Baris Baykant Alagoz, Cemal Keles, Asim Kaygusuz

Electrical Electronics Engineering Department

Inonu UniversityMalatya, Turkey

3rd International Istanbul Smart Grid Congress and Fair 29-30 April, 2015

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Digital Era of Energy Systems

Basic Topologies

Some Useful Properties of Tree Topology for Energy Grid

Hierarchical Tree (HT) Topology for Smart Grid

A Stochastic Analysis of HT Grid

Upward Balance Spread in HT Grid and Energy Efficiency

Single Path Point to Point Energy Dispatching and Local Balance

Power Flow Analyses for AC Electrical Grid Established in HT Topology

Dynamic HT Grid for Self Healing

Digital era of technology transforms communication and information systems in a revolutionarily way, which makes our applications more integrated, more connected and smarter.

One of challenging tasks for the digital era of energy systems is the transforming traditional static consumer concept to the active user concept, so-called prosumers [1]. Prosumers are expected to, (i) exhibit renewable energy generation potential (ii) share own generation by other prosumers.

The solution in future Smart Grids is Energy Webs [2], which provides two ways energy dispatching between prosumers.

In analogy with information systems,(i) Smart Grid should provide point to point energy dispatching.(ii) Energy packages should be transmitted in the shortest path to improve energy efficiency . (The shorter path reduce transmission losses)

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Network topology http://en.wikipedia.org/wiki/Network_topology?oldid=633380470

Tree topology,•presents acyclic graph that introduces single path from a node to another•allows defining hierarchical family relations.

Nature uses tree like network topologies

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Tree topology on the landscape with hierarchical node organization 4/13

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1) Tree topology provides an acyclic grid structure. This provides unique path from a node to another in grids.This property considerably facilitate routing process of energy dispatches between nodes.

2) Tree topology provides a scalable grid structure.Grids with tree topology can fractionate or unit easily and it does not alloy its tree properties.

3) Tree topology defines family relationships between nodes. This property allows defining node domains that provide local management or localization of system parameter. Family(D)={E,F,G}

Family(A)={B,C, D, Family(D)}

Single path from A to B

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Domain of 2

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(a) Hierarchical illustration of HT grid with respect to node orders. All prosumers are connected at the bottom nodes.

(b) The grid with HT topology on a landscape. The node domains are shown for local energy balance management by local dynamic pricing control [3]

Energy balance error of a node in a HT grid can be expressed in the form of cumulative demand and cumulative generation modeling as follows,

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j : Balance error of node q in layer j

eij <0 : State of excessive generation

eij >0 : State of energy shortage

Cqj : Total demand of node q in layer j

Gqj : Total generation of node q in layer j

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Simulated HT grid:Totally 900 prosumersNumber of bottom nodes at the first layer is 9Number of second layer nodes is 3and 1 root nodes.

In the figure, energy supplier (ES) state probability of stochastic prosumers are denoted by PES . For PES = 0.73, energy balance error of nodes can converged to zero. This indicates that the grid with random prosumer model can reaches energy balanced state. As transmission loss is decreased, PES probability for energy balance decreases to 0.5.

Result:When prosumers are in ES mode with the probability above 0.73, it is possible to preserve the energy balance in the simulated HT grid.

Stochastic prosumer model was used for the stochastic analysis. Prosumers can be either energy supplier mode or energy consumer mode any time, randomly.

Energy shortage

Excessive generation

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In order to minimize transmission losses and improve energy efficiency of HT grids, local balance at bottom nodes is necessary.

In the case of all bottom nodes are energy balanced, the other nodes above the bottom nodes towards the root node becomes energy balanced.This effect is called as the upward balance spread.

When all bottom nodes are energy balanced, energy flows among nodes stop. This prevents transmission loses and improve energy efficiency of the whole system.

Energy balance at the bottom nodes means local energy balance. When local demand is supplied by local generation, the local energy balance takes place and HT grid works energy efficient due to reduced transmission loss

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Energy balance at the bottom nodes

upward balance spread

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Due to family relations among the nodes, HT grid tends to preserve energy balance locally. This property localizes energy dispatching between local nodes for energy balance and decreases transmission losses.

According to grid structure in Figure, the balance state is reached at the layer 3 node 2 and this node is called the balance node for the point to point energy dispatching between node 5 and node 8 in bottom layer.

We observed : (i) Energy imbalance state is localized due to family relation of HT grids. The rest of grid is not affected.(ii) Point to point energy dispatching between two nodes takes place by single path due to acyclic grid structure of HT grids.

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Bus 5 Bus 6 Bus 7 Bus 8

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In order to compare HT grid with mesh topology, we turned HT grid into a mesh grid by connecting Bus 3 and Bus 4 as shown bellow. Simulations was done PowerWorld Simulator

Energy balance states in HT grid and point to point single path energy dispatching among local nodes [4]. (Energy flow takes place by 5 links and 2 branch)

Energy balance states in mesh grid and multi-path irregular energy dispatching between nodes.(Energy flow takes place by 7 links and 4 branch)

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One drawback of HT grids is the split of HT topology, when a connection between nodes is cut. For instance, in the case of transmission line faults, a fraction of HT grid disconnects from the rest of grid. Mesh topology exhibits advantages in such circumstances because the nodes may have more than one connection to other nodes. In order to improve HT grids, we suggest dynamic HT grid structure [4], which is implemented on a mesh grid by switching on or off appropriate links between nodes.

The dynamic HT grid implemented by appropriate switching in a mesh grid.

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The healing of dynamic HT grid by switching on A5, when the connection with dotted line is faulty.

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[1] S. Grijalva, M.U. Tariq, “Prosumer-based smart grid architecture enables a flat, sustainable electricity industry”, IEEE PES Innovative Smart Grid Technologies (ISGT) Conference, pp.1-6, 2011.

[2] K.S. Reddy, M. Kumar, T.K. Mallick, H. Sharon, S. Lokeswaran, “A review of Integration, Control, Communication and Metering (ICCM) of renewable energy based smart grid”, Renewable and Sustainable Energy Reviews vol. 38, pp.180-192, 2014.

[3]B.B. Alagoz, A. Kaygusuz, M. Akcin, S. Alagoz, “A closed-loop energy price controlling method for real-time energy balancing in a smart grid energy market”, Energy vol. 59, pp.95-104, 2013.

[4] B.B. Alagoz, “Değişken Üretim ve Değişken Talep Koşullarında Akıllı Şebekelerde Enerji Dengeleme”, Doktora Tezi, İnönü Üniversitesi,2015.

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