As there are relatively few electric vehicle chargers in use today, the issues and application of this equipment has yet to be seen. In this article, GE Energy identifies and discusses the standards to which electric vehicle charging stations are designed and built, and describes the common features now available.

With the sporty Tesla Roadster and Mitsubishi i-MiEV currently available, and the Nissan Leaf set to be launched in 2012, the proliferation of plug-in electric vehicles (PEVs) has started. Given their desirable features of lower operational cost and lower CO2 emissions, PEVs are likely to be embraced by the driving public and will eventually represent a growing portion of the total light vehicle fleet.

Since PEVs are designed to be recharged by connection to the power grid, some accommodation for them may be desired, if not needed in industrial and commercial power systems. This article will discuss charging stations and their application with respect to the current draft standards in Australia.

While certain aspects of electric vehicle (EV) charging stations are controlled by international industry standards, electric vehicle supply equipment (EVSE) may differ from one model or manufacturer to another. Understanding the various aspects of these charging stations will help the designer to select the best choice for a given application.

There are three levels of EV charging stations defined by the draft Australian EVSE Standard:

• Level 1: Trickle charge is the simplest and slowest method of charging an electric vehicle, typically using a 240V AC single phase supply with around 10A of current being drawn. The vehicle usually is charged via a GPO. Recharging time averages around eight hours to fill a completely discharged battery.

• Level 2: Standard charging is capable of providing 240V/415V AC 1/3 phase and usually 32A of continuous current. Level 2 chargers are typically hard-wired into a power system for dedicated charging. These chargers usually have pilot protection incorporated into the design for addition safety. This level of charging has the capacity to provide an electric vehicle a full charge in as little as 1 hour depending on the EV’s onboard inverter specifications.

• Level 3: Fast charging involves a high DC voltage of approximately 400V DC, with a maximum rated continuous current of 600A. This level of charging is designed to recharge a car battery in ten to fifteen minutes.

The first thing that must be understood about EV charging stations, particularly those defined for applications under IEC 61851 Level 2 charging, is that this equipment is not a charger that makes a direct connection with the vehicle battery but instead is a connection interface between the vehicle on-board battery charger and a fixed power distribution system. In essence, EVSE is a smart connector that not only connects the vehicle to the grid, but it provides user features to facilitate and limit its operational characteristics and includes mandatory control and protection features required by the IEC and current draft Australian standards.

An EV charging station will typically include following components:

• Overcurrent and leakage protective devices for use on overloads, short circuits and earth faults.

• A contactor is used to send power to the connector, and keep the connector’s terminals de-energised when not plugged in.
• A controller interfaces with the vehicle’s on-board charging system and provides residual current protection. The controller may also have some power metering capabilities.
• Displays and indicators on the exterior provide status and alarm information, guides the user through the operational sequence.
• Conductive socket(s) that allow a cable connection.
• A mechanical interlock for protecting a customer’s cable when connected to the charger.

The mandatory performance and characteristics of the charging stations and their components are regulated by several codes and standards. Foremost among these is IEC 61851-1 as it provides the general requirements of EV conductive charging systems.

Additional relevant Standards that apply include:

• IEC 62196-2 Plugs, outlets, vehicle couplers and vehicle inlets.
• IEC 60364-4-41 Address the requirements for protection against electrical shock.
• EN 61439 Low-voltage switchgear and control gear assemblies.
• EN 60068 Environmental testing.
• IEC 61851.1 Electric Vehicle (EV) conductive charging System – General requirements.
• IEC 61851.21 Electric Vehicle (EV) conductive Charging System – Electric vehicle requirements for conductive connection to an AC/DC supply.
• IEC 61851.22 Electric Vehicle (EV) conductive Charging System – AC Electric vehicle charging station.
• IEC 55022/AS/NZS 60950 Information technology equipment – Radio disturbance characteristics – limits and methods for measurement.
• EN 61000-3-2 Electromagnetic compatibility (EMC).
• IEC 61008-1 Ed. 2.1/AS/NZS 61008/AS/NZS 3190 Residual current operated circuit breakers without integral overcurrent protection for household and similar uses (RCCBs).
• AS/NZS 60335.2.29 Battery chargers.

Note that AS/NZS 3000 and AS/NZS 3100 are also considered.

Typical charging

A typical operational sequence would commence once the user inserts one end of their IEC 62196-2 plug into the charging station and then the other end into his/her vehicle. Please note that the current electric vehicles in Australia use a SAE J1772 interface connection. A typical cable configuration would therefore have an IEC 62196-2 (1/3 phase) connector on one end and a SAJ 1772 (single phase) connector on the other.

While charging is in process, the safety ground between the charging station and the EV is continuously monitored. The charging process can be interrupted simply by removing the plug from the EV.

RCBOs

In Australia, AS/NZS 61008 lists requirements for residual current operated circuit breakers without integral overcurrent protection.

The basic operation of an RCBO is that it cuts off the supply once the residual current generated reaches a set level.

These devices typically have:

• Residual current detection of 30mA.
• Combined overcurrent and short circuit protection.
• Double insulation.
• Reinforced insulation.

In general, one of the more common combinations permitted will be basic insulation between circuit parts and accessible parts along with a RCD device with a trip setting not greater than 30mA.

Electrical considerations

EV charging stations in compliance with IEC 61851 and in reference to the draft Australian Standards are designed to be connected to either 240V AC single phase or 415V AC 3-phase supplies. The most commonly available models have a maximum continuous current rating of 32A. For charging stations the ultimate overload protection is set between 1.13 and 1.45 times the nominal rated current of the EV charging stations.

A typical installation example would be a 32A-rated EV charging station being fed from a dedicated 40A breaker/RCD and conductor upstream. An EV charging station can contribute a significant sized load that can be applied in areas that previously had only a light electrical load. A parking area may require some minimal power for lighting purposes and the power density of these loads averaged over the surface area of the parking spaces is very little.

The load of an EV charging station at 32A at 415V AC represents a 23kVA load. Locating a concentrated number of these among parking spaces will result in large power densities across small areas. Such power densities are more similar to those of data centers, and previously unheard of in parking areas.

The power demands required to serve a concentrated area of several EV charging stations may surprise those designers who attempt it for the first time.

Site considerations

The location of EV charging stations can involve several considerations. Primarily the location of the charger can be critical in certain parking spaces, the consideration of the required cable length and specifications are outlined in the IEC 60245-66 Standards. It should be recognised that there will need to be new codes implement when it comes to charging stations and parking. Also drivers who are disabled, and have EV will also need to be considered when additional parking spaces are being installed. Additional access space to allow the use of a wheel chair around the vehicle is typically required. Operation of the EV charging station from a wheelchair attitude should be considered. Further cables connecting the EVSE to the vehicle should not obstruct pathways subject to heavy foot traffic.

Future capabilities

The battery within the vehicle represents a potential power source that is an exciting topic of discussion among utility engineers and EVSE manufacturers.

This energy source could be very valuable if it could be tapped into during times when power failures are imminent. Smart grid capabilities in conjunction with 2-way inverters in EVs may eventually allow utilities to use the batteries of connected PEVs as temporary power sources. This would be done with some intelligence built into the system. That is, the PEV would have a sufficient charge level on the battery for the vehicle to reach its next destination at the expected time that the vehicle driver normally requires it.

Conclusion

The benefits of PEVs and the need to support drivers of PEVs will stimulate the installation and use of EV charging stations in industrial and commercial power systems. EV charging stations are well defined by several standards for operational characteristics and personal protection safeguards. Still there may be a variety of features and options available depending on the manufacturer or model. EV charging stations constitute a significant load. In serving a concentrated number of EV charging stations, the distribution system serving these loads will need to have a much higher capacity than previously used in vehicle parking applications.