Changsha Mining and Metallurgy Research Institute (China)

In the sensorless control system of permanent magnet synchronous motors (PMSM), the traditional sliding mode observer (SMO) exhibits significant estimation errors. To improve the accuracy of rotor position observation, a fast super-twisting sliding mode observer (FST-SMO) based on hill climbing method for position error compensation is proposed. First, an FST-SMO based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d-q</i> coordinate system is designed using an improved fast super-twisting algorithm, which enables the estimation of rotor speed and position while reducing chattering and ripples in the estimated back electromotive force (EMF). Second, to eliminate phase fluctuations and drifts in the observed position angle, a phase-locked loop (PLL) is constructed to extract estimation information, avoiding the use of low-pass filters and the reconstruction of position errors, thereby enhancing dynamic performance and observation accuracy. In response to non-ideal factors such as control delays, installation errors, and parameter variations, an intelligent hill climbing control method is employed to optimize and compensate for the observed error angle, further improving observation accuracy. Experimental results demonstrate that this method achieves accurate speed and rotor position observation with excellent performance.

To investigate the fire prevention and suppression characteristics of coal gangue slurry grouting in goafs and the enhanced regulatory mechanisms of additives, the slurry-forming performance of coal gangue slurry was tested. The effects of heating temperature, grouting thickness, and heating duration on the surface temperature distribution characteristics were analyzed. Temperature-programmed experiments were conducted to examine the influence of various additives on the spontaneous combustion propensity of coal gangue, with a comparative analysis of the inhibitory effects between ammonium polyphosphate (APP) and other additives. The results demonstrate that the prepared coal gangue slurry exhibited no segregation or sedimentation, with a plasticity index consistent with standard grouting material requirements, confirming its superior stability. The central, maximum, and minimum surface temperatures of the slurry showed polynomial functional relationships with heating temperature. Surface temperature initially increased and then decreased with grouting thickness, with 10 cm identified as the critical thickness for temperature transition. Overall, the central, maximum, and minimum surface temperatures increased progressively with rising heating temperatures. In addition, under all tested conditions, the average surface temperature remained below 80 °C for slurries with &gt;5 cm grouting thickness, meeting fire prevention requirements. However, the CO and CO2 concentrations increased significantly as heating temperatures rose from 100 °C to 300 °C. At grouting thicknesses of 9–12 cm, CO and CO2 emissions occurred only at 300 °C and decreased with increasing thickness. The coal gangue slurry modified with ammonium polyphosphate (APP) additives exhibited optimal antioxidant performance, significantly suppressing CO and CO2 emissions, which further diminished with higher additive dosages. The findings of this study provide critical insights into the fire prevention performance of coal gangue slurry grouting and the application of additives in this field.

Filling with phosphogypsum is one of the important ways to realize the sustainability development of phosphate mines. This study is based on the extensive on-site experiments conducted at the Dayukou phosphate mine. Over a period of 60 days, different proportions of phosphogypsum, cement, and mineral powder were used to fill the voids in the No. 1 and No. 2 test ore pillars. The results of strength testing during the experimental process indicate that the strength development of the filling material at various stages is normal, meeting all the requirements for mining production. The environmental protection monitoring station in the city conducted water quality analysis during the filling process, indicating that the concentrations of major elements such as Cu, Zn, Mn, Pb, Cd, and Hg in the water samples meet the industrial wastewater discharge standards. The fluoride content ranges from 3.28 to 6.90 mg/L, which is below the first-level standard of 10 mg/L specified in the “Comprehensive Wastewater Discharge Standards” (GB8978-1996). This suggests that the filling process has a minimal impact on the groundwater environment. After the completion of the filling, the pre-embedded pressure boxes function normally, and the data are generally stable, experiencing pressures ranging from 0.11 to 2.53 MPa. This on-site expanded trial indicates the feasibility of using cement, mineral powder, and phosphogypsum for underground filling. It demonstrates the potential for reutilizing the solid waste phosphogypsum as filling aggregate.