The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

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Power Electronics Converters Applications And Design

The virtual impedance concept is increasingly used for the control of power electronic systems. Generally, the virtual impedance loop can either be embedded as an additional degree of freedom for active stabilization and disturbance rejection, or be employed as a command reference generator for the converters to provide ancillary services. This paper presents an overview of the virtual-impedance-based control strategies for voltage-source and current-source converters. The control output impedance shaping attained by the virtual impedances is generalized first using the impedance-based models. Different virtual impedances and their implementation issues are then discussed. A number of practical examples are demonstrated to illustrate the feasibility of virtual impedances. Emerging applications and future trends of virtual impedances in power electronic systems conclude this paper.

Virtual-Impedance-Based Control for Voltage-Source and Current-Source Converters

Resistive switching (RS) phenomena are reversible changes in the metastable resistance state induced by external electric fields. After discovery ∼50 years ago, RS phenomena have attracted great attention due to their potential application in next-generation electrical devices. Considerable research has been performed to understand the physical mechanisms of RS and explore the feasibility and limits of such devices. There have also been several reviews on RS that attempt to explain the microscopic origins of how regions that were originally insulators can change into conductors. However, little attention has been paid to the most important factor in determining resistance: how conducting local regions are interconnected. Here, we provide an overview of the underlying physics behind connectivity changes in highly conductive regions under an electric field. We first classify RS phenomena according to their characteristic current–voltage curves: unipolar, bipolar, and threshold switchings. Second, we outline the microscopic origins of RS in oxides, focusing on the roles of oxygen vacancies: the effect of concentration, the mechanisms of channel formation and rupture, and the driving forces of oxygen vacancies. Third, we review RS studies from the perspective of statistical physics to understand connectivity change in RS phenomena. We discuss percolation model approaches and the theory for the scaling behaviors of numerous transport properties observed in RS. Fourth, we review various switching-type conversion phenomena in RS: bipolar-unipolar, memory-threshold, figure-of-eight, and counter-figure-of-eight conversions. Finally, we review several related technological issues, such as improvement in high resistance fluctuations, sneak-path problems, and multilevel switching problems.

Resistive switching phenomena: A review of statistical physics approaches

This paper proposes a distributed two-layer control structure for ac microgrids. Inverter-based distributed generators (DGs) can operate either as voltage-controlled voltage source inverters (VCVSI) or current-controlled voltage source inverters (CCVSI). VCVSIs provide the voltage and frequency support, whereas CCVSIs regulate the generated active and reactive powers. The proposed control structure has two main layers. The first layer deals with the voltage and frequency control of VCVSIs. The second layer regulates the active and reactive powers of CCVSIs. These controllers are implemented through two communication networks with one-way communication links and are fully distributed; each DG only requires its own information and the information of its neighbors on the communication network graph. The proposed control framework is verified on a microgrid test system and IEEE 34 test feeder.

A Multiobjective Distributed Control Framework for Islanded AC Microgrids

This article presents a review and a comparison of the conventional matrix converter (CMC), multimodular matrix converter (MMMC), and multilevel matrix modular converter (M3C) topologies, which are three of the main topologies of the matrix family. The study of the CMC supplies basic knowledge for these structures and then the concept of multilevel matrix converters used in MMMC and M3C topologies is approached. The study addresses modulation strategies and switching sequences for the topologies to provide implementation guidelines and harmonic content reduction. The design is also carried out and results of the three topologies are shown to exemplify their operation. Finally, the article presents a comparison between the topologies to highlight the advantages and challenges of each one. This study contributes information on the three topologies, which are not easily found in the literature, especially in terms of modulation and switching strategies. It also highlights applications and research points that have to improve.

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Review, Challenges and Potential of AC/AC Matrix Converters CMC, MMMC, and M3C

This paper presents a full analysis on a single-phase PFC (Power Factor Correction) Flyback rectifier. The study approaches all design equations, including input filter and leakage inductance loss, for operation in DCM (Discontinuous Conduction Mode) and in CCM (Continuous Conduction Mode). Both operation modes are compared in the paper using a designed example. In addition, it is introduced a single-stage bridgeless Flyback rectifier and it is compared with other isolated and non-isolated similar topologies. Finally, in order to make the bridgeless version a modular solution, it is designed to operate in interleaved with 3 modules, tripling the rated power and reducing the input filter.

Single-Stage Bridgeless AC-DC PFC Flyback Interleaved

This paper proposes an isolated modular single–phase inverter for high–input voltage applications. The topology is composed of conventional and modular full–bridge inverters with series–connected inputs and magnetically–connected outputs. All input bus capacitors are connected in series and thus the dc voltage is divided among the inverter modules. The full–bridge outputs are connected by a multiple–winding low– frequency transformer, the inverters employ a typical three–level modulation with phase–shift carriers and when an appropriate modulation is used a multilevel output voltage is supplied for the load. The auto–balance of the input capacitor voltages is verified and a harmonic analysis is performed in order to investigate the exchange of active and reactive power between the inverter modules at low and high frequency. An 8 kW prototype with three modules, a multiple–winding transformer with a transform ratio of 1:1:1:1, 1200 V dc input source and 220 V/ 60 Hz ac output voltage was built and tested in order to verify the proposed topology.

/pdf/a-single-phase-inverter-based-on-full-bridge-modules-with-56g4z65nvn.pdf

A Single-phase Inverter Based On Full-bridge Modules With Inputs In Series-connection And Outputs Coupled By A Multiple-winding Transformer

This paper proposes a single-phase SEPIC rectifier that works in discontinuous conduction mode (DCM). The proposed rectifier employs a three-stage switch and a voltage-doubler structure. Hence, it works as two half-wave rectifiers with the output voltages series-connected and thus it provides a higher voltage gain. The paper presents the theoretical analysis of the proposed structure and it also discusses a comparison between the proposed converter and the classic SEPIC rectifier, which shows that the proposed converter might either provide reduced voltage stress on the semiconductors to the same output voltage level, or it might supply double the gain in the output voltage with the same voltage stress. In both cases, the novel rectifier maintains the high power factor with no current control from the classical DCM SEPIC rectifier. The study was verified by experimental results obtained with a prototype of 1000 W, 220 V at input voltage, 400 V at output voltage and 50 kHz at switching frequency. Testes at rated power provided a current THD equal to 3.2%, a power factor of 0.9992 and an efficiency of 94.34%.

Single-phase/-switch voltage-doubler DCM SEPIC rectifier with high power factor and reduced voltage stress on the semiconductors

This paper covers the self‐sharing analysis of dc‐dc nonisolated converters with input parallel–output parallel (IPOP) configuration and operating in discontinuous conduction mode (DCM). The main contribution of the proposed system is its capability of providing self‐sharing of the currents on both sides of each individual converter, without average current sharing control, even in the face of parametric variations. This self‐balance only occurs for DCM. When the addressed converters operate in continuous conduction mode (CCM), the self‐sharing does not occur naturally under parametric differences among them, requiring the use of additional control loops. The use of self‐sharing converters in nonisolated converters simplifies the control system, it makes the modular solution being attractive for many applications, and it increases the power range that the DCM converters may be applied. This paper brings the theoretical study of self‐sharing of the current mechanism to six basic nonisolated converters operating in DCM. The self‐sharing is verified by experimental results, which are obtained from three modules of dc‐dc SEPIC converters. Both converters were designed to operate with 200‐V input voltage, 125‐V output voltage, 1500‐W rated power (500 W each module), and switching frequency at 30 kHz.

Input parallel–output parallel connected modular nonisolated DC‐DC converters with current self‐sharing capability operating in discontinuous conduction mode

Telles Brunelli Lazzarin

Papers

Review, Challenges and Potential of AC/AC Matrix Converters CMC, MMMC, and M3C

Single-Stage Bridgeless AC-DC PFC Flyback Interleaved

A Single-phase Inverter Based On Full-bridge Modules With Inputs In Series-connection And Outputs Coupled By A Multiple-winding Transformer

Single-phase/-switch voltage-doubler DCM SEPIC rectifier with high power factor and reduced voltage stress on the semiconductors

Input parallel–output parallel connected modular nonisolated DC‐DC converters with current self‐sharing capability operating in discontinuous conduction mode