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Details of Grant 

EPSRC Reference: EP/K019333/1
Title: Ultra-efficient grid-tie inverter technology
Principal Investigator: McNeill, Dr N
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Electrical and Electronic Engineering
Organisation: University of Bristol
Scheme: First Grant - Revised 2009
Starts: 01 September 2013 Ends: 31 May 2015 Value (£): 98,795
EPSRC Research Topic Classifications:
Power Electronics
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:
Panel DatePanel NameOutcome
11 Mar 2013 Engineering Prioritisation Meeting 11/12 March 2013 Announced
Summary on Grant Application Form
A grid-tie inverter (GTI) is an essential sub-system when feeding power from a renewable energy source into the grid. A GTI is a power electronic circuit that takes unregulated power, normally in dc form, produced by the source and converts it into ac form at the correct frequency and magnitude. When converting power from, for example, a small domestic photo-voltaic (PV) solar panel array, the inverter is normally a single-phase type and is typically rated at 1kW. Desirable features in a GTI are:

i. High efficiency over a wide load range to maximize the return on investment (ROI);

ii. Low cost-per-watt, again to maximize ROI. Compared with power electronic circuitry operating at similar voltages, such as computer power supplies, the cost-per-watt is high;

iii. High reliability. Again, compared with other power electronic circuitry, reliability is poor.

Given the probability density function of the available power from a renewable energy source, the GTI's part-load efficiency is important. Whilst efficiency is highly desirable to maximize the ROI from a solar panel installation, a corollary is low inverter losses. This implies low internal temperature rises. Limiting the temperature rises of the power semiconductor devices is essential if high reliability is to be attained. Forced-cooling is not normally feasible in GTIs due to the cooling fan's limited reliability and lifetime. Furthermore, the parasitic energy load of the forced cooling system itself is not insignificant. Limiting the amount of power dissipation at source is therefore important.

Recent years have seen significant improvements in the switching and conduction capabilities of power semiconductors. Silicon carbide (SiC) and other technologies are seen as potent alternatives to the established silicon (Si) IGBT in high efficiency power conversion. Due to the relatively high costs of the new devices their initial application is foreseen in areas where ultra-high efficiency and/or high power to weight are a paramount requirement.

The objective of this application will be to investigate different inverter topologies, power semiconductor devices and passive component designs with the objective of attaining very high conversion efficiencies over the wide range of operating conditions encountered in real world applications. The specific research outcomes will be:

i. A methodology for identifying and evaluating the optimal inverter topology and device combinations for ultra high efficiency power conversion;

ii. New high fidelity models for the selected switching devices within the chosen circuit implementations, capable of estimating the loss over the full operating range of powers and conditions;

iii. Improved calorimetric test methods and practices for measuring the loss within ultra-high efficiency power conversion systems, at a component and system level.

The proposed research will culminate in a fully characterised prototype inverter operating from a 400V to 450V dc rail and supplying up to 1kW into a 230V mains supply with an efficiency of over 99.2% over a load range from 20% to 100%.

The research is timely due to current concerns over global warming and the need for alternative low carbon energy sources. Academic research into GTIs in the UK has tended to focus on issues such as grid synchronization algorithms, maximum efficiency point tracking (MEPT) techniques, control and power quality. In contrast, relatively little has been done on the topic of efficiency in the UK and this will be the main theme of the proposed research. The prior art here has mainly originated in Germany and the USA. The proposed research will help to identify the UK with this theme. Although the primary intended objective is in GTIs for PV installations, the technology will have applications in many other areas, for example, in machine-drive inverters and electric vehicle drives.

Key Findings
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Potential use in non-academic contexts
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Date Materialised
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Organisation Website: http://www.bris.ac.uk