617 research outputs found
Nonlinear Control of an AC-connected DC MicroGrid
New connection constraints for the power network (Grid Codes) require more
flexible and reliable systems, with robust solutions to cope with uncertainties
and intermittence from renewable energy sources (renewables), such as
photovoltaic arrays. A solution for interconnecting such renewables to the main
grid is to use storage systems and a Direct Current (DC) MicroGrid. A "Plug and
Play" approach based on the "System of Systems" philosophy using distributed
control methodologies is developed in the present work. This approach allows to
interconnect a number of elements to a DC MicroGrid as power sources like
photovoltaic arrays, storage systems in different time scales like batteries
and supercapacitors, and loads like electric vehicles and the main AC grid. The
proposed scheme can easily be scalable to a much larger number of elements.Comment: IEEE IECON 2016, the 42nd Annual Conference of IEEE Industrial
Electronics Society, October 24-27, 201
Plug-and-play and coordinated control for bus-connected AC islanded microgrids
This paper presents a distributed control architecture for voltage and
frequency stabilization in AC islanded microgrids. In the primary control
layer, each generation unit is equipped with a local controller acting on the
corresponding voltage-source converter. Following the plug-and-play design
approach previously proposed by some of the authors, whenever the
addition/removal of a distributed generation unit is required, feasibility of
the operation is automatically checked by designing local controllers through
convex optimization. The update of the voltage-control layer, when units plug
-in/-out, is therefore automatized and stability of the microgrid is always
preserved. Moreover, local control design is based only on the knowledge of
parameters of power lines and it does not require to store a global microgrid
model. In this work, we focus on bus-connected microgrid topologies and enhance
the primary plug-and-play layer with local virtual impedance loops and
secondary coordinated controllers ensuring bus voltage tracking and reactive
power sharing. In particular, the secondary control architecture is
distributed, hence mirroring the modularity of the primary control layer. We
validate primary and secondary controllers by performing experiments with
balanced, unbalanced and nonlinear loads, on a setup composed of three
bus-connected distributed generation units. Most importantly, the stability of
the microgrid after the addition/removal of distributed generation units is
assessed. Overall, the experimental results show the feasibility of the
proposed modular control design framework, where generation units can be
added/removed on the fly, thus enabling the deployment of virtual power plants
that can be resized over time
Review on Control of DC Microgrids and Multiple Microgrid Clusters
This paper performs an extensive review on control schemes and architectures applied to dc microgrids (MGs). It covers multilayer hierarchical control schemes, coordinated control strategies, plug-and-play operations, stability and active damping aspects, as well as nonlinear control algorithms. Islanding detection, protection, and MG clusters control are also briefly summarized. All the mentioned issues are discussed with the goal of providing control design guidelines for dc MGs. The future research challenges, from the authors' point of view, are also provided in the final concluding part
Centralized and Decentralized control of Microgrids
ABSTRACT
Microgrid can be seen as an important controllable sub-system in future power systems. As a part of distribution network, the microgrid can operate in grid-connected or islanded mode to supply its local loads, and it consists of different renewable and non-renewable distribution generations that are connected to the system through power electronics (PE) interfaces. However, the control of microgrids is one of the important issues to focus on in order to overcome the challenges raised by high penetration of of renewable energy sources (RES). Depending on the responsibilities assumed by the different control levels, the microgrid can be controlled in centralized or decentralized modes. In centralized approach, the microgrid central controller (MGCC) is mainly responsible for the maximization of the microgrid value and optinization of its operation, and the MGCC determines the amount of power that the microgrid should import or export from the upstream distribution system by optimizing the local production or consumption capabilities. However, the MGCC should always consider the market prices of electricity, grid security concerns and ancillary services requested by the DSO when taking decisions. In this case an optimized operating scenario is realized by controlling the microsources and controllable loads within the microgrid, where non-critical, flexible loads can be shed, when profitable. Furthermore, the actual active and reactive power of the components are monitored. When a full decentralized control is implemented, the Management Center (MC) takes responsibilities and it competes or collaborates to optimize the production, satisfy the demand and provide the maximum possible export to the grid but all is done by considering the real time market prices. This thesis discusses the concepts of centralized and decentralized control of MG, where the main chapters introduce different control methods and PE interfaces that are involved in the microgrid control, while the final work presents simulation models that demonstrate how microgrids are controlled through inverters and the results. Using MATLAB/Simulink environment, PQ and V/f control modes of inverter are simulated and the results are discussed to point out their significant effect on balancing the voltage magnitude, maintaining the frequency and power sharing
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