EV: Overcoming the Constraints of Electricity Grids

Article By : M. Di Paolo Emilio

Electric mobility provides ample challenges for engineers of next generation EV battery solutions.

Electric mobility will change the energy and automation market, contributing to significant investment in smart cities. These changes coincide with the evolution toward a cleaner, more decentralized, and digitized environment. Electric vehicle (EV) charging could create local constraints and stability problems on electricity grids and reduce the environmental benefits of electrification. Investment and infrastructure to support electric mobility will change significantly from one place to another.

The infrastructure will have the objective of distributing energy — in combination with grid edge technologies, such as microgrid and intelligent buildings — and integrating it into smart grids, in order to fully exploit the flexibility of electric mobility while allowing the stability of the energy system.

The battery market will make electric vehicle efficiency more convenient, and smart charging services will reduce costs. Digitization will help simplify and improve the customer experience — supporting efficient infrastructure management, as well as enabling new services such as shared mobility. And charging stations will acquire the right to become hubs for smart city services.

Battery for EV
One of the main factors to take into consideration is the capacity and efficiency of the battery. The performance of the vehicle and, above all, its autonomy depends on them. The parameter that measures efficiency is given by the energy used per kilometer and is generally expressed in kWh/100 km or km/kWh. The capacity of a battery, on the other hand, expresses the amount of energy that it can hold and equals the full fuel in the tank of a traditional car; the relationship between its value and consumption indicates the average theoretical autonomy of the vehicle (Figure 1).

Figure 1: The autonomy expressed in miles varies with the capacity of the battery (kWh) for seven different efficiency values (miles/kWh) (Source: InsideEVs).

The increase in battery capacity for the same size unit is the center of attention for the leading market players who want to announce greater autonomy without having to modify the vehicles substantially. A Bloomberg study, based on a survey involving 50 companies in the automotive sector and accumulators, points out that in 2010 the price of lithium batteries was well over $1,000 per kWh and that in 2025 it will reach $100 per kWh (Figure 2). Now, lithium-ion batteries guarantee to maintain an 80% efficiency for a longer duration, on average 8 years, compared to those with nickel-metal hydride (Ni-MH) technology.

Figure 2: Battery in an EV. (Source: Nissan)

Smart Charging

Batteries are the key challenge for running electric vehicles. Several studies address the issue by highlighting how batteries and smart charging could also be the key to reducing energy sector emissions, thus increasing efficiency. The main problem is the simultaneous charging of electric vehicles at the same time because it is a power and network problem. Batteries have remained an elusive problem to solve for electric vehicles, as engineers try to develop a way to make them last longer and manage their end optimally (Figure 3). 

Figure 3: Components of an electric vehicle.

“Large-scale electric vehicles can offer ample electric storage capacity, but if all users were to load their cars in the morning or evening at the same time, the power grids would be stressed,” explains Dolf Gielen, director of the Innovation Center and IRENA technology. “Charging times are therefore fundamental.”

The autonomy of an electric vehicle does not depend only on the capacity of the batteries installed, but is affected by the temperature of the environment in which it operates, the consumption of the auxiliary services on board, and the type of driver’s driving .

An advanced smart charging approach is vehicle-to-grid (V2G), already tested in the United Kingdom, the Netherlands, and Denmark; the technology allows the columns to “talk” with the networks, using the car battery it is connected to like a storage system.

With V2G applications, the electric car ideally becomes a large mobile battery, powered by renewable energy produced and managed in a bidirectional way. Depending on the needs, the available energy is transferred from the house to the car or the network, with an economic return for those who supply it. In these smart grids of the future, cars will also become an essential link in the clean energy value chain.

The application of V2G also leads to other advantages: In addition to reducing pollution and indirect environmental protection, there will be economic advantages both for the operator and for the vehicle owner. The energy stored in the batteries can be used to satisfy part of the local energy demand — to lower the peaks of the load profile. This reduces stress on the power plants, reduces the energy present in the distribution system, and consequently reduces losses. The lowering of the peak, therefore, allows for reducing the cost of electricity during periods of maximum load. One of the critical aspects of the development of V2G is to create and spread stable, standard overtime for communication with smart grids. The electric vehicle must integrate perfectly with the electrical system, so the charging process requires excellent communication between the vehicle, the charging column, and the network.

Various studies have investigated appropriate standards for communication between the vehicle and network management systems. Various projects have examined the opportunities for using IEC 62056 DLMS/COSEM, exploiting technical aspects of the protocol for forwarding information to intelligent network management systems — such as a load balancing controller.

An alternative approach is to use the IEC 61850 protocol to support communications between substation automation systems for purposes such as energy flow management among renewable energy resources. A specific extension has been proposed to allow interaction with various V2G ISO/IEC 15118 interfaces. Figure 4 shows how this reference project proposes a combination of ISO/IEC 15811 and IEC 61850 protocols to implement end-to-V2G communication.

Figure 4: Vehicle charging station using V2G communication. (Source: Fraunhofer)

STMicroelectronics’ ST2100 STreamPlug integrates a configurable Arm9 core capable of supporting multiple HomePlug AV or HPGP ports. The device is designed to enable a single-chip solution to various smart use cases such as EV charging. The Arm core provides sufficient processing power to host intelligent charging applications and protocol stacks such as IEC 61850 or DLMS/COSEM, as proposed for communication with intelligent network management systems (Figure 5).

Figure 5: Block diagram for ST2100. (Source: STMicroelectronics)

The electric vehicle scenario covers many technologies. Right now, the market is dedicating its resources to infrastructure that can support network capacity, rather than increasing overall electricity production. The use of photovoltaic energy as energy harvesting to power battery-powered cars helps make car journeys much more affordable. Electric mobility creates opportunities for new products and services that include maintenance and operation of vehicles, installation, operation, maintenance, and service of recharging points, software solutions for energy management.

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