PEVs, Smart Grids And Energy Storage Systems

The large scale penetration of Plug-in Electric Vehicles (PEVs) in the transportation segment makes the utility power network more stressed and less efficient due to negative impacts of integration of PEVs for charging the batteries. This article describes the PEV technology, charging strategies of PEVs, smart grids and integration of PEVs and types of energy storage systems...  - K Ramalingam, C S Indulkar

The Plug-in Electric Vehicle technology is fast emerging for modernizing transport segment and offset climatic challenges due to fossil fuel depletion. The technology causes negative impacts to power utility systems that are used to charge the batteries in PEVs. Research advances are progressing towards resolving the technical and economical issues to bring down ownership costs of PEVs. The large scale penetration of PEVs in the transportation segment makes the utility power network more stressed and less efficient due to negative impacts of integration of PEVs for charging the batteries. Integration of PEVs with the power network at high penetration level demands a new technology, that is, a smart grid to integrate renewable energy sources and to operate the grid more efficiently, which includes time flexible demand side management. The smart grid technology with the two way communication of digital information and power flow monitoring is emerging to operate the grid smarter with intermittent renewable sources and reduced generation of fossil-fuel fired traditional power generators. The power from renewable sources is from the intermittent solar and wind farms that are seasonal and uncertain. A new technology on Electrical Energy Storage Systems, with storage capacity in megawatt scale, is emerging to store off-peak period energy, and supply to the grid on-peak period appropriately to balance the load side management. All the three technologies are emerging fast, and are complimentary to each other. A comprehensive overview of the three technologies is presented in this article.

The Plug-in Electric Vehicles (PEVs)

The Plug-in Electric Vehicles (PEVs) are the Battery Electric Vehicles (BEVs) and Plug-in Hybrid Electric Vehicles (PHEVs). PEVs will dominate the transportation in the personal mobility mode and in the automobile market by 2030. The focus on promoting use of electric vehicles in road transportation is very essential to meet the climate change targets and manage the ever hiking prices. However, there are lots of uncertainties in the market about the acceptability of PEVs by customers due to the capital and operation costs and inadequate infrastructure for charging systems. Manufacturers are also not sure of the market, even though predictions are strong and attractive. Major manufacturers, however, are already ready with their plans to introduce electric vehicles in the mass market. The use of PEVs has both technological and market issues and impacts. Series of research works have been reported to address the issues related to PEV technologies and its impacts on political, economic, environmental, infrastructural and market potential aspects.

The new vehicle technology in transportation segment is the Plug-in–Electric Vehicles. PEVs need battery charging infrastructure to operate charging stations by utility network systems. PEV charging stations are located at business centres, retail stores, colleges, workplaces, parks and libraries. Charging station technologies are advancing rapidly with faster charging capabilities, increased communications, improved controls and lower capital costs. Electric vehicles support fuel independence, cleaner air, and economic growth. The technologies, economics, and support for clean energy have created a new market opportunity. The adoption and roll out of PEVs can accelerate with continued collaboration around EVSE (Electric Vehicle Support Equipment) infrastructure, utilities, vendors and their collective customers, and play a key role in the world economy and environment.

The environmental benefits of plug-in electric vehicles increase with use of ‘green’ sources such as solar, wind or small-scale hydroelectricity. PEVs typically emit less greenhouse gas emissions than conventional vehicles. The technology is, therefore, promoted with incentives from Governments.

PEVs Technologies

A Plug-in Electric Vehicle (PEV) uses electric energy from a battery power source. The storage batteries, which supply power to the vehicle, need to plug-in to recharge. There are several types of plug-in electric vehicles, each with different features. The types of electric drive vehicles, other than PEVs, are: Photovoltaic Electric Vehicles (PVEVs) and Fuel Cell Electric Vehicles (FCVs).

-A Battery Electric Vehicle (BEV) is fully electric and powered by the on-board battery. The vehicle is capable to go up to 100 miles on full charge. The batteries are then plugged- in to a power source to recharge.
-An Extended Range Electric Vehicle (EREV) is similar to BEVs, but it may have an on-board gasoline fuelled generator to provide additional energy, when the batteries are low. These may have up to about 50 miles range on the initial battery energy.
– A Plug-in Hybrid Electric Vehicle (PHEV) has both an electric motor and a typical gasoline or diesel engine to power the car. A plug-in-hybrid electric vehicle is designed with types of configurations such as series-hybrid, parallel-hybrid, or combined series-parallel hybrid:

  • Series-Hybrid: Only the electric motor provides power to drive the wheels. Sources of electrical energy are either the battery pack (or ultra-capacitors) or a generator powered by a thermal engine. Such vehicles are Extended-Range Electric Vehicles.
  • Parallel-Hybrid: Both the electric motor and fossil powered engine provide power in parallel to the same transmission.
  • Power split or series/parallel hybrid: This allows running the vehicle in an optimal way by using the electric motors only, or both the IC Engine and the electric motors together, depending on the driving conditions.

The PEVs system has the following components of the drive train.

  • Electric Motors: This device converts the electrical energy from the battery to mechanical energy, thus propelling the vehicle by AC or DC motor.
  • Electric Generators: The generator converts mechanical energy to electrical energy. In some vehicles the two functions are combined into a single device by motor-generator.
  • Inverters Battery packs invariably supply DC current: The AC motor in a PEV is coupled with the battery pack using an inverter. The inverter converts the DC from the battery to AC and powers the AC motor.
  • Chargers: It converts the AC electrical output from the generator into DC and charges the battery pack. A charge controller optimises the charging process that prolongs the life of the battery. The Electric Vehicle Support equipment (EVSE) includes 120 V/ 240 V AC plug-in, Control device, Charging cable cord, Connector and Coupler.
  • Large Battery Packs Battery packs store the energy to power a PEV. The variants of electric vehicles use different types of battery packs: lead acid, NiMH, Li-ion.

Challenges and Opportunities

The use of PEVs has technical and commercial challenges as well as business opportunities.The technical impacts are: Technology is not fully developed. The technology is evolving with time to bring down purchase cost comparable to a conventional vehicle. The issues and challenges are:

  • The development of battery technology and raw materials to keep the cost affordable with Vehicle size and to meet the expected range of travel.
  • Public awareness on its availability, cheap in cost, less in operational cost and better economic and environmental impacts at large.
  • Use of PEVs as source of power by utility to manage peak load-shaving in power grids.
  • Development of grid infrastructure to integrate PEVs with Smart Grids.
  • Development and investment of Charging Infrastructure by Utilities.
  • Managing the load balancing, peak hour Shaving, Off-peak charging tariff structure and economic and cost effective user billing infrastructure by utilities.
  • Development and investment on manufacturing, Tariff regulations, and incentives to promote PEVs.
  • Development and management of Information Communication Technology (ICT) infrastructure in the Smart Grids.
  • A drive to focus on PEVs penetration in the transport sector, establishment of Smart Grids, and integration of PEVs and renewable energy sources.
  • Development and management of Energy Storage Systems to maintain an efficient operation of the power network .

The use of PEVs has technical impacts in distribution power network. The impacts vary with the vehicle penetration levels, charging pattern, fleet charging profile, distribution network power losses, integration of PEVs at the transformer levels, vehicle driving pattern, and Demand Response (DR) strategy to reduce peak loads, driving distance, battery sizes, and tariffs. Widespread use of PEVs with new vehicle technology has a positive impact on environment and economy. It helps in clean transportation, energy independence and reduces emission of gases, such as carbon dioxide, nitrogen oxides and sulphur oxides.

Other impacts on power grid due to increased penetration of PEVs are: Increase in additional power load for charging PEVs in uncontrolled scenario. However, off-peak charging of PEVs improves the load curve for electric utilities. Therefore, the use of high penetration PEVs should be properly optimized under different charging scenarios and technologies.

The charging scenarios are either controlled or uncontrolled. Certain strategies are required to manage charging behaviour to limit the daily charging peak. The charge management methods are: tariff rates such as Real Time Pricing (RTP) under Time of Use (TOU) tariff and Controlled charging from Smart Grid under Critical Peak Pricing (CPP) tariff.

The battery capacity determines the charging time, and is inversely proportional to the State Of Charge (SOC) of the battery. The electric load curve in power system network depends on the percentage of PEVs penetration and the charging strategies.

The charging station has single phase AC/DC conversion devices. DC distribution with super- capacitor energy storage device supplies power to the battery, when the power demand for the charger exceeds the average demand of the grid. A 230 kVA Transformer is required for every 50 parking spaces, and accordingly, infrastructure for charging station and system integration of BEVs to the grid operation is needed.

Demand Response (DR) is another dynamic benefit to the grid by interrupting the PEVs demand on peak hours. The Plug-in bidirectional Vehicle-To-Grid system (V2G) batteries in smart grid charging become distributed storage systems for the electrical grid. The energy supplied to the grid is priced to pay back the cost of Vehicle to Grid (V2G) batteries in PEVs. The distributed storage would make the grid more stable, secure and resilient by frequency regulation and spinning reserve as backup capacity within the distribution system. V2G system allows greater penetration of wind and solar resources into the grid.

A large scale penetration of PEVs will introduce several technical challenges and will impact different aspects of the power system grid:

  • Impose uncertainty in load in the distribution system, need reliable communication network, impose cyber security issues and quality and stability of the overall distribution system.
  • Other challenges are focus on charging and control strategies for coordination and integration of PEVs with grid, grid interface technologies, energy management issues, demand response services, power losses, voltage and frequency regulation issues.
  • The average operating temperature of transformers will increase under the additional load of charging PEVs. This could shorten their life, thus adding costs to the electricity grid.
  • There will be potential power supply shortage, if the aggregated battery charging profile includes the on-peak period.
  • The batteries should be storing electricity from the lowest carbon emitting sources, namely nuclear energy and renewable energy. But, the challenge is then to make the demand and supply load curves coincide. The battery load curve depends on the time for recharging and charging power.
  • The new PEVs fleet impacts the electricity transport and generation capacity. The electricity grid operators require innovative management methods to tackle the issues.

The utility operators of the electricity grid deploy new techniques to monitor, and remotely control the electricity demand. Beyond such a mono-directional power flow management from the electricity grid to the vehicle battery, more integration methods are being explored. These innovations are also being considered in the framework of research and development efforts towards a smart and reliable grid, as needed by the growing role of distributed energy resources, including intermittent renewable energy resources.

The utility needs to meet additional expenditure for up-gradation of the electrical system to meet the additional load due to sudden charging by PEVs cluster at a time. As a mitigation strategy, most utilities are developing PEV charging permit requirements.

An accurate and up-to-date data about line and transformer capacity will be the key for development. Advanced Distribution Management Systems (DMS) with intelligent line and transformer sensors and smarter meters help operators in real-time to effectively manage the network. Advanced Metering Infrastructure (AMI) and Integrated System Model (ISM) are used to manage the changing distribution environment. Charging station should have communication facilities that transfer information on PEVs and battery storage status to the utility DMS. Utility needs investment on this real-time monitoring process.

A smart charger ensures that the plug-in batteries are charged only when the electricity is at its cheapest, saving money. Moreover, utilities could temporarily turn off chargers in thousands of homes or businesses to keep the grid safe during peak hour demand.

High penetration of PEVs in electric grid has specific impacts on distribution network systems. They are:

  • Phase imbalance: Lower percentage of PEVs using single phase charging results in larger variation in current imbalance, but the lower total load reduces the voltage imbalance. However, when higher numbers of PEVs are charging, then the diversity increases and so lowers the current imbalance and keeps the voltage imbalance within limits.
  • Power Quality issues: The non-linear elements such as inverters and battery chargers in PEVs increase voltage distortion and current harmonics significantly. Harmonic currents cause excessive neutral current and transformer hotspots. New designs of chargers are in the market to control harmonics with low TDH of 30% against the present 60-70 % TDH.
  • Transformer degradation and failures: The load pattern on deployment of PEVs will change and the power system may not be capable of handling the new load pattern with the additional load demand. A study reports that harmonic distortion, load distortion, increased temperature and higher penetration rate of PEVs in a transformer and charging characteristics degrade the transformer life span by 40 % per year and increase failure rate.
  • Circuit Breakers and Fuse Blow-outs: The harmonic distortion affects the interruption capability of circuit breaker. High harmonic current on fuse behavior has thermal effects and dissimilar current.

The use of PEVs creates opportunities to automotive industries, electricity utilities, vehicle charging companies, battery manufacturers and all levels of Government organisations and most importantly consumers. Governments are driven to adopt PEVs in the transport sector to increase the fuel economy standards, meeting the local air quality standards, energy security and compulsion to reach the target of climate change.

The market challenges are high initial cost of PEVs due to high battery costs, limited drive range, high charging time and limited charging infrastructures. Other challenges are: lack of consumer education and acceptance, smart grid integration, lack of familiarity to PEVs.

Market penetration of PEVs would largely depend on public policies from regulatory bodies. The regulatory bodies for policies and regulation of electric vehicles are:

  • World Electric Vehicle Association (WEVA)
  • Electric Drive Transportation Association (EDTA)
  • Electric Vehicle Association of Asia Pacific (EVAAP)
  • European Association for Battery, Hybrid and Fuel Cell Vehicles (AVERE)

1.3 Electric Vehicle Market Forecasts

The major PEVs markets are in North America, Western Europe, and Asia Pacific with compound annual growth rate of 23.7 percent through 2023, according to Navigant Research Report. Various published research reports predict PEVs annual growth projections of 16 to 20%. Governments worldwide are keen to increase penetrations of PEVs due to the environmental, economic, and energy security benefits. As such, government incentives to spur growth in PEV development have been fundamental to growing Plug-In Electric Vehicle (PEV) penetration within the vehicle market.

Promotional Programs on PEVs

The Governments in Canada, China, Europe, India, Japan and United States have special promotional programmes to promote adoption of PEVs. The programs provide incentives by way of rebate for new PEVs and preferences to use Government charging stations, parking spots and priority lane for driving and provides subsidies for sale, and annual tax exemption.

Europe provides, for new PEVs, tax exemption and penalty charges on carbon-dioxide related taxes. Some states provide income tax rebate and tax deduction on investment on external recharging station infrastructure, exemption from road taxes, tax breaks, annual bonuses, exemption from first registration taxes, free parking in public parking spaces, exemption from annual circulation taxes, exemption from all non-recurring vehicle fees, waiver of import tax and 100% discount on London congestion charges. Greener Vehicle Discount (GVD) and Ultra Low Emission Discount (ULED) schemes are also operative.

Indian Government provides 20% subsidy of ex-factory price of PEVs and exemptions on road taxes, VAT and registration charges. There would be customs/excise duty reduction. The government has set up a National Mission for Hybrid and Electric Vehicles to encourage manufacture and sale of electric vehicles.

Japanese Government provides subsidies up to 50% on clean energy vehicles and provides tax deduction and exemptions on environment friendly vehicles that meet the environmental performance criterion. The PEVs are exempted from both the acquisition tax and the tonnage tax, and 50% reduction of the annual automobile tax.

US Government grants tax credits on new purchase and on the cost of installing home-based charging station. Other facilities are free charging of electric vehicles in public charging stations and work place charging stations, preferred parking spots in public parking spaces and reduced interest rates on vehicle loans for employees.

Smart Grids

India is the third largest country in the world in Electrical Transmission and Distribution. Therefore, it needs an efficient and strong system for distribution, where the smart grid concept could help. Smart Grid is an integration of Electrical and Digital technologies, and, Information and Communication. Smart grid delivers and monitors electrical power to the consumers using two way digital technology. Figure 1 shows the smart grid concept of integrating fuel based and renewable energy sources and information and communication infrastructure.

The smart grid with integrated PEVs is a modernized electric grid that uses communication network to collect information about the power network and monitors the grid for efficient operation. The components of power network grid are power supply, batteries and battery chargers with optimized charging system and converters. The smart grid has communication network to communicate to various electric devices in the power network through wired and wireless networks. The communication network comprises five levels viz.

  • Wide Area Network (WAN) to connect substation and control centers in the distribution system,
  • Neighborhood Area Network (NAN) through wireless networks, power line communication networks or Ethernet to connect smart meters and data collectors in the distribution system,
  • Field Area Network (FAN) for monitoring and information exchanging between PEVs and control centers,
  • Home Area Network (HAN) to control and monitor PEVs, Smart Meters and Energy Management System, and
  • Control Area Network (CAN) to connect charge controller and charging station.

Fig.1 The smart grid concept…

Secure and bidirectional control and communication mechanisms for accommodating PEVs is needed for reliable billing, demand response arrangements for V2G integration, reliable and stable load balance and cyber security in case of security breaches to meet the integrity and availability of PEV integrated system in the communication network. The cyber attack on integrated PEV System has severe negative effects on electric power and transportation infrastructure simultaneously. The cyber security challenges are categorized as follows:

  • Payment security with authentication and data encryption technologies to protect secured payment transactions from frauds,
  • Smart metering with real-time data acquisition of accurate energy consumption for pricing,
  • Cyber physical critical infrastructure to protect devices and PEVs in the network against malicious cyber-attacks or firmware infections,
  • Cyber attacks in data transmission in the wireless network,
  • Cyber attack on client privacy of PEVs on information such as location, identity, distance travelled and energy exchange patterns.

There are two methods to detect data intrusion, namely, Anomaly Detection methods and Misuse Detection methods to identify malicious data

Smart Grid Technology

The smart grid technologies are grouped into five key areas:

  • Integrated communications will allow for real-time control, information and data exchange to optimize system reliability, asset utilization, and security. Areas for improvement include: substation automation, demand response, distribution automation, supervisory control and data acquisition (SCADA), energy management systems, wireless mesh networks and other technologies such as power-line carrier communications and fiber-optics.
  • Sensing and measurement will evaluate congestion and grid stability, monitor equipment health, energy theft prevention, and support control strategies. Technologies include: smart meter, wide-area monitoring systems, electromagnetic signature measurement/analysis, time-of-use and real-time pricing tools, advanced switches and cables, backscatter radio technology, and digital protective relays.
  • Advanced Metering Infrastructures (AMI) use digital meters that record usage in real time. The communications infrastructure such as wires, fiber, Wi-Fi, cellular, or power-line carrier are used to get the data backup to the utility.
  • Phasor Measurement Units (PMUs) is high speed sensors that are distributed throughout a transmission network to monitor the electric system.
  • Other Advanced Components are innovations in superconductivity, fault tolerance, storage, power electronics, and diagnostics components that are changing the abilities and characteristics of grids.

The smart grid must be self-healing, allow active participation of consumers in operation, ensure higher quality power, accommodate all generators and storage options, enable more efficient operation, enable new electricity markets and enable higher penetration of intermittent renewable power generation sources. IEEE is developing guidelines and standards on how the grid should operate using the latest in power engineering, communications and information technology. A secure and reliable real-time two way high speed communications infrastructure is an essential part of the smart grid reality. Research advances on smart grid technology include communication architecture network technologies and integration technology of PEVs and renewable energy sources with energy storage system coordination.

The most serious concern for utilities is controlling the (EVSE) Electric Vehicle Supply Equipment, which add load to the grid. A high percentage of consumers will instinctively charge their EVs at home, which has a serious impact on peak grid demand. The home charging stations typically draw electricity load of 6.6 kW (240V and 30 amps) in addition to the house load of 7 kW. Even low levels of EV adoption in a particular neighborhood can strain existing power infrastructure.

The Electric Power Research Institute (EPRI) report suggests that if two customers on the same transformer plugged in 6.6 kW charging stations during a peak time, their additional charging load may exceed the emergency rating of roughly 40 percent of the distribution transformers.

The Smart Grid is the key to smart EV charging. The Smart Grid provides the visibility and control needed to mitigate the load impacts and protect components of the distribution network from being overloaded by EVs, thus ensuring electricity generating capacity is used most efficiently. With a Smart Grid, utilities can manage when and how EV charging occurs while still adhering to customer preferences.

Smart Grid integration of EVs enables utilities to provide consumers to know the cost of ‘fueling,’ positive impact on the environment and ability to set charging preferences. A Smart Grid also allows utilities to collect EV-specific meter data, offers specific rates for EV charging, engages consumers with information on energy transmission, and collects data for greenhouse gas abatement credits.

Utilities can remotely monitor charging stations and allow for the comprehensive management of EV charging. Utilities can also troubleshoot charging issues without unnecessary on-site service calls and manage when connected EVs are charged.

Communication Demands Of Smart Grid

Integrated communication involves data acquision, protection and control. Therefore, the communication infrastructure is the most important priority in building a smart grid.

With the Smart Grid, utility offices will be able to support, integrate and optimise EV charge management as part of an integrated Demand Side Management (DSM) operation. This approach requires systems that manage EV charging and optimize with other Demand Response (DR) programs.

The Smart Grid also allows utilities to seamlessly integrate an EVSE meter with the Advanced Metering Infrastructure (AMI) system. This allows a utility to break out EV charging from the primary meter and bill for EV charging at a separate rate. AMI integration can also make it easy for utilities to track and report EV charging usage for greenhouse gas credits and use data to predict local reliability issues.

A novel load management solution is necessary for coordinating the charging of multiple Plug-in Electric Vehicles (PEVs) in a smart grid system. Utilities are becoming concerned about the potential stresses, performance degradations and overloads that may occur in distribution systems with multiple domestic PEV charging activities. Uncontrolled and random PEV charging can cause increased power losses, overloads and voltage fluctuations, which are all detrimental to the reliability and security of newly developing smart grids. Therefore, a real-time smart load management (RT-SLM) control strategies are being developed for the coordination of PEV charging based on real-time and minimization of total cost of generating the energy plus the associated grid energy losses. This approach enables PEVs to begin charging as soon as possible considering priority-charging time zones, while complying with network operation criteria such as losses, generation limits, and voltage profile.

Successful integration of plug-in electric vehicles into the power system is a major challenge for the future smart grid, such as charging and control strategies of PEVs, Vehicle-to-Grid (V2G) technology, and several application domains, such as wind energy integration, frequency regulation, design of parking areas and participation in electricity markets.

DC Fast Charging Equipment

DC fast charging equipment can reduce the time in less than an hour to a full charge on a standard BEV. A new connector, that combines Alternating Current (AC) and DC fast charging in one unit, is now available. The Society of Automotive Engineers (SAE) standards have defined PEV charging levels. AC level 1 and 2 charging stations convert the AC to DC power through the PEVs on-board chargers. DC Level 1 and 2 charging stations provide electricity from AC to DC through an of-board charger. DC power is directly delivered to the vehicle. AC Level 1 charging uses 120 V single phase outlet with current ratings 15A and 20A, and is suitable for home charging. AC Level 2 charging is used for both private and public charging facilities. It provides a range of 15-20 miles per hour of charging time. DC Level charging is for commercial and public applications. DC Level charging offers a range of 40 miles to a PEV per hour of charging time.

There are two alternative charging methods: inductive charging or wireless charging and battery swapping. Wireless charging is convenient and can address many issues related to costs, driving range and battery capacity and life.

The Wireless Power Transfer (WPT) charger transfers power wirelessly to the vehicle charging circuit that feeds the Energy Storage System in the vehicle. However, the WPT technology and standards are still under research and development for large scale deployment. Battery Swapping is a method by which the dead battery is replaced with fresh battery at Battery Swapping Stations. However, battery Swapping Stations have technical challenges such as upfront investment in battery packs, difficult to standardise, huge investment in Swapping Station infrastructure and manpower, and big concern on safety and reliability of service.

Charging Strategies

The number of PEVs in the near future will increase and stress the already overloaded power grid, creating new challenges for the distribution network. To mitigate this issue, several researchers have proposed the idea of charging PEVs using renewables coupled with smart charging strategies. There are researches on control algorithms, smart charging techniques and different power electronic topologies for photovoltaic charging facilities (PCFs).

A group of Plug-in Electric Vehicles (PEVs) is controlled by an ‘aggregator.’ The aggregator is responsible for making the charging schedule for each PEV and also participates in power system regulation or electricity market bidding. However, practically, to coordinate the charging of large scale PEVs in power system, the diversities in charging infrastructure, PEV types and local operational constraints in the power system needs to be well considered.

Therefore, hierarchical control of PEVs is regarded as an effective way to achieve charging cost minimization and system operational security. Hierarchical control frameworks for PEV charging includes coordinated charging strategy for charging station, coordinated charging strategy for battery swapping station, hierarchical coordinated charging strategy for multiple charging stations and a three level coordinated charging framework for large scale of PEVs. The hierarchical charging control framework and optimization methods reduce peak demand and charging costs.

The uncertainties on place and time of charging by Plug-in Electric Vehicles (PEVs) use stochastic based approaches to identify the load scenarios and the impacts of a new type of load of the PEVs battery charging.

It incorporates several PEV models with different charging strategies, such as non-controlled charging, multiple tariff policies and controlled charging. It uses a stochastic model to simulate PEVs movement in a geographic region and a Monte Carlo method to create different scenarios of PEVs charging. It calculates the maximum number of PEVs that can be safely integrated in a given network and the changes in the load diagrams by PEVs, voltage profiles, lines loading and energy losses.

A Model Predictive Control (MPC) framework could control in real-time the charging processes of a set of plug-in electric vehicles (PEVs) located in a load area (LA). The Electric Vehicle Supply Equipment (EVSE) is used to recharge the batteries, and a share of generation from Renewable Energy Sources (RES). The framework works regardless of the EVSE technology and power level, either direct current, alternating current, single phase or three phases.

Integration Of PEVs In Smart Grid

The integration of Electric Vehicles in electric power systems poses challenges on technical, economic, policy and regulatory issues that should be managed with new architectures, concepts, algorithms, and procedures. PEVs offer an uncommon opportunity to address energy security, air quality, climate change and economic growth. However, market growth is uncertain due to policy, economics and technical challenges and easy adoption of PEVs nationwide.

Next-generation transmission and distribution infrastructure will handle bidirectional energy flows, allowing for Distributed Generation (DG), such as from photovoltaic panels, fuel cells, charging to/from the batteries of electric cars, wind turbines, pumped hydroelectric power, and other sources. Classic grids were designed for one-way flow of electricity, but if a local sub-network generates more power than it is consuming, the reverse flow can raise safety and reliability issues. A smart grid with integrated PEVs improves voltage level and operates the grid in stand-alone mode also.

Communications and metering technologies inform smart devices, during the high cost peak usage periods, to reduce demand. The utility companies have the ability to reduce consumption by communicating to devices directly and prevent system overloads. Consumers and businesses will consume less during high demand periods, if consumers are aware of the high price premium at peak periods.

Demand Response (DR) support allows generators and loads to interact in real time, coordinating demand to flatten spikes, thus eliminate the cost of adding reserve generators, extend the life of equipment, and allow the low priority devices to use energy, only when it is the cheapest.

Use of robust 2-way communications, advanced sensors, and distributed computing technology will improve the efficiency, reliability and safety of power delivery. It also opens up the potential for entirely new services such as fire monitoring and alarms that can shut off power and make phone calls to emergency services. The benefits associated with the smart grid include:

  • More efficient transmission of electricity,
  • Quicker restoration of electricity after power disturbances,
  • Reduced operations and management costs for utilities, and ultimately lower power costs for consumers,
  • Reduced peak demand, which help lower electricity rates,
  • Increased integration of large-scale renewable energy systems,
  • Better integration of customer-owner power generation systems, including renewable energy systems,
  • Improved security.

Electrical Energy Storage (EES) Systems

The developments made in storage technologies and solutions have shown that electricity can be stored now in megawatt scale. These electricity energy storage (EES) applications are increasingly becoming viable around the world in the context of smart grid environment.

The Electrical Energy Storage (EES) is a key technology with unique capability to meet the hourly variation of power demand and electricity pricing in smart grid systems. Smart grids encourage more renewable energy sources in the grid system to reduce CO2 reduction.

EES reduces the cost of electricity use by charging storage batteries during off-peak hours and supplying energy to the grid during peak hours. EES improves reliability of supply by supporting users during power failures due to disaster periods. It maintains and improves power quality, frequency and voltage stability when connected in the power network.

Renewable energy sources have excessive power fluctuations and undependable supply. EES solves these problems with the use of large amount of renewable energy sources, when connected on grid. During off-grid period, plug-in electric vehicles with batteries are the most promising technology to replace the fossil fuels from electricity mostly from renewable energy sources.

Smart grid technologies keep the grid more flexible and interactive with consumers with information on low pricing of electricity and availability of opportunity to sell power to the grid between power production and consumption. EES is one of the key elements in developing a smart grid.

The power demand must be met by equal amount of power generation at the same time. Load demand varies with time and is unpredictable. Power generation cannot follow the demand exactly. There will be always imbalance between supply and demand and that will negatively impact the stability and power quality of frequency and voltage. The power system is a grid network of connecting the generators and consumers that are widely disbursed. The location of generators and the concentration of consumers cause congestion in power transmission. These characteristics of power supply system create different technical issues.

During peak periods generation is costlier than the cost of generation during off-peak periods. Accordingly, the power network becomes stressed and causes problems that need extra cost to maintain stability of the system to meet the demands. In such situations, the grid charges energy storage systems during off-peak hours and the ESS feed back to grid during peak periods, and thus keep the system less stressed and reduce the cost of electricity generation. Cost-free surplus power from renewable energy sources viz. Photovoltaic solar cells and Wind power generation can be used to charge energy storage systems intermittently as and when these sources are available. Power supply should be available continuously and flexible with time to consumers. The generators, therefore, produce power sufficiently to meet the demand and power to control the stable frequency accurately to maintain power output variations second by second.

Renewable energy sources do not have such facilities to control frequency regulations. The Energy Storage Systems (ESS) such as pumped hydro with large amount of power generation capacity and stationary batteries with quick response capability can support renewable energy output and support critical loads during power failures or low voltage situations to consumers. ESS is a suitable solution to supply power to congested transmission line and remote areas as standalone system.

The emerging trends for ESS technology is to use more renewable energy sources and to make the future smart grids more efficient. The use of ESS is thus summed up: Time shifting of load balancing, power quality by frequency control, mitigating the congestion in the power flow in the transmission line, supplying power to isolated grids, providing emergency power supply to protection and control equipments, and time shifting of power from renewable sources to recharge batteries, when power demand is low in the grid.

Types Of EES

Energy storage technologies encompass a large set of diverse technologies. They are broadly classified into mechanical, electrochemical, chemical, electrical and thermal energy storage systems. Mechanical systems include Pumped Hydro System-PHP, Compressed air-CAES and Flywheel- FES energy systems. The Electrochemical systems are secondary batteries, Flow batteries and chemical Hydrogen systems. The Electrical systems are: Double Layer Capacitors-DLC, Superconducting magnetic coil-SMES, thermal systems and sensible heat storage systems.


Storage Technologies: Storage technology is lagging behind other critical PEV technologies. The United States Advanced Battery Consortium (USABC) has focused on research in advanced battery technology for BEVs and hybrids. The Matrix battery concept can help optimize BEV performance to match vehicle dynamics.

Hydrogen gas is increasingly recognized as an important fuel and energy storage sector of the future. The overall demand for hydrogen as a fuel is projected to grow. However, use of hydrogen has grown for the power-to-gas market combined with its use in the fuel cell sector.

Lithium Batteries Research is going on advanced battery technologies with a magnesium-sulphur combination over lithium, which ranks high in longer storage hours, weight, reliability and life. Lithium’s energy density is a hindrance for successful applications both in automobiles and electronics devices. The new magnesium-sulphur batteries are likely to be in production by 2020. Battery performance: The key performance parameters of batteries are: Energy, Power, Lifetime, Safety and cost. Batteries make up roughly one-third of the cost of today’s electric vehicles. Lithium- ion batteries are the most commonly used batteries for vehicle applications.

Nickel Metal Hydride (NiMH): NiMH batteries have reached their maximum potential. Car makers are moving to lithium-ion batteries, especially due to higher energy density and low self-discharge rate. It meets the energy storage requirements for PEVs.

Battery disposal: The poisonous battery metals, especially lead and cadmium would likely leak into the environment, and that affect human health and eco-system. However, there is the need for an efficient recycling system for used batteries.

Battery costs: Lithium-ion battery costs are lower than NiMH batteries but the range of 600- 700 $/kWh is seen more realistic. The high production volumes of Lithium-ion battery could significantly decline the cost.

Lithium supply security: Lithium, heavy metals and other rare elements such as neodymium, boron and cobalt are used for the batteries and power train of PEVs. The demand for these materials is expected to grow significantly for use in plug-in electric vehicles. Some of the largest world reserves of lithium and other rare metals are found in China and South America.

Hazard to pedestrians: The visually impaired people consider the noise of combustion engines a helpful aid to cross streets. Electric Vehicles operate at below 30 km/h speed, that cannot be audible by all road users and is a hazard to users. Japan, U.S. and the European Union have legislations to regulate the minimum level of sound for plug-in electric vehicles to help visually impaired people.

Wireless Power Transfer Technology (WPT) has been developed to address battery limitations. WPT is the transmission of electrical power from the power source to the electrical load without physical connectors. WPT charging technology requires lesser energy storage device, if the vehicle is powered wirelessly, while driving. Dynamic WPT enabled infrastructure would allow power delivery, while PEVs in motion. EVs equipped with such technology would not require large amount of energy storage.


The Plug-in Electric Vehicles (PEVs) is a new vehicle technology that has evolved with time. There are various issues related to technical, political, economical and environmental aspects to improve the penetration level of adopting use of Plug-in Electric Vehicles. A scalable and viable business model for public charging infrastructure has yet to fully emerge. The technical issues are in respects of charging stations, infrastructure installations, development of cost-effective quality batteries and its characteristics for use in PEVs. There is need to building the infrastructure for PEVs, policies on pricing, regulations to vehicle integration, building smart electric grid, manufacturing safe components such as batteries and electrical components, building battery charging installations, operational infrastructure including manpower development, funding for infrastructure building and policies on regulation of services of the new technology.

The new technology of modernising the grid is the smart grid that is emerging to integrate the power network with a smart digital technology of communication network. The smart power grids are more efficient with the use of Information Communication Technology and integration of variable renewable energy sources, PEVs and electrical energy storage technologies. There are opportunities and challenges to these technologies related to manufacturers, electric utilities, vehicle charging companies, battery manufacturers and all levels of governments, and the power and vehicle users.

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