MODELLING AND CONTROL DESIGN OF NON-ISOLATED AND HIGH-FREQUENCY ISOLATED V2G/G2V SYSTEMS

Student thesis: Master's Thesis

Abstract

Renewable energies are replacing conventional sources in order to overcome the dependence and pollution of fossil fuels. As a result of the increase of renewable energies in the electrical grid, it is needed to overcome the inherent variability of their resources by store systems. Thereby, there exists a trend to develop battery electric vehicles (BEV), whose batteries could be used to tackle this variability. Thus, chargers must be able to charge batteries and to feed the grid, what is known as Grid-to-Vehicle (G2V) and Vehicle-to-Grid (V2G) applications.
The aim of this thesis is to develop a high-frequency isolated bidirectional charger for high power applications, concretely 45 kW, and to compare it with the performance of other bidirectional chargers. The advantages and drawbacks of several topologies are highlighted, paying special attention to the implementation of non-isolated chargers against high-frequency isolated chargers. 3-Phase Inverter, Dual Active Bridge and Buck-Boost are considered the outstanding topologies to build up the high-power charger. Indeed, there are three proposals: high-voltage non-isolated topology, comprised of a 3-Phase Inverter; low-voltage non-isolated topology, comprised of a 3-Phase Inverter and a Buck-Boost; low-voltage high-frequency isolated topology, comprised of a 3-Phase Inverter, a Dual Active Bridge and a Buck-Boost. According to the literature, the optimum elements have been calculated for each converter.
Furthermore, several PI controllers have been included and designed in order to carry out the most common battery charging methodologies and V2G application for every proposal. Linear models for each control were obtained to select the adequate PI constants, studying the Phase Margin, Gain Margin and cross-over frequency. Anti-windup technique is presented to improve the control when the dynamic response is slower than the control design, as it occurs in battery voltage control. Then, the results were confirmed in a non-linear model based on different MATLAB/Simulink models.
Once the three converters reached objectives, a comparison of their performance is presented, mainly focus on FFT and efficiency studies. Galvanic isolation benefits are evaluated against the non-isolated topology advantages, and an experimental test was realized to confirm the possibility of building up the converters designed in this paper.
Finally, it is discussed if V2G application is a recommendable alternative to the store systems regarding the results obtained.
Date of Award2 Sep 2019
Original languageEnglish

Keywords

  • V2G
  • electric vehicles
  • Bidirectional converter
  • High power chargers

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