Web-of-Cells distributed control concept

Short description

The Web-of-Cells distributed control concept represents a novel way to manage and restore frequency and balancing in the future power system in a bottom-up manner, based on local observables. It as well proposes a more active voltage management approach. 

Main technical features

The proposed Web-of-Cells control concept foresees to manage the future power system in a distributed manner, based on local observables.  It proposes to organize the power system in a cellular manner, where each cell has the responsibility to provide balance and frequency restoration services based on local observables. There is no restriction in how cells are connected to each other (e.g. one or multiple tie-lines) and cells may span multiple voltage levels. The optimal sizing of a cell is determined by two parameters: 1) A cell must be large enough to have sufficient self-balancing capacity/reserves, and 2) it must be small as needed to allow secure reserves activation checking in a computational manageable time. The Web-of-Cells control concept aims to implement a  ‘solve local problems locally’ paradigm, as an alternative to a centrally directed approach, based on intensified TSO-DSO coordination and associated communication and calculation challenges.
It depends on a slightly modified wholesale market architecture, where generation and consumption forecasts contain information that allows as the result of the market clearing process – to determine cell import/export profiles over the (sum of) the tie-lines that connect cells to neighbouring cells. It is important to explicitly note here that it is fine for cells to import from or export energy to other cells. So, there is no requirement that it can be fully self-sustainable. The only requirement is that it has sufficient reserves capacity to correct its own aggregated generation or consumption forecast errors or small incidents, i.e. it must be able to restore its own cell balance, which is defined as the market cleared import/export profile, by monitoring and correcting its (aggregated) tie-line power flows. 
By doing so, system balance is restored in a bottom-up manner, by the aggregated effect of the restoration of all cell balances (Balance Restoration Control).  This is done by deciding on activations based on local observables (tie-line power flows) in line with the solve local problems locally paradigm.  As cells are physically connected to each other and sense each other’s imbalance, there is a local collaboration of neighbours (whereas the decision to activate reserves is based on local observables only, the amount of activation also depends on the frequency deviation to ensure that also frequency gets restored).
It is proposed and assumed that fast acting invertor coupled reserves can be used for the restoration (e.g. batteries or thermostatically controlled loads).  This way, the balance restoration is also capable of containing frequency deviations.  Nevertheless, to support the balance restoration, an adaptive frequency containment control (aFCC) is proposed) which differs from the current FCC by the fact that its activation is steered to mainly/only take place in cells that cause a deviation.  This is done to avoid that FCC activation that act on just a global frequency deviation causes imbalances in cells and breaks the solve local problems locally paradigm. 
The distributed bottom-up balance restoration means that more reserves activations will be needed because the system wide imbalance netting is lost.  The exact impact of this needs further analysis, but it is expected that this could be acceptable in case of the use of zero emission zero fuel cost reserves for the balancing (e.g. thermostatically controlled loads).  Even so, a separate control, Balance Steering Control, has been defined to mitigate the problem, by adjusting cell balance (tie-line power flow profile) set-points in a way that two neighbouring cells can agree to not each individually restore their balance, but they do it together in a way that requires less reserves activations from each of them, while still contributing in the same manner to the system balance restoration.  This can be considered as a peer to peer explicit imbalance netting approach.
Next to balance/frequency restoration, the Web-of-Cells concept advocates a more active voltage control in cells.  It proposes a Periodic Proactive recalculation of optimal voltage setpoints to ensure a robust and efficient (minimal losses) operation.  This is called Post-Primary Voltage control.

 

Innovative aspects

Technology Readiness Level: TRL 4 

Applications

Trademark pending. The mark is owned in equal parts by all the ELECTRA partners. Management and exploitation of the mark will be in charge to EERA AISBL and, specifically, to EERA JP smart grids, to which all the ELECTRA partners belong. In this frame, each ELECTRA partner will have all the applicable rights to use the trademark.

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Contact person details
Details
Showcase ID
JP.EERA.5488:Web-of-Cells distributed control concept
Joint Programme / IRP / ECRIA
IRP ELECTRA
Development stage
Development phase – Laboratory tested
IPR / IPR Status
Trademark (Pending)
Exploitation status
N/C
Technology keyword(s)
smart grids,Distributed real-time control,Balance restoration,Frequency containment,Frequency control,Voltage control