It is also important to consider the constraints' relay coordination R11—R14 and R21—R24 which is applied to the network reconfigurability. In the conventional radial system reconfiguration by branch exchange, this coordination necessitates the avoidance of some branch operations  Bhattacharya, S. In approaching the optimization problem with DC link placement, this constraint is also not relevant, thereby allowing more choices.
In case there is excess generation due to distributed sources in phase a1 in one part of the grid and local power deficit due to high demand in phase c2 in another part, the power can be redirected easily, efficiently, and rapidly by reconfiguring the converters without synchronization issues. This redirection may be beneficial in low-voltage microgrids with local pockets of power surplus and deficits.
An adequate control algorithm for the DC links can offer flexibility in the operation of the distribution grid. Phase-to-phase interlinking with reconfigurable DC links. If a bipolar configuration is employed, the system can be reconfigured to operate in a monopolar mode for limited time  Chandra Mouli, G. Protection continues to remain a bottleneck. The DC link suffers from high short circuit currents due to the absence of inductive drop.
In general, there is a trade-off between stability and short circuit current limit with respect to the capacitance of the DC link. Power electronic converters installed near residential areas can be a source of noise. Multi-level converter operating with frequencies beyond 20 kHz can be used for noiseless operations. Converters are the least reliable components in the proposed system. Outage due to fault can increase the grid downtime. With the use of modular converters, this downtime can be reduced. Furthermore, redundancies due to reconfigurability of the DC link, as suggested in this paper, will improve reliability and ensure uninterrupted operations during contingencies.
A reliable and coordinated protection strategy is perhaps the greatest hindrance toward a truly interconnected meshed DC network  Planas, E. However, the use of switches, which are prone to failure, and the nature of the DC current itself make protection one of the biggest challenges in DC links.
So far, DC point-to-point connections have only been protected via the use of AC breakers. This is also the reason why we limit ourselves in highlighting the potential of point-to-point reconfigurable DC links. In the case of Line-Commutated current-sourced convertors technology, the thyristor valves can block their operation and thus prevent the AC side from feeding the DC fault. However, this is not possible in the case of voltage-sourced convertors. As soon as a fault occurs, the control is blocked and the converter operates as a diode bridge continuously feeding the fault until a means of isolation is activated.
Distributed reconfigurable control strategies for switching topology networked multi-agent systems.
Unless a DC grid is in place, no fast DC fault isolation is required, as the faulty DC line can no longer assist the normal power flow and it will need to be shut down for maintenance  Kontos, E. IEEE Trans. The problem of protection becomes more prominent in the case of meshed DC grids. As soon as a DC fault occurs, there are three distinct stages of grid reaction. First, the DC fault needs to be detected. Second, the grid assets need to be protected and the fault needs to be isolated before the fault currents reach a critical level.
Finally, the operation should be restored as soon as possible in the grid part that is not affected by the fault, minimizing the overall economic losses  Kontos, E. Previous research has been conducted on the DC fault currents developing stages, as well as on DC fault selective detection and localization methods  Kontos, E.
Moreover, several studies have investigated the design of DC circuit breakers [20, 21] Mokhberdoran, A. Bucher, M.
Merlin, M. However, the proposed solutions have many design trade-offs and thus require a high level of optimization to define the best possible design of a protection system in DC grids. Installing reconfigurable DC links in existing AC distribution networks can offer modularity and redundancy, flexibility of operation, and optimized power flow with loss minimization, as well as better availability and performance during faults. The novel ideas presented in this paper open an entirely new research direction in designing future hybrid power systems with a more involved AC and DC integration.
Hardware reconfigurability to achieve a modular AC—DC link operation not only allows grid operators to test the operational benefits of DC power transfer, but also gives them the option to revert to AC operation during contingencies like link converter fault, which are the least reliable part of the proposed system.
Common use of circuit breakers and cables during AC and DC operations offers savings in infrastructure costs incurred. Network reconfigurability with DC link breaks a limiting radial constraint that the AC distribution system imposed in the load balancing and loss minimization problems. The proposed concept is scalable to multi-terminal DC systems. In fault reconfiguration requirements, it is argued that the proposed architecture would be better with minimum operation of tie-line, better voltage profile, and lower losses.
The constraints put by a protection relay coordination in restructuring the network for feeder redistribution are also alleviated.
Semi-distributed Control for FPGA-based Reconfigurable Systems
The vision of this paper of creating a platform for systematic transition from an all-AC distribution network toward a universal DC system is developed. We thank all the project partners for their involvement. We would like to thank the distribution network operators from Dutch utility companies like Alliander, Enexis and Stedin for helping us understand the challenges in designing the evolving grids of the future. TABLE 1.
Skip to Main Content. Search in: This Journal Anywhere. Advanced search. Submit an article Journal homepage. View further author information. Pages Received 18 Nov In this article Close Abstract 1. Introduction 2. Challenges and Opportunities 3. Integrating Green Energy Resources 4. Conclusion References. Original Articles. Abstract While the scientific community recognizes the benefits of DC power transfer, the distribution network operators point out the practical and economic constraints in refurbishing the existing AC network at a medium-voltage level.
Reconfigurable Distributed Control by Hector Benitez-Perez | | Booktopia
Introduction Increasing integration of dispersed renewable energy sources in existing electricity supply systems has enabled bidirectional power flows in the AC distribution networks. Published online: 16 January CSV Display Table. Challenges and Opportunities 2. Increase in Power Demand A shift toward electric energy from traditional fossil fuel use in vehicles and heat pumps may trigger the need to enhance the capacity of existing distribution grids  Shekhar, A. Display full size.
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Integrating Green Energy Resources At a low-voltage distribution level, emerging grid components will need to be integrated into an AC or DC interconnection while carrying out the designated role in energy generation, storage, consumption, and protection. Meshing and Redundancies The ability to revert to AC when the DC link operation fails during contingency is an important requirement, particularly at critical locations of bulk power transfer. Operational Flexibility Big data applications in power utilities appear to be the next logical step toward smarter grids  Lai, C.
Network Reconfiguration The idea of reconfiguring the conventional AC network by redirecting power from one feeder to another to achieve system level loss minimization and load balancing is proposed in [11, 12] Baran, M. Protection A reliable and coordinated protection strategy is perhaps the greatest hindrance toward a truly interconnected meshed DC network  Planas, E.
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