EV charging - electrical architectures
Integration of EV supply equipment into an existing installation
The integration of EV charging supply equipment requires an integration of several high-power loads and an adaptation to the existing electrical infrastructure.
This section presents basic principles for designing the EV charging infrastructure and its integration into the existing electrical installation.
EV charging power demand lower than the installed power demand
If the amount of charging points and their capacity is significantly lower than the installed power, an option to investigate could be to integrate the EV chargers into the existing electrical installation.
A preliminary audit is required to assess the capacity of the existing installation to absorb the power demand of the new loads. It should be checked that:
- the utility can provide the new power demand
- the existing busbar is adequately sized to absorb the new power demand,
- the existing LV panel is adequately sized to absorb the new power demand, and to integrate the additional protection equipment for the EV circuits.
- overcurrent protection selectivity can be achieved between the main circuit breaker and the circuit breakers at the EV circuits.
- selectivity can be achieved for the residual current protections between the main Residual Current Device (RCD) and the RCDs in the EV circuits.
- the RCDs of the existing installation can operate in the presence of DC leakage currents induced by the EV supply equipment.
- overvoltage protection including the new EV charging stations is achieved, with the addition of SPDs if necessary (risk assessment)
The integration of EV chargers into the existing electrical infrastructure is an interesting option if it does not require significant changes or replacement of equipment.
It is important at this stage to perform an audit to identify the power load that can be added without changing the existing electrical infrastructure. Energy efficiency measures could be proposed to reduce the existing consumption and therefore increase the power demand that can be added. Local power supplies and storage could be proposed to compensate for the impact of integrating the EV charging equipment.
If the existing LV switchboard cannot accommodate the additional power and/or devices required, the option described in next paragraph is recommended.
EV charging power demand equivalent to or higher than the existing power demand
If the power demand of the new EV loads is equivalent to or higher than that of the existing electrical installation, it could be preferable to install a new main LV switchboard to integrate all EV loads.
The existing electrical infrastructure will be connected to this new main LV switchboard. An overcurrent and residual current protection selectivity need to be achieved between the existing installation feeder and the new main incomer.
If there are several EV chargers located at the same area, secondary LV switchboards could be installed close to the EV charging area in order to optimize the cable length.
The creation of a new main LV switchboard presents the advantage of minimizing the changes to the existing electrical installation. In addition, it offers the opportunity to coordinate protection devices, and thus optimize the power availability.
Use of local energy supplies to compensate for the EV charging power demand
The integration of EV loads increases the power demand of the electrical installation significantly.
An extension of the local energy infrastructure is often required. A switch from a LV grid connection to a MV grid connection could be necessary in certain cases.
In addition to the electrical infrastructure, the electricity contract with the energy provider needs to be reviewed.
To limit or avoid these types of significant modifications to the existing local installation, local energy power supplies can be added, such as:
- Photovoltaic system: for local energy production and a commitment to sustainability
- Energy storage system: to avoid power demand peaks and optimize solar production use
- Combined heat and power (CHP): combined heat and power production if relevant
Local power supplies can be connected to the new main LV switchboard. Their integration into an existing electrical infrastructure requires a preliminary audit.
Examples of EV charging installations
The examples below are used to illustrate the implementation of the design rules described in "electrical installation design" (power demand and diversity factor, protection against electric shocks, etc.). They also show that EV charging requirements can vary significantly depending on the application: charging station powers and quantities, to fit the times and speeds of charging for each targeted end user, and so on.
Example of architecture with mode 3 charging stations according to different load management strategies
Several countries have already set some regulatory goals for retail buildings, requiring that a minimum percentage of parking slots be equipped with charging stations.
It is a required minimum, and as the speed of adoption of electrical vehicles is not clearly known, and because these regulations will probably become more stringent in the near future, it may be advisable to prepare the electrical installation for future upgrading. Busways (busbar trunking systems) are particularly suitable to facilitate this future evolution. The load management strategy will also impact the sizing of the installation.
In this example, we consider a retail building with 30 parking slots. The objective is to provide 10% of parking slots with charging stations, so 3 slots equipped with EV supply equipment (EVSE), with a possible later extension to 7 slots, e.g. 7 charge points. Charging mode 3 only is selected.
Solution 1: without load management system
With such a solution, the electrical installation is sized for the complete power, including future extension to 7 EVSE. Because there is no load management system, all charging points may be used simultaneously, so the diversity factor is 1 (IEC 60364-7-722).
The busway is sized for 7x 22kW = 154kW e.g. ~225A.
All 7 charging stations can be used simultaneously at full charging power to supply 7 electric vehicles.
Solution 2: with static load management system
The electrical installation is sized for the complete power, including future extension, but with a diversity factor of 0.4, and therefore a power limitation of the EV charging stations to stay below 100A. A Load Management System is set up with a static setpoint of 100A; it communicates with the EVSE to ensure that the total power consumed by the EV charging stations remains below 100A. It will never use more than 100A for EV charging, even if the available power from the electrical installation is higher at certain times.
The busway is therefore sized for 100A.
All 7 charging stations can be used simultaneously but not at full charging power, up to a max total of 100A. For example, it is only possible to supply 3 electric vehicles simultaneously at full charging point power.
Solution 3: with dynamic load management system
The electrical installation is sized for the complete power, including future extension, but with a diversity factor of 0.7, e.g. up to 160A for EV charging. A dynamic load management system will allocate 100% of the electrical installation’s available power dynamically, therefore allowing the number of vehicles charged simultaneously to be increased when the other site’s loads are not used.
The busway is sized for 160A.
All 7 charging stations can be used simultaneously but not at full charging power, up to a max total of 160A. With this solution, it is possible to supply 3 to 5 vehicles simultaneously and at full charge, according to the site’s other load consumption.
This solution is suitable for installation where the peak building load is not correlated to car charging requirements: a hotel at night, for example.
Synthesis
| Solution | Diversity factor | Busway sizing | Utility subscribed power | No. of vehicles charging simultaneously | Type of LMS |
|---|---|---|---|---|---|
| Solution 1 | 1 | 250 A | 250 kVA | 7 | no LMS |
| Solution 2 | 0.4 | 100 A | 170 kVA | 3 | Static |
| Solution 3 | 0.7 | 160 A | 170 kVA | 3-5 | Dynamic |
| Busway
type |
Busway
rating |
EVlink Wallbox - Wallbox plus | EVlink Smart Wallbox | ||||
|---|---|---|---|---|---|---|---|
| Single phase | Three phase | Single phase | Three phase | ||||
| 3.7kW / 16A | 7.4kW / 32A | 11kW / 16A | 22kW / 32A | 7.4kW / 32A (8A) | 22kW / 32A (8A) | ||
| KNA63 | 63 A | 9 | 3 | 3 | 1 | 3 (21) | 1 (7) |
| KNA100 | 100 A | 18 | 9 | 6 | 3 | 9 (36) | 3 (12) |
| KNA160 | 160 A | 27 | 12 | 10 | 5 | 12 (60) | 5 (20) |
| KSA250 | 250 A | 45 | 21 | 15 | 7 | 21 (93) | 7 (31) |
- The values indicate the quantity of EVLink Wallbox that can be installed on the busway, with following assumptions:
- network 230/400V,
- single phase EVSEs distributed evenly on the 3 phases
- diversity factor defined as 1 (no load management system, e.g. EV chargers always at full charging power, and all chargers can be used simultaneaously) - The additional numbers between parenthesis are for the same assumptions, but for a maximum charging current limited to 8A
For all 3 solutions: The 1A and 300mA RCDs shown on the single-line diagrams are type A (and not type B), only because these Schneider Electric type A RCDs can operate properly in presence of the DC leakage current generated by the seven downstream charging stations protected by type B RCDs. See chapter F – RCDs selection in presence of DC earth leakage currents and part 4 of this chapter for more details.
Architecture with various charging time requirements: Example of a car dealership
Charging areas and charging capacity
Car dealers are faced with the following major trends:
- new models and enlarged offer portfolio
- expected volume growth for electric vehicles (both BEV and PHEV)
- EV battery capacities increasing substantially over the coming years
As a result, car dealerships need an adequate charging infrastructure to get the EVs charged.
This charging infrastructure is created taking the assumed needs of the different areas and activities at dealerships where electric vehicles should be charged into consideration.
| Zone | EV charging requirements |
|---|---|
| Demo cars and company cars | The charging recommendation for demo cars and company cars will depend on their use. This application may require relatively rapid EV charging (22kW AC or more) during the day. |
| Delivery area for new cars | New cars are usually partially charged before delivery to retailers. They should be fully charged (at 100%) before delivery to the customer. This type of charging can be done at night, at the 7.4kW power range. |
| Test drives | Electric vehicles for test drives should be charged rapidly in order to maximize their availability. The main charging can be done at night. A top-up charge may be required during the day. The charging should be relatively rapid in such case – for example 22kW AC charging. |
| Courtesy car service | Both BEV and PHEV courtesy cars should be fully charged before delivery. The charging could be done at night at 7.4kW or 22kW. |
| Serviced and repaired customer cars | Serviced and repaired customer cars should be fully charged after maintenance for a premium customer service. Ideally the charging should be done in few hours, usually during the day, with EV charging stations at 22kW. Additional DC EV supply equipment may be required to perform tests with DC charging (e.g. 50kW DC) |
| Customer parking (part of BMW Retail Standards) | Car dealership customers may need to charge their electric vehicle during their visit. This charging will be done during the day. For a premium customer service, the use of 22kW EV charger is recommended. |
| Employee parking | Car dealership employees should have the opportunity to recharge their electric vehicle at their workplace. As employees’ cars will stay in the car park for several hours, the EV chargers could be in the 7.4 kW power range. The charging is done during the day. |
Example of EV charging infrastructure design
The figure hereafter presents an example of an EV charging infrastructure corresponding to the described assumptions.
All EV loads are connected to a new Main Low Voltage Switchboard (MLVS).
- Each EV circuit is protected by a circuit breaker and a 30mA type B residual current device (RCD), as required by IEC 60364-7-722 (check whether an RCD is already integrated into the EV charging station).
- EVSE should be protected against transient overvoltages due to lightning strikes. Surge protection devices may be required on the EVSE depending on the building’s lightning protection, the location of the EVSE (indoor or outdoor), and the distance between the EVSE and the SPD at the LV switchboard.
- EVSE should provide means for automatic disconnection
- Residual current and overcurrent protection can be combined in one device (as in the EVSE 150 kW circuit). It should be checked whether the EVSE has built-in galvanic isolation between the AC and DC side, and the protection equipment selected accordingly.
- As there are several single phase EVSE of 7.4kW, it is recommended these are connected equally among the 3 phases to avoid unbalance
- As there are several EVSE located in the same area (customer parking), it could be worth installing a LV sub panel nearby for these EV loads in order to optimize the quantity and length of cables.
- As there are several EVSE located in the same area (employee parking), a busbar trunking system can be used to provide a flexible, cost effective and future proof solution
- As the existing dealership installation is connected to the new main LV switchboard, overcurrent and residual current protection selectivity need to be considered.
The new EV loads increase the power demand significantly. An additional photovoltaic system and storage can help to partially compensate for the increased power demand.
