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

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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 authors develop a linear model of a vector-controlled permanent-magnet synchronous motor (PMSM) from the nonlinear model and present the overall transfer function. They also develop digital models for a vector-controlled PMSM drive system with single-rate and multirate sampling. This model is used to investigate the effects of the sampling time on the stability of the drive system. >

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Development of digital models for a vector controlled permanent magnet synchronous motor drive

Switched reluctance machines (SRMs) are normally designed to operate in the saturated region, and phase currents have some overlap to achieve better output torque performance. This results in mutual saturation effects. These effects are analyzed in detail in this paper. The experimental results show the influence of both the magnitude and direction of the leading phase current and the influence of the trailing phase current on the flux linkage of the working phase. In addition, the effect of the mutual saturation on the output torque is also demonstrated. It shows that a change of the phase winding connections can increase the output torque.

Improved torque performance of switched reluctance Machines by reducing the mutual saturation effect

This paper introduces the development of a solid oxide fuel cell (SOFC) emulator that mimics the behavior of an actual fuel cell for testing, design, control and optimization. The emulator is developed from a lumped solid oxide fuel cell model in a Matlab/Simulink environment, and programmed to a dSPACE and/or DSP controller for real-time applications. The controller generates an output control voltage, which is fed to a linear power amplifier capable of high output current. The emulator is tested for various cell temperatures, flow rate concentrations and load changes to predict the static and dynamic response. The test results are compared with experimental data to validate the SOFC emulator.

The Development of Solid Oxide Fuel Cell (SOFC) Emulator

The search for low noise SRM designs, has encouraged this research to focus on the effects of different lamination shapes on vibration. Five different shapes are considered, with one emerging as the best candidate for the 12/8 pole combination considered. The implications of using different phase numbers in the design are also explored from a vibration and noise point of view.

Low vibration design of SRMs for automotive applications using modal analysis

Torque ripple of permanent magnet motors can be classified into four types depending on the nature of their origin The four types are pulsating torque, fluctuating torque, reluctance cogging torque, and inertia and mechanical system torque Pulsating torques are inherently produced by the trapezoidal back-EMFs and trapezoidal currents used in certain permanent magnet adjustable-speed motors The torque ripples caused by pulsating torques may be reduced by purposely produced fluctuating counter torques Air-gap torque assessments are conducted on a sample motor Experimental results agree with theoretical expectations

Pragasen Pillay

Papers

Development of digital models for a vector controlled permanent magnet synchronous motor drive

Improved torque performance of switched reluctance Machines by reducing the mutual saturation effect

The Development of Solid Oxide Fuel Cell (SOFC) Emulator

Low vibration design of SRMs for automotive applications using modal analysis

Nature and assessments of torque ripples of permanent-magnet adjustable-speed motors