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

It is no exaggeration to consider electric vehicles a reality in our current society. Comparing to combustion vehicles they have better efficiency and monetary profitability by distance traveled. However, the necessary infrastructure for the proper functioning of EVs, as batteries, individual chargers, charge stations, etc., are still precarious in several places. This paper introduces a new interleaved model for a low voltage battery pack charger for neighborhood electric vehicles (NEV). The system has two power stages, a SEPIC PFC rectifier and a DC-DC Buck converter, which process 1.5 kW per cell a total of 4.5 kW. The proposed system is adequate to lower power single-phase systems, which the battery pack voltage is lower than the grid.

Two-Stage SEPIC-Buck Topology for Neighborhood Electric Vehicle Charger

This paper presents experimental results for a three-phase direct ac-ac converter based on switched capacitor principle in delta and wye configuration. This converter employs only capacitors and switches in the power stage, it has a fixed gain, it operates in open loop with constant duty cycle and constant switching frequency and the topology is bidirectional. One advantage of the proposed converter is a power stage with no magnetic elements, which makes the converter appropriated to build solid state autotransformers. A complete analysis of output voltages (phase-shift and amplitude) that are obtained regarding the delta and wye connections of converter is approached and it is corroborated with experimental results for resistive, inductive and nonlinear loads. A 220 V/110 V/3.5 kVA/100 kHz (in switching frequency) prototype was built and tested. For delta and wye connections of the modules, an efficiency of 90.4% and 95.05% was obtained in the rated load, respectively.

Experimental validation of a proposal for a 3.5 kVA three-phase magnetic-less solid-state autotransformer (SSAT) based on the switched-capacitor principle

This paper presents a new forward inverter topology for low power applications. The proposed converter is a voltage fed inverter, which makes it suitable for renewable source integration and has current source type output, which matches with grid-connected applications. This solution combines forward based topology in continuous conduction mode, providing MPPT capability and unity power factor in a single-stage converter. These features are obtained with a slow input voltage control and a fast output current control, in a cascaded control-loop. The forward transformer provides isolation and voltage gain in a small volume, hence, the structure can be applied as a step-up inverter. Principles of operation, static analysis, transfer functions, power and control design are developed in the paper. In order to verify the theoretical analysis, simulation results using PSIM are shown, considering a 500 W structure, with 72 V of input voltage and 220 V of grid voltage. The results show that the proposed topology has high output power factor, low current distortion, with the possibility of being applied in any renewable power source ranging from 300 W up to 1 kW.

Single-stage grid-connected forward inverter in continuous conduction mode

This paper addresses the study of the switched-capacitor differential boost inverter (SCDBI) for the connection to the electrical grid. The corroboration of the theoretical analysis is made through experimental results obtained in a 250 W prototype connected to a 127 V RMS voltage grid, considering a variation rate in input voltage from 50 to 70 V. The topology efficiency peak was 90% and grid current presented THD less than 3%.

250 W Single Stage Step-up Inverter Connected to the Grid

This paper presents a partial power processing and an efficiency analysis of dc-dc differential converters based on the use of two basic converters of the same group: the positive or negative group. The paper contributes theoretical analysis and demonstrates that the differential converters based on the positive group process has more power than the load requires, and that the differential converters based on the negative group process has less power than the load needs. This is an important advantage of the negative group converters, since a parcel of the output power is directly transferred by the input source to the load, resulting in partial power processing. In order to verify the theoretical analysis herein developed, ten prototypes are evaluated considering an input voltage of 20 V and output power of 100 W.

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Telles Brunelli Lazzarin

Papers

Two-Stage SEPIC-Buck Topology for Neighborhood Electric Vehicle Charger

Experimental validation of a proposal for a 3.5 kVA three-phase magnetic-less solid-state autotransformer (SSAT) based on the switched-capacitor principle

Single-stage grid-connected forward inverter in continuous conduction mode

250 W Single Stage Step-up Inverter Connected to the Grid

Partial Power Processing and Efficiency Analysis of dc-dc Differential Converters