New Control Approach of Multicell Stacked Cell Inverter for Solar Photovoltaic System

Yonga, François; Welba, Colince; Dadjé, Abdouramani; Djongyang, Noël

doi:https://doi.org/10.1155/2022/9619266

International Journal of Photoenergy

On this page

Abstract Introduction Results and Discussion Conclusion Data Availability Conflicts of Interest References Copyright Related Articles

Special Issue

Dispatch Strategy and Power System Analysis for Optimized Solar Energy Conversion

View this Special Issue

Research Article | Open Access

Volume 2022 | Article ID 9619266 | https://doi.org/10.1155/2022/9619266

New Control Approach of Multicell Stacked Cell Inverter for Solar Photovoltaic System

François Yonga,¹Colince Welba,²Abdouramani Dadjé,³and Noël Djongyang¹

Academic Editor: Shezan Arefin

Received13 Feb 2022

Revised06 Mar 2022

Accepted23 Mar 2022

Published11 Apr 2022

Abstract

This paper presents the study, modelling, and simulation of the DCSVM (Duty Cycle Space Vector Modulation) control technique applied to a new inverter topology dedicated to isolated or grid-connected photovoltaic systems using the MATLAB/Simulink software. This inverter is based on the structures of a stacked multicell converter (SMC) and an H-bridge. This new topology allows the voltage stresses of the converter to be distributed among several switching cells. It also allows the input voltage to be divided into several fractions so that the number of switching power semiconductors is reduced. The DCSVM is a control technique that generates control signals to the two-level voltage converter as well as the intermediate times. The main advantage of this control technique is the reduction in the number of calculations, especially for the trigonometric functions and the generation of the reference voltage. In this contribution, the general topology of this microinverter is described and the DCSVM control technique is presented. Finally, simulation results, the efficiency of this topology, and the validity of the DCSVM control in a grid-connected PV generation system are discussed. The results obtained are very satisfactory.

1. Introduction

The inverter is considered the most important component of an on-grid photovoltaic (PV) system. In recent years, the topology of power converters, system stability, and control of grid-connected PV power plants have all attracted a lot of attention [1, 2]. Existing technologies are insufficient for large-scale photovoltaic facilities. Extensive research has been conducted over the previous two decades to suggest novel inverter topologies [1, 3, 4]. This difficulty is solved by the structure of multilayer inverters, which have three or more layers. By splitting the DC voltage at the inverter input, this form of design allows for voltage stress on the switches to be limited. In an on-grid photovoltaic (PV) system, proper inverter control is required to achieve moderate power loss, low total harmonic distortion (THD), and security and grid reliability [5, 6]. The combination of a multilevel architecture with judicious control of the power switches can also eliminate certain families of harmonic lines and therefore improve the spectral content of the output signals (voltage and current) [1, 2]. The duty cycle modulation (DCM) method discussed in [7] has the particularity of producing fewer harmonics [8]. A DCM is a modulation in which an input signal is transformed into a switching wave train where the duty cycle and period of the modulated signal vary simultaneously with the control signal [7–11]. A new, simpler, and better DCM was then proposed by Nneme and Mbihi [7]. Another particularity of the DCM is its modulation frequency, which is a function of the amplitude of the modulating signal. The work of [9] presents DCM as an effective tool in modulating transmission signals via high-quality results. However, the work in [10] presents an application of DCM in the control of a single-phase inverter. This control strategy, initiated in 2005 [11] for industrial instrumentation purposes, has been the subject of further scientific work [12, 13] that has proven its reliability and efficiency. Since a theoretical study based on virtual simulations has already been completed successfully in recent works on a new IDCM topology [14], this scientific paper deals with a new control approach applied to a new five-level three-phase multicell inverter (5 L–SMC H-bridge) topology based on a controller with a duty cycle. This strategy is called duty cycle space vector modulation (DCSVM). The principle of the DCSVM control is based on the advantages of the DCM control and the classical SVM control. This modulation provides very good performance and generates less current harmonics [5]. However, in practice, determining the sequences necessitates calculating the tangent of the angle of the vector, which results in undesired singularities. This makes it easier to think about the duty cycle modulation strategy for generating SVPWM signals. In this paper, the modelling and simulation of a new control strategy, as an alternative to the classical SVPWM, implemented with a duty cycle controller using the MATLAB/Simulink software, to be used for the control of static converters is presented. To test the feasibility of DCSVM controllers, simulations have been carried out, the results obtained agree perfectly with those obtained with a conventional SVPWM controller.

After Introduction, a brief description of the studied inverter topology as well as its modelling is presented in Section 2. Section 3 is devoted to the presentation and analysis of the proposed DCSVM control technique. Section 4 includes simulation results and discussion. Finally, the conclusion is presented in Section 5.

2. Description of the Studied Topology

2.1. Proposed Topology

Figure 1(a) shows an SMC converter. This converter structure is an evolution of the serial multicellular converter [15]. It was patented in 2000 in France [16, 17] and 2001 in the world [18]. In Figure 1(b), a modification of the basic NPC (Neutral Point Clamped) topology is presented. This variant of the NPC topology (three-level ANPC) makes it possible to push back certain limitations of the basic structure, such as the inequality of the reverse voltages supported by the diodes [19].

(a)

(b)

The basic cell of a multicellular converter can be made up of 4, 6, or 8 switches. The outer branches are made up of two 3-segment switches. The switches must be connected in series for voltage withstand. The voltage withstand of all the switches is equal to E/2. The middle branch is made up of two switches placed in opposition. For these switches, the maximum voltage withstand is equal to E/2; they do not need to be passed [15]. Figure 2 shows a new five-level three-phase multicell inverter (5 L–SMC H-bridge) topology based on stacked semiconductors and implemented using the PSIM software environment.

This inverter topology is based on the single-phase model of a three-level inverter (3 L – SMC H-bridge), two variants of which are given in Figure 3.

(a)

(b)

Figure 4 shows a stacked multicell converter and a half H-bridge. The multicell converter consists of two branches of stacked semiconductors (Cell+ and Cell-) connected to the T-Type bridge. However, by using an appropriate control, our converter provides a DC signal and a three-level AC signal (3 L) which can be filtered and fed into the public distribution network [20, 21]. The switches K3, K4, K7, and K8 make it possible to raise the voltage level and prevent the direct voltage source from being short-circuited (directly connected to ground) [22]. Switches K1 and K2 (Cell H), constituting the H-bridge, balance the voltage level at the output of the inverter.

The superimposed cells (Cell+ and Cell-) are the opposition of two semiconductors of the same control so as to form a bidirectional switch on blocking. Putting two switches in opposition does not increase switching losses, because only one of the two switches at the switching frequency, while the other switching only twice per modulation period. Unlike in the case of multicellular converters with floating capacitors (FC), the Cell+ and Cell- cells are not connected to each other by floating capacitors. The distribution of the voltage stress is linked to the state of the switches (on or off) [23]. As for the SMC, it is possible to double these switches to obtain a structure with switches whose voltage resistance is identical. These will switch at a lower switching frequency (on the order of the modulation frequency). But this increases the number of switches even further: the total number of switches per phase is then 8 semiconductor components. The purpose of this study is, above all, to balance the DC bus. So, for more simplicity in the control, each switch has to hold a tension of V/2, which is considered unique [15].

2.2. Modeling the Converter

To develop a mathematical model of the multicellular converter, consider that (i)Semiconductors are perfect(ii)The switches of the same switching cell operate in a complementary manner(iii)The supply voltage is continuous

In practice, the upper and lower branches of the structure can contain one or two semiconductors in series. The voltage applied to each switching cell in the off state is constant and is equal to [3, 23]: with .

In the presence of a single switch, it must withstand a voltage stress twice as high as those of the middle branch. In order to standardize the distribution of the voltage stress, two identical semiconductors can be connected in series or in opposition; their commands being similar [3, 4, 23]. In this assumption, the stress in tension of all the switches of the structure is worth with , where and represent, respectively, the number of stages and number of cells associated with the converter.

In Figure 4, the upper (Cell+) and lower (Cell-) branches of the structure contain two opposing semiconductors. The voltage applied to each switching cell in the off state is with

The opposition of switches of the outer branches is necessary for voltage withstand. The voltage withstand of all the different switches is V/2. Indeed, levels -V/2 and V/2 can be achieved in 2 different ways and level 0 in 3 different ways, as presented in Table 1.

One of the main drawbacks of this structure is the number of components that compose it. The structure of our inverter model can include 8 to 14 switches with different voltage resistances. Indeed, in each basic structure, the switches of the outer branches must hold a voltage V while those of the inner branch must hold a voltage of V/2. Doubling the switches increases switching losses, because the two switches switch simultaneously at the switching frequency. The middle branch is made up of two switches placed in opposition. For these switches, the maximum voltage withstand is equal to V/2, they do not need to be doubled. This converter is used to generate high output voltage levels. This new topology makes it possible to distribute the voltage constraints of the converter between several switching cells. It also makes it possible to divide the input voltage into several fractions so as to lower the number of switching power semiconductors. Compared to competing topologies in this field of application, the SMC converter has excellent dynamic performance thanks to the multiplication of the chopped voltage frequency and the increase in the number of levels [23–25]. The stacked multicellular structure can be adapted to all configurations: chopper or inverter mounting.

Figure 5 shows some possible combinations of the three-phase five-level multicell inverter (5 L–SMC H-bridge).

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

(i)

(j)

(k)

(l)

The number of output levels is equal to 5 [-V, -V/2, 0, + V/2, + V]. In comparison with the 5-level NPC structure, the advantage of this structure is that it has redundancies for certain levels.

Table 2 shows a comparison between the different types of existing inverters with the new 5 L – SMC H-bridge three-phase multicell inverter.

Where is the number of stages in the converter. From the above, it appears that the new 5 L – SMC H-bridge structure gives more advantages (absence of looping diodes and capacitors) over its competitors NPC, SMC, and H-bridge. The major drawback to note is the high number of switches used.

Multicellular topologies, on the other hand, use the series connection of switches, thus ensuring the distribution of the voltage stress of the converter over several switching cells. The interlacing or shifting of the controls allows these converters to reveal voltage levels and to multiply the apparent frequency at the output. These improvements induce a harmonically better quality output voltage spectrum and significantly reduce filtering requirements (volume, stored energy, and cost) [23].

3. New Proposed Command

The DCSVM control principle is based on the advantages of both the DCM control and the traditional SVM control. The implementation of the DCSVM strategy is carried out in the following steps:

Step 1. Determination of reference voltage (, ).
The generation of vectors in the Concordia landmark (d, q) from the three-phase signals (, , ) is given by the relation (4):

Step 2. Cartesian to polar transformation.
The system of equations given in Eq. (6) transforms corresponding elements of the two-dimensional Cartesian coordinate arrays and q into polar coordinates (, ).

Step 3. Generation of control signals and intermediate times.
The Simulink model is used to determine the control signals for switches T_ag, T_bg, and T_cg and the intermediate times T₁, T₂, and T_o.
Furthermore, assuming that the reference voltage vector V_ref is synthesized from the two basic vectors, the operating time of two basic vectors can be calculated according to the volt-second equilibrium principle [26]. where T₁ and T₂ are the times allocated to vectors and , T_O is the time shared between the two null vectors and , and T_S is the half-carrier time period.
After determining the times T₁, T₂, and T_o, the time of the closing all keys to the rack at work is determined. In each sector, the switching time of each key is different and is expressed in (8):

Step 4. Generation of the output voltage
The formula for determining output voltage (which should be achieved by modulation) depending on the standard vector of boundary voltages and the closing time of the key: where and
Substitute equation (8) into equation (6): where the voltage modulation ratio can be expressed as .

This modulation provides very good performance and generates fewer current harmonics [6]. However, during practical implementation, the determination of the sequences involves a calculation of the tangent of the angle of the vector which causes unwanted singularities. This led us to consider the duty cycle modulation technique to generate the SVPWM signals.

4. Results and Discussion

In the instance of a 5 L – SMC H-bridge three-phase multicell inverter, the simulation work was done with the MATLAB/Simulink software. The FFT block in Powergui is used to calculate THD percent values. The performance and ruggedness of the 5 L-SMC H-bridge three-phase multicell inverter are demonstrated and validated using simulation data. Table 3 lists the electrical simulation parameters.

Using conventional SVM control, the simulation of the system allows us to obtain the characteristics of the voltage and the current, as well as their harmonic spectra in Figures 6–9.

(a)

(b)

(a)

(b)

(a)

(b)

(a)

(b)

After the application of the DCSVM, the characteristics of the voltage and the current, as well as their harmonic spectra, are obtained in Figures 10–13. Figures 10 and 11 present, respectively, signals of the phase-to-neutral voltages and that of the currents produced by the inverter.

(a)

(b)

(a)

(b)

(a)

(b)

(a)

(b)

Figure 11 shows the harmonic spectrum of the phase-to-neutral voltages and that of the currents produced by the 5 L-SMC H-bridge inverter.

Figures 12 and 13, respectively, show the line voltages with its harmonic spectrum (Figures 12(a) and 12(b)) and the filtered line voltages with its harmonic spectrum (Figures 13(a) and 13(b)).

Table 4 reports the performance of simulations of the 5 L-SMC three-phase H-bridge inverter using SVM and DCSVM commands.

It is observed that the voltages (between phase and neutral, line) at the output of the inverter present a THD and reduced fundamentals using the DCSVM command compared to the results that the SVM command can obtain. On the other hand, with the DCSVM command, the THD and the fundamental of the current are raised compared with the SVM command that gives low values. However, the THDs of the voltage and current are too high compared to the limits set by the standard IEC 61000.

The power loss distribution in each switch of the 5 L-SMC H-bridge inverter is shown in Figure 14. When compared to the H-bridge 5 L-SMC construction, the major advantage of stacked multicell converters is that they reduce losses. However, despite the fact that not all components switch at the switching frequency and during the modulation period, this structure is component-intensive. The power losses of the 5 L-SMC H-bridge inverter, including switching loss and conduction loss, are investigated to assess the effectiveness of the suggested DCSVM control technique. The equivalent on-state resistance and forward voltage drops define conduction losses, whereas the linear approximation of the voltage and current across the kth switch estimates switching losses [27]. The MATLAB/Simulink was used to calculate the power losses.

With DCSVM control, the 5 L-SMC H-bridge inverter can be controlled to distribute the losses to the individual semiconductor components. However, the energy stored in the individual switches is a limitation to extending this structure to more levels. There are always several power components in series that generate the output current, which increases the conduction and switching losses. These losses are not evenly distributed among the different power components.

Table 5 compares the results of DCSVM with sinusoidal pulse width modulation (SPWM) [26], model predictive control (MPC) [5], or discontinuous pulse width modulation (DPWM) [28].

These results show that the energy losses generated by the production of harmonics are recovered and materialized by the increase in voltage and current in the case of DCSVM. From the above, the 5 L-SMC H-bridge multicell inverter gives better performance in terms of THD of the output voltage (41.29%) and current (9.49%) when using a DCSVM controller compared to SPWM, MPC, DPWM, and SVM controls. This converter appears as an interesting structure when the number of output voltage levels increases [15, 20, 23].

5. Conclusion

In this paper, a new three-phase converter structure with DCSVM control is presented. This topology allows the converter voltage stresses to be distributed among several switching cells. It also allows the input voltage to be divided into several fractions to reduce the number of power semiconductors to be switched. The application of DCSVM control to the 5 L-SMC inverter structure reduces the computational effort and faithfully reproduces the same output vectors as a conventional SVM. The simulation results obtained are better than those of the classical SVM control for similar simulation conditions. It should be noted that the voltages and currents give 41.19% for neutral voltages, 41.29% for line voltages, 11.63% for filtered line voltages, and 9.49% for currents, respectively, with fundamental values of 61.51 V, 106.7 V, 98.45 V, and 5.42 A. The THDs of the voltage and current are too high compared to the limits set by the standard IEC 61000. However, many studies can still be conducted for experimental verification of this work.

Data Availability

The data used to support the findings of this study are included within the article

Conflicts of Interest

On behalf of all authors, the corresponding author states that there are no conflicts of interest.

References

Z. E. T. Ternifi, P. Petit, G. Bachir, and M. Aillerie, “New topology of photovoltaic micro inverter based on boost converter,” Energy Procedia, vol. 119, pp. 938–944, 2017.
View at: Publisher Site | Google Scholar
C. Benzazah, M. AitLafkih, and L. Lazrak, “Comparative study between two topologies three-phase inverters, conventional 2-level and NPC 3-level with two methods different of control, SPWM and SWM,” International Journal of Innovation and Applied Studies, vol. 9, no. 2, pp. 841–852, 2014.
View at: Google Scholar
F. Zhao, G. Xiao, T. Zhu, X. Zheng, Z. Wu, and T. Zhao, “A coordinated strategy of low-speed and start-up operation for medium-voltage variable-speed drives with a modular multilevel converter,” IEEE Transactions on Power Electronics, vol. 35, no. 1, pp. 709–724, 2020.
View at: Publisher Site | Google Scholar
A. Khoshkbar-Sadigh, V. Dargahi, R. R. Khorasani, K. A. Corzine, and E. Babaei, “Simple active capacitor voltage balancing method without cost function optimization for seven-level full-bridge flying-capacitor-multicell inverters,” IEEE Transactions on Industry Applications, vol. 57, no. 2, pp. 1629–1643, 2021.
View at: Publisher Site | Google Scholar
A. K. Podder, M. Habibullah, M. Tariquzzaman, E. Hossain, and S. Padmanaban, “Power loss analysis of solar photovoltaic integrated model predictive control based on-grid inverter,” Energies, vol. 13, no. 18, p. 4669, 2020.
View at: Publisher Site | Google Scholar
I. Bouyakoub, R. Taleb, H. Mellah, A. Zerglaine et al., “Implementation of space vector modulation for two level three-phase inverter using dSPACE DS1104,” Indonesian Journal of Electrical Engineering and Computer Science, vol. 20, no. 2, pp. 744–751, 2020.
View at: Publisher Site | Google Scholar
L. N. Nneme and J. Mbihi, “Modeling and simulation of a new duty-cycle modulation scheme for signal transmission systems,” American Journal of Electrical and Electronic Engineering, vol. 2, no. 3, pp. 82–87, 2014.
View at: Publisher Site | Google Scholar
L. B. Monfo, J. Mbihi, and N. L. Nneme, “A low cost and high quality duty-cycle modulation scheme and applications,” International Journal of Electrical, Computer, Energetic, Electronic and communication Engineering, vol. 8, no. 3, pp. 577–582, 2014.
View at: Google Scholar
L. N. Nnem, B. M. Lonla, G. B. Sonfack, and J. Mbihi, “Review of a multipurpose duty-cycle modulation technology in electrical and electronics engineering,” Journal of Electrical Engineering, Electronics, Control and Computer Science, vol. 4, no. 12, pp. 9–18, 2018.
View at: Google Scholar
O. A. Biyobo, N. L. Nneme, and J. Mbihi, “A novel sine duty-cycle modulation control scheme for photovoltaic single-phase power inverters,” WSEAS Transactions on Circuits and Systems, vol. 17, pp. 105–113, 2018.
View at: Google Scholar
J. Mbihi, B. Ndjali, and M. Mbouenda, “Modelling and simulation of a class of duty-cycle modulators for industrial instrumentation,” Iranian Journal of Electrical and Computer Engineering, vol. 4, no. 2, pp. 121–128, 2005.
View at: Google Scholar
J. Mbihi, B. Ndjali, and M. Mbouenda, “A novel analog-to-digital conversion technique using duty-cycle modulation,” International Journal of Electronics and Computer Science Engineering, vol. 1, no. 3, pp. 818–825, 2012.
View at: Google Scholar
J. Mbihi, “Dynamic modeling and virtual simulation of duty-cycle modulation control drivers,” International Journal of Electrical, Electronic Science and Engineering, vol. 11, no. 4, pp. 472–477, 2017.
View at: Google Scholar
A. O. Biyobo, L. N. Nneme, J. Mbihi, F. Pauné, and B. L. Moffo, “Étude expérimentale d’un nouveau modèle d’onduleur solaire monophasé à modulation en rapport cyclique,” Afrique Science, vol. 16, no. 2, 2020.
View at: Google Scholar
A. Leredde, Etude, Commande et Mise en œuvre de Nouvelles Structures Multiniveaux, [Ph.D. thesis], Energie électrique, Institut National Polytechnique de Toulouse-INPT, 2011.
T. A. Meynard and H. Foch, “Dispositif Electronique de Conversion d’Energie Electrique,” Tech. Rep., French Patent 91.09582, 1991.
View at: Google Scholar
G. Gateau, T. A. Meynard, and H. Foch, “Dispositif de Conversion d’Energie Multicellulaire,” Tech. Rep., French Patent 0006786, 2000.
View at: Google Scholar
G. Gateau, T. A. Meynard, and H. Foch, “Device for converting multicell energy,” Tech. Rep., Worlwide Patent 0193412, 2001.
View at: Google Scholar
K. A. Tehrani, Conception, Synthèse et Application d’une Nouvelle Commande Robuste par PID Fractionnaire pour Les Onduleurs Multiniveaux, [Ph.D. thesis], Université de Lorraine-Institut National Polytechnique de Lorraine (INPL), 2010.
M. Baghli, C. Delpha, D. Diallo, Hallouche, Mba, and Wang, “Three-level NPC inverter incipient fault detection and classification using output current statistical analysis,” Energies, vol. 12, no. 7, p. 1372, 2019.
View at: Publisher Site | Google Scholar
K. Zeb, W. Uddin, M. A. Khan et al., “A comprehensive review on inverter topologies and control strategies for grid connected photovoltaic system,” Renewable and Sustainable Energy Reviews, vol. 94, pp. 1120–1141, 2018.
View at: Publisher Site | Google Scholar
S. Kouro, J. I. Leon, D. Vinnikov, and L. G. Franquelo, “Grid-connected photovoltaic systems: an overview of recent research and emerging PV converter technology,” IEEE Industrial Electronics Magazine, vol. 9, no. 1, pp. 47–61, 2015.
View at: Publisher Site | Google Scholar
A.-M. Lienhardt, Etude de la Commande et de l’Observation d’une Nouvelle Structure de Conversion d’Energie de type SMC (Convertisseur Multicellulaire Superposé), [Ph.D. thesis], Institut National Polytechnique de Toulouse, 2006.
H. El Jihad, Contribution à l’étude des convertisseurs multi-niveaux moyenne tension: réduction d’harmoniques BF et linéarisation de leur tension, Energie électrique, Université de Lorraine, 2019.
P. Mehta, S. Sahoo, and M. Kumar, “A fault-diagnosis and tolerant control technique for five-level cascaded H-bridge inverters,” IET Circuits, Devices & Systems, vol. 15, 2021.
View at: Publisher Site | Google Scholar
S. Singh and A. N. Tiwari, “Simulation and Comparison of SPWM and SVPWM Control for Two Level Inverter,” in Conference: 2017, First International Conference on Smart Technologies in Computer and Communication (SmartTech-2017), Amity University Rajasthan (AUR), India, 2017.
View at: Google Scholar
S. Xu, Z. Sun, C. Yao, K. Liu, and G. Ma, “Model predictive control of a hybrid stacked multicell converter with voltage balancing and fault tolerance capability,” IET Power Electronics, vol. 14, no. 7, pp. 1300–1312, 2021.
View at: Publisher Site | Google Scholar
S. Mukherjee, S. Giri, and S. Banerjee, “A flexible discontinuous modulation scheme with hybrid capacitor voltage balancing strategy for three-level NPC traction inverter,” IEEE Transactions on Industrial Electronics, vol. 66, no. 5, pp. 3333–3343, 2019.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2022 François Yonga et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

410

Downloads

461

Citations