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:
a) indicating that EV and EV Charger are connected;
b) Signal the maximum current the EV is allowed to draw;
c) Signal that the EV wants to receive power and;
d) (When both EV and EV charger are capable) Indicate that ISO15118 protocol should be used;