Electric Vehicle Charging Using Photovoltaic based ... - CyberLeninka

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ScienceDirect Energy Procedia 103 (2016) 213 – 218

Applied Energy Symposium and Forum, REM2016: Renewable Energy Integration with Mini/Microgrid, 19-21 April 2016, Maldives

Electric Vehicle Charging Using Photovoltaic based Microgrid for Remote Islands Abdul Rauf Bhattia,c, Zainal Salama,b,*, Ratil H. Ashiquea a

Centre of Electrical Energy Systems (CEES), Universiti Teknologi Malaysia (UTM), 81310 Johor Bahru, Johor, Malaysia b Insitute of Future Energy, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia c Department of Electrical Engineering, Government College University Faisalabad, Faisalabad 38000, Pakistan

Abstract This paper presents a real-time energy management scheme for electric vehicle (EV) charging using photovoltaic (PV) and energy storage, connected to the microgrid. The scheme is based on the heuristic rule-based strategies to optimize energy flow within microgrid. Preliminary results from the tests at Uligamu Island show that EV charging using proposed scheme is economical compared to charging from standalone generator. Using the PV as the main source for charging EVs, the burden on the microgrid is reduced significantly. It seems that this work is the first attempt to demonstrate the application of PV-EV charging from microgrid in remote island. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2016 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and/or peer-reviewofunder responsibility of REM2016 Peer-review under responsibility the scientific committee of the Applied Energy Symposium and Forum, REM2016: Renewable Energy Integration with Mini/Microgrid. Keywords: Photovoltaic (PV); Microgrid; Electric Vehicle (EV); Real-time energy management; Heuristic rule-based strategy; Autonomous EV charging; Island.

1. Introduction The microgrid is considered to be the most viable option for small and remote island power system. Despite its effectiveness, one of the main concerns is the continuity and cost of the fuel for its electric generators. In addition, the need to preserve the nature, ecological stability and environment are also factors that limit the excessive use of fossil fuels. This is particularly crucial for the island that depends on tourism as a major source of income. At the same time, there is an urgent need for an efficient transportation system that increases mobility and enhances economic activities. These requirements appear conflicting to each other because the transportation requires fuel that is needed for the generators. One possible solution to this dilemma is to introduce electric vehicle (EV). Depending on the geographical layout of the island and the need of the population, EV can be in the form of electric * Corresponding author. Tel.: +6075536187; fax: +6075566272. E-mail address: [email protected].

1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the Applied Energy Symposium and Forum, REM2016: Renewable Energy Integration with Mini/Microgrid. doi:10.1016/j.egypro.2016.11.275

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car/van/bus, scooter/motorcycle or bicycle. However, these vehicles require electricity to charge their battery banks; since the energy source is limited by the availability of generators and fuel, it has to compete for the power with other local loads. Increasing the number of generators is not a preferable option due to the environment concern and the need to import additional fuel. This paper proposes a concept, whereby the EV is charged from the microgrid that is supported by solar photovoltaic (PV) and energy storage unit (ESU) [1]. With the rapid decrease in the price of PV modules, the long-term economic benefit of such system can be tremendous [2]. Furthermore, PV system is almost maintenance free and environmentally friendly; thus, this solution is ideal for islands that need to preserve their natural environment. Despite these merits, unlike the electric generators, PV is an intermittent source that lacks the consistency in producing the output power. Due to the volatility of the solar irradiance, the power available for charging is unpredictable. Besides, there is a need to ensure that the EV is charged continuously without adversely affecting other users on the microgrid. Therefore, it is proposed that an energy storage unit (lead-acid battery pack) be incorporated into the grid. However, with the addition of these two new sources, the complexity of the microgrid system increases significantly. This is where an optimized energy management comes into the picture. Thus, part of the paper is devoted to describing a scheme to optimize the sources, when the EV charging is in operation. To demonstrate the feasibility of proposed idea, the existing PV based microgrid system on Uligamu (or sometimes known as Uligan)—a remote island of Maldives is considered in this study [1]. 2. The Proposed PV-Microgrid EV Charging System Fig. 1 shows the proposed microgrid system located on the Uligamu Island. The rated values of all main components, i.e. the PV array, diesel generator and the ac load are selected according to [1]. Despite the out-dated data, it is not of concern because the interest is to demonstrate the concept of EV charging using the combination of microgrid and PV. The Uligamu Island system is only a case study that is made as an example application; the idea can be extended to other places with similar conditions.

Fig. 1. The structure of PV based microgrid on Island covering local as well as EV load

The island has two diesel generators (GenSet1 and GenSet2), with generating a capacity of 31 and 20 kW, respectively [1]. Similarly, the PV array has the rated capacity of 13 kW [1]. The profile of the load demand for one typical year is shown in Fig. 2 [3]. These data were available by month and is separated into commercial, government, and residential users. The solar irradiance profile for the whole year in given in Fig. 3 [3].The energy storage unit (ESU) consists of lead-acid batteries stacks, with a total capacity of 65 kWh [1]. For the EV, it is assumed that at the time of departure from the charging station (after being charged), its battery state-of-charge (SOC) should be at least 80% of its full capacity.


Fig. 2. Average monthly Load in the Uligamu Island Consumed by different sectors [3]

Fig. 3. Average monthly Solar Radiation in the Uligamu Island [3]

3. The Proposed Real-time Energy Management Scheme Electrical Energy is the lifeline of domestic, industrial, agricultural and approximately every field of life [4-6]. The real-time energy management scheme is required to coordinate the interaction between various energy sources, in conjunction with the load demand (Ld_Dmd) as well as EV charging demand (EV_Dmd). The objective is to minimize the fuel for the electric generator. It has been an important area of research for stand-alone microgrid systems with hybrid energy sources, as demonstrated by the [7-10]. In this work, an energy management scheme using the heuristic rule-based strategies is developed [11]. It is based on human expertise (engineering knowledge), heuristic, intuition and mathematical model. The focus is to be able to charge the EV during day-time without interruption to the ac load demand. The rulebased consists of six operating modes, applied in four different scenarios. Using this approach, the generation side is centrally controlled and the user has the full autonomy to charge the EV at any time of the day [12]. 3.1 Operating Modes The overall operation of the microgrid has been divided into six operating modes. The operating modes control the direction of power flow for optimized usage of the available energy. The proposed operating modes are summarized as: Mode 1: PV to EV If the PV power (PV_Pwr) is sufficient to fulfill the EV_Dmd, then the charging is entirely done by the PV via the onboard charger [11]. The PV will independently charge the EV without the involvement of ESU or GenSet. Mode 2: ESU to EV If PV_Pwr is completely unavailable but the ESU has sufficient amount of energy to fulfill EV_Dmd by itself, then this mode is activated. It decreases the burden on GenSet in the absence of PV power.

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Mode 3: GenSet to EV On the other extreme, if the PV and ESU both are totally incapable of supplying any power, the EV will be charged directly from GenSet. Mode 4: PV to ESU When there is no EV to be charged and PV_Pwr is less or equal to the required SOC of ESU, then all PV_Pwr goes to ESU. This decreases the GenSet dependency by storing energy in the ESU for future use. Mode 5: PV to Load When there is no EV to be charged and ESU has already achieved the maximum limit of SOC, while the PV is generating power, all the energy is sold to the local grid at a price lower than the LCOE of GenSet. Mode 6: GenSet to Load When the surplus PV_Pwr is not sufficient to meet the demand of ac load, the GenSet provides the power to the local load. 3.2 Charging Scenarios The power flow among PV, ESU, GenSet and ac load is coordinated by a central controller. The EV charging is totally decentralized i.e. not being interrupted or shifted to microgrid’s off-peak time (valleyfilling i.e. VF) due to any power constraint from PV, ESU or GenSet. This uninterrupted and unconditional (i.e. no VF, V2G or V2V operation) charging of EV is termed as an autonomous charging. The operation of microgrid for charging EVs as well as for providing the demand of ac load has been divided into the four scenarios. These scenarios decide the execution of different operating modes depending upon PV power and EV/ac load demand. The proposed scenarios have been summarized in Table 1 due to space constraint. Table 1. Application of heuristic rule-based strategies for the operation of microgrid to cover local as well as EV load No.

Scenario

Circumstances

1

No load condition

PV_Pwr is available but EV_Dmd is zero

Operating Modes Mode 4, 5

2

Overload condition

EV_Dmd is greater than the PV_Pwr

Mode 1, 2, 3

3

Under load condition

EV_Dmd is less than PV_Pwr

Mode 1, 4, 5

4

Ac load demand condition

Ld_Dmd must be fulfilled without any interruption

Mode 5, 6

4. Results and Discussion Each EV is fitted with a 4 kWhr battery. It is charged by a Level 2 charger: 240 Vac/17 A (3.3kW). The estimated charging time is from 35 minutes to 3 hours, depending upon the SOC and charging rate [13]. For simplicity, it is assumed that the charging is completed within one hour. From [1], the diesel generator electricity price is 39 cents/kWh. The levelized cost of electricity (LCOE) for PV is 16.7 cents/kWh while for ESU it is 15 cents/kWh including the replacement cost [12]. The operation of the microgrid based on the proposed real-time energy management scheme is executed for 5, 7 and 9 EVs. The power profiles among the various components of the microgrid in the presence of 5, 7, and 9 EVs are shown in Figs. 4 (a), (b) and (c), respectively. The positive values of the ESU power (ESU_Pwr) mean that the energy is flowing from the ESU to the EV and negative value of ESU_Pwr shows that ESU is getting charged from PV. As can be seen from the results in Fig. 4, the PV_Pwr can sufficiently fulfill the EV_Dmd and the ESU charging. In addition, the extra energy is supplied to the load (PV 2 Ld) through the microgrid. At around 12൞2 pm, there is no need for generator power (Gen_Set1 and Gen_Set2), as shown in Fig. 4 (a). Moreover, there is the very limited contribution of ESU in the charging operation because PV_Pwr profile with high magnitude is for summer (June). However, the role of ESU will be more prominent when the number of EV increases, as shown in Figures 4 (b) and (c).

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(a)

(b)

(c) Fig. 4. The power profiles during the operation of microgrid when charging: (a) 5 EVs; (b) 7 EVs; (c) 9 EVs Table 2. Comparison of charging cost and load on GenSet while charging EV using GenSet directly and proposed scheme Per day charging cost in USD while charging EVs using

Maximum EV load on GenSet in kW while charging EVs using

GenSet only

Proposed scheme

Percentage decrease in charging cost

GenSet only

Proposed scheme

Percentage decrease in burden

5

20.58

8.73

57.59

10.69

0

100

7

30.25

12.75

57.84

16.94

0

100

9

43.23

18.08

58.16

24.71

0

100

No. of EVs

Similarly, the participation of ESU in EV charging would be more significant during cloudy weather conditions or winter season. During the absence of PV_Pwr, the Ld_Dmd is fulfilled by the GenSet1 or GenSet2 or both. By limiting the use of ESU for the EV charging only, the lifetime of the ESU can be extended. The results in Figure 4 show, that EVs are being charged autonomously without any interruption or condition. Another exciting feature of the proposed scheme is the reduction of per day charging cost. The results in Table 2 show that by applying the proposed scheme, per day charging price reduces to approximately 58% compared to the charging directly from GenSet. Moreover, the maximum load on GenSet due to EV charging has been reduced 100% by applying the proposed scheme on the microgrid. The percentage of load reduction can be reduced from the mentioned value by increasing the number of EVs to be charged. 5. Conclusion This paper presents a day-time charging scheme for EVs using PV based microgrid. The proposed realtime energy management scheme has been tested on the microgrid located on the Uligamu, which is a remote island of the Republic of Maldives. The charging algorithm provides a decentralized coordinated

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scheme, comprising the heuristic rule-based strategies. The proposed scheme has the capability of charging EVs autonomously. Moreover, the results show that the charging of EV using PV based microgrid in the presence of proposed scheme is more economical as compared to the charging from the standalone generator. Furthermore, the scheme helps the microgrid to reduce EV charging burden on the GenSet൞resulting fuel cost saving. It is envisaged that this work will provide an exciting prospect to the researchers in the field of EV charging, particularly for remote islands. Acknowledgments The authors would like to thank Universiti Teknologi Malaysia and the Ministry of Higher Education, Malaysia for providing the financial support (Grant No. Q.J130000.3009.00M38) to conduct this research. References [1] J. Camerlynck. Modelling of renewable energy systems in the Maldives. The Netherlands: Utrecht University, 2004. [2] A.R. Bhatti, Z. Salam, M.J.B.A. Aziz, K.P. Yee. A Comprehensive Overview of Electric Vehicle Charging using Renewable Energy. IJPEDS 2016; 7: 114-123. [3] C. Nayar, M. Tang, W. Suponthana, Wind/PV/diesel micro grid system implemented in remote islands in the Republic of Maldives, in ICSET, 2008, pp. 1076-1080. [4] A.R. Bhatti, A.G. Bhatti, M. Amjad, Y. Saleem, T. Izhar, F. Hayat. A Comparison of Output Waveforms of Different Alternating Current Sources and Uninterruptible Power Supplies of Various Brands. Life Sci J 2012; 9: 637-642. [5] A.G. Bhatti, A.R. Bhatti, I.A. Chaudhary, M.N. Javed. Energy crisis in pakistan, adaptation and mitigation measures. Energy crisis in pakistan, adaptation and mitigation measures 2012; 19: 67-82. [6] R. Liaqat, A.R. Bhatti, Management and conservation of electrical energy in industrial units, in PGSRET, 2010. [7] C. Changsong, D. Shanxu. Optimal Integration of Plug-In Hybrid Electric Vehicles in Microgrids. IEEE Trans. Ind. Informat. 2014; 10: 1917-1926. [8] M. van der Kam, W. van Sark. Smart charging of electric vehicles with photovoltaic power and vehicle-to-grid technology in a microgrid; a case study. Appl Energ 2015; 152: 20-30. [9] L. Tribioli, M. Barbieri, R. Capata, E. Sciubba, E. Jannelli, G. Bella. A real time energy management strategy for plug-in hybrid electric vehicles based on optimal control theory. Energy Procedia 2014; 45: 949-958. [10] N. Liu, Q. Chen, J. Liu, X. Lu, P. Li, J. Lei, J. Zhang. A Heuristic Operation Strategy for Commercial Building Micro-grids Containing EVs and PV System. IEEE Trans. Ind. Electron. 2014; PP: 1-1. [11] A.R. Bhatti, Z. Salam, M.J.B.A. Aziz, K.P. Yee, R.H. Ashique. Electric vehicles charging using photovoltaic: Status and technological review. Renew Sust Energ Rev 2016; 54: 34-47. [12] A.R. Bhatti, Z. Salam, M.J.B.A. Aziz, K.P. Yee. A critical review of electric vehicle charging using solar photovoltaic. Int J Energ Res 2015; 40: 439-461. [13] L. Zhang. Optimal power management of parking-lot electric vehicle charging. United States: The University of Texas at Dallas, 2014.