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Standards

There are various international standard that are applicable to EV Charging. We’ll sumarize them here.

SAE J1772

This is probably the oldest standard and some of the others are derived from it. This standard describes the PWM signal communication between EV and EV Charger. It also describes the EV side of the protocol as well as the proximity protocol as available in the Type 1 plug.

SAE stands for Society of Automotive Engineers. The organisation behind it is SAE International and is US based.

Noteworthy to mention is that there are no sockets defined for the EV Charger. The cable cannot be disconnected from the EVSE and thus forms an integral part of the EVSE.

You can read more here: https://en.wikipedia.org/wiki/IEC_62196

IEC 61851

The IEC 61851 has adopted many, if not all, specifications from the SAE 1772. For instance the PWM signal defined in this standard is fully compatible with it.

The IEC, International Electrotechnical Commission is based in Zwitseland and its standards are more focussed on the electric domain that the automotive domain. Needless to say that EVs are connected to the grid, making it an electric appliance.

IEC 62196

The IEC 62196 is a standard which defines the physical dimensions of sockets and the plugs for EVs and EV Chargers. The IEC 62196-2 refers to AC charging and the specific plug and sockets used for that.

The IEC 62196-3 refers to DC charging plugs and sockets.

For AC and DC plugs, it defines various shapes and standards which differ in shape, number of (electrical) connections, locking, and protocol. Most often those standard can be related to various countries or regions. For instance, a Type 1 plug, which is typically used in North America and Japan, doesn’t have support for three phases: The North American Network has 1 or 2 phases only.

The AC plugs Type 1 and Type 2 are physically not compatible but on the communciation level (IEC61851/SAE J1772) they are. This means that a charge cable can have a Type 2 plug on EV Charger side and a Type 1 plug on EV side.

Noteworthy to mention is that to prevent cables to be used as extension cord, the Type 2 female (on EV side) will not fit a Type 2 male (on Charger side).

Read further here: https://en.wikipedia.org/wiki/IEC_62196

ISO 15118

The ISO 15118 is a standard to add more possibilities for communication between EV and EV Charger. With this standard, EV’s can let the charger know their State of Charge of the battery. Also an unique owner or EV ID can be send to the EV Charger which can be used for authentication and thus billing. This makes it unnecessary to start a charging session with an RFID card or an app on your phone.

The ISO 15118 is a protocol on top of the PWN Signal. It will always be used in conjunction with IEC 61851 (or SA J1772). Both EV and EV Charger must have implemented ISO 15118 to start the more advanced communication and make use of the advanced features.

You can read more here: https://en.wikipedia.org/wiki/ISO_15118

Charge Controller

The Charge Controller is the interface module between EV and the mains power supply. It tells the EV what the maximum current is that the EV is allowed to draw. As the available current might fluctuate, the signal indicating this current can vary. It is a PWM sigal where the duty cycle encodes the current. Influence that can cause the current to vary are:

Load balancing – Other EV Chargers requesting power;

Smart Charging – other applicances consuming power or solar pannels providing power.

The Charge Controller also is responsble for disconnecting the EV from the mains when the EV is not requesting power. It does that by activating and deactivting the contactor.

Plug & Charge

Plug & Charge Charge controllers offer a very simple way of charging; there is no authentication. As soon as the user connects the EV to the EV Charger, the charging process will start. This is very conveniant for charging at private property. It might be less suitable for public charging as authentication is required for billing.

EV Chargers with sockets will still lock the plug in the EV Charger and secure the cable against theft. The way to unlock the plug is by disconnecting it from the EV. As by that, the pilot signal is lost, the Charge controller will release the lock.

While Plug & Charge don’t require authentication, an electronic key lock can be fitted to prevent unautorised users from connecting.

PWM Signal

The EV charger communicates with the EV via one wire (and the earth connection of the supply is the return path). This communciation wire, called Communication Pilot, carries a signal which is either constant +12 Volt or a PWM signal. PWM stands for Pulse Width Modulation and is a square wave signal. The signal alternates between +12 Volt and -12 Volt with a frequency of 1 kHz. Via this communication signal the charger can detect the presence of the EV and the charger can mandate the maximum charge current an EV is allowed to consume. The EV can signal to the charger that it wants to receive power.

States

The EV Charger that sends the PWM signal to the EV can be in one of 3 states: No EV, EV Connected and EV Requesting power. These are respectivily state A, state B and state C (or D). There is also an error state called State E. This state is entered if the connected EV doesn’t provide the correct response.

State A

State A is the state where the Charger doesn’t detect the presence of the EV. The communication signal is 12 Volt (or 12 Volt PWM). As the EV is not connected, there is no current flowing through the communication wire and no votage drop detected by the charger.

State B

The transition to state B is achieved as soon as the charge cable connects the charger with the EV. The EV connects the communication pin to the earth pin via a resitor and a diode. The value of the resistor is 2740 Ohm and will cause a voltage drop to 9 volt. The diode will only allow the positive part of the PWM signal to pass. This is to make sure it really is an EV that is connected and not a child’s finger. Figure shows the circuit in the EV.

State C

At some point in time the EV wants to start the charging process. This can be directly after detecting state B, when the user locks the car or other configurations in the EV. Now the EV initiates State C. It does do that by decreasing the resistor value to 880 Ohm. The positive voltage of the PWM signal drops to 6 volts. The charger now will activate the supply by switching the contactors or relays in the charger. This makes the power available. When the EV has charged its batteries, it can transition back to State B. The charger will deactivate it’s contactors and the EV is disconnected from the mains supply. Thus, only in state C the cable and EV are powered.

Mode 3 and Mode 3 simplified charging

The state changes from A to B (by the user connecting the cable) and B to C (by the EV requesting power) are called the Mode 3 charging. However there is also Mode 3 simplified charging. This is if the EV transitions directly to state C. The circuit for that looks like this:

The EV skips state B and, by that, state B is not detected by the chargers. The Voltage on the communication wire drops from 12 Volt to 6 volt. While Mode 3 simplified is official described in the standard, not all chargers support it. Mode 3 simplified is often used by Light Electric Vehicles and adapters as it is more simple to implement.

Maximum current

The PWM signal must indicate the maximum power the EVSE is able to supply. This makes it possible for any EV to charge at any charge point (EVSE) without overloading the mains supply. The maximum current is coded in the duty cycle of the PWM signal. As we have seen, the communication signal alternates from +12 Volt to -12 Volt with a 1 Khz. This means it completes 1 cycle (of +12 Volt and – 12 Volt) in 1 millisecond (ms). However, the PWM signal can vary how long it will stay positive (+12 Volt) and negative (-12 Volt). The sum is always 1 ms. For example, if the PWM signal is 50/100 ms positive and 50/100 ms negative, the PWM ducty cycle is 50%. If the postive signal is only 17/100 ms, the negative signal will last 83/100 ms. Now the duty cycle is 17%. The charge current may vary between 6 ampère and 80 ampère and