This paper proposes a novel control approach for fault-tolerant control of dual three-phase permanent magnet synchronous motor(PMSM) under one-phase open-circuit fault.A modified six-phase static coordinate transforma...This paper proposes a novel control approach for fault-tolerant control of dual three-phase permanent magnet synchronous motor(PMSM) under one-phase open-circuit fault.A modified six-phase static coordinate transformation matrix and an extended rotating coordinate transformation matrix are investigated considering the influence of the fifth harmonic space on fault-tolerant control. These mathematical models are further analyzed in the fundamental space and the fifth harmonic space after the fault and to eliminate the coupling between the d-q axis voltage equation in the fundamental wave space and the d-q axis voltage equation in the fifth harmonic space, a secondary rotation coordinate transformation matrix is proposed. To achieve the purpose of reducing torque ripple, the fault-tolerant control method proposed in this paper not only takes the minimum copper loss as the constraint condition, but also injects the fifth harmonic current. The experimental result of current and torque is used to verify the accuracy of fault-tolerant control.展开更多
We investigate theoretically the spectral shift of the high-order harmonic generation(HHG)in ZnO driven by a combined laser field by solving the two-band semiconductor Bloch equations(SBEs)in the velocity gauge.The co...We investigate theoretically the spectral shift of the high-order harmonic generation(HHG)in ZnO driven by a combined laser field by solving the two-band semiconductor Bloch equations(SBEs)in the velocity gauge.The combined laser field is synthesized by a fundamental laser pulse and its seventh-frequency laser pulse.When the seventh-frequency laser pulse is added to the rising or falling parts of the fundamental laser field,we find that the spectral blueshift or redshift appears,which is due to the unequal contribution of the rising and falling parts in the fundamental laser field to the harmonics.By analyzing the time-dependent conduction band population in k space,we found that,in addition to the tunneling ionization channel,there is also the resonant electron injection channels which is induced by the seventh-frequency laser pulse.The harmonics generated by the different channels show the spectral redshift or the spectral blueshift,respectively.Through analyzing the k-integrated transient conduction band population of the electrons from different channels,we found that if there is a certain delay in the process of the electron excitation,it will lead to the delay in the harmonic emission,which results in the spectral redshift of the harmonics.展开更多
The equivalent circuit of single-cavity multiple-device fundamentaloscillator(SCMDFO)and that of single-device harmonic oscillator(SDHO)proposed byK.Kurokawa and K.Solbach,respectively,are extended and applied to a si...The equivalent circuit of single-cavity multiple-device fundamentaloscillator(SCMDFO)and that of single-device harmonic oscillator(SDHO)proposed byK.Kurokawa and K.Solbach,respectively,are extended and applied to a single-cavitymultiple-device harmonic oscillator(SCMDHO).By means of describing the functions ofnonlinearity of Gunn diodes,the performances of the SCMDHO are analyzed.It is foundthat the voltage amplitudes are similar to those of SDHO,and the ratio of maximum pow-er of harmonic to that of fundamental is identical to that in SDHO when the devices havesame parameters.The harmonic injection locking behavior is also investigated.The injec-tion locking range is greater than that of SDHO if locking gain remains constant.A2-Gunn diode harmonic oscillator was designed.It delivers 30mW output power at103GHz.The mechanical tuning range is 4.15GHz when the output power remains morethan 10mW.The desired operation mode is stable.展开更多
Second-harmonic generation allows for coherently bridging distant regions of the optical spectrum,with applications ranging from laser technology to self-referencing of frequency combs.However,accessing the nonlinear ...Second-harmonic generation allows for coherently bridging distant regions of the optical spectrum,with applications ranging from laser technology to self-referencing of frequency combs.However,accessing the nonlinear response of a medium typically requires high-power bulk sources,specific nonlinear crystals,and complex optical setups,hindering the path toward large-scale integration.Here we address all of these issues by engineering a chip-scale second-harmonic(SH)source based on the frequency doubling of a semiconductor laser self-injection-locked to a silicon nitride microresonator.The injection-locking mechanism,combined with a high-Q microresonator,results in an ultra-narrow intrinsic linewidth at the fundamental harmonic frequency as small as 41 Hz.Owing to the extreme resonant field enhancement,quasi-phase-matched second-order nonlinearity is photoinduced through the coherent photogalvanic effect and the high coherence is mapped on the generated SH field.We show how such optical poling technique can be engineered to provide efficient SH generation across the whole C and L telecom bands,in a reconfigurable fashion,overcoming the need for poling electrodes.Our device operates with milliwatt-level pumping and outputs SH power exceeding 2 mW,for an efficiency as high as 280%/W under electrical driving.Our findings suggest that standalone,highly-coherent,and efficient SH sources can be integrated in current silicon nitride photonics,unlocking the potential of x(2)processes in the next generation of integrated photonic devices.展开更多
Reducing the converter loss,sub-module voltage ripple and handling DC short-circuit faults in high-voltage direct current systems are crucial for the economical and reliable operation of modular multilevel converters(...Reducing the converter loss,sub-module voltage ripple and handling DC short-circuit faults in high-voltage direct current systems are crucial for the economical and reliable operation of modular multilevel converters(MMCs).This study proposes a coordinated control method of power loss reduction and capacitor voltage balancing for AC voltage boosted full-bridge sub-module(FBSM)-MMC by controlling the second harmonic component in the circulating current.The relationship between converter loss and second harmonic circulating current(SHCC)is firstly derived for AC voltage boosted FBSM-MMC.From the analysis,it can be seen that the converter loss and ripple can be optimised by injecting the SHCC into the arm current when compared with SHCC elimination.Simulation results of an AC voltage boosted FBSM-MMC with typical parameters using PSCAD/EMTDC confirm the feasibility and validity of the proposed loss and ripple reduction method.展开更多
Unvoiced/voiced classification of speech is a challenging problem especially under conditions of low signal-to-noise ratio or the non-white-stationary noise environment. To solve this problem, an algorithm for speech ...Unvoiced/voiced classification of speech is a challenging problem especially under conditions of low signal-to-noise ratio or the non-white-stationary noise environment. To solve this problem, an algorithm for speech classification, and a technique for the estimation of palrwise magnitude frequency in voiced speech am proposed. By using third order spectrum of speech signal to remove noise, in this algorithm the least spectrum difference to get refined pitch and the max harmonic number is given. And this algorithm utilizes spectral envelope to estimate signal-to-noise ratio of speech harmonics. Speech classification, voicing probability, and harmonic parameters of the voiced frame can be obtained. Simulation results indicate that the proposed algorithm, under complicated background noise, especially Gaussian noise, can effectively classify speech in high accuracy for voicing probability and the voiced parameters.展开更多
We investigate two-photon transitions to the electron-hole scattering continuum in monolayer transition-metal dichalcogenides, and identify two contributions to this nonlinear optical process with opposite circularly ...We investigate two-photon transitions to the electron-hole scattering continuum in monolayer transition-metal dichalcogenides, and identify two contributions to this nonlinear optical process with opposite circularly polarized valley selection rules. In the non-interacting limit, the competition between the two contributions leads to a crossover of the selection rule with the increase of the two-photon energy. With the strong Coulomb interaction between the electron and hole, the two contributions excite electron-hole scattering states in orthogonal angular momentum channels, while the strength of the transition can be substantially enhanced by the interaction. Based on this picture of the two-photon transition, the second harmonic generation(SHG) in the electron-hole continuum is analyzed, where the Coulomb interaction is shown to greatly alter the relative strength of different cross-circular polarized SHG processes. Valley current injection by the quantum interference of one-photon and two-photon transition is also investigated in the presence of the strong Coulomb interaction, which significantly enhances the injection rate.展开更多
A method to generate the optical quadruple frequency millimeter-wave with high power efficiency is pro- posed and demonstrated based on the combination of the injection 2nd-order rational harmonic mode- locked fiber r...A method to generate the optical quadruple frequency millimeter-wave with high power efficiency is pro- posed and demonstrated based on the combination of the injection 2nd-order rational harmonic mode- locked fiber ring laser technique and the fiber grating notch filter. In this approach, the fiber Bragg grating notch filter is inserted into the laser cavity to prevent the undesired optical carrier, so that the pump power can be converted to 2nd-order harmonic wave more efficiently. In our experiment, the power efficiency of optical quadruple frequency millimeter-wave (40 GHz) generation is ten folds of that of our previous method based only on the rational harmonic mode-locked technique.展开更多
基金supported by the National Natural Science Foundation of China under Grant 61603263。
文摘This paper proposes a novel control approach for fault-tolerant control of dual three-phase permanent magnet synchronous motor(PMSM) under one-phase open-circuit fault.A modified six-phase static coordinate transformation matrix and an extended rotating coordinate transformation matrix are investigated considering the influence of the fifth harmonic space on fault-tolerant control. These mathematical models are further analyzed in the fundamental space and the fifth harmonic space after the fault and to eliminate the coupling between the d-q axis voltage equation in the fundamental wave space and the d-q axis voltage equation in the fifth harmonic space, a secondary rotation coordinate transformation matrix is proposed. To achieve the purpose of reducing torque ripple, the fault-tolerant control method proposed in this paper not only takes the minimum copper loss as the constraint condition, but also injects the fifth harmonic current. The experimental result of current and torque is used to verify the accuracy of fault-tolerant control.
基金the National Natural Science Foundation of China(Grant Nos.12074142 and 11904122).
文摘We investigate theoretically the spectral shift of the high-order harmonic generation(HHG)in ZnO driven by a combined laser field by solving the two-band semiconductor Bloch equations(SBEs)in the velocity gauge.The combined laser field is synthesized by a fundamental laser pulse and its seventh-frequency laser pulse.When the seventh-frequency laser pulse is added to the rising or falling parts of the fundamental laser field,we find that the spectral blueshift or redshift appears,which is due to the unequal contribution of the rising and falling parts in the fundamental laser field to the harmonics.By analyzing the time-dependent conduction band population in k space,we found that,in addition to the tunneling ionization channel,there is also the resonant electron injection channels which is induced by the seventh-frequency laser pulse.The harmonics generated by the different channels show the spectral redshift or the spectral blueshift,respectively.Through analyzing the k-integrated transient conduction band population of the electrons from different channels,we found that if there is a certain delay in the process of the electron excitation,it will lead to the delay in the harmonic emission,which results in the spectral redshift of the harmonics.
基金The Project Supported by National Science Foundation of China
文摘The equivalent circuit of single-cavity multiple-device fundamentaloscillator(SCMDFO)and that of single-device harmonic oscillator(SDHO)proposed byK.Kurokawa and K.Solbach,respectively,are extended and applied to a single-cavitymultiple-device harmonic oscillator(SCMDHO).By means of describing the functions ofnonlinearity of Gunn diodes,the performances of the SCMDHO are analyzed.It is foundthat the voltage amplitudes are similar to those of SDHO,and the ratio of maximum pow-er of harmonic to that of fundamental is identical to that in SDHO when the devices havesame parameters.The harmonic injection locking behavior is also investigated.The injec-tion locking range is greater than that of SDHO if locking gain remains constant.A2-Gunn diode harmonic oscillator was designed.It delivers 30mW output power at103GHz.The mechanical tuning range is 4.15GHz when the output power remains morethan 10mW.The desired operation mode is stable.
基金funded by ERC grant PISSARRO(ERC-2017-CoG 771647).
文摘Second-harmonic generation allows for coherently bridging distant regions of the optical spectrum,with applications ranging from laser technology to self-referencing of frequency combs.However,accessing the nonlinear response of a medium typically requires high-power bulk sources,specific nonlinear crystals,and complex optical setups,hindering the path toward large-scale integration.Here we address all of these issues by engineering a chip-scale second-harmonic(SH)source based on the frequency doubling of a semiconductor laser self-injection-locked to a silicon nitride microresonator.The injection-locking mechanism,combined with a high-Q microresonator,results in an ultra-narrow intrinsic linewidth at the fundamental harmonic frequency as small as 41 Hz.Owing to the extreme resonant field enhancement,quasi-phase-matched second-order nonlinearity is photoinduced through the coherent photogalvanic effect and the high coherence is mapped on the generated SH field.We show how such optical poling technique can be engineered to provide efficient SH generation across the whole C and L telecom bands,in a reconfigurable fashion,overcoming the need for poling electrodes.Our device operates with milliwatt-level pumping and outputs SH power exceeding 2 mW,for an efficiency as high as 280%/W under electrical driving.Our findings suggest that standalone,highly-coherent,and efficient SH sources can be integrated in current silicon nitride photonics,unlocking the potential of x(2)processes in the next generation of integrated photonic devices.
基金the National Basic Research Program China(973 Program)under grant no.2014CB247400.
文摘Reducing the converter loss,sub-module voltage ripple and handling DC short-circuit faults in high-voltage direct current systems are crucial for the economical and reliable operation of modular multilevel converters(MMCs).This study proposes a coordinated control method of power loss reduction and capacitor voltage balancing for AC voltage boosted full-bridge sub-module(FBSM)-MMC by controlling the second harmonic component in the circulating current.The relationship between converter loss and second harmonic circulating current(SHCC)is firstly derived for AC voltage boosted FBSM-MMC.From the analysis,it can be seen that the converter loss and ripple can be optimised by injecting the SHCC into the arm current when compared with SHCC elimination.Simulation results of an AC voltage boosted FBSM-MMC with typical parameters using PSCAD/EMTDC confirm the feasibility and validity of the proposed loss and ripple reduction method.
文摘Unvoiced/voiced classification of speech is a challenging problem especially under conditions of low signal-to-noise ratio or the non-white-stationary noise environment. To solve this problem, an algorithm for speech classification, and a technique for the estimation of palrwise magnitude frequency in voiced speech am proposed. By using third order spectrum of speech signal to remove noise, in this algorithm the least spectrum difference to get refined pitch and the max harmonic number is given. And this algorithm utilizes spectral envelope to estimate signal-to-noise ratio of speech harmonics. Speech classification, voicing probability, and harmonic parameters of the voiced frame can be obtained. Simulation results indicate that the proposed algorithm, under complicated background noise, especially Gaussian noise, can effectively classify speech in high accuracy for voicing probability and the voiced parameters.
基金supported by the Croucher Foundation(Croucher Innovation Award)the Research Grants Council(HKU17305914P,C7036-17W)
文摘We investigate two-photon transitions to the electron-hole scattering continuum in monolayer transition-metal dichalcogenides, and identify two contributions to this nonlinear optical process with opposite circularly polarized valley selection rules. In the non-interacting limit, the competition between the two contributions leads to a crossover of the selection rule with the increase of the two-photon energy. With the strong Coulomb interaction between the electron and hole, the two contributions excite electron-hole scattering states in orthogonal angular momentum channels, while the strength of the transition can be substantially enhanced by the interaction. Based on this picture of the two-photon transition, the second harmonic generation(SHG) in the electron-hole continuum is analyzed, where the Coulomb interaction is shown to greatly alter the relative strength of different cross-circular polarized SHG processes. Valley current injection by the quantum interference of one-photon and two-photon transition is also investigated in the presence of the strong Coulomb interaction, which significantly enhances the injection rate.
基金supported by the National "973" Program of China under Grant No. 2006CB302806
文摘A method to generate the optical quadruple frequency millimeter-wave with high power efficiency is pro- posed and demonstrated based on the combination of the injection 2nd-order rational harmonic mode- locked fiber ring laser technique and the fiber grating notch filter. In this approach, the fiber Bragg grating notch filter is inserted into the laser cavity to prevent the undesired optical carrier, so that the pump power can be converted to 2nd-order harmonic wave more efficiently. In our experiment, the power efficiency of optical quadruple frequency millimeter-wave (40 GHz) generation is ten folds of that of our previous method based only on the rational harmonic mode-locked technique.