Wireless Grid Integration of Electric Vehicles with Two-Way Power Flow: New Concepts

Abstract

With the emergence of vehicle-to-grid (V2G) and grid-to-vehicle (G2V) concepts, electric vehicles (EVs) have been proposed as energy storage devices for dynamic demand management. Bidirectional contactless grid interfaces, based on inductive power transfer (IPT) technology, are gaining popularity as an attractive solution for V2G and G2V systems. Such systems typically include an AC-DC and DC-AC two-stage energy conversion process with a large electrolytic capacitor to maintain a stiff DC-link. In order to minimize the ripple of the grid current, a large input inductor is also employed. Inclusion of these two energy storage devices leads to an expensive, bulky and less reliable converter system. This thesis proposes a single-phase matrix converter (MC) that directly generates voltages at high frequency from the utility grid to drive resonant networks of the bidirectional contactless interface. An MC is a direct AC-AC converter with inherent bidirectional power flow capabilities. Hence, large energy storage elements are not employed in the proposed MC based bidirectional contactless grid interface. A comprehensive mathematical model that predicts the steady state voltages, currents as well as the power drawn from the mains grid is developed to gain an insight into the operation of the proposed MC based interface. Utilizing the mathematical model, a modulation strategy is also proposed to attenuate low order harmonics in the grid current. Experimental results, obtained from a 1 kW prototype, show excellent agreement with those obtained from the mathematical model, validating the accuracy of the mathematical model. Experimental results of total harmonic distortion (THD), power factor, active power delivery and efficiency have been presented to evaluate the performance of the MC. A three-phase to single-phase matrix converter (TSMC) based bidirectional contactless grid interface is also proposed in this thesis for high power EV charging and discharging applications. Simulation results of voltages, currents of converters and grid currents, obtained from a 10 kW MATLAB/Simulink model, are presented to demonstrate the feasibility of the proposed contactless grid interface. As an alternative to MCs, which employ complex commutation algorithms, a singlephase bidirectional contactless grid interface without a DC-link capacitor and an input inductor is also proposed. The proposed grid interfaces consist of two back-to-back connected converters. In contrast to conventional bidirectional grid converters, the proposed grid interface employs a simpler switching strategy with a lower switching frequency. A mathematical model, which predicts the behaviour of the proposed grid interface, is also proposed. The feasibility of the proposed grid interface and the accuracy of the mathematical model are demonstrated through experimental results of a 1.1 kW prototype. Therefore, this thesis contributes to the field of contactless EV charging and discharging by proposing cost effective, flexible and efficient solutions. Such solutions are expected to be beneficial to both electric vehicle users and electric power networks.