A smart charging algorithm based on a fast charging station without energy storage system

With the growing popularity of electric vehicles (EV), there is an urgent demand to solve the stress placed on grids caused by the irregular and frequent access of EVs. The traditional direct current (DC) fast charging station (FCS) based on a photovoltaic (PV) system can effectively alleviate the stress of the grid and carbon emission, but the high cost of the energy storage system (ESS) and the under utilization of the grid-connected interlinking converters (GIC) are not very well addressed. In this paper, the DC FCS architecture based on a PV system and ESS-free is first proposed and employed to reduce the cost. Moreover, the proposed smart charging algorithm (SCA) can fully coordinate the source/load properties of the grid and EVs to achieve the maximum power output of the PV system and high utilization rate of GICs in the absence of ESS support for FCS. SCA contains a self-regulated algorithm (SRA) for EVs and a grid-regulated algorithm (GRA) for GICs. While the DC bus voltage change caused by power fluctuations does not exceed the set threshold, SRA readjusts the charging power of each EV through the status of the charging (SOC) feedback of the EV, which can ensure the power rebalancing of the FCS. The GRA would participate in the adjustment process once the DC bus voltage is beyond the set threshold range. Under the condition of ensuring the charging power of all EVs, a GRA based on adaptive droop control can improve the utilization rate of GICs. At last, the simulation and experimental results are provided to verify the effectiveness of the proposed SCA.