observe) algorithm is the
most efficient under normal operating conditions.
The P&O MPPT algorithm operates by analyzing the derivative of both the PV generator power and
voltage, represented by
𝑑𝑃
𝑑𝑉
. To gain a clearer insight, Figure 5 displays the flowchart depicting the MPPT
P&O algorithm used in the proposed control scheme. The MPPT control involves the measurement of PV
voltage and current, which are subsequently fed as inputs to the MPPT block. The P&O algorithm generates
the PV voltage reference, which is refreshed periodically.
Figure 4. Example of P-V characteristics of the PV panel
Figure 5. The flowchart of the MPPT P&O algorithm used for qZSI
2.2.2. Grid synchronization
Grid synchronization is an adaptive process in which the control algorithm of the grid-connected
converter generates a specific grid variable, typically the fundamental component of the grid voltage. This
adaptive process is essential for ensuring the stable and reliable operation of grid-connected power
converters, which are critical components of modern power systems. The synchronization process allows to
know the phase angle of the grid voltage, and it is used to regulate the active and reactive power supplied by
a power converter connected to the grid.
𝑃
𝑝𝑣(𝑊)
288
162
200
0
𝑣𝑝𝑣(𝑉)
𝑣𝑜𝑐
𝑣𝑚𝑝𝑝
𝑝𝑚𝑝𝑝
𝑷(𝒊) = 𝑽(𝒊) ∗ 𝑰(𝒊)
Decrease 𝑽𝒓𝒆𝒇
Yes
No
No No
Yes Yes
𝑷(𝒊) > 𝑷(𝒊 − 𝟏) ?
𝑽(𝒊) > 𝑽(𝒊 − 𝟏) ?
𝑽(𝒊) > 𝑽(𝒊 − 𝟏) ?
Measure 𝑽(𝒊) & 𝑰(𝒊)
Increase 𝑽𝒓𝒆𝒇 Increase 𝑽𝒓𝒆𝒇 Decrease 𝑽𝒓𝒆𝒇

1429
Synchronous reference frame phase locked loop (PLL) is used in this work, due to its simple
implementation and ability to estimate quickly and accurately the phase/frequency in normal grid condition
[30]. Initially, the sensed grid phase voltages 𝑣𝑔𝑎𝑏𝑐 are converted into the synchronous d-q frame. Then, the
PI controller is subsequently employed to regulate the q variable, with the output of this PI serving as the grid
frequency. The utility phase angle is derived by integrating the aforementioned grid frequency [30].
2.2.3. ZSVM control technique
In contrast to the conventional VSI, which does not permit the existence of the ST state, qZSI allows
this state by utilizing an impedance network. The ST state must be incorporated into any of the zero states, in
order to avoid any impact on the active states. Consequently, on the output AC voltage.
The traditional PWM techniques used for the conventional inverter are not adapted to the qZSI. In
fact, several modified PWM are used for controlling the qZSI. Therefore, miscellaneous PWM techniques
have been proposed in the literature, which can be broadly categorized into two distinct methods, namely,
sinusoidal PWM (SPWM) and SVM. Among the SPWM techniques are the simple boost, maximum boost
[13], and maximum constant boost [14], which were the first methods introduced. The conventional space
vector modulation (SVPWM) technique has gained widespread popularity due to its ability to produce a high
DC voltage with reduced harmonic distortion. Owing to these benefits, the concept of SVPWM has been
extended to control the qZSI [15].
The conventional VSI is commonly operated using the traditional SVPWM technique. This
technique uses eight voltage space states, which consist of six active states and two zero states, resulting in
the generation of six sectors as it is shown in Figure 6. The modified SVPWM are commonly called ZSVM.
According to [15], the ZSVM used for qZSI employs six active vectors, two zero vectors, and an additional
shoot-through (ST) vector. The reference output voltage can be expressed in (7):
𝑈𝑟𝑒𝑓 =
𝑇1
𝑇𝑠
𝑈1 +
𝑇2
𝑇𝑠
𝑈2 +
𝑇0−𝑇𝑠ℎ
𝑇𝑠
𝑈0 +
𝑇𝑠ℎ
𝑇𝑠
𝑈𝑠ℎ (7)
where:
{
𝑇1 = 𝑇𝑠𝑀 𝑠𝑖𝑛(
𝜋
3
𝑖 − 𝜃)
𝑇2 = 𝑇𝑠𝑀 𝑠𝑖𝑛( 𝜃 −
𝜋
3
(𝑖 − 1))
𝑎𝑛𝑑 {
𝑇0 = 𝑇𝑠 − 𝑇1 − 𝑇2, 𝑇𝑠ℎ = 𝐷𝑇𝑠
𝑀 = √3
𝑈𝑟𝑒𝑓
𝑉𝑑𝑐
Where, i denotes 𝑖𝑡ℎ
sector (1 to 6), 𝑇0 is the time interval of zero vector 𝑈0, 𝑈𝑠ℎ is the vector of the ST state,
𝑇1 and 𝑇2 are the duration of active vectors 𝑈1 and 𝑈2, respectively, and 𝜃 is the angle between 𝑈𝑟𝑒𝑓 and 𝑈1
as shown in Figure 6. M is the modulation index.
The ST state is incorporated during the time intervals of the zero state. It is pertinent to note that the
active state remains unaffected and maintains its state as in conventional SVM. The total duration of the ST
state 𝑇𝑠ℎ involves the use of the desired duty cycle ratio 𝐷. Subsequently, the 𝑇𝑠ℎ is divided into several
segments per switching cycle [15]. Each of these segments is independently introduced between the active
state vector and the zero-state vector.
Figure 6. SVPWM vectors and generated sectors I

 ISSN: 2088-8708
1430
According to the number of parts on which the total ST time is divided and the way of their
placement during the switching cycle. Three variants of ZSVM have been described in the literature, namely
ZSVM6, ZSVM4, and ZSVM2. The theoretical details, as well as the characteristics and limitations of each
technique have been extensively discussed in [15].
Based on the in-depth discussion presented in [15], the current work has adopted ZSVM4 due to its
perceived advantages over other variants. The ZSVM4 technique involves dividing the total ST time 𝑇𝑠ℎ into
six parts, which are inserted according to the schematic representation presented in Figure 7. Compared to the
conventional SVM, ZSVM4 requires the modification of four switching control signals. Therefore, the suffix
“4” is added to its name to indicate this distinction.
Figure 7. Switching time of ZSVM4 in sector I
For a reference vector 𝑈𝑟𝑒𝑓 that belongs to sector I, the Figure 7 presents switching control signals.
A similar analysis is employed for the other sectors to determine their corresponding switching patterns by
using the mathematical expressions provided in (8) and (9).
𝑇
𝑇0
4 𝑚𝑖 𝑑
𝑇0
4
𝑇1
2
𝑇0
4
𝑇1
2
𝑇2
2 𝑚𝑎𝑥𝑚𝑖𝑛
(8)
{
𝑇𝑚𝑖𝑛 + = 𝑇𝑚𝑖𝑛 + −
𝑇𝑠ℎ
6
𝑇𝑚𝑖𝑛 − = 𝑇𝑚𝑖𝑛
{
𝑇𝑚𝑖 𝑑+ = 𝑇𝑚𝑖 𝑑
𝑇𝑚𝑖 𝑑− = 𝑇𝑚𝑖 𝑑 +
𝑇𝑠ℎ
6
{
𝑇𝑚𝑎𝑥 + = 𝑇
𝑇𝑠ℎ
6 𝑚𝑎𝑥
𝑇𝑚𝑎𝑥 − = 𝑇
𝑇𝑠ℎ
3 𝑚𝑎𝑥
{
(9)
2.2.4. Control schemes for the grid connected
The control system for the grid-connected qZSI in PV systems is not similar to the constant DC
input source qZSI system. The control structure of the system comprises two primary stages. The first stage
is the DC-side control, The primary function of this step is to regulate the DC-link voltage. Whereas, the
0
Tmin-
Tmid-
Tmax-
Ts /2
S5
S2
Ts / 2 Ts / 2
t
S3
S4
S6
S1
Tmin+
Tmid
Tmax+
Tmax
Tmin
Tsh /6
Tsh /6
Tsh /6
Tsh /3
Modifieds signals
4
0
T _
T2 / 2 T2 / 2 T1 / 2
6
Tsh
4
0
T
6
Tsh
6
Tsh
6
Tsh
4
0
T
_ _
2
1
T
Tmid++
SVM
SVM
ZSVM4

1431
second stage is the AC-side control, which is composed of two cascaded controller loops. Specifically, the
system includes ZSVM block, phase locking loop (PLL), Clark transformation from 𝑎𝑏𝑐 to αβ, and park
transformation from dq to αβ. These components are essential for the system to operate effectively and
produce the desired output.
a. DC side voltage control
On the DC-side control, a dual-loop PI-based control scheme is employed to effectively maintain a
constant peak DC-link voltage at the desired value. As depicted in Figure 3, the control scheme uses the
adjustment of the voltage across the capacitor (𝑉𝐶1) and the inductor current (𝑖𝐿) to generate the shoot-
through duty ratio D.
In order to ensure the appropriate regulation of voltage 𝑉𝑑𝑐, it becomes necessary to compare its
actual value with the desired value. However, due to the pulsating nature of 𝑉𝑑𝑐, the measurement of its
actual value calls for the utilization of specialized and expensive circuitry. Therefore, to address this
challenge, the indirect 𝑉𝑑𝑐 control method is employed, wherein the estimation of 𝑉𝑑𝑐 is derived from the
measurement of 𝑉𝐶1 using the formula specified in (5) and (6).
As it is shown in Figure 3, the error between the desired value 𝑉𝑑𝑐
∗
and the actual value 𝑉𝑑𝑐 is
processed through a PI regulator. This regulator serves to furnish the reference current 𝑖𝐿
∗
for the inner loop’s
inductor. Subsequently, another PI regulator utilizes the error between 𝑖𝐿
∗
and the present inductor current 𝑖𝐿
to generate the shoot-through duty cycle D.
b. AC side power control
In the proposed control scheme, the AC side control is similar to a voltage VSI, the qZSI assumes
the responsibility of regulating both the active and reactive power through the modulation index M. In
order to address the objective of AC side control, a d-q reference frame aligned with the grid voltage is
employed to achieve the decoupling of active and reactive power control. In fact, the currents and voltages
of the three-phase grid are measured and subsequently converted into d-q components. Additionally, the
three-phase AC voltages undergo routing through a phase locking loop to obtain the three-phase voltage
phases.
To accomplish the decoupling of active and reactive power control, two cascaded control loops
are employed to regulate these powers. The outer loop serves the purpose of power control, while the inner
loop is employed for current regulation. The imposition of the reactive power reference is conducted
externally, while the active power is contingent upon the power extracted from the photovoltaic panel.
As expected in Figure 3, the MPPT algorithm is used to determine the reference for the d-axis of the
current (𝑖𝑑) injected into the grid, while a value of zero is enforced on the q-axis current (𝑖𝑞) component
reference.
For the inner loop, two feedback controls are implemented to regulate 𝑖𝑑 and 𝑖𝑞 individually, due to
the contribution of the decoupling terms as shown in Figure 8. Each of these controls utilizes PI regulators to
accurately track their respective current references. The resulting output variables from these controllers are
the compensation terms (voltage references) 𝑣𝑑
∗
and 𝑣𝑞
∗
. By employing the 𝑑𝑞/𝑎𝑏𝑐 transformation, the
voltage references for the inverter output can be derived 𝑣𝑎
∗
, 𝑣𝑏
∗
and 𝑣𝑐
∗
. Finally, these voltage references and
duty ratio cycle (derived from DC side control) are subsequently employed in ZSVM algorithm to generate
the gate PWM signals required to drive the inverter.
Figure 8. AC-side control decoupling terms
+ _
𝑖𝑑
∗
𝑖𝑞
PI
+
𝑖𝑞
∗
= 0
PI
𝑖𝑑
_
𝐿𝑔
𝐿𝑔
+
+
_
+
+
+
𝑣𝑑
∗
𝑣𝑞
∗
𝑣𝑑
𝑣𝑞

 ISSN: 2088-8708
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3. RESULTS AND DISCUSSION
The proposed structure depicted in Figure 3 was implemented using MATLAB/Simulink and
PLECS. The operation and control of the proposed control scheme for the qZSI in a PV system are simulated.
Various irradiation levels are taken into account during the simulation to assess the system’s performance
under different solar intensity conditions. The achieved outcomes are presented in this section.
3.1. Simulation specifications
To evaluate the performance and effectiveness of the proposed control system, a trapezoidal solar
irradiation profile is applied to the PV generator while assuming a constant cell temperature. The solar
irradiation level is depicted in Figure 9. Initially, from 0 to 6 s, the irradiation level is set at 500 W/m2
.
Subsequently, it progressively increases in a linear manner, reaching 800 W/m2
between 6 and 12.5 s.
Finally, it decreases linearly back to 500 W/m2
. The solar panel specifications used in this study is shown in
Table 1 while the Table 2 illustrates the main designed parameters of the grid-connected qZSI system.
Figure 9. Applied irradiance profile
Table 1. PV generator specifications
PV generator parameters Values
Maximum power 𝑃𝑀𝑃𝑃 288 W
𝑉𝑀𝑃𝑃 162 V
𝐼𝑀𝑃𝑃 1.93 A
𝑣𝑜𝑐 200 V
capacitor value at PV generator terminals 𝐶𝑃𝑉 500 µF
Table 2. Designed parameters of the grid-connected qZSI system
qZSI and grid parameters Values
Maximum voltage at grid terminals 100 V
Grid frequency 50 Hz
Switching frequency 10 kHz
Grid filter 𝐿𝑔 = 2 𝑚𝐻 ; 𝑅𝑔 = 0.5 Ω
Impedance network 𝐶 = 𝐶1 = 𝐶2 = 200 µ𝐹
𝐿 = 𝐿1 = 𝐿2 = 50 µ𝐻
DC-link voltage reference 200 V
3.2. Simulation results and discussion
Both the power effectively extracted from the PV generator and its maximum power is presented in
Figure 10. It is evident from the plot that during steady-state conditions, the PV output power aligns closely
with the maximum power. It can be inferred that Figure 10 demonstrates the effective control of active power
in response to changes in irradiance.
Figure 11 displays the simulation results showing the injected current and grid voltage. In Figure 11(a)
the grid’s injected current and grid voltage are depicted across the entire simulation duration, whereas
Figure 11(b) shows a zoomed-in area of the current and grid voltage. From Figure 11(b) it can be seen that the
grid current and voltage are in phase, indicating that the system operates at a unity power factor. In addition, the
grid current exhibits significantly reduced harmonics due to eliminating the dead-time between the upper and
lower devices within a single phase-leg. Without forgetting the impact of the implementation of SVM technique
over the harmonics. On the other hand, we can conclude from Figure 12 that the PV output voltage (𝑉𝑝𝑣)
closely tracks the MPPT reference voltage (𝑉𝑟𝑒𝑓) which progressively converges towards the voltage 𝑉
𝑚𝑝𝑝
associated with MPP operation.

1433
Figure 10. Simulation results, PV output power
(a) (b)
Figure 11. Simulation results (a) grid 𝑖𝑎 current and grid voltage 𝑣𝑎 and (b) zoomed-in area of 𝑖𝑎 and 𝑣𝑎
Figure 12. Simulation results MPPT reference voltage (𝑉𝑟𝑒𝑓 ) and PV output voltage (𝑉𝑝𝑣)
On the subject of the DC-link voltage, Figure 13 illustrates the simulation results for both the DC-
link voltage and the ST duty ratio. it is possible to observe from Figure 13 that the voltage is effectively
regulated at the predetermined set value 200 V. Indeed, the change of the irradiance has no apparent impact
on the peak DC-link voltage which is almost the same as it shown in Figure 13(a).
The oscillation of the PV output voltage during the MPP search results in oscillations of the ST duty
ratio, as it presented in Figure 13(b) which ensures the stability of the DC-link voltage. Otherwise, in the
steady-state of the PV output voltage, it is evident that the ST duty ratio remains stable and confirming the
relationship between PV output voltage and DC-link voltage as presented in (6). Based on the
aforementioned results and a comparison with the findings reported in [10], [21]–[23], [27], it is evident that
the proposed control strategy effectively achieves maximum power extraction from the PV generator while
simultaneously regulating the DC-link voltage and ensuring unity power factor operation. On other hand the
proposed control strategy extracts maximum power while exhibiting fewer steady-state oscillations compared
to the method proposed in [23], [26].

 ISSN: 2088-8708
1434
(a) (b)
Figure 13. Simulation results (a) DC-link voltage and (b) shoot-through duty ratio
4. CONCLUSION
The qZSI used for grid connected PV applications are studied in this paper. A decoupled control
scheme is proposed based on the MPPT algorithm, ZSVM technique and PI controllers. The main objective
of proposed scheme control is to harvest the maximum power from the PV, regulating DC-link voltage and
monitoring the power factor of the grid. The operating principle and modeling of qZSI are firstly presented,
then the proposed scheme control is described and analyzed. The decoupled control law successfully drove
the qZSI to inject three-phase current into the grid, presenting excellent synchronization and achieving a low
total THD of 5%. While the results obtained are satisfactory, there is still potential for improvement in the
control strategy. The use of an adaptive step MPPT P&O technique can enhance the response time and
mitigate steady-state power oscillations. In parallel with ongoing efforts to improve the proposed control
strategy, the next step is the experimental realization by implementation on a platform consisting of a
dSPACE electronic board and the RTbox simulator.
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BIOGRAPHIES OF AUTHORS
Essaid Jaoide was born in 27 January 1990 in Beni Mellal, Morocco. He is a
Ph.D. student in Laboratory of Radiation-Matter and Instrumentation (RMI), Faculty of
Sciences and Technology, Hassan 1st
University, Morocco. he received his Master degree in
electrical engineering from Cadi Ayyad University Marrakech, in 2013. He also obtained the
Agrégation degree in Electrical Engineering in 2018. His researches are in fields impedance
source power electronic converters and grid-connected photovoltaic systems. He can be
contacted at email: e.jaoide@uhp.ac.ma.
Faicel El Aamri received his Ph.D. on PV systems from Hassan first University
in 2018. He currently works as Professor at Hassan II University, Faculty of Sciences and
technologies of Mohammedia, Morocco. His area of research interest is the control of
Grid-connected PV inverters and power electronics. He can be contacted at email:
f.elaamri@gmail.com.

 ISSN: 2088-8708
1436
Mbarek Outazkrit received the M.S. degree in electrical engineering from Cadi
Ayyad University in 2014. He also obtained the Aggregation degree in electrical engineering
in 2016. Mbarek works in Ph.D. at Ph.D. Center of physics and engineering sciences in
Hassan First University. His area of interest is modular multilevel converters MMC, power
converter applications in power systems, grid integration of renewable energy sources. He can
be contacted at email: m.outazkrit@uhp.ac.ma.
Abdelhadi Radouane was born in 1969. He received the Aggregation degree in
electrical engineering from the ENSET of Rabat, Morocco in 1996. In 2017, he obtained a Ph.D.
in automatic control. Since 2018, he joined the FST Settat, Hassan First University of Settat,
Morocco as assistant-professor. He can be contacted at email: radouane.abdelhadi@gmail.com.
Azeddine Mouhsen was born in 10 July 1967, he is professor of physics at
Hassan First University, Morocco, since 1996. He holds a Ph.D. from Bordeaux I University
(France) in 1995 and a thesis from Moulay Ismail University, Morocco, in 2001. He
specializes in instrumentation and measurements, sensors, applied optics, energy transfer,
radiation-matter interactions. He has taught courses in physical sensors, chemical sensors,
instrumentation, systems technology, digital electronics and industrial data processing. He has
published over 30 papers and he is the co-inventor of one patent. Actually, he is the Director
of Laboratory of radiation-matter and Instrumentation. He can be contacted at email:
az.mouhsen@gmail.com.

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