A Solar PV, BES, Grid and DG Set Based Hybrid Charging Station for Uninterruptible Charging at Minimized Charging Cost

Abstract

In this paper, a charging station (CS) is proposed that uses a solar photovoltaic (PV) array, a battery energy storage system (BES), the grid and a diesel generator (DG) set to provide uninterruptible charging of electric vehicles (EVs). However, these energy sources are utilized in a way that minimizes the operational cost of the CS. Therefore, it reduces the charging cost of the electric vehicles (EVs). To achieve uninterruptible charging and to minimize the charging cost, a charging strategy is proposed that prioritizes the use of energy sources. Based on this, the solar PV and BES energy are used as a priority. After that, the grid is used, and finally, a DG set is used when all energy sources are not accessible. This strategy is based on the cost of electricity per kWh. Normally, the rooftop solar PV array offers power at INR 4.5-5/kWh. The grid offers power at INR 10/kWh, and DG set offers at INR 17-20/kWh. To further minimize the charging cost, the single phase two winding self-excited induction generator (SEIG) based DG set is operated at the single point of saturation characteristic to generate much high power than its rated power. Moreover, a single two-leg voltage source converter (VSC) does multiple tasks such as, 1) generation of sinusoidal voltage in standalone mode, 2) regulation of generator voltage and frequency, 3) management of power flow, 4) reactive power compensation and harmonics current elimination and it also reduces the initial cost of the CS. To obtain ceaseless charging while connecting the grid/DG set to the CS, the point of common coupling (PCC) voltage is synchronized with the grid/DG set voltage. The CS provides both AC and DC output ports for charging the EVs. To charge the EVs on AC port, the CS uses solar PV array and BES energy to generate a sinusoidal voltage of 220V and 50Hz. Moreover, with both grid and DG, the CS draws power at unity power factor (PF) with current total harmonics distortion (THD) less than 5% as required by an IEEE 519 standard.