8 research outputs found
Maximum torque per ampere and maximum power per ampere sliding mode control for interior permanent magnet synchronous motors
No full text© 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper presents novel maximum torque per ampere (MTPA) and maximum power per ampere (MPPA) sliding mode control (SMC) approaches for interior permanent-magnet synchronous motors (IPMs). We first derive the first-order SMC methods to improve the field-oriented control's resiliency against the external perturbations, extraneous noise and modelling uncertainties. After that, we propose the higher-order SMC to significantly reduce the chattering phenomenon, which is inherent in the first-order sliding mode method. Based on the comparison studies, the conventional proportional-integral-derivative based field oriented control shows sluggish response and is more sensitive to parameter perturbations and external torque disturbances. By introducing the novel SMC methods, both the speed and torque regulation performance of interior permanent magnet synchronous motor can be greatly improved. Computer simulation studies have demonstrated the superior performance of the first-order and higher-order sliding mode controllers for interior permanent magnet synchronous motor speed and torque regulation applications
Structural Evolution of Paramagnetic Lanthanide Compounds in Solution Compared to Time- and Ensemble-Average Structures
No full textAnisotropy in the magnetic susceptibility strongly influences
the
paramagnetic shifts seen in nuclear magnetic resonance (NMR) and magnetic
resonance imaging (MRI) experiments. A previous study on a series
of C3-symmetric prototype MRI contrast agents showed that
their magnetic anisotropy was highly sensitive to changes in molecular
geometry and concluded that changes in the average angle between the
lanthanide–oxygen (Ln–O) bonds and the molecular C3 axis due to solvent interactions had a significant impact
on the magnetic anisotropy and, consequently, the paramagnetic shift.
However, this study, like many others, was predicated on an idealized
C3-symmetric structural model, which may not be representative
of the dynamic structure in solution at the single-molecule level.
Here, we address this by using ab initio molecular dynamics simulations
to simulate how the molecular geometry, in particular the angles between
the Ln–O bonds and the pseudo-C3 axis, evolves over
time in the solution, mimicking typical experimental conditions. We
observe large-amplitude oscillations in the O–Ln–C̃3 angles, and complete active space self-consistent field spin–orbit
calculations show that this leads to similarly large oscillations
in the pseudocontact (dipolar) paramagnetic NMR shifts. The time-averaged
shifts show good agreement with experimental measurements, while the
large fluctuations suggest that an idealized structure provides an
incomplete description of the solution dynamics. Our observations
have significant implications for modeling the electronic and nuclear
relaxation times in this and other systems where the magnetic susceptibility
is exquisitely sensitive to the molecular structure
Structural evolution of paramagnetic lanthanide compounds in solution compared to time- and ensemble-average structures
No full textAnisotropy in the magnetic susceptibility strongly influences the paramagnetic shifts seen in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) experiments. A previous study on a series of C3-symmetric prototype MRI contrast agents showed that their magnetic anisotropy was highly sensitive to changes in molecular geometry, and concluded that changes in the average angle between the lanthanide-oxygen (Ln-O) bonds and the molecular C3 axis due to solvent interactions had a significant impact on the magnetic anisotropy and, consequently, the paramagnetic shift. However, this study, like many others, was predicated on an idealised C3-symmetric structural model, which may not be representative of the dynamic structure in solution at the single-molecule level. Here, we address this by using ab initio molecular dynamics simulations to simulate how the molecular geometry, in particular the angles between the Ln-O bonds and the pseudo-C3 axis, evolves over time in solution, mimicking typical experimental conditions. We observe large-amplitude oscillations in the O-Ln-3 angles, and complete active space self-consistent field spin-orbit calculations show that this leads to similarly large oscillations in the pseudocontact (dipolar) paramagnetic NMR shifts. The time-averaged shifts show good agreement to experimental measurements, while the large fluctuations suggest that an idealised structure provides an incomplete description of the solution dynamics. Our observations have significant implications for modelling the electronic and nuclear relaxation times in this and other systems where the magnetic susceptibility is exquisitely sensitive to the molecular structure.</p
Tris-Silanide f-Block Complexes:Insights into Paramagnetic Influence on NMR Chemical Shifts
No full textThe paramagnetism of f-block ions has been exploited in chiral shift reagents and magnetic resonance imaging, but these applications tend to focus on 1H NMR shifts as paramagnetic broadening makes less sensitive nuclei more difficult to study. Here we report a solution and solid-state (ss) 29Si NMR study of an isostructural series of locally D3h-symmetric early f-block metal(III) tris-hypersilanide complexes, [M{Si(SiMe3)3}3(THF)2] (1-M; M = La, Ce, Pr, Nd, U); 1-M were also characterized by single crystal and powder X-ray diffraction, EPR, ATR-IR and UV-Vis-NIR spectroscopies, SQUID magnetometry and elemental analysis. Only one SiMe3 signal was observed in the 29Si ssNMR spectra of 1-M, whilst two SiMe3 signals were seen in solution 29Si NMR spectra of 1-La and 1-Ce. This is attributed to dynamic averaging of the SiMe3 groups in 1-M in the solid state due to free rotation of the M–Si bonds, and dissociation of THF from 1-M in solution to give the locally C3v-symmetric complexes [M{Si(SiMe3)3}3(THF)n] (n = 0 or 1), which show restricted rotation of M–Si bonds on the NMR timescale. Density functional theory and complete active space self-consistent field spin-orbit calculations were performed on 1-M and desolvated solution species to model paramagnetic NMR shifts. We find excellent agreement of experimental 29Si NMR data for diamagnetic 1-La, suggesting n = 1 in solution, and reasonable agreement of calculated paramagnetic shifts of SiMe3 groups for 1-M (M = Pr and Nd); the NMR shifts for metal-bound 29Si nuclei could only be reproduced for diamagnetic 1-La, showing the current limitations of pNMR calculations for larger nuclei
Tris-Silanide f-Block Complexes:Insights into Paramagnetic Influence on NMR Chemical Shifts
No full textThe paramagnetism of f-block ions has been exploited in chiral shift reagents and magnetic resonance imaging, but these applications tend to focus on 1H NMR shifts as paramagnetic broadening makes less sensitive nuclei more difficult to study. Here we report a solution and solid-state (ss) 29Si NMR study of an isostructural series of locally D3h-symmetric early f-block metal(III) tris-hypersilanide complexes, [M{Si(SiMe3)3}3(THF)2] (1-M; M = La, Ce, Pr, Nd, U); 1-M were also characterized by single crystal and powder X-ray diffraction, EPR, ATR-IR and UV-Vis-NIR spectroscopies, SQUID magnetometry and elemental analysis. Only one SiMe3 signal was observed in the 29Si ssNMR spectra of 1-M, whilst two SiMe3 signals were seen in solution 29Si NMR spectra of 1-La and 1-Ce. This is attributed to dynamic averaging of the SiMe3 groups in 1-M in the solid state due to free rotation of the M–Si bonds, and dissociation of THF from 1-M in solution to give the locally C3v-symmetric complexes [M{Si(SiMe3)3}3(THF)n] (n = 0 or 1), which show restricted rotation of M–Si bonds on the NMR timescale. Density functional theory and complete active space self-consistent field spin-orbit calculations were performed on 1-M and desolvated solution species to model paramagnetic NMR shifts. We find excellent agreement of experimental 29Si NMR data for diamagnetic 1-La, suggesting n = 1 in solution, and reasonable agreement of calculated paramagnetic shifts of SiMe3 groups for 1-M (M = Pr and Nd); the NMR shifts for metal-bound 29Si nuclei could only be reproduced for diamagnetic 1-La, showing the current limitations of pNMR calculations for larger nuclei
Paramagnetic NMR Shifts of Tris-Hypersilanide Early f-Block Metal(III) Complexes
No full textThe paramagnetism of f-block ions has been exploited in chiral shift reagents and magnetic resonance imaging, but these applications tend to focus on 1H NMR shifts as paramagnetic broadening makes less sensitive nuclei more difficult to study. Here we report a solution and solid-state (ss) 29Si NMR study of an isostructural series of locally D3h-symmetric early f-block metal(III) tris-hypersilanide complexes, [M{Si(SiMe3)3}3(THF)2] (1-M; M = La, Ce, Pr, Nd, U); 1-M were also characterized by single crystal and powder X-ray diffraction, EPR, ATR-IR and UV-Vis-NIR spectroscopies, SQUID magnetometry and elemental analysis. Only one SiMe3 signal was observed in the 29Si ssNMR spectra of 1-M, whilst two SiMe3 signals were seen in solution 29Si NMR spectra of 1-La and 1-Ce. This is attributed to dynamic averaging of the SiMe3 groups in 1-M in the solid state due to free rotation of the M–Si bonds, and dissociation of THF from 1-M in solution to give the locally C3v-symmetric complexes [M{Si(SiMe3)3}3(THF)n] (n = 0 or 1), which show restricted rotation of M–Si bonds on the NMR timescale. Density functional theory and complete active space self-consistent field spin-orbit calculations were performed on 1-M and desolvated solution species to model paramagnetic NMR shifts. We find excellent agreement of experimental 29Si NMR data for diamagnetic 1-La, suggesting n = 1 in solution, and reasonable agreement of calculated paramagnetic shifts of SiMe3 groups for 1-M (M = Pr and Nd); the NMR shifts for metal-bound 29Si nuclei could only be reproduced for diamagnetic 1-La, showing the current limitations of pNMR calculations for larger nuclei
