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Research on the Stability Analysis Method of dc microgrid Based on Bifurcation and Strobe Theory

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Energy Engineering 2024年第4期121卷 987-1005页

作者： Wei Chen Nan Qiu Xusheng Yang School of Electrical Engineering and Information Engineering Lanzhou University of TechnologyLanzhou730050China

During the operation of a dc microgrid,the nonlinearity and low damping characteristics of the dc bus make it prone to oscillatory instability.In this paper,we first establish a discrete nonlinear system dynamic model of a dc microgrid,study the effects of the converter sag coefficient,input voltage,and load resistance on the microgrid stability,and reveal the oscillation mechanism of a dc microgrid caused by a single source.Then,a dc microgrid stability analysis method based on the combination of bifurcation and strobe is used to analyze how the aforementioned parameters influence the oscillation characteristics of the system.Finally,the stability region of the system is obtained by the Jacobi matrix eigenvalue method.Grid simulation verifies the feasibility and effectiveness of the proposed method.

关键词： dc microgrid bifurcation nonlinear dynamics stability analysis oscillation characteristics

Distributed Secondary Control Based on Dynamic Diffusion Algorithm for Current Sharing and Average Voltage Regulation in dc microgrids

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Journal of Modern Power Systems and Clean Energy 2024年第2期12卷 597-607页

作者： Dawei Liao Fei Gao Daniel J.Rogers Wentao Huang Dong Liu Houjun Tang Department of Electrical Engineering Shanghai Jiao Tong UniversityShanghaiChina Department of Engineering Science University of OxfordOxford OX12JDU.K. IEEE

This paper introduces a distributed secondary control scheme for achieving current sharing and average voltage regulation objectives in a dc microgrid.The proposed scheme employs a dynamic diffusion algorithm(DDA)instead of the consensus algorithm to enable distributed communication among converters.To help understand DDA,the relation of DDA and other diffusion algorithms is discussed in detail and its superiority is shown by comparison with diffusion and consensus algorithms.Furthermore,considering the discrete nature and different sampling time of the digital controller and communication network,a z-domain model of the entire dc microgrid is established.The influence of communication and secondary control parameters on the system stability is investigated.Based on the established model,the tolerable communication rates are obtained.Real-time simulations conducted on the OPAL-RT platform validate the effectiveness of the proposed scheme,showcasing its advantages in terms of convergence speed and stability.

关键词： Cooperative control dc microgrid diffusion algorithm discrete-time modeling distributed secondary control

Robust Control Strategy for Inductive Parametric Uncertainties of dc/dc Converters in Islanded dc microgrid

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Journal of Modern Power Systems and Clean Energy 2023年第1期11卷 335-344页

作者： Salisu Abdullahi Tao Jin P.M.Lingom School of Electrical Engineering and Automation Fuzhou UniversityFuzhouChina

Direct current(dc) microgrid consists of many parallel power converters that share load currents through the inductance of dc/dc converters. Usually, the inductance parameters are dependent on the physical implementation of the system, and their values may not match their nameplates. Such disparities could lead to unequal response characteristics of the system, which can potentially reduce the performances of the dc microgrid operation. This paper proposes a robust control strategy for inductive parametric uncertainties of dc/dc converters using an optimal control method with integral action. To achieve such a goal, the system model parameters with nominal values are transformed into parametric unmatched uncertainties to form a robust control problem, which is then transformed into a linear quadratic regulator problem. The inductance uncertainties are stabilized with the uncertainty dynamic algebraic Riccati equation(UDARE) using state feedback gain under linear quadratic regulator. The closed-loop control with integral action is adopted to achieve a steady-state error of zero on the dc-link voltage at any uncertainty of the inductive parameter, which subsequently ensures the equal load current sharing. Off-line simulations and real-time validations based on OpalRT have been conducted to demonstrate the effectiveness and robustness of the proposed robust control strategy.

关键词： dc/dc converter dc microgrid OpalRT optimal control parametric uncertainty robust control

A Review on Challenges in dc microgrid Planning and Implementation

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Journal of Modern Power Systems and Clean Energy 2023年第5期11卷 1375-1395页

作者： Kolampurath Jithin Puthan Purayil Haridev Nanappan Mayadevi Raveendran Pillai Harikumar Valiyakulam Prabhakaran Mini IEEE Department of Electrical Engineering College of Engineering TrivandrumAPJ Abdul Kalam Technological University(APJAKTU)ThiruvananthapuramKeralaIndia Tata Consultancy Services(TCS) KochiKeralaIndia

dc microgrids are gaining more attention with the increased penetration of various dc sources such as solar photovoltaic systems, fuel cells, batteries, etc., and dc loads. Due to the rapid integration of these components into the existing power system, the importance of dc microgrids has reached a salient point. Compared with conventional AC systems, dc systems are free from synchronization issues, reactive power control, frequency control, etc., and are more reliable and efficient.However, many challenges need to be addressed for utilizing dc power to its full potential. The absence of natural current zero is a significant issue in protecting dc systems. In addition,the stability of the dc microgrid, which relies on inertia, needs to be considered during system design. Moreover, power quality and communication issues are also significant challenges in dc microgrids. This paper presents a review of various value streams of dc microgrids including architectures, protection schemes, power quality, inertia, communication, and economic operation. In addition, comparisons between different microgrid configurations, the state-of-the-art projects of dc microgrid, and future trends are also set forth for further studies.

关键词： Architecture communication dc microgrid economic operation inertia protection power quality

A Unified Control of Super-capacitor System Based on Bi-directional dc-dc Converter for Power Smoothing in dc microgrid

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Journal of Modern Power Systems and Clean Energy 2023年第3期11卷 938-949页

作者： Xialin Li Pengfei Li Leijiao Ge Xunyang Wang Zhiwang Li Lin Zhu Li Guo Chengshan Wang Key Laboratory of Smart Grid of Ministry of Education Tianjin UniversityTianjin 300072China School of Information and Electronic Engineering Hebei University of EngineeringHandan 056038China Binhai Power Supply Bureau of State Grid Tianjin Electric Power Company Tianjin 300480China

To improve the equivalent inertia of dc microgrids(dcMGs),a unified control is proposed for the first time for a bi-directional dc-dc converter based super-capacitor(SC)system,whereby power smoothing and SC terminal voltage regulation can be achieved in a dcMG simultaneously.The proposed control displays good plug-and-play features using only local measurements.For quantitative analysis and effective design of the critical parameter of unified control,two indices,equivalent power supporting time and inertia contributed by the unified controlled SC system,are introduced firstly.Then,with a simple but effective reduced-order model of a dcMG,analytical solutions are obtained for the two indices.In addition,a systematic design method is presented for the proposed unified control.Finally,to verify the proposed unified control,a switching model is developed for a typical dcMG in PSCAD/EMTdc,and theoretical analyses are conducted for different operating conditions.

关键词： dc microgrid dc-dc converter super-capacitor unified control equivalent power supporting time and inertia power smoothing

Graph Convolutional Network Based Fault Detection and Identification for Low-voltage dc microgrid

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Journal of Modern Power Systems and Clean Energy 2023年第3期11卷 917-926页

作者： Ambuj Pandey Soumya R.Mohanty Department of Electrical Engineering Indian Institute of Technology(BHU)VaranasiUttar PradeshIndia IEEE

This paper presents a novel fault detection and identification method for low-voltage direct current(dc)microgrid with meshed configuration.The proposed method is based on graph convolutional network(GCN),which utilizes the explicit spatial information and measurement data of the network topology to identify a fault.It has a more substantial feature extraction ability even in the presence of noise and bad data.The adjacency matrix for GCN is developed by considering the network topology as an inherent graph.The bus voltage and line current samples after faults are regarded as the node attributes.Moreover,the dc microgrid model is developed using PSCAD/EMTdc simulation,and fault simulation is carried out by considering different possible events that include environmental and physical conditions.The performance of the proposed method under different conditions is compared with those of different machine learning techniques such as convolutional neural network(CNN),support vector machine(SVM),and fully connected network(FCN).The results reveal that the proposed method is more effective than others at detecting and classifying faults.This method also possesses better robustness under the presence of noise and bad data.

关键词： dc microgrid graph convolution network fault detection topological information

Distributed Real-time Optimal Power Flow Strategy for dc microgrid Under Stochastic Communication Networks

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Journal of Modern Power Systems and Clean Energy 2023年第5期11卷 1585-1595页

作者： Jian Hu Hao Ma Power Dispatching Control Center Nanjing Power Supply CompanyState Grid Corporation of ChinaNanjing 210019China School of Electrical Engineering Zhejiang UniversityHangzhouChina

This paper addresses a distributed real-time optimal power flow(RTOPF) strategy for dc microgrids. In this paper, we focus on the scenarios where local information sharing is conducted in stochastic communication networks subject to random failures. Most existing real-time optimal power flow(OPF) algorithms for the dc microgrid require all controllers to work in concert with a fixed network topology to maintain a zero gap between estimated global constraint violations. Thus, the high reliability of communication is required to ensure their convergence. To address this issue, the proposed RTOPF strategy tolerates stochastic communication failures and can seek the optimum with a constant step size considering the operation limitations of the microgrid. These aspects make the strategy suitable for real-time optimization, particularly when the communication is not reliable. In addition, this strategy does not require information from non-dispatchable devices, thereby reducing the number of sensors and controllers in the system. The convergence of the proposed strategy and the optimal equilibrium points are theoretically proven. Finally, simulations of a 30-bus dc microgrid are performed to validate the effectiveness of the proposed designs.

关键词： dc microgrid distributed optimization stochastic communication network consensus algorithm

Distributed dc-Bus Signaling Control of Photovoltaic Systems in Islanded dc microgrid

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CSEE Journal of Power and Energy Systems 2022年第6期8卷 1741-1750页

作者： Noushin Poursafar M.J.Hossain Seyedfoad Taghizadeh Macquarie University SydneyNew South WalesAustralia

The stability of an islanded dc microgrid(dcMG)is highly dependent on the presence and performance of the backup energy storage system(BESS),due to the lack of main grid support.This condition makes the dcMG vulnerable to the critical situation of absence of the BESS,which could be caused by a fault or being fully charged or flat.This paper presents an enhanced distributed dc-bus signaling control strategy for converters of photovoltaic systems(PVs)to make the islanded dcMG less dependent on the BESS.Unlike a conventional control approach that utilizes PVs to operate in maximum power point tracking(MPPT)mode and the BESS solely regulating dc-bus voltage,the proposed control method maintains dc-bus voltage via intelligently managing output powers of the PVs.The proposed control method continuously monitors dc-bus voltage and regulates the output powers of all the PVs via switching between MPPT mode and voltage regulating mode.Accordingly,if the dc-bus voltage level is less than a predefined maximum level,the PVs work in MPPT mode;otherwise,the PVs work in voltage regulating mode to maintain dc-bus voltage at an acceptable range.Such switching between MPPT and voltage regulating control operations results in protecting the dcMG from unavoidable shutdowns conventionally necessary during the absence of the BESS unit.Moreover,the proposed control method reduces oscillations on the dc-bus voltage during existence of the BESS.The performance and effectiveness of the proposed control strategy are validated through different case studies in MATLAB/Simulink.

关键词： dc microgrid voltage stability islanding mode distributed control distributed generator(DG)

A new hybrid control technique for operation of dc microgrid under islanded operating mode

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Protection and Control of Modern Power Systems 2022年第1期7卷 646-656页

作者： Vahid Mortezapour Sajjad Golshannavaz Edris Pouresmaeil Amin Yazdaninejadi School of Electrical and Computer Engineering University of Tehran16th Azar St.Enghelab Sq.TehranIran Electrical Engineering Department Urmia University11Km SERO RoadUrmia CityIran Department of Electrical Engineering and Automation Aalto UniversityAalto University Foundation srPO BOX 11000FI-00076 AaltoFinland Department of Electrical Engineer-ing Shahid Rajaee Teacher Training UniversityShabanlouQFJR+2MPTehranTehran ProvinceIran.

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.

关键词： Hybrid control technique Modern power system dc microgrid Islanded operating mode