Decentralized secondary control for frequency regulation based on fuzzy logic control in islanded microgrid (original) (raw)
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Fully Distributed Cooperative Secondary Frequency and Voltage Control of Islanded Microgrids
IEEE Transactions on Energy Conversion, 2017
This paper proposes a new distributed cooperative secondary control for both frequency and voltage restoration of an islanded microgrid with droop-controlled, inverter-based distributed generations (DGs). Existing distributed methods commonly design secondary control based on the minimum real part of the nonzero Laplacian matrix eigenvalues related to the microgrid communication graph, which, however is global information. In contrast to the existing distributed methods, in this paper we design a fully distributed adaptive control based on the dynamic model of DG units and on information from neighboring units. Therefore, the proposed control scheme increases the system reliability, decreases its sensitivity to failures, and eliminates the need for a central processing unit. The fully distributed controllers restore the islanded microgrid frequency and voltage magnitudes to their reference values for all DG units irrespective of parametric uncertainties and disturbances while providing accurate real power sharing. Furthermore, the proposed method considers the coupling between the islanded microgrid frequency and voltages. Finally, we have conducted comprehensive simulation studies in the MATLAB/SimPowerSystems toolbox to verify the proposed control strategy performance.
—One of the well-known methods to share active and reactive power in microgrids (MGs) is droop control. A disadvantage of this method is that in steady state the frequency of the MG deviates from the nominal value and has to be restored using a secondary control system (SCS). The signal obtained at the output of the SCS is transmitted using a communication channel to the generation sources in the MG, correcting the frequency. However, communication channels are prone to time delays, which should be considered in the design of the SCS; otherwise, the operation of the MG could be compromised. In this paper, two new SCSs control schemes are discussed to deal with this issue: 1) a model predictive controller (MPC); and 2) a Smith predictor-based controller. The performance of both control methodologies are compared with that obtained using a conventional proportional integral-based SCS using simulation work. Stability analysis based on small signal models and participation factors is also realized. It is concluded that in terms of robustness, the MPC has better performance.
Microgrids have been defined as an efficient and practical concept to cover flaws in traditional power system related to system expansion and renewable energy utilization. By increasing demand energy, the need to generate more electric power is raised. However, the distance between generation centers and consumption centers causes more energy loss in power system and power system expansion is considered costly and to some extent infeasible. In addition, nowadays using renewable energies such as wind energy is inevitable, as a result using power electronic mediums is necessary. Microgrids are mostly preferable because of the ability to perform in islanded mode. In order to have stable-islanded Microgrid, electric loads inside the network should be shared on Voltage Source Converters respect to their nominal capacity. Droop control has been known as a method to share loads in decentralized way, although it has shortcomings. In this paper by introducing novel method named Frequency Tracking and applying that on droop control system, electric loads inside an islanded Microgrid are shared on generation units properly with fast and acceptable dynamics and droop control system is modified. Simulation results in PSCAD are confirmation of proposed system to have stable islanded Microgrid.
Frequency regulation by fuzzy and binary control in a hybrid islanded microgrid
Journal of Modern Power Systems and Clean Energy, 2014
Islanded microgrids must be self-sufficient in terms of frequency and voltage control due to their islanded operation. A control strategy for frequency regulation by combining the operation of a wind generator, a diesel generator, a battery energy storage system and a dump load in a microgrid is proposed in this paper. In the proposed strategy, the control task is partitioned into two subtasks: 1) choosing the appropriate element to be used for regulation, and 2) providing frequency regulation. A global controller chooses the element to operate. Then, the frequency regulation is provided by separate individual controllers. The proposed control strategy is tested on a microgrid with mixed types of generation and modeled on Simulink. By monitoring the power of individual elements and system frequency, it is shown that the proposed control strategy operates efficiently. The proposed strategy facilitates the integration of renewable energy sources and enhances frequency regulation.
Frequency control of islanded microgrid using fuzzy-PI and autotuned controllers
International Journal of Advances in Applied Sciences (IJAAS) , 2019
Any mismatch between generation and demand causes frequency to deviate from nominal value which affects the microgrid operation and reliability of power flow. The load frequency changes abnormally, which is fuzzy in nature, due to low system inertia and unpredictable variation in wind and solar irradiance level. So a frequency controller is needed to solve this problem meeting generation and demand of an islanded microgrid system considering the fuzziness in frequency fluctuation. This paper presents a case study of a hybrid microgrid system consisting of PV system, wind turbine generator set, diesel generator set along with storage facility and equipped with a proposed fuzzy-PI controller for frequency control under islanded condition. This controller shows satisfactory steady-state response. Further, performance of the proposed fuzzy-PI controller is verified with that of an autotuned PI controller to get faster response. The change in frequency is found minimum in case of autotuned PI controller as compared to fuzzy-PI controller. The proposed fuzzy-PI controller is validated based on ITAE (4-7%) which is higher than that attained form autotuned-PI controller. The developed model is simulated in Matlab/Simulink environment in this case study.
Distributed Secondary Control for Islanded Microgrids—A Novel Approach
IEEE Transactions on Power Electronics, 2000
This paper presents a novel approach to conceive the secondary control in droop-controlled microgrids (MGs). The conventional approach is based on restoring the frequency and amplitude deviations produced by the local droop controllers by using an MG central controller (MGCC). A distributed networked control system is used in order to implement a distributed secondary control (DSC), thus avoiding its implementation in MGCC. The proposed approach is not only able to restore frequency and voltage of the MG but also ensures reactive power sharing. The distributed secondary control does not rely on a central control, so that the failure of a single unit will not produce the fail down of the whole system. Experimental results are presented to show the feasibility of the DSC. The time latency and data drop-out limits of the communication systems are studied as well.
IET Smart Grid, 2018
This study presents a fully distributed control paradigm for secondary control of islanded AC microgrid (MG). The proposed method addresses both voltage and frequency restoration for inverter-based distributed generators (DGs). The MG system has droop controlled DG units with predominantly inductive transmission lines and different communication topologies. The restoration scheme is fully distributed in nature, and the DGs need to communicate with their neighbours using a sparse communication network. The proposed control scheme is efficient to provide quick restoration of the voltage and frequency whilst accurate power-sharing is achieved despite disturbances. Further, convergence and stability analysis of the proposed control scheme is presented. The proposed algorithm avoids the need for a central controller and complex communication structure thereby reducing the computational burden and the risk of single-point-failure. The performance of the proposed control scheme has been verified considering variations in load and communication topologies and link delay by pursuing an extensive simulation study in MATLAB/SimPowerSystem toolbox. The proposed control scheme supports plug-and-play demand and scalability of MG network. The proposed control scheme is also compared with the neighbourhood tracking error based distributed control scheme and observed that the former exhibit faster convergence and accurate performance despite disturbances in MG network.
IEEE Transactions on Power Electronics, 2020
In an islanded microgrid composed of droopcontrolled parallel inverters, the system frequency endures deviations as the load changes. To compensate for frequency deviation without involving communication infrastructures among distributed generators (DGs), the proportional-integral regulator based secondary frequency control (PI-SFC) method has been proposed in the literature. However, PI-SFC may incur real powersharing errors because the integrator accumulates disturbances and noise in each DG, leading to different compensation values of nominal real power. To achieve frequency restoration while maintaining equal real power sharing among DGs, this article proposes a small-ac-signal injection-based secondary frequency control (SACS-SFC) method, which is implemented by injecting an additional ac signal into the output voltage of each DG. Furthermore, a droop relation between the frequency of the injected SACS and the compensation value of nominal real power is innovatively established to trim the output real power of each DG to be equal. Frequency deviations caused by primary droop control are thus eliminated, and even real power sharing can be maintained among DGs. Moreover, the control parameters of the proposed SACS-SFC are comprehensively designed via steady state and dynamic model of the system. Simulation and experimental results demonstrate the effectiveness of the proposed method.
International Transactions on Electrical Energy Systems, 2017
The increasing penetration of renewable energy resources in power systems has improved microgrid's implementation. A microgrid is a localized grouping of electricity sources and loads that normally operates connected to and synchronous with the traditional centralized grid but can disconnect and function autonomously as physical and economic conditions dictate. Main factors to control in a microgrid are mainly frequency and voltage regulation, energy management, operation, and control scheme. This high penetration of renewable generation systems with their intermittent nature and unpredictable output power fluctuations might cause many control problems and large frequency/voltage deviation in microgrid stand-alone operation. Thus, to maintain the microgrid stability, an efficient and highly reliable control scheme is required. In this paper, a newly proposed fuzzy logic-based robust control mechanism is used to stabilize the frequency and direct current bus voltages in large fluctuations caused by sudden changes in power generation or load side. Also, supercapacitor and battery energy storage system are used to stabilize direct current bus voltages. This proposed method ensures the system efficiency and stability by reducing the system complexity and transient time, minimizing the frequency deviations, and preventing synchronous generator units from surpassing their power ratings in response to these disruptions. Simulation results also validate the effectiveness of the proposed controller in comparison with previous techniques.
A New Decentralized Control Scheme for Improving Frequency Stability in Islanded Micro-grids
2019
Usually Micro grids (MGs) are portion of low voltage distribution feeder including two type sources: slow response for frequency control such as Micro turbine (MT), diesel generator, Fuel cell (FC) and fast dynamic response source such as Battery storage systems (BSs) that can play an important role in restoring balance between supply and demand. In this paper, a new decentralized method for enhancement power sharing between distributed generation resources (DGs) is presented for transient stats in the islanded MGs. This method by changing the conventional droop characteristic of DGs in load variation times improves the MG stability with no communication link. The Overload (OL) ability of the BS is employed for fast handling of the frequency control at transient times of loads variation. To achieve this purpose, by considering the batteries OL characteristic and slow dynamic of some sources, a new power control scheme is developed for improving power sharing. Using the introduced me...