Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Multilevel inverters: a survey of topologies, controls, and applications

This paper gives an overview of medium-voltage (MV) multilevel converters with a focus on achieving minimum harmonic distortion and high efficiency at low switching frequency operation. Increasing the power rating by minimizing switching frequency while still maintaining reasonable power quality is an important requirement and a persistent challenge for the industry. Existing solutions are discussed and analyzed based on their topologies, limitations, and control techniques. As a preferred option for future research and application, an inverter configuration based on three-level building blocks to generate five-level voltage waveforms is suggested. This paper shows that such an inverter may be operated at a very low switching frequency to achieve minimum on-state and dynamic device losses for highly efficient MV drive applications while maintaining low harmonic distortion.

Medium-Voltage Multilevel Converters—State of the Art, Challenges, and Requirements in Industrial Applications

Multilevel inverters have created a new wave of interest in industry and research. While the classical topologies have proved to be a viable alternative in a wide range of high-power medium-voltage applications, there has been an active interest in the evolution of newer topologies. Reduction in overall part count as compared to the classical topologies has been an important objective in the recently introduced topologies. In this paper, some of the recently proposed multilevel inverter topologies with reduced power switch count are reviewed and analyzed. The paper will serve as an introduction and an update to these topologies, both in terms of the qualitative and quantitative parameters. Also, it takes into account the challenges which arise when an attempt is made to reduce the device count. Based on a detailed comparison of these topologies as presented in this paper, appropriate multilevel solution can be arrived at for a given application.

Multilevel Inverter Topologies With Reduced Device Count: A Review

This paper introduces a new multilevel converter topology that has many steps with fewer power electronic switches. The proposed circuit consists of series-connected submultilevel converters blocks. The optimal structures of this topology are investigated for various objectives, such as minimum number of switches and capacitors, and minimum standing voltage on switches for producing maximum output voltage steps. A new algorithm for determination of dc voltage sourcespsila magnitudes has also been presented. The proposed topology results in reduction of the number of switches, losses, installation area, and converter cost. The operation and performance of the proposed multilevel converter has been verified by the simulation and experimental results of a single-phase 53-level multilevel converter.

A Cascade Multilevel Converter Topology With Reduced Number of Switches

Renewable energy sources such as wind turbine generators and photovoltaics produce fluctuating electric power. The fluctuating power can be compensated by installing an energy storage system in the vicinity of these sources. This paper describes a 6.6-kV battery energy storage system based on a cascade pulsewidth-modulation (PWM) converter with focus on a control method for state-of-charge (SOC) balancing of the battery units. A 200-V, 10-kW, 3.6-kWh (13-MJ) laboratory system combining a cascade PWM converter with nine nickel metal hydride (NiMH) battery units is designed, constructed, and tested to verify the validity and effectiveness of the proposed balancing control.

State-of-Charge (SOC)-Balancing Control of a Battery Energy Storage System Based on a Cascade PWM Converter

A programmed switching system for converting direct current into alternating current or some other variable current, or for converting alternating current of one frequency into alternating current of another frequency. The system employs a number of stages connected in cascade. Each stage includes an electrical energy source or an electrical energy storage unit and switch means adapted to bypass the energy source or storage unit, to interconnect the source or storage unit with other electrical energy source or storage units across a load in a programmed fashion, and to reverse the direction of current flow in the load to apply, for example, a quasi-sinusoidal voltage across the load.

Electric power converter

A voltage waveform synthesizer whereby an ac waveform (which may be varied in frequency) is synthesized from dc or unidirectional voltages in a programmable fashion, the power carried by the waveform being controllable from zero to some maximum value and the harmonic content of the waveform also being controllable. The synthesizer per se is described and it is shown in combination with a rotating electric machine to provide, for example, a variable speed drive mechanism.

Voltage waveform synthesizer and a system that includes the same

A variable speed electronic motor having wound polyphase armature and field windings each of which is energized by a polyphase source whose voltage and frequency are variable in a controlled fashion. Provision is made to control the excitation of the armature and field windings so that the torque output is optimized for all loads and speeds. Also, the machine disclosed can be made to function in a generating mode; hence, there can be flow of both electrical and mechanical energy to and from the machine and the amount of each can be carefully regulated. In addition, a variation of the machine, acting purely in a generating mode, can be programmed to regulate electrical output of the machine independent of the angular velocity of the machine, and output power can be similarly regulated, all within reasonable limits. Also, for some requirements one winding can be energized at a constant frequency and voltage and the other can be excited at variable frequency and voltage.

Variable speed electronic motor and the like

Apparatus wherein a segmented fluid stream consisting of a plurality of contiguous segments of, for example, mercury and ferrofluid, are caused to move within an insulating tube whose inner volume is filled with the fluid and to perform electricrelated functions by virtue of the different electro-magnetic characteristics of the fluids that compose the stream. The system described in greatest detail is an electric switch wherein, in its simplest form, electric current between two electrodes will flow or not depending upon whether the space between the electrodes is bridged by mercury or ferrofluid, respectively.

Apparatus wherein a segmented fluid stream performs electrical switching functions and the like

/pdf/radio-frequency-interferometry-a-new-technique-for-studying-4vhual346r.pdf

Richard H. Baker

Papers

Electric power converter

Voltage waveform synthesizer and a system that includes the same

Variable speed electronic motor and the like

Apparatus wherein a segmented fluid stream performs electrical switching functions and the like

Radio-frequency interferometry-A new technique for studying glaciers