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Power Electronics, IEEE Transactions on

Issue 8 • Date Aug. 2014

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Displaying Results 1 - 25 of 57
  • Table of Contents

    Page(s): C1 - C4
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    Freely Available from IEEE
  • IEEE Transactions on Power Electronics publication information

    Page(s): C2
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    Freely Available from IEEE
  • Editorial: Special Issue on High-Frequency-Link Power-Conversion Systems, 2014

    Page(s): 3849 - 3851
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  • A Review of High-Frequency Power Distribution Systems: For Space, Telecommunication, and Computer Applications

    Page(s): 3852 - 3863
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2012 KB) |  | HTML iconHTML  

    High-frequency AC (HFAC) power distribution systems have been the subject of great interest over the last several decades. This paper presents a thorough review of different HFAC power distribution architectures on which the authors have worked in the last 30 years. The review is focused on the HFAC power architectures and topologies for space, telecommunications, and computer applications. Detail of each architecture is given and evaluated in terms of performance specific to each application. View full abstract»

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  • A Load-Power Adaptive Dual Pulse Modulated Current Phasor-Controlled ZVS High-Frequency Resonant Inverter for Induction Heating Applications

    Page(s): 3864 - 3880
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (17637 KB) |  | HTML iconHTML  

    A new prototype of an efficiency-improved zero voltage soft-switching (ZVS) high-frequency resonant (HF-R) inverter for induction heating (IH) applications is presented in this paper. By adopting the dual pulse modulation mode (DPMM) that incorporates a submode power regulation scheme such as pulse density modulation, pulse frequency modulation, and asymmetrical pulse width modulation into main one of the resonant current phase angle difference ( θ) control, the IH load power can be widely regulated under the condition of ZVS, while significantly improving the efficiency in the low output power setting. The essential performances on the output power regulations and ZVS operations with the DPMM schemes are demonstrated in an experiment based on a 1 kW-60 kHz laboratory prototype of the ZVS HF-R inverter. The validity of each DPMM scheme is originally compared and evaluated from a practical point of view. View full abstract»

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  • Design and Implementation of Three-Phase Two-Stage Grid-Connected Module Integrated Converter

    Page(s): 3881 - 3892
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2006 KB) |  | HTML iconHTML  

    Module integrated converters (MICs) in single phase have witnessed recent market success due to unique features such as improved energy harvest, improved system efficiency, lower installation costs, plug-and-play operation, and enhanced flexibility and modularity. The MIC sector has grown from a niche market to mainstream, especially in the United States. Assuming further expansion of the MIC market, this paper presents the microinverter concept incorporated in large size photovoltaic (PV) installations such as megawatts (MW)-class solar farms where a three-phase ac connection is employed. A high-efficiency three-phase MIC with two-stage zero voltage switching (ZVS) operation for the grid-tied PV system is proposed which will reduce cost per watt, improve reliability, and increase scalability of MW-class solar farms through the development of new solar farm system architectures. The first stage consists of a high-efficiency full-bridge LLC resonant dc-dc converter which interfaces to the PV panel and produces a dc-link voltage. A center points iteration algorithm developed specifically for LLC resonant topologies is used to track the maximum power point of the PV panel. The second stage is comprised of a three-phase dc-ac inverter circuit which employs a simple soft-switching scheme without adding auxiliary components. The modeling and control strategy of this three-phase dc-ac inverter is described. Because the dc-link capacitor plays such an important role for dual-stage MIC, the capacitance calculation is given under type D voltage dip conditions. A 400-W prototype was built and tested. The overall peak efficiency of the prototype was measured and found to be 96% with 98.2% in the first stage and 98.3% in the second stage. View full abstract»

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  • A Soft-Switched Hybrid-Modulation Scheme for a Capacitor-Less Three-Phase Pulsating-DC-Link Inverter

    Page(s): 3893 - 3906
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2543 KB) |  | HTML iconHTML  

    A soft-switched hybrid-modulation (HM) scheme is outlined for a dc-link-capacitor-less three-phase high-frequency (HF) pulsating-dc link (PDCL) isolated multistage inverter. The overall inverter comprises a front-end isolated dc/pulsating-dc converter followed by a pulsating-dc/ac converter. Because the two stages are directly connected without a dc-link capacitor, the intermediate link is a PDCL instead of a fixed-dc link as in conventional HF-link inverters. The HM modulates the pulsating-dc/ac converter such that, two of its converter legs are line-switched, while the third leg of the pulsating-dc/ac converter is switched under zero-voltage-switching condition. This is achieved by first modulating the dc/pulsating-dc converter to achieve a specific encoding of the PDCL signal, which in turn, is exploited by the modulation scheme of the pulsating-dc/ac converter to mitigate its switching loss without requiring any auxiliary circuit. Operation of the pulsating-dc/ac converter using the soft-switched HM scheme is validated using a prototype 1 kW, 72-V (dc)/208-V (ac) HF inverter. View full abstract»

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  • A High-Frequency Link Single-Stage PWM Inverter With Common-Mode Voltage Suppression and Source-Based Commutation of Leakage Energy

    Page(s): 3907 - 3918
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1861 KB) |  | HTML iconHTML  

    This paper presents a single-stage bidirectional high-frequency transformer (HFT) link dc/ac converter topology for a three-phase adjustable magnitude and frequency PWM ac drive. This type of converters find a wide range of applications including UPS systems, drives involving renewable energy sources (Solar, Fuel cell), and energy storage systems (typically low voltage dc to high voltage PWM ac). The HFT results in reduction in cost and weight along with a considerable increase in power density. The adverse effects of common-mode voltage are well known in this kind of applications. The proposed topology along with a modulation technique reduces common-mode voltage to practically zero and generates high-quality output voltage waveform comparable to conventional space vector PWM (CSVPWM). A source-based commutation method, presented in this paper, to commute the energy stored in the leakage inductance of the HFT resulting in the following advantages 1) no need for any auxiliary circuits with passive components; 2) almost complete recovery of the leakage energy; 3) soft switching of the output side converter for all load conditions; and 4) minimization of common-mode voltage switching due to commutation. The converter along with the suggested control has been analyzed in detail. The presented simulation and experimental results confirm the operation of the proposed converter. View full abstract»

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  • Single-Stage Multistring PV Inverter With an Isolated High-Frequency Link and Soft-Switching Operation

    Page(s): 3919 - 3929
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1334 KB) |  | HTML iconHTML  

    A grid-tied multistring photovoltaic (PV) inverter with a high-frequency ac (HFAC) link, soft-switching operation, and high-frequency (HF) galvanic isolation is introduced. This single-stage topology can handle an arbitrary number of PV strings with different electrical parameters, locations, and orientations. Using a dedicated maximum power point tracker for each PV string, this inverter can harvest the highest possible power from each string independently, even though they might be at dissimilar irradiance levels and operating temperatures. The isolated HFAC link is formed by the magnetizing inductance of a small-sized HF transformer and two small ac capacitors without the use of bulky short-life electrolytic capacitors. The link is responsible for transferring the PV strings' power to the grid along with creating zero-voltage switching for the power devices. Therefore, the converter has the advantages of high power density, high reliability, as well as high efficiency. After describing the control scheme and the operating algorithm of the proposed multistring inverter, a detailed analysis is carried out. The experimental results of the developed 1-kW two-string prototype with different PV strings at various PV conditions are also shown. The results verify the effectiveness of the topology in tracking the maximum power of each string independently without affecting the operating condition and control of the other string. View full abstract»

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  • A Comparison Study of High-Frequency Isolated DC/AC Converter Employing an Unfolding LCI for Grid-Connected Alternative Energy Applications

    Page(s): 3930 - 3941
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3161 KB) |  | HTML iconHTML  

    A high-frequency (HF) isolated dc/ac converter including an unfolding line connected inverter can be used as the interface between a small-scale alternative energy generation system and the utility line. This paper presents the review of operation of several different topologies of HF isolated dc/ac converters. They are designed for illustration purpose and compared for their performance. It is found that the dual-LCL series resonant dc/ac converter can maintain zero-voltage switching (ZVS) operation for all switches with low line-current total harmonics distortion (THD) and high efficiency. Experimental results on a 500-W prototype converter are included for validation purpose. View full abstract»

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  • Sparse AC-Link Buck–Boost Inverter

    Page(s): 3942 - 3953
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1680 KB) |  | HTML iconHTML  

    Due to their remarkable merits, the soft-switching ac-link universal power converters have received noticeable attention during the last few years. These converters, which can be configured as dc-dc, dc-ac, ac-dc, or ac-ac, are compact, reliable, and offer longer life time compared to the other types of converters. However, they require more switches, which make the control process more complicated. This paper proposes a modified configuration for the dc-ac power conversion, which reduces the number of switches without changing the principles of operation. This converter, which is named sparse ac-link buck-boost inverter, reduces the number of switches from 20 to 18. Despite reducing the number of switches, the partial resonant time, during which no power is transferred, is as short as the original configuration. An important feature of this inverter is that it can be fabricated by IGBT modules, which are more compact and more cost-effective compared to the discrete devices. This paper presents the principles of the operation of this configuration, and compares the efficiency, the failure rate, and the current rating of the switches in the proposed and original inverters. It is shown that the failure rates of the sparse configuration are lower than the original configuration. Therefore, they have longer lifetime. The efficiency of the sparse configuration is slightly lower than that of the original configuration. However, by using reverse blocking IGBTs in the sparse configuration, the efficiency of the proposed inverter will be improved significantly. This paper evaluates the performance of the proposed inverter through simulation and experiment. View full abstract»

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  • Optimal ZVS Modulation of Single-Phase Single-Stage Bidirectional DAB AC–DC Converters

    Page(s): 3954 - 3970
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4190 KB) |  | HTML iconHTML  

    A comprehensive procedure for the derivation of optimal, full-operating-range zero voltage switching (ZVS) modulation schemes for single-phase, single-stage, bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. The converter topology consists of a DAB dc-dc converter, receiving a rectified ac line voltage via a synchronous rectifier. The DAB comprises primary and secondary side full bridges, linked by a high-frequency isolation transformer and a series inductor. ZVS modulation schemes previously proposed in the literature are either based on current-based or energy-based ZVS analyses. The procedure outlined in this paper for the calculation of optimal DAB modulation schemes (i.e., combined phase-shift, duty-cycle, and switching frequency modulation) relies on a novel, more accurate, current-dependent charge-based ZVS analysis, taking into account the amount of charge that is required to charge the nonlinear parasitic output capacitances of the switches during commutation. Thereby, the concept of “commutation inductance(s)” is shown to be an essential element in achieving full-operating-range ZVS. The proposed methods are applied to a 3.7 kW, bidirectional, and unity power factor electric vehicle battery charger which interfaces a 400 V dc-bus with the 230 Vac, 50-Hz utility grid. Experimental results obtained from a high-power-density, high-efficiency converter prototype are given to validate the theoretical analysis and practical feasibility of the proposed strategy. View full abstract»

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  • Power Electronic Traction Transformer: Efficiency Improvements Under Light-Load Conditions

    Page(s): 3971 - 3981
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4388 KB)  

    Power electronic transformer (PET), a converter technology that utilizes power semiconductors in combination with medium-frequency transformers, is considered a promising solution for certain applications requiring flexible galvanic isolation. Among are those where space occupied by bulky low-frequency transformers is of concern and/or where advanced power quality control features are needed. In this paper, the PET for a single-phase traction on-board application is discussed with emphasis on the efficiency improvements and reductions of energy consumption during the operation on the vehicle. Several control algorithms devised to improve efficiency under light-load conditions are tested on a low-voltage prototype of the PET, and experimental results are presented demonstrating the effectiveness of the proposed algorithms. View full abstract»

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  • Design and Demonstration of a 3.6-kV–120-V/10-kVA Solid-State Transformer for Smart Grid Application

    Page(s): 3982 - 3996
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1517 KB) |  | HTML iconHTML  

    Solid-state transformer (SST) has been regarded as one of the most important emerging technologies for traction system and smart grid application. This paper presents the system design and performance demonstration of a high-voltage SST lab prototype that works as the active grid interface in smart grid architecture. Specifically, the designs of the key components of the system, including both power stage and controller platform, are presented. In addition, the advanced control system is developed to achieve high-performance operation. Furthermore, integration issues of SST with dc microgrid are presented. Lastly, tests under different scenarios are conducted to verify the following advanced features of the presented SST technology: 1) VAR compensation; 2) voltage regulation; 3) source voltage sag operation; and 4) microgrid integration. View full abstract»

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  • Design and Implementation of a Two-Stage Grid-Connected High Efficiency Power Load Emulator

    Page(s): 3997 - 4006
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1499 KB) |  | HTML iconHTML  

    The need to reduce the time consumption in developing and implementing power converters, and to improve the effectiveness of the test equipment, continues to grow. This trend is further accelerated through the development of electricity-based technology, such as the electric or hybrid vehicle. As the price of energy continues to increase, regenerative test equipment used for validating power converters are gaining importance and attention. This paper focuses on the development of a two-stage regenerative power load emulator. This type of intelligent load requires a connection to the network interface, which, for some applications, should be bidirectional and must possess a galvanic isolation. The development of such grid-connected unit that processes ac-dc conversion is treated in this paper. A 5 kW prototype is used as a base to model, simulate, design, implement, and test such a system. The stability of the interconnection between the two conversion stages is established and tested in real-time applications. The prototype was tested at 180, 220, and 260 V RMS. The measured efficiency is higher than 90%, and the power factor is 0.99 over a wide range of operation. View full abstract»

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  • A Single-Stage Dual-Active-Bridge-Based Soft Switched AC–DC Converter With Open-Loop Power Factor Correction and Other Advanced Features

    Page(s): 4007 - 4016
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1029 KB) |  | HTML iconHTML  

    A dual-active-bridge-based single-stage ac/dc converter may find a wide range of emerging applications such as interfacing plug-in hybrid vehicles with the ac grid, interconnection of dc grid, etc. This type of converter can be used due to unique features such as 1) high-frequency isolation resulting in a) high power density and b) safety and voltage matching; 2) bidirectional power flow; 3) soft switching leading to higher efficiency. In this paper, a modulation strategy has been proposed that results in 1) open-loop power factor correction; 2) zero current switching in the ac-side converter for all load conditions; 3) linear power relationship for easy control implementation; and 4) Zero voltage switching in the load side converter. The converter with the proposed control has been analyzed. Simulation and experimental results on a 1-KW prototype confirm the advantages. View full abstract»

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  • The High-Efficiency Isolated AC–DC Converter Using the Three-Phase Interleaved LLC Resonant Converter Employing the Y-Connected Rectifier

    Page(s): 4017 - 4028
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2572 KB) |  | HTML iconHTML  

    The power conversion efficiency of an isolated ac-dc converter is a dominant factor in the overall efficiency of dc distribution systems. To improve the power conversion efficiency of the dc distribution system, a three-phase interleaved full-bridge LLC resonant converter employing a Y-connected rectifier is proposed as the isolated ac-dc high-frequency-link power-conversion system. The proposed Y-connected rectifier has the capability of boosting the output voltage without increasing the transformer's turn ratio. Especially, the frequency of the rectifier's output ripple is six times higher than the switching frequency, thereby reducing the output capacitor and the secondary transformer's RMS current. However, the tolerance of the converter's resonant components in each primary stage causes the unbalance problem of output ripple current. It cannot be solved using conventional control techniques since the structure of the three-phase interleaving has the limitations of individual control capability for each converter. To solve the current unbalance problem, a current balancing method is proposed for the output rectifying current. The performance of the proposed converter and the current balancing method has been verified through experiments using a 10 kW (300 V/33.3 A) prototype converter. View full abstract»

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  • A SiC-Based Matrix Converter Topology for Inductive Power Transfer System

    Page(s): 4029 - 4038
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1857 KB) |  | HTML iconHTML  

    Typical inductive power transfer (IPT) systems employ two power conversion stages to generate a high-frequency primary current from low-frequency utility supply. This paper proposes a matrix-converter-based IPT system, which employs high-speed SiC devices to facilitate the generation of high-frequency current through a single power conversion stage. The proposed matrix converter topology transforms a three-phase low-frequency voltage system to a high-frequency single-phase voltage, which, in turn, powers a series compensated IPT system. A comprehensive mathematical model is developed and power losses are evaluated to investigate the efficiency of the proposed converter topology. Theoretical results are presented with simulations, which are performed in MATLAB/Simulink, in comparison to a conventional two-stage converter. Experimental evident of a prototype IPT system is also presented to demonstrate the applicability of the proposed concept. View full abstract»

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  • Design and Test of a 35-kJ/s High-Voltage Capacitor Charger Based on a Delta-Connected Three-Phase Resonant Converter

    Page(s): 4039 - 4048
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1783 KB) |  | HTML iconHTML  

    This paper describes the design, implementation, and analysis of a 35 kJ/s high-voltage capacitor charger based on a delta-connected three-phase series resonant converter that provides a constant charging current with high efficiency and high-power density. In order to obtain the maximum output power for various charging voltages, each high-voltage transformer supplied by a delta-connected resonant inverter is designed with two secondary windings and voltage-doubled rectifiers. This configuration allows not only a flexible output current and voltage with fixed output power but also a high power factor on the input side. On the basis of the analysis of the series-loaded resonant converter operating at a discontinuous conduction mode, the details of the design procedure for the resonant inverter are provided. Furthermore, the implementation of the high-voltage transformers and rectifiers is also explained while considering insulation and compactness. Experiments were carried out on the developed charger with different types of capacitors, depending on their applications, and the results are discussed. In addition, malfunctioning tests were conducted for the open, short, and misfiring during charging conditions. Finally, the developed high-voltage capacitor charger was shown to be very reliable, even under faulty operating conditions in the system. View full abstract»

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  • A Bidirectional High-Frequency-Link Single-phase Inverter: Modulation, Modeling, and Control

    Page(s): 4049 - 4057
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1570 KB) |  | HTML iconHTML  

    This paper proposes a high-performance high-frequency-link (HFL) single-phase inverter. It offers bidirectional two-stage galvanic isolation power conversion without bulky dc link capacitors. An active clamper circuit and corresponding modulation strategy is developed to enable the proposed HFL rectifier to operate in soft-switching modes and be free of voltage spikes during device commutation. A succinct circuit model and high-performance plug-in repetitive control scheme are also developed to enable it to equally function as a high-performance conventional pulse width modulation (PWM) inverter. The experiment results on a 20-kHz HFL inverter prototype demonstrate the efficacy of the soft-switching HFL inverter and its highly promising control performance. The proposed HFL inverter offers a high-reliability, high-efficiency, high-power-density, and high-performance power conversion solution to extensive applications. View full abstract»

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  • New Bidirectional Intelligent Semiconductor Transformer for Smart Grid Application

    Page(s): 4058 - 4066
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1891 KB) |  | HTML iconHTML  

    This paper proposes a new bidirectional intelligent semiconductor transformer (BIST) for the smart distribution system and smart grid. The proposed BIST consists of high-voltage high-frequency ac/dc converter, bidirectional low-voltage dc/dc converter, and hybrid-switching dc/ac inverter. It features 1) input-to-output isolation with a high-frequency transformer; 2) bidirectional power flow; 3) small size and light weight; 4) capability of compensating voltage sag and/or swell; and 5) realization of three-phase structure based on single-phase module. The operational feasibility of proposed transformer was verified not only by computer simulation with PSCAD/EMTDC software but also by a hardware prototype with rating of 1.9 kV/127 V, 2 kVA, allowing a three-phase transformer of 3.3 kV/220 V, 6 kVA with three-phase construction. View full abstract»

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  • Improved Instantaneous Current Control for High-Power Three-Phase Dual-Active Bridge DC–DC Converters

    Page(s): 4067 - 4077
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1878 KB) |  | HTML iconHTML  

    With the increasing share of renewable and decentralized power sources, the need for power electronics and especially for efficient high-frequency high-power dc-dc converters is expected to grow. The three-phase dual-active bridge is a promising technology, as it has a high-power density and inherently features galvanic isolation. A highly dynamic method to control the current and thus the transferred power for this converter type has recently been published. The published approach is easy to implement and gives excellent results for transformers with a high transient time constant, i.e., low winding resistance. However, the method can be improved for transformers with increased winding resistance. This paper suggests two approaches that reach steady state in one-third of a switching period and half a switching period, respectively. Independent of the winding resistance, the suggested control schemes give superior results and oscillations of the dc current are completely eliminated. The control schemes are investigated in detail and derived mathematically. These exact solutions are linearized for ease of implementation in digital control circuitry. Simulations and an experimental verification on a laboratory prototype confirm the outstanding performance of the developed approach. View full abstract»

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  • Flux Balancing of Isolation Transformers and Application of “The Magnetic Ear” for Closed-Loop Volt–Second Compensation

    Page(s): 4078 - 4090
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5276 KB) |  | HTML iconHTML  

    Semiconductor switches possess nonideal behavior which, in case of isolated dc-dc converters, can generate dc-voltage components which are then applied to the isolation transformer. This dc-voltage component is translated into a dc flux density component in the transformer core, increasing the risk of driving the core into saturation. In this paper, a novel noninvasive flux density measurement principle, called “The Magnetic Ear,” based on sharing of magnetic path between the main and an auxiliary core is proposed. The active compensation of the transformer's dc magnetization level using this transducer is experimentally verified. Additionally, a classification of the previously reported magnetic flux measurement and balancing concepts is performed. View full abstract»

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  • Overview of Dual-Active-Bridge Isolated Bidirectional DC–DC Converter for High-Frequency-Link Power-Conversion System

    Page(s): 4091 - 4106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1630 KB) |  | HTML iconHTML  

    High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies. View full abstract»

    Open Access
  • High-Frequency Operation of a DC/AC/DC System for HVDC Applications

    Page(s): 4107 - 4115
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2017 KB) |  | HTML iconHTML  

    Voltage ratings for HVdc point-to-point connections are not standardized and tend to depend on the latest available cable technology. DC/DC conversion at HV is required for interconnection of such HVdc schemes as well as to interface dc wind farms. Modular multilevel voltage source converters (VSCs), such as the modular multilevel converter (MMC) or the alternate arm converter (AAC), have been shown to incur significantly lower switching losses than previous two- or three-level VSCs. This paper presents a dc/ac/dc system using a transformer coupling two modular multilevel VSCs. In such a system, the capacitors occupy a large fraction of the volume of the cells but a significant reduction in volume can be achieved by raising the ac frequency. Using high frequency can also bring benefits to other passive components such as the transformer but also results in higher switching losses due to the higher number of waveform steps per second. This leads to a tradeoff between volume and losses which has been explored in this study and verified by simulation results with a transistor level model of 30-MW case study. The outcome of the study shows that a frequency of 350 Hz provides a significant improvement in volume but also a penalty in losses compared to 50 Hz. View full abstract»

    Open Access

Aims & Scope

IEEE Transactions on Power Electronics covers fundamental technologies used in the control and conversion of electric power.

Full Aims & Scope