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Special Issue "Multilevel Converters: Analysis, Modulation, Topologies, and Applications"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Electrical Power and Energy System".

Deadline for manuscript submissions: closed (20 December 2018)

Special Issue Editors

Guest Editor
Prof. Dr. Gabriele Grandi

Department of Electrical, Electronic, and Information Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy
Website | E-Mail
Interests: Power Electronics; Electric Vehicles; Renewable Energies
Co-Guest Editor
Prof. Dr. Alexander Ruderman

Department of Electrical and Computer Engineering, Nazarbayev University, 53 Kabanbay Batyr Ave, Astana 010000, Kazakhstan
Website | E-Mail
Interests: high frequency PWM and low frequency synchronous optimal modulation for multilevel converters; current quality (THD) theoretical evaluation; natural voltage / current balancing in voltage / current source converters

Special Issue Information

Dear Colleagues,

Neutral Point Clamped (NPC) and Flying Capacitor (FC) converter were introduced 35 and 25 years ago respectively. Since then, multilevel converters became a standard for such applications as medium voltage drives, HVDC grids, and are promising for lower voltage applications, such as battery chargers, active filters, static compensators, dynamic voltage restorers, rectifiers, grid-tied inverters and more. Renewable energy sources and storage systems (photovoltaics, wind generators, batteries, and fuel cells) can feed isolated loads in stand-alone systems using multilevel converters as an interface, with reduced filter requirements. Low voltage MOSFET devices use in multilevel converters with relatively high level count contributes to improvement of efficiency and performance. Increased efficiency and reduced harmonic distortion are beneficial for photovoltaic systems and uninterruptible power supplies. Introduction of multilevel topologies changed power converter design paradigm including control and modulation strategies, components selection and requirements, reliability aspects and more. While relatively low power applications employ high frequency PWM, for high voltage/ current ones the switching frequency of the power semiconductors is limited to few kHz by switching loss considerations and the use of multilevel converters becomes mandatory.

This special issue is intended to motivate further research and development of multilevel converters, refreshing the state of the art, pointing out the benefits of emerging topologies, and investigating novel modulation schemes and for new applications. Original contributions including experimental validation are expected. The topics of interest include, but are not limited to:

  • multilevel capacitor based inverter, chopper, and rectifier topologies;
  • multilevel inverter modulation strategies and capacitor natural voltage balancing;
  • active capacitor voltage balancing including special auxiliary circuits;
  • multilevel inverters for renewable energy applications (photovoltaic, wind energy and fuel-cells);
  • multilevel converters for high-power electric vehicle battery chargers;
  • common mode voltage reduction in multilevel inverters;
  • current source multilevel inverters with natural inductor current balancing;
  • current source multilevel inverters with active inductor current balancing;
  • fault tolerant multilevel converters.

Prof. Dr. Gabriele Grandi
Guest Editor
Prof. Dr. Alexander Ruderman
Co-Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • pulse-width modulated multilevel inverters
  • low frequency synchronous optimal modulation (optimized pulse patterns) for multilevel inverters
  • single-, three- and multiphase multilevel inverter topologies and modulation strategies
  • multilevel inverters for distributed generation (wind, PV etc)
  • current THD evaluation for multilevel grid-tied inverters
  • voltage (current) source inverters with LCL (CL)-filters
  • multilevel matrix converters; modulation induced machine losses
  • natural voltage / current balancing in voltage / current source multilevel converters

Published Papers (28 papers)

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Research

Open AccessArticle
Multi-Level Open End Windings Multi-Motor Drives
Energies 2019, 12(5), 861; https://doi.org/10.3390/en12050861
Received: 20 December 2018 / Revised: 23 February 2019 / Accepted: 25 February 2019 / Published: 5 March 2019
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Abstract
A multi-level open-end winding converter topology for multiple-motor drives is presented featuring a main multi-level inverter processing the power delivered to the motors and an active filter based on an auxiliary two-level inverter. The main inverter operates at the fundamental frequency in order [...] Read more.
A multi-level open-end winding converter topology for multiple-motor drives is presented featuring a main multi-level inverter processing the power delivered to the motors and an active filter based on an auxiliary two-level inverter. The main inverter operates at the fundamental frequency in order to achieve low switching power losses, while the active filter is Pulse Width Modulation (PWM) operated to suitably shape the motor currents. The proposed configuration features less phase current distortion than conventional multi-level inverters operating at the fundamental frequency, while achieving a higher efficiency compared to PWM multi-level inverters. Experimental results confirm the effectiveness of such a configuration on both multiple motors-single converter and multiple motor-multiple converter drives. Full article
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Open AccessArticle
A Method for the Simultaneous Suppression of DC Capacitor Fluctuations and Common-Mode Voltage in a Five-Level NPC/H Bridge Inverter
Energies 2019, 12(5), 779; https://doi.org/10.3390/en12050779
Received: 7 December 2018 / Revised: 18 February 2019 / Accepted: 20 February 2019 / Published: 26 February 2019
Cited by 1 | PDF Full-text (3796 KB) | HTML Full-text | XML Full-text
Abstract
To suppress the direct current (DC) capacitor voltage fluctuations and the common-mode voltage (CMV) in a three-phase, five-level, neutral-point-clamped (NPC)/H-bridge inverter, this paper analyzes the influence of all voltage vectors on the neutral point potential of each phase under different pulse mappings in [...] Read more.
To suppress the direct current (DC) capacitor voltage fluctuations and the common-mode voltage (CMV) in a three-phase, five-level, neutral-point-clamped (NPC)/H-bridge inverter, this paper analyzes the influence of all voltage vectors on the neutral point potential of each phase under different pulse mappings in detail with an explanation of the CMV distribution. Then, based on the traditional space vector pulse width modulation (SVPWM) algorithm, a dual-pulse-mapping algorithm is proposed to suppress the DC capacitor fluctuations and the CMV simultaneously. In the algorithm, the reference voltage synthesis selects the voltage vector that has the smallest CMV value as the priority. In addition, the two kinds of pulse mappings that have opposite effects on the neutral point potential are switched to output. At the same time, regulating factors are introduced to adjust the working time of each voltage vector under the two pulse mappings; then, the capacitor voltages can be balanced. Both the simulation and experiment demonstrate the algorithm’s effectiveness. Full article
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Open AccessArticle
Power Flow Analysis of the Advanced Co-Phase Traction Power Supply System
Energies 2019, 12(4), 754; https://doi.org/10.3390/en12040754
Received: 18 December 2018 / Revised: 26 January 2019 / Accepted: 18 February 2019 / Published: 24 February 2019
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Abstract
The development of the traction power supply system (TPSS) is limited by the existence of the neutral section in the present system. The advanced co-phase traction power supply system (ACTPSS) can reduce the neutral section completely and becomes an important research and development [...] Read more.
The development of the traction power supply system (TPSS) is limited by the existence of the neutral section in the present system. The advanced co-phase traction power supply system (ACTPSS) can reduce the neutral section completely and becomes an important research and development direction of the railway. To ensure the stable operation of ACTPSS, it is necessary to carry out an appropriate power analysis. In this paper, the topology of advanced co-phase traction substation is mainly composed by the three-phase to single-phase cascaded converter. Then, the improved PQ decomposition algorithm is proposed to analyze the power flow. The impedance model of the traction network is calculated and established. The power flow analysis and calculation of the ACTPSS with different locations of locomotive are carried out, which theoretically illustrates that the system can maintain stable operation under various working conditions. The feasibility and operation stability of the ACTPSS are verified by the simulations and low power experiments. Full article
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Open AccessArticle
An Averaged-Value Model of an Asymmetrical Hybrid Multi-Level Rectifier
Energies 2019, 12(4), 589; https://doi.org/10.3390/en12040589
Received: 30 December 2018 / Revised: 1 February 2019 / Accepted: 6 February 2019 / Published: 13 February 2019
Cited by 1 | PDF Full-text (9789 KB) | HTML Full-text | XML Full-text
Abstract
The development and the validation of an averaged-value mathematical model of an asymmetrical hybrid multi-level rectifier is presented in this work. Such a rectifier is composed of a three-level T-type unidirectional rectifier and of a two-level inverter connected to an open-end winding electrical [...] Read more.
The development and the validation of an averaged-value mathematical model of an asymmetrical hybrid multi-level rectifier is presented in this work. Such a rectifier is composed of a three-level T-type unidirectional rectifier and of a two-level inverter connected to an open-end winding electrical machine. The T-type rectifier, which supplies the load, operates at quite a low switching frequency in order to minimize inverter power losses. The two-level inverter is instead driven by a standard sinusoidal pulse width modulation (SPWM) technique to suitably shape the input current. The two-level inverter also plays a key role in actively balancing the voltage across the DC bus capacitors of the T-type rectifier, making unnecessary additional circuits. Such an asymmetrical structure achieves a higher efficiency compared to conventional PWM multilevel rectifiers, even considering extra power losses due to the auxiliary inverter. In spite of its advantageous features, the asymmetrical hybrid multi-level rectifier topology is a quite complex system, which requires suitable mathematical tools for control and optimization purposes. This paper intends to be a step in this direction by deriving an averaged-value mathematical model of the whole system, which is validated through comparison with other modeling approaches and experimental results. The paper is mainly focused on applications in the field of electrical power generation; however, the converter structure can be also exploited in a variety of grid-connected applications by replacing the generator with a transformer featuring an open-end secondary winding arrangement. Full article
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Open AccessArticle
On PWM Strategies and Current THD for Single- and Three-Phase Cascade H-Bridge Inverters with Non-Equal DC Sources
Energies 2019, 12(3), 441; https://doi.org/10.3390/en12030441
Received: 19 December 2018 / Revised: 15 January 2019 / Accepted: 26 January 2019 / Published: 30 January 2019
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Abstract
Cascade H-bridge (CHB) inverter is an attractive choice for integration of DC sources of different nature, e.g., for distributed generation with energy storage, photovoltaic generation, etc. In general, non-equal DC voltage sources can affect the total harmonic distortion (THD) of the CHB by [...] Read more.
Cascade H-bridge (CHB) inverter is an attractive choice for integration of DC sources of different nature, e.g., for distributed generation with energy storage, photovoltaic generation, etc. In general, non-equal DC voltage sources can affect the total harmonic distortion (THD) of the CHB by introducing undesirable low-frequency subharmonics. This paper investigates different level-shifted (LS) and phase-shifted (PS) pulse width modulation (PWM) strategies for single- and three-phase cascade H-bridge inverters with non-equal DC sources from the load current THD minimization perspective. The best current quality is provided by LS PWM, as reported in the literature. The paper provides a simple time domain explanation of LS PWM superiority. However, PS PWM may be a preferable choice for practical applications due to fair power and loss sharing across individual H-bridges. The paper explains how to obtain the best current quality by PS PWM carriers’ order arrangement (DC sources switching sequence selection). Full article
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Open AccessFeature PaperArticle
A Reverse Model Predictive Control Strategy for a Modular Multilevel Converter
Energies 2019, 12(2), 297; https://doi.org/10.3390/en12020297
Received: 19 December 2018 / Revised: 13 January 2019 / Accepted: 15 January 2019 / Published: 18 January 2019
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Abstract
In recent years, modular multilevel converters (MMCs) have developed rapidly, and are widely used in medium and high voltage applications. Model predictive control (MPC) has attracted wide attention recently, and its advantages include straightforward implementation, fast dynamic response, simple system design, and easy [...] Read more.
In recent years, modular multilevel converters (MMCs) have developed rapidly, and are widely used in medium and high voltage applications. Model predictive control (MPC) has attracted wide attention recently, and its advantages include straightforward implementation, fast dynamic response, simple system design, and easy handling of multiple objectives. The main technical challenge of the conventional MPC for MMC is the reduction of computational complexity of the cost function without the reduction of control performance of the system. Some modified MPC scan decrease the computational complexity by evaluating the number of on-state sub-modules (SMs) rather than the number of switching states. However, the computational complexity is still too high for an MMC with a huge number of SMs. A reverse MPC (R-MPC) strategy for MMC was proposed in this paper to further reduce the computational burden by calculating the number of inserted SMs directly, based on the reverse prediction of arm voltages. Thus, the computational burden was independent of the number of SMs in the arm. The control performance of the proposed R-MPC strategy was validated by Matlab/Simulink software and a down-scaled experimental prototype. Full article
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Open AccessArticle
Modified State-of-Charge Balancing Control of Modular Multilevel Converter with Integrated Battery Energy Storage System
Energies 2019, 12(1), 96; https://doi.org/10.3390/en12010096
Received: 22 November 2018 / Revised: 21 December 2018 / Accepted: 24 December 2018 / Published: 28 December 2018
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Abstract
Modular multilevel converter with integrated battery energy storage system (MMC-BESS) has been proposed for energy storage requirements in high-voltage applications. The state-of-charge (SOC) equilibrium of batteries is essential for BESS to guarantee the capacity utilization. However, submodule voltage regulation can lead to over-modulation [...] Read more.
Modular multilevel converter with integrated battery energy storage system (MMC-BESS) has been proposed for energy storage requirements in high-voltage applications. The state-of-charge (SOC) equilibrium of batteries is essential for BESS to guarantee the capacity utilization. However, submodule voltage regulation can lead to over-modulation of individual submodules, which will limit the efficiency of SOC balancing control. Focusing on this problem, a modified SOC balancing control method with high efficiency is proposed in this paper. The tolerance for battery power unbalance is defined to quantize the convergence of SOC balancing control. Both the DC component and AC component are considered while regulating submodule voltage. The linear programming method is introduced to realize the maximum tolerance for battery power unbalance in different operation modes. Based on the analysis, by choosing appropriate submodule voltage regulation method, the efficiency of SOC balancing control is improved greatly. In addition, the SOC controller is also optimally designed to avoid over-modulation of submodules. Finally, the detailed simulation and experiment results verify the effectiveness of the analysis and proposed control strategy. Full article
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Open AccessArticle
A Full-bridge Director Switches based Multilevel Converter with DC Fault Blocking Capability and Its Predictive Control Strategy
Energies 2019, 12(1), 91; https://doi.org/10.3390/en12010091
Received: 23 October 2018 / Revised: 19 December 2018 / Accepted: 21 December 2018 / Published: 28 December 2018
Cited by 1 | PDF Full-text (5600 KB) | HTML Full-text | XML Full-text
Abstract
Voltage source converter-based high-voltage direct current transmission system (VSC-HVDC) technology has been widely used. However, traditional half-bridge sub module (HBSM)-based module multilevel converter (MMC) cannot block a DC fault current. This paper proposes that a full-bridge director switches based multi-level converter can offer [...] Read more.
Voltage source converter-based high-voltage direct current transmission system (VSC-HVDC) technology has been widely used. However, traditional half-bridge sub module (HBSM)-based module multilevel converter (MMC) cannot block a DC fault current. This paper proposes that a full-bridge director switches based multi-level converter can offer features such as DC side fault blocking capability and is more compact and lower cost than other existing MMC topologies. A suitable predictive control strategy is proposed to minimize the error of the output AC current and the capacitor voltage of the sub-module while the director switches are operated in low-frequency mode. The validity of the proposed topology and control method is demonstrated based on simulation and experimental studies. Full article
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Open AccessArticle
A Simplified Model Predictive Control for T-Type Inverter with Output LC Filter
Energies 2019, 12(1), 31; https://doi.org/10.3390/en12010031
Received: 14 November 2018 / Revised: 18 December 2018 / Accepted: 19 December 2018 / Published: 22 December 2018
Cited by 1 | PDF Full-text (6488 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a model predictive control scheme for the T-type inverter with an output LC filter is presented. A simplified dynamics model is proposed to reduce the number of the measurement and control variables, resulting in a decrease in the cost and [...] Read more.
In this paper, a model predictive control scheme for the T-type inverter with an output LC filter is presented. A simplified dynamics model is proposed to reduce the number of the measurement and control variables, resulting in a decrease in the cost and complexity of the system. Furthermore, the main contribution of the paper is the approach to evaluate the cost function. By employing the selection of sector information distribution in the reference inverter voltage and capacitor voltage balancing, the execution time of the proposed algorithm is significantly reduced by 36% compared with conventional model predictive control without too much impact on control performance. Simulation and experimental results are studied and compared with conventional finite control set model predictive control to validate the effectiveness of the proposed method. Full article
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Open AccessArticle
A Novel Fault-Tolerant Control of Modular Multilevel Converter under Sub-Module Faults Based on Phase Disposition PWM
Energies 2019, 12(1), 20; https://doi.org/10.3390/en12010020
Received: 14 November 2018 / Revised: 10 December 2018 / Accepted: 18 December 2018 / Published: 21 December 2018
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Abstract
Each arm of modular multilevel converter (MMC) consists of a large number of sub-module (SM) units. However, it also increases the probability of SM failure during the long-term system operation. Focusing on the fault-tolerant operation issue for the MMC under SM faults, the [...] Read more.
Each arm of modular multilevel converter (MMC) consists of a large number of sub-module (SM) units. However, it also increases the probability of SM failure during the long-term system operation. Focusing on the fault-tolerant operation issue for the MMC under SM faults, the traditional zero-sequence voltage injection fault-tolerant control algorithm is analyzed detailed and its disadvantages are concluded. Based on this, a novel fault-tolerant control strategy based on phase disposition pulse-width modulation (PD-PWM) is proposed in this paper, which has three main benefits: (i) it has carrier and modulation wave dual correction mechanism, which control ability is more higher and flexible; (ii) it only needs to inject zero-sequence voltage in half a cycle of the modulation wave, which simplifies the complexity of traditional zero-sequence voltage injection control algorithms and much easier for implement; (iii) furthermore, the zero-sequence voltage can even be avoided injecting under the symmetrical fault conditions. Finally, the effectiveness of the proposed control strategy is verified with the simulation and experiment studies under different fault conditions. Full article
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Open AccessArticle
A Highly Efficient Single-Phase Three-Level Neutral Point Clamped (NPC) Converter Based on Predictive Control with Reduced Number of Commutations
Energies 2018, 11(12), 3524; https://doi.org/10.3390/en11123524
Received: 16 November 2018 / Revised: 14 December 2018 / Accepted: 14 December 2018 / Published: 18 December 2018
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Abstract
This paper proposes a highly efficient single-phase three-level neutral point clamped (NPC) converter operated by a model predictive control (MPC) method with reduced commutations of switches. The proposed method only allows switching states with none or a single commutation at the next step [...] Read more.
This paper proposes a highly efficient single-phase three-level neutral point clamped (NPC) converter operated by a model predictive control (MPC) method with reduced commutations of switches. The proposed method only allows switching states with none or a single commutation at the next step as candidates for future switching states for the MPC method. Because the proposed method preselects switching states with reduced commutations when selecting an optimal state at a future step, the proposed method can reduce the number of switchings and the corresponding switching losses. Although the proposed method slightly increases the peak-to-peak variations of the two dc capacitor voltages, the developed method does not deteriorate the input current quality and input power factor despite the reduced number of switching numbers and losses. Thus, the proposed method can reduce the number of switching losses and lead to high efficiency, in comparison with the conventional MPC method. Full article
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Open AccessArticle
A Novel Multilevel Bidirectional Topology for On-Board EV Battery Chargers in Smart Grids
Energies 2018, 11(12), 3453; https://doi.org/10.3390/en11123453
Received: 31 October 2018 / Revised: 4 December 2018 / Accepted: 6 December 2018 / Published: 10 December 2018
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Abstract
This paper proposes a novel on-board electric vehicle (EV) battery charger (EVBC) based on a bidirectional multilevel topology. The proposed topology is formed by an AC-DC converter for the grid-side interface and by a DC-DC converter for the battery-side interface. Both converters are [...] Read more.
This paper proposes a novel on-board electric vehicle (EV) battery charger (EVBC) based on a bidirectional multilevel topology. The proposed topology is formed by an AC-DC converter for the grid-side interface and by a DC-DC converter for the battery-side interface. Both converters are interfaced by a split DC-link used to achieve distinct voltage levels in both converters. Characteristically, the proposed EVBC operates with sinusoidal grid-side current, unitary power factor, controlled battery-side current or voltage, and controlled DC-link voltages. The grid-side converter operates with five voltage levels, while the battery-side operates with three voltage levels. An assessment, for comparison with classical multilevel converters for EVBCs is considered along the paper, illustrating the key benefits of the proposed topology. As the proposed EVBC is controlled in bidirectional mode, targeting the EV incorporation into smart grids, the grid-to-vehicle (G2V) and vehicle-to-grid (V2G) operation modes are discussed and evaluated. Both converters of the proposed EVBC use discrete-time predictive control algorithms, which are described in the paper. An experimental validation was performed under real operating conditions, employing a developed laboratory prototype. Full article
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Open AccessArticle
Experimental Evaluation of the Performance of a Three-Phase Five-Level Cascaded H-Bridge Inverter by Means FPGA-Based Control Board for Grid Connected Applications
Energies 2018, 11(12), 3298; https://doi.org/10.3390/en11123298
Received: 22 October 2018 / Revised: 21 November 2018 / Accepted: 22 November 2018 / Published: 26 November 2018
Cited by 2 | PDF Full-text (41705 KB) | HTML Full-text | XML Full-text
Abstract
Over the last decades, plants devoted to the generation of green energy significantly increased their number, together with the demand of same electrical energy, also stored in battery systems. This fact produced the growth of energy conversion systems with advanced performances with respect [...] Read more.
Over the last decades, plants devoted to the generation of green energy significantly increased their number, together with the demand of same electrical energy, also stored in battery systems. This fact produced the growth of energy conversion systems with advanced performances with respect to the traditional ones. In this circumstance, multilevel converters play a significant role for their great advantages in performances, flexibility, fault-tolerability, employment of renewable energy sources and storage systems and finally yet importantly reduced filter requirements. In this context, this paper faces the performance of a cascaded H-bridge 5 level inverter in terms of harmonic distortion generated and injected into the grid. Through an accurate analysis that takes into account the pulse width modulation (PWM) multicarrier modulation techniques (phase disposition PD, phase opposition disposition POD, alternative phase opposition disposition APOD, phase shifted PS) and related reference signals (sinusoidal reference; third harmonic injection THI reference, switching frequency optimal SFO reference), a framework of distorting harmonics is presented by comparing twelve cases. The results obtained from the simulations are reproduced and validated in a prototype system of five level cascaded H-bridge multilevel inverter. A deep discussion of control and filtering system is provided to justify the choice of the best modulation technique to adopt. Full article
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Open AccessArticle
Capacitors Voltage Switching Ripple in Three-Phase Three-Level Neutral Point Clamped Inverters with Self-Balancing Carrier-Based Modulation
Energies 2018, 11(12), 3244; https://doi.org/10.3390/en11123244
Received: 23 October 2018 / Revised: 13 November 2018 / Accepted: 19 November 2018 / Published: 22 November 2018
Cited by 3 | PDF Full-text (6947 KB) | HTML Full-text | XML Full-text
Abstract
This paper provides a comprehensive analysis of the capacitors voltage switching ripple for three-phase three-level neutral point clamped (NPC) inverter topologies. The voltage ripple amplitudes of the two dc-link capacitors are theoretically estimated as a function of both amplitude and phase angle of [...] Read more.
This paper provides a comprehensive analysis of the capacitors voltage switching ripple for three-phase three-level neutral point clamped (NPC) inverter topologies. The voltage ripple amplitudes of the two dc-link capacitors are theoretically estimated as a function of both amplitude and phase angle of output current and the inverter modulation index. In particular, peak-to-peak distribution and maximum amplitudes of the capacitor voltage switching ripple over the fundamental period are obtained. A comparison is made considering different carrier-based pulse-width modulations in the case of almost all sinusoidal load currents, representing either grid connection or passive load with a negligible current ripple. Based on the voltage switching ripple requirements of capacitors, a simple and effective original equation for a preliminary sizing of the capacitors has been proposed. Numerical simulations and experimental tests have been carried out in order to verify the analytical developments. Full article
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Open AccessFeature PaperArticle
An Improved Imperialist Competitive Algorithm to Solve the Selected Harmonic Elimination Pulse-Width Modulation in Multilevel Converters
Energies 2018, 11(11), 3080; https://doi.org/10.3390/en11113080
Received: 18 October 2018 / Revised: 5 November 2018 / Accepted: 5 November 2018 / Published: 8 November 2018
Cited by 1 | PDF Full-text (2851 KB) | HTML Full-text | XML Full-text
Abstract
The traditional intelligent algorithms for the selected harmonic elimination pulse-width modulation (SHEPWM) of multilevel converters provide low convergent rate and low accuracy of solutions when solving quarter-wave symmetry nonlinear equations. To obviate this problem and obtain a better modulating performance, an improved imperialist [...] Read more.
The traditional intelligent algorithms for the selected harmonic elimination pulse-width modulation (SHEPWM) of multilevel converters provide low convergent rate and low accuracy of solutions when solving quarter-wave symmetry nonlinear equations. To obviate this problem and obtain a better modulating performance, an improved imperialist competition algorithm is proposed. The proposed algorithm enhances the global search ability by using moving imperialists. Also, a novel type of particles, named independent countries, are proposed to help the algorithm jump out of the local optimum. These independent countries change their positions using swarm intelligence. Compared with the existing particle swarm algorithm and genetic algorithm, the proposed algorithm has significant advantages by improving the accuracy of solutions and the rate of convergence. Finally, the correctness and effectiveness of the proposed algorithm are verified and evaluated by simulation and experimental results. Full article
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Open AccessFeature PaperArticle
Voltage Balance Control Analysis of Three-Level Boost DC-DC Converters: Theoretical Analysis and DSP-Based Real Time Implementation
Energies 2018, 11(11), 3073; https://doi.org/10.3390/en11113073
Received: 28 September 2018 / Revised: 14 October 2018 / Accepted: 26 October 2018 / Published: 8 November 2018
Cited by 1 | PDF Full-text (4953 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, a step-by-step description to get a unique three-level boost DC–DC converter (TLBDC) (DC—direct current) small signal model is first presented and validated through simulations and experiments. This model allows for overcoming the usage of two sub-models as in the conventional [...] Read more.
In this paper, a step-by-step description to get a unique three-level boost DC–DC converter (TLBDC) (DC—direct current) small signal model is first presented and validated through simulations and experiments. This model allows for overcoming the usage of two sub-models as in the conventional modeling approach. Based on this model, voltage balance (VB) controllers are designed and VB control analysis is presented. Two VB controllers, namely Proportional Integral (PI) and Fuzzy, were analyzed when the VB control was applied on both TLBDC switches or only one. According to the obtained simulation and experimental results, the proposed model gives an accurate approximation in dynamic, small perturbations around an operating point and steady state modes. Moreover, it has been shown that VB is achieved in a reduced time when VB control is applied on both the TLBDC’s switches. Furthermore, the Fuzzy controller performs better than PI controller for VB control. Full article
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Open AccessArticle
Design and Controller-In-Loop Simulations of a Low Cost Two-Stage PV-Simulator
Energies 2018, 11(10), 2774; https://doi.org/10.3390/en11102774
Received: 2 September 2018 / Revised: 27 September 2018 / Accepted: 3 October 2018 / Published: 16 October 2018
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Abstract
A PV-Simulator is a DC power source in which the current-voltage (I-V) characteristics of different PV arrays can be programmed. With a PV-simulator, the operation of the solar power conditioning systems can be validated at a laboratory level itself before actual field trials. [...] Read more.
A PV-Simulator is a DC power source in which the current-voltage (I-V) characteristics of different PV arrays can be programmed. With a PV-simulator, the operation of the solar power conditioning systems can be validated at a laboratory level itself before actual field trials. In this work, design, operation and controls for a two-stage programmable PV-simulator required for the testing of solar power conditioning systems are presented. The proposed PV-simulator consists of a three-level T-type active front-end converter in the first stage and a buck-chopper-based DC-DC converter in the second stage. An active front-end rectifier using a three-level T-type IGBT-based converter is used at the input stage to help in operating the system at unity power factor. A DC-DC converter at the output stage of the simulator is regulated to obtain the I-V characteristics of the programmed PV-Array. Hardware-In-Loop simulations are carried out to validate the proposed system and the associated controls implemented in the controller. As a case study, this PV-simulator is programmed with electrical parameters of a selected PV-array and the characteristics obtained from the PV-simulator are compared with the actual PV-array characteristics. The dynamic response of the system for sudden changes in the load and sudden changes in irradiance values are studied. Full article
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Open AccessArticle
FPGA-Based Controller for a Permanent-Magnet Synchronous Motor Drive Based on a Four-Level Active-Clamped DC-AC Converter
Energies 2018, 11(10), 2639; https://doi.org/10.3390/en11102639
Received: 3 August 2018 / Revised: 26 September 2018 / Accepted: 28 September 2018 / Published: 2 October 2018
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Abstract
This paper proposes a closed-loop control implementation fully-embedded into an FPGA for a permanent-magnet synchronous motor (PMSM) drive based on a four-level active-clamped converter. The proposed FPGA controller comprises a field-oriented control to drive the PMSM, a DC-link voltage balancing closed-loop control (VBC), [...] Read more.
This paper proposes a closed-loop control implementation fully-embedded into an FPGA for a permanent-magnet synchronous motor (PMSM) drive based on a four-level active-clamped converter. The proposed FPGA controller comprises a field-oriented control to drive the PMSM, a DC-link voltage balancing closed-loop control (VBC), and a virtual-vector-based modulator for a four-level active-clamped converter. The VBC and the modulator operate in consonance to preserve the DC-link capacitor voltages balanced. The FPGA design methodology is carefully described and the main aspects to achieve an optimal FPGA implementation using low resources are discussed. Experimental results under different operating conditions are presented to demonstrate the good performance and the feasibility of the proposed controller for motor-drive applications. Full article
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Open AccessFeature PaperArticle
An Input-Parallel-Output-Series Switched-Capacitor Three-level Boost Converter with a Three-Loop Control Strategy
Energies 2018, 11(10), 2631; https://doi.org/10.3390/en11102631
Received: 2 September 2018 / Revised: 22 September 2018 / Accepted: 28 September 2018 / Published: 2 October 2018
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Abstract
There has been increasing interest for industry applications, such as solar power generation, fuel cell systems, and dc microgrids, in step-up dc-dc converters with reduced number of components, low component stress, small input ripples and high step-up ratios. In this paper, an input-parallel-output-series [...] Read more.
There has been increasing interest for industry applications, such as solar power generation, fuel cell systems, and dc microgrids, in step-up dc-dc converters with reduced number of components, low component stress, small input ripples and high step-up ratios. In this paper, an input-parallel-output-series three-level boost (IPOS-SC-TLB) converter is proposed. In addition to achieving the required performance, the input and output terminals can share the same ground and an automatic current balance function is also achieved in the IPOS-SC-TLB converter. Besides, a capacitor voltage imbalance mechanism was revealed and a three-loop control strategy composed of output voltage loop, input current loop and voltage-balance loop was proposed to address the voltage imbalance issue. Finally both simulation and experiment studies have been conducted to verify the effectiveness of the IPOS-SC-TLB converter and the three-loop control strategy. Full article
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Open AccessArticle
A Novel Phase Current Reconstruction Method for a Three-Level Neutral Point Clamped Inverter (NPCI) with a Neutral Shunt Resistor
Energies 2018, 11(10), 2616; https://doi.org/10.3390/en11102616
Received: 1 September 2018 / Revised: 24 September 2018 / Accepted: 25 September 2018 / Published: 1 October 2018
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Abstract
This paper presents three phase current reconstruction methods for a three-level neutral point clamped inverter (NPCI) by measuring the voltage of a shunt resistor placed in the neutral point of the inverter. In order to accurately acquire the phase currents from the shunt [...] Read more.
This paper presents three phase current reconstruction methods for a three-level neutral point clamped inverter (NPCI) by measuring the voltage of a shunt resistor placed in the neutral point of the inverter. In order to accurately acquire the phase currents from the shunt resister, the dwell time of the active voltage vectors need to exceed the minimum time. On the other hand, if the time of active voltage is shorter than the minimum time, the current measurement becomes impossible. In this paper, unmeasurable regions for current are classified into three areas. Area 1 is a region in which both phase currents can be measure. Therefore, it is not necessary to restore the current. In Area 2, only one phase current can be measured. Thus, an estimation or restoration method is needed to measure another phase current. In this paper, the current estimation method using an electrical model of the motor is proposed. Area 3 is the region in which both phase currents can not be measured. In this case, it is necessary to move the voltage vector to the current measurable area by injecting the voltage. In this paper, Area 3 is divided into 36 sectors to inject optimal voltage. The proposed methods have the advantages of high current measurement accuracy and low THD (total harmonic distortion). The effectiveness of the proposed methods are verified through experimental results. Full article
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Open AccessArticle
Low-Harmonic DC Ice-Melting Device Capable of Simultaneous Reactive Power Compensation
Energies 2018, 11(10), 2596; https://doi.org/10.3390/en11102596
Received: 4 August 2018 / Revised: 13 September 2018 / Accepted: 26 September 2018 / Published: 29 September 2018
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Abstract
As a result of the high efficiency of ice-melting and the small power supply capacity, DC ice-melting devices are widely used in relation to transmission lines in the power grid. However, it needs to consume reactive power when ice-melting, and voltage fluctuation of [...] Read more.
As a result of the high efficiency of ice-melting and the small power supply capacity, DC ice-melting devices are widely used in relation to transmission lines in the power grid. However, it needs to consume reactive power when ice-melting, and voltage fluctuation of the substation may be caused when the demand for reactive power is large. It also generates a large number of 5th and 7th harmonics when ice-melting. In this paper, combined with the demand for ice-melting for transmission lines and the dynamic reactive power of substations, a low-harmonic DC ice-melting device capable of simultaneous reactive power compensation is studied. The function of ice-melting and reactive power compensation can be operated simultaneously and the rectifier’s main harmonics can be eliminated. The simulation and experimental research on the device was carried out in the 500 kV Chuanshan substation. The actual ice melting was carried out on the 500 kV Chuansu I line and took only 68 min to melt the ice. The 500 kV bus voltage had no negative deviation, and the positive deviation decreased from +3.09% to +1.57% within 24 h of testing. The results prove the feasibility of the proposed DC ice-melting device in this paper. Full article
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Open AccessFeature PaperArticle
FPGA-Based Implementation of MMC Control Based on Sorting Networks
Energies 2018, 11(9), 2394; https://doi.org/10.3390/en11092394
Received: 6 August 2018 / Revised: 6 September 2018 / Accepted: 10 September 2018 / Published: 11 September 2018
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Abstract
In Modular Multilevel Converter (MMC) applications, the balancing of the capacitor voltages is one of the most important issues for achieving the proper behavior of the MMC. The Capacitor Voltage Balancing (CVB) control is usually based on classical sorting algorithms which consist of [...] Read more.
In Modular Multilevel Converter (MMC) applications, the balancing of the capacitor voltages is one of the most important issues for achieving the proper behavior of the MMC. The Capacitor Voltage Balancing (CVB) control is usually based on classical sorting algorithms which consist of repetitive/recursive loops. This leads to an increase of the execution time when many Sub-Modules (SMs) are employed. When the execution time of the balancing is longer than the sampling period, the proper operation of the MMC cannot be ensured. Moreover, due to their inherent sequential operation, sorting algorithms are suitable for software implementation (microcontrollers or DSPs), but they are not appropriate for a hardware implementation. Instead, in this paper, Sorting Networks (SNs) are proposed due to their convenience for implementation in FPGA devices. The advantages and the main challenges of the Bitonic SN in MMC applications are discussed and different FPGA implementations are presented. Simulation results are provided in normal and faulty conditions. Moreover, a comparison with the widely used bubble sorting algorithm and max/min approach is made in terms of execution time and performance. Finally, hardware-in-the-loop results are shown to prove the effectiveness of the implemented SN. Full article
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Open AccessArticle
A Harmonic Voltage Injection Based DC-Link Imbalance Compensation Technique for Single-Phase Three-Level Neutral-Point-Clamped (NPC) Inverters
Energies 2018, 11(7), 1886; https://doi.org/10.3390/en11071886
Received: 15 May 2018 / Revised: 10 July 2018 / Accepted: 11 July 2018 / Published: 19 July 2018
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Abstract
In three-level neutral-point-clamped (NPC) inverters, the voltage imbalance problem between the upper and lower dc-link capacitors is one of the major concerns. This paper proposed a dc-link capacitor voltage balancing method where a common offset voltage was injected. The offset voltage consists of [...] Read more.
In three-level neutral-point-clamped (NPC) inverters, the voltage imbalance problem between the upper and lower dc-link capacitors is one of the major concerns. This paper proposed a dc-link capacitor voltage balancing method where a common offset voltage was injected. The offset voltage consists of harmonic components and a voltage difference between the upper and the lower capacitors. Here, both the second-order harmonics and the half-wave of the second-order component were injected to compensate for the unbalanced voltage between the capacitors. In order to show the effectiveness of the proposed voltage injection, the theoretical analyses, simulations, and experimental results are provided. Since the proposed method does not require any hardware modifications, it can be easily adapted. Both the simulations and the experiments validated that the voltage difference of the dc-link could be effectively reduced with the proposed method. Full article
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Open AccessArticle
Hybrid Modulated Model Predictive Control in a Modular Multilevel Converter for Multi-Terminal Direct Current Systems
Energies 2018, 11(7), 1861; https://doi.org/10.3390/en11071861
Received: 17 May 2018 / Revised: 10 July 2018 / Accepted: 11 July 2018 / Published: 17 July 2018
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Abstract
In this paper a hybrid modulated model predictive control (HM2PC) strategy for modular-multilevel-converter (MMC) multi-terminal direct current (MTDC) systems is proposed for supplying power to passive networks or weak AC systems, with the control objectives of maintaining the DC voltage, voltage [...] Read more.
In this paper a hybrid modulated model predictive control (HM2PC) strategy for modular-multilevel-converter (MMC) multi-terminal direct current (MTDC) systems is proposed for supplying power to passive networks or weak AC systems, with the control objectives of maintaining the DC voltage, voltage stability and power balance of the proposed system. The proposed strategy preserves the desired characteristics of conventional model predictive control method based on finite control set (FCS-MPC) methods, but deals with high switching frequency, circulating current and steady-state error in a superior way by introducing the calculation of the optimal output voltage level in each bridge arm and the specific duty cycle in each Sub-Module (SM), both of which are well-suited for the control of the MMC system. In addition, an improved multi-point DC voltage control strategy based on active power balanced control is proposed for an MMC-MTDC system supplying power to passive networks or weak AC systems, with the control objective of coordinating the power balance between different stations. An MMC-HVDC simulation model including four stations has been established on MATLAB/Simulink (r2014b MathWorks, Natick, MA, USA). Simulations were performed to validate the feasibility of the proposed control strategy under both steady and transient states. The simulation results prove that the strategy can suppress oscillations in the MMC-MTDC system caused by AC side faults, and that the system can continue functioning if any one of the converters are tripped from the MMC-MTDC network. Full article
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Open AccessArticle
Small-Scale Modular Multilevel Converter for Multi-Terminal DC Networks Applications: System Control Validation
Energies 2018, 11(7), 1690; https://doi.org/10.3390/en11071690
Received: 16 May 2018 / Revised: 22 June 2018 / Accepted: 22 June 2018 / Published: 28 June 2018
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Abstract
This paper presents the design and implementation of a digital control system for modular multilevel converters (MMC) and its use in a 5 kW small-scale prototype. To achieve higher system control reliability and multi-functionality, the proposed architecture has been built with an effective [...] Read more.
This paper presents the design and implementation of a digital control system for modular multilevel converters (MMC) and its use in a 5 kW small-scale prototype. To achieve higher system control reliability and multi-functionality, the proposed architecture has been built with an effective split of the control tasks between a master controller and six slave controllers, one for each of the six arms of the converter. The MMC prototype has been used for testing both converter and system-level controls in a reduced-scale laboratory set up of a Multi-Terminal DC transmission network (MTDC). The whole control has been tested to validate the proposed control strategies. The tests performed at system level allowed exploration of the advantages of using an MMC in a MTDC system. Full article
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Open AccessArticle
Fault Detection and Location of IGBT Short-Circuit Failure in Modular Multilevel Converters
Energies 2018, 11(6), 1492; https://doi.org/10.3390/en11061492
Received: 14 May 2018 / Revised: 1 June 2018 / Accepted: 5 June 2018 / Published: 7 June 2018
Cited by 1 | PDF Full-text (5042 KB) | HTML Full-text | XML Full-text
Abstract
A single fault detection and location for Modular Multilevel Converter (MMC) is of great significance, as numbers of sub-modules (SMs) in MMC are connected in series. In this paper, a novel fault detection and location method is proposed for MMC in terms of [...] Read more.
A single fault detection and location for Modular Multilevel Converter (MMC) is of great significance, as numbers of sub-modules (SMs) in MMC are connected in series. In this paper, a novel fault detection and location method is proposed for MMC in terms of the Insulated Gate Bipolar Translator (IGBT) short-circuit failure in SM. The characteristics of IGBT short-circuit failures are analyzed, based on which a Differential Comparison Low-Voltage Detection Method (DCLVDM) is proposed to detect the short-circuit fault. Lastly, the faulty IGBT is located based on the capacitor voltage of the faulty SM by Continuous Wavelet Transform (CWT). Simulations have been done in the simulation software PSCAD/EMTDC and the results confirm the validity and reliability of the proposed method. Full article
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Open AccessArticle
A Novel Three-Level Voltage Source Converter for AC–DC–AC Conversion
Energies 2018, 11(5), 1147; https://doi.org/10.3390/en11051147
Received: 26 March 2018 / Revised: 26 April 2018 / Accepted: 27 April 2018 / Published: 4 May 2018
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Abstract
This paper presents a novel three-level voltage source converter for AC–DC–AC conversion. The proposed converter based on H-bridge structure is studied in detail. The control method with traditional double-closed-loop control strategy and voltage balancing algorithm is applied to the rectifier side. Correspondingly, a [...] Read more.
This paper presents a novel three-level voltage source converter for AC–DC–AC conversion. The proposed converter based on H-bridge structure is studied in detail. The control method with traditional double-closed-loop control strategy and voltage balancing algorithm is applied to the rectifier side. Correspondingly, a simplified modulation algorithm is applied to the inverter side, and the voltage balancing of inverter side is realized through the optimal selection of switching combination. Then, the application of the proposed topology is assessed in general and ideal operation conditions. Furthermore, the proposed topology with a variable voltage variable frequency (VVVF) is verified in experimental conditions. The performance of the proposed converter and control strategy is evaluated by experimental and simulation results. Full article
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Open AccessArticle
Theoretical and Experimental Investigation of the Voltage Ripple across Flying Capacitors in the Interleaved Buck Converter with Extended Duty Cycle
Energies 2018, 11(4), 1017; https://doi.org/10.3390/en11041017
Received: 25 March 2018 / Revised: 17 April 2018 / Accepted: 18 April 2018 / Published: 21 April 2018
Cited by 1 | PDF Full-text (2535 KB) | HTML Full-text | XML Full-text
Abstract
The interleaved buck converter with an extended duty cycle is analyzed in terms of unexplored parasitic switching states that diminish the switch utilization and its safety due to high-magnitude charging and discharging currents. The analysis explains the origin of the states and their [...] Read more.
The interleaved buck converter with an extended duty cycle is analyzed in terms of unexplored parasitic switching states that diminish the switch utilization and its safety due to high-magnitude charging and discharging currents. The analysis explains the origin of the states and their effects and demonstrates their correlation with the existing voltage ripple on flying capacitors. The article further demonstrates that the voltage ripple can no longer be arbitrarily chosen as parasitic states emerge whenever the ripple exceeds an identified critical value being equal to the twofold voltage drop on the diode. A simple design criterion for flying capacitance is proposed. For a limited set of battery-powered DC–DC converters, a solution permitting the use of smaller capacitance by adding an extra switch is proposed. The derived findings are verified using experimental and simulation results. Full article
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