High Power Density Drivetrain Integrated Electric Vehicle Charger

Anwar, Usama

Graduate Thesis Or Dissertation

High Power Density Drivetrain Integrated Electric Vehicle Charger Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/hd76s038s

Abstract

This thesis presents a new architecture for an isolated level 2 on-board electric vehicle (EV) battery charger which is integrated with the EV's drivetrain. The integration with the drivetrain is done by leveraging many of the existing stages of a highly efficient and power-dense composite-architecture-based drivetrain boost converter that acts as an interface between the traction battery and the motor drive and allows the input voltage of the motor drive to be adjusted dynamically to maximize drivetrain efficiency. This composite boost converter comprises a buck stage, a boost stage and a dc transformer (DCX) stage, providing multiple means to integrate on-board charger functionality. In this thesis four alternative approaches to drivetrain integration are identified, analyzed and compared quantitatively in terms of added weight and charging losses. Out of the considered approaches, the selected charging architecture provides an effective tradeoff between added weight and charging losses. This drivetrain-integrated charger leverages the buck stage and part of the DCX stage of the composite boost converter, and adds only a bridgeless-boost based power factor correction (PFC) ac-dc stage, an H-bridge and a single winding to the composite boost converter, to achieve high-power on-board charging functionality without substantial additional weight. Hence, the proposed charger architecture comprises a boost PFC rectification stage, a dual-active bridge isolation stage and a boost current regulation stage. This thesis also presents detailed power stage and controller design of the boost converter based PFC ac-dc stage and introduces a generalized methodology for developing hybrid feedforward control for power converters. Two PFC bridgeless-boost implementations are presented: the first utilizes traditional feedback control, while the second utilizes hybrid feedforward control. Zero crossing distortion effects observed in PFC converters are studied and methods to mitigate these effects are developed and implemented. In case of traditional feedback control, it is shown that the new control, introduced in this thesis, mitigates zero crossing distortion and allows the PFC converter to achieve near-ideal PFC rectifier performance. In the case of hybrid feedforward control architecture, good boost PFC rectifier performance is also demonstrated. The thesis also presents control architectures for the dual-active bridge stage acting as an isolation and voltage regulation stage, and the boost stage acting as a power regulation stage. Finally, two 6.6 kW prototypes of the proposed charger's PFC stage have been designed, fabricated and tested. One prototype utilizes Silicon devices, while the other utilizes Silicon Carbide devices. It is shown that the proposed charger architecture's PFC stage achieves greater than 97% peak efficiency and the on-board charging functionality can be added with only 34% increase in the weight of the composite boost converter.

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