How does EVSE work? What are control pilot and proximity contact signals?
The function of control pilot (CP) is explained in Annex A of the IEC standard 61851-1:2017.
The control pilot signal enables basic communication between the EVSE (charger) and EV (electrical vehicle):
- The charger sends the information about its maximum charging current in the form of a 1 kHz ±12 V pulse-width modulated (PWM) signal to the electric vehicle. The electric vehicle then reads this signal and determines the maximum charging current it is permitted to draw.
- In order to ensure that the charging is done in a safe and controlled manner signalling in the opposite direction is required as well. The standard IEC 61851-1 defines a set of EVSE states shown in the table below. The electric vehicle signals its presents (state B), the request for charging (state C) or request for ventilated charging (state D) by applying a relevant resistor between the control pilot (CP) and protective earth (PE). The charger will enter state B, C or D upon detecting the required voltage across CP-PE (see the table below):
- +9V means that an electric vehicle is connected.
- when charger detects +6V it enters into charging mode.
- when the charger detects +3V it enters into charging mode if it can provide ventilation in the charging area. Not all chargers have this feature.
Besides states B, C and D, several other states are defined:
- A – electric vehicle not connected to charger
- E – error condition
- F – fault condition
The proximity function (PP) is explained in Annex B of standard IEC 61851-1:2017.
Depending on the type of connector, there are two different functions of the proximity contact:
- Type 1 connectors have an auxiliary switch (the top part of the connector in Figure 1). The charger detects when the electric vehicle is connected and additionally, whether the switch has been latched or not. The EVSE connector is safely attached to EV only if the auxiliary switch is in latched position.
- In case of Type 2 connectors there is no auxiliary switch. The proximity signal is used for simultaneous proximity detection and current capability coding of the cable assembly. The value of the resistor connected between the proximity contact (PP) and the earthing contact (PE) determines the maximum current capability of the cable assembly (e.g. 13A, 20A, 32A, 63A or 70A). When the charger detects a certain value of the resistance it should adjust its maximum current according to the maximum current signalled by the cable resistor. This maximum current value will be then communicated to electric vehicle via the control pilot (CP) communication protocol described above.