Current diffusion is an old issue, nevertheless, the relationship between the current diffusion and the efficiency of light emitting diodes(LEDs) needs to be further quantitatively clarified. By incorporating current ...Current diffusion is an old issue, nevertheless, the relationship between the current diffusion and the efficiency of light emitting diodes(LEDs) needs to be further quantitatively clarified. By incorporating current crowding effect(CCE) into the conventional ABC model, we have theoretically and directly correlated the current diffusion and the internal quantum efficiency(IQE), light extraction efficiency(LEE), and external quantum efficiency(EQE) droop of the lateral LEDs.However, questions still exist for the vertical LEDs(V-LEDs). Here firstly the current diffusion length L_s(I) and L_s(II) have been clarified. Based on this, the influence of CCE on the EQE, IQE, and LEE of V-LEDs were investigated. Specifically to our V-LEDs with moderate series resistivity, L_s(III) was developed by combining L_s(I) and L_s(II), and the CCE effect on the performance of V-LEDs was investigated. The wall-plug efficiency(WPE) of V-LEDs ware investigated finally. Our works provide a deep understanding of the current diffusion status and the correlated efficiency droop in V-LEDs, thus would benefit the V-LEDs' chip design and further efficiency improvement.展开更多
为了实现直驱式永磁风力发电系统安全稳定并网,提出一种基于双补偿下垂与多重准比例谐振(multiple quasi proportional resonance,MQPR)相结合的并网控制策略。该策略源于传统下垂控制,在电压控制环节引入直流电压补偿量,能快速调节直...为了实现直驱式永磁风力发电系统安全稳定并网,提出一种基于双补偿下垂与多重准比例谐振(multiple quasi proportional resonance,MQPR)相结合的并网控制策略。该策略源于传统下垂控制,在电压控制环节引入直流电压补偿量,能快速调节直流母线电压达到稳定;在电流控制环节引入电容电流补偿量,能有效减小滤波电容造成的电流误差影响;同时,设计出MQPR控制器替代内环电流的PI控制器,可以滤除系统中多次谐波电流。通过建立仿真模型,与双闭环PI和传统下垂控制策略进行对比,验证所提控制策略的有效性。展开更多
电压源型直流输电(voltage sourced converter-high voltage direct current,VSC-HVDC)具有控制灵活且易于在送受端扩展新落点等优点,有助于新能源的友好接入,因而在新能源基地的直流输电中具有广阔的应用前景。随着柔直送端电网新能源...电压源型直流输电(voltage sourced converter-high voltage direct current,VSC-HVDC)具有控制灵活且易于在送受端扩展新落点等优点,有助于新能源的友好接入,因而在新能源基地的直流输电中具有广阔的应用前景。随着柔直送端电网新能源占比不断增加,导致送端电网系统等效惯量持续降低、调频能力大幅减弱。针对高新能源渗透率的送端电网系统,利用VSC-HVDC对有功功率的独立与快速调节的特点,在传统的定有功功率控制中引入有功功率-频率(P-f)斜率特性,设计反下垂控制策略,使其参与送端交流系统的频率调节。并在PSCAD/EMTDC中搭建两端柔性直流输电电网模型进行仿真验证。结果表明,所提出的控制策略提高了送端系统的频率稳定性,具备一定的有效性与可行性。展开更多
基金Project supported by the National Key Research and Development Program of China(Grant No.2018YFB0406702)the Professorship Start-up Funding(Grant No.217056)+2 种基金the Innovation-Driven Project of Central South University,China(Grant No.2018CX001)the Project of State Key Laboratory of High-Performance Complex Manufacturing,Central South University,China(Grant No.ZZYJKT2018-01)Guangzhou Science&Technology Project of Guangdong Province,China(Grant Nos.201704030106 and 2016201604030035)
文摘Current diffusion is an old issue, nevertheless, the relationship between the current diffusion and the efficiency of light emitting diodes(LEDs) needs to be further quantitatively clarified. By incorporating current crowding effect(CCE) into the conventional ABC model, we have theoretically and directly correlated the current diffusion and the internal quantum efficiency(IQE), light extraction efficiency(LEE), and external quantum efficiency(EQE) droop of the lateral LEDs.However, questions still exist for the vertical LEDs(V-LEDs). Here firstly the current diffusion length L_s(I) and L_s(II) have been clarified. Based on this, the influence of CCE on the EQE, IQE, and LEE of V-LEDs were investigated. Specifically to our V-LEDs with moderate series resistivity, L_s(III) was developed by combining L_s(I) and L_s(II), and the CCE effect on the performance of V-LEDs was investigated. The wall-plug efficiency(WPE) of V-LEDs ware investigated finally. Our works provide a deep understanding of the current diffusion status and the correlated efficiency droop in V-LEDs, thus would benefit the V-LEDs' chip design and further efficiency improvement.
文摘为了实现直驱式永磁风力发电系统安全稳定并网,提出一种基于双补偿下垂与多重准比例谐振(multiple quasi proportional resonance,MQPR)相结合的并网控制策略。该策略源于传统下垂控制,在电压控制环节引入直流电压补偿量,能快速调节直流母线电压达到稳定;在电流控制环节引入电容电流补偿量,能有效减小滤波电容造成的电流误差影响;同时,设计出MQPR控制器替代内环电流的PI控制器,可以滤除系统中多次谐波电流。通过建立仿真模型,与双闭环PI和传统下垂控制策略进行对比,验证所提控制策略的有效性。
文摘电压源型直流输电(voltage sourced converter-high voltage direct current,VSC-HVDC)具有控制灵活且易于在送受端扩展新落点等优点,有助于新能源的友好接入,因而在新能源基地的直流输电中具有广阔的应用前景。随着柔直送端电网新能源占比不断增加,导致送端电网系统等效惯量持续降低、调频能力大幅减弱。针对高新能源渗透率的送端电网系统,利用VSC-HVDC对有功功率的独立与快速调节的特点,在传统的定有功功率控制中引入有功功率-频率(P-f)斜率特性,设计反下垂控制策略,使其参与送端交流系统的频率调节。并在PSCAD/EMTDC中搭建两端柔性直流输电电网模型进行仿真验证。结果表明,所提出的控制策略提高了送端系统的频率稳定性,具备一定的有效性与可行性。
