DC active electrical energy meters: Accuracy tests

With the increasing spread of electric vehicles, the measurement of DC active electrical energy becomes relevant for billing purposes again. Given the large numbers of DC charging stations, efficiency is key. Calibration and testing must be highly automatised and multiple meters must be tested at the same time, as it is common practice for AC electrical energy meters. However, neither isolated current transformers nor multi secondary voltage transformers exist for DC. This paper proposes an alternative method for simultaneous testing of closed-link electrical energy meters that is suitable for DC.Often, DC active electrical energy meters differ considerably from AC electrical energy meters. For instance, the resolution of the pulse output may be the same as the resolution of the register on the display. Therefore, this article analyses the implications of using the pulse output or the register. Examples of uncertainty budgets for the two most common measurement methods, the pulse comparison method and the energy comparison method, are discussed.