Power-Sharing Enhancement Using Harmonized Membership Fuzzy Logic Droop Control Based Micro-Grid

The contribution of Renewable Energy Resources(RER)in the process of power generation is significantly high in the recent days since it paves the way for overcoming the issues like serious energy crisis and natural contamination.This paper deals with the renewable energy based micro-grid as it is regarded as the apt solution for integrating the RER with the electrical frameworks.As thefixed droop coefficients in conventional droop control approaches have caused various limitations like low power-sharing and sudden drops of grid voltage in the Direct Current(DC)side,the Harmonized Membership Fuzzy Logic(MFL)droop control is employed in this present study.This proposed droop control for the hybrid PV-wind-battery system with MFL assists in achieving proper power-sharing and minimizing Total Harmonic Distortion(THD)in the emer-gency micro-grid.It eradicates the deviations in voltage and frequency with itsflexible and robust operation.The THD is reduced and attains the value of 3.1%compared to the traditional droop control.The simulation results of harmo-nized MFL droop control are analogized with the conventional approaches to vali-date the performance of the proposed method.In addition,the experimental results provided by the Field Programmable Gate Array(FPGA)based laboratory setup built using a solar photovoltaic(PV)and wind Permanent Magnet Synchro-nous Generator(PMSG)reaffirms the design.

DROOP法实现CPU负载电压调节的设计

本文通过对输出电感DCR电流信号采样、运算,采用Droop法调节计算机处理器负载电压。经测试证明该方法满足1毫欧负载线斜率的设计要求。

高性能CPU电源Droop检测优化设计实现

高性能中央处理器(CPU)进入到纳米工艺设计时代,集成度和性能大幅度提高的同时,功耗和时钟之间的平衡优化已经成为当前面临的主要问题。物理供电寄生阻抗增加明显,功耗急速增加过程导致电源网络动态压降明显,抑制了主频进一步提高。本文提出了一种基于全数字快速高精度Droop Sensor的供电监测优化方法。该方法采用易于集成于处理器核数字域内的单数字供电Droop Sensor进行本地供电实时监测。当Droop Sensor检测到电压快速垂降时,实时指导所在处理器核的时钟域进行时钟降频,帮助处理器度过低压危险时期,待垂降结束后再恢复正常的时钟频率。实现了局部压降的针对性时钟优化,避免了整体功耗性能损失。本文采用12 nm数字工艺实现了Droop Sensor设计。仿真结果表明,该传感器可在100 ps内进行一阶Droop的快速响应,帮助CPU度过瞬间大幅度的压降期;高阶Droop响应的阈值调节精度可达3%,支持CPU的供电水平多阈值控制。

Temperature-dependent efficiency droop behaviors of GaN-based green light-emitting diodes

The efficiency droop behaviors of GaN-based green light-emitting diodes （LEDs） are studied as a function of temperature from 300 K to 480 K. The overall quantum efficiency of the green LEDs is found to degrade as temperature increases, which is mainly caused by activation of new non-radiative recombination centers within the LED active layer. Meanwhile, the external quantum efficiency of the green LEDs starts to decrease at low injection current level （1 A/cm2 ） with a temperature-insensitive peak-efficiency-current. In contrast, the peak-efficiency-current of a control GaN-based blue LED shows continuous up-shift at higher temperatures. Around the onset point of efficiency droop, the electroluminescence spectra of the green LEDs also exhibit a monotonic blue-shift of peak energy and a reduction of full width at half maximum as injection current increases. Carrier delocalization is believed to play an important role in causing the efficiency droop in GaN-based green LEDs.

Robust Controller Synthesis and Analysis in Inverter-Dominant Droop-Controlled Islanded Microgrids

This work investigates the problem of controller design for the inverters in an islanded microgrid.Robust-synthesis controllers and local droop controllers are designed to regulate the output voltages of inverters and share power among them,respectively.The designed controllers alleviate the need for additional sensors to measure the states of the system by relying only on output feedback.It is shown that the designed-synthesis controller properly damps resonant oscillations,and its performance is robust to the control-loop time delay and parameter uncertainties.The stability of a droop-controlled islanded microgrid including multiple distributed generation(DG)units is analyzed by linearizing the nonlinear power flow model around the nominal operating point and applying theorems from linear algebra.It is indicated that the droop controller stabilizes the microgrid system with dominantly inductive tie-line impedances for all values of resistive-inductive loads,while for the case of resistive-capacitive loads the stability is conditioned on an upper bound on the load susceptances.The robust performance of the designed-synthesis controller is studied analytically,compared with the similar analysis in an control(benchmark)framework,and verified by simulations for a four DG benchmark microgrid.Furthermore,the robustness of the droop controllers is analyzed by Monte Carlo simulations in the presence of local voltage fluctuations and phase differences among neighboring DGs.

An Integrated Control Strategy Adopting Droop Control with Virtual Inductance in Microgrid

As there exists sorts of distributed generators in microgrid, an integrated control strategy containing different control methods against corresponding generators should be applied. The strategy in this paper involves PQ control and droop control methods. The former aims at letting generators like PV output maximum power. The latter stems from inverter parallel technique and applies to controlling generators which can keep the network voltage steady to make the parallel system reach the minimum circulation point. Due to the unworthiness of droop control applied in low-voltage microgrid of which the impedance ratio is rather high, the paper adopts the droop control introducing virtual generator and virtual impedance. Based on theoretical analysis, simulation in Matlab is also implemented to verify the feasibility of the strategy.

Efficiency droop suppression in GaN-based light-emitting diodes by chirped multiple quantum well structure at high current injection

Gallium nitride （GaN） based light-emitting diodes （LEDs） with chirped multiple quantum well （MQW） structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs with uniform quantum wells （QWs）, LEDs with chirped MQW structures have better internal quantum efficiency （IQE） and carrier injection efficiency. The droop ratios of LEDs with chirped MQW structures show a remarkable improvement at 600 mA/mm2, reduced down from 28.6% （conventional uniform LEDs） to 23.7% （chirped MQWs-a） and 18.6% （chirped MQWs-b）, respectively. Meanwhile, the peak IQE increases from 76.9% （uniform LEDs） to 83.7% （chirped MQWs-a） and 88.6% （chirped MQWs-b）. The reservoir effect of chirped MQW structures is the significant reason as it could increase hole injection efficiency and radiative recombination. The leakage current and Auger recombination of chirped MQW structures can also be suppressed. Furthermore, the chirped MQWs-b structure with lower potential barriers can enhance the reservoir effect and obtain further improvement of the carrier injection efficiency and radiative recombination, as well as further suppressing efficiency droop.

Efficiency droop alleviation in blue light emitting diodes using the InGaN/GaN triangular-shaped quantum well

The InGaN/GaN blue light emitting diode（LED） is numerically investigated using a triangular-shaped quantum well model,which involves analysis on its energy band,carrier concentration,overlap of electron and hole wave functions,radiative recombination rate,and internal quantum efficiency.The simulation results reveal that the InGaN/GaN blue light emitting diode with triangular quantum wells exhibits a higher radiative recombination rate than the conventional light emitting diode with rectangular quantum wells due to the enhanced overlap of electron and hole wave functions（above 90%） under the polarization field.Consequently,the efficiency droop is only 18% in the light emitting diode with triangular-shaped quantum wells,which is three times lower than that in a conventional LED.

Research on Aerodynamic Characteristics of Hovering Rotor Based on Leading Edge Droop

In view of the reduction of hovering efficiency near high tension when a helicopter rotor hovers,a numerical simulation method of lifting rotor hovering aerodynamic characteristics based on leading edge droop is established in this paper. It is dominated by Reynolds average N-S equation in integral form. Firstly,VR-12 airfoil is taken as the research object,and the influence of leading edge droop angle on the aerodynamic characteristics of two-dimensional airfoil is studied. Secondly,the modified 7 A rotor is taken as the research object,and the effects of different leading edge droop angles at the position of blade r/R=0.75—1 on the aerodynamic characteristics in hover are explored. It is found that the leading edge droop can significantly improve the aerodynamic characteristics of two-dimensional airfoil and three-dimensional hovering rotor near high angle of attack,and can effectively inhibit the generation of stall vortex.

大型连退线传动系统DROOP功能的应用

介绍了马钢(合肥)公司冷轧连退线传动系统中DROOP功能的应用,并对传动系统应用的效果进行了分析。冷轧连续退火线是对冷轧薄板的热处理过程,在同一个张力段内,带钢缠绕在不同的辊道上,因此要求辊道转速既能跟随给定速度,又要输出一定的负荷均衡能力,也就是说要求调速系统的外特性适度下垂,因此采用DROOP功能,适当引入从转速调节器输出到输入的负反馈,进而当同一张力段内多台变频器共同驱动时,使电机速度下垂,最终达到负荷平衡。

Current diffusion and efficiency droop in vertical light emitting diodes

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.

Effects of hole-injection through side-walls of large V-pits on efficiency droop in Ⅲ–nitride LEDs

Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition(MOCVD)growth of multiple quantum wells(MQWs) in Ⅲ–nitride LEDs, and thus affecting the carrier dynamics of the LEDs.Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells(QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.

Variation of efficiency droop with quantum well thickness in In GaN/GaN green light-emitting diode

In GaN/GaN multiple quantum well（MQW） green light-emitting diodes（LEDs） with varying In GaN quantum well layer thickness are fabricated and characterized. The investigation of luminescence efficiency versus injection current reveals that several physical mechanisms may jointly influence the efficiency droop, resulting in a non-monotonic variation of droop behavior with increasing quantum well（QW） thickness. When the QW is very thin, the increase of In GaN well layer thickness makes the efficiency droop more serious due to the enhancement of polarization effect. When the QW thickness increases further, however, the droop is alleviated significantly, which is mainly ascribed to the enhanced nonradiative recombination process and the weak delocalization effect.

Improved efficiency droop characteristics in an InGaN/GaN light-emitting diode with a novel designed last barrier structure

In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.

Effects of Mg doping in the quantum barriers on the efficiency droop of GaN based light emitting diodes

The effects of Mg doping in the quantum barriers（QBs） on the efficiency droop of GaN based light emitting diodes（LEDs） were investigated through a duel wavelength method. Barrier Mg doping would lead to the enhanced hole transportation and reduced polarization field in the quantum wells（QWs）, both may reduce the efficiency droop. However,heavy Mg doping in the QBs would strongly deteriorate the crystal quality of the QWs grown after the doped QB. When increasing the injection current, the carriers would escape from the QWs between n-GaN and the doped QB and recombine non-radiatively in the QWs grown after the doped QB, leading to a serious efficiency droop.

一种分布式电源的DROOP控制方法

分布式电源控制是实现微电网控制及可靠运行的前提。本文设计了一种分布式电源的DROOP控制方法,根据Droop典型微电源控制方法的基本原理,利用Matlab/Simulink仿真环境建立了仿真模型,通过仿真,验证了各模型的正确性和有效性。由仿真结果可知,电流内环能够实现无差跟踪调节;电压外环的动态响应能力更好,两者共同作用可使系统稳定性更好;在低频段时Z(S)呈现感性,而在高频段时呈现阻性,从而可以很好地实现Droop控制中的下垂特性,同时又会有一定抑制谐波的能力,最后通过分析,证明了本文控制参数取值的合理性以及有效性。

载流子复合机制对InGaN绿光LED的Droop效应和调制带宽的影响

传统的ABC模型被广泛应用于研究InGaN量子阱中的载流子复合动态过程。本文从实验样品中分析数据,提取绿光LED的ABC模型参数。基于ABC模型,经过理论计算,随着有效有源区厚度或者量子阱层厚度的增加,在注入电流增大时,内量子效率IQE下降趋势变缓,Droop效应的拐点电流明显增加;在不同的注入电流下,随着有效有源区厚度的下降,Droop效应下降非常明显。在低注入电流下,俄歇复合损失比随着注入电流增大而快速上升;在高注入电流下,俄歇复合损失比接近于饱和状态,上升速率很慢。随着有效有源区的厚度下降,俄歇复合损失比上升。随着注入电流的增大,绿光LED的调制带宽明显增大。在相同的注入电流下,随着有效有源区厚度的增加,调制带宽明显下降;在500 mA的注入电流下,调制带宽从684 MHz下降到85 MHz。在相同的注入电流下,随着InGaN量子阱宽度的增加,调制带宽有所下降;在500 mA注入电流下,调制带宽从684 MHz下降到372 MHz。

Efficiency droop in InGaN/GaN-based LEDs with a gradually varying In composition in each InGaN well layer

Temperature-dependent and driving current-dependent electroluminescence spectra of two different InGaN/GaN multiple quantum well structures SA and SB are investigated,with the In composition in each well layer(WL)along the growth direction progressively increasing for SA and progressively decreasing for SB.The results show that SB exhibits an improved efficiency droop compared with SA.This phenomenon can be explained as follows:owing to the difference in growth pattern of the WL between these two samples,the terminal region of the WL in SB contains fewer In atoms than in SA,and therefore the former undergoes less In volatilization than the latter during the waiting period required for warming-up due to the difference in the growth temperature between well and barrier layers.This results in SB having a deeper triangular-shaped potential well in its WL than SA,which strongly confines the carriers to the initial region of the WL to prevent them from leaking to the p-GaN side,thus improving the efficiency droop.Moreover,the improvement in the efficiency droop for SB is also partly attributed to its stronger Coulomb screening effect and carrier localization effect.

Analysis of Transmission Loss in Droop Control of a Multi-Terminal HVDC System

High Voltage Direct Current (HVDC) electric power transmission is a promising technology for integrating offshore wind farms and interconnecting power grids in different regions. In order to maintain the DC voltage, droop control has been widely used. Transmission line loss constitutes an import part of the total power loss in a multi-terminal HVDC scheme. In this paper, the relation between droop controller design and transmission loss has been investigated. Different MTDC layout configurations are compared to examine the effect of droop controller design on the transmission loss.

Research on the Impacts of the Inertia and Droop Control Gains from a Variable-Speed Wind Turbine Generator on the Frequency Response

System frequency must be kept very close to its nominal range to ensure the stability of an electric power grid.Excessive system frequency variations are able to result in load shedding,frequency instability,and even generator damage.With increasing wind power penetration,there is rising concern about the reduction in inertia response and primary frequency control in the electric power grid.Converter-based wind generation is capable of providing inertia response and primary frequency response;nevertheless,the primary frequency and inertia responses of wind generation are different from those of conventional synchronous fleets;it is not completely understood how the primary frequency and inertia responses affect the given system under various disturbances and available kinetic energy levels.Simulations are used to investigate the influences of inertia and droop control strategies on the dynamic frequency responses,particularly the index of the second frequency drop under various disturbance and wind conditions.A quantitative analysis provides insight into setting of inertia and droop control coefficients for various wind and disturbance conditions to facilitate adequate dynamic frequency responses during frequency events.