Imperial College London

Professor Tim Green, FREng

Faculty of EngineeringDepartment of Electrical and Electronic Engineering

Professor of Power Engineering
 
 
 
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Contact

 

+44 (0)20 7594 6171t.green Website CV

 
 
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Location

 

Energy Futures Lab, Electrical Eng BuildingElectrical EngineeringSouth Kensington Campus

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Summary

 

Overview

My principal research focus at present is the control, stability and protection of electrical power grids when almost all resources (generators, energy storage and flexible demand) are inverter-based resources rather and synchronous machines. This change away from rotating electrical generators makes dramatic changes to the dynamics of the systems. Perturbations to the system (such as a sudden change in generator output) causes much faster changes to the angle, frequency or amplitude of the system voltages. These three types of system dynamics were previous quite separate which aided analysis of stability but now, for instance, frequency dynamics are much faster than before sand couple to angle dynamics. A further complicating factor is that inverters are largely defined by their control software rather than their physical properties. Thus the dynamic model of an inverter is generally commercially confidential rather than openly known. This means there is an emphasis on developing grey-box models (somewhat more open than black-box models) and data-driven models, perhaps based on measure frequency spectrum data.

I also pursue the use of power electronics to create flexibility and enhance functionality in existing power networks. Although power electronics is a relatively expensive technology compared with traditional transformers and cables, it can provide facilitate much better use of existing assets and thus make a good case for investment.

My thesis is that power electronics has the greatest role to play at the two ends of the electricity network. At the “top”, we need to reinforce our national and international transmission networks to transfer bulk power. The flows we are interest in are from very large windfarms in the North Sea and to and from other European countries. We can foresee a set of subsea connections around the British coast and these cables will need to be operated on DC.  A large fraction of my work and recent publications are in how to optimise the design of very large DC to AC power converters to interface these links. This work has been supported by EPSRC and Alstom Grid. I am also interest in how DC links can be controlled to actively support operation of the main on-shore AC network (in addition to simply transferring energy).

The other end of the system, the “tail”, is the final distribution from the local substation into homes and offices. We anticipate that this well established network will soon be under stress from greater power flows as we connect more electric vehicle charging points and more roof top-top photovoltaic panels. Here power electronics can play a vital role in realising greater power flow capacity from existing assets by managing voltage control better. This avoids the expense and disruption of digging up pavements and roads to replace cables. Here I am interested in power electronics to create fast-acting tap change transforms and to provide controlled meshing of radial networks using soft open points. This work has been in conjunction with MR and UK Power Networks with support from EPSRC.

 

Recent Ph.D. Completions

Pérez Olvera, Ph.D., December 2020, “Active Network Management for Improved Flexibility in Distribution Networks”

T.R. F de Mendonća, Ph.D., December 2019, “A Distributed Control and Coordination Strategy Based on Voltage Sensitivity for Network Management”

Xin Xiang, Ph.D., March 2019, “The Modular Multilevel DC Converters for MVDC and HVDC Applications”

J. Wylie, Ph.D., January 2019, “Reliability Analysis of Modular Multi-level Converters for High and Medium Voltage Applications”

G.P. Chaffey, Ph.D., January 2017, “The Impact of Fault Blocking Converters on HVDC Protection”

P. Judge, Ph.D., November 2016, “Power Converter Design for HVDC”

C. Sheridan, Ph.D., January 2016, “Assessment of HVDC Technologies for an Offshore MTDC Grid”

C.E. Spallarossa, Ph.D., September 2015, “Frequency and Voltage Stability of Mixed AC and DC Systems”

T. Lüth, Ph.D., December2014, “DC/DC Converters for High Voltage Direct Current Transmission”

M. Collins, Ph.D., December 2013, “Multi-Agent System Control and Coordination of Distributed Energy Resources in Electrical Power Networks”

N. Bottrell, Ph.D., October 2013, “Small-signal Analysis of Active Loads and Large-signal Analysis of Faults in Inverter Interfaced Microgrid Applications”

M. Sokolov, Ph.D., June 2013, “Small-Signal Modelling of Maximum Power Point Tracking for Photovoltaic Systems”

M.M.C. Merlin, Ph.D., January 2012, “Hybrid Multi-Level HVDC Converter and Multi-Terminal DC Networks”

J.M. Bloemink, Ph.D., December 2012, “Distribution Level Power Electronics: Soft Open Points

Y. Pipelzadeh, Ph.D., July 2012, “Coordination of Damping Control in Transmission Networks with HVDC links”

S. Sudtharalingam, Ph.D., May 2012, “Micro Combined Heat and Power Units in the UK: Feasibility Assessment Using Real Time Pricing and Analysis of Related Policies”

P.R. Clemow, Ph.D., December 2011, “Smoothing wind farm output power through co-ordinated control and short term wind speed prediction”

C.A. Plet, Ph.D.,  November, 2011, “Fault Response of Inverter-based Distributed Generation”

K. Gandu, Ph.D., March 2011, “Power Processing for Electrostatic Microgenerators”

D.J. Rogers, Ph.D., February 2011, “Hybrid And Thin Power Electronics For Electrical Power Networks”

A.R. Ahmadi, Ph.D., November 2010, “Distribution Network Optimisation for an Active Network Management System”

S.L. Payyala, Ph.D., December 2009, "Integration of Biomass Power Generation into Distribution Networks: A Techno-Economic perspective"

M. Brucoli, Ph.D., October 2008, “Fault behaviour and fault detection in islanded inverter-only microgrids”

C.-W. Tan, Ph.D., July 2008, "Analysis and Control of Building Integrated Photovoltaic Systems Incorporating Storage"

N. Pogaku, October 2006, “Analysis, Control and Testing of Inverter-Based Distributed Generation in Standalone and Grid-Connected Applications” Abstract 


 

Collaborators

Prof Xifang Wang, Xi'an Jiatong University, China, HVDC and Renewable Energy Integration, 2013 - 2016

Prof. Guangfu Tang, EPRI Electric Power Engineering Co. Ltd, State Grid Corporation of China (SGCC), HVDC Converter Technology and Control, 2013

Research Staff

Clemow,PR