Permanent magnet synchronous motor(PMSM)has been widely used in position control applications.Its performance is not satisfactory due to internal uncertainties and external load disturbances.To enhance the control per...Permanent magnet synchronous motor(PMSM)has been widely used in position control applications.Its performance is not satisfactory due to internal uncertainties and external load disturbances.To enhance the control performance of PMSM systems,a new method that has fast response and good robustness is proposed in this study.First,a modified integral terminal sliding mode controller is developed,which has a fast-sliding surface and a continuous reaching law.Then,an extended state observer is applied to measure the internal and external disturbances.Therefore,the disturbances can be compensated for in a feedforward manner.Compared with other sliding mode methods,the proposed method has faster response and better robustness against system disturbances.In addition,the position tracking error can converge to zero in a finite time.Simulation and experimental results reveal that the proposed control method has fast response and good robustness,and enables high-precision control.展开更多
The position synchronization control(PSC) problem is studied for networked multi-axis servo systems(NMASSs) with time-varying delay that is smaller than one sampling period. To improve the control performance of the s...The position synchronization control(PSC) problem is studied for networked multi-axis servo systems(NMASSs) with time-varying delay that is smaller than one sampling period. To improve the control performance of the system, time-varying delays, modeling uncertainties, and external disturbances are first modeled as a lumped disturbance. Then, a linear extended state observer(LESO) is devised to estimate the system state and the lumped disturbance, and a linear feedback controller with disturbance compensation is designed to perform individual-axis tracking control. After that, a cross-coupled control approach is used to further improve synchronization performance. The bounded-input-bounded-output(BIBO) stability of the closedloop control system is analyzed. Finally, both simulation and experiment are carried out to demonstrate the effectiveness of the proposed method.展开更多
Atomically precise metal nanoclusters(MNCs),as a potential type of photoacoustic(PA)contrast agent,are limited in application due to their low PA conversion efficiency(PACE).Here,with hydrophilic Au25SR18(SR=thiolate)...Atomically precise metal nanoclusters(MNCs),as a potential type of photoacoustic(PA)contrast agent,are limited in application due to their low PA conversion efficiency(PACE).Here,with hydrophilic Au25SR18(SR=thiolate)as model NCs,we present a result that weakly polar solvent induces aggregation,which effectively enhances PA intensity and PACE.The PA intensity and PACE are highly dependent on the degree of aggregation,while the aggregation-enhanced PA intensity(AEPA)positively correlates to the protected ligands.Such an AEPA phenomenon indicates that aggregation actually accelerates the intramolecular motion of Au NCs,and enlarges the proportion of excited state energy dissipated through vibrational relaxation.This result conflicts with the restriction of intramolecular motion mechanism of aggregation-induced emission.Further experiments show that the increased energy of AEPA originates from the aggregation inhibiting the intermolecular energy transfer from excited Au NCs to their surrounding medium molecules,including solvent molecule and dissolved oxygen,rather than restricting radiative relaxations.This study develops a new strategy for enhancing the PA intensity of Au NCs,and contributes to a deeper understanding of the origin of the PA signal and the excited state energy dissipation processes for MNCs.展开更多
The exit measures of super-Brownian motions with branching mechanism $\psi (z) = z^\alpha ,1< \alpha \leqslant 2$ from a bounded smooth domain D in ?d+1 are known to be absolutely continuous with respect to the sur...The exit measures of super-Brownian motions with branching mechanism $\psi (z) = z^\alpha ,1< \alpha \leqslant 2$ from a bounded smooth domain D in ?d+1 are known to be absolutely continuous with respect to the surface area on ?D if $d< \frac{2}{{a - 1}}$ whereas in the case $d > 1 + \frac{2}{{a - 1}}$ they are singular. However, if the branching is restricted to a singular hyperplane, it is proved that they have absolutely continuous states for alld≥1.展开更多
文摘Permanent magnet synchronous motor(PMSM)has been widely used in position control applications.Its performance is not satisfactory due to internal uncertainties and external load disturbances.To enhance the control performance of PMSM systems,a new method that has fast response and good robustness is proposed in this study.First,a modified integral terminal sliding mode controller is developed,which has a fast-sliding surface and a continuous reaching law.Then,an extended state observer is applied to measure the internal and external disturbances.Therefore,the disturbances can be compensated for in a feedforward manner.Compared with other sliding mode methods,the proposed method has faster response and better robustness against system disturbances.In addition,the position tracking error can converge to zero in a finite time.Simulation and experimental results reveal that the proposed control method has fast response and good robustness,and enables high-precision control.
基金supported by the National Natural Science Foundation of China(NSFC)(61822311)the NSFC-Zhejiang Joint Fund for the Intergration of Industrialization and Informatization(U1709213)。
文摘The position synchronization control(PSC) problem is studied for networked multi-axis servo systems(NMASSs) with time-varying delay that is smaller than one sampling period. To improve the control performance of the system, time-varying delays, modeling uncertainties, and external disturbances are first modeled as a lumped disturbance. Then, a linear extended state observer(LESO) is devised to estimate the system state and the lumped disturbance, and a linear feedback controller with disturbance compensation is designed to perform individual-axis tracking control. After that, a cross-coupled control approach is used to further improve synchronization performance. The bounded-input-bounded-output(BIBO) stability of the closedloop control system is analyzed. Finally, both simulation and experiment are carried out to demonstrate the effectiveness of the proposed method.
基金Natural Science Foundation of Shandong Province,Grant/Award Number:ZR2020MB063Taishan Scholar Program of Shandong Province,Grant/Award Number:ts201511027。
文摘Atomically precise metal nanoclusters(MNCs),as a potential type of photoacoustic(PA)contrast agent,are limited in application due to their low PA conversion efficiency(PACE).Here,with hydrophilic Au25SR18(SR=thiolate)as model NCs,we present a result that weakly polar solvent induces aggregation,which effectively enhances PA intensity and PACE.The PA intensity and PACE are highly dependent on the degree of aggregation,while the aggregation-enhanced PA intensity(AEPA)positively correlates to the protected ligands.Such an AEPA phenomenon indicates that aggregation actually accelerates the intramolecular motion of Au NCs,and enlarges the proportion of excited state energy dissipated through vibrational relaxation.This result conflicts with the restriction of intramolecular motion mechanism of aggregation-induced emission.Further experiments show that the increased energy of AEPA originates from the aggregation inhibiting the intermolecular energy transfer from excited Au NCs to their surrounding medium molecules,including solvent molecule and dissolved oxygen,rather than restricting radiative relaxations.This study develops a new strategy for enhancing the PA intensity of Au NCs,and contributes to a deeper understanding of the origin of the PA signal and the excited state energy dissipation processes for MNCs.
文摘The exit measures of super-Brownian motions with branching mechanism $\psi (z) = z^\alpha ,1< \alpha \leqslant 2$ from a bounded smooth domain D in ?d+1 are known to be absolutely continuous with respect to the surface area on ?D if $d< \frac{2}{{a - 1}}$ whereas in the case $d > 1 + \frac{2}{{a - 1}}$ they are singular. However, if the branching is restricted to a singular hyperplane, it is proved that they have absolutely continuous states for alld≥1.
