In wind power transmission via modular multilevel converter based high voltage direct current(MMCHVDC)systems,under traditional control strategies,MMC-HVDCcannot provide inertia support to the receiving-end grid(REG)d...In wind power transmission via modular multilevel converter based high voltage direct current(MMCHVDC)systems,under traditional control strategies,MMC-HVDCcannot provide inertia support to the receiving-end grid(REG)during disturbances.Moreover,due to the frequency decoupling between the two ends of the MMCHVDC,the sending-end wind farm(SEWF)cannot obtain the frequency variation information of the REG to provide inertia response.Therefore,this paper proposes a novel coordinated source-network-storage inertia control strategy based on wind power transmission via MMC-HVDC system.First,the grid-side MMC station(GS-MMC)maps the frequency variations of the REG to direct current(DC)voltage variations through the frequency mapping control,and uses submodule capacitor energy to provide inertial power.Then,the wind farm-side MMC station(WF-MMC)restores the DC voltage variations to frequency variations through the frequency restoration control and power loss compensation,providing real-time frequency information for the wind farm.Finally,based on real-time frequency information,thewind farmutilizes the rotor kinetic energy and energy storage to provide fast and lasting power support through the wind-storage coordinated inertia control strategy.Meanwhile,when the wind turbines withdraw from the inertia response phase,the energy storage can increase the power output to compensate for the power deficit,preventing secondary frequency drops.Furthermore,this paper uses small-signal analysis to determine the appropriate values for the key parameters of the proposed control strategy.A simulation model of the wind power transmission via MMCHVDC system is built in MATLAB/Simulink environment to validate and evaluate the proposed method.The results show that the proposed coordinated control strategy can effectively improve the system inertia level and avoid the secondary frequency drop under the load sudden increase condition.展开更多
Aiming at solving the problem of missed detection and low accuracy in detecting traffic signs in the wild, an improved method of YOLOv8 is proposed. Firstly, combined with the characteristics of small target objects i...Aiming at solving the problem of missed detection and low accuracy in detecting traffic signs in the wild, an improved method of YOLOv8 is proposed. Firstly, combined with the characteristics of small target objects in the actual scene, this paper further adds blur and noise operation. Then, the asymptotic feature pyramid network (AFPN) is introduced to highlight the influence of key layer features after feature fusion, and simultaneously solve the direct interaction of non-adjacent layers. Experimental results on the TT100K dataset show that compared with the YOLOv8, the detection accuracy and recall are higher. .展开更多
Two-dimensional(2D)transition metal dichalcogenides(TMDCs),due to their unique physical properties,have a wide range of applications in the next generation of electronics,optoelectronics,and valleytronics.Large-scale ...Two-dimensional(2D)transition metal dichalcogenides(TMDCs),due to their unique physical properties,have a wide range of applications in the next generation of electronics,optoelectronics,and valleytronics.Large-scale preparation of high-quality TMDCs films is critical to realize these potential applications.Here we report a study on metal-organic chemical vapor deposition(MOCVD)growth of wafer-scale MoSe_(2)films guided by the crystalline step edges of miscut sapphire wafers.We established that the nucleation density and growth rate of MoSe_(2)films were positively correlated with the step-edge density and negatively with the growth temperature.At a certain temperature,the MoSe_(2)domains on the substrate with high step-edge density grow faster than that with low density.As a result,wafer-scale and continuous MoSe_(2)films can be formed in a short duration(30 min).The MoSe_(2)films are of high crystalline quality,as confirmed by systematic Raman and photoluminescence(PL)measurements.The results provide an important methodology for the rapid growth of wafer-scale TMDCs,which may promote the application of 2D semiconductors.展开更多
基金funded by State Grid Corporation of China Central Branch Technology Project(52140024000C).
文摘In wind power transmission via modular multilevel converter based high voltage direct current(MMCHVDC)systems,under traditional control strategies,MMC-HVDCcannot provide inertia support to the receiving-end grid(REG)during disturbances.Moreover,due to the frequency decoupling between the two ends of the MMCHVDC,the sending-end wind farm(SEWF)cannot obtain the frequency variation information of the REG to provide inertia response.Therefore,this paper proposes a novel coordinated source-network-storage inertia control strategy based on wind power transmission via MMC-HVDC system.First,the grid-side MMC station(GS-MMC)maps the frequency variations of the REG to direct current(DC)voltage variations through the frequency mapping control,and uses submodule capacitor energy to provide inertial power.Then,the wind farm-side MMC station(WF-MMC)restores the DC voltage variations to frequency variations through the frequency restoration control and power loss compensation,providing real-time frequency information for the wind farm.Finally,based on real-time frequency information,thewind farmutilizes the rotor kinetic energy and energy storage to provide fast and lasting power support through the wind-storage coordinated inertia control strategy.Meanwhile,when the wind turbines withdraw from the inertia response phase,the energy storage can increase the power output to compensate for the power deficit,preventing secondary frequency drops.Furthermore,this paper uses small-signal analysis to determine the appropriate values for the key parameters of the proposed control strategy.A simulation model of the wind power transmission via MMCHVDC system is built in MATLAB/Simulink environment to validate and evaluate the proposed method.The results show that the proposed coordinated control strategy can effectively improve the system inertia level and avoid the secondary frequency drop under the load sudden increase condition.
文摘Aiming at solving the problem of missed detection and low accuracy in detecting traffic signs in the wild, an improved method of YOLOv8 is proposed. Firstly, combined with the characteristics of small target objects in the actual scene, this paper further adds blur and noise operation. Then, the asymptotic feature pyramid network (AFPN) is introduced to highlight the influence of key layer features after feature fusion, and simultaneously solve the direct interaction of non-adjacent layers. Experimental results on the TT100K dataset show that compared with the YOLOv8, the detection accuracy and recall are higher. .
基金This work was supported by the National Key Research and Development Project(Nos.2018YFA0305800,2019YFB2205402,and 2022YFA1404201)the National Natural Science Foundation of China(Nos.51772145,62222509,and U22A2091)the Technology Innovation Fund of Nanjing University。
文摘Two-dimensional(2D)transition metal dichalcogenides(TMDCs),due to their unique physical properties,have a wide range of applications in the next generation of electronics,optoelectronics,and valleytronics.Large-scale preparation of high-quality TMDCs films is critical to realize these potential applications.Here we report a study on metal-organic chemical vapor deposition(MOCVD)growth of wafer-scale MoSe_(2)films guided by the crystalline step edges of miscut sapphire wafers.We established that the nucleation density and growth rate of MoSe_(2)films were positively correlated with the step-edge density and negatively with the growth temperature.At a certain temperature,the MoSe_(2)domains on the substrate with high step-edge density grow faster than that with low density.As a result,wafer-scale and continuous MoSe_(2)films can be formed in a short duration(30 min).The MoSe_(2)films are of high crystalline quality,as confirmed by systematic Raman and photoluminescence(PL)measurements.The results provide an important methodology for the rapid growth of wafer-scale TMDCs,which may promote the application of 2D semiconductors.
