Plugged In: Explaining Electric & Hybrid Vehicle Tech | October 2020
EV Charging Standards and infrastructure
All Electric and Plug-in Hybrid Vehicles require a source of AC (Alternating Current) or DC (Direct Current) power to recharge their batteries.
The power is usually supplied from the power grid, and in Australia residential charging is usually sourced from a 230V/240V single-phase 10-amp socket. Although there are variants such as 15A outlets and other specialised industrial applications, most vehicles will be connected to a 10amp socket in the home environment. In this case the power available to charge the vehicle is limited to 240V x 10A = 2400 Watts.
Electric vehicles are usually supplied with a charger that has a wall socket on one end and a vehicle plug on the other end. In addition, the vehicle will most likely be supplied with another charging lead to allow connection to a fast charger.
Ok, so nothing you didn’t already know here. But maybe we should take a deeper dive into charging connections and how they work?
High Power Charging
A hardwired single-phase charger can provide much higher levels of power than connecting to a standard 10A domestic socket. The exact amount of power available will depend upon the individual premises and grid connection. However, increases in power availability up to around 7.2kW can be achieved with a single-phase connection.
To supply the higher levels of power required for even faster charging, a three-phase connection is required. It’s worth noting at this point that a three-phase connection could be wasted when charging some PHEV’s (plug-in hybrids) and EVs since they are not capable of taking a higher rate of charge, so a hardwired single-phase charger may be sufficient.
Three-phase is commonly used in industrial applications and can provide higher levels of power due to the fact that there are three active phases 120° apart at a frequency of 50Hz supplied at around 400/415V. Three-phase chargers are not commonly used in residential applications.
DC fast charging
Due to the complexity of the equipment and the amount of power needed, DC fast chargers are rarely found in residential premises. Most EVs have an on-board charger that rectifies AC from the mains grid and then provides DC to charge the batteries. Cost and thermal constraints will limit how much power the on-board rectifier can handle. For charge rates exceeding around 240V/30A, it is better to have an external charge station provide a vehicle with DC.
Power limitation when charging from a DC fast charger is more likely to be constrained by what the vehicle can accept rather than the supply side.
There are a number of options available to manufacturers when designing a vehicle. Some cater for single-phase, three-phase and/or DC fast charging. The type of connector used will depend on the EV manufacturer, country of origin etc. I will describe the operation of the Type 1 or SAE J1772 connection in some detail. Other connectors will employ similar protocols to satisfy safety and operation requirements.
Type 1. Alternate names:
J1772 or SAE J1772 FIGURE 1
The Type 1 plug is a five-pin design used by Mitsubishi and some pre-2018 EV’s. It is the plug standard in North America and Japan.
Two pins are used to communicate between the vehicle and the charging station to determine the maximum current to the vehicle and to prevent the vehicle from moving while connected to the charger.
The three remaining pins are used as AC lines for charging and a line to ground.
The J1772 standard includes several levels of shock protection which is essential since vehicles will be recharged in a range of conditions including wet weather. When not connected, there is no power at the pins. Power is not present at the pins until commanded by the vehicle.
Figure 1 shows the charging connection of a Mitsubishi Outlander with J1772 and CHAdeMO connectors.
- The charger signals the presence of AC power.
- The vehicle detects the plug by a proximity circuit which prevents the vehicle being driven away while connected.
- Detects when the latch is pressed in anticipation of plug removal to prevent arcing.
- The charger detects the vehicle.
- The charger indicates when ready to supply charge.
- Electric vehicle ventilation requirements (a code requirement for charging infrastructure/battery types).
- Charging equipment current capacity provided to EV.
- The EV commands the power/current flow.
- EV and supply equipment both monitor continuity of safety ground.
- Charge continues and charge rate determined by the Electric vehicle.
- Charge can be interrupted by removing the plug.
Control Pilot Operation
Control Pilot Mode
The charging station generates a 12V 1KHz square wave which is fed to the vehicle. A resistor and diode in series connects to the protected earth on the vehicle. When a charging cable is connected to the vehicle, a voltage drop occurs due to a voltage divider set up between the charging station and the vehicle. The 12V 1KHz square wave drops to a 9V square wave. Charging is activated by adding a parallel 1.3KΩ resistor which drops the voltage further to 6V. FIGURE 2 Control Pilot (Current Limit).
The charging station can use the square wave to indicate the maximum current that is available from the charging station by using PWM (pulse width modulation). A 16% PWM is a 10 Amp maximum, 25% is 16 Amp maximum, and so on.
PWM duty cycle indicating charge current capacity.
The following schematic shows a typical charger to EV connection J1772. FIGURE 3.
The proximity pin also uses a voltage division loop set up between the charging station and the vehicle. In the charger to EV schematic below it can be seen that the loop consists of a switch, 150Ω and 330Ω resistances on the charging station side and 5v supply, 330Ω and 2.7kΩ on the vehicle side.
When opening the release actuator, a 330Ω resistance is added which gives a voltage shift on the line to allow the EV to initiate a controlled shut-off prior to disconnection of the charge power pins.
IEC 62196 mandates the Proximity pin is also used to indicate the cable capacity.
Type 2. Alternate names: IEC 62196, Mennekes (A manufacturer of industrial electrical products).
- This plug standard is currently used by other EV manufacturers and is now the standard for Australian EVs. This standard also uses proximity pilot and control pilot.
The Type 2 plug is a seven-pin design. The extra two pins mean 3-phase charging can be supported. The Type 2 plug is the standard for Europe.
CHAdeMO. An abbreviation for “Charge de move”, French for “move using charge”.
The CHAdeMO Association was formed by the Tokyo Electric Power Company, Nissan, Mitsubishi and Subaru. Toyota later joined, followed by Hitachi, Honda and Panasonic. CHAdeMO research and development started in 2005. The aim is to develop a public infrastructure of EV fast charge chargers which will enable people to drive EVs without the worry of battery range.
CCS Combo. Short for combined charging system.
CCS has two variants using Type 1 and Type 2 AC plugs. This standard is used by Volkswagen, BMW, Ford and Hyundai.
Tesla Superchargers use the same design as Type 2 AC plugs. They can deliver much more power by using two of the pins for DC current. Although the plug design is shared, Tesla Superchargers will only charge Tesla vehicles.
Despite different physical differences, all charge connector standards share the same following basic features:
- large gauge power delivery wire, a protective earth connection, some sort of bi-directional signalling system, and a latch to secure the connector in the charging port.
- • Both the SAE and IEC standard connectors use a pair of wires known as Charge Pilot and Proximity Pilot for communication and signalling.
- CHAdeMO standard uses a more complex set of signals as well as a CAN bus for communication between the supply equipment and the vehicle.
- Communication between the power source and the vehicles on-board charger / battery management system is essential to ensure safety and longevity of the battery. The vehicle must detect when the plug is fully inserted to ensure a safe connection between both sides and safe to touch.
- The vehicle must detect when the latch is pressed on the connector so that the vehicle stops charging prior to unplugging which prevents arcing.
- The vehicle must communicate what voltages and currents it can accept and whether ventilation is required to prevent overheating.
- The supply equipment must continually monitor for ground faults and the vehicles chassis must remain isolated from the battery and charging station.
- The vehicles on-board power unit will handle all AC rectification, DC-DC conversion (voltage levels) as needed. e.g. charging a 600V system from 400V.
- It will work with the BMS (Battery Management System) to rectify and boost supply voltage, provide constant current or constant voltage charging and stop charging should any critical fault be detected.
Just about all modern EV’s offer scheduling via the infotainment system to allow charging to take place at specific times which allows a driver to take advantage of
off-peak electricity rates.
As mentioned earlier Tesla uses proprietary protocols which prevents others from using their public chargers although this could change sometime in the future as it would be relatively easy for Tesla to make an adapter allowing other protocols to connect.
Charging is fastest between 20 per cent and 80 per cent. Ideally you would proceed along a route, charge when you reach 20 per cent and be on your way once you have achieved 80 per cent.
As supporting infrastructure in Australia improves, it will be easier to achieve such a scenario as most EVs have the capability in their infotainment system to provide charging station locations, battery range etc.
To maximise efficiency, it will be important to keep vehicle databases up to date so that all charging locations are included. In some countries, demand for EV chargers has outpaced infrastructure growth and a penalty fee is applied if an EV is left plugged in after charging. This encourages drivers to move their vehicle so that another vehicle can be connected to the station.
In conclusion, while there are numerous charge connector types, similar safety considerations and vehicle compatibility protocols must be met to achieve satisfactory EV charging outcomes. The challenge for EV infrastructure design and support, is to ensure that we have adequate numbers of charging stations in a range of locations to support the foreseen growth of the EV market.
Until next time work safe and take care.
8 October 2020