Investigation of Multifunctional Off-Board EV Battery Charger with Solar PV Grid Interface

Abstract

Increasing environmental pollution and limiting petroleum fuels resulted in two significant changes in the world. The first change is adopting renewable energy sources (RESs) by replacing conventional energy sources, and the second is adopting electric vehicles (EVs) by replacing combustion engine-based vehicles. However, in the current scenario, an enormous increase in EVs resulted in the massive installation of charging stations powered mainly by the grid. As a result, grid power quality (PQ) issues, such as voltage and current distortions, appear in the power system. Therefore, designing a multifunctional charging infrastructure that can be used for EV charging and simultaneously improve grid PQ is essential. Considering the PQ issues, this thesis deals with designing, controlling, and implementing the multifunctional EV charging system to power the EV batteries and simultaneously provide grid support services. Furthermore, integrating Solar PV and storage systems into the EV Charging system reduces the energy needed from thermal generating stations. It promotes reduced greenhouse gas emissions, charging costs, environmental constraints, and EV grid dependability. The multifunctional chargers are designed to operate in grid connected operation and standalone operation, with smooth and seamless transition from one to another to provide uninterruptable power to EVs and utility loads. In addition, the charger locally mitigates harmonic distortions that appear at the grid side due to EV charging and nonlinear charging station loads to avoid penalty on the charger owner. The charger facilitates bidirectional active power exchange in grid-to-vehicle (G2V) and vehicle-to grid (V2G) operating modes. Furthermore, the charger provides other multifunctional operations in charger-for-grid (C4G) operations like grid current harmonic compensation (GCHC), reactive power compensation (RPC), and reactive power support (RPS) to the grid. Moreover, the charger also supports vehicle-to-home (V2H), Energy storage-to-home (E2H), vehicle-to-energy storage (V2E), and vehicle-to vehicle (V2V) operation, which increases the operational efficiency of the charger. In this thesis, a single excited three-phase seven-level cascaded H-bridge bidirectional AC-DC converter (CHBDC) topology is adopted for the grid converter of the charger. During multifunctional operation, the CHBDC control algorithm manages energy management between sources, maximum power point tracking of solar photovoltaic (PV), DC link voltage regulation, and PQ services. Particularly, different CHBDC control algorithms are presented to achieve efficient multifunctional operation of the charger without compromising grid PQ, irrespective of abnormal system conditions like grid outages, load fluctuations, and nonideal grid voltages (unbalanced and distorted). The presented multifunctional EV charger configurations are modeled in Sim Power System (SPS)/ MATLAB Simulink environment, and the same has been validated by an experimental prototype developed in the laboratory. Furthermore, the thesis analyzes and presents the charger performance during various steady state and dynamic conditions.