RHYTHM: Resilient Hybrid Technology for High-Value Microgrids
Lead Research Organisation:
Imperial College London
Department Name: Electrical and Electronic Engineering
Abstract
Microgrids for uninterruptable power supply systems (UPS) have been used in high-value service provider buildings for many years. Despite they use conventional network topologies with relatively conventional control and protection systems, the use of low voltage DC to supply information technologies (IT) loads is rapidly becoming standard. In these systems, DC is is seen as an opportunity to improve reliability and to reduce energy losses and costs. Today the market of photovoltaics, batteries, power electronics and IT hardware keeps growing as these technologies become more cost-competitive. Thus, the use of DC could be extended to further types of loads, generation and storage giving rise to hybrid AC-DC microgrids. When considering the current business-as-usual approach to electrical network design, planning and operation, the growth of renewables and power electronics is often seen as a threat to electrical networks. However, by exploiting the controllability of power electronics it would be possible to build highly-reliable, energy-efficient and cost-effective networks with low carbon impact. High-value buildings today present interesting opportunities to test new concepts of microgrids that could be used at a larger scale in the future. However, multiple technical questions still remain unanswered, such as: "how much can microgrid design be optimised while preserving high reliability?" or "how does low level control for transient stability affect battery life span and how can it be improved?" to name a few. This project seeks to answer these questions by bringing together world leading expertise on microgrids, network planning, energy storage, power converter design and power electronic control from the UK and Korea. The project will consider hybrid AC-DC microgrids with loads, generation and energy storage connected in either side. It will focus on applications to high-value service provider buildings with the ambition of generating knowledge that will be useful in other applications and at greater distribution network scale.
Planned Impact
Around the world there is a growing emphasis on the resilience and security of energy supply being addressed at local level to a greater extent and in preference to achieving this through measures only at the national scale electricity system. A common expression of this is the micro-grid. Microgirds aid resilience through the ability to manage critical loads and supply them as first priority from local resources, the resources being local generation supplemented by local energy storage. Further, a mircogrid can use its resources of generation, storage and dispatchable load offer control and support services to neighbouring microgrids and to the larger grid beyond. Establishing the cost-benefit case for providing resilience in this fashion will have impact on approaches to planning networks that could yield substantial cost savings.
A hybrid AC + DC microgird offers a transition to new forms of energy distribution in buildings. The DC element could, when established, yield cost savings in integrating roof and façade PV and battery energy storage and in interfacing IT and lightning loads in offices and homes. The hybridisation with an AC element allows traditional equipment and high power equipment to be accommodated readily. Demonstrating the feasibility and efficacy of the hybrid approach will have impact on the design of building services.
A key element of the hybrid microgrid is the multi-port power converter at its hub. By working closely with power electronics manufacturers we aim to be able to provide a ready route to commercialise such a technology.
A hybrid AC + DC microgird offers a transition to new forms of energy distribution in buildings. The DC element could, when established, yield cost savings in integrating roof and façade PV and battery energy storage and in interfacing IT and lightning loads in offices and homes. The hybridisation with an AC element allows traditional equipment and high power equipment to be accommodated readily. Demonstrating the feasibility and efficacy of the hybrid approach will have impact on the design of building services.
A key element of the hybrid microgrid is the multi-port power converter at its hub. By working closely with power electronics manufacturers we aim to be able to provide a ready route to commercialise such a technology.
Publications
Barreras J
(2018)
Derating Strategies for Lithium-Ion Batteries in Electric Vehicles
Gan L
(2019)
Limitations in Energy Management Systems: A Case Study for Resilient Interconnected Microgrids
in IEEE Transactions on Smart Grid
Gan L
(2021)
Data-Driven Energy Management System With Gaussian Process Forecasting and MPC for Interconnected Microgrids
in IEEE Transactions on Sustainable Energy
Goncalves J
(2018)
Submodule Temperature Regulation and Balancing in Modular Multilevel Converters
in IEEE Transactions on Industrial Electronics
Gu Y
(2019)
Transfverter: Imbuing Transformer-Like Properties in an Interlink Converter for Robust Control of a Hybrid AC-DC Microgrid
in IEEE Transactions on Power Electronics
Gu Y
(2018)
Reduced-Order Models for Representing Converters in Power System Studies
in IEEE Transactions on Power Electronics
Hussain A
(2019)
Impact of Uncertainties on Resilient Operation of Microgrids: A Data-Driven Approach
in IEEE Access
Lachichi A
(2019)
Comparative Optimization Design of a Modular Multilevel Converter Tapping Cells and a 2L-VSC for Hybrid LV ac/dc Microgrids
in IEEE Transactions on Industry Applications
Lachichi A
(2017)
Power converters design for hybrid LV ac/dc microgrids
Li Y
(2018)
A Three-Phase Active Rectifier Topology for Bipolar DC Distribution
in IEEE Transactions on Power Electronics
Oulis Rousis A
(2018)
Design of a Hybrid AC/DC Microgrid Using HOMER Pro: Case Study on an Islanded Residential Application
in Inventions
Rousis A
(2019)
An AC OPF with voltage - frequency coupling constraints for addressing operational challenges of AC/DC microgrids
in Energy Procedia
Rousis A
(2020)
A Planning Model for a Hybrid AC-DC Microgrid Using a Novel GA/AC OPF Algorithm
in IEEE Transactions on Power Systems
Siwakoti Y
(2018)
A New Seven-Level Active Boost Neutral Point Clamped (7L-ABNPC) Inverter
Siwakoti Y
(2019)
A Novel Seven-Level Active Neutral-Point-Clamped Converter With Reduced Active Switching Devices and DC-Link Voltage
in IEEE Transactions on Power Electronics
Son S
(2019)
High Step-Up Resonant DC/DC Converter With Balanced Capacitor Voltage for Distributed Generation Systems
in IEEE Transactions on Power Electronics
Wang Y
(2019)
H5+ Converter: A Bidirectional AC-DC Converter With DC-Fault-Blocking and Self-Pre-Charge Capabilities
in IEEE Transactions on Power Electronics
| Description | The UK team in the Rhythm collaboration have explored various aspects of how to configure, design and operate hybrid microgrids comprising AC and DC supply buses with in a building or a cluster of buildings. Network optimisation tools have been applied to case-study buildings in order to determine what performance benefits and cost reductions might be achievable by a move to a microgrid structure. Currently there are too many options around designing a microgrid; choices have to be made regarding sizing of the connection to grid, converters linking AC and DC, hybrid energy storage, EV charging infrastructure, Distributed Generation etc. while ensuring that all operational constraints are met and critical loads can be maintained in islanding conditions at minimum cost. We have developed a novel planning approach combining traditional optimization techniques with genetic algorithms, enabling us to handle the non-linear search space that arises and identify economic and robust microgrid designs. Emphasis has been placed on stability studies of microgrids and AC+DC microgrids in particular. These studies are greatly aided by having reduced-order dynamic models which represent the relevant features with fewer states and a reduced computational burden. A new, more accurate, approach to model-order reduction for inverters and has been proposed and verified. Slow dynamics are retained with physically meaningful state variables and non-linearities preserved and the portion of fast dynamics that interact with the slow are extracted and retained with the rest discarded. The concept of transfverter has been proposed: a power electronic converter between the two subsystems in hybrid AC/DC buildings would be controlled to couple the dynamics of both subsystems in a similar way as a transformer would do. This enables all sources of power in the system to contribute to the regulation of the network, a role that is often assigned to a single generator unit on either side; the proposed design methodology enables seamless transition in islanding conditions. The project has also addressed hardware development. We have proposed an inverter topology that can interrupt DC short circuits and deliver a controlled amount of current under collapsed DC-side conditions with little penalty on the converter cost and its efficiency. We have also proposed a converter that can be connected to existing distribution transformers to generate a DC supply with two independent voltage levels (pole-to-pole and pole-to-ground). A new fully-controllable four-port isolated converter has also been invented, analysed and prototyped. The converter contains only four active devices. This circuit is intended to manage power flow on a low voltage (100-400V) bipolar DC microgrid for high value buildings. We have developed a networked scaled 24-node microgrid system in order to study complex energy management interactions and control challenges that occur at the millisecond to second timescales. |
| Exploitation Route | Micrograms are key part of the strategy in Korea to ensure high security of supply. Industrial partners collaborating in the project are in a position to start exploiting the new design and analysis techniques. In the UK, the cost-benefit assessment of investment in microgrid facilities is still a matter of debate and will be using our findings to help inform that debate. |
| Sectors | Energy |
| Description | Prof Green and Dr Gu have been engaged by UK Power Networks to review designs for power converters and their controllers for an installation in their network in London and the South East. These design reviews are intended to give expert advice on best practice and potential pitfalls and a good proportion of that expertise was built up during the Rhythm project. |
| First Year Of Impact | 2019 |
| Sector | Energy |
| Description | Collaboration Oxford-INU |
| Organisation | Incheon National University |
| Country | Korea, Republic of |
| Sector | Academic/University |
| PI Contribution | Oxford hosted a visit from a researcher at INU. Developed ideas for joint research and co-authorship of papers. Exchanged algorithm relating to battery modelling and microgrids. |
| Collaborator Contribution | Exchanged algorithm relating to control of microgrids. |
| Impact | no outputs yet |
| Start Year | 2017 |
| Description | Collaboration on design of Power Converters for Microgrids with Pohang University of Science and Technology |
| Organisation | Pohang University of Science and Technology |
| Country | Korea, Republic of |
| Sector | Academic/University |
| PI Contribution | The collaboration is just beginning we have had one exploratory visit by researchers from Pohang in 2017 and another in 2018. We shared our expertise on optimisation of converters with high-frequency transformer isolation. |
| Collaborator Contribution | The partner secured funding locally to support a 5 month research secondment to Imperial College to collaborate design of power converters for microgrids. |
| Impact | None at this point |
| Start Year | 2018 |
| Description | Secondment to INU |
| Organisation | Incheon National University |
| Country | Korea, Republic of |
| Sector | Academic/University |
| PI Contribution | The RHYTHM project is focused on exploring the feasibility and features of hybrid AC and DC micro-girds. Prof Green and Dr Gu at Imperial have developed a theoretical approach to designing stable control of the interface between the DC and AC portions of a hybrid micro-grid that is robust to variations in the proportion of load on the DC and AC buses. This has been validated in simulation studies but needed further verification through experiment |
| Collaborator Contribution | The experimental facilities in INU include recent additions that enable DC + AC hybrid micro-grids to be run. During the secondment the experimental facility was adapted to enable stability testing under various load conditions. |
| Impact | The collaboration is not yet complete but when a full set of experimental evidence has been gathered an academic publication will be submitted describing the new, verified, control system design method. |
| Start Year | 2018 |
| Description | A poster presentation at the Cigre-UK NGN 10 year celebration event in Manchester |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Industry/Business |
| Results and Impact | Engineers and researchers from industry and academia in the UK attended this event to celebrate 10 years of Cigre UK NGN (Next Generation Network). NGN is an association within Cigre that has the mission to develop the next generation of professional engineering for the power industry. The event was a networking event where people were invited to share and present their latest work. Mr Yitong Li, attended the meeting and brought a poster to present his ongoing work on AC/DC converters for building microgrids and give a general overview of the RHYTHM project. During the meeting he had the chance to talk different people, mainly PhD students from other UK universities. |
| Year(s) Of Engagement Activity | 2017 |
| URL | https://www.eventbrite.co.uk/e/celebrating-10-years-of-the-ngn-evening-event-tickets-35536090403 |
| Description | A talk about Electricity and Climate Change explaining the role of AC and DC to Year 8 students |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Schools |
| Results and Impact | This talk was prepared and delivered by Dr Amel Lachichi and it was given twice. The first time it was held at Imperial and it was attended by a group of 25 year 8 students from St Paul's Way Trust school; the second one was given to a group of 6 students of mixed ages at the William Perkins school. The purpose of the talk was to introduce the students to the concept of AC and DC current and to explain why they are preferred in different applications. The talk involved a small experiment using lab equipment. The ultimate goal of the talk was to attract the attention of young children to engineering. |
| Year(s) Of Engagement Activity | 2018 |
| Description | Talk for the Building Research Establishment (BRE) UK |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Professional Practitioners |
| Results and Impact | 40 minute talk on DC microgrids for commercial and residential buildings. Included participation in a 30 min panel Q&A session. |
| Year(s) Of Engagement Activity | 2017 |
| Description | Tutorial on Energy Storage at the Power Systems Computation Conference (PSCC'18) in Dublin |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | International |
| Primary Audience | Professional Practitioners |
| Results and Impact | Three of the investigators involved in the project, Dr Dave Howey, Dr Adria Junyent-Ferre and Dr Ioannis Konstantelos, were invited to give a tutorial about energy storage in power systems at the Power Systems Computation Conference, PSCC'18, which was held in Dublin in June 2018. This is an international conference that takes place every two years. It is attended by professionals from the power systems engineering field both from industry and academia. The conference includes a single tutorial and it is a whole-day event on the first day of the conference with no other activities programmed for the day. The tutorial was given together with 5 other speakers. Dr Howey's part of the tutorial covered modelling of electrochemical energy storage, Dr Junyent-Ferre's part was about modelling of power electronic converters for battery storage grid interfaces and Dr Konstantelos talked about economic, environmental and security of supply benefits of energy storage. The three talks were linked to the research activities the groups at Imperial College London and University of Oxford were doing within the RHYTHM project. |
| Year(s) Of Engagement Activity | 2018 |
| URL | http://www.pscc2018.net |