Modeling and Control of a Mining Microgrid Consisting of Multiple Electrified Drill Rigs

Sammanfattning

The electrification of large-scale mining equipment poses significant challenges for weak and remote power networks, where high inrush currents, low Power Factor (PF), Total Harmonic Distortion (THD), and stability concerns can severely degrade system performance. Existing studies have often addressed stability and power quality separately, leaving a lack of integrated analysis for weak mining grids. This thesis investigates the dynamic behavior of Direct-On-Line motor (DOL), Passive Front-End rectifier (PFE), and Active Front-End converter (AFE) in Grid-Following (GFL) and Grid- Forming (GFM) modes, to clarify their comparative suitability for mining Microgrid (MG). A state-space modeling framework is developed to capture the interaction between converters, Induction Motor (IM), and the weak grid. The approach incorporates LCL Filter (LCL) sizing, inner current/voltage loop dynamics, Phase-Locked Loop (PLL), and Droop control (Droop), and is analyzed through eigenvalue and root-locus techniques. The models are validated against nonlinear time-domain simulations, showing close agreement in both stable and unstable regimes. Case studies on a representative open-pit mining feeder illustrate the comparative performance of different front-end configurations, with evaluation metrics including startup current overshoot, steady-state PF, current THD, and stability margins. The results highlight the critical influence of PLL tuning on GFL stability, the synchronization aggressiveness of GFM Droop control, and the benefits of hybrid configurations. In particular, replacing part of the DOL-based rigs with AFE is shown to substantially improve both power quality and stability boundaries, without requiring a complete system overhaul. The thesis contributes in four main aspects: 1. Establishment of converter–grid state-space models tailored for weak mining grids; 2. Identification of key control parameters shaping stability under GFL and GFM operation; 3. Validation of the analytical framework through detailed simulation; and 4. Comparative evaluation of front-end technologies, leading to practical deployment guidelines. Together, these findings bridge device-level modeling with system-level engineering practice and provide a pathway for the reliable integration of electrified mining equipment in weak-grid environments.