I'm building an AC-charging device for electric vehicles (the standard calls it an "ICCPD" or an "In Cable Control and Protective Device") and I'm facing some EMC issues due to the PWM Signal on the CP-wire.
The CP wire is used for the communication between the vehicle and the ICCPD. Basically it carries a PWM signal and the duty cycle indicates the maximum charging current. The frequency, amplitude and rise-time is defined in the standard.
- positive amplitude = 6/9/12V (relative to PE)
- negative amplitude = -12V (relative to PE)
- rise/fall time = <2us
The following figure shows the conduced emissions with PWM signal ON (turquoise) and without PWM signal...const +12V (blue) measured on the neutral line. Cable length was 9m. Measured with Rohde&Schwarz Precompliance test equipment (HMS-X and HM6050-2).
Is there any way to reduce the conducted emissions due to the CP-Signal?
Reducing the cable length and/or shielding the CP-wire is not possible.
conduced emissions according to Andy's suggestion/ thought experiment:
- Turquoise line: PWM Signal on CP wire inside the cable
- Blue Line: PWM signal connected to a separated wire (no PWM signal on CP wire in the cable)