Smart parking lot to minimize residential grid losses based on customer priorities

2013 International Conference on Power, Energy and Control (ICPEC)

Smart Parking Lot to Minimize Residential Grid Losses Based on Customer Priorities 1

Sayed Saeed Hosseini, 1Ali Badri, Masood Parvania

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Department of Electrical Engineering, Shahid Rajaee Teacher training University, Tehran, Iran [email protected], [email protected], [email protected]

Abstract—The growth of customer preferences towards plug-in hybrid electrical vehicles (PHEVs) is becoming more than before. The batteries of these vehicles need to be charged through plugging-in electric grids at home or parking station. By increasing number of PHEVs, these electric loads might have the impacts on the power system efficiency. The impacts specifically could endanger the distribution and micro grids performance, via difficulties such as overloading, power quality or voltage regulation. To overcome this problem charging scenarios are represented that optimize EVs charging at home from a standard outlet. But regarding the importance of smart parking lots, this work explores solving these challenges by replacing PHEVs in a parking station. The paper analyzes charging scenarios in the context of a parking lot. A residential grid is considered to verify this concept. In a new approach smart parking lot is developed and located based on customer priorities. The paper also investigates the integration of renewable energy into the parking lot to supply PHEVs. Keywords- smart parking lot; renewable energy; customer priorities; charging scenarios; plug-in hybrid electric vehicles;

I.

INTRODUCTION

The prospect of vehicles plugging into the electric grids as known plug-in electric vehicles (PEVs) bolsters by the undeniable economic and national-security benefits that result in independence from petroleum and displacing gasoline with electricity [1]. The EVs have potential to reduce fuel cost, gas consumption and decrease harmful emission. The EVs which can plug into the grid include PHEVs and battery electric vehicles (BEVs) but PHEVs have fuel flexibility and so have more acceptance. PHEVs reduce fuel consumption to 70% compared with HEVs. The charging time duration of PHEVs is about 8-10 hours for 40 miles traveling. Most PHEVs are managed to support a travel rate between 13-60 miles in electric mode dependent on battery size [2]. The trend towards PHEVs makes them an important end user in the near future and brings challenges about their requirements. The large number of PHEVs has allowed charging them from the electric grid to be desirable even inevitable [1]. Accordingly, they have a potential to put an undue strain on power systems if they are not supported by smart grid technologies. Particularly, the charging of PHEVs can bring about problems in the performance of distribution systems and micro grids. Because that a PHEV has a large battery which consumes a significant amount of electrical 978-1-4673-6030-2/13/$31.00 ©2013 IEEE

energy. Therefore, PHEVs fleet can raise difficulties such as overloading, power quality, voltage regulation and undesirable peaks as unwanted loads [3]. To overcome these challenges PHEVs are planned to be charged through a charging scenario which makes PHEV’s impacts more limited. Such scenario is introduced as optimal or coordinated charging scenario which is against uncoordinated charging. The former makes PHEVs charging a serious problem for distribution systems. PHEVs can be charged at home from a standard outlet or at a charging station. The first concept has been the main object of previous researches for identifying an optimal charging scenario for PHEVs [3-4]. On the other hand, the importance of parking lots equipped to charging facilities such as fast charging in order to accelerate PHEVs acceptance is undeniable. In addition, they will help V2G concept to be successful as fast and simple as possible. These benefits of charging stations could be manipulated in a platform known as Smart Parking Lot. Therefore, this work focuses on the second concept and analyzes charging scenarios by replacing PHEVs in a parking station. The paper explores solving distribution system challenges of PHEV batteries in the context of a parking lot. This parking lot is developed in a residential grid. In a new approach the paper concentrate on customer concerns to locate the place of parking lot not based on grid perspectives. Because customer satisfaction has a deep influence to make parking lot development be successful. The concept is developed to verify grid losses compared to the first concept. In order to define optimal PHEV charging schedule, the paper also investigates the integration of solar energy into parking lot. II.

SMART PARKING LOTS: OPPORTUNITIES AND CHALLENGES

The emergence of smart parking lots to serve PEVs requirements in power system and generally distribution sector is so remarkable. This concept is appropriate due to PEVs faster development in comparison with smart grid technologies. These technologies that include communication infrastructures and intelligent devices are very essential for PEV charging schedule and especially the success of coordinated charging scenario. Parking lots are easier and faster to equip with these technologies than individual houses. They reduce the need to establish communication platforms for PEVs management and equip the infrastructures with facilities such as higher levels of power for fast charging. In addition, smart parking lots help to make V2G concept being more feasible. Furthermore, the 728

2013 International Conference on Power, Energy and Control (ICPEC)

Parking lots are still limited due to some issues regarding their utilization. An important unanswered question is that who pays for recharging infrastructure in public spaces, e.g. parking lots. The business case for investing these improvements is weak due to high costs and initial consumer preferences for home charging [7-8]. Battery swapping and fast charging would be added to the cost of a parking lot infrastructure. Battery swapping makes challenges for EVs manufactures and fast charging makes significant effects such as battery life degradation, safety problem related to high voltage and stress on region power grid [7-8]. However, these facilities are so remarkable for customers’ deep satisfaction. For example, a discharged battery could be swapped with a charged one in less than two minutes without getting out of the car [7]. According to all limitations on smart parking lots, it is undeniable that they have an effective role in existing power grids and could be so useful regarding charging requirements.

Figure 1.Typical structure of a parking lot for V2G system [5]

Figure 2.The eleven buses residential grid used in problem modeling

III.

PROBLEM MODELING AND SPECIFICATION

A. Grid Topology The distribution network used for this work is a residential grid shown in Fig.2. This system is a radial, three-phase unbalanced grid for a total 48 consumers. Buses 2, 3, and 6-11 are load buses that each one has two houses connected to phase transformer for a 120V voltage. The overhead grid conductors are 336,400 26/7 ACSR (Linnet) for phases and 4/0 6/1 ACSR for the neutral. Each node prepares a connection with a randomly chosen PHEV which needs to be charged. B. Load Profile Scenarios An hourly base load profile for a day during winter is considered as shown in Fig.3 [4]. Two other load profiles are generated by ±2 hours time shifting and each house randomly chooses one of them as the base load profile [3]. 800 700 600 L o ad (W )

success of optimal charging scenario is so affected by owner behaviors which are very stochastic and unpredictable. Most owners prefer to charge their PEVs immediately after returning home which usually meets peak periods. Therefore, charging preferences at home can make problem for coordinated charging scenario. Parking lot can also solve the customers’ unforeseen behaviors because charging schedule in a parking lot is not determined by owners and is based on parking rules and desires. Charging stations can also overcome customers’ uncertainty about the infrastructure support outside home as a serious concern for PEVs acceptance. Therefore, parking of PEVs within parking lots can prepare opportunities to practically provide the most important PEVs requirements for an optimal charging scenario. A typical structure of smart parking lot is showing in Fig.1 [5]. Moreover, constructing the parking lots in the low-load areas of grid or the areas with high capacity lines and transformers could help the power system to bear the PEVs energy requirements. Parking lots can also serve fast and safe charging (defined as a less than 20 minute public charge facility) that has a strong influence on customer satisfaction. Fast charging draws strong interest among customers and facilitates a greater adaptation to PEVs technology. It should be mentioned that at-home charging concept is so regarded because consumer charging preferences still expect to charge PEVs primarily at home [6]. Therefore, interest in public charging is very important for success of this approach. Educating and informing customers regarding available parking lots will be necessary to help promote public charging options for those who may not have charging accessibility at home. Also it will be desirable for those who are reluctant for buying an PEV due to its necessity for at-home charging devices such as plug types (i.e., voltage), wiring requirements and etc [6].

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Figure 3.Daily load profile of single house

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2013 International Conference on Power, Energy and Control (ICPEC) C. PHEVs Specifications Surveys found that the customer preferences across the world for PHEVs move towards mid-size and small-size sedans especially the first one [7]. Therefore, Chevrolet Volt is chosen as one of the most advanced PHEVs in 2011 [2]. Volt drives for a range of 35 miles on its battery. The battery of this car has a maximum storage capacity of 16 kWh and could be charged from empty in about 8-10 hours from a 120V outlet or 3-4 hours using a 240V outlet [2].

(1) Subject to (2) (3) (4) (5)

D. Parking Lot Structure and Customer Priorities

IV.

CASE STUDY IMPLEMENTATION

The performance of the parking lot is investigated at the context of charging scenarios compared to at-home charging concept. The loss minimization algorithm is applied on the residential grid to analyze coordinated charging scenario. System power follows are solved by using forward back ward sweep method. In the case of at-home charging PHEVs are randomly placed at grid nodes after the selection of each house load profile. Monte Carlo simulation is used for this purpose at the levels of 25%, 50%, 75%, and 100% of PHEVs. In the parking lot concept PHEV penetrations are considered in parking station. Solar energy supplies PHEVs when it is necessary taking into account grid limitations and specifications. It is assumed that PHEVs are connected to a 120V outlet that results in a charger with a maximum output power of 1800W. Fast charging is not considered for parking lot. Charging period is started at 18:00h with a fully empty battery and continues until 6:00h the next day. In order to analyze the coordinated charging scenario the charging power for each PHEV could not exceed from the maximum power of the charger. In addition PHEVs must be fully charged at the end of the charging period. Therefore, the minimization problem could be formulated as below:

Where Sd,t : the load at node d at time t Vd,t : the voltage at node d at time t Id,t : the current of line l at time t Pch,t : the power delivered for each PHEV at time t Pchmax: the maximum out power of the charger Cfullcharge: the full capacity of the PHEV battery V.

RESULT AND DISCUSSION

For each aspect, smart parking lot and at-home charging, grid losses and load profiles are analyzed for all penetration levels. In the case of at-home charging, the number of Monte Carlo iterations to achieve the steady state solution is around 500 runs as shown in Fig. 4. First it is assumed that there is no solar energy for supplying PHEVs and parking lot provides required energy via power system. Obviously, uncoordinated charging in both cases adds a significant load at all PHEVs penetrations. As seen in Fig.5 coordinated charging in parking lot could supply more PHEVs in comparison with at-home in peak hours. It is important from the perspective of customers’ satisfaction. Slight difference between load profiles in hours in which no PHEVs are plugged in is due to random home load profile chosen. Since base load for each home is much lower than batteries load, this difference does not make a remarkable impact in grid losses and could be neglected. 200 Uncoordinated charging for 25% penetration Uncoordinated charging for 50% penetration Coordinated charging for 25% penetration Coordinated charging for 50% penetration

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The researches show that the location of a parking lot has the most motivation for customers to use a public charge station. Almost two third (62%) of reported customers define that 1-5 blocks (1 block is about 201.168 meters) would be too far for them to use a public parking lot. Therefore, for this case parking lot is located so that the farthest customers have the same distance from that and this distance is less than 660 feet (1 block). On the other hand, parking lot space is determined based on Volt dimensions and required space for charge [9]. Moreover, it is assumed that the roof of this parking lot is covered with solar panels that are necessary for this investigation. A typical PV module is used for parking installation that is 200 watts and about 14 square feet. It should be noted that every location on earth has an average "Peak Sun Hours" ranging from 4-6 hours for good solar production. These peak sun hours occur between 10am and 3pm [10]. Therefore, 4 hours solar production is considered for the model.

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Figure 4.Grid losses for 25% and 50% PHEVs penetration

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Figure 5.Load profiles for two charging aspects at 25% PHEVs penetration

The growth in PHEVs numbers at level of 50% and upper leads to a large amount of load demand at parking lot node. This could make overloading at this node and can be recognized in power flow computation. Therefore, to overcome this challenge an energy supplier for PHEVs has to be considered in integration of parking lot. Here it is presumed that the parking lot roof is covered with solar panels. It should be noted that this challenge could permanently occur in every level of residential grids that includes 120V and 230V grids. On the other hand, parking lot could not be located in far areas with higher voltage levels to meet customer desires and concerns. As given, the location of parking lot has a deep influence on customers’ satisfaction and thus, in turn could make parking lots useless. On the other hand, it is not desirable to utilize distributed energy (DG) sources in parking lots due to their high investments. For instance, for this number of PHEVs considered here, a very large investment is needed to equip parking lot roof with solar panel technology [10]. Note that, even without a DG resource a parking station still has high costs which is not clear who pays for. In addition, the required space is another problem in residential grids that in this case all parking station roof is used to install solar panels. This capacity of solar energy supplies PHEVs as much as possible and the demand surplus is supplied by the power grid. Figs. 6-8 shows load profiles for other penetrations of PHEVs in each aspect. As shown in Fig.6 the solar energy capacity is capable to supply all PHEVs at level of 50% penetration and this can decrease the grid losses to the base load rate. In the other cases the load excess of PHEVs is prepared by the grid in uncoordinated and coordinated charging scenarios. Integration of parking lot and solar energy can considerably decrease the demand of PHEVs and relieve peak loads. This reduced demand is so useful for system operator (SO) and decreases the need for future generation investment for supplying PHEVs requirements. It also reduces the need for keeping power plant on due to load increasing in off peak periods. On the other hand, parking lot charging ignores the necessity of infrastructure investment for at-home charging and noticeably relieves SO costs.

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Figure 6.Load profiles for two charging aspects at 50% PHEVs penetration

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Figure 7.Load profiles for two charging aspects at 75% PHEVs penetration

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Figure 8.Load profiles for two charging aspects at 100% PHEVs penetration

Therefore, parking lot charging aspect would lead to a significant reduction in grid losses as seen in Fig.9. Using solar energy in parking lot can significantly decrease grid losses even without coordinated charging scenario compared to athome coordinated charging. In 25% PHEVs level without solar energy both parking lot charging scenarios result in lower losses in comparison with at-home charging scenarios. Note that in 50% penetration solar energy can completely supply

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ResearchDesign and Survey Results”, 2010, May. [Online]. Available: http://my.epri.com/portal/server.pt?Abstract_id=000000000001022728. [7] Deloitte. ,“Unplugged: Electric vehicle realities versusconsumer expectations”, 2011, September. [Online]. Available: http://www.deloitte.com/view/en_GX/global/search/index.htm?searchKe ywordsField=Unplugged%3A+Electric+vehicle+realities+versus+consu mer+expectations [8] Accenture news, “Changing the game: Plug-in electric vehicle pilots”, 2011, [Online]. Available: http://newsroom.accenture.com/article_display.cfm?article_id=5151 [9] Electric Drive WA, “Seattle Office of Sustainability and Environment: Demand for Electric Vehicle Charging Station”, 2012, May. [Online]. Available: http://www.electricdrive.wa.gov [10] The Daily Green, [Online]. Available: http://www.thedailygreen.com/environmental-news/latest/solar-powersolar-panels-460409

, Figure 9.Grid losses reduction over parking lot charging

VI.

CONCLUSION

This work has explored PHEVs charging scenarios by replacing them in a parking lot that has been equipped with solar energy. This aspect results in great improvements for SO in terms of, peak load and grid losses reduction. It could be deduced that SO could gain excellent benefits with parking lot development in residential grids. Furthermore, from this outlook SO would solve the concerns about parking lot investments especially with regard to its high costs. In fact, SO could have income from selling the excessive energy obtained from providing smart parking lots with coordinated charging strategy. This would be a great incentive for SO to facilitate parking lots and encourage PHEV owners to utilize from them. This concept could be noticed as future work relating to parking lot charging. REFERENCES [1]

[2]

[3]

[4]

[5]

[6]

S. Letendre, P. Denholm, and P. Lilienthal, “Electric & Hybrid Cars: New Load or New Resource?,” Public Utilities Frotnightly, 2006, Dec. [Online]. Available: http://www. fortnightly.com/pur_search_r.cfm. Energy Power Research Institue (EPRI), “Pluging in: A Customer’s Guid to the Electric Vehicle”, 2011. [Online]. Available: http://my.epri.com/portal/server.pt?Abstract_id=000000000001023161 E. Sortomme, M. M. Hindi, S. D. James MacPherson, and S. S. Venkata, “Coordinated Charging of Plug-in Hybrid Electric Vehicles to Minimize Distribution System Losses”, IEEE Transaction on Smart Grid, vol. 2, no. 1, p.p. 198-205, 2011. K. Clement-Nyns, E. Haesen, and J. Driesen, “The Impact of Charging Plug-in Hybrid Electric Vehicles on a Residential Distribution Grid”, IEEE Transaction on Power Systems, vol. 25, no. 1, p.p. 371-380, 2010. C. Hutson, G.K. Venayagamoorthy, and K.A. Corzine, “Intelligent Scheduling of Hybrid and Electric Vehicle Storage Capacity in a ParkingLot for Profit Maximization in Grid Power Transactions”, IEEE Conference on Energy 2030, p.p. 1-8, 2008. Energy Power Research Institue (EPRI), “Characterizing Consumers’ Interestin and Infrastructure Expectationsfor Electric Vehicles:

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