A modular, expandable network requiring little or no calibration is something that is well sought after and would offer great benefits when used for distributed energy generation. Intelligent and adaptive control of such a network offers stability of supply from intermittent sources which, to date, has been hard to achieve.



Key to the effective use of such control systems is communications, specifically the exchange of commands and status information between the control systems and the attached devices. Power-line communications has been used in various applications for years and would offer a good mechanism for interconnecting devices on a power grid without the expense of laying new cabling.



By using clusters of devices managed by an IEMS (Intelligent Energy Management System) in a branching network fashion (not unlike the grid itself) it would be possible to manage large numbers of devices and high speed with relatively low bandwidth usage increasing the usable range of transmission. Implications of this include improving network efficiency through managed power distribution and increased security of supply

Bedford, Adam

Howe, Joseph Mark

Liu, Xiongwei

Mokhtar, Maizura

English

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European Association for theDevelopment of Renewable Energies,Environment and Power Quality (EA4EPQ)International Conference on Renewable Energies and Power Quality(ICREPQ'11)Las Palmas de Gran Canaria (Spain), 13th to 15th April 2011Energy Network Communications and Expandable Control MechanismsAdam Bedford, Maizura Mokhtar, Xiongwei Liu and Joe HoweCentre for Energy and Power Management,Computing, Engineering and Physical Sciences,University of Central Lancashire, Preston, Lancashire, United KingdomTel: +44 1772 893235Email: abedford1@uclan.ac.uk, mmokhtar@uclan.ac.uk, xliu9@uclan.ac.uk,jmhowe@uclan.ac.ukAbstractA modular, expandable network requiring little or no cal-ibration is something that is well sought after and wouldoﬀer great beneﬁts when used for distributed energy gen-eration. Intelligent and adaptive control of such a net-work oﬀers stability of supply from intermittent sourceswhich, to date, has been hard to achieve.Key to the eﬀective use of such control systems is com-munications, speciﬁcally the exchange of commands andstatus information between the control systems and theattached devices. Power-line communications has beenused in various applications for years and would oﬀer agood mechanism for interconnecting devices on a powergrid without the expense of laying new cabling.By using clusters of devices managed by an IEMS (Intel-ligent Energy Management System) in a branching net-work fashion (not unlike the grid itself) it would be pos-sible to manage large numbers of devices and high speedwith relatively low bandwidth usage increasing the usablerange of transmission. Implications of this include im-proving network eﬃciency through managed power dis-tribution and increased security of supply.1 IntroductionThe concept of an expandable power network which canbe altered in real time without any signiﬁcant repro-cusions for consumers is something that would beneﬁtthe utilities and the consumers alike. However, such anetwork would require signiﬁcant interactivity betweendevices and grid areas requiring further development ofcommunications and control systems. The following in-troduces the key concepts and technologies which are dis-cuss herein.Powerline Communications:Powerline communciations uses multiple overlayed fre-quencies to transmit data along transmission lines. Eachfrequency can then be ﬁltered out and interpreted toyield the transmitted data.Powerline communications has been considered and usedfor many applications over the years including broadbandinternet, grid monitoring and most recently smart me-tering for buildings. However, its usage has always beenlimited by factors inherent to the grids themselves and itis often used in combination with other types of commu-nications. Companies such as Landis+Gyr[1] and ElsterSolutions[2] oﬀer smart metering solutions using somedegree of powerline communications, whilst Echelon[3]oﬀers a development platform for powerline networkinggrid devices.Despite the interest and work done in this area, systemsthat rely entirely on powerline communications, fromgeneration to consumer, are virtually non-existant andas such there is scope for the development of new tech-nology and techniques in this area.Smart Meters:The smart meters currently being installed allow for nearreal-time monitoring of household or business power us-age, scheduled handling of certain devices, for examplewashing machines, heaters, etc., and the option to re-motely connect or disconnect devices.[1,2] All of this isdone on the understanding that it can save the consumermoney on electricity bills.The hope with this (and other) work is that devices canbe developed which can monitor and regulate the ﬂow ofpower into a property without the need for user interac-tion, however, this requires a great deal of interactivitybetween devices as well as some knowledge of how eachdevice behaves.Micro-Grids:The main focus of most power grid research has been thegreater integration and interactivity of grid components.Grid components in this case meaning properties, viasmart meters, and the utilities. As part of this workmicro-grids are being considered to be potentially grid-independant/child systems which connect to the parentgrid only when necessary and otherwise rely on their owngeneration and power storage. The same mechanismsthat allow the eﬀective use of stand-alone generation andstorage however, have implications on larger grids.2 Expandable Power GridsWithin this work an expandable power grid is describedas;"A power grid that can operate equally well at both amicro and macro-grid level without requiring signiﬁcantchanges,"the concept being that such a grid can operate modularlyin a larger grid structure or independently. The key fac-tors to creating a successful expandable grid system are;• the inclusion of an Intelligent Energy ManagementSystem (IEMS),• the ability for each device to communicate with theIEMS,• the capacity for the IEMS to enact measures to con-trol all attached generation and storage, and someconnected loads,• that each device contains a mechanism for reportingpower usage and status including it's priority.The easiest way to look at this is to view the micro-gridcase and then look at the considerations that would needto be made to expand from micro to macro.In a completely independant micro-grid we must assumethat there is suﬃcient average power generation to sup-port the attached loads at any given time. In the case ofthe majority of renewables this is diﬃcult without someform of energy storage which must therefore also be in-cluded within the micro-grid structure.If such a grid is to be based entirely on renewables suchas wind and solar, which are inherently intermittent, theFigure 1: empirical Representation of a Semi-IndependantMicro-Gridenergy storage is essential to maintaining the requiredaverage power output. Regulation of such storage de-vices, in conjuction with the control of non-vital loads(loads that can be safely disconnected and reconnectedwithout incident) will help to use the generation more ef-fectively and eﬃciently. An empirical structure for sucha micro-grid is shown in Figure 1.The "vital loads" in Figure 1 represent those devices thatcannot be disconnected remotely, whereas the "non-vitalloads" can be disconnected or reconnected without inci-dent. Although the micro-grid has been shown having anexternal grid connection this would only be true wherethe grid was being used as a backup power source in thecase of insuﬃcient primary power.For ease of installation, powerline communications wouldconnect all attached devices allowing for monitoring andcontrol. This eliminates the need for additional cablingwhich should in turn help to reduce the expense of suchinstallations.3 Concept SystemsIEMS: The concept IEMS's structure is described bythe block diagram shown in Figure 2.Figure 2: IEMS Block StructureThe blue paths represent power connections and the redrepresent data connections. Each IEMS contains twomain processors. The most powerful being the EMS CPUbecause this is the processor required to run the poten-tially complex EMS algorithms. The MPU is the sec-ond processor which mediates all data transactions andcommands. Two synchronous buﬀers separate the pro-cessors transferring devices speciﬁc data and commands.User input and interfaces are provided but should be sec-ondary to the EMS algorithms.The block diagram also illustrates the diﬀerent hardwarelevels that exist within the device with the EMS algo-rithm being autonomous at the highest level. This dia-gram includes 2 communications modules which may notalways be required depending on the application. Thesecond communications module is required for the bilat-eral version of the IEMS which links across grids andis used in the mass distribution concept which will bedescribed later.Figure 3: IEMS Communications and ID AssignmentAlgorithmsThe ﬂowchart shown in Figure 3 represents the conceptcommunications system platform embedded in the IEMSthat handles connections to all attached devices. Devicesare assigned IDs as they are detected which then serveto facilitate communications between the IEMS and thedevice.These algorithms run in the ﬁrmware layer thatinterfaces the main IEMS algorithms and the devices.In reference to Figure 3;A: "A" attempts to contact all discovered devices insequence, upon successful contact data and com-mands are exchanged between the device and theIEMS. In the event of a failed contact control ispassed to B. Once all IDs have been checked, con-trol passes through to DB: "B" will remove the failed ID from the systemto prevent it from slowing operations down andprogress ID forward passing control back to A un-less the removed ID is the last ID, in which casecontrol passes through to DC: "C" broadcasts the next available ID for detectionby any devices which do not already have an ID.Once this operation has timed out, control passesback to AD: "D" attempts to contact the next unstored ID, if aresponse is received then that ID is added to the IDlist. Whether a response is received or not, controlthen passes to CDevices: Each connected device will need to have at-tached or embedded hardware capable of interfacing withthe IEMS. The concept device structure is described inFigure 4.Figure 4: Device Block StructureThe device structure is a good deal simpler than theIEMS as it does not have high level control algorithmsand only requires a single communications module. Userinput is still an option, however, this will depend on theplacement of the device.Figure 5: Device Communications and ID AssignmentAlgorithmsIn reference to Figure 5;A: "A" interfaces with process C from the IEMS algo-rithms and will pickup and store the new ID beingbroadcast when the device is ﬁrst activated.B: "B" monitors the transmissions from the IEMS, onreceipt of an initiator command code it will checkthe attached ID and, if correct, it will respond andproceed with the exchange of data and commandswith the EMS.For each round transmission and reception event thereis a sub process which must be observed to maintainthe ﬁdelity of the transmission. During data encoding,error correction information will be added to the data tohelp maintain data integrity, this is used to determinesuccessful transmission during the reception stage. Thisoccurs on all transmission-reception pairs.Figure 6: Transmission Process FlowchartFigure 7: Reception Process FlowchartBoth these mechanisms will report errors in the event onnon-receipt, however the error management algorithmshave not been included here. In most cases there willbe numerous pieces of data to be transmitted, thereforecontaining the transmission loop, where as the receptionprocess is the same process repeated for each incomingtransmission.It should be noted that whilst using these mechanismsthe IDs are volatile and will be erased if there is a lossof power. This was deliberately included as a part of themethodology. Any device that suﬀers a loss of power willreconnect and will have its ID re-assigned by the IEMS.This was included as part of the failure response mech-anism allowing the IDs of failed devices to be taken bynew ones as they are added and preventing the numberof IDs exceeding the number of devices. Also, should adevice which had previously had an ID be added to anIEMS where that ID was already present it would causeproblems similar to clashing IP addresses on a computernetwork.The bandwidth in this concept system has deliberatelybeen kept low for two reasons;1. by designing both devices and IEMSs to operate atlow bandwidths necessetates that they be very eco-nomical with their data resulting in reduced proces-sor demands and speciﬁcations, resultin in a moreinexpensive device as a whole,2. bandwidth is related to the frequency used for trans-mission, as the bandwidth increases so must thetransmission frequency, low frequencies transmitfurther down transmission lines therefore reducingthe bandwidth helps to increase transmission range.The losses associated with frequency can be linked to thereactive losses in the inherent capacitance of the trans-mission lines themselves. Since both transmission linesand the ground can both be considered conductors theycan be considered to be a large parallel plate capacitor.An equivalent circuit approximation of a transmissionline is shown in Figure 8.Figure 8: Transmission Line Approximation EquivalentCircuitReactive power generated by a transmission line with thecapacitance C would be;Q = IRMSVRMS (1)=V 2RMSX (2)where;X =12piCf(3)therefore;Q = 2piCfV 2RMS (4)The generation of this reactive power causes additionallosses and, in the case of a data signal, signal degreda-tion. As such reducing the frequency should improvetransmission range for the same signal quality.4 Expanding the ScopeBilateral IEMSs: The bilateral IEMS mentioned ear-lier is the mechanism that allows for the expandabilitywithin these systems. Each IEMS would be able to han-dle a certain number of connected devices but there willbe a limit due to the use of IDs. This limits the use-fulness of a single IEMS unless there is a way to utilisethem in a branching structure.Figure 9: Bilateral IEMS Grid SchematicThis is where the bilateral IEMS is useful because it con-nects to two diﬀerent network branches, in general on ei-ther side of a substation. A bilateral IEMS is in essencea IEMS with a device interface on the back. On oneside are the devices that the IEMS controls and on theother side is a device interface connected to a "superior"IEMS. A bilateral IEMS can be used with or without the"superior" IEMS.The main purpose of a bilateral IEMS structure is toallow for greater coordination of resources. On a mostbasic level, a superior IEMS can command a subordinateIEMS to vary its output and in turn that IEMS will com-mand its connected devices (and subordinate IEMSs) toincrease their outputs or if that is not possible return anerror saying why. Using this method each IEMS can havea limited number of connected devices and is responsiblefor delegating tasks to the IEMSs below it. A basic ex-plaination would be the superior IEMS demands power,the subordinates go and ﬁnd it.This has additional beneﬁts with the introduction of lo-cal storage for distributed generation in that it can helpto reduce losses within transmission lines and thereforeimprove the overall eﬃciency of the grid. In Figure 9 A& B represent local grids that are geographically closewhile C represents a distant grid. If, when either A orB exceeds their local resource (including storage), poweroutput is increased from the neighbouring grid (B or Arespectively), rather than C, then transmission losses arereduced and eﬃciency is increased. If power loss in trans-mission lines is assumed to follow;P = I2R (5)Figure 10: Bilateral IEMS Grid Schematicwhere;R ∝ L (6)and L is the length of the transmission line, then an in-crease in the power being transmitted down a long trans-mission line will cause substantially higher losses thantransmitting that power down a shorter line for the samevoltage. Transmission at lower voltages is less eﬃcientbecause of the proportionally higher currents however itis still more advantageous to move power locally thannationally in most circumstances. It may seem counterintuitive to potentially have some areas storing an excesswhile others are draining storage to suppliment a loss,but for limited periods it may improve overall networkeﬃciency. In order for this to work however controllablestorage, generation or loads must be available in eachlocal grid.The nature of a bilateral IEMS makes it possible to createa cascading network structure where a cental IEMS cancontrol the entire infrastructure. However the changeablenature of the grid due to the remapping IDs makes creat-ing a complete network picture a little diﬃcult. Includedin the concept is a mechanism that allows for individualdevices to be queried for information. Should a user orIEMS request information about a speciﬁc address thenthat request is relayed between IEMSs until it reachesthe device. Retrieved information is that passed backthrough the network to the requesting IEMS.Figure 11 shows an IEMS Cascade Infrastructure. Eachcircle represents an IEMS while squares represent at-tached devices. On each level of the cascade the EMSswork to maintain the stability of the grid beneath them,working from a local or even building level to a nationalone. Since each EMS is treated as a device by the oneshigher up it makes the control mechanisms simple, anddue to the reduced amount of information required to op-erate in this way, bandwidth for these applications canbe relatively low without needing to waste MPU time oncompression.Figure 11: Multi-level EMS CascadeFigure 12: Close-up of Relational Addressing NumbersFigure 12 shows how a cascade address would be cre-ated. Each address indicates the path taken through thenetwork, however, its quite possible that the length ofthese addresses would vary substantially from region toregion. This mechanism would likely only be utilisedby the user interface for determining device speciﬁca-tions, most of which would come from a database refer-encing product code numbers transmitted along the net-work. Constantly updating information about deviceswould require too much bandwidth so as a device wascreated it would need to be registered with the appropri-ate databases so that successful queries can be made.5 ConclusionsThis paper illustrates the beneﬁts of and the necessarysteps to create and intelligent energy management sys-tem and related hardware.The use of IEMSs in a cascade infrastructure, such asthe one described previously, would allow for a very ver-satile and almost inﬁnitely expandable network capableof operating at low bandwidth and long range. The useof low bandwidth may limit the data capacity of suchan infrastructure, however it should increase the rangeof transmission where the signal integrity is unimpared.Inceasing range reduces the need for extra hardware, suchas repeaters, and improves response times within the net-work.Intelligent control of energy storage makes it possible toselectively route power within a network. This preventslarge, lossy transfers from other areas of the network,improving overall grid eﬀciency. This is only possibleusing distributed/local generation and storage but couldhave implications for the entire grid.Storage plays another vital role in the ability to regulatethe power being fed into a grid to prevent overpowering.This can prevent excessive losses by absorbing the neces-sary fraction of power output upon transmission. It canalso do the reverse, discharging power to ﬁll a deﬁcit.Combined it can help to maintain a safe operating level,minimising grid ﬂuctuations. Regulated output makesbest use of rated lines and helps to prevent damage tolocal grid systems.Overall, Intelligent system control coupled with a lowbandwidth, cascading architecture should provide notice-able beneﬁts to all users of the grid through increasedeﬃciency and more reliable supply. The low-bandwidthhardware IEMSs and devices are inexpensive to produceand install with no extra cabling required because of thepowerline communications.References1. Landis+Gyr, "http://www.landisgyr.com"2. Elster Solutions, "http://www.elstersolutions.com"3. Echelon, "http://www.echelon.com"4. Harrison, A.; "The Essence of Electric Power Systems;"(1996)

Energy Network Communications and Expandable Control Mechanisms

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