Fig. 1. Sorting the concepts of smart grid in signals and systems view. Cause and effect relations which lead to establishing a novel sort of electric grids are clarified.

Developing Next Generation of Electric Grids for Fulfilling Deficiencies of Conventional Grids in

Supporting Today’s Requirements

Abstract- From the initial days of establishment of power system in the late 20 century up to now, no fundamental improvement has been taken place in power distribution systems; on the other hand many innovations have taken place in both demand and generation sides of power systems. These innovations have introduced new requirements which electric grids should be able to support. The majority of these innovations have held during recent decades. All these have made conventional electric grids somehow deficient. Our aim of this presentation is to develop the next generation of electric grids which fulfills conventional grids and support all new requirements. So at first we investigate innovations and also new requirements which conventional electric grids are not able to support. Then we obtain semantics which next generation of electric grids should be able to support. For implementation of these semantics some infrastructures should be developed, the result is obtaining required pragmatic functions. Finally we investigate achievements. These achievements satisfy the requirements that we introduced firstly which today`s grids should be able to support.

I. INTRODUCTION

Recent innovations in both electric generation and demand sides have resulted in the deficiency of traditional electric grids. New sort of generation such as renewable power plants and distributed resources and other issues such as environmental concerns and high prices of fossil fuels have affected the generation, transmission and distribution sides. On the other hand in demand side new sort of requirements have been turned up. During recent decades electronic

devices on the consumer side have taken the major consumption, these devices require high power quality; furthermore electric energy has taken the place of other energy sources in areas such as transportation, due to these cases reliability issues are more highlighted. New architecture of electric grids should be designed to support these new requirements. In this architecture monitoring, efficiency and intelligent condition based decision making should be considered. To attain the desired architecture bidirectional data and power follow should be available between all levels of the grid. Fortunately as the above innovations have taken place in electric energy production and consumption, great innovations have taken place in communication and intelligent microprocessor based systems. Therefore the tactful solution to solve deficiencies of traditional electric grids is to fortify these grids with communication and intelligent microprocessor based systems. The resultant grid in a general word is called smart grid. In this paper we first define the problem by introducing the impact of new innovations on generation and demand sides, and then we consider the solutions to these conditions; here we introduce the concept of smart grid. After that we examine the contexts which will be enhanced by implementing the smart grid.

In fig.1 the author has considered all the above supporting and obligatory issues which leads to sort a new generation of electric grids. All these cause and effect relations will be investigated in this paper. In fact fig. 1 is a glance over this paper.

Kiarash Ahi Faculty of Electrical Engineering, K.N Toosi University of Technology;

Institute of Electric Power Systems, Leibniz Universität Hannover, 30167 Hannover, Germany; ahi@kiarash-ahi.com

Proceedings of the 2011 International Conference on Power Engineering, Energy and Electrical Drives Torremolinos (Málaga), Spain. May 2011

978-1-4244-9843-7/11/$26.00 ©2011 IEEE

II. NEW INNOVATIONS IN GENERATION SIDE

Issues such as continual risings in full price, global warming concerns due to emission of greenhouse gases (GHG) and Air pollution concerns due to burning of fossil fuels, large investment requirements for renewing and extending generation, transmission and distribution facilities due to rising in electric energy demand, and also due to large difference between peak and mean demand and new concepts such as electric market liberalization, have resulted in (i) tendencies to make electric generation, transmission and distribution more efficient, (ii) peak curtailments programs, (iii) more penetration of Renewable Energy Sources (RES), (iv) participation of Distributed Energy Resources (DER) .

To make the context clearer, in this section we introduce four above issues in detail. A. Efficiency

As fuel prices have been sharply increased during recent years, energy wastes costs more. So efficiency in electric generation, transmission and distribution is being more critical. To enhance the efficiency, the following listed approaches are examined:

1. DER and Micro Grids As a noticeable waste of electricity happens in

transmission and distribution level; by enabling DER in micro and island grids these amount of waste will be greatly mitigated.

2. DC power instead of AC power The major portion of today`s consumption of electricity in

residential and commercial regions is used in electronic devices, which consumes DC power, so AC power should be converted to DC in each of the devices. In these conversions a large amount of losses occurs. On the other hand by increasing renewable power plants and distributed sources, Plug-in Hybrid Electric Vehicles (PHEVs) and battery storages another DC/AC conversion should be done in production side. Therefore a considerable amount of losses which is up to 35% will be imposed on the system. On the other hand in this situation so many unnecessary convertors are included in the devices and cause increases in prices. Eliminating the need for multiple conversions could also

potentially translate into lower maintenance requirements, longer-lived system components, and lower operating costs [1]. In such a condition almost the only devices which need AC power supply are AC motors which are almost used in refrigerator, HVAC compressors and also laundry machines which have already modified by power electronics variable frequency drives [2]. Therefore In such a distribution system, DC power could follow through the whole wires of buildings without the need for a great investing to adopt devices. Such a situation is illustrated in Fig. 2 [3].

Also in transmission level due to new technologies such as innovations in High Temperature Superconductor (HTS) cables, HVDC is now more efficient. HTS cables can conduct 150 times the electrical current of copper of the same dimensions. HTS wire enables power transmission and distribution cables with three to five times the capacity of conventional underground AC cables and up to ten times the capacity of DC cables. With almost zero impedance of HTS cables; wastes in transmission levels will be totally eliminated. Just a few amount of energy which is less than half of the eliminated wastes is to be consumed in chilling utilities to maintain the operation temperature (700 K) of these cables. Not only as copper price constantly rising up in compare of HTS price which is constantly lowering, but also the energy consumption of chilling utilities are cutting due to continual progressing in their technology. [4].

Other pros of DC power which is achieved due to progresses in power electronics is intelligent universal transformer (IUT), as reference [1] clarifies “the IUT which is currently in the very early stages of development, is an advanced power electronic system concept that would entirely replace conventional distribution transformers. An IUT is a solid-state transformer, similar to the power supply in a desktop computer, as such, the device would eliminate power quality problems and convert loads to sinusoidal and unity power factor, which would enhance the efficiency of the entire distribution grid. IUTs also eliminate secondary power faults, supply DC offset loads, and have very low no-load losses. At the same time, the IUT contains none of the hazardous liquid dielectrics found in conventional

Fig. 2. Possible DC power system for tomorrow’s residential buildings [3].

transformers, avoiding the hazards and costs of spills. Component costs for IUTs are steadily falling, compared with components in standard transformers, which are steadily rising in price.”

As efficiency of the generation, transmission and distribution equipment extremely reduce during peak demand time, peak demand curtailment programs, which are described in the next section, has also important role in efficiency enhancements. B. Peak demand curtailment

During peak demand time the generation, transmission and distribution equipment reach their maximum margins. In this situation efficiency of the equipment extremely reduce. On the other hand difference between peak and average demands impose large unnecessary investments for extending equipment. “Top line of Fig. 3 is an example of a typical load duration curve. In this load duration curve, roughly 50% of the generation capacity is used 100% of the time while only 5% (about 400 hours/year) of the time greater than 90% of the capacity is used. Usually the most costly and inefficient generation is used during these peak periods.” [6].

After introducing some prerequisites, we will introduce peak mitigation approaches in the next sections. The bottom line in Fig. 3 is correspondent to such a mitigation which will be described later.

Fig. 3. (Top line) typical asset utilization of generation and (bottom line)

distribution shows potential for improvement [6]. C. Penetration of Renewable Energy Sources (RES)

New concerns about environment protection and global warming and also sharp rising in fuel prices has created great tendency to renewable energy sources. The major part of renewable energy production is affected by intermittency and variability. Fig. 4 shows an example of variability of wind resource output. [7]. One aggravate the situation is the fact that power output of these renewables is not coinciding with demand patterns Due to this volatility of renewables, in conventional power systems we should consider backup for every MW of renewable power plants, this backup is one of the hindrances which limit penetration extension of renewables. D. Participation of Distributed Energy Resources (DER)

Distributed Generation (DG), Demand Response (DR), and Distributed Energy Storage (DES) are new concepts which are now effecting both electric generation and costumer sides. In this paper we refer to these resources collectively as distributed energy resources (DER). All of these concepts may be observed as active costumer

participation in power systems. This resulted in economic benefits for both consumers and electric utilities. Another benefit of DER is mitigation of environmental impacts, this obtained due to (i) almost all DG is from renewable energies and (ii) DER mitigates the need for constructing new transmission facilities because it enables island grids. But for enabling DER wide span grid monitoring, bidirectional power follow and real time electricity pricing are required. In the next sections of this paper we will examine how the new innovations due to realization of smart grid would enable DER.

Fig. 4. An example of variability of wind resource output.

III. NEW INNOVATIONS IN DEMAND SIDE

During recent decades electronic devices on the consumer side have taken the major consumption, these devices require high power quality; furthermore electric energy has taken the place of other energy sources in areas such as transportation, due to these cases reliability issues are more highlighted.

Fig.2 best describes new innovations in demand side. Plug-in Hybrid Electric Vehicles (PHEVs), electronic devices and DG are new concepts which effect residential and commercial consumers. DC power and DERs benefits are described in the previous section. So in this section we describe effect of the innovations on PHEVs, reliability and power quality. A. Plug-in Hybrid Electric Vehicles (PHEVs)

As ref. [7] clarifies “PHEVs become more popular as environmental concerns increase. They are a significant means to reduce reliance on fossil fuels and emission of greenhouse gases (GHG). They will be a major factor in load growth with a potential to eventually consume 600 TWh/year. This estimate assumes 30 kwh for a 100-mile trip”, so they consume high, but their benefit is that this consumption can easily be shifted to low demand times of the grid. Another benefit of PHEVs is their capability to store electric energy in low demand time and sell it back during peak demand time. This capability will be enabled as DER enables with realization of smart grid as described in the section 2.D. The mechanisms of smart grid to made DER enable will be discussed in next sections. B. Electricity is taking place of other energy sources

In many contexts electricity is taking place of other energy sources. As an example in public transportation such as

municipal trains, fossil fuels are replaced with electricity. So the reliability of electricity is more highlighted today. In this case an outage affects larger group of energy consumers and more recompense will impose to people and utilities.

C. Power quality issues

As during recent decades electronic devices on the consumer side have taken the major consumption, power quality has taken up more important issues.

IV. NEW ARCHITECTURE FOR ELECTRIC GRIDS

In sections II and III we described new innovations in generation, transmission, distribution and consumption levels. To support these innovations electric grids should be redesigned. Redesigning electric grids will be resulted in the concept of smart grid.

By realization of smart grid it is expected to happen great enhances in efficiency, utility and consumers economics,

reduction in investments for installing new equipment, enhancing grid reliability, enabling high power quality and mitigating emission of GHG due to global concerns and environment protection plans. These aims will be available by the functions such as wide spread and intelligent grid monitoring, increasing renewable energies penetration, DERs, PHEVs and micro-grids. Before adding these functions to the grids some semantics should be defined and then some infrastructure should be adopt to realize the Semantics. So after considering the requisites which made us to redesign conventional grids and switch to smart grid, it`s the turn to introduce the semantics, then we should examine the infrastructure to realize the semantics, after that we consider smart grid functions (pragmatic occasions) and finally we assess resultant achievements of realizing the whole concept of the smart grid. Fig. 5 shows this suggested road map. So we began with examination of first block elements.

.

Fig. 5. Suggested classification of smart grid issues.

A. Load control Load control shapes the consumption pattern. Due to the

direct load control ability and dynamic price setting policies of the smart grid, peak demand can be totally mitigated, so it`s capable to have a smooth demand profile by using the smart grid. Some methods to aim this goal are to control HVACs thermostats, PEHVs, lighting and so on during the peak demand hours by real time pricing strategies and also direct load control. In the case of direct load control utility

directly control consumer devices based on the contracts between consumer and operators. In real time pricing, utility sends real time price signals which are determined by demand and response; in this case load control done either manually by costumer or smart meters on costumer side which control devices according to patterns which are set by costumer. As an example of this case, the U.S. peak summer demand is 81.5GW so as table-1 shows by implementation of load control strategies 92% of this peak can be mitigated. [1, 10].

I) Load control Real time pricing Direct load control II) Generation and Demand forecasting III) Production forecasting IV) Auto error detection and correction Self healing

I) Wide spread monitoring

II) Intelligent investigation

III) Dynamic algorithms and condition based decision making

IV) Communication infrastructures

V) Measurement equipment

VI) Weather forecasting

I) Increasing renewable energies penetration.

II) Enabling and take advantage of DERs

III) Easing application of PHEVs in electric grids

IV) Enabling island and micro grids

I) Peak mitigation II) High power quality III) Reliable electricity IV) More efficiency V) Lower stress on equipment VI) Economical benefits for both utilities and consumers VII) Environment protection VIII) Delaying or removing the need for capacity expansion

Semantics Infrastructures

Achievements Pragmatic Occasions

Also by enabling load control, penetration of intermittent renewable sources will also easily increases; in this case when production is high, controllable loads due to lowering in electricity price or direct load control would be turned on and then the need for storage due to intermittency of these renewables will be eliminated. B. Generation and Demand forecasting

To set load and generation control strategies, operators should know generation and demand patterns in advance. So many parameters affect generation and consumption. One of these parameters which have the major effect is the weather condition. In very low and very high temperature demand sharply increases. Also production of renewables is depended on weather condition. To reach the best result from load control, operators should know the effect of every change in load on the electricity consumption pattern exactly in advance, as an example it should predict lowering temperature of a specific building HVAC for 10C for 1hour is better to peak curtailment or lowering it for 20C for half an hour. Reference [11], examine such a condition. For attaining this goal the US Department Of Energy (DOE) has developed an intelligent software named “Energy Plus”. This software get building plan, type and heat conductivity of the building glazes and walls, geographic location of the building, current and long term history of weather conditions and etc., then determines the effect of load control strategies on energy consumption pattern of the building. This useful software is free and downloadable from the reference [12]. C. Auto error detection and correction

One of the main goals of redesigning electric grids is to have a self-healing system. This will be enabled by wide span monitoring. The approach is to detect and remove initial errors before they causes adverse events. For enabling this case measuring and analyzing wave forms of every point of the network is being performed. For the measurement level, sensors are embedded in different points

of the network. Measurement data will be sent to operation unit, where analysis and control perform. Analyzing these data is substantial and sensitive part of detection. As reference [13] illustrates “initial failure modes of inline switches, capacitor banks, transformers, etc., may be manifested for weeks with signal levels that are very low in magnitude in comparing to hundreds amperes of load current.” In HV level same condition attain by using the Phasor Measurement Units (PMUs), which are sensors that measure the electric wave forms in real time condition that is in both phase and magnitude, to make the acquired measurement data (which are attained from country wide network) analyzable PMUs stamped their data packet with global positioning system (GPS) time set. PMUs measurement rate are very high in compare to conventional measurement units, they available wave form snapshots for more than 60time a second. Again for gathering data from PMUs a strong communication infrastructure should be available. [10]. D. Communication infrastructures The blood of the smart grid is bidirectional follow of information. As so far mentioned for almost all smart grid functions information from all level of the power system should be available. For communicate between control units, generation units, customers, transmission and distribution lines and posts a reliable and secure communication system should be adopt. To attain this goal in some studies the internet protocol that is TCP/IP is adopted. The mean of transferring the data is difference depending on the situation. For example in most cases PLC is adopted to communicate between utilities and smart meters, while the wireless based on zigbee protocol is using for transferring data between the smart grid and devices (for example home appliances). In this paper we don’t focus on communication protocols and signal transmission means. Fig.6 makes a comparison between power and information flow in traditional utility environment and under smart grid [8].

TABLE-I “The U.S. Peak Summer Demand Reduction Potential in 2010 (GW). Note EE is Energy Efficiency (Gellings, et al., 2006)” [1]

(a)

(b) Fig. 6. (a) Power and information flows in traditional utility environment. (b) Power and information flows under smart grid [8].

E. Pragmatic occasions

Now as Fig.5 shows after establishing semantic and infrastructure concepts the Pragmatic occasions (functions) can be implemented. Here we introduce the realization of these functions.

(i) Increasing renewable energies penetration: The major portion of renewables production such as wind and solar is affected by intermittency and variability. This variability is shown in Fig.4. This variability in production pattern is not corresponding to demand patterns, so in conventional grids storage should be observed for the major portion of renewables production. But due to wide span monitoring, demand and production forecasting, and especially load control which can according to the production pattern shape the demand pattern, by realization of the smart grid increasing penetration of renewables is expectable.

(ii) Enabling and taking advantage of DERs: Again due to the wide span monitoring, forecasting, bidirectional power follow, load control and especially the real time pricing mechanisms; penetration of DERs will be greatly increased. In this case consumers sell electricity to network during high price peak time. Consumers can store electricity in their storage devices such as batteries of their PHEVs during off-peak time, when price of electricity is low, and sell it back to the network during peak time when price of electricity is high. The same conditions can be happened by adopting DG by consumers, they can store their generation in batteries and inject it to the network during high price times. By such methods negative bills for consumers is expectable i.e. then the utilities will pay to such consumers except the consumers pay the utility. On the other hand utilities gain from peak curtailment and also equipment stress mitigation. Fig.3 shows such a condition that participation of DERs “during the peak400hours/year makes significant savings by reducing the necessary capacity by 10%. The potential to increase asset utilization in the distribution system is even more dramatic. In this case, a typical distribution feeder will use no more than half of its capacity only 40% of the time. By engaging DERs to address the peak 400 hours/year of use, 25% of

the feeder capacity would become unnecessary. This translates to delaying or removing the need for capacity expansion”. [6]. Therefore enabling DERs is beneficial for both costumer and utilities.

(iii) Easing application of PHEVs in electric grids: Direct load control and real time pricing are going to make PHEVs usage more convenience. As stated in section 3.1 PHEVs consume large amount of electricity. These vehicles consume the electricity to recharge their batteries, so the major part of this consumption can be shifted to low demand times. Then PHEVs can play a major role in peak curtailment. Furthermore by enabling DER in smart grid PHEVs batteries can participate in the grid as distributed storages.

(iv) Enabling island and micro-grids: As intelligent systems embedded into all levels of grid and make dynamic algorithms and condition based decision making available, DG and distributed storage, real time pricing and wide span control adding to grids, micro grids in one building (As showed in Fig. 2) or a vicinity will interact to make lowering net demand from higher levels of distribution grid. This will resulted in lowering stress on distribution and transmission facilities and this translates to delaying or removing the need for capacity expansion as well as lowering energy waste in transmission and distribution facilities.

F. Resultant achievements Again consider Fig. 5. So far we have described semantics,

infrastructure and pragmatic occasions which are needed to realize smart grid. These elements are tightly interconnected. Interaction of these will result a desired power grid which supports the new requirements that we introduced in the beginning of the paper. We divided these requirements into two parts, one in operator side and another in consumer side. By defining semantics and then provide needed infrastructures to realize them we attained the following four functions: I) Increasing renewable energies penetration, II) Enabling and take advantage of DERs, III) Easing application of PHEVs in electric grids, IV) Enabling island and micro-grids.

As described in this section the following characteristics will be achieved by establishing the described semantics, infrastructure and functions: I) Smooth demand profile with no peak. II) High power quality. III) Reliable electricity. IV) The most efficiency. V) Lower stress on the equipment. VI) Economical benefits for both utilities and consumers. VII) Environment protection. VIII) Delaying or removing the need for capacity expansion. In each of three semantics, infrastructures and functions classes we have investigated what sort of these eight expected results turn up.

After establishment of semantics, providing required infrastructures, obtaining to add the four above functions to the grid and then achieving eight above consequent results, deficiency of tradition grid will be eliminated. In literatures

the resultant system is called smart grid. In Fig. 7 which is originally presented by EPRI [5] we illustrate such a grid. Note that fig. 7 is graphical scheme which illustrates concepts of Fig. 5 in a symbolic power grid.

V. CONCLUSIONS

In this paper we examined why traditional power grids are deficient today. We introduced the innovations that have taken place in generation and demand sides. We investigated new requirements due to these innovations and showed traditional grids are not able to satisfy these requirements. Here the problem defined and after that we searched for the solutions. By establishing some semantics we tried to make a solution for the situation; to realize the semantics some infrastructures introduced and some new functions added to the grids. After that we examined the results. Finally we investigated that the suggested solution is fit enough to solve the problem.

Fig.7. A simplified illustration of the smart grid network.

.

REFERENCES [1] Clark W. Gellings, The smart grid: enabling energy efficiency and

demand response, Lilburn, GA: The Fairmont Press, 2009. [2] Kiarash Ahi, Electric Machinery, Tehran: International Publication of

Tehran, 2010. [3] The Galvin Electricity Initiative, www.galvinpower.org [4] American Superconductor Corporation, www.amsc.com [5] EPRI, Smart Grid Demonstration Overview, Electric Power Research

Institute (EPRI), September. 2009. [6] Eric M. Lightner and Steven E. Widergren, “An Orderly Transition to a

Transformed Electricity System”, IEEE Trans. Smart Grid, vol. 1, no. 1, pp. 3 – 10, June. 2010.

[7] Khosrow Moslehi and Ranjit Kumar “A Reliability Perspective of the Smart Grid”, IEEE Trans. Smart Grid, vol. 1, .no. 1, pp. 57 – 64, June. 2010.

[8] Farrokh Rahimi and Ali Ipakchi “Demand Response as a Market Resource under the Smart Grid Paradigm”. IEEE Trans. Smart Grid, vol. 1, no. 1, pp. 82 – 88, June. 2010.

[9] Department of energy (DOE), “The Smart Grid: an Introduction”, 2010.

[10] Kiarash Ahi “The Smart Grid in Present and Prospective Views” presented at the 13th Int. Conf. ISCE, Tarbiat Modarres University, Tehran, 2010.

[11] Ruiz, N. Cobelo and I. Oyarzabal, J.” A Direct Load Control Model for Virtual Power Plant Management”, IEEE Trans. Power Syst., pp. 959-966, May. 2009.

[12] US Department Of Energy. www.doe.gov [13] Russell, B.D.; Benner, C.L. “Intelligent Systems for Improved

Reliability and Failure Diagnosis in Distribution Systems”, IEEE Trans. Smart Grid, vol. 1, no. 1, pp. 48 – 56, June. 2010.

Kiarash Ahi was born in Tehran-Iran in 1986. He received the B.Sc. degree in Electronics and Electrical Engineering from C.T.B.I.A.U as outstanding graduate, Tehran-Iran in 2009. He is now a M.S student in Electrical Power Engineering at K.N.T.U and Leibniz Universität Hannover-Germany. He has authored three university course books in Persian, and he also has presented more than seven technical papers. He is

a keen interested in increasing penetration of clean energy sources to save the earth from being polluted. His general research interests are design and operation of micro-grids, smart grid applications and sustainable energy alternatives.

Conventional power plants Modern

distribution posts

Control unit

Business and industrial area including DG, storages and controllable loads

Residential area including DG, plug in hybrid vehicles, controllable loads

Renewable Plants