In this work it is shown that the kinetic energy and the exchange-correlation energy are mutual dependent on each other.This aspect is first derived in an orbital-free context.It is shown that the total Fermi potentia...In this work it is shown that the kinetic energy and the exchange-correlation energy are mutual dependent on each other.This aspect is first derived in an orbital-free context.It is shown that the total Fermi potential depends on the density only,the individual parts,the Pauli kinetic energy and the exchange-correlation energy,however,are orbital dependent and as such mutually influence each other.The numerical investigation is performed for the orbital-based non-interacting Kohn-Sham system in order to avoid additional effects due to further approximations of the kinetic energy.The numerical influence of the exchange-correlation functional on the non-interacting kinetic energy is shown to be of the orderof a few Hartrees.For chemical purposes,however,the energetic performance as a function of the nuclear coordinates is much more important than total energies.Therefore,the effect on the bond dissociation curve was studied exemplarily for the carbon monoxide.The data reveals that,the mutual influence between the exchange-correlation functional and the kinetic energy has a significant influence on bond dissociation energies and bond distances.Therefore,the effect of the exchange-correlation treatment must be considered in the design of orbital-free density functional approximations for the kinetic energy.展开更多
基频调制主动换相型电流源换流器(fundamental frequency modulation-based current source converter,FFM-CSC)无需子模块电容,且不需要大量无功补偿装置和滤波器组,有望成为远海风电直流送出的更优选择。然而现有FFM-CSC远海风电送出...基频调制主动换相型电流源换流器(fundamental frequency modulation-based current source converter,FFM-CSC)无需子模块电容,且不需要大量无功补偿装置和滤波器组,有望成为远海风电直流送出的更优选择。然而现有FFM-CSC远海风电送出方案存在以下不足:1)海上汇集频率为工频,轻型化效果有限;2)集中送出时,一旦海上汇集系统发生故障,交流电压无法建立;3)电流源换流器(current source converter,CSC)与风电机组协同控制交流电压需要大量通信。对此,提出一种基于FFM-CSC的中频分布式远海风电直流输电系统,介绍其拓扑结构和数学模型;接着,提出了无需通信的海上CSC与风电场群协调控制交流电压策略;同时,针对风电场群风速不同造成的直流过电压问题提出双端直流电压协同控制;针对海上汇集系统故障提出一种双端CSC协同旁通与风机耗能装置相配合的故障穿越策略;最后,在PSCAD中对方案进行仿真验证,结果验证了基于FFM-CSC的中频分布式远海风电直流输电系统及其控制策略的有效性。展开更多
基金The project was supported by the Fund for Scientific Research in Flanders (FWO-Vlaanderen) for Research Grant G021115N.
文摘In this work it is shown that the kinetic energy and the exchange-correlation energy are mutual dependent on each other.This aspect is first derived in an orbital-free context.It is shown that the total Fermi potential depends on the density only,the individual parts,the Pauli kinetic energy and the exchange-correlation energy,however,are orbital dependent and as such mutually influence each other.The numerical investigation is performed for the orbital-based non-interacting Kohn-Sham system in order to avoid additional effects due to further approximations of the kinetic energy.The numerical influence of the exchange-correlation functional on the non-interacting kinetic energy is shown to be of the orderof a few Hartrees.For chemical purposes,however,the energetic performance as a function of the nuclear coordinates is much more important than total energies.Therefore,the effect on the bond dissociation curve was studied exemplarily for the carbon monoxide.The data reveals that,the mutual influence between the exchange-correlation functional and the kinetic energy has a significant influence on bond dissociation energies and bond distances.Therefore,the effect of the exchange-correlation treatment must be considered in the design of orbital-free density functional approximations for the kinetic energy.
文摘基频调制主动换相型电流源换流器(fundamental frequency modulation-based current source converter,FFM-CSC)无需子模块电容,且不需要大量无功补偿装置和滤波器组,有望成为远海风电直流送出的更优选择。然而现有FFM-CSC远海风电送出方案存在以下不足:1)海上汇集频率为工频,轻型化效果有限;2)集中送出时,一旦海上汇集系统发生故障,交流电压无法建立;3)电流源换流器(current source converter,CSC)与风电机组协同控制交流电压需要大量通信。对此,提出一种基于FFM-CSC的中频分布式远海风电直流输电系统,介绍其拓扑结构和数学模型;接着,提出了无需通信的海上CSC与风电场群协调控制交流电压策略;同时,针对风电场群风速不同造成的直流过电压问题提出双端直流电压协同控制;针对海上汇集系统故障提出一种双端CSC协同旁通与风机耗能装置相配合的故障穿越策略;最后,在PSCAD中对方案进行仿真验证,结果验证了基于FFM-CSC的中频分布式远海风电直流输电系统及其控制策略的有效性。
