Category: Charge Controller Plug&Charge

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

The Communication Pilot is a wire connection between EV and EV Charger. It is primarily a saftey measure for the charging process. Without the Communciation Pilot no EV will start charging.

The Communication Pilot is a 1 kHz signal with a ± 12 Volt DC square wave generated by the EV Charger. This is a PWM signal. More details on PWN and the associated state model can be found here.

Initially the Communication Pilot served as a simple safety feature communicating the maximum current an EV was allowed to draw and disconnecting mains power when EV is not charging.

In later years, it was realised that the simple analog PWN signal was to restricted. While it can do some forms of smart charging from the perspective of the supply, it cannot do things like EV authentication, vehicle to grid charging and smart charging while taking into account EV’s State of Charge. Therefore an extra protocol is added to the Communication Pilot. For backward compatibility, this protocol is superpositioned on the PWM signal. Effectively it is a 20Mhz signal on top of the 1 Khz squarewave. For EVs or EV Chargers that don’t support this protocol, it is invisible. When both the EV and the EV Charger are enabled for this protocol, then it can make use of the advanced features it offers.

While the base signal, the 1 kHz square wave is described in the IEC 61851, the 20Mhz on top of this signal is described in the ISO 15118.

Let’s have a look at the primary functions of the PWM signal. The functions are:

Proximity Pilot (PP) serves as a charge cable detection and current limitation. The Proximity Pilot is implemented differently in Type 1 and Type 2 plugs. For Type 1 plugs only, the Proximity Pilot also takes care of mechanical locking and sparkleless disconnections.

Charge Cable Detection

It is important for the EV to ‘know’ that the EV is connected to an EV Charger. While with fuel cars it occasionally happens that people drive away with the hose still inserted, with electric charging the likeliness of this happening is much bigger as one will not be waiting next to the car for the charging to finish. The Proximity Pilot in the plug serves this purpose by creating a circuit via a resistor to the PE pin.

The value of the resistor differs in the Type 1 and the Type 2 plug. In the Type 1 plug it is 150 Ohm. In the Type 2 plug it can have different values. The most common two are 680 Ohm and 220 Ohm although the standard does define 1500 Ohm and 100 Ohm too.

Current Limitation (Type 2 only)

The function of current limiting applies only to Type 2 plugs. The reason is that Type 2 plugs are both on vehicle side as on charger side. This is a main difference from the Type 1 plug which only has a vehicle side plug. In North America and Japan, who don’t use type 2, the cable is always tethered to the charger making it integral part of the Electric Vehicle Supply Equipment (EVSE). This implies that the current capacity of the cable is compatible with the charger. For a cable that is not part of the EVSE, the cable can have conductor thickness which is not enough to carry the maximum current the EV can draw and thus overheating the cable resulting in dangerous situations.

The resistor value in the type 2 plug indicates the conductor size of the cable. The conductor size determines the maximum current the cable can handle. The following values apply:

Resistor	Conductor size	Maximum Current
100 Ohm	10 mm2	63 Ampère*
220 Ohm	6 mm2	32 Ampère
680 Ohm	2.5 mm2	20 Ampère**
1500 Ohm	1.5 mm2	10 Ampère

* In a 1 phase system it maximum current may be even 70 ampère.

** In many European countries, the local regulations demand a maximum of 16 Ampère for fixed wiring of 2.5 mm2. Also regular over current protection is maximised at 16 Ampère. Therefor 16 Ampère is most often used for home chargers.

Sparkeless Disconnect (Type 1 only)

As the type 1 has a fixed 150 ohm resistor, no current limitation can be indicated. For charger points with a socket, the Type 2 plug connected at the charge point will indicate the current capacity to the charge point. For tethered cables, it is assumed the current limitation is set in accordance with the power supply and the cable capacity, which ever has the lowest value. See also PWM Signal for how this is enforced.

The Type 1 plug has a button with a mechanical lever which hooks into the socket of the car. The position of the lever is monitored with a (micro)switch. The plug can only be disconnected from the car if the button is pressed and thus activating the switch. This will cause the proximity pilot resistor to change from 150 Ohm to 500 ohm. With this, the EV will detect the attempt to disconnect the charge cable and will stop the charging process immediately. As the contacts will not carry current anymore, there are no sparks. It is safe and the contacts will last longer. How this is achieved in a type 2 plug can be read here.