Pulse-width modulation(PWM)sprays can improve flow accuracy by adjusting duty cycle and frequency signal which accurately controls the relative proportion of opening time of solenoid valve.The objective of this resear...Pulse-width modulation(PWM)sprays can improve flow accuracy by adjusting duty cycle and frequency signal which accurately controls the relative proportion of opening time of solenoid valve.The objective of this research was to determine the impacts of PWM duty cycle and frequency on spray drift characteristic.Spray tests were conducted in a wind tunnel with a PWM variable-rate spraying system.The airborne drift and sediment drift were determined with tracer method,and the drift potential reduction(DPR)compared with reference condition of 100%duty cycle at vertical profile and horizontal planes were calculated,respectively.The results show that,at a given frequency,droplet size decreases with the increase of duty cycle,the main reason is that the liquid does not reach full pattern development at lower duty cycle.Duty cycle has a greater impact than the frequency on spray drift,the influence weights of duty cycle on airborne drift and sediment drift were 88.32%and 77.89%,respectively.At a lower PWM frequency,in addition to the droplet size,the spray drift may be affected by the pulsed spray pattern.From the perspective of reducing spray drift,it is recommended that the PWM duty cycle should be set in the range of 20%-70%to reduce the potential drift in PWM sprays.This research provides a pesticide drift reduction scheme for variable spraying technology,which can serve as a theoretical basis for PWM parameter selection.展开更多
To realize the continuous production of hydrogen energy,the efficient photocatalysts are required in the heterogeneous reaction for water splitting.Herein,we reported a surface modulation strategy,via doping oxygen at...To realize the continuous production of hydrogen energy,the efficient photocatalysts are required in the heterogeneous reaction for water splitting.Herein,we reported a surface modulation strategy,via doping oxygen atoms to tune the surface state of ZnIn_(2)S_(4)nanosheets with cocatalyst MoS_(2)modification,to enhance water adsorption and surface catalytic reaction for boosting the photocatalytic activity.Consequently,MoS_(2)/O-ZnIn_(2)S_(4)photocatalysts showed a remarkably superior photocatalytic H_(2)production performance of 4.002 mmol g^(-1)h^(-1)and an apparent quantum yield(AQY)of~2.53%,5.4 folds higher than ZnIn_(2)S_(4).Using operando infrared spectroscopy and DFT calculation,we revealed the dynamic structural evolution,as well as the active sites for water adsorption and the catalytic reaction at the MoS_(2)/O ZnIn_(2)S_(4)interface.This work reveals the effect of surface modulation on the photocatalytic activity for MoS_(2)/O-ZnIn_(2)S_(4)and offers a feasible method to devise excellent nanomaterial photocatalysts for H_(2)production.展开更多
三相并网逆变器在新能源发电系统和电动汽车等领域起着重要的作用,为确保系统安全稳定运行,孤岛检测是十分必要的。对基于空间矢量控制的三相并网逆变器,传统的主动频移法(active frequency drift,AFD)不能直接应用,存在检测盲区的问题...三相并网逆变器在新能源发电系统和电动汽车等领域起着重要的作用,为确保系统安全稳定运行,孤岛检测是十分必要的。对基于空间矢量控制的三相并网逆变器,传统的主动频移法(active frequency drift,AFD)不能直接应用,存在检测盲区的问题,且施加的频率扰动量会对三相进网电流波形质量造成一定的影响。提出一种基于空间矢量脉宽调制(space vector pulse width modulation,SVPWM)控制三相并网逆变器的AFD孤岛检测方法,其对锁相环(phase-locked loop,PLL)计算出的相角施加扰动,但不属于主动移相法。分析孤岛检测盲区的成因以及消除盲区的可能性,并对施加扰动后的三相电流进行谐波分析,提出抑制谐波的改进半解耦控制算法,最后给出仿真和实验结果。展开更多
基金The authors acknowledge that this research was financially supported by National Key R&D Program of China(2019YFD1101102-3)National Natural Science Foundation of China(32071907)+1 种基金Outstanding Scientist Cultivation Project of Beijing Academy of Agriculture and Forestry Sciences(JKZX202205)Qingyuan Smart Agriculture Research Institute+New R&D Institutions Construction in North and West Guangdong(2019B090905006).
文摘Pulse-width modulation(PWM)sprays can improve flow accuracy by adjusting duty cycle and frequency signal which accurately controls the relative proportion of opening time of solenoid valve.The objective of this research was to determine the impacts of PWM duty cycle and frequency on spray drift characteristic.Spray tests were conducted in a wind tunnel with a PWM variable-rate spraying system.The airborne drift and sediment drift were determined with tracer method,and the drift potential reduction(DPR)compared with reference condition of 100%duty cycle at vertical profile and horizontal planes were calculated,respectively.The results show that,at a given frequency,droplet size decreases with the increase of duty cycle,the main reason is that the liquid does not reach full pattern development at lower duty cycle.Duty cycle has a greater impact than the frequency on spray drift,the influence weights of duty cycle on airborne drift and sediment drift were 88.32%and 77.89%,respectively.At a lower PWM frequency,in addition to the droplet size,the spray drift may be affected by the pulsed spray pattern.From the perspective of reducing spray drift,it is recommended that the PWM duty cycle should be set in the range of 20%-70%to reduce the potential drift in PWM sprays.This research provides a pesticide drift reduction scheme for variable spraying technology,which can serve as a theoretical basis for PWM parameter selection.
基金supported by the National Natural Science Foundation of China(22005164)the Natural Science Foundation of Shandong Province(BS2015CL002)the Basic Research Project of Qingdao Source Innovation Program Fund(17-1-1-82-jch)。
文摘To realize the continuous production of hydrogen energy,the efficient photocatalysts are required in the heterogeneous reaction for water splitting.Herein,we reported a surface modulation strategy,via doping oxygen atoms to tune the surface state of ZnIn_(2)S_(4)nanosheets with cocatalyst MoS_(2)modification,to enhance water adsorption and surface catalytic reaction for boosting the photocatalytic activity.Consequently,MoS_(2)/O-ZnIn_(2)S_(4)photocatalysts showed a remarkably superior photocatalytic H_(2)production performance of 4.002 mmol g^(-1)h^(-1)and an apparent quantum yield(AQY)of~2.53%,5.4 folds higher than ZnIn_(2)S_(4).Using operando infrared spectroscopy and DFT calculation,we revealed the dynamic structural evolution,as well as the active sites for water adsorption and the catalytic reaction at the MoS_(2)/O ZnIn_(2)S_(4)interface.This work reveals the effect of surface modulation on the photocatalytic activity for MoS_(2)/O-ZnIn_(2)S_(4)and offers a feasible method to devise excellent nanomaterial photocatalysts for H_(2)production.
