Smart Charging Solutions for Hybrid and Electric Vehicles. Группа авторов

a charging infrastructure smart vary, but all the ideas converge to the following goals:

      1 i. Guaranteed service to the users as required by optimizing all the entities’ operations and energy management in the system

      2 ii. Grid-friendly charging of EVs considering peak shaving; grid-friendly charging of EVs is done when the utility grid has required or surplus power (off-peak hours) after meeting the need of a precedented connected load

      3 iii. Renewable integration: the smart charging of EVs should promote the use of renewables. The use of local energy storage systems (ESS) has shown promising results in integrating renewable energy sources to the utility grid. The energy generated from the renewables can be stored in the ESS and supplied to the utility grid when the grid is at stress. EVs act as distributed energy sources by allowing the bidirectional flow of power, hence, EVs can pivot the integration of renewables.

      4 iv. Increase reliability and stability: smart charging monitoring and control algorithms should focus on the utility grid’s demand and supply of power. The requirements of all the stakeholders in a power system should be met optimally.

Based on the discussions in the previous paragraphs, a comparison is presented in Table 1.1. Meeting the goals of smart charging is challenging, but its implementation gives an assurance of meeting the specified goals. The impact of smart charging is discussed in the next section.

Table 1.1 A comparison between different types of charging techniques for EVs.

Types of charging	Impact on the grid	Advantages	Disadvantages	Maturity
Uncoordinated	Leads to issues such as increased load demand and change in the shape of load profile, imbalance in phases, and lower power quality	It is user friendly and the deployment does not demand any support services or establishmentThe capital investment cost is the least	Increased power losses in transmission line and componentsVoltage and frequency fluctuationsPhase imbalancePower quality issues such as an increase in total harmonic distortionDegradation of transformers and transmission lines	High (Product readily available in the market and used by consumers)
Coordinated	Reduces negative impact by providing ancillary services and frequency control	Performs peak shaving and demand responseIncreased utilization options to EV users such as providing ancillary services and support to the grid by charging and discharging considering grid conditionsLoad management which reduces power loss and deterioration in the transmission line and transformersOpportunity to engage users in the electricity market	The cooperation of EV users is required, which is uncertainThe incoming and outgoing of EVs is not predictable, hence relying on EVs for ancillary services and regulation can put the power system at riskThe requirement of communication infrastructure will demand huge capital investmentThe assurance of a positive impact on the electricity grid is missing	Medium (pilot project implementation)
Smart	Helps in peak shaving or valley filling, power management on the grid side and energy management on the EV side, ancillary services, voltage and frequency regulation, improvement in power quality, and renewable energy integration	Eases the integration of renewable energy sources in the gridThe use of local energy storage adds flexibility to select power source-grid or energy storage for chargingImproved grid stability and reliabilityControl, operation, management, and monitoring of system at easePromotes usage of EVs due to increased satisfaction of EV owners and PSO	Implementation challenge due to complexityHigher risk operation as the operation and control in the infrastructure are dependent on communication systemsDemand commitment from both EV users and PSOVariability in market operations interferes with the workings of the infrastructure	Low

1.3 Impact of Smart Charging on Global Energy Systems

      The global energy system is characterized by the interconnected electricity grid which comprises of generation, transmission, and distribution systems, as well as the utilization of renewable energy sources. The price of electricity varies for regions around the world. Each country tries to ensure energy security by planning generations within the boundary. In most cases, renewables come to the rescue because recent advancements in local energy storage systems have not increased energy security. EVs are also considered as mobile/local energy storage due to the capacity of batteries used to power the drivetrain. Hence, an increase in the number of EVs in a country has achievable implications to impact the global energy system.

      The direction of the flow of power plays a significant role in determining the impact of smart charging. In the case of charging, two types of viz., unidirectional and bidirectional, are described in the literature. In the case of unidirectional, there is a controlled power flow from the utility grid to the EVs to charge, while in bidirectional the power flow is exchanged between EVs and the utility grid [3, 5, 23, 24, 28-31]. When the grid is in peak load hours, controlled power flow from EVs to the utility grid meets the surplus demand and while during off-peak hours, the EVs charge using surplus power in the grid. Note that the charging process is spread out over the day and mostly controlled using algorithms. Of the two, the bidirectional flow of power is found to be better in reducing the impact of uncoordinated charging. A study by the International Renewable Energy Agency (IRENA) states that, in the short term, bidirectional smart charging is able to reduce more curtailment when compared to unidirectional smart charging [32].

      Further, CO₂ emissions are also reduced more in the bidirectional case, compared to the unidirectional. The long-term analysis by IRENA is done considering renewables’ integration, which includes solar and wind-based isolated systems. For the long-term, a reduction in CO₂ is noticeable in bidirectional viz. when power renewables augment power production as compared to unidirectional. Hence, smart charging promotes the integration of renewables [27, 32].

      The impact of smart charging is not limited to supporting the integration renewables, it also helps reduce stress on various equipment in the utility grid’s infrastructure. The impact is widely discussed in the subsequent subsections.

      1.3.1 On the Grid Side

      Smart charging’s grid-side infrastructure consists of transmission lines, transformers, substations, connected loads, and the PSO. Uncoordinated charging is widely discussed for various negative impacts it superimposes on the utility grid, such as components (transmission lines, transformers) overloading, power loss, voltage and frequency instability, and increased peak demand [24, 31]. With an increase in load due to the charging of EVs, the utility grid’s existing components are overloaded, which increases the demand for generation and transmission. The lifespan of all the components is adversely affected. Increased demand for active power leads to an increase in power loss in the distribution system [23-25]. Further, the financial losses incurred due to the components’ damage are mostly not reported in the literature, however, the PSO suffers huge losses due to added investment capital.

      Subsection 2.3 described the goals of smart