Smart Charging Solutions for Hybrid and Electric Vehicles. Группа авторов

Apart from charging EVs, the power sources also feed load connected and cater services to increase the utility grid’s reliability. Charging EVs adds an extra load to the power sources. Three types of charging consider the management and distribution of power due to the addition of load from EV charging are widely discussed in the literature: viz., uncoordinated, coordinated, and smart [9, 10].

      1.2.1 Uncoordinated Charging

      The utility grid connecting to the load from a power source is designed to meet a particular region’s power demand. Further, the utility grid operators perform demand response or load distribution analysis to serve consumers with reliability. If an unprecedented load is added to the utility grid, the possibility of voltage fluctuations and blackouts increases [11]. Uncoordinated charging transpires when the EV’s charge is done in the form of unprecedented loads, i.e., the time to charge EVs is not scheduled in coordination with the utility grid [12, 13].

The impact of uncoordinated charging to the utility grid can be described in two ways: increased load demand and change in the shape of load profile. Increased load demand refers to the need for more kilowatts at a particular instant, as noted previously. In contrast, the change in shape of the load profile corresponds to a change in the timing of peak load and offpeak load hours. Literature reports that even a low adoption of EVs could significantly change the load profile and affect electricity infrastructure. The impacts of uncoordinated charging are not limited to the load demand and shape; phase imbalance, power quality issues, such as an increase in total harmonic distortion, increased power loss, line loading, and equipment degradation, such as transformers and circuit breakers, also impact the utility grid [11]. However, the impact of uncoordinated charging is seen on all three segments of the utility grid, namely, generation, transmission, and distribution systems, but the distribution section of the utility grid is the worst affected [14].

      1.2.2 Coordinated Charging

      Coordinated charging is characterized by charging EVs in coordination with the utility grid. The coordination is required to identify the present condition (load connected) of the grid or power source that will supply the power to charge EVs. The peak load and off-peak load hours of a utility grid vary based on residential, industrial, or commercial regions. In general, for the residential area, the utility grid is in peak load at evening and night hours, while the off-peak load hours are noted during late nights when people sleep. The load demand for an industrial area will depend on the working shifts and operation of factories. For commercial areas, the peak load hours will be at consumer visiting hours, i.e., during the evening. The off-peak load hours will be during the morning [6, 15].

      In the case of coordinated charging, based on the regions, the process of charging is scheduled during off-peak load hours. However, it is ensured that EV owners are not barred from the services. The literature is flooded with works done to perform coordinated charging by developing optimizing algorithms, demand response strategy, load scheduling, controllers, dynamic pricing methodology, electricity market operation strategy, and time of use (ToU) [16-22]. Although the works in the literature are diverse, each of them shares the following common goals:

      1 a. The EV owners’ need to charge at any time of the day should not be denied, irrespective of the loading in the utility grid

      2 b. The power system operator (PSO) constraints should be coordinated and supported in the quest to charge EVs

      3 c. Necessary support services from the EV owner to the PSO and the PSO to the EV owners should be provided via necessary coordination

      4 d. Increased penetration of local energy storage and renewable energy sources in the utility grid

      Coordinated charging of EVs is complicated, expensive, and needs standard infrastructure support for implementations. However, the benefits are immense compared to uncoordinated charging. Coordinated charging helps solve two major issues: first, congestion management, which is defined as an increase in thermal loading in transformers and cables and, second, voltage drops, which are most commonly experienced due to the addition of any unprecedented load, such as EVs [15, 23-25].

      The type of charging is also a significant factor to be considered when working with coordinated charging [8, 11]. A fast-charging requires a higher amount of power to be transferred to the EV batteries in a short duration of time. In contrast, in slow charging, the requirement of power is reduced, but time is increased. The ToU and dynamic pricing algorithms are the most commonly presented in the literature to cater to the requirements of power for different charging types. Although coordinated charging solves the basic requirements of charging EVs in consideration to the utility grid’s constraints and managing EVs as a load, it fails to be a future proof system where both the EV owner and the PSO are guaranteed an optimized charging process [10, 18].

      1.2.3 Smart Charging

      Uncoordinated and coordinated charging worked on two different objectives. Uncoordinated charging prioritizes the requirements of EV users. In contrast, coordinated charging tries to optimize utility grid operation considering the grid’s requirements and ensuring satisfactory service to the EV users. Although coordinated charging, to some extent, meets the requirement of both the utility grid and EV users, the algorithms and controller developed are inclined to only one segment of operation, the utility grid [9, 26].

The smart charging process, on one hand, lets the EV user decide the priority and, on the other hand, adapts the charging process to meet the requirements of the PSO. For example, suppose a user opts to charge EV during off-peak load hours. In that case, incentives are given in the form of cost reduction in electricity billing. If a user prioritizes to charge rather than considering the grid’s condition, especially during peak-load hours, the electricity billing is higher. The user is not barred from getting the desired service, but an optimal solution is met between the EV owner and the PSO [27]. The smart control ensures the charging of batteries in EVs within a given time and considers PSO constraints, such as voltage and frequency regulations. The smart charging’s prime concern is to reduce the impact of EV charging and enhance grid reliability and stability. For a better understanding, Figure 1.1 shows the list of expected functionalities to define the level of smartness in the charging system.

The platform for electro-mobility (2016) in the European Union (EU) defines smart charging as: “consist[ing] of adapting EV battery charging patterns in response to market signals, such as time-variable electricity prices or incentive payments, or response to acceptance of the consumer’s bid, alone or through aggregation, to sell demand reduction/increase (grid to vehicle) or energy injection (vehicle to grid) in organized electricity markets or for internal portfolio optimization” [26]. Smart charging demands intelligent monitoring, control, and operation [1, 3, 4]. Hence, communication and coordination between the charging infrastructure entities is a must to realize smart charging. In smart charging, the entities are not just a mere power transfer system, but rather a data-rich monitoring system that can monitor, control, coordinate, communicate, forecast, and optimize the operations [2, 7]. A brief description of the various approaches presented in the literature is shown in Figure 1.2.

Figure 1.1 Flow diagram to understand and judge the level of smartness based on functionalities.

Figure 1.2 A brief on different approaches to smart charging techniques.

The definitions and requirements