A Review on Utilization of Electric Vehicles for Mitigating the Power Quality Issues in Power Systems

Abstract

The widespread adoption of EVs can alleviate strain on power grids and enhance power quality in multiple ways. First, the integration of EVs enables better utilization of renewable energy sources by serving as mobile energy storage units. During periods of peak renewable energy generation, excess power can be stored in EV batteries, reducing curtailment and maximizing resource efficiency. Second, smart charging infrastructure and vehicle-to-grid (V2G) technology allow EVs to interact with the grid intelligently. Through V2G systems, EVs can supply power back to the grid during high-demand periods, effectively functioning as decentralized energy storage units. This bidirectional energy flow helps stabilize voltage and frequency fluctuations, ultimately improving overall power quality. Furthermore, EVs can facilitate load balancing by enabling charging during off-peak hours, spreading the electricity demand more evenly throughout the day. This approach minimizes the strain on the grid during peak times and enhances system stability. In summary, electric vehicles not only reduce emissions and promote sustainability but also contribute to optimizing power generation, storage, and distribution, leading to a more resilient and higher-quality power supply. In this chapter, the impact of electric vehicles on improving the quality of power in the voltage and frequency sections has been investigated.

1. Introduction

Electric vehicles (EVs) represent a greener alternative to conventional vehicles as they do not emit CO₂. Auto manufacturers are actively producing EVs and promoting their adoption over traditional vehicles. To charge EVs, charging stations are used. However, the amount of power EVs draw during charging varies due to factors like battery technology and charging methods (slow, fast, ultra-fast/flash charging). Flash charging, for instance, can fully charge an EV in under a minute by drawing a significant amount of power from the grid. The diversity in EV charging behaviors poses challenges to the distribution grid, including overloading, stability issues, power quality problems, voltage imbalances affecting other users on the same grid, etc. In the near future, EV adoption is set to surge, with annual sales projected to reach 23–43 million by 2030. This will considerably strain the grid, potentially requiring a capacity increase of 640–1110 TWh by 2030 [1]. The widespread adoption of electric vehicles (EVs) brings both benefits and challenges to the electrical distribution network. The most important challenges are depicted in Figure 1.

1. Overloading: The sudden and simultaneous charging of multiple EVs, especially during peak periods, can lead to increased demand on the distribution network. If the infrastructure is not designed to handle this increased load, it can result in the overloading of transformers, feeders, and other components, potentially leading to equipment failures and service disruptions [2, 3].

2. Stability problems: Rapid changes in power demand caused by EV charging can lead to voltage fluctuations and frequency deviations. These variations can impact the overall stability of the distribution network, potentially causing voltage sags, swells, or even voltage collapses. Voltage instability can result in equipment damage and reduced system reliability.

3. Power quality problems: The introduction of EVs can cause power quality issues such as harmonic distortion and poor power factor. These issues can lead to increased losses, decreased efficiency, and potential interference with sensitive equipment connected to the same network.

4. Voltage profile issues: The dynamic nature of EV charging can lead to voltage fluctuations that affect not only the charging stations but also other connected consumers. Low-voltage conditions can hinder proper charging, while high-voltage conditions can stress and damage equipment. Maintaining a stable voltage profile becomes a challenge when dealing with the variable power demands of EVs.

5. Distribution network planning: The increased load due to EV charging might require costly upgrades to the distribution network’s infrastructure. Proper network planning and investment are necessary to accommodate the growing number of EVs without compromising the system’s reliability [4].

Figure 1.

EVs challenges to the electrical distribution network.

To address these challenges and minimize their adverse impacts, various strategies and solutions can be considered:

• Smart charging: Implementing smart charging solutions that consider the distribution network’s capacity and load constraints can help distribute the charging load more evenly and reduce the likelihood of overloading [5].

• Demand response programs: Incentivizing EV owners to participate in demand response programs, where charging is scheduled during off-peak periods, can help mitigate peak load demands and reduce stress on the distribution network.

• Grid-integrated charging infrastructure: Developing charging stations that are integrated with the grid and can communicate with the utility can enable better load management and coordination, thus reducing the impact of EV charging on the network [6].

• Advanced metering and monitoring: Using advanced metering and monitoring systems, utilities can gain real-time insights into network conditions and adjust operations accordingly to maintain stability and power quality [7].

• Distribution network upgrades: In cases where demand from EVs is substantial, targeted distribution network upgrades may be necessary to accommodate the increased load safely and efficiently.

• Energy storage integration: Integrating energy storage systems into the distribution network can help smooth out load fluctuations caused by EV charging and provide additional stability.

• Regulatory and policy measures: Governments and regulatory bodies can play a role by implementing policies that incentivize responsible charging behaviors, promote smart charging infrastructure deployment, and ensure that the grid can handle the transition to EVs.

On the other hand, we can also mention the importance of power quality. Power quality is integral to the reliable and efficient operation of power systems and the equipment they serve. Addressing power quality issues requires a combination of monitoring, analysis, and corrective measures to ensure a stable and high-quality power supply for consumers, industries, and critical infrastructure. Here are some key reasons highlighting the importance of power quality in power systems:

1. Equipment performance and reliability: Many modern devices and equipment are sensitive to variations in voltage, frequency, and waveform quality. Poor power quality, such as voltage sags, surges, harmonics, and flickers, can lead to equipment malfunctions, downtime, and premature wear and tear. Maintaining good power quality ensures the reliable and optimal performance of a wide range of equipment, from industrial machinery to sensitive electronic devices [8].

2. Energy efficiency: Efficient operation of electrical equipment often requires a stable voltage supply at the rated frequency and waveform. Deviations from these parameters can result in increased energy consumption, reduced efficiency, and unnecessary heat losses in equipment.

3. Economic impact: Power quality issues can lead to production disruptions, equipment failures, and increased maintenance costs for industries. In commercial settings, poor power quality can impact transaction processing, data centers, and communication networks. These disruptions can result in significant financial losses [9].

4. Voltage stability and balance: Fluctuations in voltage levels can impact the stability of the power system and the voltage supplied to consumers. Unstable voltage levels can lead to equipment malfunction, flickering lights, and decreased equipment lifespan.

5. Harmonics and power factor: The presence of harmonics (nonlinear voltage and current components) and poor power factor (a measure of how effectively power is utilized) can lead to increased losses, lower system efficiency, and decreased system capacity.

6. Electromagnetic interference (EMI): Poor power quality can lead to electromagnetic interference, which can affect the proper operation of electronic devices, communication systems, and other sensitive equipment [10].

7. Voltage profile and voltage regulation: Maintaining a stable voltage profile throughout the distribution network is essential to ensure the proper functioning of equipment and minimize voltage-related issues, such as overvoltage or undervoltage conditions.

8. Renewable energy integration: With the increasing integration of renewable energy sources like solar and wind, power quality becomes more critical. Fluctuating output from these sources can introduce voltage and frequency variations, requiring grid management strategies to maintain overall power quality.

9. Customer satisfaction: Consistently providing reliable power with good quality is essential for customer satisfaction. Homeowners, businesses, and industries rely on uninterrupted power supply and consistent performance of their electrical equipment.

10. Regulatory compliance: Power utilities often have to adhere to regulations and standards that define acceptable levels of power quality. Failure to meet these standards can result in penalties and regulatory actions.

11. Public safety: Poor power quality can pose safety risks, especially when it affects critical systems like emergency lighting, fire alarm systems, and medical equipment.

According to the mentioned things, it can be said that the purpose of writing this chapter of the book is to investigate the role of electric vehicles in improving power quality and how it affects them. The organization of this chapter is as follows. After the introduction in Section I, Section II deals with the concept and definition of power quality in the power system. In Section III, electric vehicles and their effects on important parts of power quality, including frequency and voltage, will be discussed. At the end and in Section IV, the findings will be categorized and summarized.

2. Power quality problem

The concept of ‘power quality’ pertains to ensuring that the power system maintains voltage and current waveforms that are nearly sinusoidal, with magnitudes and frequencies in line with specifications [11]. Power quality can be influenced by multiple factors, including deviations in voltage and frequency, imbalances, interruptions, flickering, and harmonics [12, 13]. Consequently, maintaining power quality holds significance in ensuring the dependable and secure functioning of smart grids, and this aspect is expected to be affected as the demand for EVs experiences imminent growth. The passage suggests that the increasing adoption of EVs could potentially impact power quality. The charging of EVs and their connection to the grid might introduce additional demands on the system, potentially leading to voltage and frequency variations or other PQ issues. Therefore, it is of great significance to investigate the PQ issues in smart grids while considering EVs [14, 15, 16]. Power quality issues in power systems can impact the reliability, efficiency, and overall performance of the electrical supply. The main power quality issues that power systems may encounter are shown in Figure 2.

• Voltage sags and dips: Also known as voltage drops, these are short-term reductions in voltage levels. They can be caused by faults, sudden changes in load, or other disturbances in the system. Voltage sags and dips can affect sensitive equipment and cause malfunctions or disruptions [17].

• Voltage swells: Voltage swells are short-term increases in voltage levels. They can be caused by sudden load reduction, switching operations, or other disturbances. Like sags, voltage swells can stress equipment and lead to malfunction or damage.

• Voltage fluctuations and flicker: Rapid variations in voltage levels can result in flickering lights. These fluctuations are often caused by changing loads, such as the starting of large motors or other dynamic equipment.

• Harmonic distortion: Non-sinusoidal waveforms can introduce harmonics into the system. Harmonics are integer multiples of the fundamental frequency (50 or 60 Hz) and are often produced by nonlinear loads like computers, variable frequency drives, and other electronic devices. Harmonics can cause overheating in equipment and interfere with other equipment operations [18].

• Voltage unbalance: In three-phase systems, voltage unbalance occurs when there are significant differences in voltage levels among the three phases. This can lead to unequal distribution of power and increased losses.

• Frequency variations: Deviations from the standard frequency (50 or 60 Hz) can affect the operation of clocks, timers, and equipment that relies on precise timing.

• Voltage surges and transients: These are sudden and brief increases in voltage levels. They can be caused by lightning strikes, switching operations, or other disturbances. Voltage surges and transients can damage sensitive electronics and equipment.

• Interruptions: Power interruptions are complete losses of power supply and can be caused by faults, equipment failures, or maintenance activities. They can disrupt operations and cause inconvenience.

• Power factor issues: A low power factor indicates inefficient use of electrical power. It can result from reactive power consumption by devices like motors, leading to higher energy consumption and losses.

• Voltage regulation: Poor voltage regulation can lead to voltage levels that are outside the acceptable range, affecting equipment performance and potentially causing damage.

• Resonance: Resonance occurs when the natural frequency of a system matches the frequency of a disturbance, leading to excessive voltages or currents. Resonance can cause equipment failures.

• Electromagnetic interference (EMI): EMI involves the generation of electromagnetic signals that can interfere with the proper functioning of sensitive electronic devices.

• Voltage flicker: Similar to fluctuations, voltage flicker is a repetitive variation in voltage levels, often caused by dynamic loads like arc furnaces.

• Voltage stability: Voltage stability issues can arise when the system is unable to maintain steady voltage levels, particularly during stressful conditions or extreme events.

• Poor grounding: Inadequate grounding can result in safety hazards, as well as introduce unwanted noise and distortions into the system [19].

Figure 2.

The main power quality issues.

Addressing these power quality issues requires a combination of proper design, equipment selection, maintenance practices, and monitoring tools to ensure the smooth and reliable operation of power systems. Pertaining to transient-based power quality (PQ) concerns, their classification can be based on their highest magnitudes, frequency components, as well as their characteristics concerning rise time and duration. Issues are categorized into short-duration and long-duration types based on their time spans and are further differentiated by the extent of magnitude fluctuations. The assessment of power system waveform distortion is often led by the analysis of total harmonic distortion (THD) and the harmonic spectrum. In terms of technical evaluation, the concept of intermittency serves as a valuable indicator for effectively identifying voltage fluctuations [20].

2.1 PQ issues in conventional power systems

Typically observed in conventional power systems characterized by sizeable centralized generators, overhead transmission and distribution lines, and passive user consumption, the primary instigators of power quality (PQ) issues are the presence of nonlinearities within loads or predominant system equipment. The ramifications of PQ problems encompass a range of consequences, including motor overheating, transformer saturation, system resonance, capacitor overloading, impaired protection mechanisms, fluctuations in light intensity, mechanical harm to generators and turbine shafts, production losses, and potential human health effects such as discomfort, irritation, and headaches [20].

2.2 PQ issues in modern power systems

Over recent decades, there has been a noticeable and continuous rise in the extensive deployment of distributed energy resources (DERs). Alongside this trend, there has been an increasing inclination toward employing power electronic-based interfaces. Unlike conventional power systems, where power electronic devices, acting as rigid nonlinear loads, have been used, their adoption has been more limited compared to contemporary power systems. The global drive to reduce emissions aligns with the growing adoption of electric vehicles (EVs), augmenting the significance of electrified transportation. Consequently, a transformation in both generation technology and the nature of electrical loads has occurred. Modern power systems are now subject to increased nonlinearity from both the generation and demand perspectives. The proliferation of electronic smart home appliances further accentuates concerns for power quality (PQ) issues among system operators.

Emerging factors such as adjustable speed drives (ASDs) and LED lamps introduce new elements that can adversely influence PQ metrics. The evolution of high-voltage direct current (HVDC) lines, the expansion of power line communications, and the ongoing shift from overhead lines to underground cables contribute to altering the traditional power system landscape. Additionally, the economic ramifications amplify the urgency for research that delves into the characteristics, origins, and techno-economic as well as environmental consequences of PQ concerns [20].

2.3 PQ problems associated with EV charging infrastructure

An electric vehicle (EV) charging station, also known as electric vehicle supply equipment (EVSE), serves the purpose of delivering electrical power to recharge the batteries of plug-in electric vehicles (PEVs) and other EVs. These charging stations are categorized based on the characteristics of the charging current, the speed of charging, and their geographical placement. A typical public EV charging station encompasses components such as a grid power source, a dedicated transformer, power quality measurement instruments, switchgear panels, chargers, and more. Compliance with IEC 61000-4-30 necessitates the installation of power quality meters at the point of common coupling, equipped to assess parameters like harmonics (including supra harmonics), voltage fluctuations such as sag and swell, as well as voltage flicker and disruptions [21]. Charging stations can be differentiated into AC charging and DC charging, contingent on the location of the AC/DC conversion process. AC charging occurs when the AC/DC conversion transpires within the vehicle itself. Conversely, if the AC/DC conversion occurs externally, within the EVSE, it is categorized as DC charging.

Charging stations can be categorized based on the charging speed or the duration required to attain a 100% state of charge (SoC) for the battery. These classifications include slow charging and fast charging. Slow charging refers to the method of charging that typically occurs overnight, spanning approximately 6–8 hours or more to fully charge an EV battery pack. In contrast, fast charging denotes a setup that expedites the charging process, requiring considerably less time. Fast charging setups are characterized by high-power output, enabling a vehicle to achieve an 80% charge within approximately 15 minutes. Currently, such charging stations are prevalent and typically possess power ratings within the range of 10–50 kW [22]. Charging solutions operating at the 100 kW level may become available in the medium-term timeframe. The rate of charging is contingent upon both the power rating of the EVSE and the capacity of the battery. A higher power rating results in a swifter charging rate. When the charging time is less than 30 minutes, the charger is commonly referred to as an ultrafast, superfast, flash charging, or rapid charger.

Charging stations can be categorized based on the location of the charging process, differentiating between home/residential charging and public charging stations. Home charging is a prevalent practice among EV owners due to its cost-effectiveness. This approach generally employs slow chargers, taking advantage of the flexibility in available charging time. EV owners often opt to charge their vehicles overnight at their home EVSE, capitalizing on lower electricity tariffs compared to the commercial or industrial rates applicable in public charging infrastructure. Approximately 80% of EV charging occurs within the confines of the owner’s home charging station.

Public charging stations, on the other hand, are facilities established and operated by utility companies or private entities with relevant licenses. These stations provide charging services for EVs beyond residential settings. The concept of vehicle to grid (V2G) involves EVs supplying power back to the grid during peak demand periods, effectively functioning as prosumers. Prosumers are entities that both consume electric power from the grid and contribute power back to the grid at the same point of connection (PoC) [21]. This practice of V2G has the potential to curtail peak power generation requirements and foster a balance between electricity demand and generation.

3. EVs for PQ improvement

Before we discuss the impact of EVs on power quality, it is necessary to know the different types of EVs. Nowadays, we can encounter different types of EVs, according to their engine technology. In general, they are sorted into five types as shown in Figure 3.

• Battery EVs (BEVs): BEVs exclusively rely on electric power for their propulsion. Unlike internal combustion engine vehicles, BEVs lack an internal combustion engine and do not utilize liquid fuels of any kind [23]. Typically, BEVs utilize sizeable battery packs to ensure a satisfactory driving range. A standard BEV can cover distances ranging from 160 to 250 kilometers on a single charge, although certain models can achieve up to 500 kilometers with a single charge. A notable illustration of this vehicle category is the Nissan Leaf [24], a fully electric vehicle equipped with a 62 kWh battery that provides a driving range of 360 kilometers.

• Plug-in hybrid electric vehicles (PHEVs): PHEVs operate on a hybrid propulsion system consisting of a conventional internal combustion engine and an electric motor. The electric motor can be charged from an external electric source via a plug connection. PHEVs are engineered to store a sufficient amount of grid-supplied electricity, thereby substantially reducing their reliance on conventional fuels during typical driving scenarios. An instance of this category is the Mitsubishi Outlander PHEV [25], which is furnished with a 12 kWh battery enabling an electric-only range of approximately 50 kilometers. It’s important to note, however, that the fuel efficiency of PHEVs often surpasses the figures provided by manufacturers [26].

• Hybrid electric vehicles (HEVs): HEVs operate through a dual power system, combining a conventional internal combustion engine with an electric motor. Unlike plug-in hybrid electric vehicles (PHEVs), HEVs lack the capability to be connected to the electrical grid for recharging. Notably, the energy source for the electric motor in HEVs is the vehicle’s combustion engine. In more contemporary models, the batteries can also be charged through regenerative braking, where kinetic energy is transformed into electrical energy. A notable example is the fourth-generation hybrid model of the Toyota Prius [27], which features a 1.3 kWh battery. This battery theoretically grants the vehicle an electric-only driving range of up to 25 kilometers.

• Fuel cell electric vehicles (FCEVs): FCEVs are equipped with an electric motor that operates using a combination of compressed hydrogen and oxygen drawn from the air. The sole byproduct of this process is water [28]. While FCEVs are commonly regarded as vehicles with “zero emissions,” it is important to note that although some hydrogen is produced from environmentally friendly sources (green hydrogen), a substantial portion is extracted from natural gas. An illustrative instance of this vehicle category is the Hyundai Nexo FCEV [29], capable of covering a distance of 650 kilometers without the need for refueling.

• Extended-range EVs (ER-EVs): ER-EVs closely resemble those in the BEV category. However, ER-EVs are additionally equipped with a supplementary combustion engine capable of recharging the vehicle’s batteries if required. It is worth noting that unlike the engines found in PHEVs and HEVs, the combustion engine in ER-EVs serves solely for the purpose of battery charging and is not mechanically connected to the vehicle’s wheels. An example of this vehicle type is the BMW i3 [30], furnished with a 42.2 kWh battery that allows an electric driving range of 260 kilometers. Additionally, users can access an extended-range mode, granting an extra 130 kilometers of travel distance.

Figure 3.

EVs taxonomy.

Electric Vehicles (EVs) have the potential to enhance power quality in power systems through their integration with smart charging and vehicle-to-grid (V2G) technologies. By leveraging EV batteries as distributed energy storage resources, power systems can benefit from load balancing, voltage regulation, and frequency stability. These capabilities enable EVs to absorb excess power during periods of low demand and inject it back into the grid during peak hours, effectively reducing grid stress and enhancing overall stability. Additionally, EVs can participate in demand response programs, allowing their charging rates to be adjusted based on grid conditions. This assists utilities in managing peak loads and mitigating voltage fluctuations. The integration of EVs also incentivizes grid modernization efforts, fostering the deployment of advanced communication systems and grid management tools that further improve power quality. Overall, as EV adoption continues to grow, their intelligent interaction with the grid presents an opportunity to enhance power quality and reliability while supporting the integration of renewable energy sources. In this section, we will discuss the impact of EVs and the main components of power quality, i.e., voltage and frequency.

3.1 Role of EVs in voltage section

The dynamic charging behavior of electric vehicles (EVs) introduces a substantial stability challenge to power system networks. The substantial demand for EV charging places significant stress on utilities worldwide. For instance, in North America, power companies had to construct additional generating facilities to accommodate the augmented load from EVs [31]. The proliferation of EVs poses a notable challenge to voltage stability, particularly when they achieve high market penetration [32]. Previous research endeavors have consistently highlighted that EV charging exacerbates voltage instability. This issue is exacerbated by the presence of single-phase loads from EVs within distribution networks, leading to voltage imbalances. Moreover, the substantial inrush current triggered by EV charging gives rise to voltage dips for residential consumers, frequently coinciding with peak household load periods [33]. Investigations concerning the European Union’s low voltage network unveiled that controlled charging often led to voltage violations at the feeder endpoints [34].

In Ref. [35], researchers delved into the voltage imbalance issue stemming from suboptimal charging methods. The investigation explored two distinct charging approaches: uncontrolled charging and tariff-based charging. The findings underscored that uncontrolled charging results in voltage imbalances surpassing a critical threshold of 2%. To address this, a tariff-based charging strategy was implemented, aiming to incentivize EV owners to charge during off-peak hours when electricity tariffs are lower. This approach was primarily designed to alleviate congestion during peak periods. The introduction of a substantial number of EVs has led to voltage drops and power losses in distribution, exacerbated by traffic congestion on road networks [36].

An examination of the charging patterns of plug-in hybrid EVs (PHEVs) was conducted to assess their influence on load profiles due to EV integration. The studies indicated that charging at public locations led to a 24–29% rise in daily energy consumption compared to home charging [37]. An evaluation of the Canadian distribution system concluded that the impact of fast charging systems is more pronounced than that of slow chargers [38]. Research on the Chinese distribution system highlighted that uncoordinated charging of EVs at different penetration levels resulted in voltage stability issues and phase imbalances. A parallel study adopted a smart charging approach to optimize charging cycles and ensure uninterrupted power flow within the system [39]. In Ref. [40], the analysis demonstrated that when EV penetration reached 0.28%, certain distribution networks encountered both low voltage stability concerns and transformer overload breaches. Although the present level of EV penetration did not forecast any issues, escalating penetration levels brought forth both low voltage instability and overload infractions for varying adoption rates. Particularly, at an EV penetration of 37.68%, the network faced complete collapse due to inadequate voltage regulation. Simulation results prominently identified voltage instability as the primary contributor to overall instability.

Charging electric vehicles (EVs) can induce voltage-related issues in the power network, encompassing voltage drops and fluctuations. A multitude of scholars have undertaken investigations into the repercussions of EV charging on network voltage. To account for the uncertainties surrounding EV availability, the Monte Carlo simulation method was employed in one study to scrutinize how EV charging impacts system voltage [41]. The extent of these impacts can either be substantial or negligible, contingent on factors such as the quantity of EVs, network attributes, and the characteristics of EV charging [42].

Research endeavors have yielded divergent outcomes. For instance, a study [43] underscored that the effect of the charging power of these vehicles on an urban distribution network remains minor when EV penetration is low. Conversely, in contrast to the findings in Ref. [43], another investigation [39] established that with a 50% EV penetration rate, network voltage deviations surpass established standards. Furthermore, in Ref. [44], outcomes revealed that the deployment of six EVs equipped with fast charging technology leads to violations of the prescribed network voltage standard.

Various research studies have explored the utilization of voltage regulation techniques and strategies to uphold network voltage within specified norms. Traditional methodologies, such as the strategic placement of optimal capacitor banks and the implementation of tap changers, can be employed to counteract voltage deviations within the network [45]. An alternative avenue involves managing the charging of electric vehicles (EVs) to enhance network voltage profiles. In this context, Masoum et al. [46] investigated a sophisticated control strategy for load management, focusing on the coordinated charging of EVs. The findings of this study highlighted that the synchronization of EV charging, facilitated by a practical tariff structure and a prioritized time zone scheme, effectively contributes to the voltage regulation of the system.

Furthermore, an effective strategy for managing electric vehicle (EV) chargers involves the decoupled control of active and reactive power, which proves instrumental in network voltage regulation. The active power control mechanism facilitates the manipulation of EV charging operations, while the reactive power control facet contributes by infusing reactive power into the grid to fortify network voltage levels. In Ref. [47], a prototype of a three-phase off-board EV charger was devised and put into operation. This charger not only maintains a steady DC-link voltage but also adeptly regulates network voltage within acceptable thresholds. This is achieved through the injection of reactive power, all the while ensuring no detrimental impact on the charging process. In the contemporary context, the management of EV charging to enhance voltage profiles stands as a viable consideration for both distribution and transmission service providers.

• LV distribution networks: Primary challenges include voltage drops during peak loads and voltage elevation caused by active power injection from photovoltaic (PV) systems. To address the voltage elevation issue, Marra et al. [48] introduced a coordinated approach between electric vehicle (EV) loads and PV systems, illustrated through a simulation involving a residence with rooftop PV and an EV. The simulation outcomes underscored the effectiveness of this approach [48]. Furthermore, Alam et al. [49] assessed this coordination strategy on an actual Australian distribution system employing genuine PV and EV data. Conversely, Akhtar et al. [50] proposed an alternative solution involving smart loads equipped with back-to-back converters to mitigate voltage disturbances arising from EVs and PVs in LV networks. The findings revealed that the application of smart loads alongside such converters could adeptly regulate bus voltage, albeit necessitating the use of two converters [50].

• MV-level networks: In the context of MV-level networks, García-Triviño et al. [51] conducted a study focused on voltage regulation employing a rapid charging station alongside a decentralized energy management system (EMS). The findings highlighted the viability of this innovative approach in voltage control through decentralized methods, independent of a communication interface [51]. Additionally, Torreglosa et al. [52] delved into a similar area by investigating a decentralized EMS for a charging station. This study employed model predictive control (MPC) to effectively regulate bus voltage within MV networks.

• Transmission network: An investigation [53] explored the potential contribution of end-user devices, such as electric vehicles (EVs), in the voltage control of the grid. The study introduced an active support group for frequency regulation and a reactive support group to oversee voltage control at the transmission bus. In a separate study, Rana et al. [54] explored a modified droop control technique incorporating EV aggregators, wind and solar units, and diesel generators to manage the frequency within a microgrid. The EV aggregator, in this scenario, adjusts the charging and discharging rates to align with set points while considering EVs and state of charge (SoC) limits [54]. Additionally, EV converters can inject active and reactive power into the grid to provide support during voltage ride-through conditions. During instances of renewable energy-related transients, EVs can mitigate transient stress on the grid by injecting active power. A subsequent study [55, 56] underscored the ability of EVs to effectively regulate both reactive and active power during voltage ride-through scenarios.

3.2 Voltage unbalance mitigation in electric distribution system with EVs

A phase reconfiguration strategy offers a means to mitigate voltage imbalance concerns. In Ref. [57], the financial implications of adopting a phase reconfiguration approach to alleviate the adverse effects of unbalanced electric vehicles (EVs) on a low voltage (LV) distribution system were examined. The results affirmed that employing a phased reconfiguration strategy, in conjunction with a time-of-use tariff, could effectively mitigate the imbalance impact of EVs. Furthermore, effective management of EV charging and discharging can contribute to alleviating phase unbalance issues [58]. The process of achieving voltage balance involves making optimal decisions regarding connection points (phases a, b, or c), charging and discharging power rates, as well as the charging and discharging status. In the pursuit of coordinated smart charging for all EVs and boosting the load profile tied to the electrical grid network, a control mechanism is under development [59]. This coordination relies on a communication infrastructure enabling data collection and transmission between EVs and an aggregator. To standardize voltage profiles, the load profile is smoothed. The implementation of voltage regulators can effectively reduce network imbalance indices. Improved power quality (PQ) concerning voltage imbalances and variations can be attained through the use of energy storage devices, feeder capacitors, and D-STATCOM [60].

It’s noteworthy that some EVs may occasionally experience elevated peak voltages. Unlike a central controller, a decentralized controller charges EVs locally, thereby minimizing communication infrastructure costs [61]. The electric vehicle current charger does not consider the neutral current stemming from phase voltage imbalances. Given the dynamic nature of input from distributed energy resources, both distributed energy resources and EVs necessitate coordination to address neutral current and voltage imbalance [62, 63]. An analysis of the merits and drawbacks of centralized and decentralized EV charging coordination models is presented. In the context of smart charging within the electrical distribution system, active power balance can be achieved through the implementation of the droop controller topology. Although power electronics devices like rectifiers and switching converters contribute reactive power into the distributed network, potentially burdening the distribution network, a droop controller-based mechanism was described in Ref. [64] to achieve a balanced system. Reactive power correction can be attained through auxiliary equipment specified in Ref. [65]. To mitigate voltage imbalance, techniques for generating zero and negative sequence voltages are employed. In Table 1, various approaches to mitigate the impact of EVs on voltage quality are summarized.

Impacts	Mitigation techniques	Description
Unbalanced voltage impact	Voltage regulators, phase reconfiguration technique, EV charging and discharging management.	Optimizing EV and phase reconfiguration techniques to mitigate voltage imbalances. Voltage unbalance can be reduced by utilizing flywheels, supercapacitors, battery storage systems, capacitive energy storage systems, superconducting magnetic storage systems, DVRs, and DSTATCOMs [66, 67].
Impact on voltage fluctuations	Control strategies for active and reactive power, voltage regulators, and charging management.	Voltage fluctuations can be reduced with transformer tap changes and capacitor banks. In order to reduce voltage fluctuations, EV charging is coordinated in a controlled manner to regulate network voltage [47, 66, 68].
Impacts on voltage profile	Traditional voltage regulators. Charging management of EVs. Control strategy for active and reactive power that is decoupled.	Voltage regulation [46, 47]: Feeder capacitor bank.; Tap changer.; A smart load management control [57]: Coordinating EV charging.; EV charging provides active power control, and reactive power injection regulates network voltage by injecting reactive energy into the grid [67, 69].

Table 1.

Approaches to mitigate impact of EVs on voltage quality.

3.3 Role of EVs in frequency section

In power systems, maintaining a real-time equilibrium between generation and load is crucial to prevent deviations in grid frequency from the established norm. When a substantial charging load from electric vehicles (EVs) is introduced to the grid, additional power generation becomes imperative to uphold grid frequency within acceptable limits [70]. Moreover, the unpredictability inherent in the departure and arrival times of EVs introduces uncertainty into power systems, amplifying uncertainty from the demand side [71]. To rectify this, strategies such as load curtailment or demand-side management (DSM) initiatives can be implemented to align load and generation within the grid. Employing coordinated control of EVs serves to harmonize power distribution within the power system [70, 72]. Notably, EV aggregators possess the potential to play a significant role across energy and ancillary service markets. In terms of ramping capability, EVs outperform gas turbines, and they offer a more cost-effective alternative in comparison to traditional energy storage systems [70, 71, 73, 74].

As a subset of energy storage technology, electric vehicles (EVs) hold promising potential for active involvement in frequency regulation (FR) systems. This potential stems from the widespread proliferation of EVs and the continual advancements in vehicle-to-grid (V2G) technology. By adeptly adjusting their charging and discharging rates, EVs can effectively counteract frequency fluctuations originating from intermittent energy sources like wind and solar power. Research affirms that a smart grid can receive substantial frequency support through the utilization of EV fleets, harnessed as manageable loads. Employing a multiple model predictive control approach, Pahasa and Ngamroo [75] address EV charging/discharging and state-of-charge (SOC) control to stabilize microgrid frequency fluctuations. This methodology capitalizes on the expansive EV fleet, significantly enhancing the capabilities of V2G. Similarly, in Ref. [76], a virtual synchronous generator mechanism is integrated into an EV charging station, governing the bidirectional power flow to reinforce frequency stability. In Ref. [77], primary frequency control via V2G is accomplished by combining droop control and inertial response, facilitated by SOC management.

In the process of system frequency regulation (FR), electric vehicles (EVs) exhibit swift responsiveness to frequency deviations by adjusting their charging and discharging activities. However, it’s imperative to acknowledge that while EVs can play a role in FR, their fundamental purpose as modes of transportation introduces considerations related to traffic patterns and drivers’ demands. The manageable energy of EVs, influenced by driving regulations, demonstrates temporal variability within a day, thereby impacting the efficacy of system FR. Addressing this, Janjic and Velimirovic [78] establishes day-ahead optimal EV allocation for FR utilizing queuing theory and a fuzzy multi-criteria approach, yet this scheduling approach overlooks the inherent driving regulations of EVs. Given the essential transportation function of EVs, achieving driving demands remains essential in participating in optimal scheduling or FR endeavors. An optimal scheduling strategy aimed at EV charging and discharging is devised using mixed integer linear programming [79] to regulate system frequency; however, specific EV driving rules are omitted from consideration. In Ref. [80], an aggregator computes the FR capacity and anticipated FR output of EVs, categorizing their charging behaviors into maintaining or adjusting the battery state of charge (SOC). Nonetheless, the timing of EVs’ grid connection is at odds with daily driving regulations.

Furthermore, certain existing research on frequency regulation (FR) strategies overlook the dynamic changes in electric vehicles’ (EVs) manageable energy, resulting in impractical distribution of FR demand power. Load frequency control (LFC) models, as presented in Refs. [81, 82], involve EVs in secondary FR via distinct control approaches. However, in these literature instances, conventional units and EVs are engaged in FR independently, without considering their coordination. In a coordinated FR strategy involving both EVs and traditional units, the accurate calculation of EVs’ controllable energy profoundly influences the effectiveness of FR demand power allocation. Many pertinent studies have either neglected or simplified factors such as traffic patterns and vehicle owners’ demands, leading to inaccurate estimations of EVs’ real-time manageable energy. Furthermore, due to the inherent variability in vehicle usage, EVs’ controllable energy fluctuates dynamically. When the distribution ratio of FR demand power between EVs and traditional unit’s remains fixed, the energy storage potential of EVs remains underutilized, and the FR impact becomes suboptimal.

Zhang et al. [83] conduct a comprehensive analysis of state transition behaviors within the context of the FR process. Building upon this foundation, the study formulates dynamic models for real-time controllable capacity and energy of electric vehicles (EVs). Subsequently, an adaptive scheme is introduced to dynamically adjust system FR coefficients in response to EVs’ controllable energy, thereby enhancing the rationality of FR demand power allocation. Furthermore, a selection strategy is outlined for identifying specific EVs to partake in FR while accounting for driver preferences. The simulation outcomes affirm the viability and efficacy of the proposed methodologies.

The swift reactivity of electric vehicles (EVs) enhances the dynamic capabilities of the load frequency control (LFC) system. The engagement of EVs in frequency regulation services also opens avenues for supplementary economic gains within the frequency regulation markets. Consequently, the integration of EVs into frequency regulation services is poised for imminent encouragement. A novel concept, known as an “EV aggregator,” introduced in Ref. [84], addresses the minimal regulation capacity required in frequency regulation markets. However, the participation of EV aggregators in frequency regulation services can introduce time-varying delays to the LFC problem. Researchers in Ref. [85] investigate delay-dependent stability within LFC incorporating EV aggregator participation in frequency regulation services. The stability analysis of time-delayed LFC systems with EV aggregators is tackled in Ref. [86], leveraging Lyapunov theory and the linear matrix inequality (LMI) technique. Moreover, the ramifications of load sharing between EV aggregators and conventional generators on stability delay margins are explored in [87, 88] within a multi-area power system context. In scenarios where a substantial number of EVs are aggregated within the EV aggregator, the latter must possess Automatic Generation Control (AGC) capabilities to adjust each EV’s power output in real time. This entails a communication network for control signal exchange between the EV aggregator and EVs in the AGC system. Ref. [89] outlines a model for the AGC system comprising multiple EV aggregators, accounting for time-delay characteristics in response to control signals while considering the communication network within each area of the power system’s EV aggregator domain. This approach not only enhances dynamic performance but also significantly reduces communication overhead and computation expenses, all while maintaining control efficiency.

The literature offers several approaches related to electric vehicles (EVs) engagement in power frequency control (PFC). For instance, Floch et al. [90] delve into the optimal EV charging to shape the load. In Ref. [91], a model-free controller design strategy for EVs is proposed. Sun et al. [92] present a control strategy relying on filters for EVs. A risk-constrained decision tool is put forth in Ref. [93] to incorporate EV aggregators into frequency regulation and energy markets. Latif et al. [94] suggest fractional order controllers for EVs’ participation in secondary frequency control (SFC) within microgrids. Investigating interconnected power systems with thermal and hydropower plants featuring fuzzy fractional controllers, Arya [95] analyzes the influence of EVs on SFC. Arani and Mohamed [96] explore the cooperative provision of primary frequency control (PFC) by wind turbines and EVs. A state-space model facilitating real-time power control for aggregated EVs with minimal communication requirements is proposed in Ref. [97]. In Ref. [98], a stability margin-based strategy tunes the frequency-droop controllers of EVs for PFC participation. Moghadam et al. [99] investigate the randomization of EVs for PFC contribution. While numerous strategies are suggested for EV participation in PFC, their impact on generating unit wear and tear has yet to be explored.

4. Discussion and conclusion

In this chapter, the role of EVs in improving the voltage and frequency of power systems was analyzed. In conclusion, we can say that EVs have the potential to contribute to voltage stability in power systems by providing voltage regulation, reactive power support, and load management services. Strategic deployment and integration of EVs, along with appropriate technological and regulatory developments, can help enhance grid voltage stability and overall system reliability. Also, they have the potential to enhance frequency stability in power systems by providing demand response, energy storage, and ancillary services. However, their integration requires careful planning, technological development, and regulatory support to maximize their benefits while mitigating potential drawbacks. The classification of mechanisms affecting EVs in voltage stability is shown in Figure 4.

1. Voltage regulation: EVs with bidirectional charging capabilities, enabled by vehicle-to-grid (V2G) technology, can adjust their charging and discharging rates in response to grid voltage fluctuations. When the grid voltage is high, EVs can absorb excess electricity, thereby reducing the voltage. Conversely, when the grid voltage is low, EVs can inject stored energy back into the grid, helping to raise the voltage to appropriate levels.

2. Reactive power injection: EVs equipped with power electronics can provide reactive power support to the grid. Reactive power is essential for maintaining voltage levels within the desired range. EVs can inject or absorb reactive power as needed, helping to regulate voltage and improve grid stability.

3. Voltage support for weak grids: In areas with weak distribution infrastructure, voltage levels might drop significantly during peak demand periods. EVs connected to these grids can provide local voltage support by discharging energy, thereby alleviating voltage drop issues and maintaining a stable supply.

4. Peak shaving and load flattening: Charging EVs during periods of low electricity demand and discharging them during peak demand periods can help flatten the load curve. This can contribute to maintaining more stable voltage profiles by reducing voltage variations associated with sudden load changes.

5. Integration of renewables: EVs can help integrate renewable energy sources by absorbing excess energy from intermittent sources during periods of high production and releasing it when renewable generation is low. This helps stabilize voltage levels as well.

6. Avoiding overloading transformers and lines: By using EVs as controllable loads, grid operators can manage the loading on transformers and distribution lines more effectively, preventing overloads and maintaining proper voltage distribution.

Figure 4.

Several mechanisms that EVs can contribute to voltage stability through them.

However, there are considerations to keep in mind:

• Battery health: Frequent cycling of EV batteries for voltage support purposes might impact battery health and longevity.

• Coordination and control: Effective coordination and control mechanisms are essential to ensure that a large number of EVs can provide voltage support in a harmonized manner without causing operational issues.

• Standardization and infrastructure: Like with any grid interaction technology, standardization of communication protocols and necessary charging infrastructure are critical for successful integration.

Electric vehicles (EVs) can potentially participate in Frequency Regulation (FR) strategies through three distinct approaches:

1. Localized decision making: The first method involves individual chargers configuring their charge/discharge power based on local information such as load variations, EV arrival schedules, and the local frequency of the area [100, 101].

2. Decentralized FR signals: In the second configuration, FR signals are generated according to operating voltage and power loss, and then transmitted to aggregators. These aggregators subsequently forward the signals to a control center in a decentralized manner [102, 103].

3. Centralized decision mechanism: The third approach commonly employed for FR involves a centralized decision mechanism. In this scenario, a control center manages the chargers by utilizing a communication system [104, 105].

Frequency fluctuations can lead to a range of problems, including equipment damage, blackouts, and overall instability of the power grid. Electric vehicles play a pivotal role in maintaining frequency stability, as depicted in Figure 5.

1. Demand response and V2G technology: EVs can act as a flexible load or even a source of power by utilizing V2G technology. During periods of high electricity demand, EVs can reduce their charging rate or temporarily discharge electricity back into the grid. This demand response capability helps balance supply and demand, stabilizing grid frequency.

2. Frequency regulation: Grid operators need to continuously match electricity generation with demand to maintain a stable frequency. EVs, when aggregated and controlled, can provide a distributed source of regulation services. They can respond rapidly to grid frequency changes by adjusting their charging or discharging rates, helping to stabilize frequency variations caused by sudden changes in generation or load.

3. Integration of renewable energy: Renewable energy sources like solar and wind are variable in nature. Their output depends on weather conditions, which can lead to fluctuations in the power supply. EVs can absorb excess electricity during periods of high renewable energy production and release it during low production periods, thereby helping to smooth out these fluctuations and maintain grid stability.

4. Energy storage: EVs effectively function as mobile energy storage units. When connected to the grid, their batteries can store excess electricity and inject it back into the grid when needed. This can mitigate frequency deviations caused by sudden changes in supply or demand.

5. Reduced need for conventional reserves: Traditional power plants often maintain spinning reserves to respond to sudden changes in demand. With a larger fleet of EVs equipped with V2G capabilities, these reserves could potentially be reduced as EVs can provide a distributed and responsive source of power.

6. Ancillary services: EVs can participate in providing ancillary services such as frequency regulation, voltage control, and reactive power support. These services are essential for maintaining stable grid operations.

Figure 5.

Several mechanisms that EVs can contribute to frequency stability through them.

However, there are also challenges to consider:

• Battery degradation: Frequent charging and discharging of EV batteries for grid services could accelerate their degradation, impacting the overall lifespan of the batteries.

• Infrastructure and standardization: Widespread implementation of V2G technology requires standardized communication protocols, infrastructure investment, and regulatory frameworks to ensure safe and efficient operation.

• User preferences: The ability to use an EV’s battery for grid services might be subject to user preferences and priorities. Some EV owners might prioritize their vehicle’s own battery life over grid services.