Reconfigurable Distribution Networks

Lead Research Organisation: Imperial College London
Department Name: Electrical and Electronic Engineering

Abstract

The "SmartGrid" is a concept that has emerged from its initial discussion in engineering circles into the wider public arena because its importance has been recognised for securing future electricity supply and facilitating the de-carbonisation of electricity. Much of the SmartGrid debate has so far focused customers with "smart homes" or "smart appliances" being engaged in managing the electricity system through their reactions to signals about price or availability of renewable energy. Behind the scenes, there is a parallel debate about how new control methods for existing electricity plant and equipment may enable electricity networks to offer the flexibility needed to incorporate low-carbon energy sources.

This proposal expands the SmartGrid debate in two directions. First, large numbers of people in developing countries suffer from an intermittent electricity supply. The supply companies use "rota disconnection" schemes to ration the limited energy available in some regions. Having electricity for, say, just 4 hours a day adversely impacts education, health care and economic development. "Micro-grids" able to run "off-gird" with local solar or micro-hydro energy are interesting in this context. Our proposal here is to design "on-off grids" in which supply companies adjust their rota disconnection to account for local resources in the micro-grids and the micro-grids are configured with power electronic interfaces that can manage the frequent transitions between on-grid and off-gird operation. The consortium members in India will build a demonstration version of such a micro-grid to allow control and optimisation ideas to be explored and assessed. The use of energy storage technology will be a key part of this scheme.

Second, developed countries do not suffer rota-disconnections except in emergencies. However, the security and adequacy of their existing electricity distribution networks may become compromised by the injection of significant amounts of solar energy at household level and the heavy loading anticipated from electric vehicle charging. Here we propose to develop power electronic equipment that enables the rapid reconfiguration of the possible supply routes in a network in order to optimise the power flows and voltage levels. The questions are not so much on can power electronic devices achieve this (we are confident they can) but rather how is it achieved efficiently and with a good equipment lifetime. The UK members of the consortium will design, build and test new forms of "soft meshing" power electronics to meet these objectives.

The "reconfigurable distribution network" presents a great opportunity in both the Indian and UK context. It also present research challenges on a number of fronts: innovation in power electronic equipment to reduce power losses and increase lifetime; the need to design new control algorithms to exploit the new flexible equipment to the benefit of consumers and network operators and the need to create new optimisation and planning tools to indicate where exactly the new equipment should be deployed and to determine how robust its business case can be.

Planned Impact

Networks in developed nations such as the UK must deliver the increases in capacity and flexibility required to support extensive PV in-feed and the rapid growth in EV penetration and in developing nations such as India, shortfalls in generation and unreliable supplies to rural areas will continue to affect many millions of people, and this must be managed to enhance quality of life and facilitate economic development. Reconfigurable distribution networks, as envisioned by this proposal, are an important part of achieving both of these objectives in a cost effective manner. In developed countries, the move to a meshed network topology will increase the utilisation of existing network assets by allowing lightly loaded or generation rich feeders to support weak or heavily loaded parts of the network, avoiding or postponing costly network upgrades. In developing nations and rural areas, shortfall in generation may be managed through dynamic reconfiguration of the distribution network, ensuring critical loads remain connected and that local small-scale generation and storage is managed in an effective manner. The economic impact of a move towards fully reconfigurable distribution networks is clear in both contexts and the proposed research program seeks to address key issues on the way to delivering these networks.
Critical technology such as the Soft Open Point and hybrid dis-connector to be developed in this project will underpin much of the functionality of these networks. Both India and UK/Europe are well placed to design, manufacture and supply this type of equipment, for example, large power electronic systems are supplied by three major European headquartered companies (Siemens, ABB and Alstom Grid) and an emerging Indian industrial base.
Expertise in the planning, operation and control of reconfigurable distribution networks will be developed under the programme, assisting network operators themselves and engineering consultancies in the understanding of technology capabilities and their associated risks and benefits. In particular, an understanding of the competing objectives of increasing system reliability whilst achieving a reduction in the number of redundant devices will play an important role in determining the economic impact derived from a move to such network designs.
Reconfigurable distribution networks offer different societal benefits in developed and developing nations. It is well known that access to reliable electricity supplies play a critical role in improving quality of life in the developing world and is a basic requirement for effective industrialisation of rural areas. By providing options for the control of loads and by lowering the cost of supply through reduction of redundancy, reconfigurable distribution networks will help facilitate rapid electrification and increase economic output.

Publications

10 25 50
 
Description As part of RDN, we developed a method to quantify the benefit of interconnecting distribution networks, along with a prototype lab-scale power electronic converter that would implement this interconnection in a fault-tolerant manner. A key result was to demonstrate that in many cases these interlinking converters need only produce a small series voltage between two network nodes in order to increase significantly load and generation hosting capacity of both networks. The use of such part-rated converters has the advantage of reducing the capital cost and increasing the apparent efficiency of power electronics systems on the distribution network.

A new format of power converter has also been proposed as a coupling interface for medium voltage microgrids. It is direct AC to AC converter based the modular multi-level principle. The proposed circuit reduces the number of modules required (with benefits in physical size and power efficiencies) while preserving the ability to mitigate the effect of network faults and prevent flow of excessive fault current.

A problem that has held back the deployment of power electronics in electricity network applications is the short thermal time-constant (rapid heating) of power semiconductors which makes them unable to survive the short-circuit currents found under network fault conditions. A new concept of integrating phase-change materials (PCM) in power semiconductor modules has been proposed and tested, with application-oriented trade-off between latent heat capacity and thermal conductivity. This would allow grid-connected inverters to source the required fault current for grid faults to be detected and located and also all series-compensation network conditioners to allow the passage of fault current without harming the equipment. Making use of the latent heat capacity of the PCM, this has enabled power semiconductors to conduct and switch large current over a short period of time.

In a case-study of deployment of power electronic devices, in this case point-of-load compensators, it has been that they improve voltage control in distribution networks and enhance voltage-driven demand response capability as compared to the substation and/or feeder level control especially, during high loading conditions. A stochastic high resolution domestic electricity demand model based on occupant time-use data was used to quantify the enhanced demand response capability over a 24-hour period (including the seasonal variations) which could be exploited by the system operators as part of their balancing service portfolio. The capacity (i.e. size and cost) of the part-rated compensators were evaluated to weigh the benefits against the necessary investment.

Our partners in India also installed and commissioned a large Microgrids test facility with the following features:
Design & Development of proposed hybrid microgrid system with communication and control layout
Solar PV system modeling with different Inverter technologies
Wind turbine emulator and generator modeling
Long term performance analysis of Solar PV system with different Inverter and sun tracking system
Design and development of Hybrid Microgrid distribution panel
Hierarchical control of hybrid microgrid system for network reconfiguration
Exploitation Route The collaboration has produced findings of several different types with different routes to use. Innovations in power converter design have already been shown to UK manufacturers with a view to creating a demonstration prototype for field testing. The use of power converters for interconnecting substations and feeders is now receiving attention from network operators and we continue to look for ways to trial the technology in the field. The findings on phase-change materials for providing short-term additional current rating are very new and so a approaches will need to be made to module manufacturers to find routes to market.

The expertise established on medium voltage microgrid interfaces has broader application to power electronics used within conventional grids to increase power flow control options. This expertise is already being used to support innovation projects in UK Power Networks.
Sectors Electronics,Energy

 
Description Smart Systems Forum
Geographic Reach National 
Policy Influence Type Membership of a guideline committee
Impact BEIS and OFGEM developed plans to remove barriers, improve market and regulatory framework, catalyse innovation, and shape roles and responsibilities in the shift towards a smart, more flexible energy system which meets the needs of consumers and businesses now and in the future.
 
Description Secondment for Imperial RA to IIT Kanpur from 15/10/17 to 26/11/17 to facilitate collaboration on optimal configuration of medium voltage power converters. 
Organisation Indian Institute of Technology Kanpur
Country India 
Sector Academic/University 
PI Contribution Dr Chaffey and Prof Green have expertise in design of multi-level converters for creating high-power interfaces in electronic networks and in particular the assessment of physical volume (power density) and power losses. We applied this to the use-case of a wooer converter acting as a micro gird interface at medium voltage (11kV) in the context of allowing a section of distribution network in India running as a micro-grid after a grid failure.
Collaborator Contribution Professor Sensarma of IIT Kanpur has expertise in micro gird design for the context in India. He wished to extend his work from LV (400 V) to MV (11kV) examples for larger micrograms. The visit by Dr Chaffey enabled a transfer of expertise in both directions.
Impact The output will be an academic publication which is still in preparation.
Start Year 2017
 
Description CIRED Conference - Flexibility from distributed energy resources: generation, storage and responsive demand 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Presenting modelling related to importance of flexibility and smart operation in future low carbon energy systems
Year(s) Of Engagement Activity 2017
 
Description CIRED Electricity Distribution Conference 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Talk on the future role of energy storage as part of a panel discussion
Year(s) Of Engagement Activity 2015
 
Description Give speech 'Role and value of flexibility in the future low carbon energy systems' at 7th China International Conference on Electricity Distribution 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Give a speech at 7th China International Conference on Electricity Distribution regarding 'Role and value of flexibility in the future low carbon energy systems' and inform the potential development of electricity market in China.
Year(s) Of Engagement Activity 2016
 
Description Participate in ETP on Smart grids - General Assembly 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact Gave Keynote speech on "The need for a fundamental review of electricity networks reliability standards"
Year(s) Of Engagement Activity 2016