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

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.

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

Energies ◽

10.3390/en12122253 ◽

2019 ◽

Vol 12 (12) ◽

pp. 2253 ◽

Cited By ~ 2

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.

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Island DC Microgrid Hierarchical Coordinated Multi-Mode Control Strategy

Energies ◽

10.3390/en12153012 ◽

2019 ◽

Vol 12 (15) ◽

pp. 3012 ◽

Cited By ~ 3

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.

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Feedback Linearization-Based Control Strategy for Interlinking Inverters of Hybrid AC/DC Microgrids with Seamless Operation Mode Transition

Energies ◽

10.3390/en14185613 ◽

2021 ◽

Vol 14 (18) ◽

pp. 5613

Author(s):

Thanh Hai Nguyen ◽

Tan Luong Van ◽

Asif Nawaz ◽

Ammar Natsheh

Keyword(s):

Control Strategy ◽

Feedback Linearization ◽

Operation Mode ◽

Harmonic Distortion ◽

Load Condition ◽

Mode Switching ◽

Voltage Source ◽

Dc Microgrid ◽

Nonlinear Load ◽

Dc Microgrids

This study proposes an advanced control scheme for the interlinking inverters of the hybrid AC/DC microgrids, which facilitates a seamless transition between grid-connected and stand-alone/islanding modes for the microgrid. Due to a nonlinear relationship between the terminal voltages of the voltage-source inverter (VSI) interfacing through inductor–capacitor (LC) filters with the grid voltages and currents, a feedback linearization technique (FLT) is employed to control the interlinking VSI under both grid-connected and islanding operations. The FLT-based current controllers are applied in the grid-connected mode, in which they adjust the power exchange between the DC and AC subgrids and mitigate the distortion of the grid currents produced by nonlinear loads. Under the stand-alone operation, the AC bus voltages are directly regulated by the FLT-voltage controllers of the interlinking VSI. In order to reduce the inrush currents and voltage overshot at the instant of mode switching, the FLT-based controllers are performed all the time regardless of the operating modes, where the voltage references for the VSI are not changed abruptly. The control performance of the VSI is highly satisfactory with low-transient overshoot values of the voltages and currents and low total harmonic distortion (THD) values of the grid currents and AC bus voltages are about 3.5% and 2.7%, respectively, under the nonlinear load condition. The validity of the new control strategy is verified by the simulation work, which investigates the operation of a hybrid AC/DC microgrid.

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Trihalomethane Formation Potential and Disinfection

Water Quality Research Journal ◽

10.2166/wqrj.1992.011 ◽

1992 ◽

Vol 27 (1) ◽

pp. 185-202

Author(s):

C.R. Erland Jansson

Keyword(s):

Hydroxyl Radicals ◽

Giardia Lamblia ◽

Test Results ◽

Formation Potential ◽

Trihalomethane Formation Potential ◽

Resistant Species ◽

Low Levels ◽

High Concentrations ◽

Operational Data ◽

Surface Water Supply

Abstract The UVOX process was developed to reduce the high concentrations of trihalomethanes, a potentially hazardous disinfection by-product found in a surface water supply for a community in northeastern Saskatchewan. Pilot plant tests were conducted at a throughput of 1.25 l/s utilizing UV to produce hydroxyl radicals from photolysis of H2O2 with air cooled UV units. These tests continued through 1985 andl986 to provide operational data for all seasons of the year. Test results indicated that the UVOX process was effective in reducing trihalomethane formation potential to very low levels. Recent concerns have also centred on the biocidal effectivenesss of disinfectants, particularly when applied to inactivation of resistant species of microogranisms, such as the cysts of Giardia lamblia. The UVOX process in a single pass configuration slightly enhanced the ability of UV to inactivate Giardia cysts.

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Distributed Cooperative Hierarchical Control for DC Microgrid

11th IET International Conference on Advances in Power System Control, Operation and Management (APSCOM 2018) ◽

10.1049/cp.2018.1771 ◽

2018 ◽

Author(s):

Chunyuan Guo ◽

Li Qiu ◽

Bo Zhang ◽

Jianping Yuan

Keyword(s):

Hierarchical Control ◽

Dc Microgrid

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Novel Control Strategy for Enhancing Microgrid Operation Connected to Photovoltaic Generation and Energy Storage Systems

Electronics ◽

10.3390/electronics10111261 ◽

2021 ◽

Vol 10 (11) ◽

pp. 1261

Author(s):

Dina Emara ◽

Mohamed Ezzat ◽

Almoataz Y. Abdelaziz ◽

Karar Mahmoud ◽

Matti Lehtonen ◽

...

Keyword(s):

Energy Storage ◽

Control Strategy ◽

Voltage Stability ◽

Storage Systems ◽

Voltage Source ◽

Stable Operation ◽

Energy Storage Systems ◽

Dc Microgrid ◽

Photovoltaic Generation ◽

Dc Voltage

Recently, the penetration of energy storage systems and photovoltaics has been significantly expanded worldwide. In this regard, this paper presents the enhanced operation and control of DC microgrid systems, which are based on photovoltaic modules, battery storage systems, and DC load. DC–DC and DC–AC converters are coordinated and controlled to achieve DC voltage stability in the microgrid. To achieve such an ambitious target, the system is widely operated in two different modes: stand-alone and grid-connected modes. The novel control strategy enables maximum power generation from the photovoltaic system across different techniques for operating the microgrid. Six different cases are simulated and analyzed using the MATLAB/Simulink platform while varying irradiance levels and consequently varying photovoltaic generation. The proposed system achieves voltage and power stability at different load demands. It is illustrated that the grid-tied mode of operation regulated by voltage source converter control offers more stability than the islanded mode. In general, the proposed battery converter control introduces a stable operation and regulated DC voltage but with few voltage spikes. The merit of the integrated DC microgrid with batteries is to attain further flexibility and reliability through balancing power demand and generation. The simulation results also show the system can operate properly in normal or abnormal cases, thanks to the proposed control strategy, which can regulate the voltage stability of the DC bus in the microgrid with energy storage systems and photovoltaics.

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Hierarchical Control in Islanded DC Microgrids With Flexible Structures

IEEE Transactions on Control Systems Technology ◽

10.1109/tcst.2020.3038495 ◽

2020 ◽

pp. 1-14

Author(s):

Pulkit Nahata ◽

Alessio La Bella ◽

Riccardo Scattolini ◽

Giancarlo Ferrari-Trecate

Keyword(s):

Hierarchical Control ◽

Flexible Structures ◽

Dc Microgrids

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Integrated Nonlinear Hierarchical Control and Management of Hybrid AC/DC Microgrids

IEEE Systems Journal ◽

10.1109/jsyst.2021.3050334 ◽

2021 ◽

pp. 1-12

Author(s):

Mojtaba Biglarahmadi ◽

Abbas Ketabi ◽

Hamid Reza Baghaee ◽

Josep M. Guerrero

Keyword(s):

Hierarchical Control ◽

Dc Microgrids ◽

Control And Management

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A Hierarchical Control Methodology for Renewable DC Microgrids Supporting a Variable Communication Network Health

Electronics ◽

10.3390/electronics7120418 ◽

2018 ◽

Vol 7 (12) ◽

pp. 418 ◽

Cited By ~ 3

Author(s):

Muhammad Shahid ◽

Muhammad Khan ◽

Jianming Xu ◽

Khurram Hashmi ◽

Salman Habib ◽

...

Keyword(s):

Power Flow ◽

Renewable Energy Sources ◽

Hierarchical Control ◽

Network Connectivity ◽

Voltage Regulation ◽

Monitoring And Control ◽

Dc Microgrids ◽

Communication Links ◽

Microgrid Control ◽

And Control

The monitoring and control of renewable energy sources (RESs) based on DC (Direct Current) microgrids (DC MG) are gaining much consideration at this time. In comparison with the isolated individual control of converters in a microgrid, DC microgrids provide better voltage regulation and harmonized energy generation/consumption. To address the inherent vulnerability of communication links, robust methods have been proposed that improve the resilience of communication-based control. However, the failure of the communication links in microgrid control layers remains a considerable issue that may lead to one or more nodes being disconnected and operating as a communication island. Such types of communication islanding may cause the unpredictable behavior of the system and further destabilization may lead to a cascaded failure. This paper proposes a fast algorithm to detect and evaluate network connectivity based on the information stored at every node in the form of a look-up table. The control structure has been modified under communication islanding, and a communication connectivity observer is used at every node to detect and address power flow issues under communication islanding. The proposed method has been verified through mathematical analysis, simulation, and experimental results.

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