Performance Evaluation of MLI Based DVR in Grid Fed EV Fast Charging Station

This article proposes a power quality (PQ) solution for the compensation of voltage sag on grid fed electric vehicle fast charging stations (EVFCS) using a T-type 5-level inverter based dynamic voltage restorer (DVR). In this work, a lithium-ion battery pack with a rating of 48 V, 10 Ah, and 5 A is used as an electric vehicle (EV) battery. Firstly, the voltage sag shows a significant effect on the performance of EVFCS. The analysis of the effect of voltage sag on different characteristics of EVFCS, such as DC-bus voltage, battery current, state-of-charge (SOC), and battery voltage, is carried out in MATLAB/Simulink and through experimentation. Further, the design of the charging system is carried out using a 1-Phi rectifier and DC-DC converter with closed loop current control. The performance of a closed loop current controlled buck converter is investigated experimentally for different magnitudes of sag (0%, 25% and 50%). Furthermore, the $ \alpha \beta$ to dq transformation based synchronous reference frame (SRF) theory operated closed loop voltage controller is employed for 1-Phi DVR to mitigate a voltage sag of 50%. This DVR maintains rated DC-bus voltage (110 V) and rated battery current (5 A) under a severe voltage sag condition of 50%. Also, DVR protects the PCC (grid) from voltage harmonics generated by the EVFCS, reducing the PCC voltage THD to 2.42% from 9.8%. Moreover, the control strategies of both the buck converter and DVR are developed on the hardware platform using the STM32 microcontroller. The simulation results are validated mathematically and experimentally. Lastly, simulation and experimental results confirm the beneficial use of T-type 5-level DVR for better performance of EVFCS.