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Multilevel inverters (MLIs) are playing a pivotal role in the power sector with potential applications, such as interfacing renewable energy sources with the grid and several industrial drive applications. MLIs with a smaller number of switching devices are more promising due to their compact size, reduced cost, and higher efficiency compared with their traditional counterparts. This paper, therefore, presents a new three-phase seven-level inverter. This topology is a combination of two cascade-connected two-level voltage-source inverters (VSIs) and H-bridge cells with flying capacitors (FCs). This paper presents the operating principle and the balancing technique for the dc-link capacitors and FCs. The generation of various output voltage levels and the limitation of the sinusoidal pulsewidth modulation control for FC voltage balancing is also presented. The number of components in the proposed circuit configuration and their voltage ratings are considerably lower compared with the recently proposed topologies. The behavior of the proposed circuit configuration is first assessed with simulation studies and is then tested with a laboratory prototype. The simulation and experimental results validate the effectiveness of the proposed topology and the voltage balancing technique. [ABSTRACT FROM AUTHOR]

This paper presents an improved dc-link voltage balancing algorithm for a three-level neutral-point-clamped inverter by considering phase current direction. Detailed studies on the effects of change in load current direction on the dc-link capacitor voltages are presented. A maximum value of power factor is numerically derived, above which it affects the capacitor voltage balancing capability. Compared with the previously presented research work, the inputs to the space-vector pulsewidth-modulation block are the three phase currents and the difference between the two capacitor voltages. Depending on the states of the two dc-link capacitor voltages and phase current direction, redundant voltage vector sequences are selected. The selected vectors keep the capacitor voltage deviations within 5% of the total dc-link voltage. Two zero switching vectors (i.e., PPP and NNN) are also removed from all subsectors of the earlier proposed strategy, which one used to produce higher common-mode voltages. Detailed simulation and experimental results are presented in this paper for a 6.0-kW surface permanent-magnet synchronous machine. Both the simulation and experimental results show the required performance of the proposed system. [ABSTRACT FROM AUTHOR]

Multilevel converters are a proven solution for medium-voltage and high-power applications, including renewable energy conversion. Developing 6.6-kV converters is a key goal for the wind turbines industry. Considering the voltage rating of commercially available semiconductors, five-level converters are necessary to reach 6.6 kV. The five-level active neutral-point-clamped converter (5L-ANPC) is one of the most advantageous topologies among five-level multilevel converters. This paper presents a new 5L-ANPC topology that overcomes the features of the previously employed 5L-ANPC topology. Along this paper, the properties and working principle of this new 5L-ANPC are explained. Finally, the validity of the new converter is validated via simulation and experimental results. [ABSTRACT FROM AUTHOR]

Multilevel converters with floating capacitors (FCs) are widely applied in recent years in a wide range of industrial applications from high-voltage direct current systems to high power drives. However, some FC topologies lack complete FC voltage balancing capability due to the inherent topology limitation or the insufficient switching state for capacitor balancing. This will result in large ripples on capacitors at low frequency (such as fundamental frequency), limiting their performance and application, particularly, when the fundamental frequency is very low in low-speed drive operations. Typical examples of those multilevel converters are modular multilevel converters (MMC), nested neutral-point-clamped (NNPC) converter, etc. In order to improve the FC balancing for this kind of multilevel converters, this paper proposes a carrier-based pulse-width modulation (PWM) method, named stair edge PWM method. This method can obtain sufficient redundant switching states for FC voltage balancing by producing multiple levels in one PWM period. The FC voltage balancing is thus achieved at switching frequency, which can greatly reduce the capacitor voltage ripple and therefore enable the use of much smaller FCs. Meanwhile, the voltage stress on each device and low $dv/dt$ feature are still the same as the normal multilevel operation, reserving two of the most salient features of multilevel converters. The proposed method also features much simpler and easier implementation compared with space-vector-based approaches, particularly when high-level converters are considered. An application example using a four-level NNPC converter is provided in this paper. The effectiveness and performance of the proposed method are verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

A multi-level boost topology based on a flying capacitor is compared in this work with the hybrid, multi-level, partial power processing topology already presented in the literature for use as a highly efficient and compact dc/dc stage in 1500-V, two-stage, grid-connected PV systems. Different variations of the resonant stage of the hybrid topology are analyzed and compared in terms of losses, volume and complexity. Full multivariable optimization is conducted for the multi-level boost topology with different number of levels and for all the analyzed variations of the resonant stage of the hybrid topology. Appropriately rated new classes of 650-V and 900-V WBG devices are included in the optimization algorithm. It is concluded that due to the dominant conduction losses and gap in the voltage rating of the commercially available WBG devices between 650V and 200V, increase of the number of levels over 4 leads to the deteriorated loss and volume performances. All the analysis related to the resonant stage of the hybrid topology is confirmed by detailed and comprehensive measurements of two prototypes of 4kW of nominal and 7kW of maximal power. Additionally, all the loss models applied in the optimization algorithms presented in this paper are confirmed by detailed measurements, thermal calibration and finite element thermal simulations of the wide bandgap devices and inductor designs employed in this work. [ABSTRACT FROM AUTHOR]

This paper proposes a new isolated three-port bidirectional dc–dc converter for simultaneous power management of multiple energy sources. The proposed converter has the advantage of using the least number of switches and soft switching for the main switch, which is realized by using an inductor–capacitor–inductor ( $LCL$) -resonant circuit. The converter is capable of interfacing sources of different voltage–current characteristics with a load and/or a dc microgrid. The proposed converter is constructed for simultaneous power management of a photovoltaic (PV) panel, a rechargeable battery, and a load. Simulation and experimental results show that the proposed converter is capable of maximum power point tracking control for the PV panel, when there is solar radiation, and controlling the charge and discharge of the battery, when there is surplus energy and power deficiency with respect to the load, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents the performance analysis and comparison of two types of bidirectional dc–dc converters—cascaded buck–boost capacitor in the middle and cascaded buck–boost inductor in the middle for use in plug-in electric and hybrid electric vehicles. The comparison of the two converters is based on device requirements, rating of switches and components, control strategy, and performance. Each of the converter topologies has some advantages over the other in certain aspects. Efficiency analysis has been carried out for specific scenarios in vehicle applications. The simulation and experimental results are provided for both converter types. [ABSTRACT FROM PUBLISHER]

This article proposed a nonisolated symmetrical interleaved multilevel boost converter for high-voltage microgrid applications. The proposed converter configuration is derived from the integration of a voltage multiplier (VM) circuit with the front-end structure of the classical two-phase interleaved converter. Moreover, equal voltage rating capacitors and diodes are suitable to design multiple stages of the proposed converter. The proposed converter can feed from two independent sources or single source in the interleaved approach. The continuous input current, high-voltage gain, reduced voltage rating of capacitor (that causes reduction in cost), reduced components, and flexibility in number of sources make the proposed converter more attractive for renewable dc-microgrid applications such as, photovoltaic (PV) system, fuel cell (FC) system, and hybrid PV-FC system. Furthermore, the voltage gain of the converter can be increased by just adding similar stages of VM without preferring the high-voltage rating capacitors and without disturbing the front-end structure of the converter. Nonidealities are considered to analyze the proposed converter in a more practical way. The characteristics and operation of the proposed converter are discussed in this article with the continuous conduction mode and Discontinuous Conduction Mode boundary conditions. The design of the reactive components and selection of semiconductor devices are discussed. Additionally, the proposed converter is compared with recently proposed dc–dc multilevel converters. To support the proposed work, simulation and experimental results are provided which shows a good agreement with the analytical approach. [ABSTRACT FROM AUTHOR]

This paper introduces a new zero current switching topology for parallel balancing of serially connected batteries string. The main advantage of the balancing concept in this study is that energy is transferred only when the cells are unbalanced. As a result, the power losses are significantly reduced since no current circulates through the system when balanced. This has been enabled by a modification of an isolated series-resonant converter operating in a discontinuous conduction mode. A single transformer for two cells is used, as opposed to conventional isolated topologies that require a transformer per cell. The realization is simple and sensorless. Experimental results have been obtained by a prototype of two modules balancing four series-connected batteries. [ABSTRACT FROM AUTHOR]

The integration of switched-capacitor techniques into multilevel inverters (MLIs) with a dc source string contributes to the boosting of voltage gain, renders it particularly attractive in reducing the number of input dc sources in the series string. However, the recent two-stage MLI topologies suffer from high voltage stress across the backend H-bridge. Addressing this concern, an improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper. An extended topology of 1SC-MLI is also established by appropriate incorporation of another switched-capacitor circuit. The two proposed topologies are endowed with voltage boosting capability. They also feature low switch count and low number of dc sources. More importantly, they resolve the high voltage stress problem in the existing counterparts. Their corresponding operational analysis and comparisons with recent MLI topologies are discussed. Simulation and experimental results from a laboratory prototype are presented to validate the effectiveness of the proposed topologies. [ABSTRACT FROM AUTHOR]

An improved bridgeless (BL) Cuk converter-based electric vehicle (EV) battery charger with high power factor and increased efficiency is designed and developed in this paper. It provides low cost and high-power-density-based charging solution for the EV. This charger incorporates less number of devices operating over one switching cycle, which reduces the additional conduction loss incurred by a diode bridge rectifier of the conventional charger. Hence, it improves the charger's efficiency. The added advantage of the proposed topology is that the unwanted capacitive coupling loop is removed, as well as the unwanted conduction through the body diode of the inactive switch in the previously developed BL Cuk converter is avoided. This significantly improves the charger's efficiency. For the constant current and constant voltage charging, the commands are synchronized by a flyback converter. The proposed charger draws a sinusoidal current from ac mains and the total harmonic distortion in the supply current is reduced to the limits specified by the IEC 61000-3-2 guidelines. The improved efficiency and power quality indices of the proposed charger are investigated to demonstrate its satisfactory charging operation at all operating conditions. [ABSTRACT FROM AUTHOR]

Fault-tolerant permanent magnet synchronous generator (PMSG) drives for wind turbine applications play a major role in improving reliability and availability levels, since power converters are very prone to fail. In this paper, a fault-tolerant converter with the ability to handle power switch open-circuit faults is addressed. The main concern of the proposed converter topology is the minimization of the hardware requirements, leading to a low increase of the system cost. First, the employed fault diagnostic technique does not require additional measurements, nor high computational effort. Secondly, the circuit topology reconfiguration implies a minimum number of extra components as well as minimal oversizing of the standard ones. Accordingly, a four-switch three-phase converter with the dc bus midpoint connected to the transformer neutral point and a three-switch three-phase rectifier are adopted for post-fault operation of the grid- and PMSG-side converters, respectively. Vector control strategies are proposed for both converters under analysis, focusing the issues of capacitor voltages balancing and torque ripple minimization. The performance of the proposed fault-tolerant PMSG drive is analyzed by means of experimental results. [ABSTRACT FROM PUBLISHER]

High-brightness light-emitting diodes (HB-LEDs) are becoming omnipresent across all aspects of illumination products, due to their incredible characteristics such as efficiency, reliability, long lifetime, controllability, etc. This paper proposes power conversion topologies to drive medium to high power HB-LEDs in three-phase power grids when these connections are available. For that reason, an evaluation of several drivers for medium to high power HB-LEDs in three-phase power grids is done. Moreover, a new topology is proposed, which complies with IEC 1000-3-2 Class C requirements, achieves high power factor, low total harmonic distortion, and the capability to have a flicker free behavior while disposing of the bulk capacitor and having galvanic isolation. The HB-LED driver is based on a modular approach with several cells working together with their inputs connected to the three-phase network and their outputs connected in parallel generating a dc output. Each one of these cells is a dc–dc converter operating as a loss free resistor. In order to validate the concept, a prototype has been built by the use of flyback converters operating in discontinuous conduction mode. Furthermore, it operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and it supplies an output voltage of 48 V with maximum power of 90 W. [ABSTRACT FROM AUTHOR]

Three-phase voltage-source inverters typically feature a significant amount of dc energy storage to maintain a stiff dc bus. In these cases, the dc-link capacitor is sized to store enough energy to maintain several tens of cycles of ac output at the rated power. In this paper, we propose to reduce the size of the dc-link capacitor dramatically to store enough energy to provide just one high-frequency switching cycle of the ac output power. The dc bus is no longer stiff, and hence, classical sinusoidal pulse-width modulation cannot be used. However, the stored energy modulation (SEM) proposed herein synthesizes high-quality sinusoidal output voltage waveforms, even with such tiny dc-link capacitors. In SEM, the switching intervals of the interconnecting switches are carefully determined nonlinear functions of various operating parameters such as reactive component sizing, switching frequency, load levels, etc. This paper presents the analytical and detailed design development of the SEM approach along with circuit simulation, experimental results, and comparative evaluation of a dc-to-three-phase system example. [ABSTRACT FROM PUBLISHER]

This paper proposes an electronic driver for public lighting systems. The input stage is based on the integration of two flyback converters with different polarities, in order to avoid the use of the input diode bridge rectifying stage. The output stage is a boost converter with an output current control. The proposed circuit is introduced and analyzed, and a design example for a 50-W light-emitting diode lamp is presented. The most relevant simulation and experimental results are also shown, in order to validate the idea. A comparison in terms of efficiency for the input stage is carried out between the proposed topology and the conventional flyback converter, showing an efficiency enhancement in the proposed converter. However, the most important advantage of the proposed converter is outlined in the final part of this paper. This advantage comes from the avoidance of the input diode bridge, thus enabling the bidirectional power flow at the input stage. Therefore, the topology can be used to deliver energy into the power grid. In recent lighting applications, the use of micro renewable generators in lighting points has made the use of special electronics to handle the energy flows in the ballast necessary. The present topology is an alternative to standard bidirectional input stages. [ABSTRACT FROM AUTHOR]

This paper proposes a high-frequency isolated dc/dc converter, whose switching frequency is 20 MHz. Meanwhile, the switch voltage stress is reduced based on optimal switch impedance. In the proposed converter, the switch can operate in ZVS condition, which can help to reduce the switching loss. A mathematical model of the proposed high frequency converter is built, which provides an effective design method for the system parameters. Meanwhile, the design method for PCB air-core transformer has been proposed and depicted. To verify the feasibility of the proposed converter and mathematic model, a 10 W prototype is built. [ABSTRACT FROM AUTHOR]

In this paper, a highly reliable back-to-back (BTB) power converter is proposed for doubly fed induction generator-based wind turbines (DFIG-WTs). When a power switch open-circuit fault is encountered in either the grid-side converter (GSC) or the rotor-side converter (RSC), a four-switch three-phase (FSTP) topology is formed to avoid using redundant bridge arms, which reduces the power circuit complexity and minimizes the conduction and switching losses. A simplified space vector pulsewidth modulation technique is used to eliminate sector identification and complex trigonometric calculations. In addition, the influence of dc-bus capacitor voltage unbalance on the electromagnetic torque is analyzed in detail. The offset current components are calculated, and they are deducted from the reference values in the modified control strategies to suppress the dc-bus voltage deviation. Moreover, the power loss model of a BTB converter is analyzed in detail, and the efficiency study is performed in various post-fault situations. Simulations in MATLAB/Simulink are carried out to verify the performance of a DFIG-WT based on a FSTP BTB converter. Furthermore, the control hardware-in-the-loop setup with RSC and GSC separately simulated in a digital real-time simulator is applied for experimental verification of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a nine-level transformer-based inverter requiring only eight switches. The envisaged structure consists of two standard H-bridges fed from a single dc source. Besides, a single-phase transformer is employed to aid the process of intermediate voltage level generation. An ad-hoc pulsewidth modulation scheme based on boolean logic form equations is developed to derive the gating pulses. An effortless extension of the proposed inverter to a higher number of voltage levels is also achieved by generalizing the switching functions. Furthermore, the superior performance of the proposed topology is demonstrated through a comprehensive cost-based analysis. Finally, the validation of the proposed topology is accomplished through experiments on a down-scale prototype, and the measurement results are included. [ABSTRACT FROM AUTHOR]

Parallel ac-link universal power converters are a relatively new class of power converters that can be configured as dc–dc, dc–ac, ac–dc, and ac–ac. These converters are extensions of a buck–boost converter in which the current of the inductor is alternating and the input and output can have any number of phases with any forms, voltage amplitude, or frequency. By placing a small capacitor in parallel with the link inductor, all the switches can benefit from soft switching. The main limitation of the parallel ac-link universal power converter is its large number of switches. A three-phase ac–ac configuration requires 24 unidirectional switches. This paper proposes two topologies based on the parallel ac-link universal power converters that significantly reduce the number of switches. One of the proposed topologies reduces the number of switches in a three-phase ac–ac configuration to 16. The other topology reduces the number of switches to 10. The latter can offer galvanic isolation with only a single-phase high-frequency transformer. This paper presents the principles of the operation of the proposed topologies and evaluates them through simulation and experiments. [ABSTRACT FROM AUTHOR]

In this paper, a novel multilevel dc–ac inverter is proposed. The proposed multilevel inverter generates seven-level ac output voltage with the appropriate gate signals’ design. Also, the low-pass filter is used to reduce the total harmonic distortion of the sinusoidal output voltage. The switching losses and the voltage stress of power devices can be reduced in the proposed multilevel inverter. The operating principles of the proposed inverter and the voltage balancing method of input capacitors are discussed. Finally, a laboratory prototype multilevel inverter with 400-V input voltage and output 220\ \textV\text{rms}/2\,{\text{kW}} is implemented. The multilevel inverter is controlled with sinusoidal pulse-width modulation (SPWM) by TMS320LF2407 digital signal processor (DSP). Experimental results show that the maximum efficiency is 96.9% and the full load efficiency is 94.6%. [ABSTRACT FROM AUTHOR]

Various kinds of differential power processing converters and voltage equalizers have been proposed for series-connected photovoltaic (PV) modules to prevent negative influences of partial shading, such as significant reduction in power generation and the occurrence of multiple maximum power points (MPPs), including local and global MPPs, that hinders and confuses MPP tracking algorithms to operate properly. However, since conventional topologies are based on multiple individual dc–dc converters, the required switch count increases proportionally to the number of modules connected in series, increasing the complexity. A two-switch voltage equalizer using an LLC resonant inverter and voltage multiplier is proposed in this paper. The circuitry can be dramatically simplified compared with conventional topologies due to the two-switch configuration. Detailed operation analyses for the LLC resonant inverter and voltage multiplier are separately performed. Experimental equalization tests emulating partially shaded conditions were performed for four PV modules connected in series. With the proposed voltage equalizer, local MPPs successfully disappeared, and extractable maximum power increased compared with those without equalization, demonstrating the effectiveness and performance of the proposed voltage equalizer. [ABSTRACT FROM PUBLISHER]

This paper proposes an offline single-stage light-emitting diode (LED) driver based on a novel approach to reduce low-frequency ripple in LED arrays supplied from mains, while assuring high input power factor (PF). The proposal employs a series resonant dc–dc converter integrated into a bridgeless boost power factor correction (PFC) stage. The resonant stage works to reduce the low-frequency ripple transmitted from the output of the PFC stage to the LEDs with only small power losses. This solution achieves three main goals: 1) reduction of the bulk capacitance used at the dc bus, allowing for the use of long-life film capacitors; 2) increase in the overall efficiency of the LED driver owing to the low switching and conduction losses in the shared switching network; and 3) assuring high input PF. Experimental results of a driver without electrolytic capacitors for a 100-W street lighting LED luminaire are presented, showing overall efficiency in excess of 92%, input PF greater than 0.97, and line current harmonic content in compliance with the IEC 61000-3-2 standard. [ABSTRACT FROM AUTHOR]

This paper presents a high-power-density high-power-factor GaN-based two-stage electrolytic-free offline LED driver. The LED driver achieves high power density through the use of a hybrid film–ceramic stacked switched capacitor (SSC) energy buffer, and a comprehensive optimization methodology that evaluates various converter topologies and designs and minimizes overall system volume while maintaining high efficiency. Based on this optimization approach, a totem-pole bridgeless boost power factor correction (PFC) converter is selected for the first stage, while a stacked-input isolated LLC dc–dc converter is selected for the second stage. The optimization procedure also minimizes the passive volume of the SSC energy buffer incorporating the volumetric energy density of commercially available capacitors. The optimized SSC energy buffer utilized in the proposed LED driver has 50% less passive volume than a capacitor-only solution. A 600-W prototype LED driver designed using the proposed approach for universal input voltage ${{(90}}-{ 305 \ \text{V}}_{{\text{rms}}})$ and 24-V output voltage is built and tested. The PFC stage achieves a peak efficiency of 98% while the LLC stage achieves a peak efficiency of 95%. The prototyped LED driver achieves a power density of 28 W/in3. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage light-emitting diode (LED) driver based on a bridgeless power factor correction (PFC) converter and a half-bridge CLCL resonant converter for street lighting applications. The proposed single-stage topology integrates the PFC converter and the CLCL resonant converter by sharing active power switches. The bridgeless PFC converter adopts two buck–boost circuits operating in discontinuous-conduction mode to achieve input-current shaping. It uses two diodes instead of a rectifier bridge to reduce the power loss caused by the diodes. Owing to its superior soft-switching characteristics, the CLCL resonant converter is used. The proposed LED driver has superior features, such as high efficiency, near unity power factor, low total harmonic distortion, and relatively few diodes. A 100-W lab prototype is successfully implemented, and the experimental results verify the effectiveness and feasibility of the proposed LED driver. [ABSTRACT FROM AUTHOR]

Transformer-less grid-connected photovoltaic (PV) systems face the challenge of keeping low leakage current due to their nonisolation configurations. To better attenuate the leakage current in the single-phase systems, a few neutral-point-clamped (NPC) topologies have been proposed. This paper further proposes an active NPC method by only employing one additional switch to connect the midpoint dc link and the freewheeling circuit of traditional single-phase PV inverters. After exploring the operational principles of freewheeling circuits, the construction method and the implementation of active NPC circuits in transformer-less single-phase inverters are elaborated in detail. Since only the leakage current flows through the additional NPC switch, the presented single-phase NPC inverters could still maintain the high operational efficiency with the further attenuated leakage current. The experimental results verified the theoretical findings. [ABSTRACT FROM PUBLISHER]

In order to increase the output voltage levels and reduce the isolated dc sources, a symmetrical hybrid nine-level inverter for high-speed motor drive applications is presented in this paper. Each phase of this inverter is composed of a five-level dc/dc converter cell and an H-bridge cell. The dc/dc converter is operated at high frequency with low-voltage devices and the H-bridge is operated at fundamental frequency with high-voltage devices. The three phases are connected to a common dc-link and each drives an isolated winding of an open-winding motor. The operating principles and modulation method are introduced. A detailed analysis of the average currents through the flying capacitor and neutral point of the dc-link is presented and a capacitor voltage balancing method based on phase-shifted pulse-width modulation is proposed. Simulation and experimental results are presented to demonstrate the feasibility of this topology and control method. [ABSTRACT FROM PUBLISHER]

Boost-derived hybrid converter (BDHC) is a single-stage converter that produces both dc and ac output voltages. The operation of BDHC under continuous conduction mode is satisfactory. However, the nonzero discontinuous conduction mode (NZ-DCM) and standalone ac operation restrict the stable operation of the converter. To mitigate these limitations, modified BDHC (MBDHC) is proposed in this paper. The main idea behind these changes is to redeem NZ-DCM by forced continuous conduction mode (FCM). The adverse effect of NZ-DCM in a BDHC is analyzed in terms of ac output voltage total harmonic distortion, and dc output voltage ripple. This analysis is further extended for MBDHC to highlight the benefits of FCM. Moreover, for hybrid loads, the efficiency of MBDHC is compared with its counterpart BDHC and cascaded boost inverter. [ABSTRACT FROM PUBLISHER]

A novel hybrid five-level voltage-source converter for high-efficiency applications is investigated in this paper. Compared with traditional multilevel converters, this hybrid multilevel converter generates desired staircase voltage levels with a reduced number of power devices and isolated drivers at higher voltage levels. It has redundant switching state combinations in hybrid multilevel converter, which makes it easy to balance flying capacitor voltages and realize fault-tolerant operation. A voltage-balancing control strategy based on switching state redundancies is presented for the hybrid multilevel converter to generate desired levels and also keep voltage balance of flying capacitors at the same time. The performance of the hybrid multilevel converter under various operating conditions is investigated in MATLAB/Simulink. The effectiveness of the proposed hybrid multilevel converter is validated by experiment results. [ABSTRACT FROM AUTHOR]

Three-phase inverters in uninterrupted power supply, electric vehicles, and hybrid electric vehicles use an intermediate dc-link electrolytic capacitor, which has reliability issues and is one prominent cause of inverter failure and limited life. The large volume of an electrolytic capacitor increases the size and cost of the system. Recent research on electrolytic capacitorless inverters using six-pulse modulation technique along with high-frequency power conversion has attempted to address this issue. However, closed-loop operation and control has some issues due to capacitorless dc-link. In this paper, closed-loop operation, design, and implementation of an electrolytic capacitorless inverter is presented. A proof-of-concept 1-kW hardware prototype has been built and tested in a laboratory under different loading conditions. In total, 98% rated efficiency of the inverter is obtained with total harmonic distortion within 2%. Transient results during start-up and load change are smooth, demonstrating safe operation of the inverter. [ABSTRACT FROM AUTHOR]

The hybrid modular multilevel converter with cascaded full bridges (HMMC-CFB) is a recently proposed dc fault tolerant converter topology for high-power applications. It has a director part (DP) consisting of a series of connected half-bridge submodules, and a wave-shaping part (WSP) composed of a series of connected full-bridge submodules (FBSMs). The submodules in DP avoid high voltage stresses and improve synchronization between DP and WSP by slowing down the change rate of DP output voltage. This slowdown is achieved by using a trapezoidal reference signal for DP. The WSP attenuates the voltage harmonics produced by DP. However, the energy exchanged by WSP changes with modulation index, which may cause improper voltage regulation of the submodule capacitors. This paper proposes a new control technique to regulate the energy exchanged by WSP, which uses a variable slope trapezoidal reference signal of DP. To obtain this slope, the feedforward and feedback controllers are used. The feedforward controller gives the value of slope depending on the modulation index (mv) to keep the energy exchanged by WSP nearly equal to zero, whereas the losses and nonideality of the converter are taken care of by the feedback controller. This technique guarantees proper voltage regulation of the submodule capacitors for all modulation indices. The efficacy of the proposed technique is confirmed using simulations and experimentations. This paper also presents a circulating current suppressing controller for HMMC-CFB. The proposed control schemes and dc fault tolerant capability of HMMC-CFB are tested on a grid-connected model built in PSCAD. [ABSTRACT FROM AUTHOR]

This paper proposes and analyzes a new power electronics circuit topology for wireless inductive power transfer application using current-fed half-bridge converter with CCL-LC resonant network. The major focus is analysis and implementation of a new current-fed resonant topology with current-sharing and voltage doubling features. Generally, inductive power transfer circuits with current fed converter use parallel CL resonant tank to transfer power effectively through air gap. However, in medium power application, this topology suffers from a major limitation of high voltage stress across the inverter semiconductor devices owing to high reactive power consumed by loosely coupled coil. In proposed topology, this is mitigated by adding a capacitor in series with the coil developing series-parallel CCL tank. The power flow is controlled through variable frequency modulation. Soft-switching of the devices is obtained irrespective of the load current. For grid-to-vehicle or solar-to-vehicle, the converter is analyzed and detailed design procedure is illustrated. Experimental results are presented to verify the analysis and demonstrate the performance. [ABSTRACT FROM AUTHOR]

For the high-voltage direct-current (HVDC) power transmission system of offshore wind power, dc/dc converters are the potential solution to collect the power generated by off-shore wind farms to HVDC terminals. The converters operate with high-voltage gain, high efficiency, and fault tolerance over a wide range of operating conditions. In this paper, an isolated ultrahigh step-up dc/dc converter with a scalable modular structure is proposed for HVDC offshore wind power collection. A flyback-forward converter is employed as the power cell to form the expandable electrically isolated modular dc/dc converter. The duty ratio and phase-shift angle control are also developed for the proposed converter. Fault-tolerant characteristics of the converter are illustrated through the redundancy operation and fault-ride-through tests. Redundancy operation is designed to maintain high operation efficiency of the converters and fault-ride-through operation improves the converter reliability under harsh operating conditions. Analytical studies are carried out, and a 750-W prototype with three modular cells is built and experimentally tested to verify the performance of the proposed modular dc/dc converter. [ABSTRACT FROM AUTHOR]

This paper proposes a multilevel series compensator (MSC) to deal with voltage sags/swells, harmonic compensation, or reactive power compensation. Such a device can be considered as a dynamic voltage restorer or a series active power filter (Series-APF). The MSC can improve the power quality of loads located in stiff systems. The configuration is based on three-phase bridge (TPB) converters connected by means of cascaded single-phase transformers. This arrangement permits the use of a single dc-link. A generalization for $K$ -stages in which $K$ -transformers are coupled with $K$-TPB converters is presented. The topology permits generating a high number of levels in the voltage waveforms with a low number of power switches in comparison with a classic topology. The multilevel waveforms are generated by the converters through a suitable pulsewidth modulation (PWM) strategy that takes into consideration the transformer turns ratios. Modularity and simple maintenance make the proposed MSC an attractive solution compared with some conventional configurations. Model, PWM strategy, and overall control are discussed in this paper. Simulation and experimental results are presented as well. [ABSTRACT FROM PUBLISHER]

This paper proposes an isolated universal-link ac–ac power converter suitable for grid connection. The proposed power converter can have multiple ports to connect various loads or electric energy sources, and the configuration can be arranged according to the situation. The proposed power converter does not need to employ the large interface inductor at input side and the huge electrolytic capacitor at dc link. Moreover, it utilizes high-frequency transformers for the galvanic isolation instead of bulky line-frequency transformers. These characteristics of the proposed power converter result in the reduction of the system volume and weight remarkably. The proposed power converter is the modular structure, and an H-bridge works as a basic module of the converter. By stacking the modules, the power converter can be adapted to the high-voltage grid and the various types of loads and/or sources. This paper addresses the structure of the proposed power converter and the fundamental principle of power flow. The operation of the proposed converter is verified by both computer simulations and experimental results with a laboratory-level prototype system. [ABSTRACT FROM AUTHOR]

Recently multilevel inverters (MLIs) have received wide attention from industry and academia, as they are changing into a viable technology for diverse applications. To produce high-quality output using less switch count, development of novel reduced switch MLI (RS MLI) topologies has been a focus of current research theme. This paper presents design and control of a switched-diode dual source single switch MLI (SDDS MLI). The generalized SDDS MLI is first designed using an asymmetric basic unit. Proposed SDDS MLI requires less switch count and driver circuit count compared with the few recently developed RS MLI topologies. To improve the voltage quality by eliminating targeted low-order harmonics, a modified version of fish swarm optimization algorithm is examined for computing optimum switching angles required to control the SDDS MLI. Moreover, suitability and superiority of the derived algorithm are established by comparing with traditional selective harmonic elimination techniques. The developed topology is investigated through several MATLAB simulations as well as experimental tests in the laboratory applying the modified control approach. [ABSTRACT FROM AUTHOR]

The fault-tolerant multilevel converters are gaining increased interests for high-voltage direct current (HVDC) applications due to their ability to suppress the fault current during dc-side faults. However, most of these topologies use full-bridge submodules (FBSMs) resulting in the requirement of a large number of semiconductor switches. In this paper, a new generalized cross-connected SM (GX-SM) structure is presented, which requires lesser number of switching devices and provides the same functionality as the FBSM. A comparison of the switches required in the different converter topologies using FBSMs and GX-SMs is performed. The performance evaluation of two of the dc-side fault-tolerant converter topologies, namely alternate arm modular multilevel converter (AAMMC) and hybrid cascaded modular multilevel converter (HCMC) with the GX-SM, is performed using simulation studies done in PSCAD/EMTDC. The modulation and control schemes for these GX-SMs-based converters are presented. A new mixed-SM configuration of AAMMC is proposed which utilizes an optimal combination of GX-SMs and half-bridge SMs. The study results demonstrate the effectiveness of the proposed GX-SM structure, and satisfactory responses of the GX-SMs-based AAMMC and HCMC systems controlled using the presented modulation and control strategies under various system conditions. [ABSTRACT FROM PUBLISHER]

This paper proposes three dynamic voltage restorer (DVR) topologies. Such configurations are able to compensate voltage sags/swells in three-phase four-wire (3P4W) systems under balanced and unbalanced conditions. The proposed systems use two independent dc links. Proposed configurations present advantages in terms of switch blocking voltages and consequently lower dc-link voltage rating. The complete control system, including the pulsewidth modulation (PWM) technique, is developed, and comparisons between the proposed configurations and a conventional one are performed. Simulation and experimental results are provided to validate the theoretical approach. [ABSTRACT FROM AUTHOR]

This paper presents an isolated auxiliary power supply for medium-voltage power electronics systems. The proposed converter comprises two stages: a non-isolated ac/dc stage that connects directly to the medium-voltage line, and an isolated dc/dc stage that provides 100-W output power at 24 V, with 10 kV isolation. The proposed modular ac/dc stage uses just one active semiconductor device per module, features an internal capacitor voltage balancing, and achieves power factor correction by employing predictive current control. High switching frequency operation of both converter stages enable a reduction in system size and weight when compared to traditional low-frequency transformer-based approach. The proposed converter is simulated and its operation is validated experimentally on a 100-W prototype. [ABSTRACT FROM AUTHOR]

This paper presents the development, analysis, and performance evaluation of a new topology for an isolated dc power electronic converter (PEC). The proposed topology (called the reverse flyback dc PEC) is developed to process a discontinuous input voltage and produce a continuous output voltage. The reverse flyback dc PEC is operated based on charging the inductive element in the high-frequency transformer, while discharging the energy to the output side through on–off actions of the switching element, which is located on the secondary side of the high-frequency transformer. A prototype for the proposed reverse flyback dc PEC is constructed to evaluate its performance under different operating conditions. Performance results show that the reverse flyback dc PEC is capable of processing discontinuous input voltages with different duty ratios and maintaining continuous output voltages with a minor sensitivity to the load type of ratings. [ABSTRACT FROM AUTHOR]

A switching-capacitor-based buck–boost converter (with common ground) for point of load applications is proposed in this paper. It is capable of operating in stand-alone buck or boost mode in addition to its primary operation of performing the buck–boost conversion. The striking feature of the proposed converter is low source current ripple content irrespective of its mode of operation (buck–boost, buck, or boost). First, feasible pulsewidth modulation schemes for the proposed converter are identified and thereafter the corresponding circuit performance analysis, steady-state analysis, and state-space modelling is established. Through steady-state analysis, voltage gain expressions are formulated and equations defining L-C components are derived in terms of their ripple quantities. The state-space models are used to formulate small-signal analysis and to obtain the relevant transfer functions required in the controller design. A voltage-mode/current-mode controller is designed, with a tradeoff in bandwidth, to control the proposed converter and transit it from buck to boost mode or vice versa seamlessly. A 30–55 W, 100 kHz, prototype point of load converter with 36-V input dc source is built to supply power at constant load voltage of either 48 or 28 V. The proposed converters’ effectiveness is demonstrated experimentally in terms of reduced source current ripple along with seamless transition from buck to boost mode and vice versa. [ABSTRACT FROM AUTHOR]

A single-stage offline power supply for LED lighting applications, based on the integration of a buck power factor corrector (PFC) and a tapped buck dc/dc converter, is presented in this paper. In addition to the high step-down capability and the output current regulation, the proposed topology effectively provides PFC to comply with the harmonic injection and energy-saving standards EN 61000-3-2 and Energy Star. The low bus voltage level, resulting from the use of an input step-down PFC stage, actually allows the use of film technology capacitors, instead of short lifetime electrolytic capacitors, to filter the bus voltage and reduce the LED current ripple component at twice the line frequency. Due to the high reliability, the simple structure, the good line-side spectral performance, and the low component count, the proposed topology effectively results to be very suitable for medium-power solid-state lighting applications, as in the case of LED downlighting. The issues related to the operation of the presented solution and to its design optimization will be carefully discussed. A prototype of the proposed ac/dc converter has been built and tested. The main experimental results will be described. [ABSTRACT FROM PUBLISHER]

This paper presents a dual-purpose offline LED driver with illumination control and visible light communications (VLC). LEDs, due to their nonlinear $I$– $V$ characteristics, are driven by constant current sources. The proposed dual-purpose offline LED driver realizes a constant current source by a buck converter without a capacitor using average current mode control. VLC is implemented through variable pulse position modulation scheme using a shunt switch in parallel to LED string. Conventional LED drivers are typically designed to perform illumination control with pulsewidth modulation (PWM) dimming at low frequencies ( $<$ 20 kHz), which results in audible noise due to the mechanical vibrations of inductors and piezoelectric properties of ceramic capacitors. The proposed converter presents an illumination control with PWM dimming frequencies above the audible range. The detailed control and modeling of the proposed dual-purpose LED driver using high-frequency model of LED string is discussed. The effects of the phosphor on phosphor-based white LEDs for VLC are reported. The proposed driver is experimentally evaluated on 110/120 ac mains with 450-lm output. The linear characteristics of PWM dimming for data transfer of 2 Mb/s are demonstrated. Detailed simulation and experimental results to validate the operation of the proposed converter are presented. [ABSTRACT FROM AUTHOR]

In this paper, a fifth-order boost point-of-load converter is developed by cascading a modified fourth-order boost converter with a combination of L–C and diode. This topology has the following salient features: Single-switch topology, common ground between source and load, low-voltage stress across intermediate capacitors, and voltage gain same as other reported fifth-order boost converters with no common ground. Steady-state and dynamic analyses demonstrate the proposed converter's boosting feature and dynamic performance, respectively. A contoured robust Bode plot methodology is employed to design the robust voltage-mode controller to ensure load voltage regulation in the presence of uncertainties. The necessary and sufficient conditions under which the designed controller guarantees the load voltage regulation and robust stability are obtained. A step-by-step robust controller design procedure is outlined. The salient features of the proposed converter and its robust performance are studied analytically, using the MATLAB platform, and validated experimentally on a 60-W prototype module. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents a new nonisolated buck/boost-type multilevel dc–dc converter suitable for high-power and medium/high-voltage application. The main features of the proposed topology are as follows: low voltage across the semiconductors, low switching losses, and reduced volume of the output filter. The theoretical analysis is carried out for a five-level bidirectional structure of the proposed converter, operating in Buck mode. The proposed topology presents some capacitors, and their voltage must be balanced for proper operation of the converter. Thus, a capacitor voltage balancing active control using a feedforward technique is proposed and analyzed in detail. In order to validate the theoretical analysis, a prototype with 10 kW output power capability, 1.3 kV to 800 V input-to-output voltage, and 20 kHz of switching frequency was built and experimented. The results attest the advantages of the new dc–dc topology, as well as the new capacitor voltage control technique. [ABSTRACT FROM AUTHOR]

This article presents a new hybrid three-phase cascaded modular multilevel inverter developed with a reduced switch count concept for harvesting renewable energy. The basic module of the proposed inverter consists of six switches, three asymmetric dc links, and two blocking diodes. The inverter can generate six positive voltage states, which are negatively polarized by the end-side H-bridge unit. As a result, a higher number of voltage levels are obtained with a minimum number of switches that ensure reduced total harmonic distortion in the grid current. Additionally, the proposed inverter can operate at a comparatively lower switching frequency, which decreases the switching losses. Most of the switches in each individual module conduct for a small period resulting in low conduction losses. The reduced switch count with the low switching and conduction losses increases the compactness and the efficiency of the proposed inverter. Multiple high-frequency magnetic links are utilized for the dc sources required for the proposed inverter to achieve inherent dc-link voltage balancing ability and galvanic isolation. The performance of the proposed inverter is validated by simulation and experimental investigations. [ABSTRACT FROM AUTHOR]

This paper presents a novel topology for a nonisolated bidirectional dc–dc converter with soft-switching capabilities, which usually operates at a zero-voltage-switching (ZVS) condition. A nonisolated dc–dc converter combines a buck converter and a backward boost converter into one circuit, which consists of a half-bridge power switch, an inductor, and capacitors. In order to realize ZVS conditions, the proposed converter utilizes a coupled inductor, a small independent inductor, and auxiliary switches and diodes. Due to ZVS, switching stress on switch components is reduced, and the reverse recovery problem of MOSFET antiparallel body diodes is also eliminated. Moreover, the operating modes of the proposed converter can be switched between a ZVS mode and a conventional hard-switching mode on the basis of load conditions. The soft-switching mode is for heavy loads, and the hard-switching mode is for light-load conditions. Therefore, the highest efficiency can be obtained at almost all load ranges. The detailed theoretical analyses in each mode are presented, and a 1-kW prototype is also built to verify the principle of the circuit and the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper reports an elegant approach to address two major challenges of transformerless grid-connected microinverters, common-mode earth leakage current and double-frequency power pulsation across the photovoltaic (PV) terminal. The proposed solution uses an embedded decoupling capacitor in a doubly grounded boost–buck ( $\acute{\mathrm{C}}$ uk) derived topology. An intelligent switching scheme ensures that a large swing of the decoupling capacitor voltage is easily accommodated. Thus, film capacitors can be used instead of electrolytic capacitors, which helps increase equipment lifetime. Details of circuit operation are provided along with dynamic modeling and controller design for close-loop operation. Simulation and experimental results are presented for performance validation of the microinverter. [ABSTRACT FROM AUTHOR]

This paper proposes a new high-gain soft-switching dc–dc topology based on a switched inductor boost converter (SIBC). A conventional SIBC as a high gain boost topology has the issues of high conduction loss in switching diodes and high switching loss in the main switches. Also, it has severe electromagnetic interference (EMI) issue due to high-frequency ringing formed by parasitic inductance and diode junction capacitors. The new topology is derived with the objective of achieving zero voltage switching (ZVS) turn on of the main switch. Instead of adding extra active clamp zero voltage transition (ZVT) path at the switching node, the proposed topology augments the auxiliary ZVT path to the switching diode path. This is achieved by replacing the switching diodes with synchronous switches. The new topology can achieve soft switching for all the switches and alleviate the EMI issue. All the diodes achieve zero current switching (ZCS) turn off without reverse recovery. Auxiliary switches have ZCS turn on and ZVS turn off, and the main switches have ZVS turn on. The soft-switching SIBC also reduces the conduction loss in the switching diodes. A numerical simulation in PLECS and a prototype hardware are built corresponding to a micro-inverter application with 100 kHz switching frequency. Peak power conversion efficiency of 94.76% is achieved in the hardware prototype with Si devices. [ABSTRACT FROM PUBLISHER]

In this paper, a hybrid bidirectional dc–dc converter is presented, which is a combination of a switched-capacitor converter and an inductor-based converter with low component counts. The input current ripple and peak charging current are small with the help of the inductor. The proposed converter is applicable in the battery charge/discharge systems, such as the distributed renewable energy systems, battery equalizer, auxiliary power supplies, traction drive system, and dual-voltage automotive systems based in new electrical architecture concept, where common ground is not required and within the voltage-gain range of 2–6. A comprehensive analysis of the steady-state operation, small-signal model, and component stress is given. The comparison with an alternative topology shows the advantages of low component counts, low total capacitor voltage stress, low inductor current, and low total active switch stress for the 42/14 V voltage level. A 42/14 V prototype rated at 20–120 W with a peak efficiency of 97.8% in boost mode and 97.62% in buck mode was built to verify the analysis. [ABSTRACT FROM AUTHOR]