Voltage-based droop control of converter-interfaced distributed generation units in microgrids

Sinds de laatste jaren is er in het elektrisch energienet een enorme toevloed aan kleine decentrale generatoren, vaak op basis van hernieuwbare energiebronnen. De distributienetten werden echter niet gebouwd om injectie van energie toe te laten. Hierdoor komen steeds meer problemen in de distributienetten voor, zoals bijvoorbeeld overspanningen tijdens zonnige periodes. Dit bemoeilijkt de verdere integratie van hernieuwbare energiebronnen. In deze context werd het microgrid concept voorgesteld om een gecoordineerde koppeling van decentrale generatoren in het net mogelijk te maken. Microgrids zijn kleine subnetten die lokaal hun elementen, zoals de generatoren en de lasten regelen om bepaalde doeleinden te bereiken. Ze kunnen bijvoorbeeld de spanningsregeling in hun net verzorgen of als een geheel meespelen in de energiemarkten. Een karakteristiek van microgrids is dat ze onafhankelijk van het net kunnen werken, in het zogenaamde eilandbedrijf. In eilandbedrijf moeten het verbruik en de opwekking op ieder tijdstip op elkaar afgesteld zijn. Aangezien microgrids erg verschillende eigenschappen hebben van het gewone elektrisch net, zijn hier specifieke regelstrategieen voor vereist. In deze doctoraatsverhandeling wordt een dergelijke regelstrategie uitgewerkt, de zogenaamde spanningsgebaseerde droop (proportionele) regeling. Het spanningsniveau wordt als de niet-conventionele parameter gebruikt om het microgrid te regelen

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

Overview of AC microgrid controls with inverter-interfaced generations

Distributed generation (DG) is one of the key components of the emerging microgrid concept that enables renewable energy integration in a distribution network. In DG unit operation, inverters play a vital role in interfacing energy sources with the grid utility. An effective interfacing can successfully be accomplished by operating inverters with effective control techniques. This paper reviews and categorises different control methods (voltage and primary) for improving microgrid power quality, stability and power sharing approaches. In addition, the specific characteristics of microgrids are summarised to distinguish from distribution network control. Moreover, various control approaches including inner-loop controls and primary controls are compared according to their relative advantages and disadvantages. Finally, future research trends for microgrid control are discussed pointing out the research opportunities. This review paper will be a good basis for researchers working in microgrids and for industry to implement the ongoing research improvement in real systems

A survey on modeling of microgrids - from fundamental physics to phasors and voltage sources

Microgrids have been identified as key components of modern electrical systems to facilitate the integration of renewable distributed generation units. Their analysis and controller design requires the development of advanced (typically model-based) techniques naturally posing an interesting challenge to the control community. Although there are widely accepted reduced order models to describe the dynamic behavior of microgrids, they are typically presented without details about the reduction procedure---hampering the understanding of the physical phenomena behind them. Preceded by an introduction to basic notions and definitions in power systems, the present survey reviews key characteristics and main components of a microgrid. We introduce the reader to the basic functionality of DC/AC inverters, as well as to standard operating modes and control schemes of inverter-interfaced power sources in microgrid applications. Based on this exposition and starting from fundamental physics, we present detailed dynamical models of the main microgrid components. Furthermore, we clearly state the underlying assumptions which lead to the standard reduced model with inverters represented by controllable voltage sources, as well as static network and load representations, hence, providing a complete modular model derivation of a three-phase inverter-based microgrid

Islanding Detection and Power Quality Analysis in Microgrid

芝浦工業大学2019年

Smart microgrids and virtual power plants in a hierarchical control structure

In order to achieve a coordinated integration of distributed energy resources in the electrical network, an aggregation of these resources is required. Microgrids and virtual power plants (VPPs) address this issue. Opposed to VPPs, microgrids have the functionality of islanding, for which specific control strategies have been developed. These control strategies are classified under the primary control strategies. Microgrid secondary control deals with other aspects such as resource allocation, economic optimization and voltage profile improvements. When focussing on the control-aspects of DER, VPP coordination is similar with the microgrid secondary control strategy, and thus, operates at a slower time frame as compared to the primary control and can take full advantage of the available communication provided by the overlaying smart grid. Therefore, the feasibility of the microgrid secondary control for application in VPPs is discussed in this paper. A hierarchical control structure is presented in which, firstly, smart microgrids deal with local issues in a primary and secondary control. Secondly, these microgrids are aggregated in a VPP that enables the tertiary control, forming the link with the electricity markets and dealing with issues on a larger scale

Evolution of microgrids with converter-interfaced generations: Challenges and opportunities

© 2019 Elsevier Ltd Although microgrids facilitate the increased penetration of distributed generations (DGs) and improve the security of power supplies, they have some issues that need to be better understood and addressed before realising the full potential of microgrids. This paper presents a comprehensive list of challenges and opportunities supported by a literature review on the evolution of converter-based microgrids. The discussion in this paper presented with a view to establishing microgrids as distinct from the existing distribution systems. This is accomplished by, firstly, describing the challenges and benefits of using DG units in a distribution network and then those of microgrid ones. Also, the definitions, classifications and characteristics of microgrids are summarised to provide a sound basis for novice researchers to undertake ongoing research on microgrids