Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results.Un...Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results.Unfortunately, how many MEIs need to be included in the fitting process for a material is unclear a priori,which limits the results obtained by these conventional methods. Based on linear spin-wave theory but without performing matrix diagonalization, we show that for a general quadratic spin Hamiltonian, there is a simple relation between the Fourier transform of MEIs and the sum of square of magnon energies(SSME). We further show that according to the real-space distance range within which MEIs are considered relevant, one can obtain the corresponding relationships between SSME in momentum space. By directly utilizing these characteristics and the experimental magnon energies at only a few high-symmetry k points in the Brillouin zone, one can obtain strong constraints about the range of exchange path beyond which MEIs can be safely neglected. Our methodology is also generally applicable for other Hamiltonian with quadratic Fermi or Boson operators.展开更多
The motion equation of the rotor suspended by active magnetic bearing (AMB)is given in this paper after considering the nonlinear characteristics of the force.Fromthe response equation resulted from this Eq.we gained ...The motion equation of the rotor suspended by active magnetic bearing (AMB)is given in this paper after considering the nonlinear characteristics of the force.Fromthe response equation resulted from this Eq.we gained the functions of the jump ra-nge,and examined the effects of the A MB's parameters.展开更多
A wide speed range permanent magnet synchronous generator(PMSG)system is studied in this paper,including the PMSG design and comparative study on control strategies with a pulse width modulation(PWM)rectifier,the purp...A wide speed range permanent magnet synchronous generator(PMSG)system is studied in this paper,including the PMSG design and comparative study on control strategies with a pulse width modulation(PWM)rectifier,the purpose of which is to regulate the DC-link voltage.It is of great importance to study the foregoing DC power system based on the PMSG and PWM rectifier,where vector control(VC)can be implemented and the corresponding field-weakening strategy can be realized by injecting a field-weakening current component without any auxiliary devices.Large machine inductance is desired in order to limit the short-circuit current and the loaded voltage drop.Different control strategies including VC,direct torque control(DTC)and direct voltage control(DVC)are studied and compared with both simulations and experiments.展开更多
基金Supported by the National Natural Science Foundation of China (Grant Nos. 11834006, 12004170, and 12104215)the Natural Science Foundation of Jiangsu Province,China (Grant No. BK20200326)+1 种基金the Excellent Programme in Nanjing Universitythe support from the Tencent Foundation through the XPLORER PRIZE。
文摘Magnetic exchange interactions(MEIs) define networks of coupled magnetic moments and lead to a surprisingly rich variety of their magnetic properties. Typically MEIs can be estimated by fitting experimental results.Unfortunately, how many MEIs need to be included in the fitting process for a material is unclear a priori,which limits the results obtained by these conventional methods. Based on linear spin-wave theory but without performing matrix diagonalization, we show that for a general quadratic spin Hamiltonian, there is a simple relation between the Fourier transform of MEIs and the sum of square of magnon energies(SSME). We further show that according to the real-space distance range within which MEIs are considered relevant, one can obtain the corresponding relationships between SSME in momentum space. By directly utilizing these characteristics and the experimental magnon energies at only a few high-symmetry k points in the Brillouin zone, one can obtain strong constraints about the range of exchange path beyond which MEIs can be safely neglected. Our methodology is also generally applicable for other Hamiltonian with quadratic Fermi or Boson operators.
文摘The motion equation of the rotor suspended by active magnetic bearing (AMB)is given in this paper after considering the nonlinear characteristics of the force.Fromthe response equation resulted from this Eq.we gained the functions of the jump ra-nge,and examined the effects of the A MB's parameters.
基金Supported by the National Science Foundation of China(NSFC 51377140)and China Scholarship Council(CSC)。
文摘A wide speed range permanent magnet synchronous generator(PMSG)system is studied in this paper,including the PMSG design and comparative study on control strategies with a pulse width modulation(PWM)rectifier,the purpose of which is to regulate the DC-link voltage.It is of great importance to study the foregoing DC power system based on the PMSG and PWM rectifier,where vector control(VC)can be implemented and the corresponding field-weakening strategy can be realized by injecting a field-weakening current component without any auxiliary devices.Large machine inductance is desired in order to limit the short-circuit current and the loaded voltage drop.Different control strategies including VC,direct torque control(DTC)and direct voltage control(DVC)are studied and compared with both simulations and experiments.
