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.

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.

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.

Droop Control Methods for PV-Based Mini Grids with Different Line Resistances and Impedances

Different droop control methods for PV-based communal grid networks (minigrids and microgrids) with different line resistances (R) and impedances (X) are modelled and simulated in MATLAB to determine the most efficient control method for a given network. Results show that active power-frequency (P-f) droop control method is the most efficient for low voltage transmission networks with low X/R ratios while reactive power-voltage (Q-V) droop control method is the most efficient for systems with high X/R ratios. For systems with complex line resistances and impedances, i.e. near unity X/R ratios, P-f or Q-V droop methods cannot individually efficiently regulate line voltage and frequency. For such systems, P-Q-f droop control method, where both active and reactive power could be used to control PCC voltage via shunt-connected inverters, is determined to be the most efficient control method. Results also show that shunt-connection of inverters leads to improved power flow control of interconnected communal grids by allowing feeder voltage regulation, load reactive power support, reactive power management between feeders, and improved overall system performance against dynamic disturbances.

Control Efficacy of Validamycin A·(0.2 Billion Spores/ml) Paenibacillus polymyxa DN-1 3% AS for Rice Sheath Blight

With validamycin A.（0.2 billion spores/ml） Paenibacillus polymyxa DN-1 3% AS as the test agent, the effects of different dosage and different application time on the control efficacy for＇ rich sheath blight were investigated. The results of two- year test showed that when the application amount was in the range of 45-90 g.a.i/ hm^2, the field efficacy of validamycin A-（0.2 billion spores/ml） P. polymyxa DN-1 3% AS in the initial infection stage of rich sheath blight （Le., the diseased plant rate was below 5%） reached 80.38%-89.06%, and that in the peak infection stage （i.e., the diseased plant rate was higher than 10%） reached only 41.12%-53.26%. The field efficacy of validamycin A.（0.2 billion spores/ml） P. polymyxa DN-1 3% AS at the early onset of rich sheath blight was significantly better than that at the onset, so that the application time of validamycin A .（0.2 billion spores/ml） P. polymyxa DN-1 3% AS should be appropriately brought forward in the prevention and control of rice sheath blight.

基于双补偿下垂—MQPR的直驱式风电机组并网控制

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。

Review on grid-forming converter control methods in high-proportion renewable energy power systems

Grid-forming(GFM)converters can provide inertia support for power grids through control technology,stabilize voltage and frequency,and improve system stability,unlike traditional grid-following(GFL)converters.Therefore,in future“double high”power systems,research on the control technology of GFM converters will become an urgent demand.In this paper,we first introduce the basic principle of GFM control and then present five currently used control strategies for GFM converters:droop control,power synchronization control(PSC),virtual synchronous machine control(VSM),direct power control(DPC),and virtual oscillator control(VOC).These five strategies can independently establish voltage phasors to provide inertia to the system.Among these,droop control is the most widely used strategy.PSC and VSM are strategies that simulate the mechanical characteristics of synchronous generators;thus,they are more accurate than droop control.DPC regulates the active power and reactive power directly,with no inner current controller,and VOC is a novel method under study using an oscillator circuit to realize synchronization.Finally,we highlight key technologies and research directions to be addressed in the future.

State coordinated voltage control in an active distribution network with on-load tap changers and photovoltaic systems

Decreasing costs and favorable policies have resulted in increased penetration of solar photovoltaic(PV)power generation in distribution networks.As the PV systems penetration is likely to increase in the future,utilizing the reactive power capability of PV inverters to mitigate voltage deviations is being promoted.In recent years,droop control of inverter-based distributed energy resources has emerged as an essential tool for use in this study.The participation of PV systems in voltage regulation and its coordination with existing controllers,such as on-load tap changers,is paramount for controlling the voltage within specified limits.In this work,control strategies are presented that can be coordinated with the existing controls in a distributed manner.The effectiveness of the proposed method was demonstrated through simulation results on a distribution system.

Distributed Secondary Control and Optimal Power Sharing in Microgrids

We address the control problem of microgrids and present a fully distributed control system which consists of primary controller, secondary controller, and optimal active power sharing controller. Different from the existing control structure in microgrids, all these controllers are implemented as local controllers at each distributed generator. Thus, the requirement for a central controller is obviated. The performance analysis of the proposed control systems is provided, and the finite-time convergence properties for distributed secondary frequency and voltage controllers are achieved. Moreover, the distributed control system possesses the optimal active power sharing property. In the end, a microgrid test system is investigated to validate the effectiveness of the proposed control strategies. © 2014 Chinese Association of Automation.

Moving fast, thinking fast:The relations of physical activity levels and bouts to neuroelectric indices of inhibitory control in preadolescents

Background:Structured vigorous physical activity(VPA)can improve cognitive control in children,but studies relating daily physical activity(PA)to cognitive control have yielded conflicting findings.While objectively measured daily PA summarizes all occurrences of PA within a registered period,a minimum duration of continuous PA is required for registration of a PA bout.Because brief bouts of high-intensity PA can account for a large proportion of children’s daily activity-related energy expenditure,this study assessed whether daily and bouted VPA were selectively related to cognitive control in preadolescents relative to other PA intensities.Methods:A total of 75 children between the ages of 8 and 10 years(49%girls)wore an ActiGraph wGT 3 X+on the hip for 7 days.The acceleration signal from the vertical axis was summarized over 1 s,5 s,and 15 s epochs.Daily and boutecd modercate PA,moderate-to-vigorous PA,and VPA were measured.PA bouts were expressed as the frequency and time spent in 2 different continuous PA bouts,one lasting≥10 s and the other lasting≥30 s at a given intensity.Inhibitory control was assessed using behavioral responses to a modified flanker task(mean reaction time(RTmean)and accuracy).Attentional resource allocation and co gnitive processing speed were measured using the amplitude and latency of the P3 component of event-related brain potentials,respectively.Associations between PA,behavioral indices of inhibitory control,P3 amplitude,and latency were assessed using hierarchical regression models.Results:Daily VPA was not related to RTmean or accuracy on either congruent or incongruent trials.In contrast,more time spent in VPA bouts lasting≥30 s predicted shorter P3 latency across epochs and flanker congruencies(allβ≤-0.24,all p≤0.04).The associations between shorter P3 latency and the time spent in moderate-to-vigorous PA bouts lasting≥30 s were less consistent and largely limited to congruent trials(congruent:β(-0.3 1,-0.34)).No significant associations were observed upon correction for false discovery rate.Conclusion:The pattern of uncorrected associations aligns with the dose-response literature and suggests that brief VPA bouts may yield the greatest benefits to cognitive processing speed in preadolescents.Future studies using measures of brain structure and function are needed to understand the mechanisms linking bouted VPA to neurocognitive function during childhood.

A New Predictive Direct Power Control Solution for Three-phase Grid-Connected Inverters

This paper proposes a new Predictive Direct Power Control(P-DPC) solution for three-phase grid-connected inverters, which combines direct power control strategy with the predictive control strategy and space vector pulse width modulation(SVPWM), obtaining both high transient performance and a constant switching frequency. This control solution can achieve decoupling control for active and reactive power and an adjustable power factor. Meanwhile, the grid-connected current can approximately be sinusoidal. The feasibility and advantages of the control strategy are verified by the simulation and experiment compared with another existing P-DPC.

Fuzzy Controller Based 3Phase 4Wire Shunt Active Filter for Mitigation of Current Harmonics with Combined p-q and Id-Iq Control Strategies

As more and more variable frequency drives (VFDs), electronic ballasts, battery chargers, and static Var compensators are installed in facilities, the problems related to harmonics are expected to get worse. As a result Active power filter (APF) gains much more attention due to excellent harmonic compensation. But still the performance of the active filter seems to be in contradictions with different control strategies. This paper presents detailed analysis to compare and elevate the performance of two control strategies for ex-tracting reference currents of shunt active filters under balanced, un-balanced and non-sinusoidal conditions by using Fuzzy controller. The well known methods, instantaneous real active and reactive power method (p-q) and active and reactive current method (id-iq) are two control methods which are extensively used in active filters. Extensive Simulations are carried out with fuzzy controller for both p-q and Id-Iq methods for different voltage conditions and adequate results were presented. Simulation results validate the superior per-formance of active and reactive current control strategy (id-iq) with fuzzy controller over active and reactive power control strategy (p-q) with fuzzy controller.

AUTOMATIC SEAM TRACKING SYSTEM OF SUBMERGED ARC WELDING BASED ON FUZZY-P CONTROLLER

An automatic seam tracking system used in submerged arc welding is presented.In the system, the linear CCD vision sensor is installed in front of the welding torch. Laserstructure light emitted by the semiconductor laser irradiates on a slant to work-piece surface andforms a structure light strip on work-piece surface. Scatter light of the strip is received bylinear CCD on top of the seam and the image information of seam can be obtained. By way of imageprocessing and applying Fuzzy-P controller in tracking process, automatic seam tracking has beenrealized accurately. Anti-disturbing ability of the system to work-piece surface status has beenenhanced largely by classified microadjustment of torch height.

Multiobjective Optimization for Controller Design

用 multiobjective 优化方法的控制器设计被考虑，在哪个为设计控制器的目的和限制被分析并且改善。以便同时地满足目的，一个新 multiobjective 优化算法被介绍进设计一个最佳的 PID 控制器，由织物 P 系统启发了。控制器的参数根据联系的膜的规则被编码并且演变。唯一的设计是结构的整个人口被划分成几 subpopulations 减少计算复杂性。模拟结果证明算法快收敛，答案形成精确前面并且一致地散布。P 系统的变体设计的控制器有令人满意的性能。而且，答案的分析证明新算法对学习在性能之间的关系并且调节参数合适。建议方法为设计并且评估不同控制器是有用的。

MAS Based Distributed Automatic Generation Control for Cyber-Physical Microgrid System

The microgrid is a typical cyber-physical microgrid system (CPMS). The physical unconventional distributed generators (DGs) are intermittent and inverter-interfaced which makes them very different to control. The cyber components, such as the embedded computer and communication network, are equipped with DGs, to process and transmit the necessary information for the controllers. In order to ensure system-wide observability, controllability and stabilization for the microgrid, the cyber and physical component need to be integrated. For the physical component of CPMS, the droop-control method is popular as it can be applied in both modes of operation to improve the grid transient performance. Traditional droop control methods have the drawback of the inherent trade-off between power sharing and voltage and frequency regulation. In this paper, the global information (such as the average voltage and the output active power of the microgrid and so on) are acquired distributedly based on multi-agent system (MAS). Based on the global information from cyber components of CPMS, automatic generation control (AGC) and automatic voltage control (AVC) are proposed to deal with the drawback of traditional droop control. Simulation studies in PSCAD demonstrate the effectiveness of the proposed control methods. © 2014 Chinese Association of Automation.

Anti-control of chaos in p Ge photoconductor

We present a scheme for the anti-control of chaos in the p-Ge photoconductor system by using a chaotic laser to irradiate and disturb this system. The numerical simulations show that this scheme can be effectively used to control periodic states in this t^Ge system into chaotic states. Moreover, the different chaos states with different chaotic orbits can be obtained by appropriately adjusting the disturbance intensity and disturbance frequency, and by increasing this intensity or reducing this frequency, this p-Ge system gradually evolves to fully developed chaotic states.

Adaptive adjustment of iterative learning control gain matrix in harsh noise environment

For the robustness problem of open-loop P-type iterative learning control under the influence of measurement noise which is inevitable in actual systems, an adaptive adjustment algorithm of iterative learning nonlinear gain matrix based on error amplitude is proposed and two nonlinear gain functions are given. Then with the help of Bellman-Gronwall lemma, the robustness proof is derived. At last, an example is simulated and analyzed. The results show that when there exists measurement noise, the proposed learning law adjusts the learning gain matrix on line based on error amplitude, thus can make a compromise between learning convergence rate and convergence accuracy to some extent： the fast convergence rate is achieved with high gain in initial learning stage, the strong robustness and high convergence accuracy are achieved at the same time with small gain in the end learning stage, thus better learning results are obtained.

Application of pH control to a tubular flow reactor

Tubular flow reactors are mainly used in chemical industry and waste water discharged units. Control of output variables is very difficult because of the existence of high dead-time in these types of reactors. In the present work, sodium hydroxide and acetic acid solutions were sent to the tubular flow reactor. The aim was to control p H at 7 in the nonlinear region. The p H control of a tubular flow reactor with high time delay and a highly nonlinear behavior in p H neutralization reaction was investigated experimentally in the face of the various load and set point changes. Firstly, efficiency of conventional Proportional-Integral-Derivative(PID) algorithm in the experiments was tested. Then self-tuning PID(STPID) control system was applied by using the ARMAX model. The model parameters were calculated from input–output data by using PRBS signal as disturbance and Bierman algorithm. Lastly, the experimental fuzzy control of p H based on fuzzy model was achieved to compare the success of fuzzy approach with the performance of other control cases studied.