IEC 61851 and ISO 15118 Firmware Compliance

Six control-pilot states A-F. A: nothing connected. B: cable connected, EV not ready. C: charging (12V amplitude, PWM). D: charging with ventilation (for some vehicles). E: short to protective earth. F: fault.

Correct state transitions and correct PWM duty cycle per current limit are the two things certification labs verify. Bugs are usually in the PWM math (off by 0.1% duty is a real current mismatch), or in the transitions (State B to C can fail spuriously if the CP driver has ground bounce).

Wrong PWM duty for current signalling. For duty cycles between 10% and 85%, the relationship is duty% = current_A / 0.6 (so 32A maps to ~53% duty). Above 85% duty (up to about 96%), the formula changes to duty% = (current_A + 64) / 2.5 for high-power chargers. Getting the boundary wrong, or applying one formula across the whole range, is a common firmware bug and a common certification finding.

Missing State F on real faults. The CP is supposed to go to State F when the charger detects a safety condition. Firmware that doesn't drive the CP low on RCD trip, over-temperature or comms loss fails compliance.

PP resistor readings ignored. The proximity pilot signals cable current rating. Firmware that draws more than the PP allows is a hazard and fails compliance.

Even AC chargers can support 15118 for Plug and Charge. The hardware needs a PLC modem for the EV-to-charger comms; the firmware needs the 15118-2 or 15118-20 message stack.

For firmware-only readiness (hardware not yet PLC-capable), the state machine and API surface can be designed to slot in the 15118 stack later. This lets you ship a charger that upgrades to PnC via firmware when the hardware roadmap supports it.

Book the lab session in advance and pre-check with a portable EV simulator. Send the firmware version and expected test outcomes ahead. Have an engineer on-site or on-call during the tests so findings can be fixed and re-tested the same day.

Certification takes days when everything works. It takes weeks when firmware bugs surface at the accredited lab and require a round trip. Pre-compliance testing before the formal slot is the difference.

• CP state transitions A through F verified with an EV simulator
• PP resistor reading and current derating validated across cable ratings
• RCD response timing tested against IEC 62955 limits
• Connector lock actuation verified under fault and normal cases
• PWM duty cycle accuracy measured across the full current range
• Fault state entry verified for over-current, over-voltage and thermal events
• Emergency stop path tested from every triggering source

• PLC modem on the CP line, or hardware roadmap that adds it
• V2G TLS with certificate handling on the charger side
• Contract certificate flow from CMS through charger to EV
• Backend Plug and Charge support with a trusted PKI root
• Firmware architecture that leaves 15118-2 and 15118-20 upgradable in place