State-of-the-art research to solve the grid congestion due to EVs is focused on smart charging and using (centralized, de-centralized, vehicle-to-grid) stationery energy storage as a buffer between times of peak and off-peak demand. On the other hand, the charging of EVs introduces new challenges and opportunities. This can prove to be beneficial for the EV aggregator as well as to consumers, regarding the economy. Also, EV as distributed storage makes the grid more steady, secure, and resilient by regulating frequency and the spinning reserve as backup power. However, the charging time and range anxiety lead to peak challenges for the use of EVs. In this chapter battery swapping station (BSS) as solution to the EV charging station is discussed.
Top1 Introduction
Issues like climate change, energy security, and declining fossil fuel reserves have caught the attention of the present world economies (Singh et al. 2020). The transportation sector is a major contributor to these issues. With the transportation sector being a cornerstone of the economic development of a country, efforts are being done to make it sustainable in the long run. A part of the solution is to replace the polluting and fossil fuel-based fleet with environmental friendly Electric Vehicles (EVs). Apart from reducing emissions, EVs offer reduced dependency on foreign economies for procurement of fossil fuel (oil), thus increasing the energy security of a country. Apart from the economic and environmental benefits, EVs have numerous technical advantages also. One of the unique advantages is the technology of Vehicle-to-Grid (V2G), in which EVs act as dynamic Energy Storage System and assist the grid with services like peak load shaving, load profile regulation, active and reactive power support, spinning reserve, energy backup, frequency regulation etc. However, mass penetration of EVs also increase the load on the grid. The present practice of uncoordinated charging leads to overloading of the grid and increase in peak load as the charging period of EVs generally coincide with the evening peak period of a residential area. Implementation of smart EV charging strategies offer multiple advantages. Not only the battery life of EV is enhanced but helps in regulating voltage and frequency (Asaad et al. 2017b, a; Shariff et al. 2019). The smart charging strategies comprises of optimization of one or many of following objective functions viz.:
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Integration of renewable based generation
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Minimization of peak load, power and energy cost
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Aggregator profit maximization
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Load profile regulation and demand side management
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Operating cost reduction
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Increase in grid reliability
According to (Amjad et al. 2018), the following factors determines the design of smart EV charging strategy:
Duration of charging: The period and duration of charging (amount of energy consumption) is generally related to EV owner’s choice and incentives for charging during non-peak load period.
Mobility of EV: The parking and moving of EV also decides the location, time and duration of charging.
Charging methods: For EV charging, the centralized or decentralized methods are commonly used. Based on power level, fast charging (higher power) and slow charging is employed.
EV to Grid connectivity: The unidirectional or bidirectional capability of V2G connection determines whether the EV will act only as a load or as both energy source and load.
EV Fleet Characteristics: Charging of a large EV fleet during peak load period drastically affect local grid voltage profile. Using demand side management to shift residential and commercial EV fleet charging to off-peak periods increases the dependability of grid.
EV Battery State of Charge: The state of charge (SOC) of EV batteries are estimated to properly schedule the charging of EVs. Information pertaining to batteries like remaining power, charging level (fast or slow), depth of discharge, operating temperature etc. are communicated to central entity for this purpose.
Power requirements of charging station: The fast (or commercial) charging station require comparatively higher power (higher current and voltage) compared to slow (or residential) charging station. Proper optimization of EV charging results in elimination of fluctuations in grid voltage and current.