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 paper describes the design and control of a two-stage on-board battery charger for small electric vehicles, with slow and fast charging capacity. Although little discussed in the literature, this type of application requires greater attention due to the low nominal battery voltage, which results in high output current during the fast charging operation. To ensure a good quality of the grid current for both power conditions, a modified bridgeless boost rectifier is used as front-end converter. At the second stage a phase-shifted full-bridge with a current doubler rectifier is selected to ensure zero voltage switching and reduce the transformer secondary winding current. Moreover, an active power decoupling cell is employed in order to reduce dc-link capacitance and, consequently, increase the converter reliability and power density. Finally, the operation of the proposed battery charger under steady-state and dynamic conditions is verified by means of simulations.

A Two-Stage Battery Charger with Active Power Decoupling Cell for Small Electric Vehicles

In this paper, a modular inverter topology conceived by input series connection of H-bridge (ISHB) is presented and verified trough experimental results. The proposed converter is naturally appropriate for open-end split winding induction motor drive due to the galvanic isolation offered by the machine. Each sub-module is composed by a H-bridge inverter, which is characterized for a modulation with three levels, using phase-shifted PWM modulation strategy. All bus capacitor related to a phase of inverter are connected in series to reach the desired voltage level that is required in high power and high input voltage applications requirements. The proposed structure has a voltage self-balance in the series-connected input capacitors, which provides a stable operating point and ensures proper power distribution between each submodule. A prototype was build in order to validate the theoretical results for a 7.50kW induction motor, that has three-open winding per phase.

http://ieeexplore.ieee.org/iel7/7413933/7420013/07420104.pdf

A novel modular multilevel inverter for medium-voltage open-end split winding machines based on single-phase submodules with input-series connection

/pdf/unidirectional-single-phase-bridgeless-boost-rectifier-with-1az048ep02.pdf

Unidirectional Single-phase Bridgeless Boost Rectifier With Switched Capacitor Cell

This paper proposes a network communication system applied in a control strategy for parallel-connected multi-inverters, which is based on a distributed control system and a redundant communication system. The control system is produced by a Phased-Locked Loop (PLL) synchronism algorithm, a voltage controller and a parallelism controller. All control systems are based on instantaneous values and in the parallelism control the inverters share a single voltage reference signal. The communication system, which is the main focus of the paper, is based on two buses: one analog, which is a measurement taken from the electrical grid; and one digital, comprised of a Controller Area Network (CAN). The former allows the reference voltage of all inverters to be in synchronism and the latter keeps the reference voltage in synchronism even during a grid power outage. There is a PLL algorithm in each Voltage Source Inverter (VSI), which ensures the synchronism between the internal reference and external signal received from the grid or from the CAN. The proposed networked control system was verified in three 5 kVA three-phase VSIs operating in parallel. Experimental results with static and dynamic tests and with electrical grid interruption and return, were obtained. The networked control system is redundant and it provides increased reliability, thus it can be applied in the parallel operation of an on-line Uninterruptible Power Supply (UPS).

Control System for Multi-Inverter Parallel Operation in Uninterruptible Power Systems

A high-gain dc-dc converter, which integrates a quadratic boost flyback converter through coupled inductors is proposed in this paper. The integration generates a converter with high-gain using only one switch. The structure allows using the energy stored in the leakage inductance of the first coupled inductor on the load. Enabling this converter can be used in renewable energy systems, small wind turbines, compressed air systems, among others. The works contributes with a detailed analysis of the topology considering the leakage and the magnetizing of the coupled inductors. To validate the study, the numerical simulations were performed, as well as the tests in an experimental platform. The results, both theoretical and experimental, are in agreement which corroborates the proposed topology and the developed analysis. Thus, the converter shows up with great potential for the industrial sector.

Telles Brunelli Lazzarin

Papers

A Two-Stage Battery Charger with Active Power Decoupling Cell for Small Electric Vehicles

A novel modular multilevel inverter for medium-voltage open-end split winding machines based on single-phase submodules with input-series connection

Unidirectional Single-phase Bridgeless Boost Rectifier With Switched Capacitor Cell

Control System for Multi-Inverter Parallel Operation in Uninterruptible Power Systems

Quadratic Boost-Flyback DC-DC Converter With Coupled Inductors