scholarly journals A Stability Preserving Criterion for the Management of DC Microgrids Supplied by a Floating Bus

2018 ◽  
Vol 8 (11) ◽  
pp. 2102 ◽  
Author(s):  
Daniele Bosich ◽  
Andrea Vicenzutti ◽  
Samuele Grillo ◽  
Giorgio Sulligoi
Keyword(s):  
Power Systems ◽  
Basin Of Attraction ◽  
Careful Analysis ◽  
Lyapunov Theory ◽  
Continuation Methods ◽  
System Stability ◽  
Smart Power ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Bus Voltage

Direct current (DC) distribution is one of the most important enabling technologies for the future development of microgrids, due to the ease of interfacing DC components (e.g., batteries, photovoltaic systems, and native DC loads) to the grid. In these power systems, the large use of controlled power converters suggests the need of a careful analysis of system stability, as it can be impaired in particular conditions. Indeed, in DC power systems, a destabilizing effect can arise due to the presence of inductor/capacitor (LC) filtering stages (installed for power quality requirements) and high-bandwidth controlled converters, behaving as constant power loads (CPLs). This issue is even more critical when the CPL is potentially fed only by the battery, causing the DC bus to be floating. In this context, Lyapunov theory constitutes a valuable method for studying the system stability of DC microgrids feeding CPLs. Such a theory demonstrates how the region of asymptotic stability (RAS) shrinks as the state of charge of the battery diminishes (i.e., as the bus voltage decreases). Once the accuracy of the RAS is validated by comparing it to the real basin of attraction (BA), numerically derived using continuation methods, a smart power management of the CPL can be proposed to preserve the system stability even in the presence of a low bus voltage. Indeed, a suitably designed criterion for limiting the load power can guarantee the invariance of RAS and BA for each equilibrium point. An electric vehicle was used herein as a particular DC microgrid for evaluating the performance derating given by the power limitation.

Codimension-Two Bifurcation Analysis in DC Microgrids Under Droop Control

2016 ◽  
Vol 26 (02) ◽  
pp. 1650028 ◽  
Author(s):  
Eduardo Lenz ◽  
Daniel J. Pagano ◽  
André P. N. Tahim
Keyword(s):  
Power Systems ◽  
Bifurcation Analysis ◽  
Electrical Power ◽  
Droop Control ◽  
Electrical Power Systems ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Codimension Two ◽  
Bus Voltage ◽  
Codimension Two Bifurcation

This paper addresses local and global bifurcations that may appear in electrical power systems, such as DC microgrids, which recently has attracted interest from the electrical engineering society. Most sources in these networks are voltage-type and operate in parallel. In such configuration, the basic technique for stabilizing the bus voltage is the so-called droop control. The main contribution of this work is a codimension-two bifurcation analysis of a small DC microgrid considering the droop control gain and the power processed by the load as bifurcation parameters. The codimension-two bifurcation set leads to practical rules for achieving a robust droop control design. Moreover, the bifurcation analysis also offers a better understanding of the dynamics involved in the problem and how to avoid possible instabilities. Simulation results are presented in order to illustrate the bifurcation analysis.

Under Frequency Load Shedding Techniques for Future Smart Power Systems

2019 ◽  
pp. 188-202
Author(s):  
H. H. Alhelou
Keyword(s):  
Power Systems ◽  
Power System ◽  
Active Power ◽  
Load Shedding ◽  
System Stability ◽  
Special Focus ◽  
Power Demand ◽  
Synchronous Generators ◽  
Smart Power ◽  
System Frequency

It is critical for today's power system to remain in a state of equilibrium under normal conditions and severe disturbances. Power imbalance between the load and the generation can severely affect system stability. Therefore, it is necessary that these imbalance conditions be addressed in the minimum time possible. It is well known that power system frequency is directly proportional to the speed of rotation of synchronous machines and is also a function of the active power demand. As a consequence, when active power demand is greater than the generation, synchronous generators tends to slow down and the frequency decreases to even below threshold if not quickly addressed. One of the most common methods of restoring frequency is the use of under frequency load shedding (UFLS) techniques. In this chapter, load shedding techniques are presented in general but with special focus on UFLS.

scholarly journals Distributed Control Strategy for DC Microgrids of Photovoltaic Energy Storage Systems in Off-Grid Operation

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2637 ◽  
Author(s):  
Mingxuan Chen ◽  
Suliang Ma ◽  
Haiyong Wan ◽  
Jianwen Wu ◽  
Yuan Jiang
Keyword(s):  
Energy Storage ◽  
Power Systems ◽  
Distributed Control ◽  
Control Strategy ◽  
Storage System ◽  
Voltage Stabilizer ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Photovoltaic Energy ◽  
Operation Conditions

DC microgrid systems that integrate energy distribution, energy storage, and load units can be viewed as examples of reliable and efficient power systems. However, the isolated operation of DC microgrids, in the case of a power-grid failure, is a key factor limiting their development. In this paper, we analyze the six typical operation modes of an off-grid DC microgrid based on a photovoltaic energy storage system (PV-ESS), as well as the operational characteristics of the different units that comprise the microgrid, from the perspective of power balance. We also analyze the key distributed control techniques for mode transformation, based on the demands of the different modes of operation. Possible reasons for the failure of PV systems under the control of a voltage stabilizer are also explored, according to the characteristics of the PV output. Based on this information, we propose a novel control scheme for the seamless transition of the PV generation units between the maximum PV power tracking and steady voltage control processes, to avoid power and voltage oscillations. Adaptive drooping and stabilization control of the state of charge of the energy storage units are also considered, for the protection of the ESS and for reducing the possibilities of overcharging and/or over-discharging. Finally, various operation conditions are simulated using MATLAB/Simulink, to validate the performance of the proposed control strategy.

scholarly journals Island DC Microgrid Hierarchical Coordinated Multi-Mode Control Strategy

Energies ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 3012 ◽  
Author(s):  
Zhongbin Zhao ◽  
Jing Zhang ◽  
Yu He ◽  
Ying Zhang
Keyword(s):  
Power Systems ◽  
Control Strategy ◽  
Voltage Stability ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Mode Control ◽  
Load Power ◽  
Power Dispatch ◽  
Operation Modes ◽  
Multi Mode

As renewable energy sources connecting to power systems continue to improve and new-type loads, such as electric vehicles, grow rapidly, direct current (DC) microgrids are attracting great attention in distribution networks. In order to satisfy the voltage stability requirements of island DC microgrids, the problem of inaccurate load power dispatch caused by line resistance must be solved and the defects of centralized communication and control must be overcome. A hierarchical, coordinated, multiple-mode control strategy based on the switch of different operation modes is proposed in this paper and a three-layer control structure is designed for the control strategy. Based on conventional droop control, a current-sharing layer and a multi-mode switching layer are used to ensure the stable operation of the DC microgrid. Accurate load power dispatch is satisfied using a difference discrete consensus algorithm. Furthermore, virtual bus voltage information is applied to guarantee smooth switching between various modes, which safeguards voltage stability. Simulation verification is carried out for the proposed control strategy by power systems computer aided design/electromagnetic transients including DC (PSCAD/EMTDC). The results indicate that the proposed control strategy guarantees the voltage stability of island DC microgrids and accurate load power dispatch under different operation modes.

Cyber-Physical System for Smart Grid

2021 ◽  
pp. 301-323
Author(s):  
Nagi Faroug M. Osman ◽  
Ali Ahmed A. Elamin ◽  
Elmustafa Sayed Ali Ahmed ◽  
Rashid A. Saeed
Keyword(s):  
Smart Grid ◽  
Power Systems ◽  
Smart Grids ◽  
Power Grid ◽  
Vital Role ◽  
Computing Methods ◽  
System Stability ◽  
Smart Meters ◽  
Smart Power ◽  
Power Resources

A smart grid is an advanced utility, stations, meters, and energy systems that comprises a diversity of power processes of smart meters, and various power resources. The cyber-physical systems (CPSs) can play a vital role boosting the realization of the smart power grid. Applied CPS techniques that comprise soft computing methods, communication network, management, and control into a smart physical power grid can greatly boost to realize this industry. The cyber-physical smart power systems (CPSPS) are an effective model system architecture for smart grids. Topics as control policies, resiliency methods for secure utility meters, system stability, and secure end-to-end communications between various sensors/controllers would be quite interested in CPSPS. One of the essential categories in CPSPS applications is the energy management system (EMS). The chapter will spotlight the model and design the relationship between the grid and EMS networks with standardization. The chapter also highlights some necessary standards in the context of CPSPS for the grid infrastructure.

A Descriptive Approach for Power System Stability and Security Assessment

2013 ◽  
pp. 1527-1545
Author(s):  
A. G. Tikdari ◽  
H. Bevrani ◽  
G. Ledwich
Keyword(s):  
Power Systems ◽  
Power System ◽  
Large Scale ◽  
Renewable Energy Sources ◽  
Control Measures ◽  
System Stability ◽  
Security Assessment ◽  
Electrical Measurements ◽  
Emergency Control ◽  
Bus Voltage

Power system dynamic analysis and security assessment are becoming more significant today due to increases in size and complexity from restructuring, emerging new uncertainties, integration of renewable energy sources, distributed generation, and micro grids. Precise modeling of all contributed elements/devices, understanding interactions in detail, and observing hidden dynamics using existing analysis tools/theorems are difficult, and even impossible. In this chapter, the power system is considered as a continuum and the propagated electromechanical waves initiated by faults and other random events are studied to provide a new scheme for stability investigation of a large dimensional system. For this purpose, the measured electrical indices (such as rotor angle and bus voltage) following a fault in different points among the network are used, and the behavior of the propagated waves through the lines, nodes, and buses is analyzed. The impact of weak transmission links on a progressive electromechanical wave using energy function concept is addressed. It is also emphasized that determining severity of a disturbance/contingency accurately, without considering the related electromechanical waves, hidden dynamics, and their properties is not secure enough. Considering these phenomena takes heavy and time consuming calculation, which is not suitable for online stability assessment problems. However, using a continuum model for a power system reduces the burden of complex calculations. Finally, a new power system emergency control framework based on descriptive study of electrical measurements and electromechanical wave propagation in large electric power systems is introduced. Since, fast and accurate detection of instability is essential in initiating certain emergency control measures, the proposed methodology could be also useful to detect the contingency condition and performing the well-known islanding and load shedding techniques. The chapter is supplemented by some illustrative nonlinear simulations on large scale test systems.

Cyber-Physical System for Smart Grid

2022 ◽  
pp. 325-347
Author(s):  
Nagi Faroug M. Osman ◽  
Ali Ahmed A. Elamin ◽  
Elmustafa Sayed Ali Ahmed ◽  
Rashid A. Saeed
Keyword(s):  
Smart Grid ◽  
Power Systems ◽  
Smart Grids ◽  
Power Grid ◽  
Vital Role ◽  
Computing Methods ◽  
System Stability ◽  
Smart Meters ◽  
Smart Power ◽  
Power Resources

A smart grid is an advanced utility, stations, meters, and energy systems that comprises a diversity of power processes of smart meters, and various power resources. The cyber-physical systems (CPSs) can play a vital role boosting the realization of the smart power grid. Applied CPS techniques that comprise soft computing methods, communication network, management, and control into a smart physical power grid can greatly boost to realize this industry. The cyber-physical smart power systems (CPSPS) are an effective model system architecture for smart grids. Topics as control policies, resiliency methods for secure utility meters, system stability, and secure end-to-end communications between various sensors/controllers would be quite interested in CPSPS. One of the essential categories in CPSPS applications is the energy management system (EMS). The chapter will spotlight the model and design the relationship between the grid and EMS networks with standardization. The chapter also highlights some necessary standards in the context of CPSPS for the grid infrastructure.

scholarly journals Structural Improvements in Consensus-Based Cooperative Control of DC Microgrids

Electronics ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 187 ◽  
Author(s):  
Muhammad Adnan Mumtaz ◽  
Muhammad Mansoor khan ◽  
Xiangzhong Fang ◽  
Muhammad Umair Shahid ◽  
Muhammad Talib Faiz
Keyword(s):  
Cooperative Control ◽  
Voltage Regulation ◽  
Current Control ◽  
Power Sharing ◽  
System Stability ◽  
Control Loop ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
The Stability ◽  
Finite Gain

This study is dedicated to establishing a comparative analysis of the performance ofdifferent local controllers on the cooperative control of DC microgrids. One of the elementary andchallenging issues in DC microgrids is the assurance of fairness in proportional current sharingwhile accomplishing voltage regulation in parallelly connected distributed energy sources. In thiswork, structural improvements are proposed to enhance the system stability and controlperformance. A finite-gain controller was employed in the outer voltage control loop with a simpleproportional (P) controller in the inner current control loop of a converter. Due to the finite-gaincontroller, droop-like power sharing was achieved without droop coefficient. In order to furtherenhance the power-sharing accuracy and DC voltage regulation, a different method was adopted inconsensus-based cooperative control to estimate the average current and average voltage difference.Moreover, small signal analysis was used to scrutinize the stability and control performance of thelocal controller, while different communication delays and current disturbances were applied toexamine the performance of the controller. Finally, a four-node-based DC microgrid setup wasdeveloped in MATLAB/Simulink environment, and simulation results of the proposed and existingtechniques were scrutinized. The simulations results demonstrated the effectiveness of the proposedcontroller.

scholarly journals Integrated Control and Protection Architecture for Islanded PV-Battery DC Microgrids: Design, Analysis and Experimental Verification

2020 ◽  
Vol 10 (24) ◽  
pp. 8847
Author(s):  
Ali Abdali ◽  
Kazem Mazlumi ◽  
Josep M. Guerrero
Keyword(s):  
Fault Detection ◽  
Integrated Control ◽  
Storage System ◽  
Energy Storage System ◽  
Detection Algorithm ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Protection Scheme ◽  
Bus Voltage ◽  
Battery Energy

Direct current (dc) microgrids have gained significant interest in research due to dc generation/storage technologies—such as photovoltaics (PV) and batteries—increasing performance and reducing in cost. However, proper protection and control systems are critical in order to make dc microgrids feasible. This paper aims to propose a novel integrated control and protection scheme by using the state-dependent Riccati equation (SDRE) method for PV-battery based islanded dc microgrids. The dc microgrid under study consists of photovoltaic (PV) generation, a battery energy storage system (BESS), a capacitor bank and a dc load. The aims of this study are fast fault detection and voltage control of the dc load bus. To do so, the SDRE observer-controller—a nonlinear mathematical model—is employed to model the operation of the dc microgrid. Simulation results show that the proposed SDRE method is effective for fault detection and robust against external disturbances, resulting in it being capable of controlling the dc load bus voltage during disturbances. Finally, the dc microgrid and its proposed protection scheme are implemented in an experimental testbed prototype to verify the fault detection algorithm feasibility. The experimental results indicate that the SDRE scheme can effectively detect faults in a few milliseconds.

scholarly journals Proposed energy management for a decentralized DC-microgrid based PV-WT-HESS for an isolated community

2020 ◽  
Vol 11 (4) ◽  
pp. 2073
Author(s):  
Hafsi Oussama ◽  
Abdelkhalek Othmane ◽  
Hartani Mohammed Amine ◽  
Chakar Abdesselam ◽  
Soumeur Mohammed Amine
Keyword(s):  
Power Systems ◽  
Storage System ◽  
Energy Storage System ◽  
Storage Device ◽  
Small Scale ◽  
Dc Microgrid ◽  
Hybrid Energy ◽  
Discharge Operation ◽  
Bus Voltage ◽  
The Stability

Microgrids are small-scale power systems destined to supply isolated villages and optimum utilization of renewable energies. For this reason, this paper presents a DC-MG of 150 Kwp to feed an island village. The configuration of the proposed system consists of four interconnected sub-sections supplied by the centralized unit through PV and Wind Distributed Energy Resources DERs, in addition to the supercapacitor storage device. In the other hand, internal batteries of each sub-section cover its load demand separately, where electrical and chemical storage devices can be advantageous hybrid energy storage system HESS for the system. Thus, the control structure of the DC-MG is based on current hysteresis method to assure the charge/discharge operation and the stability of the DC-bus voltage, then a proposed management strategy to manage the shared energy of the DCMG system. The system behavior is tested under variable parameters and conditions using Matlab/Simulink.

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