- Publication date
- 1 January 2015
- Joint Research Centre
Fast charging is seen by users as a preferential way for electric vehicles (EV) to extend average daily mobility. Fast chargers rated power, their expected operation mostly during peak hours and clustering in designated stations, raise significant concerns. On one hand it raises concerns about power quality standard requirements, especially harmonic distortion due to the use of power electronics connecting to high loads typically ranging from 18-24 kWh, and on the other hand infrastructure dimensioning and design for those investing on such facilities.
We performed four sets of measurements during an EV complete fast charging cycles and analysed individual harmonic’s amplitude and phase angles behaviour and calculated the voltage and current total harmonic distortion (THD) and Total Demand Distortion (TDD) comparing it with IEEE519, IEC 61000/EN50160 standards. Additionally, we simulated, two vehicles being fast charged while connected to the same feeder, and analysed how the harmonic phase angles would relate.
We concluded that the use of TDD was a better indicator than THD since the first one uses the maximum current (IL) and the latter uses the fundamental current, sometimes misleading conclusions, hence suggested to be included in IEC/EN standard updates. Voltage THD and TDD for the analysed charger, were within the standards limitations 1.2% and 12% respectively, however individual harmonics (11th and 13th ) failed to comply with the 5.5% limit in IEEE 519 (5% and 3% respectively in IEC61000). Phase angles tended to have preferential range differences from the fundamental.
We found that the average difference between the same harmonic order phase angles, are lower than 90°, meaning that when more than one vehicle is connected to the same feeder the amplitudes will tend to add. Since the limits are dependable on the upstream short circuit current (ISC), if the number of vehicles increase (i.e. IL), the standard limits will decrease and eventually are broken. The harmonic limitation is hence a first binding condition, well before the power limitation is. The number of chargers will be limited first not by the power capacity of the upstream power circuit but by the harmonic limits for electric pollution