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 Equivalent Sliding Mode Controller for Stability of DC Microgrid

2021 ◽  
Vol 12 (1) ◽  
pp. 23
Author(s):  
Muhammad Rashad ◽  
Uzair Raoof ◽  
Nazam Siddique ◽  
Bilal Ashfaq Ahmed
Keyword(s):  
Reactive Power ◽  
Sliding Mode ◽  
Voltage Regulation ◽  
Pi Controller ◽  
Operating Conditions ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Central Controller ◽  
The Stability ◽  
Decentralized Architecture

DC microgrids are gaining popularity due to their lack of reactive power compensation, frequency synchronization, and skin effect problems. However, DC microgrids are not exempted from stability issues. The stability of DC microgrids based on decentralized architecture is presented in this paper. Centralized architecture can degrade system performance and reliability due to the failure of a single central controller. Droop with proportional integral (PI) controller based on decentralized architecture is being used for DC microgrid stability. However, droop control requires a tradeoff between voltage regulation and droop gain. Further, global stability through PI controller cannot be verified and controller parameters cannot be optimized with different operating conditions. To address limitations, an equivalent sliding mode (SM) controller is proposed for a DC microgrid system in this paper. Detailed simulations are carried out, and results are presented, which show the effectiveness of an equivalent SM controller.

Decentralized Voltage Balancing and Power Sharing in Islanded Bipolar DC Microgrids

2020 ◽  
Author(s):  
Saman Dadjo Tavakoli
Keyword(s):  
Transfer Functions ◽  
Control Method ◽  
Input Voltage ◽  
Voltage Regulation ◽  
Power Sharing ◽  
Dc Microgrid ◽  
Voltage Balancing ◽  
Dc Microgrids ◽  
Converter Topology ◽  
Unbalanced Loads

<div>This paper presents a decentralized control scheme for voltage balancing and power sharing in bipolar dc</div><div>microgrids. This relies on utilizing a converter topology which offers three levels of output voltage availability with the key features of boosting the input voltage and balancing the output voltages. This converter makes it possible to further improve the structure of bipolar dc microgrids as it does not require a central voltage balancer. Small-signal analysis is done and system transfer functions are derived. Based on the RGA concept the highly coupled input-output pairs are found which helps with replacing the MIMO control system of the converter by two SISO systems. The appropriate voltage and current controllers are designed based on SISO principles. Moreover, a double droop control method is proposed which fulfills the simultaneous power sharing and voltage regulation of DG units in the host microgrid. The effectiveness of the proposed control strategy is demonstrated through simulation studies conducted on an</div><div>islanded bipolar dc microgrid involving unbalanced loads, while the voltage balancing of the bipolar dc microgrid and the power sharing accuracy are evaluated.</div>

scholarly journals Decentralized Voltage Balancing and Power Sharing in Islanded Bipolar DC Microgrids

2020 ◽  
Author(s):  
Saman Dadjo Tavakoli
Keyword(s):  
Transfer Functions ◽  
Control Method ◽  
Input Voltage ◽  
Voltage Regulation ◽  
Power Sharing ◽  
Dc Microgrid ◽  
Voltage Balancing ◽  
Dc Microgrids ◽  
Converter Topology ◽  
Unbalanced Loads

<div>This paper presents a decentralized control scheme for voltage balancing and power sharing in bipolar dc</div><div>microgrids. This relies on utilizing a converter topology which offers three levels of output voltage availability with the key features of boosting the input voltage and balancing the output voltages. This converter makes it possible to further improve the structure of bipolar dc microgrids as it does not require a central voltage balancer. Small-signal analysis is done and system transfer functions are derived. Based on the RGA concept the highly coupled input-output pairs are found which helps with replacing the MIMO control system of the converter by two SISO systems. The appropriate voltage and current controllers are designed based on SISO principles. Moreover, a double droop control method is proposed which fulfills the simultaneous power sharing and voltage regulation of DG units in the host microgrid. The effectiveness of the proposed control strategy is demonstrated through simulation studies conducted on an</div><div>islanded bipolar dc microgrid involving unbalanced loads, while the voltage balancing of the bipolar dc microgrid and the power sharing accuracy are evaluated.</div>

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.

scholarly journals Comparative Study of Control Strategies for Stabilization and Performance Improvement of DC Microgrids with a CPL Connected

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2663
Author(s):  
Isaías V. de Bessa ◽  
Renan L. P. de Medeiros ◽  
Iury Bessa ◽  
Florindo A. C. Ayres Junior ◽  
Alessandra R. de Menezes ◽  
...  
Keyword(s):  
Control Strategies ◽  
Output Feedback Control ◽  
Stability Margin ◽  
Performance Indices ◽  
Dc Microgrid ◽  
Stability Margins ◽  
Dc Microgrids ◽  
Constant Power Loads ◽  
And Performance ◽  
The Stability

The DC microgrid system is composed by converters that operate like feeders and loads. Among these loads, we highlight the constant power loads (CPLs) that may cause instability in the microgrid, observed in the form of undesired oscillations due to its negative impedance behavior. Therefore, this work proposes to use performance indices and stability margins to evaluate state and output feedback control strategies for stabilization of DC microgrids. In particular, it is proposed to evaluate the stability margin of the proposed methodologies by means of the impedance relations in the microgrid based on the Middlebrook criterion. Our simulations and tests showed the relation between the performance and stability degradation and the microgrid impedances variation.

scholarly journals A Theoretical Concept of Decoupled Current Control Scheme for Grid-Connected Inverter with L-C-L Filter

2021 ◽  
Vol 11 (14) ◽  
pp. 6256
Author(s):  
Mohamad Amin Ghasemi ◽  
Seyed Fariborz Zarei ◽  
Saeed Peyghami ◽  
Frede Blaabjerg
Keyword(s):  
Control Method ◽  
Controller Design ◽  
Current Control ◽  
System Stability ◽  
State Equations ◽  
Lcl Filter ◽  
Control Scheme ◽  
Grid Connected Inverter ◽  
The Stability ◽  
Grid Side

This paper proposes a nonlinear decoupled current control scheme for a grid-connected inverter with LCL filter. Decoupling the active and reactive current control channels is one of the main demands in the control of inverters. For inverters with an L filter, the decoupling can be achieved by a proper feed-forward of grid voltages. However, the coupling of channels is a complex issue for converters with LCL filters. The resonance mode of the LCL filter may cause instability, which adds more complexity to the analysis. In this paper, state equations of the system are provided, which highlight the coupling between active and reactive currents injected into the grid. Accordingly, a non-linear control scheme is proposed which effectively decouples the channels and dampens the resonant modes of the LCL filter. The stability of the proposed control method is verified by the Lyapunov criterion. Independency of the system stability to the grid-impedance is another feature of the proposed approach. Moreover, only grid-side currents are needed for implementation of the proposed scheme, avoiding the need for additional current sensors for the output capacitor and grid-side inductor. For accurate modelling of the inverter, the computation and PWM sampling delays are included in the controller design. Finally, various case studies are provided that verify the performance of the proposed approach and the stability of the system.

scholarly journals Review of Control Strategies for DC Nano-Grid

2021 ◽  
Vol 9 ◽  
Author(s):  
Hong Fan ◽  
Weinan Yu ◽  
Shiwei Xia
Keyword(s):  
Cooperative Control ◽  
Control Strategies ◽  
High Reliability ◽  
Renewable Energy Sources ◽  
Current Control ◽  
Power Sharing ◽  
Research Progress ◽  
Control Technology ◽  
Advantages And Disadvantages ◽  
Control Technologies

As an emerging energy management technology, the DC nano-grid coordinates renewable energy sources output through demand-side management which would provide more options and flexibility for the dispatch of smart buildings and communities with high reliability and efficiency. In this context, this article has analyzed the structure and components of the DC nano-grid. The role and components in DC nano-grid are reviewed in this article. Then the crucial control technologies for the DC nano-grid in recent years are investigated from two aspects: local control and coordinated control, which contains control schemes such as voltage/current control technology, power-sharing technology and cooperative control technology. Different control strategies at various levels are compared and their application scenarios, advantages and disadvantages are also analyzed. The current research progress and challenges are summarized at the end of this article.

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