Data analysis and estimation of the conversion efficiency of bidirectional EV chargers using home energy management systems data

This study elucidates the authentic utilization of Vehicle-to-Home (V2H) system, a bi-directional DC charger for residential use and appraises power conversion losses incurred during V2H charging and discharging, utilizing data from commercial Home Energy Management Systems (HEMS). This approach offers the advantage of ascertaining operational efficiency within practical scenarios at a reduced cost relative to empirical data acquisition. The empirical examination of results revealed that V2H households exhibited more frequent connections to the charger and engaged in more substantial charging activities compared to Charging-only households. When estimating the power conversion efficiency in the context of V2H charging and discharging, a partial load efficiency curve was constructed for the input power of the V2H charger, thereby confirming that the peak efficiency closely approximated the nominal rated efficiency. These identified characteristics hold value for V2H system simulations. Furthermore, it was confirmed that a substantial standby power, ranging from 92 to 142 kWh per year, was generated when the V2H charger remained inactive in the sampled households. Additionally, the lack of reverse power flow to the external grid from the V2H system led to an observed increase in V2H partial load operation, resulting in a situation characterized by diminished conversion efficiency.