Abstracts Category : Other

DC microgrid for mobile mining equipment

by Jahromi Mohsen Ghaffarpour

Research Doctorate - Doctor of Philosophy (PhD) Electric mining excavators (rope shovels and draglines) represent a larger and the most dynamic part of the electric load at an open cut mine site. These excavators are currently undergoing an upgrade to the newly adopted high power IGBT-based AC drive technology. Such an upgrade requires that essentially every component inside an excavator is replaced by a new one. In this project an alternative upgrade solution is proposed, which is based on a transition from AC to DC form of power delivery, across the mine and to individual motors inside an electric excavator. Multiple advantages associated with such a solution are argued in the thesis. These include higher efficiency, higher power throughput for the same type of trailing cables, improved mobility due to longer trailing cables, utilisation of the existing motor fleet, potential peak power shaving and other advantages. This thesis presents a proof of concept for the DC-based power distribution system for open cut mines, including theoretical calculations, an aggregated modeling of an AC-fed excavator based on a novel approach, a detailed modeling of the internal structure of a DC-fed excavator, and extensive simulations under various realistic conditions, associated with coordinated and non-coordinated motor operation, load changes, regenerative braking, faults, etc. For a bidirectional interconnection of the external DC supply and the internal DC bus of an excavator, a particular, less known DC-DC converter type is proposed, namely, a transformerless LCL DC-DC converter. The advantages of this converter include its proven ability to operate in MW power range, reduced switching losses, soft switching operation under the full load, etc. Due to its importance for the proposed DC system, a new design procedure and a novel control scheme are proposed for this converter. Furthermore, a laboratory prototype of such a converter is developed together with the proposed novel control. Extensive experimental studies are used to validate its design, control and applicability. DC fault studies, performed in this project by simulation and experiment, confirm good fault tolerance of the proposed DC system. To address specific protection needs of an electric excavator, a comprehensive fault tolerance strategy is developed based on analysis of electrical and mechanical operation of an electric rope shovel and identification of its working cycle.Advisors/Committee Members: University of Newcastle. Faculty of Engineering & Built Environment, School of Electrical Engineering and Computing.