What is energy metering?
EV chargers deliver electric energy to EVs to charge their battery. The BMS (Battery Management System) of an EV acts as the master while the EVSE (charger) is the slave in the communication about the actual voltage and current levels, at which the battery is charged. In order to determine the delivered electric energy, the charger measures the electric current and voltage during the whole charge session in many small time periods, multiplies these 3 units, and adds up the energy values up to the accumulated delivered energy. The charger uses a particular measurement device and related sensors to accurately measure the required electric parameters internally.
What is MID?
MID stands for the European Measurement Instruments Directive 2014/32/EU, which specifies in a generic way the accuracy classes of all kind of measurement instruments, amongst which AC electricity meters. Note that the MID does not yet specify DC meters. When talking today about 'DC MID compliant' meters, we mean DC meters, which comply to a similar set of requirements as defined fin MID or AC meters, although DC meters have some characteristics, which are non-existing for AC chargers.
For electrical energy metering of EV chargers, the German association for electronics and information technology 'VDE' is defining the guideline (Anwendungsregel) VDEAR-E 2418-3-100 to specify in more detail the requirements for energy meters in EV chargers (measurement ranges of current, voltage, temperature, mechanical specifications, etc.). VDE aims to synchronize these guidelines with the international norms IEC 62053-21 for AC and -41 for DC meters, of which the latter is also still in definition phase.
What is PTB? (PTB = Eichrecht)
PTB stands for Physikalische Technische Bundesanstalt, the highest German calibration authority. They define all measurement instrument requirements as well calibration requirements for all commercially used meters. They also certify third parties to install, seal and (re)calibrate instruments in the field. For the certification of chargers with integrated electricity meters, PTB accredited VDE and CSA to do this work (in Germany).
Note that in Germany eventually the states calibration authorities (Landeseichbehörden) have the final judgement whether an EV charger is allowed to be used as a ‘measurement equipment’ in their State.
What is Eichrecht? (in Germany)
Eichrecht stands for the German calibration law. More precisely, the combination of the Calibration Law (MessEichGesetz), the Calibration Guidelines (MessEichVerordnung) and the Guideline of presenting the (end customer) price on the dispenser(Preisangabenverordnung). Together, they require accurate energy measurement according to MID, visibility for the customer of the delivered energy during the charge session, payment per amount of energy (kWh). And optionally the visibility for the customer of the actual time in case the energy delivery tariff changes at certain times of the day.
Note that the German authorities mandate that all chargers, including chargers already operational in the field, must become PTB compliant. Therefore, ABB EVI designed field-upgrade kits, and a field-calibration procedure involving a mobile validation system. (This system can also be used for other brand chargers).
Difference between MID and Eichrecht (also called PTB)
Note that so-called 'PTB compliant' chargers actually comply with the German calibration law (Eichrecht).
Eichrecht = compliance with MID + “customer protection”: the customer must be able to check charge session data hours/days/months after the actual session, preferably on smartphone or computer, and verify that they the data is not altered (by tampered meter, and/or hacked data). To assure this, the charger collects all charge session data (incl. charge session ID, charger ID, authentication ID, meter ID, start and stop time and kWh meter reading, etc.), signs it with a key, and sends it to the CPO’s (Charge Point Operator) backend via OCPP (Open Charge Point Protocol): this ia an obligation for ABB chargers. The customer will be able to access these data via an app or web portal from the EMSP (e-Mobility Service Provider) or CPO. Using the so-called Transparenz-Software (Transparency Software), the customer can verify that the data are not altered; this is an obligation for the EMSP/CPO. Note that ABB EVI will verify the end-to-end functionality, from charger to end-customer, with a few German CPOs/backoffices before completing the Eichrecht certification.
If you are interested in EV Charging energy metering or need MID RS485 Modbus Energy Meter, please feel free to contact us.
