Is income inequality persistent? Evidence using panel stationarity tests, 1870-2011

Using data on inequality for 21 OECD countries over the period 1870-2011 this paper tests the Piketty hypothesis that income inequality is likely to grow in the 21st century. It is shown that the null hypothesis of trend stationarity of inequality cannot be rejected at conventional significance levels, suggesting that shocks to income inequality are likely to be temporary

A medium-frequency transformer with multiple secondary windings for grid connection through H-bridge voltage source converters

Although the power output of today's wind turbine has exceeded 7 MW, the voltage rating of the most common generator is below 700 V. A low-frequency transformer is commonly used to step-up the voltage to the grid voltage level, e.g. 11 kV or 33 kV. These heavy and bulky low-frequency transformers significantly increase the volume and weight of nacelle. To achieve a compact and light nacelle, a medium-voltage converter with series-connected H-bridge (SCHB) topology would be an attractive technology for future wind turbines. However, the SCHB converter requires multiple isolated and balanced DC sources, which makes the application not straightforward. As an alternative approach to generate multiple isolated and balanced sources a prototype transformer with six secondary windings, 1.26 kVA and 10 kHz, is designed and developed for 1 kV five levels SCHB multilevel converters. The experimental results show that the proposed system may be attractive in grid based renewable energy systems. © 2012 IEEJ Industry Appl Soc

Transformer-less local grid based 11 kV SCHB multilevel converter for renewable energy systems

Due to the variable nature of renewable energy resources and power demand by the consumers, it is difficult to operate a power system installed with only one type of renewable energy resource. The local grid based renewable generation may be the only solution to overcome this problem. In this regard, an 11 kV Series Connected H-Bridge (SCHB) multilevel Voltage Source Converter (VSC) is proposed, which is the transformer less, cost effective solution to interface the renewable generation system to the local grid directly. This paper presents the design, simulation and analysis of a Five Level (5L)-SCHB and an Eleven Level (11L)-SCHB VSC for an 11 kV local grid based renewable energy systems. The performance, cost, modulation scheme and harmonic spectra of the converter are the bases for analysis. © 2011 IEEE

Performance and cost comparison of NPC, FC and SCHB multilevel converter topologies for high-voltage applications

The rapid increase in global energy consumption and the impact of greenhouse gas emissions have accelerated the renewable energy technology into a more competitive area. Due to the variable nature of renewable energy resources and power demand by the consumers, grid based renewable generation has gained significant popularity in the world. High-voltage converter can interconnect the renewable systems to the grid directly without introducing a lossy, costly and bulky transformer. Three popular multilevel converter topologies: Neutral Point Clamped (NPC), Flying Capacitor (FC) and Series Connected H-Bridge (SCHB) have successfully made their way into the industry and therefore can be considered a mature and proven technology for low and medium voltage applications. But most of them are not suitable for high-voltage applications. This paper presents the comparison of a Five-Level (5L)-NPC, a 5L-FC, a 5L-SCHB, an Eleven-Level (11L)-NPC, an 11L-FC and an 11L-SCHB topologies for an 11 kV Voltage Source Converter (VSC). The comparison is made in terms of number of semiconductors, semiconductor cost, Total Harmonic Distortion (THD), filter size and control complexity. © 2011 IEEE

Comparison of singular and modular structures of multiport converters for residential applications in smart grids

This paper provides a systematic study on characteristics of a multiport converter with application in residential consumers of smart grid. The proposed converter can be used as a part of renewable energy system both in off-grid and grid connected customers. The study included several characteristics like efficiency, cost, reliability, flexibility and complexity of converters. Finally, the appropriate range of power and the modular structure are selected for the multiport converter. It is shown that a modular structure is preferable for residential consumers as it covers a wide range of demands. It also improves the reliability of renewable energy system especially in case of off-grid customers. © 2014 IEEE

Simulation of PV array characteristics and fabrication of microcontroller based MPPT

In photovoltaic (PV) systems, the PV array represents about 57% of the total cost of the system, so it is very desirable to operate the PV panel at the maximum power point (MPP). The output characteristics of the solar array are nonlinear and vitally affected by solar radiation, temperature, and load conditions. In this respect simulation analysis of PV array is essential to understand the output characteristics of PV array such that it can operate at the maximum power producing point for a given atmospheric condition. This paper explores the output characteristics of a PV array in MATLAB environment and the fabrication of a microcontroller based simple maximum power point tracker (MPPT). The fabricated MMPT has the capability to track the MPP and the use of the MPPT enhances the output power by 20%. ©2010 IEEE

Design and comparison of 11 kV multilevel voltage source converters for local grid based renewable energy systems

Because the availability of renewable energy is highly variable and the power demand by the consumers could have a very different characteristic, it is very desirable to connect a renewable generation system to the grid. In this respect, the 11 kV multilevel Voltage Source Converter (VSC) has no heavy transformer and is the cost effective solution to interfacing a renewable generation system to the local grid directly. This paper presents the design and comparison of a Five-Level Neutral Point Clamped (5L-NPC), a Five-Level Flying Capacitor (5L-FC), a Five-Level Series Connected H-Bridge (5L-SCHB), an Eleven-Level Neutral Point Clamped (11L-NPC), an Eleven-Level Flying Capacitor (11L-FC), and an Eleven-Level Series Connected H-Bridge (5L-SCHB) VSC for an 11 kV local grid based converter. The cost of power semiconductors and capacitors, modulation schemes and harmonic spectra of the converters are the bases for comparison. © 2011 IEEE

Steady state characteristic simulation of DFIG for wind power system

Wind power, as an important and promising renewable resource, is widely studied. Because the wind is highly variable, it is very desirable to operate a wind turbine at variable speeds. In this respect, doubly fed induction generator (DFIG) has become popular in wind power generation system. The steady state simulation analysis of a DFIG is essential to understand the behavior of DFIG such that it can operate at maximum power producing point for a given wind speed. This paper explores the steady state characteristic of a DFIG in wind power generation system using MATLAB. ©2010 IEEE

High-frequency magnetic-link medium-voltage converter for superconducting generator-based high-power density wind generation systems

© 2015 IEEE. Recent advances in solid-state semiconductors and magnetic materials have provided the impetus for high-frequency magnetic-link-based modular medium-voltage power conversion systems, which would be a possible solution to reduce further the weight and volume of superconducting generator-based wind generation systems. To verify this new concept, in this paper, a laboratory prototype of 5 kVA high-frequency magnetic-link modular power conversion system is developed for a scaled down 1.2 kV grid application. The design and implementation of the prototyping, test platform, and the experimental results are analyzed and discussed. It is expected that the proposed new technology will have great potential for superconducting generator-based wind farm applications

Medium-frequency-link power conversion for high power density renewable energy systems

Recent advances in solid-state semiconductors and magnetic materials have provided the impetus for medium frequency-link based medium voltage power conversion systems, which would be a possible solution to reducing the weight and volume of renewable power generation systems. To verify this new concept, in this paper, a laboratory prototype of 1.73 kVA medium-frequency-link power conversion system is developed for a scaled down 1 kV grid applications. The design and implementation of the prototyping, test platform, and the experimental results are analyzed and discussed. It is expected that the proposed new technology would have great potential for future renewable and smart grid applications. © 2013 IEEE