Characterisation of the cascode gate drive of power MOSFETs in clamped inductive switching applications

This thesis proposes a novel gate drive circuit to improve the switching performance of MOSFET power switches in power electronic converters. The proposed topology exploits the cascode configuration, allowing the minimisation of switching losses in the presence of practical circuit constraints, which enables efficiency and power density improvements. Switching characteristics of the new topology are investigated and key mechanisms that control the switching process are identified. Unique analysis tools and techniques are also developed to demonstrate the application of the cascode gate drive circuit for switching performance optimisation

Projections of emissions and removals from the LULUCF sector to 2050

Summary for policy makers: • The UK reports projections for the Land Use, Land Use Change and Forestry (LULUCF) sector to inform policy concerning domestic and international climate change commitments. The full projections data are available on the NAEI website (http://naei.defra.gov.uk/reports/reports?report_id=927) • LULUCF activities can result in net annual emissions or removals of greenhouse gases, and changes in carbon stocks in the pools associated with LULUCF. This report provides projections at the UK and Devolved Administration (DA) level, with separate estimates for Scotland, England, Wales and Northern Ireland, which are summed to give the UK totals. The results presented here are based on the reporting conventions of the UNFCCC. They are not presented as potential future accounted emissions and removals under the Kyoto Protocol which are calculated formally at the end of each commitment period. • LULUCF is divided into six land use types: Forest Land (4A), Cropland (4B), Grassland (4C), Wetlands (4D), Settlements (4E), Other Land (4F). Carbon stock changes from Harvested Wood Products are reported in an additional category, Harvested Wood Products (4G). The code refers to the IPCC (2006 Guidelines) inventory category of LULUCF. There is a separate inventory sector – not presented here – dedicated to other emissions, mainly methane and nitrous oxide, from agricultural activities. • Projections are made for net emissions and removals of greenhouse gases to 2050, arising from LULUCF activities reported in the latest (1990-2014) greenhouse gas inventory, for the DAs and the UK excluding Overseas Territories and Crown Dependencies. • Five scenarios (Baseline 1, Baseline 2, Central, Low and Stretch) have been described. The scenarios were developed by BEIS, Defra and the Forestry Commission and have been updated in 2016 following discussions with all of the UK administrations. The scenarios take account of current land use policies and aspirations. The Baseline scenarios are based on climate change-related and forestry policies extant in July 2009. • The main results are: At a UK level, the LULUCF sector has been a net sink since 1990 and is predicted to remain so under all scenarios until at least 2050, although at a declining level from the mid-2020s onwards (depending on the scenario). At a DA level, England and Scotland remain net sinks under all scenarios Wales is a small net sink under the Stretch scenario, but will become an increasing net source under the other scenarios between 2034 and 2049. Northern Ireland is a small net source (except in 1998 and 1999) under the Baseline and Central scenarios, but will become a small net sink from the late 2030s onwards under the Stretch and Low scenarios. The LULUCF sector in the UK and in each of the DAs is dominated by CO2 emissions and removals, although N2O emissions also make a significant contribution. The Forest Land, Cropland and Grassland categories determine the trend in the UK and DAs. The main changes in the projections since the 1990-2013 projections are: Forestry - a methodological revision of the forest carbon accounting model CARBINE to assign carbon stock changes to the correct reporting year, and the inclusion of the National Forest Inventory data (including, for the first time, small woods between 0.1 and 0.5 hectares in size) increasing tree cover and forest carbon stocks (this differs from the submitted 1990-2014 inventory). Grassland - the revision of the emission factor used for grassland on drained organic soils has reduced the size of the grassland sink

Biodiversity 2020: climate change evaluation report

In 2011, the government published Biodiversity 2020: A strategy for England’s wildlife and ecosystem services [1]. This strategy for England builds on the 2011 Natural Environment White Paper - NEWP [2] and provides a comprehensive picture of how we are implementing our international and EU commitments. It sets out the strategic direction for biodiversity policy between 2011-2020 on land (including rivers and lakes) and at sea, and forms part of the UK’s commitments under the ‘the Aichi targets’ agreed in 2010 under the United Nations Convention of Biological Diversity’s Strategic Plan for Biodiversity 2011-2020 [3]. Defra is committed to evaluating the Biodiversity 2020 strategy and has a public commitment to assess climate change adaptation measures. This document sets out the information on assessing how action under Biodiversity 2020 has helped our wildlife and ecosystems to adapt to climate change. Biodiversity 2020 aims to halt the loss of biodiversity and restore functioning ecosystems for wildlife and for people. The outcomes and actions in Biodiversity 2020, although wider in scope, aimed to increase resilience of our wildlife and ecosystems in the face of a changing climate. In order to inform the assessment, we have defined which of the measurable outputs under Biodiversity 2020 contribute to resilience. Biodiversity 2020 included plans to develop and publish a dedicated set of indicators to assess progress towards the delivery of the strategy. The latest list (at the time of writing), published in 2017, contains 24 biodiversity indicators [4] that would help inform progress towards achieving specific outcomes, they are also highly relevant to the outputs (detailed below) that form the basis for this evaluation. The Adaptation Sub-Committee’s 2017 UK Climate Change Risk Assessment Evidence Report [5] sets out the priority climate change risks and opportunities for the UK. The ASC also produced a review of progress in the National Adaptation Programme - “Progress in preparing for climate change” [6], which highlights adaptation priorities and progress being made towards achieving them. The UK Government’s response to the ASC [7] review includes a set of recommendations, of which Recommendation 6 states that “Action should be taken to enhance the condition of priority habitats and the abundance and range of priority species”. The recommendation further iterated that “This action should maintain or extend the level of ambition that was included in Biodiversity 2020” and that “An evaluation should be undertaken of Biodiversity 2020 including the extent to which goals have been met and of the implications for resilience to climate change.” To this, end an evaluation process has been put in place to define: a. What worked and why? Which actions or activities have had the greatest benefit in terms of delivering the desired outcomes? And, conversely, what prevented progress? b. Where are the opportunities? What are the financial, political, scientific and social opportunities for furthering the desired outcomes in the future? These objectives underpin the evaluation process for actions to date, and will also inform future actions and the iteration of a new nature strategy for England

Regulating services

No abstract available

Climate control of terrestrial carbon exchange across biomes and continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ∼16 ®C (a threshold value of mean annual temperature), above which no further increase of CO,.2uptake with temperature was observed and dryness influence overrules temperature influence. © 2010 lOP Publishing Ltd

Climate control of terrestrial carbon exchange across biomes and continents

Peer reviewe

A LIN inspired optical bus for signal isolation in multilevel or modular power electronic converters

Proposed in this paper is a low-cost, half-duplex optical communication bus for control signal isolation in modular or multilevel power electronic converters. The concept is inspired by the Local Interconnect Network (LIN) serial network protocol as used in the automotive industry. The proposed communications bus utilises readily available optical transceivers and is suitable for use with low-cost microcontrollers for distributed control of multilevel converters. As a signal isolation concept, the proposed optical bus enables very high cell count modular multilevel cascaded converters (MMCCs) for high-bandwidth, high-voltage and high-power applications. Prototype hardware is developed and the optical bus concept is validated experimentally in a 33-level MMCC converter operating at 120 Vrms and 60 Hz

An improved gate driver for power MOSFETs using a cascode configuration

To overcome the limitations of existing gate drive topologies an improved gate drive concept is proposed to provide fast, controlled switching of power MOSFETs. The proposed topology exploits the cascode configuration with the inclusion of an active gate clamp to ensure that the driven MOSFET may be turned off under all load conditions. Key operating principles and advantages of the proposed gate drive topology are discussed. Characteristic waveforms are investigated via simulation and experimentation for the cascode driver in an inductive switching application at 375V and 10A. Experimental waveforms compared well with simulations with long gate charging delays (including the Miller plateau) being eliminated from the gate voltage waveform

Real time maximum power conversion tracking and resonant frequency modification for high power piezoelectric ultrasound transducer

Piezoelectric ultrasound transducers are commonly used to convert mechanical energy to electrical energy and vice versa. The transducer performance is highly affected by the frequency at which it is excited. If excitation frequency and main resonant frequency match, transducers can deliver maximum power. However, the problem is that main resonant frequency changes in real time operation resulting in low power conversion. To achieve the maximum possible power conversion, the transducer should be excited at its resonant frequency estimated in real time. This paper proposes a method to first estimate the resonant frequency of the transducer and then tunes the excitation frequency accordingly in real time. The measurement showed a significant difference between the offline and real time resonant frequencies. Also, it was shown that the maximum power was achieved at the resonant frequency estimated in real time compare to the one measured offline

Comparison of the gate drive parameter space for driving power MOSFETs using conventional and cascode configurations

Conventional voltage driven gate drive circuits utilise a resistor to control the switching speed of power MOS-FETs. The gate resistance is adjusted to provide controlled rate of change of load current and voltage. The cascode gate drive configuration has been proposed as an alternative to the conventional resistor-fed gate drive circuit. While cascode drive is broadly understood in the literature the switching characteristics of this topology are not well documented. This paper explores, through both simulation and experimentation, the gate drive parameter space of the cascode gate drive configuration and provides a comparison to the switching characteristics of conventional gate drive