Stability and Control of Power Networks with Energy Storage (STABLE-NET)

Summary:
The operations of interconnected power networks are facing unprecedented challenges which are primarily driven by new intermittent sources of generation that are replacing centralised flexible generation. Such intermittency in generation inevitably leads to difficulties in achieving reliable operation. The existing weak high voltage AC system in China suffers from stability-related problems and as a result, in 2010 17% of the electricity produced in China's top 10 wind power bases was curtailed with curtailment reaching as much as 25% in the Gansu province. A single grid fault on the 24th of February 2011 caused the disconnection of 598 wind turbines in Northwest China, resulting in a system frequency dip of 0.178 Hz, highlighting the inadequacy of the control technology currently used. A similar incident of generation outage in the UK on the 2nd of September 2010 led to a rapid decline in frequency, which disconnected about 350 MW embedded generation (mainly wind) through the action of the rate of change of frequency (RoCoF) protection. These are two of the many incidents that highlight the need for new approaches in fast system monitoring for enhanced stability and control.
Energy storage is essential to address the balance between generation and demand at different time scales. However, the description of the dynamic performance of energy storage under varied loading, and their state of charge and health monitoring are currently open problems. Complex dynamic behaviour, such as hysteresis, may manifest in storage systems. Therefore it is not clear how storage may impact power system operation, particularly with respect to stability. There have been instances of loss of generation because of the inadequate control of the power converter interface between intermittent generation and network. When the existing power converter technology is duplicated to act as an interface between storage and the grid, the poor performance is inevitable without improved understanding of local and global dynamics. Another key barrier is the lack of robust enabling technology for monitoring and control that can integrate the capabilities of storage in a time critical manner. Fast dynamic security assessment has been attempted through the energy function approach - but existing tools fail to compute the true stability margin because of the complexity of power system dynamic characteristics. All these barriers may be overcome through underpinning research in monitoring, modelling and control of storage to stabilise interconnected power network operations.

The challenges lie in fast computation, fault detection and robust control design of the interface between storage and the network. The approach proposed here is decentralised stability monitoring, assessment and control of the network. Existing network operation practice relies heavily on slow and centralised control architectures through large SCADA/EMS. The methodologies that are being proposed will thus need to rely little on system wide communication infrastructure. In addition, distributed approach to dynamic system monitoring, decentralised approaches to system wide disturbances and dynamic security assessment through distributed energy function are novel approaches. The innovations include cutting edge representations of high power low energy storage; energy functions to include asynchronous and synchronous generation with storage with resistive elements, practical applications of ground breaking decentralised fault detection and robust and reliable control between intermittent generation and the rest of the system.

Because the successful operation of interconnected power grids requires fast computation and control, as well as energy storage domain knowledge, the power system and energy storage experts in this consortium are joined by a number of leading control theory experts with experience in power networks - definitely a very unique strength of the team.

Impact Summary
Distributed control and monitoring of power grids incorporating storage is the way forward to address the intermittency of renewable generation. This will make the large population of China more energy secure and drive developments in new technology, plus it will generate huge opportunities for business and communities through enhanced economic activities.
In the UK, China and many other countries worldwide, control and computation are driving smart grid development. Network operators such as National Grid, UK and the State Grid Corporation in China (SGCC) and power and control equipment vendors such as Alstom Grid (UK and China) and ABB are clear beneficiaries as is expressed in their strong support for this proposal. Many of the investigators on both the UK and Chinese side already enjoy healthy collaborative working relationships with industrial and utility partners, primarily within their own countries. This programme will undoubtedly deliver greater bilateral exchange.
The UK Government in 2011 recognised the need for more than £110 billion investment by 2020 to build and reinforce its electricity generation and grid infrastructure. A significant part of this investment will be in transmission monitoring and control, and storage. The Chinese government has enacted a plan to develop smart grid technology. China's national utility, the State Grid Corporation of China (SGCC), announced plans to invest $250 billion in electric power infrastructure upgrades over the next five years, of which $45 billion is earmarked for smart grid technologies. Another $240 billion between 2016 and 2020 will be added to complete the smart grid project. A large number of skilled researchers who will be trained in this project will have opportunities to technically lead future projects in the respective country.
In the short to medium term this project will establish and strengthen the collaborations between the leading UK and Chinese universities engaged in research in power system stability and control theory applications for grid integration of renewable energy and storage. This will pave the way to further strengthen and expand the volume of activities through future research funding opportunities involving both countries because of the degree of challenge and opportunities afforded by power grids in both the countries.
As described in the case for support, the consortium partners from both sides bring a range of theoretical, application and laboratory experience and expertise in the areas of control theory, computation, power system stability, monitoring, renewable energy and storage into the proposal. There are differences in the approaches to power network design, control and operation and specifications on the operational performance of control devices in the UK compared to China. This will lead to novel scientific understanding validated on different contexts and systems which could not be possibly achieved by either side working in isolation. The range of such advances is detailed in the proposal. The academic advances include new models, control and monitoring algorithms, and optimal allocations of storage.
The consortium proposes a sound research exchange and dissemination plan through conferences, panel sessions in top conferences such as the IEEE Power and Energy Society General Meeting, the IEEE Conference on Decision and Control and others. The UK side of the consortium has two IEEE Transactions Editors-in-Chief (Control Systems Technology and Sustainable Energy) so the academic impact of this research is going to be high. Industrial impact is also evident given that two of the investigators hold industry chairs (Thornhill and Parisini) and the PI has worked on a number of research projects funded fully by European power industries. The China side has several technology leaders and is well connected with industry, similarly to their UK counterpart, as demonstrated by the track records and industry support.