There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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

The use of distributed energy resources is increasingly being pursued as a supplement and an alternative to large conventional central power stations. The specification of a power-electronic interface is subject to requirements related not only to the renewable energy source itself but also to its effects on the power-system operation, especially where the intermittent energy source constitutes a significant part of the total system capacity. In this paper, new trends in power electronics for the integration of wind and photovoltaic (PV) power generators are presented. A review of the appropriate storage-system technology used for the integration of intermittent renewable energy sources is also introduced. Discussions about common and future trends in renewable energy systems based on reliability and maturity of each technology are presented

/pdf/power-electronic-systems-for-the-grid-integration-of-4s5cxjhatl.pdf

Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey

The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting polymers. More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes. The energy density of these devices is 3¯5 Wh/kg with a power density of 300¯500 W/kg for high efficiency (90¯95%) charge/discharges. Projections of future developments using carbon indicate that energy densities of 10 Wh/kg or higher are likely with power densities of 1¯2 kW/kg. A key problem in the fabrication of these advanced devices is the bonding of the thin electrodes to a current collector such the contact resistance is less than 0.1 cm2. Special attention is given in the paper to comparing the power density characteristics of ultracapacitors and batteries. The comparisons should be made at the same charge/discharge efficiency.

Ultracapacitors: Why, How, and Where is the Technology

This paper presents a technology review of voltage-source-converter topologies for industrial medium-voltage drives. In this highly active area, different converter topologies and circuits have found their application in the market. This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point-clamped, cascaded H-bridge, and flying-capacitor converters. This paper presents the operating principle of each topology and a review of the most relevant modulation methods, focused mainly on those used by industry. In addition, the latest advances and future trends of the technology are discussed. It is concluded that the topology and modulation-method selection are closely related to each particular application, leaving a space on the market for all the different solutions, depending on their unique features and limitations like power or voltage level, dynamic performance, reliability, costs, and other technical specifications.

Multilevel Voltage-Source-Converter Topologies for Industrial Medium-Voltage Drives

The wavelet transform is beginning to be used widely in power engineering. Its effectiveness for analyzing transients with time localized information is now well known. Multiresolution analysis is especially suitable for feature enhancement of transients and thus makes it possible for power disturbances to be classified. In addition, the wavelet transform works well where the Fourier transform fails. A graphical insight is demonstrated in this letter.

http://ieeexplore.ieee.org/iel5/39/17037/01236745.pdf

An insight into power quality disturbances using wavelet multiresolution analysis

Research progress on understanding magnetic steel core losses is presented in this report Three major aspects have been thoroughly investigated: 1, experimental characterization of core losses, 2, fundamental physical understanding of core losses and development of core loss formulas, and 3, design of more efficient machine based on the new formulations Considerable progress has been achieved during the four years of research and the main achievements are summarized in the following: For the experimental characterization, a specially designed advanced commercial test bench was commissioned in addition to the development of a laboratory system with advanced capabilities The measured properties are core losses at low and higher frequencies, with sinusoidal and non-sinusoidal excitations, at different temperatures, with different measurement apparatus (Toroids, Epstein etc) An engineering-based core loss formula has been developed which considers skin effect The formula can predict core losses for both sinusoidal and non-sinusoidal flux densities and frequencies up to 4000 Hz The formula is further tested in electric machines The formula error range is 11% - 76% while the standard formulas can have % errors between -85% {-+} 447% Two general core loss formulas, valid for different frequencies and thickness, have been developed by analytically and numerically solvingmore » Maxwell's equations based on a physical investigation of the dynamic hysteresis effects of magnetic materials To our knowledge, they are the first models that can offer accurate core loss prediction over a wide range of operating frequencies and lamination thicknesses without a massive experimental database of core losses The engineering core loss formula has been used with commercial software The formula performs better than the modified Steinmetz and Bertotti's model used in Cedrat/Magsoft Flux 2D/3D The new formula shows good correlation with measured results under both sinusoidal and non-sinusoidal excitations A permanent magnet synchronous motor has been designed with the use of the engineering formula with Flux2D There was acceptable agreement between predictions and measurements This was further tested on an induction motor with toroid results« less

Improved Design of Motors for Increased Efficiency in Residential Commercial Buildings

This paper analyzes the capability of synchronous reluctance generators (SynRGs) to achieve successful self-excitation when operating in stand-alone systems. To initiate the self-excitation process, the machine steel core has to retain sufficient residual flux during the generator startup. This residual flux depends on the magnetic properties of the machine core as well as the previous machine operating condition. A hysteresis model is developed to simulate the flux linkage–current characteristics of the SynRG for different operating conditions. The model then calculates the machine residual flux linkage after each operation, which indicates the machine capability for self-excitation during the next startup. The simulation results show that the rotor steel core of the synchronous reluctance machine (SynRM) can be demagnetized when the generator is subjected to a short-circuit condition or when the generator shaft is subjected to abrupt deceleration. These simulation results are also validated by experimental measurements on a 5 hp SynRM.

The Loss of Self-Excitation Capability in Stand-Alone Synchronous Reluctance Generators

Electronic techniques for controlling acoustic noise and vibration depend on an accurate knowledge of the stator resonant frequency. Analytical models are developed, which allows the calculation of the first several modal frequencies. The impact of the stator stack length on the accuracy of the formulae is also examined. Experimental validation is included.

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Analytical formulae for calculating SRM modal frequencies for reduced vibration and acoustic noise design

When classical techniques are used for designing fixed-structure speed controllers for AC drives, the design is normally done around a nominal value of the controlled plant. Generally, a sensitivity analysis is subsequently done to ensure that the design specifications are met when the plant parameters change. An alternative is proposed where the parameter variations are included at the outset of the design task. The Nichols chart lends itself rather well to this application since it represents both magnitude and phase information on a single diagram. By using this alternative, it may be possible to reduce the overall time needed to complete the design. The particular technique, quantitative feedback theory (QFT), is used in conjunction with the Nichols chart. The basics of QFT are presented, and it is shown how it can be used for the design of fixed-structure controllers for parameter-sensitive plants. A design is presented and verified experimentally. >

/pdf/speed-controller-design-for-a-vector-controlled-permanent-oad1jim9fe.pdf

Pragasen Pillay

Papers

An insight into power quality disturbances using wavelet multiresolution analysis

Improved Design of Motors for Increased Efficiency in Residential Commercial Buildings

The Loss of Self-Excitation Capability in Stand-Alone Synchronous Reluctance Generators

Analytical formulae for calculating SRM modal frequencies for reduced vibration and acoustic noise design

Speed controller design for a vector-controlled permanent magnet synchronous motor drive with parameter variations