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Multilevel Converters: Topologies, Control, Modulation, Operation and Applications

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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A1: Smart Grids and Microgrids".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 23683

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Prof. Leopoldo García Franquelo

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Department of Electronics Engineering, Universidad de Sevilla, Sevilla, Spain
Interests: industrial electronics; power electronics; multilevel converters; renewable energy; electrical engineering

Prof. Dr. Sergio Vazquez Perez

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Electronic Engineering Department, Universidad de Sevilla, 41004 Sevilla, Spain
Interests: power electronics systems; modeling, modulation and control of power electronics; converters applied to renewable energy technologies
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Prof. Dr. Jose Ignacio Leon Galvan

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Department of Electronic Engineering, University of Seville, 41092 Seville, Spain
Interests: multilevel converters; renewable energy; modulation techniques
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Dear colleagues,

Multilevel converters have become a mature and attractive solution for many applications mainly for medium voltage, high power systems. Nowadays, multilevel converters can be found in the product portfolio of many manufacturers for applications such as motor drives, renewable energy sources, FACTS, and HVDC, among others. The continuous efforts of academia and industry has led to the fast development of different multilevel converter topologies, modulation techniques and control strategies to improve features such as the efficiency, robustness, fault-tolerant capability, economic cost and size, among others. The research on this topic is ongoing, and is nowadays a hot research topic.

Topics of interest include, but are not limited to:

New multilevel converter topologies
Multilevel converters for adjustable speed drives
Multilevel converters for grid-connected utilities such as active filter, AC and DC microgrids, STATCOM, FACTS, HVDC, etc.
Multilevel converters for renewable energy applications
Multilevel rectifiers and applications in regenerative systems
Modulation strategies for multilevel converters
Control methods for multilevel converters
Fault-tolerant capability of multilevel converters
High-efficiency multilevel converters

Prof. Sergio Vazquez Perez
Prof. Jose Ignacio Leon Galvan
Prof. Leopoldo García Franquelo
Guest Editors

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Keywords

multilevel converters
modulation techniques
control methods
high-power systems
renewable energy sources
motor drives

Published Papers (10 papers)

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Research

21 pages, 2546 KiB

Open AccessArticle

Quadrature Voltage Compensation in the Isolated Multi-Modular Converter

by Cristian Verdugo, Jose Ignacio Candela and Pedro Rodriguez

Energies 2021, 14(3), 529; https://doi.org/10.3390/en14030529 - 20 Jan 2021

Cited by 1 | Viewed by 1651

Abstract

Series connections of modules in cascaded multilevel converters are prone to power imbalances due to voltage differences on their DC side. When modules are connected to direct current (DC) sources, such as photovoltaic panels, the capability of withstanding power imbalances is crucial for generating the maximum power. In order to provide a possible solution for this requirement, this paper proposes a control strategy called Quadrature Voltage Compensation, which allows a wide range of power imbalances. The proposed control strategy regulates the power by introducing a circulating current between the arms and a phase angle in the output voltage. The impact of the circulating current and its effect on the phase voltage are studied. To highlight the features of the proposed strategy, an analytical model based on vector superposition is also described, demonstrating the strong capability of tolerating power differences. Finally, to validate the effectiveness of the Quadrature Voltage Compensation, simulation and experimental results are presented for a three-phase isolated multi-modular converter. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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20 pages, 4095 KiB

Open AccessArticle

A Novel Multilevel DC-Link Three-Phase T-Type Inverter

by Saddam Shueai Alnamer, Saad Mekhilef, Hazlie Mokhlis and Nadia M. L. Tan

Energies 2020, 13(16), 4186; https://doi.org/10.3390/en13164186 - 13 Aug 2020

Cited by 5 | Viewed by 1973

Abstract

This research proposes a four-level T-type inverter that is suitable for low-power applications. The presented topology outranks other types of inverters in terms of a smaller number of semiconductor devices, absence of passive components such as clamping diodes and flying capacitors, low switching and conduction losses, and high efficiency. The proposed topology is free from voltage deviation and unbalanced voltage occurrences that are present in other multilevel converters having clamping diodes or flying capacitors. The proposed inverter can extend to N levels using unequal dc-link voltage sources for medium-voltage application. The inverter employs the simple fundamental frequency staircase modulation technique. Moreover, this paper presents a current commutation strategy to prevent the occurrences of short circuit and minimizing the number of required switching devices and switching transitions, resulting in improving the efficiency of the inverter. This paper also analyses the theoretical converter losses showing lower switching and conduction losses when compared to existing four-level inverters. The experimental validation of the proposed inverter shows its operating feasibility and a low output voltage THD. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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25 pages, 2003 KiB

Open AccessArticle

Control Design and Experimental Validation of a HB-NPC as a Shunt Active Power Filter

by Gerardo Escobar, Panfilo R. Martinez-Rodriguez, Samuel Iturriaga-Medina, Gerardo Vazquez-Guzman, Jose M. Sosa-Zuñiga and Diego Langarica-Cordoba

Energies 2020, 13(7), 1691; https://doi.org/10.3390/en13071691 - 3 Apr 2020

Cited by 6 | Viewed by 1988

Abstract

This work presents the design of a control law based on the average model of a shunt active power filter considering an H-bridge neutral point clamped topology and its experimental validation. Therefore, the proposed controller is formed by three control loops, namely current (inner), regulation (outer), and balance control loops. The current loop aims to compensate both the displacement power factor and the harmonic distortion produced by nonlinear loads connected to the point of common coupling. To deal with harmonic current distortion, the current loop involves an adaptive mechanism based on a bank of resonant filters tuned at odd harmonics of the fundamental grid frequency. The regulation and balance loops are aimed to maintain the voltage of the capacitors forming the DC-link at a desired constant level. For this, proportional-integral controllers are designed. The design of all three loops considers the average model of the system. The performance of the proposed multi-loop control law is evaluated through numerical results and real-time experimental implementation, both considering a 2 kW academic benchmark with a constant switching frequency of 7 kHz. In order to provide harmonic distortion, a nonlinear load based on an uncontrolled diode bridge rectifier is considered. Additionally, step-load changes from 0.5 kW to 1 kW are considered for the nonlinear load. As a result, a suitable current tracking, voltage regulation, and balance are observed despite parametric uncertainties, load variations, and harmonic distortion. As a consequence, in steady state, simulation results indicate that the compensated grid current THD is 1.75%; meanwhile, the nonlinear load current THD is 52.5%. Experimental results indicate that the compensated grid current THD is 2.32%; meanwhile, the nonlinear load current THD is 53.8%. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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17 pages, 7751 KiB

Open AccessArticle

Real-Time Selective Harmonic Mitigation Technique for Power Converters Based on the Exchange Market Algorithm

by Abraham Marquez Alcaide, Jose I. Leon, Marta Laguna, Francisco Gonzalez-Rodriguez, Ramon Portillo, Eduardo Zafra-Ratia, Sergio Vazquez, Leopoldo G. Franquelo, Sertac Bayhan and Haitham Abu-Rub

Energies 2020, 13(7), 1659; https://doi.org/10.3390/en13071659 - 2 Apr 2020

Cited by 12 | Viewed by 2290

Abstract

Hand-in-hand with the smart-grid paradigm development, power converters used in high-power applications are facing important challenges related to efficiency and power quality. To overcome these issues, the pre-programmed Pulse-Width Modulation (PWM) methods have been extensively applied to reduce the harmonic distortion with very low power switching losses for high-power converters. Among the pre-programmed PWM techniques, Selective Harmonic Elimination (SHE) has been the prevailing solution, but recently, Selective Harmonic Mitigation (SHM) stands as a superior alternative to provide further control of the harmonic spectrum with similar losses. However, the large computational burden required by the SHM method to find a solution confines it as an off-line application, where the switching set valid solutions are pre-computed and stored in a memory. In this paper, for the first time, a real-time implementation of SHM using an off-the-shelf mid-range microcontroller is presented and tested. The Exchange Market Algorithm (EMA), initially focused on optimizing financial transactions, is considered and executed to achieve the SHM targets. The performance of the EMA-based SHM is presented showing experimental results considering a reduced number of switching angles applied to a specific three-level converter, but the method can be extrapolated to any other three-level converter topology. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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16 pages, 5891 KiB

Open AccessArticle

A High-Gain Observer-Based Adaptive Super-Twisting Algorithm for DC-Link Voltage Control of NPC Converters

by Xiaoning Shen, Jianxing Liu, Abraham Marquez, Wensheng Luo, Jose I. Leon, Sergio Vazquez and Leopoldo G. Franquelo

Energies 2020, 13(5), 1110; https://doi.org/10.3390/en13051110 - 2 Mar 2020

Cited by 6 | Viewed by 2438

Abstract

Acting as an interface between the grid and many energy systems, the active front-end (AFE) has been widely used in a large variety of industrial applications. In this paper, in order to ensure the fast dynamic performance and good disturbance rejection ability of the AFE, a high-gain observer (HGO) plus adaptive super-twisting algorithm (STA) for the three-level neutral-point-clamped (NPC) converter is proposed. Comparing with the conventional PI control strategy, the proposed controller implements the adaptive STA in the voltage regulator to provide a faster transient response. The gains of the adaptive STA keep varying according to the rules being reduced in steady state but increasing in transient conditions. Therefore, the chattering phenomenon is mitigated and the dynamic response is guaranteed. Additionally, to undermine the impact of external disturbances on the dc-link voltage, a high-efficiency HGO is designed in the voltage regulation loop to reject it. Experimental results based on a three-level NPC prototype are given and compared with the conventional PI method to validate the fast dynamic performance and high disturbance rejection ability of the proposed approach. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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20 pages, 21493 KiB

Open AccessArticle

Integral Sliding-Mode Control-Based Direct Power Control for Three-Level NPC Converters

by Hao Lin, Jose I. Leon, Wensheng Luo, Abraham Marquez, Jianxing Liu, Sergio Vazquez and L. G. Franquelo

Energies 2020, 13(1), 227; https://doi.org/10.3390/en13010227 - 2 Jan 2020

Cited by 14 | Viewed by 2648

Abstract

Three-level neutral-point-clamped (NPC) converter is widely used in energy conversion systems due to its good properties for high-power systems presenting output waveforms with reduced harmonic distortion. To obtain better system performance, an integral sliding-mode control (ISMC)-based direct power control (DPC) strategy is proposed for NPC converters. The controller achieves three objectives. First, an extended state observer (ESO)-based ISMC strategy, to enforce the active and reactive power to their reference values, is applied in the power tracking loop. ESO is used to reduce the influence of parameter uncertainties. Next, in the voltage regulation loop, a radial basis function neural network (RBFNN)-based adaptive ISMC strategy is applied to regulate the DC-link voltage. RBFNN is used to estimate the load variation, which is considered as a disturbance, to improve the system disturbance rejection ability. An adaptive law is used in the controller to reduce the chattering of reference active power which can reduce the current harmonic distortion. Finally, a proportional-integral (PI) control strategy is applied in the voltage balancing loop to achieve voltage balance between two DC-link capacitors. Experimental results show the effectiveness and superiority of the proposed control strategy for the NPC power converter compared with PI-based DPC strategy. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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13 pages, 5325 KiB

Open AccessArticle

Operation and Control of a Seven-Level V-Clamp Multilevel Converter

by Yao Xue, Xiaofeng Yang, Lutian Yuan and Trillion Q. Zheng

Energies 2019, 12(24), 4761; https://doi.org/10.3390/en12244761 - 13 Dec 2019

Cited by 5 | Viewed by 2007

Abstract

Multilevel converters are well suited for high-power and high-quality power conversion. This paper presents a new seven-level V-clamp multilevel converter (VMC) with reduced clamping devices. All phases of the VMC share common DC-link capacitors and realize bidirectional power conversion without flying capacitors. Each branch of the VMC sustains only a single-level voltage of the DC-link capacitors during its commutation process. Hence, the series switches can be controlled as simple as one switch and the dynamic voltage unbalancing issue is avoided. In this paper, the operation principle and the modulation method of the VMC are analyzed in detail. In addition, compensation control for non-ideal factors is designed to improve the output performance. The output fundamental distortion is compensated and the harmonics are reduced. Finally, a laboratory prototype of the seven-level VMC is set up to verify the feasibility of the presented topology and analysis. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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20 pages, 3232 KiB

Open AccessArticle

Wide Load Range ZVS Three-level DC-DC Converter: Modular Structure, Redundancy Ability, and Reduced Filters Size

by Yong Shi and Zhuoyi Xu

Energies 2019, 12(18), 3537; https://doi.org/10.3390/en12183537 - 15 Sep 2019

Cited by 1 | Viewed by 2124

Abstract

In future dc distributed power systems, high performance high voltage dc-dc converters with redundancy ability are welcome. However, most existing high voltage dc-dc converters do not have redundancy ability. To solve this problem, a wide load range zero-voltage switching (ZVS) three-level (TL) dc-dc converter is proposed, which has some definitely good features. The primary switches have reduced voltage stress, which is only V_in/2. Moreover, no extra clamping component is needed, which results simple primary structure. Redundancy ability can be obtained by both primary and secondary sides, which means high system reliability. With proper designing of magnetizing inductance, all primary switches can obtain ZVS down to 0 output current, and in addition, the added conduction loss can be neglected. TL voltage waveform before the output inductor is obtained, which leads small volume of the output filter. Four secondary MOSFETs can be switched in zero-current switching (ZCS) condition over wide load range. Finally, both the primary and secondary power stages are modular architecture, which permits realizing any given system specifications by low voltage, standardized power modules. The operation principle, soft switching characteristics are presented in this paper, and the experimental results from a 1 kW prototype are also provided to validate the proposed converter. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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15 pages, 2345 KiB

Open AccessArticle

Wide Load Range Capacitor Clamped ZVZCS Half Bridge Three-Level DC-DC Converter with Two Unsymmetrical Bi-directional Switches

by Yong Shi

Energies 2019, 12(12), 2362; https://doi.org/10.3390/en12122362 - 19 Jun 2019

Cited by 3 | Viewed by 2326

Abstract

This paper presents a zero-voltage and zero-current switching (ZVZCS) capacitor-clamped half bridge (HB) three-level dc-dc converter (TLDC), which is well fit for high input voltage dc-dc industrial applications. The maximum voltage stress of the primary switches is limited by the flying capacitor and input capacitors, which is very close to V_in/2. Two unsymmetrical bidirectional switches are used to replace two of the primary switches in a conventional capacitor-clamped HB TLDC, which ensure ZVZCS of the main switches in wide load range. The reverse direction MOSFETs in the unsymmetrical bidirectional switches have low on-state resistance and are controlled with soft-switching mode irrelevant to the load current. Therefore, the additional power loss can be omitted. The current of the flying capacitor is greatly reduced due to ZVZCS operation, which would result in a smaller volume flying capacitor and high system reliability. Furthermore, the current imbalance problem of the power devices is also well solved. The circuit, basic operation principles and some important technical analyses are discussed in this paper, and experimental results from a 1-kW prototype are provided to evaluate the proposed converter. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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15 pages, 2564 KiB

Open AccessArticle

Integrated Control and Modulation for Three-Level NPC Rectifiers

by Antonio Ventosa-Cutillas, Pablo Montero-Robina, Francisco Umbría, Federico Cuesta and Francisco Gordillo

Energies 2019, 12(9), 1641; https://doi.org/10.3390/en12091641 - 30 Apr 2019

Cited by 12 | Viewed by 3399

Abstract

This paper uses a novel approach for the control of three-level neutral-point-clamped (NPC) rectifiers in order to tackle the capacitor voltage balance problem. A distinctive feature of the new control approach is that it is based on a model which is written in terms of the duty ratios for each phase at each level. Hence, the system model presents nine duty cycle variables. Despite the fact that this formulation is different from the usual ones, it is shown that the control problem of currents and dc-link voltage can be formulated in a similar way to conventional methods. Furthermore, the control of the capacitor voltage balance can be expressed by means of equations that are decoupled from the currents and dc-link voltage dynamics, which results in a specific controller for the voltage balancing that does not affect the previous dynamics. A key point of the proposed approach is that part of the modulation stage is implicit in the formulation. Two particular controllers are compared in this paper. The first one fulfills the different control objectives at the expense of a large number of commutations. This problem is overcome in a new proposed controller, which presents similar performance and a satisfactory number of commutations. Experimental results are performed showing the effectiveness compared with a modified virtual space vector modulation with capacitor voltage balance capabilities. Full article

(This article belongs to the Special Issue Multilevel Converters: Topologies, Control, Modulation, Operation and Applications)

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