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This lecture introduces the concept of smart charging. The following topics are discussed:

• The definition of smart charging and vehicle-to-grid
• The need for smart charging
• The applications and benefits of smart charging
• The key challenges for smart charging

The definition of smart charging and vehicle-to-grid

Smart charging, also known as, V2G, is described with the following definition:

“Smart charging is a series of intelligent functionalities which enable the communication of information and services between electric vehicles or EVs, and the smart grid stakeholders; to supply and maintain a safe, reliable, sustainable, and user-friendly charging environment.”

These functionalities can be achieved by creating and distributing power efficiently amongst the electric vehicles. This allows us to get the most out of the charging stations in case of limited power capacity. Smart charging has several benefits, such as:

• The flexibility in terms of time and power level of charging increases
• A better utilization rate of transformers and lines. This is achieved by reducing the peak demand or by shifting the charging to low demand periods (also known as valley filling).
• Grid reinforcements can be avoided or delayed due to a better grid utilization.
• The use of renewable energy can increase, due to the increase of flexibility.
• Smart charging can create new revenue streams for EV owners from participation in ancillary services.

The need for smart charging

The need for smart charging can be understood by looking at how charging is done today. If multiple EV’s arrive at the same moment in time at a charging station, the charging powers of the EV’s will add up, because charging is done simultaneously. This is referred to as uncontrolled charging.

Controlled charging factors in different aspects, such as when the vehicle has to leave or what the energy demands of the different vehicles are. This allows the charging to be spread out throughout the day. The difference between uncontrolled and controlled charging can be seen in the figure below. It should be noted that the total energy demand is the same in both cases.

To implement smart charging, four degrees of freedom can be used. These degrees are listed below:

1. Charging power: The rate at which the EV’s are charged has to be flexible
2. Time flexibility: It should be able to control when a vehicle is charged and when not.
3. The direction of charging: With Vehicle to Grid (V2G) technology, charging is possible bidirectionally. This makes it possible to feed energy stored in the vehicle back into the grid.
4. Fast ramp rates: The EV’s need to have a fast ramp rate, such that the magnitude of power charging can be changed within milliseconds.

The application and benefits of smart charging

There are different applications and benefits for smart charging. The first application is to control the charging power of the EV based on the production of renewable energy. This will ensure an optimal use of the renewable power and makes the EV fully sustainable. Also, with V2G, electric cars can be used as storage and can help with the balance of the variable generation of renewable energy resources.

The second application is that smart charging can help with congestion management by shifting the charging time or adjusting the charging power. When the load on the grid is low, the charging power of EV can be increased. On the other hand, when the grid demand is overloaded, EV charging can be stopped.

Another application of smart charging is to use it when there is limited power for the charging of EV’s. In this case, different solutions are possible such as:

• Charge the EV’s sequentially based on priority
• Charge the EV’s simultaneously with a power limit
• Each car can be charged with a different strategy based on priority and the load.

Besides smart charging, vehicle-to-grid can play an even more prominent role in congestion management as the vehicle can act as a local power generator and provide power at the moments of grid congestions to achieve peak shaving. EV’s can for example be charged when there is an excess of renewable electricity and discharged when the demand increases. This makes the EV act as a storage element.

Another aspect is price-based smart charging. The charging power can be increased when the electricity price is low and can be decreases when the prices are high. This reduces the cost of the users and the users can even make profit with V2G. EV can store energy when it is cheap and sell energy to the grid when the electricity becomes expensive.

The last application of electric vehicles is frequency regulation. The EV power can continually be adjusted to maintain a balance between energy supply and demand. For Frequency Containment Reserve (FCR), a response is required within 30 seconds. Since EV batteries have ramp rates in the order of milliseconds, they can be used for FCR.

The key challenges of smart charging

There are a few key challenges for smart charging. These challenges are listed below:

• Market mechanisms are needed at distribution or DSO level to encourage congestion management.
• Net metering reduces the incentive to store and increase the self-consumption of energy via energy storage.
• Regulations of FCR have a minimum of bid and delivery period. Therefore, large numbers of EV’s are needed.
• A digital infrastructure for aggregating and coordinating many EV’s still needs to be build.

Conclusion

This lecture introduced the concept of smart charging. First the definition and the need of smart charging was discussed. Then, several applications and benefits were mentioned. Finally, the key challenges for smart charging were discussed.