通过对含静止无功补偿器(static var compensator,SVC)的单机无穷大(single machine infinite-bus,SIMB)系统进行电磁转矩计算,从理论上分析SVC的电压控制和阻尼调节之间的相互作用关系,既要保证同时为系统提供正的同步转矩和阻尼转矩,...通过对含静止无功补偿器(static var compensator,SVC)的单机无穷大(single machine infinite-bus,SIMB)系统进行电磁转矩计算,从理论上分析SVC的电压控制和阻尼调节之间的相互作用关系,既要保证同时为系统提供正的同步转矩和阻尼转矩,电压控制增益和阻尼控制增益的取值需满足一定的限制关系。通过对PSASP中36节点系统进行特征值分析,从广义阻尼的角度分析SVC控制参数对系统阻尼的影响。分析结果表明,电压控制增益和时间常数可改变系统的总阻尼,阻尼控制增益只能对系统的阻尼特性进行重新配置,从而改善系统的弱阻尼区间振荡模式。仿真验证了上述结论的有效性。展开更多
DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,b...DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,because the parasitic capacitances of the main equipment oscillate with the lumped inductances of the HVDC system,strong electromagnetic oscillations with multiple frequencies occur during clearance transients.These oscillations will disturb the HVDC system’s protection and control systems.Therefore,this paper focuses on the modeling of these oscillations.First,an equivalent circuit for the MMC-based HVDC system is proposed,taking into account the parasitic capacitances of the system’s major components,such as DC reactors,connecting cables,and DC circuit breakers(DCCBs).Second,four distinct oscillation stages are postulated based on action coordination of MMCs and DCCBs,and the associated analytical equations for the oscillation frequencies are derived.Third,a 200 kV MMC-based DC converter station is subjected to an 6ms/6kA pole-to-pole(PTP)short-circuit test.Electromagnetic oscillations have a frequency range of several kHz to several hundreds of kHz.The measured waveforms correspond well with simulated results,including the parasitic characteristics.Additionally,the relative errors between the simulated and measured frequencies are less than 5%.展开更多
The paper investigated the refinement effect on droplet size of Electroslag Remelting(ESR)Process by superimposing a transverse static magnetic field through physical simulation method.A transparent experimental model...The paper investigated the refinement effect on droplet size of Electroslag Remelting(ESR)Process by superimposing a transverse static magnetic field through physical simulation method.A transparent experimental model is built to visualize the ESR process under magnetic field,especially focusing on the formation and departure process of droplets on electrode tip.The results show that due to the interaction between alternating current and external transverse magnetic field,the resulting electromagnetic oscillation in the molten droplet and slag bath refined droplets remarkably, the higher the magnetic field intensity,the smaller the droplet size.However,there exists a suitable frequency of 10Hz for the current which will achieve an optimal effect of droplet's dispersing and refinement.Based on the theory of electromagnetic separation,a new mechanism of removing nonmetallic inclusions in ESR process is proposed.By a simplified circuit model,the inclusion removal efficiency is calculated and it proves that the refinement of droplets under magnetic field could increase the removal efficiency of nonmetallic inclusions in ESR significantly.展开更多
文摘通过对含静止无功补偿器(static var compensator,SVC)的单机无穷大(single machine infinite-bus,SIMB)系统进行电磁转矩计算,从理论上分析SVC的电压控制和阻尼调节之间的相互作用关系,既要保证同时为系统提供正的同步转矩和阻尼转矩,电压控制增益和阻尼控制增益的取值需满足一定的限制关系。通过对PSASP中36节点系统进行特征值分析,从广义阻尼的角度分析SVC控制参数对系统阻尼的影响。分析结果表明,电压控制增益和时间常数可改变系统的总阻尼,阻尼控制增益只能对系统的阻尼特性进行重新配置,从而改善系统的弱阻尼区间振荡模式。仿真验证了上述结论的有效性。
基金supported by the National Key Research and Development Program of China(2021YFB2400602)。
文摘DC short-circuit faults pose a hazard to the operation of a modular multilevel converter(MMC)-based high voltage direct current(HVDC)system,necessitating reliable fault clearing solutions with rapid reaction.However,because the parasitic capacitances of the main equipment oscillate with the lumped inductances of the HVDC system,strong electromagnetic oscillations with multiple frequencies occur during clearance transients.These oscillations will disturb the HVDC system’s protection and control systems.Therefore,this paper focuses on the modeling of these oscillations.First,an equivalent circuit for the MMC-based HVDC system is proposed,taking into account the parasitic capacitances of the system’s major components,such as DC reactors,connecting cables,and DC circuit breakers(DCCBs).Second,four distinct oscillation stages are postulated based on action coordination of MMCs and DCCBs,and the associated analytical equations for the oscillation frequencies are derived.Third,a 200 kV MMC-based DC converter station is subjected to an 6ms/6kA pole-to-pole(PTP)short-circuit test.Electromagnetic oscillations have a frequency range of several kHz to several hundreds of kHz.The measured waveforms correspond well with simulated results,including the parasitic characteristics.Additionally,the relative errors between the simulated and measured frequencies are less than 5%.
基金Item Sponsored by Ministry of Major Science and Technology of Shanghai[No.09dz1206401No.09dz1206402+1 种基金08DZ1130100]National High Technology Research and Development Program 863[2009AA03Z109]
文摘The paper investigated the refinement effect on droplet size of Electroslag Remelting(ESR)Process by superimposing a transverse static magnetic field through physical simulation method.A transparent experimental model is built to visualize the ESR process under magnetic field,especially focusing on the formation and departure process of droplets on electrode tip.The results show that due to the interaction between alternating current and external transverse magnetic field,the resulting electromagnetic oscillation in the molten droplet and slag bath refined droplets remarkably, the higher the magnetic field intensity,the smaller the droplet size.However,there exists a suitable frequency of 10Hz for the current which will achieve an optimal effect of droplet's dispersing and refinement.Based on the theory of electromagnetic separation,a new mechanism of removing nonmetallic inclusions in ESR process is proposed.By a simplified circuit model,the inclusion removal efficiency is calculated and it proves that the refinement of droplets under magnetic field could increase the removal efficiency of nonmetallic inclusions in ESR significantly.
