scholarly journals Monitoring interfaces for photovoltaic systems and DC microgrids: brief survey and application case

2021 ◽  
pp. 183-189
Author(s):  
Isaías González Pérez ◽  
Antonio José Calderón Godoy ◽  
José María Portalo Calero ◽  
Manuel Calderón Godoy
Keyword(s):  
Open Source ◽  
Human Operator ◽  
Photovoltaic Systems ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Energetic Interactions ◽  
Graphical Design ◽  
Special Relevance

Monitoring interfaces enable the interaction between the human operator and the monitored process. This role acquires special relevance for advanced scenarios like microgrids and renewable energiesbased facilities, which involve a large amount of magnitudes and energetic interactions. This paper performs a brief survey about monitoring interfaces applied to DC microgrids and photovoltaic systems. The software environments that are used and graphical design aspects are studied and reported. Furthermore, an experimental case applying an open-source suite (Grafana) to a DC microgrid is expounded.

scholarly journals A Bus-Sectionalized Hybrid AC/DC Microgrid: Concept, Control Paradigm, and Implementation

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3508
Author(s):  
Jing Li ◽  
Hongda Cai ◽  
Pengcheng Yang ◽  
Wei Wei
Keyword(s):  
Hierarchical Control ◽  
Mode Switching ◽  
Stable Operation ◽  
Service Reliability ◽  
Test Results ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Operation Modes ◽  
Control Paradigm ◽  
Operational Data

In the last several years, the coordination control of hybrid AC/DC microgrids (HMGs) has been gaining increasingly more attention. However, most of these discussions are focused on single-bus HMGs whose AC or DC bus is not sectionalized by AC or DC breakers. Compared with these single-bus HMGs, the bus-sectionalized HMG has more flexible topologies, more diverse operation modes, and consequently higher service reliability. However, meanwhile, these benefits also bring challenges to the stable operation of bus-sectionalized HMGs, particularly for mode switching. Relying on the national HMG demonstrative project in Shaoxing, China, this paper makes efforts to present the hierarchical control paradigm of a typical bus-sectionalized HMG toward standardization. The test results demonstrate that the proposed system provides seamless switching and uninterrupted power supply without controller reconfiguration among different operation modes. The operational data are also brought forth and analyzed to provide significant and useful experiences for designing and developing similar HMGs in the future.

scholarly journals Quantifying the Benefits of a Solar Home System-Based DC Microgrid for Rural Electrification

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 938 ◽  
Author(s):  
Nishant Narayan ◽  
Ali Chamseddine ◽  
Victor Vega-Garita ◽  
Zian Qin ◽  
Jelena Popovic-Gerber ◽  
...  
Keyword(s):  
Energy Deficit ◽  
Rural Electrification ◽  
Tier 2 ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Solar Home System ◽  
Tier 3 ◽  
Electricity Access ◽  
The Impact ◽  
Adequate Power

Off-grid solar home systems (SHSs) currently constitute a major source of providing basic electricity needs in un(der)-electrified regions of the world, with around 73 million households having benefited from off-grid solar solutions by 2017. However, in and of itself, state-of-the-art SHSs can only provide electricity access with adequate power supply availability up to tier 2, and to some extent, tier 3 levels of the Multi-tier Framework (MTF) for measuring household electricity access. When considering system metrics of loss of load probability (LLP) and battery size, meeting the electricity needs of tiers 4 and 5 is untenable through SHSs alone. Alternatively, a bottom-up microgrid composed of interconnected SHSs is proposed. Such an approach can enable the so-called climb up the rural electrification ladder. The impact of the microgrid size on the system metrics like LLP and energy deficit is evaluated. Finally, it is found that the interconnected SHS-based microgrid can provide more than 40% and 30% gains in battery sizing for the same LLP level as compared to the standalone SHSs sizes for tiers 4 and 5 of the MTF, respectively, thus quantifying the definite gains of an SHS-based microgrid over standalone SHSs. This study paves the way for visualizing SHS-based rural DC microgrids that can not only enable electricity access to the higher tiers of the MTF with lower battery storage needs but also make use of existing SHS infrastructure, thus enabling a technologically easy climb up the rural electrification ladder.

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.

scholarly journals A Generalized and Mode-adaptive Approach to the Power Flow Analysis of the Isolated Hybrid AC/DC Microgrids

2019 ◽  
Author(s):  
Yu Xiao ◽  
Chunguang Ren ◽  
Xiaoqing Han ◽  
Peng Wang
Keyword(s):  
High Performance ◽  
Power Flow ◽  
Low Cost ◽  
External Disturbance ◽  
Flow Analysis ◽  
Distributed Energy ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Binary Matrices ◽  
And Control

HybridAC/DC microgrids(HMG) are emerging as an attracting method for integrating the AC/DC distributed energy resources(DERs) with the features of high-performance and low-cost. In the isolated hybrid AC/DC microgrid (IHMG), the key problem is how to balance the power variation and regulate the voltage and frequency. Various energy storage systems (ESS)and interlinking converter (IC) technologies are viable for this application. The present study proposes a novel unified power flow model to evaluate and compare the abilities of the ESS with different connection topologies and ICs with different control approaches to maintain the voltage and frequency stability of the IHMG. In order to investigate the performance of the proposed scheme, five operation modes of the IHMG are defined and explained. The classification is based on the connection topologies and control modes of the ESS/IC in the IHMG. Then, a set of generic PF equations are derived. Moreover, three binary matrices are applied in the construction of the unified power equations. These matrices are used for describing the running state of the IHMG. Finally, in order to verify the proposed scheme, it is applied to several case studies of the IHMG. The operation characteristics of multi-DC subgrids IHMG in different modes, particularly when an external disturbance occurs, are investigated.

scholarly journals A Generalized and Mode-Adaptive Approach to the Power Flow Analysis of the Isolated Hybrid AC/DC Microgrids

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2253 ◽  
Author(s):  
Yu Xiao ◽  
Chunguang Ren ◽  
Xiaoqing Han ◽  
Peng Wang
Keyword(s):  
Power Flow ◽  
Operation Mode ◽  
Flow Analysis ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Operation Modes ◽  
Load Fluctuation ◽  
Practical Operation ◽  
Binary Matrices ◽  
The Time Domain

Hybrid AC/DC microgrids (HMG) are emerging as an attracting method for integrating AC/DC distributed energy resources (DERs). In the isolated hybrid AC/DC microgrid (IHMG), the key problem is how to balance power variation and regulate voltage and frequency. Various energy storage systems (ESS) and interlinking converter (IC) technologies are viable for this application. The present study proposes a novel unified power flow (PF) model which can be applied to compare and analyze the practical operation modes of the IHMG and, further, to evaluate and compare the abilities of the ESS with different connection topologies and ICs with different control approaches to maintain the voltage and frequency stability of the IHMG. Five operation modes of the IHMG are defined and explained. Then, a set of generic PF equations are derived. Moreover, three binary matrices are applied as input parameters of the unified power equations. These matrices enable a single operation mode of the IHMG at a time to be constructed in the power equation. Finally, the accuracy and effectiveness of the proposed scheme are verified against the time domain simulation result. The quasi-steady-state behaviors of multi-DC subgrids IHMG in different modes after a range of load fluctuation are investigated. The results show that the use of multiple grid-forming units in the AC and DC subgrids, when IC adopted normalized.

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 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 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.

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