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

Economy of Central African countries is growing very fast and the energy demand is increasing daily. As a result, the insufficient of electrical power generation is one of the major problems that slow the development. This paper is mostly focused on a technical and economical feasibility study of building integrated photovoltaic system (BIPVS) supposed to be compatible with the local consumption habit. To achieve this goal, a model of building with 263 kWh daily consumption is studied. A high efficiency dc-ac converter is modeled and controlled to interface the integrated photovoltaic system with the grid and building. A sliding mode algorithm is used to control a dc-dc converter for extracting the maximum available power from photovoltaic system. For emergencies, a battery pack is designed to supply sensitive equipment and lighting. The studied system is validated using the professional PV∗SOL software and "Matlab/ Simpower system". The results are promising and could be an efficient solution to the mentioned problems.

Design of building integrated photovoltaic system to the grid with power quality improvement features for Central African countries

This work tries to compute cogging torque in a 36-slot 6-pole SVFM where the higher coercive force N48SH magnet is in series with the lower coercive force AlNiCo9 magnet. A lumped parameter model of the SVFM is developed based on the magnetic flux lines in a slot-less machine obtained using the finite element analysis (FEA) method. The air gap flux density in the slot-less 6-pole SVFM is calculated using the developed lumped magnetic circuit model at different magnetization levels of the AlNiCo9 magnet. The error between the analytical and FEA results of air gap flux density is less than 4% at lower magnetization levels. By utilizing the air gap flux density in an equivalent slot-less machine and the relative air gap permeance function, the cogging torque of the 36-slot 6-pole SVFM is computed and compared to the analytical results at different magnetization levels of the AlNiCo9 magnet.

Cogging Torque Analysis in a Series Hybrid Variable Flux Machine Using Lumped Magnetic Circuits

Parallel hybrid linear-switched power amplifier and control strategy for machine emulation

One of the key components in photovoltaic (PV) electrical systems is the inverter. It is the unit that converters the DC power generated from the solar panels or the batteries to an AC power that can supply the electrical home appliances. The issues associated with the inverter are power quality and harmonics. This paper introduces a controller design for a single phase full bridge inverter for an off-grid PV electrical system which supplies a typical home or an office. For a pure sinewave inverter, a sinewave pulse-width modulation (SPWM) scheme is used. This puts the switching harmonics far away from the fundamental 50Hz component, which eases the filtering process by a simple low pass filter (LPF). As a result, a sinusoidal AC voltage waveform is obtained. Then, a step up voltage transformer is used to step up the voltage to 220V. As the AC load increases, the drop voltage on the LPF and the transformer primary increases significantly. This causes the secondary voltage of the transformer to drop drastically bellow 220V. To solve this issue, a cascaded voltage and current control loops are designed to control the transformer primary voltage at exactly 12V so that the secondary voltage is held always at 220V. The inverter circuit with the closed-loop control is simulated fully using Power Simulation (PSIM) software. Then, the inverter circuit is built and tested experimentally in the laboratory using only the open-loop control, and this is due to the lake of LEM voltage and current sensors in the laboratory.

Controller Design for an Off-Grid Photovoltaic Solar Inverter

The paper describes the design of a DSP-based control of a switched reluctance motor. A TMS320E15 Digital Signal Processor is used to control the conduction angle for each phase as well as the phase current. The conduction for each phase is synchronized with the rotor position by using an optical encoder shaft position sensor. Stator current control is achieved using a hysteresis current controller. Schematics and practical measurements are provided. >

Pragasen Pillay

Papers

Design of building integrated photovoltaic system to the grid with power quality improvement features for Central African countries

Cogging Torque Analysis in a Series Hybrid Variable Flux Machine Using Lumped Magnetic Circuits

Parallel hybrid linear-switched power amplifier and control strategy for machine emulation

Controller Design for an Off-Grid Photovoltaic Solar Inverter

DSP based control of switched reluctance motors