全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的...全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。展开更多
Interplanetary shocks or solar wind pressure pulses have prompted impacts on Earth's magnetospheric and ionospheric environment, especially in causing dynamic changes to the bright aurora in the polar ionosphere. ...Interplanetary shocks or solar wind pressure pulses have prompted impacts on Earth's magnetospheric and ionospheric environment, especially in causing dynamic changes to the bright aurora in the polar ionosphere. The auroral phenomenon associated with shock impingements, referred to as shock aurora, exhibits distinct signatures differing from other geophysical features on the dayside polar ionosphere. Shock aurora provides a direct manifestation of the solar wind–magnetosphere–ionosphere interaction. Imagers onboard satellites can obtain the associated large-scale auroral characteristics during shock impingement on the magnetopause. Therefore, auroral data from satellites are very useful for surveying the comprehensive features of shock aurora and their general evolution. Nonetheless, the ground-based high temporal-spatial resolution all-sky imagers installed at scientific stations play an essential role in revealing medium-and small-scale characteristics of shock aurora. Here, we focus on shock aurora imaging signatures measured by imagers onboard satellites and ground-based all-sky imagers.展开更多
采煤机四象限变频牵引工作于并网回馈状态时,易出现失控现象。通过建立变流器动态向量模型,确定一种新型电能缓冲变流器拓扑,研制40 k W/380 V变频牵引系统样机,搭建了四象限变频机组拖动平台,通过仿真分析及实物波形验证其可行性。结...采煤机四象限变频牵引工作于并网回馈状态时,易出现失控现象。通过建立变流器动态向量模型,确定一种新型电能缓冲变流器拓扑,研制40 k W/380 V变频牵引系统样机,搭建了四象限变频机组拖动平台,通过仿真分析及实物波形验证其可行性。结果表明:该研究有效抑制变频牵引系统并网制动失控。该研究为变频器实际应用设计提供有力的理论依据。展开更多
Hugoniot relations of a two-dimensional axial shock with current and magnetic field in a cylindrical shock tube were investigated by a numerical method. The radial profiles of the magnetic field, electric current, pre...Hugoniot relations of a two-dimensional axial shock with current and magnetic field in a cylindrical shock tube were investigated by a numerical method. The radial profiles of the magnetic field, electric current, pressures, flow velocities and temperatures between the up- and down-stream radial force-balanced plasma of the shock were revealed by numerical analysis. It is clearly found that the axial shock can lead to two effects： one is an inverse skin effect （i.e., the current density rises towards the center of the conductor）, the another is a reversed current effect which occurs near the edge and about a half radius. It is also found that the radial gradient of pressure, density and temperature all become very large near the center due to the axial shock.展开更多
在传统施工过程中对岩石的破碎一般使用炸药或机械胀裂的方式,但炸药使用的不可控性和危险性,使其在工程中的使用频率逐渐降低,机械结构设备存在碎岩过程效率低,机械结构易磨损等缺点,电爆等离子脉冲碎岩的原理是高压强电场通过液体时...在传统施工过程中对岩石的破碎一般使用炸药或机械胀裂的方式,但炸药使用的不可控性和危险性,使其在工程中的使用频率逐渐降低,机械结构设备存在碎岩过程效率低,机械结构易磨损等缺点,电爆等离子脉冲碎岩的原理是高压强电场通过液体时会在液体电介质中产生等离子体通道,通道中的液体迅速汽化、膨胀,迅速膨胀的气腔在水介质中产生强大的冲击波,随着放电电流和放电时间的不同,冲击波以冲量或者冲击压力的方式作用于周围介质,可实现诸多工程应用。本文采用高压脉冲电源,放电效果仿真雷击过程10/350波形,具有较好的瞬间冲击能量。高压脉冲电源的最高放电电压为40 k V,在岩石预钻孔中充满液体电介质,将电极置于其中并采用电爆丝引弧,在高压放电过程中释放高能等离子体,液体电介质产生的冲击力能够破碎岩石。本文采用室内实验的方法对混凝土、花岗岩、玄武岩进行了成功爆破,验证了高压电爆等离子体脉冲碎岩技术的可行性。展开更多
文摘全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。
基金supported by the NSFC (Grant nos. 41431072, 41674169, 41474146, and 41831072)the International Collaboration Supporting Project by the Chinese Arctic and Antarctic Administration (Grant no. IC201608)+1 种基金the National Key R&D Program of China (Grant no. 2018YFC1407304)the Chinese Meridian Project
文摘Interplanetary shocks or solar wind pressure pulses have prompted impacts on Earth's magnetospheric and ionospheric environment, especially in causing dynamic changes to the bright aurora in the polar ionosphere. The auroral phenomenon associated with shock impingements, referred to as shock aurora, exhibits distinct signatures differing from other geophysical features on the dayside polar ionosphere. Shock aurora provides a direct manifestation of the solar wind–magnetosphere–ionosphere interaction. Imagers onboard satellites can obtain the associated large-scale auroral characteristics during shock impingement on the magnetopause. Therefore, auroral data from satellites are very useful for surveying the comprehensive features of shock aurora and their general evolution. Nonetheless, the ground-based high temporal-spatial resolution all-sky imagers installed at scientific stations play an essential role in revealing medium-and small-scale characteristics of shock aurora. Here, we focus on shock aurora imaging signatures measured by imagers onboard satellites and ground-based all-sky imagers.
文摘采煤机四象限变频牵引工作于并网回馈状态时,易出现失控现象。通过建立变流器动态向量模型,确定一种新型电能缓冲变流器拓扑,研制40 k W/380 V变频牵引系统样机,搭建了四象限变频机组拖动平台,通过仿真分析及实物波形验证其可行性。结果表明:该研究有效抑制变频牵引系统并网制动失控。该研究为变频器实际应用设计提供有力的理论依据。
基金supported by National Natural Science Foundation of China (No. 10175025)in part by the JSPS-CAS Core-University Program on Plasma and Nuclear Fusion
文摘Hugoniot relations of a two-dimensional axial shock with current and magnetic field in a cylindrical shock tube were investigated by a numerical method. The radial profiles of the magnetic field, electric current, pressures, flow velocities and temperatures between the up- and down-stream radial force-balanced plasma of the shock were revealed by numerical analysis. It is clearly found that the axial shock can lead to two effects： one is an inverse skin effect （i.e., the current density rises towards the center of the conductor）, the another is a reversed current effect which occurs near the edge and about a half radius. It is also found that the radial gradient of pressure, density and temperature all become very large near the center due to the axial shock.
文摘在传统施工过程中对岩石的破碎一般使用炸药或机械胀裂的方式,但炸药使用的不可控性和危险性,使其在工程中的使用频率逐渐降低,机械结构设备存在碎岩过程效率低,机械结构易磨损等缺点,电爆等离子脉冲碎岩的原理是高压强电场通过液体时会在液体电介质中产生等离子体通道,通道中的液体迅速汽化、膨胀,迅速膨胀的气腔在水介质中产生强大的冲击波,随着放电电流和放电时间的不同,冲击波以冲量或者冲击压力的方式作用于周围介质,可实现诸多工程应用。本文采用高压脉冲电源,放电效果仿真雷击过程10/350波形,具有较好的瞬间冲击能量。高压脉冲电源的最高放电电压为40 k V,在岩石预钻孔中充满液体电介质,将电极置于其中并采用电爆丝引弧,在高压放电过程中释放高能等离子体,液体电介质产生的冲击力能够破碎岩石。本文采用室内实验的方法对混凝土、花岗岩、玄武岩进行了成功爆破,验证了高压电爆等离子体脉冲碎岩技术的可行性。
