In the islanded operation of distribution networks,due to the mismatch of line impedance at the inverter output,conventional droop control leads to inaccurate power sharing according to capacity,resulting in voltage a...In the islanded operation of distribution networks,due to the mismatch of line impedance at the inverter output,conventional droop control leads to inaccurate power sharing according to capacity,resulting in voltage and frequency fluctuations under minor external disturbances.To address this issue,this paper introduces an enhanced scheme for power sharing and voltage-frequency control.First,to solve the power distribution problem,we propose an adaptive virtual impedance control based on multi-agent consensus,which allows for precise active and reactive power allocation without requiring feeder impedance knowledge.Moreover,a novel consensus-based voltage and frequency control is proposed to correct the voltage deviation inherent in droop control and virtual impedance methods.This strategy maintains voltage and frequency stability even during communication disruptions and enhances system robustness.Additionally,a small-signal model is established for system stability analysis,and the control parameters are optimized.Simulation results validate the effectiveness of the proposed control scheme.展开更多
This paper presents the design of a high performance robust resonant controller for the islanded single-phase microgrid operation on different loads conditions. The design of the controller is done using the results o...This paper presents the design of a high performance robust resonant controller for the islanded single-phase microgrid operation on different loads conditions. The design of the controller is done using the results of Negative Imaginary approach. The performance of the proposed controller has been found much effective to track the instantaneous reference grid voltage. The simulation work has been done with the help of MATLAB/SimPower System toolbox. This shows that the proposed controller provides effective control of voltage against the uncertain load conditions.展开更多
The step load response of reciprocating engines is one of the key characteristics when considering its application in medium to large scale stationary power generation especially with islanded generation. This paper d...The step load response of reciprocating engines is one of the key characteristics when considering its application in medium to large scale stationary power generation especially with islanded generation. This paper discusses the impacts of power frequency deviation on the generators and electrical equipment in the network and presents the relationship between step load capabilities and generator operating parameters. For a power plant consisting of a number of generators both step load and power output requirements must be satisfied. An analysis method is proposed to facilitate the development of an operation strategy which can meet both step load and power demand requirements in the full load range.? Typical reciprocating engine step load curves are used to demonstrate the analysis method and the results are further optimised for lower operational cost. This analysis method provides a general approach to operation strategy of large reciprocating engines used in islanded power generation.展开更多
This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded m...This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel generator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric scheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages normally occur in two remarkable instants. The first one occurs at the beginning of the fault itself. The second one occurs at the instant when the fault is cleared. The major concern here is the overvoltage during the fault period. Due to the travelling wave effect along cables and overhead lines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the insulation level of the microgrid transmission system and related equipment. Much of the work available now is dedicated to overvoltages present in high-voltage systems leaving a gap for the study and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by the maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and overhead lines that constitute the microgrid transmission system are characterized by their R-L-C parameters. The simulations of the microgrid system are conducted using the ATP program. According to the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation Level) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV, respectively;thus, care should be taken so that the healthy phases upon which commonly appear such overvoltages are not exceeded in their insulation level.展开更多
This article presents the simulation results and analysis related to the response of the generators within a microgrid towards an accidental overload condition that will require some load shedding action. A microgrid ...This article presents the simulation results and analysis related to the response of the generators within a microgrid towards an accidental overload condition that will require some load shedding action. A microgrid overload can occur due to various reasons ranging from poor load schedule, inadequate switching of circuits within the microgrid, outage of one or more generators inside the microgrid, illegal load connections by some low voltage consumers, etc. It was observed that among the main factors that determine the survival of the microgrid during its transition from the grid connected mode to the islanded mode of operation are the size and type of the load connected (passive or dynamic load) as well as the length of time during which the unexpected load is connected. Models of a speed and voltage regulators of a diesel generator, and important for coping with the overload conditions are provided in the paper. The novelty of the work lies in the load shedding simulation and analysis of the specific generators studied herein, regarding that in many countries the microgrid technology is seen as an important alternative towards the ever increasing load demand and also to assist the system during periods of blackout.展开更多
In many developing countries, there are regions where the electrical grid is weak or nonexistent. However, in these areas, large amounts of distributed energy sources, such as hydro, are often available and could be s...In many developing countries, there are regions where the electrical grid is weak or nonexistent. However, in these areas, large amounts of distributed energy sources, such as hydro, are often available and could be suitably exploited. To this aim, the low head hydro power plants can play a significant role. In fact, recent technological advances in mini-hydro turbines and decreasing costs of static electricity conversion devices enable to realize suitable power plants for an efficient and profitable exploitation of these sites. One of the major challenges is the integration of the above-mentioned power plants into autonomous electrical systems, islanded and/or disconnectable from the main distribution network. In this paper, an innovative control strategy for a low head hydro power plant supplying users in small clusters of villages is proposed.展开更多
The present paper addresses an advanced teaching lab consisting of setting up an islanded production unit. This teaching lab takes place in the very last semester at master level for students in electrical engineering...The present paper addresses an advanced teaching lab consisting of setting up an islanded production unit. This teaching lab takes place in the very last semester at master level for students in electrical engineering with energy specialization. The purpose of this teaching lab is to combine knowledge learned in different areas such as power electronics, control, electrical machines and networks, and make use of all of them in practice. The present paper describes in detail the different steps followed by the student to set up an islanded production unit.展开更多
For providing a reliable power supply in an islanded AC microgrid,it is crucial to ensure that the operating states meet the safety constraints.However,conventional distributed secondary control methods often struggle...For providing a reliable power supply in an islanded AC microgrid,it is crucial to ensure that the operating states meet the safety constraints.However,conventional distributed secondary control methods often struggle to handle voltage and frequency constraints,limiting their practical applicability.To address these limitations,this paper proposes a novel prescribed performance control(PPC)based distributed secondary coordination method for islanded AC microgrids.The proposed method introduces a systematic framework that integrates bijective transformation with distributed secondary control.In this framework,the constrained distributed voltage and frequency control problems can be transformed into unconstrained ones,enabling strict adherence to predefined performance boundaries.Additionally,Lyapunov-Krasovskii functional analysis is employed in this paper to ensure asymptotic stability and calculate the stable boundaries in the transformed error space under time-delay conditions.The effectiveness of stability recovery and prescribed performance is tested in both MATLAB/Simulink and RTLab-based hardware-in-the-loop(HIL)experimental environments.展开更多
This paper introduces a novel hybrid optimization algorithm,Adaptive Hybrid PSO-Embedded GA(AHPEGA),which dynamically adapts to optimization performance by integrating Particle Swarm Optimization(PSO)and Genetic Algor...This paper introduces a novel hybrid optimization algorithm,Adaptive Hybrid PSO-Embedded GA(AHPEGA),which dynamically adapts to optimization performance by integrating Particle Swarm Optimization(PSO)and Genetic Algorithms(GA).The primary objective is to enhance the neuroevolutionary training of multilayer perceptron-based controllers(MLPCs)through the joint optimization of model parameters and structural hyperparameters.Traditional training methods frequently encounter issues such as premature convergence and limited generalization.AHPEGA addresses these limitations through an adaptive training strategy that dynamically adjusts parameters during the evolutionary process,thereby improving convergence speed and solution quality.By effectively reducing entrapment in local minima and balancing exploration and exploitation,AHPEGA improves the quality of neural controller design.The algorithm’s performance is evaluated against conventional optimization methods,demonstrating significant improvements in accuracy,convergence speed,and consistency across multiple runs.The practical applicability of the proposed method is demonstrated through simulation in the context of a VSC-based islanded microgrid(MG),where ensuring reliable and effective control under variable operating conditions is critical.This highlights AHPEGA’s capability to optimize intelligent control strategies in MG systems,particularly under dynamic and uncertain conditions,reinforcing its practical value in real-world energy environments.展开更多
Islanded microgrids(IMGs)offer a viable and efficient energy self-sustaining solution for distributed resources in remote areas.While without utility grid support,the frequency of IMG is susceptible to mismatches betw...Islanded microgrids(IMGs)offer a viable and efficient energy self-sustaining solution for distributed resources in remote areas.While without utility grid support,the frequency of IMG is susceptible to mismatches between demand and generation.Moreover,IMGs encounter uncertain and nonlinear load disturbances together with system parameter perturbation,which further compromises frequency stability.To this aim,this paper proposes a robust multi-virtual synchronous generators(multi-VSGs)coordinated control strategy for distributed secondary frequency regulation(DSFR)in IMGs,which exhibits minimal model dependency and avoids reliance on global information.Two critical methods are developed:(1)a robust VSG control framework that incorporates the linear active disturbance rejection control(LADRC)technique,which enables the estimation and effective elimination of uncertain load disturbances and system's parameter perturbations;(2)a novel secondorder consensus algorithm-based control law for robust secondary frequency regulation,which is featured with proper power sharing among different participants,suppressed power oscillation caused by response disparities,and reduced reliance on complex communication system.Building on methods(1)and(2),a novel multi-VSGs coordinated control strategy is proposed,providing a robust solution for IMG's frequency restoration,and its dynamic characteristics are explored in detail.The correctness and effectiveness of the proposal are verified by both simulation and the hardware-in-the-loop(HIL)experiment results across typical scenarios.展开更多
The high proportion of nonlinear and unbalanced loads results in power quality issues in islanded microgrids.This paper presents a novel control strategy for harmonic and unbalanced power allocation among distributed ...The high proportion of nonlinear and unbalanced loads results in power quality issues in islanded microgrids.This paper presents a novel control strategy for harmonic and unbalanced power allocation among distributed genera-tors(DGs)in microgrids.Different from the existing sharing strategies that allocate the harmonic and unbalanced power according to the rated capacities of DGs,the proposed control strategy intends to shape the lowest output impedances of DGs to optimize the power quality of the microgrid.To achieve this goal,the feasible range of virtual impedance is analyzed in detail by eigenvalue analysis,and the findings suggest a simultaneous adjustment of real and imaginary parts of virtual impedance.Because virtual impedance is an open-loop control that imposes DG to the risk of overload,a new closed-loop structure is designed that uses residual capacity and absorbed power as feedback.Accordingly,virtual impedance can be safely adjusted in the feasible range until the power limit is reached.In addi-tion,a fuzzy integral controller is adopted to improve the dynamics and convergence of the power distribution,and its performance is found to be superior to linear integral controllers.Finally,simulations and control hardware-in-the-loop experiments are conducted to verify the effectiveness and usefulness of the proposed control strategy.展开更多
With the high integration of power electronic technologies in microgrids,the reliability assessment considering power electronic devices has become a hot topic.However,so far no research has considered the impact of t...With the high integration of power electronic technologies in microgrids,the reliability assessment considering power electronic devices has become a hot topic.However,so far no research has considered the impact of the operation failure probability of power electronic equipment on the overall reliability of the microgrid.This paper aims to construct a holistic operation failure rate model of power electronic systems based on the overall reliability assessment of islanded microgrid with high penetration of renewable energy sources(RESs).In addition,to improve the reliability of islanded microgrid,the conventional battery energy storage system(BESS)is replaced by the hybrid energy storage system(HESS).Based on the proposed model,the operation failure models for the power electronic modules in microgrid are built and tested,and then the sensitivity analysis is performed for exploring the influence of various factors on the reliability of the microgrid.展开更多
With the proliferation of renewable energy and electric vehicles(EVs),there have been increasing uncertainties in power systems.Identifying the influencing random variables will reduce the effort in uncertainty modeli...With the proliferation of renewable energy and electric vehicles(EVs),there have been increasing uncertainties in power systems.Identifying the influencing random variables will reduce the effort in uncertainty modeling and improve the controllability of power systems.In this paper,a density-based global sensitivity analysis(GSA)method is proposed to evaluate the influence of uncertainties on islanded microgrids(IMGs).Firstly,the maximum IMG loadability evaluation model is established to assess the distance from the current operation point to the critical operation point.Secondly,the Borgonovo method,which is a density-based GSA method,is used to evaluate the influence of input variables on IMG loadability.Thirdly,to improve GSA efficiency,a modified Kriging model is used to obtain a surrogate model of IMG loadability,and Borgonovo indices are calculated based on the surrogate model.Finally,the proposed method is tested on a 38-bus IMG system.Simulation results are compared with those considering other methods to validate the effectiveness of the proposed method.Energy storage systems are considered to diminish the influence of critical uncertainties on IMG operation.展开更多
Due to the lack of support from the main grid,the intermittency of renewable energy sources(RESs)and the fluctuation of load will derive uncertainties to the operation of islanded microgrids(IMGs).It is crucial to all...Due to the lack of support from the main grid,the intermittency of renewable energy sources(RESs)and the fluctuation of load will derive uncertainties to the operation of islanded microgrids(IMGs).It is crucial to allocate appropriate reserve capacity for the economic and reliable operation of IMGs.With the high penetration of RESs,it faces both economic and environmental challenges if we only use spinning reserve for reserve support.To solve these problems,a multi-type reserve scheme for IMGs is proposed according to different operation characteristics of generation,load,and storage.The operation risk due to reserve shortage is modeled by the conditional value-at-risk(CVaR)method.The correlation of input variables is considered for the forecasting error modeling of RES and load,and Latin hypercube sampling(LHS)is adopted to generate the random scenarios of the forecasting error,so as to avoid the dimension disaster caused by conventional large-scale scenario sampling approaches.Furthermore,an optimal day-ahead scheduling model of joint energy and reserve considering riskbased reserve decision is established to coordinate the security and economy of the operation of IMGs.Finally,the comparison of numerical results of different schemes demonstrate the rationality and effectiveness of the proposed scheme and model.展开更多
An optimal operation scheme is of great significance in islanded distribution networks to restore critical loads and has recently attracted considerable attention.In this paper,an optimal power flow(OPF)model for isla...An optimal operation scheme is of great significance in islanded distribution networks to restore critical loads and has recently attracted considerable attention.In this paper,an optimal power flow(OPF)model for islanded distribution networks equipped with soft open points(SOPs)is proposed.Unlike in the grid-connected mode,the adequacy of local power generation in distribution networks is critical for islanded systems.The proposed approach utilizes the power output of local distributed generations(DGs)and the benefits of reactive power compensation provided by SOPs to allow maximum loadability.To exploit the available resources,an optimal secondary droop control strategy is introduced for the islanded distribution networks,thereby minimizing load shedding.The formulated OPF problem is essentially a mixed-integer nonlinear programming(MINLP)model.To guarantee the computation efficiency and accuracy.A successive mixed-integer second-order cone programming(SMISOCP)algorithm is proposed for handling the nonlinear islanded power flow formulations.Two case studies,incorporating a modified IEEE 33-bus system and IEEE 123-bus system,are performed to test the effectiveness of the proposed approach.展开更多
This study proposes a novel combined primary and secondary control approach for direct current microgrids,specifi-cally in islanded mode.In primary control,this approach establishes an appropriate load power sharing b...This study proposes a novel combined primary and secondary control approach for direct current microgrids,specifi-cally in islanded mode.In primary control,this approach establishes an appropriate load power sharing between the distributed energy resources based on their rated power.Simultaneously,it considers the load voltage deviation and provides satisfactory voltage regulation in the secondary control loop.The proposed primary control is based on an efficient droop mechanism that only deploys the local variable measurements,so as to overcome the side effects caused by communication delays.In the case of secondary control,two different methods are devised.In the first,low bandwidth communication links are used to establish the minimum required data transfer between the converters.The effect of communication delay is further explored.The second method excludes any communication link and only uses local variables.Accordingly,a self-sufficient control loop is devised without any communication require-ment.The proposed control notions are investigated in MATLAB/Simulink platform to highlight system performance.The results demonstrate that both proposed approaches can effectively compensate for the voltage deviation due to the primary control task.Detailed comparisons of the two methods are also provided.展开更多
A virtual synchronous generator(VSG)can provide inertial support through renewables and energy storage.It generally operates in parallel with a diesel generator(DSG)in an islanded microgrid.However,unforeseen interact...A virtual synchronous generator(VSG)can provide inertial support through renewables and energy storage.It generally operates in parallel with a diesel generator(DSG)in an islanded microgrid.However,unforeseen interactive power oscillations occur in the paralleled system when loads fluctuate.These may also burn out the VSG owing to its low overcurrent capacity.The mechanism and suppression strategy of the power oscillation of a VSG-DSG paralleled system are investigated.It reveals that the interactive power oscillation is caused essentially by the physical difference and parameter mismatch between the VSG and DSG.Then,the elimination condition of oscillation generation is derived.Subsequently,a comprehensive suppression control strategy based on virtual inductance and dynamic mutual damping technology is proposed.Finally,the experimental results verify the effectiveness of the proposed method.展开更多
In this paper,an optimal secondary control strategy is proposed for islanded AC microgrids considering communi-cation time-delays.The proposed method is designed based on the data-driven principle,which consists of an...In this paper,an optimal secondary control strategy is proposed for islanded AC microgrids considering communi-cation time-delays.The proposed method is designed based on the data-driven principle,which consists of an offine training phase and online application phase.For offline training,each control agent is formulated by a deep neural network(DNN)and trained based on a multi-agent deep reinforcement learning(MA-DRL)framework.A deep deterministic policy gradient(DDPG)algorithm is improved and applied to search for an optimal policy of the secondary control,where a global cost function is developed to evaluate the overall control performance.In addition,the communication time-delay is introduced in the system to enrich training scenarios,which aims to solve the time-delay problem in the secondary control.For the online stage,each controller is deployed in a distributed way which only requires local and neighboring information for each DG.Based on this,the well-trained controllers can provide optimal solutions under load variations,and communication time-delays for online applications.Several case studies are conducted to validate the feasibility and stability of the proposed secondary control.Index Terms-Communication time-delay,global cost function,islanded AC microgrid,multi-agent deep reinforcement learning(MA-DRL),secondary control.展开更多
For islanded microgrids(MGs),distributed control is regarded as a preferred alternative to centralized control for the frequency restoration of MGs.However,distributed control with successive communication restricts t...For islanded microgrids(MGs),distributed control is regarded as a preferred alternative to centralized control for the frequency restoration of MGs.However,distributed control with successive communication restricts the efficiency and resilience of the control system.To address this issue,this paper proposes a distributed event-triggered control strategy for the frequency secondary control in islanded MGs.The proposed event-triggered control is Zeno behavior free and enables each DG to update and propagate its state to neighboring DGs only when a specific“event”occurs,which significantly reduces the communication burden.Compared with the existing event-triggered control,a trigger condition checking period of the proposed event-triggered control is provided to reduce the computation burden when checking the trigger condition.Furthermore,using the aperiodicity and intermittent properties of the communication,a simple detection principle is proposed to detect and isolate the compromised communication links in a timely and economic fashion,which improves the resilience of the system against FDI attacks.Finally,the control effectiveness of the proposed control scheme is validated by the simulation results of the tests on an MG with 4 DGs.展开更多
This survey paper provides a critical overview of optimization formulations for planning and operation of islanded microgrids,including optimization objectives,constraints,and control variables.The optimization approa...This survey paper provides a critical overview of optimization formulations for planning and operation of islanded microgrids,including optimization objectives,constraints,and control variables.The optimization approaches reviewed address methods both for increasing the resiliency of advanced distribution systems and electrification of remote communities.This paper examines over 120 individual optimization studies and discovers that all optimizations studies of islanded microgrids are based on formulations selecting a combination of 16 possible objective functions,14 constraints,and 13 control variables.Each of the objectives,constraints,and variables are discussed exhaustively both from the perspective of their importance to islanded microgrids and chronological trends in their popularity.展开更多
基金supported by the National Natural Science Foundation of China(52007009)Natural Science Foundation of Excellent Youth Project of Hunan Province of China(2023JJ20039)Science and Technology Projects of State Grid Hunan Provincial Electric Power Co.,Ltd.(5216A522001K,SGHNDK00PWJS2310173).
文摘In the islanded operation of distribution networks,due to the mismatch of line impedance at the inverter output,conventional droop control leads to inaccurate power sharing according to capacity,resulting in voltage and frequency fluctuations under minor external disturbances.To address this issue,this paper introduces an enhanced scheme for power sharing and voltage-frequency control.First,to solve the power distribution problem,we propose an adaptive virtual impedance control based on multi-agent consensus,which allows for precise active and reactive power allocation without requiring feeder impedance knowledge.Moreover,a novel consensus-based voltage and frequency control is proposed to correct the voltage deviation inherent in droop control and virtual impedance methods.This strategy maintains voltage and frequency stability even during communication disruptions and enhances system robustness.Additionally,a small-signal model is established for system stability analysis,and the control parameters are optimized.Simulation results validate the effectiveness of the proposed control scheme.
文摘This paper presents the design of a high performance robust resonant controller for the islanded single-phase microgrid operation on different loads conditions. The design of the controller is done using the results of Negative Imaginary approach. The performance of the proposed controller has been found much effective to track the instantaneous reference grid voltage. The simulation work has been done with the help of MATLAB/SimPower System toolbox. This shows that the proposed controller provides effective control of voltage against the uncertain load conditions.
文摘The step load response of reciprocating engines is one of the key characteristics when considering its application in medium to large scale stationary power generation especially with islanded generation. This paper discusses the impacts of power frequency deviation on the generators and electrical equipment in the network and presents the relationship between step load capabilities and generator operating parameters. For a power plant consisting of a number of generators both step load and power output requirements must be satisfied. An analysis method is proposed to facilitate the development of an operation strategy which can meet both step load and power demand requirements in the full load range.? Typical reciprocating engine step load curves are used to demonstrate the analysis method and the results are further optimised for lower operational cost. This analysis method provides a general approach to operation strategy of large reciprocating engines used in islanded power generation.
文摘This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel generator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric scheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages normally occur in two remarkable instants. The first one occurs at the beginning of the fault itself. The second one occurs at the instant when the fault is cleared. The major concern here is the overvoltage during the fault period. Due to the travelling wave effect along cables and overhead lines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the insulation level of the microgrid transmission system and related equipment. Much of the work available now is dedicated to overvoltages present in high-voltage systems leaving a gap for the study and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by the maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and overhead lines that constitute the microgrid transmission system are characterized by their R-L-C parameters. The simulations of the microgrid system are conducted using the ATP program. According to the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation Level) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV, respectively;thus, care should be taken so that the healthy phases upon which commonly appear such overvoltages are not exceeded in their insulation level.
文摘This article presents the simulation results and analysis related to the response of the generators within a microgrid towards an accidental overload condition that will require some load shedding action. A microgrid overload can occur due to various reasons ranging from poor load schedule, inadequate switching of circuits within the microgrid, outage of one or more generators inside the microgrid, illegal load connections by some low voltage consumers, etc. It was observed that among the main factors that determine the survival of the microgrid during its transition from the grid connected mode to the islanded mode of operation are the size and type of the load connected (passive or dynamic load) as well as the length of time during which the unexpected load is connected. Models of a speed and voltage regulators of a diesel generator, and important for coping with the overload conditions are provided in the paper. The novelty of the work lies in the load shedding simulation and analysis of the specific generators studied herein, regarding that in many countries the microgrid technology is seen as an important alternative towards the ever increasing load demand and also to assist the system during periods of blackout.
文摘In many developing countries, there are regions where the electrical grid is weak or nonexistent. However, in these areas, large amounts of distributed energy sources, such as hydro, are often available and could be suitably exploited. To this aim, the low head hydro power plants can play a significant role. In fact, recent technological advances in mini-hydro turbines and decreasing costs of static electricity conversion devices enable to realize suitable power plants for an efficient and profitable exploitation of these sites. One of the major challenges is the integration of the above-mentioned power plants into autonomous electrical systems, islanded and/or disconnectable from the main distribution network. In this paper, an innovative control strategy for a low head hydro power plant supplying users in small clusters of villages is proposed.
文摘The present paper addresses an advanced teaching lab consisting of setting up an islanded production unit. This teaching lab takes place in the very last semester at master level for students in electrical engineering with energy specialization. The purpose of this teaching lab is to combine knowledge learned in different areas such as power electronics, control, electrical machines and networks, and make use of all of them in practice. The present paper describes in detail the different steps followed by the student to set up an islanded production unit.
基金supported by the National Natural Science Foundation of China(No.52407086)the China Postdoctoral Science Foundation(No.2023M740588)+1 种基金the Postdoctoral Fellowship Program of CPSF(No.GZC20230422)the Jiangsu Funding Program for Excellent Postdoctoral Talent(No.2023ZB391).
文摘For providing a reliable power supply in an islanded AC microgrid,it is crucial to ensure that the operating states meet the safety constraints.However,conventional distributed secondary control methods often struggle to handle voltage and frequency constraints,limiting their practical applicability.To address these limitations,this paper proposes a novel prescribed performance control(PPC)based distributed secondary coordination method for islanded AC microgrids.The proposed method introduces a systematic framework that integrates bijective transformation with distributed secondary control.In this framework,the constrained distributed voltage and frequency control problems can be transformed into unconstrained ones,enabling strict adherence to predefined performance boundaries.Additionally,Lyapunov-Krasovskii functional analysis is employed in this paper to ensure asymptotic stability and calculate the stable boundaries in the transformed error space under time-delay conditions.The effectiveness of stability recovery and prescribed performance is tested in both MATLAB/Simulink and RTLab-based hardware-in-the-loop(HIL)experimental environments.
基金financial support from the Swedish International Development Cooperation Agency(SIDA)through the research capacity-building program between Addis Ababa University and Swedish universities.
文摘This paper introduces a novel hybrid optimization algorithm,Adaptive Hybrid PSO-Embedded GA(AHPEGA),which dynamically adapts to optimization performance by integrating Particle Swarm Optimization(PSO)and Genetic Algorithms(GA).The primary objective is to enhance the neuroevolutionary training of multilayer perceptron-based controllers(MLPCs)through the joint optimization of model parameters and structural hyperparameters.Traditional training methods frequently encounter issues such as premature convergence and limited generalization.AHPEGA addresses these limitations through an adaptive training strategy that dynamically adjusts parameters during the evolutionary process,thereby improving convergence speed and solution quality.By effectively reducing entrapment in local minima and balancing exploration and exploitation,AHPEGA improves the quality of neural controller design.The algorithm’s performance is evaluated against conventional optimization methods,demonstrating significant improvements in accuracy,convergence speed,and consistency across multiple runs.The practical applicability of the proposed method is demonstrated through simulation in the context of a VSC-based islanded microgrid(MG),where ensuring reliable and effective control under variable operating conditions is critical.This highlights AHPEGA’s capability to optimize intelligent control strategies in MG systems,particularly under dynamic and uncertain conditions,reinforcing its practical value in real-world energy environments.
基金supported by the National Natural Science Foundation of China(Grant Nos.U22B20104,52407080,52277090,52207097)the International Science and Technology Cooperation Program of China(Grant No.2022YFE0129300)+2 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2023RC3102)the Excellent Innovation Youth Program of Changsha of China(Grant No.kq2209010)the Key Research and Development Program of Hunan Province(Grant No.2023GK2007)。
文摘Islanded microgrids(IMGs)offer a viable and efficient energy self-sustaining solution for distributed resources in remote areas.While without utility grid support,the frequency of IMG is susceptible to mismatches between demand and generation.Moreover,IMGs encounter uncertain and nonlinear load disturbances together with system parameter perturbation,which further compromises frequency stability.To this aim,this paper proposes a robust multi-virtual synchronous generators(multi-VSGs)coordinated control strategy for distributed secondary frequency regulation(DSFR)in IMGs,which exhibits minimal model dependency and avoids reliance on global information.Two critical methods are developed:(1)a robust VSG control framework that incorporates the linear active disturbance rejection control(LADRC)technique,which enables the estimation and effective elimination of uncertain load disturbances and system's parameter perturbations;(2)a novel secondorder consensus algorithm-based control law for robust secondary frequency regulation,which is featured with proper power sharing among different participants,suppressed power oscillation caused by response disparities,and reduced reliance on complex communication system.Building on methods(1)and(2),a novel multi-VSGs coordinated control strategy is proposed,providing a robust solution for IMG's frequency restoration,and its dynamic characteristics are explored in detail.The correctness and effectiveness of the proposal are verified by both simulation and the hardware-in-the-loop(HIL)experiment results across typical scenarios.
基金supported by the Science and Technology Project of SGCC under grant 5400-202219417A-2-0-ZN.
文摘The high proportion of nonlinear and unbalanced loads results in power quality issues in islanded microgrids.This paper presents a novel control strategy for harmonic and unbalanced power allocation among distributed genera-tors(DGs)in microgrids.Different from the existing sharing strategies that allocate the harmonic and unbalanced power according to the rated capacities of DGs,the proposed control strategy intends to shape the lowest output impedances of DGs to optimize the power quality of the microgrid.To achieve this goal,the feasible range of virtual impedance is analyzed in detail by eigenvalue analysis,and the findings suggest a simultaneous adjustment of real and imaginary parts of virtual impedance.Because virtual impedance is an open-loop control that imposes DG to the risk of overload,a new closed-loop structure is designed that uses residual capacity and absorbed power as feedback.Accordingly,virtual impedance can be safely adjusted in the feasible range until the power limit is reached.In addi-tion,a fuzzy integral controller is adopted to improve the dynamics and convergence of the power distribution,and its performance is found to be superior to linear integral controllers.Finally,simulations and control hardware-in-the-loop experiments are conducted to verify the effectiveness and usefulness of the proposed control strategy.
基金supported in part by National“111”Project,China(No.B08036)in part by Chongqing Graduate Student Research Innovation Project,China(No.CYB14015).
文摘With the high integration of power electronic technologies in microgrids,the reliability assessment considering power electronic devices has become a hot topic.However,so far no research has considered the impact of the operation failure probability of power electronic equipment on the overall reliability of the microgrid.This paper aims to construct a holistic operation failure rate model of power electronic systems based on the overall reliability assessment of islanded microgrid with high penetration of renewable energy sources(RESs).In addition,to improve the reliability of islanded microgrid,the conventional battery energy storage system(BESS)is replaced by the hybrid energy storage system(HESS).Based on the proposed model,the operation failure models for the power electronic modules in microgrid are built and tested,and then the sensitivity analysis is performed for exploring the influence of various factors on the reliability of the microgrid.
基金supported by National Natural Science Foundation of China(No.51707115).
文摘With the proliferation of renewable energy and electric vehicles(EVs),there have been increasing uncertainties in power systems.Identifying the influencing random variables will reduce the effort in uncertainty modeling and improve the controllability of power systems.In this paper,a density-based global sensitivity analysis(GSA)method is proposed to evaluate the influence of uncertainties on islanded microgrids(IMGs).Firstly,the maximum IMG loadability evaluation model is established to assess the distance from the current operation point to the critical operation point.Secondly,the Borgonovo method,which is a density-based GSA method,is used to evaluate the influence of input variables on IMG loadability.Thirdly,to improve GSA efficiency,a modified Kriging model is used to obtain a surrogate model of IMG loadability,and Borgonovo indices are calculated based on the surrogate model.Finally,the proposed method is tested on a 38-bus IMG system.Simulation results are compared with those considering other methods to validate the effectiveness of the proposed method.Energy storage systems are considered to diminish the influence of critical uncertainties on IMG operation.
基金This work was supported by the National Natural Science Foundation of China(No.51777077)the Natural Science Foundation of Guangdong Province(No.2017A030313304).
文摘Due to the lack of support from the main grid,the intermittency of renewable energy sources(RESs)and the fluctuation of load will derive uncertainties to the operation of islanded microgrids(IMGs).It is crucial to allocate appropriate reserve capacity for the economic and reliable operation of IMGs.With the high penetration of RESs,it faces both economic and environmental challenges if we only use spinning reserve for reserve support.To solve these problems,a multi-type reserve scheme for IMGs is proposed according to different operation characteristics of generation,load,and storage.The operation risk due to reserve shortage is modeled by the conditional value-at-risk(CVaR)method.The correlation of input variables is considered for the forecasting error modeling of RES and load,and Latin hypercube sampling(LHS)is adopted to generate the random scenarios of the forecasting error,so as to avoid the dimension disaster caused by conventional large-scale scenario sampling approaches.Furthermore,an optimal day-ahead scheduling model of joint energy and reserve considering riskbased reserve decision is established to coordinate the security and economy of the operation of IMGs.Finally,the comparison of numerical results of different schemes demonstrate the rationality and effectiveness of the proposed scheme and model.
基金This work was supported in part by the science and technology project of State Grid Corporation of China under Grant 5400-201955369A-0-0-00。
文摘An optimal operation scheme is of great significance in islanded distribution networks to restore critical loads and has recently attracted considerable attention.In this paper,an optimal power flow(OPF)model for islanded distribution networks equipped with soft open points(SOPs)is proposed.Unlike in the grid-connected mode,the adequacy of local power generation in distribution networks is critical for islanded systems.The proposed approach utilizes the power output of local distributed generations(DGs)and the benefits of reactive power compensation provided by SOPs to allow maximum loadability.To exploit the available resources,an optimal secondary droop control strategy is introduced for the islanded distribution networks,thereby minimizing load shedding.The formulated OPF problem is essentially a mixed-integer nonlinear programming(MINLP)model.To guarantee the computation efficiency and accuracy.A successive mixed-integer second-order cone programming(SMISOCP)algorithm is proposed for handling the nonlinear islanded power flow formulations.Two case studies,incorporating a modified IEEE 33-bus system and IEEE 123-bus system,are performed to test the effectiveness of the proposed approach.
文摘This study proposes a novel combined primary and secondary control approach for direct current microgrids,specifi-cally in islanded mode.In primary control,this approach establishes an appropriate load power sharing between the distributed energy resources based on their rated power.Simultaneously,it considers the load voltage deviation and provides satisfactory voltage regulation in the secondary control loop.The proposed primary control is based on an efficient droop mechanism that only deploys the local variable measurements,so as to overcome the side effects caused by communication delays.In the case of secondary control,two different methods are devised.In the first,low bandwidth communication links are used to establish the minimum required data transfer between the converters.The effect of communication delay is further explored.The second method excludes any communication link and only uses local variables.Accordingly,a self-sufficient control loop is devised without any communication require-ment.The proposed control notions are investigated in MATLAB/Simulink platform to highlight system performance.The results demonstrate that both proposed approaches can effectively compensate for the voltage deviation due to the primary control task.Detailed comparisons of the two methods are also provided.
基金Supported by the Science and Technology Project of China Southern Power Grid(ZBKJXM20180211).
文摘A virtual synchronous generator(VSG)can provide inertial support through renewables and energy storage.It generally operates in parallel with a diesel generator(DSG)in an islanded microgrid.However,unforeseen interactive power oscillations occur in the paralleled system when loads fluctuate.These may also burn out the VSG owing to its low overcurrent capacity.The mechanism and suppression strategy of the power oscillation of a VSG-DSG paralleled system are investigated.It reveals that the interactive power oscillation is caused essentially by the physical difference and parameter mismatch between the VSG and DSG.Then,the elimination condition of oscillation generation is derived.Subsequently,a comprehensive suppression control strategy based on virtual inductance and dynamic mutual damping technology is proposed.Finally,the experimental results verify the effectiveness of the proposed method.
基金supported by the Ministry of Education(MOE),Republic of Singapore,under grant(AcRFTIER-1 RT11/22)。
文摘In this paper,an optimal secondary control strategy is proposed for islanded AC microgrids considering communi-cation time-delays.The proposed method is designed based on the data-driven principle,which consists of an offine training phase and online application phase.For offline training,each control agent is formulated by a deep neural network(DNN)and trained based on a multi-agent deep reinforcement learning(MA-DRL)framework.A deep deterministic policy gradient(DDPG)algorithm is improved and applied to search for an optimal policy of the secondary control,where a global cost function is developed to evaluate the overall control performance.In addition,the communication time-delay is introduced in the system to enrich training scenarios,which aims to solve the time-delay problem in the secondary control.For the online stage,each controller is deployed in a distributed way which only requires local and neighboring information for each DG.Based on this,the well-trained controllers can provide optimal solutions under load variations,and communication time-delays for online applications.Several case studies are conducted to validate the feasibility and stability of the proposed secondary control.Index Terms-Communication time-delay,global cost function,islanded AC microgrid,multi-agent deep reinforcement learning(MA-DRL),secondary control.
基金supported by the National Key Research and Development Program of China(Basic Research Class)(2017YFB0903000)the National Natural Science Foundation of China(U1909201).
文摘For islanded microgrids(MGs),distributed control is regarded as a preferred alternative to centralized control for the frequency restoration of MGs.However,distributed control with successive communication restricts the efficiency and resilience of the control system.To address this issue,this paper proposes a distributed event-triggered control strategy for the frequency secondary control in islanded MGs.The proposed event-triggered control is Zeno behavior free and enables each DG to update and propagate its state to neighboring DGs only when a specific“event”occurs,which significantly reduces the communication burden.Compared with the existing event-triggered control,a trigger condition checking period of the proposed event-triggered control is provided to reduce the computation burden when checking the trigger condition.Furthermore,using the aperiodicity and intermittent properties of the communication,a simple detection principle is proposed to detect and isolate the compromised communication links in a timely and economic fashion,which improves the resilience of the system against FDI attacks.Finally,the control effectiveness of the proposed control scheme is validated by the simulation results of the tests on an MG with 4 DGs.
文摘This survey paper provides a critical overview of optimization formulations for planning and operation of islanded microgrids,including optimization objectives,constraints,and control variables.The optimization approaches reviewed address methods both for increasing the resiliency of advanced distribution systems and electrification of remote communities.This paper examines over 120 individual optimization studies and discovers that all optimizations studies of islanded microgrids are based on formulations selecting a combination of 16 possible objective functions,14 constraints,and 13 control variables.Each of the objectives,constraints,and variables are discussed exhaustively both from the perspective of their importance to islanded microgrids and chronological trends in their popularity.
