Multilevel DC-AC Converter Research Articles

Coupled-Inductor-Based DC–AC Multilevel Converter With Reduced Number of Switches

Coupled-Inductor-Based DC–AC Multilevel Converter With Reduced Number of Switches

Multilevel Converter Based on Series and Parallel Connections Using Floating Capacitor

The series connections of converter cells are interesting for high voltage applications, while parallel connections are for high current applications. The series/parallel is interesting for medium voltage and current applications because they present semiconductor devices with a lower rating in both voltage and current, thus, reducing the cost and size of the converters. This article investigates the configuration of a single-phase multilevel DC-AC converter based on series and parallel connections of H-bridges using floating capacitors to reduce the number of independent DC sources. The use of the floating capacitor has the limitation of working in certain operating regions. This article investigates which regions can work with floating capacitors and presents the mathematical model, general control strategy, pulse width modulation (PWM) strategies, and loss comparison with conventional series or parallel systems. Simulations and experimental results are presented to validate the control and PWM strategies used.

Novel Fault Analysis and Compensation in 5-Level Multilevel DC-AC Converter

Existing Neutral clamped active (NCA) inverter has the property of common mode voltage with high frequency which can reduce the severity with less voltage gain. A newly designed 5L NCA inverter can capable have achieved voltage step-up with a one stage inversion process. Proposed circuit common ground increases voltage utilization in DC link and also mitigates common mode voltage with high frequency. Proposed topology has advantage of more compact and less voltage stress over existing two stage topology. Proposed circuit has only seven power switches with two capacitors, whereas existing topology is designed with 10 switches with 3 capacitors, so arrangement can obtain more efficiency. Implementation of this proposed topology is initially design in simulink platform, and the simulation results are finally verified in a proto-type model with power rating of 2000 W to validate its feasibility and performances with its fault clearance ability.

Single-Phase AC–DC–AC Multilevel Converter Based on Parallel-/Series-Connected Three-Leg Modules

A single-phase ac-dc-ac topology composed of two three-leg modules parallel-connected at the grid side and series-connected at the load side is proposed in this paper. This topology is appropriated for applications as uninterruptible power supply, unified power quality conditioner, as well as for conversion systems in which the output voltage required is higher than the input voltage (voltage step-up applications). Circuit model equations, dc-link voltage specifications, and a technique to minimize the current in the shared legs of the converter are presented. An overall control strategy to regulate the dc-link voltages and to maintain synchronized the grid voltage and current is discussed. An interleaved pulse width modulation technique (PWM) based on four carriers was adopted to improve the number of voltage levels generated by the converter and reduce the total power losses. The dead-time effect is also analyzed. Comparisons are performed with conventional topologies in a wide range of power in terms of rating of the semiconductor devices, harmonic distortion, semiconductor losses, transformer losses, and efficiency. Compared to conventional ac-dc-ac topologies, the proposed structure has achieved the following advantages: reduced harmonic distortions, lower power ratings, lower switching losses and lower semiconductor total losses per leg, and higher efficiency. Experimental results are shown to demonstrate the feasibility of the system operation in steady-state conditions, under load transients, and supplying non-linear loads.

A generalized switched-capacitor step-up multilevel inverter employing single DC source

In this paper, a new generalized step-up multilevel DC-AC converter is proposed, which is suitable for applications with low-voltage input sources such as photovoltaic power generation and electric vehicles. This inverter can achieve a high voltage gain by controlling the series-parallel conversion of DC power supply and capacitors. Only one DC voltage source and a few power devices are employed. The maximum output voltage and the number of output levels can be further increased through the switched-capacitor unit's extension and the submodule cascaded extension. Moreover, the capacitor voltages are self-balanced without complicated voltage control circuits. The complementary operating mechanism between each pair of switches simplifies the modulation algorithm. The inductive-load ability is fully taken into account in the proposed inverter. Additionally, a remarkable characteristic of the inverter is that the charging and discharging states among different capacitors are synchronous, which reduces the voltage ripple of the frontend capacitors. The circuit structure, the working principle, the modulation strategy, the capacitors and losses analysis are presented in detail. Afterwards, the advantages of the proposed inverter are analyzed by comparing with other recently proposed inverters. Finally, the steady-state and dynamic performance of the proposed inverter is verified and validated by simulation and experiment. 1

Six-Leg Single-Phase AC–DC–AC Multilevel Converter With Transformers for UPS and UPQC Applications

This article investigates a single-phase ac–dc–ac multilevel converter composed of two three-leg converters series-connected throughout two transformers (one on the grid side and one on the load side), sharing the same dc-link. The proposed converter allows to feed the load with sinusoidal voltages (keeping constant amplitude and frequency) under grid voltage disturbances, as sags, swells, and harmonics. Besides, the converter can operate with a sinusoidal grid current with a high power factor and can be applied to systems with either equal or different voltage levels at the input and output. Circuit model equations, pulse width modulation (PWM) technique based on space vector approaches, and a control system are presented. The proposed topology is compared with the conventional one in terms of harmonic distortion, semiconductor losses, transformers losses, and total power losses. Simulation and experimental results are presented under the same conditions to validate PWM and control strategies.

A new multilevel DC-AC converter topology with reduced switch using multicarrier sinusoidal pulse width modulation

Multilevel converters have a significant role in power processing control in the power system, which has some inherent features like reduced harmonics, high power & medium voltage, reduced voltage stress. In this proposed paper, a novel multilevel inverter with reduced number of switches and without passive components. The proposed inverter generates 15 level output voltage with suitable switching pulse generation using multicarrier sinusoidal pulse width modulation (MSPWM) and different level of voltages are obtained with variation of modulation index. Also coupled inductor is used to minimize the harmonic content and smoothing output current. The scheme which includes different range of unequal voltage sources. As a result, the proposed system it reduces switching control complexity and there is no voltage balancing problem. This paper elucidates the operating modes, voltage stress minimisation and harmonic reduction are discussed. The results of the proposed multilevel dc-ac converter are verified using matlab/simulink. The simulation & hardware results of the proposed inverter were verified using matlab simulink and dsPIC controller respectively, which was analysed with different voltage level and different modulation index.

A modified asymmetric cascaded multilevel DC–AC converter with switched diodes using FPGA processor implementation

A modified cascaded multilevel DC-AC converter using switched diodes is presented in this paper. This DC-AC converter produces great amount of voltage levels with minimized components by using hybrid modulation. It has two DC-AC converters coupled in cascade. First one is high frequency DC-AC converter and second one is low frequency DC-AC converter. The high frequency DC-AC converter is only capable to generate two levels with high frequency but the low frequency DC-AC converter is capable to produce great amount of voltage level by utilizing switched diodes. It reduces switching losses, size, cost and volume. Simulation of the circuit is done through MATLAB. The switching algorithm is realized by Spartan 6 FPGA processor board. Simulation outcomes are validated through experimental setup.

An Original Hybrid Multilevel DC-AC Converter Using Single-Double Source Unit for Medium Voltage Applications: Hardware Implementation and Investigation

In this article, an original hybrid multilevel DC-AC converter configurations are proposed by using single-double source unit for medium voltage applications. The proposed topologies are derived by hybridization of single and double source units with polarity changer and cascaded with full-bridge converter for medium and high voltage applications. Two different hybrid topologies presented and each topology configured for both symmetric and asymmetric method. The proposed hybrid topologies compared with the conventional cascaded H-bridge converter (CHB), and the best topologies recommended for medium voltage applications. The comparison in terms of the number of switches, gate driver circuits, maximum blocking voltage by switches and total peak inverse voltages of switches presented. The proposed topologies require a small installation area and low cost. The validity of the proposed hybrid converter structures is verified by simulation using MATLAB/Simulink and hardware results. The simulation and hardware results show a good agreement with the theoretical approach.

Asymmetrical Multilevel Hybrid Inverter - Analysis and Experimentation

This paper describes a voltage-fed asymmetrical hybrid inverter based on a symmetrical hybrid multilevel DC-AC converter for high voltage/high power applications. The proposed inverter is controlled by two types of modulationpatterns: low frequency (single pulse) and high frequency (sinusoidal PWM), responsible for obtaining a reduced harmonic distortion in the output voltage. Furthermore, the converter is asymmetrically powered, being fed by two sources with distinct values, obtaining seven levels phase voltage output. The results are presented with two pulse width modulation strategies, aimed at reducing the harmonic distortion in the voltage output. The operation of single-phase and three-phase circuits was verified by means of simulations and results obtained with an experimental prototype operating at a frequency switching of 1.5 kHz with a fundamental frequency of 50 Hz.

A New Hybrid Multilevel DC–AC Converter With Reduced Energy Storage Requirement and Power Losses for HVDC Applications

A dc-ac converter for voltage-source converter (VSC)-HVdc technology has a significant influence on the performance of the entire power transmission system. This paper introduces a new dc-ac converter composed of submodules and series insulated-gate bipolar transistor (IGBT) switches. The basic idea of this hybrid solution is to shape the ac voltage by submodules but, per half cycle, reconnect them to different electrical points by IGBT switches. This concept can help to reduce the quantities of submodules, thereby reducing the energy storage requirement significantly. Another advantage is that the IGBT switches can be soft switched by utilizing the high controllability of the submodules. This brings extra benefit of power losses reduction. In this paper, the operating principle of this hybrid converter is explained. Its performances are also presented in detail and compared with those popular VSC dc-ac converters. The feasibility of the new concept is also verified by simulation and experimental results.

Design and Test of a New Three-Phase Multilevel Inverter for PV System Applications

This paper presents a test of a new three-phase multilevel inverter for PV system applications with reduced number of used DC sources and power switches. The topology of the inverter is designed using an electric assemblage of a two-level dc-dc boost converter (TLBC) with a simplified three-phase multilevel DC-AC converter (THPMC). The TLBC generates two balanced output DC voltages, while the THPMC converts these two DC voltages and generates three-phase AC voltages with five levels per line. Two modulation control techniques are used and tested with the proposed PV system on PSIM and on ISIS Proteus software. The achieved results prove the simplicity and efficiency of the proposed three-phase inverter.

Single-Phase AC–DC–AC Multilevel Converter Based on H-Bridges and Three-Leg Converters Connected in Series

This paper investigates an ac–dc–ac multilevel power converter. The studied configuration is composed of two single-phase ac–dc–ac three-leg modules and series-connected H-bridges in the shared part of system. Because the proposed converter has shared legs between the input and output, it is employed in applications with same input and output frequency. Uninterrupted power supply and unified power quality conditioner are application examples for this converter. Such multilevel topology has lower dc-link voltage rating, which, consequently, presents low switch blocking voltages when compared to conventional topologies. System model, a space-vector pulsewidth modulation (PWM) strategy to symmetrical and asymmetrical dc-link voltages, and an overall control strategy to adjust the system variables are presented. A power flux analysis shows the operation zone in which the individual dc-link voltage balancing is possible. PWM and control strategies are developed to reduce the semiconductor total losses, harmonic distortion, and switching stress. Two ac–dc–ac multilevel conventional structures are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter.

Single-Phase AC–DC–AC Multilevel Converter for Grid Overvoltage Based on an H-Bridge Connected in Series to the Five-Leg Converter

In this work, an ac–dc–ac multilevel power converter for grid overvoltage is investigated. The developed configuration is composed of one single-phase ac–dc–ac three-leg module and two H-bridges. One of them is connected to the shared part of the system to generate multilevel voltages at the input and output of the structure, and the other one is connected to the grid side to compensate the grid overvoltage. The converter can be employed in applications with same input and output frequency, such as uninterrupted power supply and unified power quality conditioner without isolation transformer. System model, a space vector pulsewidth modulation strategy to balance the individual dc-link voltages, and an overall control strategy to adjust the grid power factor, the amplitude, and the frequency of the load voltage are presented. The proposed converter is compared in terms of harmonic distortion and semiconductor losses with conventional structures. Simulation and experimental results demonstrate the operation of the proposed topology.

Multistage and Multilevel Power Electronic Converter-Based Power Supply for Plasma DBD Devices

This paper presents the development and performance evaluation of a compact-converter-based power supply for plasma dielectric barrier discharge (DBD) devices. The developed power supply is designed to meet weight and size requirements for applications in aeronautical systems. Multistage and multilevel switch-mode converters are employed to construct the power supply. The multistage part of the power supply is constructed from multiple dc-dc boost converters that have their inputs fed by rechargeable batteries. The outputs of the dc-dc converters are used to feed different levels of a single phase cascaded H-bridge (CHB) multilevel dc-ac converter. The switching signals for the CHB dc-ac converter are generated to facilitate the adjustments of the magnitude and/or frequency of the output voltage. Such adjustments are set to allow manipulating the generated plasma body force. A prototype for the multistage multilevel power supply is constructed for performance evaluation using a fiberglass DBD device. Performance results show an effective generation and control of plasma body force, which can be achieved by a modular, lightweight, and compact size power supply.

Hybrid and Modular Multilevel Converter Designs for Isolated HVDC–DC Converters

Efficient medium and high-voltage dc–dc conversion is critical for future dc grids. This paper proposes a hybrid multilevel dc–ac converter structure that is used as the kernel of dc–dc conversion systems. Operation of the proposed dc–ac converter is suited to trapezoidal ac-voltage waveforms. Quantitative and qualitative analyses show that said trapezoidal operation reduces converter footprint, active and passive components’ size, and on-state losses relative to conventional modular multilevel converters. The proposed converter is scalable to high voltages with controllable ac-voltage slope; implying tolerable dv/dt stresses on the converter transformer. Structural variations of the proposed converter with enhanced modularity and improved efficiency will be presented and discussed with regards to application in front-to-front isolated dc–dc conversion stages, and in light of said trapezoidal operation. Numerical results provide deeper insight of the presented converter designs with emphasis on system design aspects. Results obtained from a proof-of-concept 1-kW experimental test rig confirm the validity of simulation results, theoretical analyses, and simplified design equations presented in this paper.

A New DC-AC Multilevel Converter with Reduced Device Count

A New DC-AC Multilevel Converter with Reduced Device Count

A New Three-Phase AC–DC–AC Multilevel Converter Based on Cascaded Three-Leg Converters

This paper proposes and investigates a new three-phase ac–dc–ac multilevel conversion system obtained from cascaded three-leg converters. Such configuration presents advantages in terms of reduced switch blocking voltages and consequently lower dc-link voltage rating. Operating principles, a pulse-width modulation (PWM) technique based on vector approach, and a control strategy are presented. The operation with different dc-link voltage values and a balancing method are discussed, and is supported by simulation and experimental results. The PWM technique is able to generate multilevel voltage waveforms, which permits reducing the switching frequency stress leading to reduced semiconductor losses. Simulation results are used to compare the proposed configuration with a conventional solution in terms of harmonic distortion and semiconductor losses. Experimental results demonstrate the feasibility of the studied converter, and were obtained by using a downscaled prototype with insulated gate bipolar transistors with dedicated drives and a digital signal processor with appropriated plug-in boards and sensors.

Enhanced DC-Link Capacitor Voltage Balancing Control of DC–AC Multilevel Multileg Converters

This paper presents a capacitor voltage balancing control applicable to any multilevel dc–ac converter formed by a single set of series-connected capacitors implementing the dc link and semiconductor devices, such as the diode-clamped topology. The control is defined for any number of dc-link voltage levels and converter legs (for single-phase and multiphase systems), guaranteeing the capacitor voltage control for any modulation index value and load (from idle mode to full power). The associated control loop small-signal transfer function is presented, from which optimum compensator design guidelines are derived. The improvement in control performance is verified through simulation and experiments comparing with a previous balancing control strategy in a four-level three-phase dc–ac conversion system. The satisfactory control performance is also verified through simulation in a four-level five-phase dc–ac conversion system.

Solution trajectories for selective harmonic elimination pulse-width modulation for seven-level waveforms: analysis and implementation

A detailed analysis of a seven-level selective harmonic elimination pulse-width modulation method suitable for multilevel DC–AC converters is presented in this study. Solution trajectories that cover the normal range of modulation indices typical for the operation of multilevel inverters are documented. The properties and characteristics of these solutions with regard to the distribution of switching instants (angles) to the levels of the waveform are also reported. Selected simulation and experimental results are included for both steady state operation and under dynamic changes of the modulation index and the output frequency. The results confirm the effectiveness of the method.