Interfacing Next-Generation Grid-Scale Storage to the Electrical Power Network (Inter-Storage)

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Next generation storage technologies have a key role to play in the future electrical power system, making up the difference between what low-carbon sustainable generation can provide, and what the grid needs. This is both in terms of longer term events (shifting energy from when it is generated to when it is used several hours later) and shorter terms events (providing grid support services to 'keep the lights on'). The UK electrical grid is a legacy system - it has been designed under the assumption that grid support services and second-by-second power balancing is undertaken by large central generating units, typically several hundred megawatts in size. However future energy storage units like flywheels will not be one 500 MW flywheel connected at one point: the storage will be something like 500 individual units each of 1MW, connected individually or in clusters of a small number of units. In order for such systems to interface to, and work to support the legacy grid, the interface system (power electronics and control) must be designed to work with the new dynamics of the storage unit and the legacy requirements of the electrical grid. This means that some form of supervisory control is required to modify the local interface control of each storage unit to enable the combined system to behave as a coordinated cohesive system. A local unit would not have an oversight of how the wider network is performing or the other units are behaving and thus the overall system performance would be at best sub-optimal, and at worst individual units could end up fighting with each other - applying contradictory control effort to the system. The dynamics of the control at the point of use would need to be fast to both enable the tight control of current required by modern power electronics, and to enable the fast response required in new systems with large amounts of power electronic interfaced generation and low inertia.This project will investigate the design of the power electronics interface and its local control, considering both flywheel and compressed air energy storage. It will examine the supervisory control and telecommunications requirements needed to coordinate such systems, the required innovations in grid support services, and will formulate new methodologies to provide the required services. And it will investigate the practical constraints of implementing such a system using a real-time digital simulator (RTDS) coupled to a supervisory control system, network emulation and local controller system units.