Space vector modeling of a SAG mill drive and evaluation during mill shutdowns

Mineral grinding is one of the most important and critical stages in copper mining. Economy-scale has motivated the use of high capacity semi-autogenous (SAG) mill units whose continuous operation is essential to mine profitability. Hence, the development of modeling tools of SAG mill drive systems that help to analyze and prevent costly longtime outages, are of great benefit. Paper presents the development of phase and qd space vector models of the 2-stator winding synchronous motor used in SAG mill drives. Using a space vector rotation transformation the two shifted stator winding are modeled as an equivalent 1-stator winding. Combining these motor models to two 6-pulse, one 12-pulse, and one ideal cycloconverters, three space models of the complete drive system are developed. The space vector models are evaluated during a normal stop sequence of an 8.2 MW SAG mill drive. The stop sequence includes a decelerating ramp, a holding torque and a rollback triangular reference. Results show that the developed models are powerful and precise tools that allow the evaluation of the SAG mill drive system during any dynamic or transient event.