A control plan for the stable operation of microgrids during grid-connected and islanded modes (original) (raw)
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Influence of power control strategies on the voltage profile in an islanded microgrid
14th International Conference on Harmonics and Quality of Power (ICHQP), 2010
The emergence of large amounts of distributed energy resources (DER) poses new challenges for the active participation of those units in the control of the grid. In this context, a recent development is the microgrid, which presents a coordinated approach for integrating the DER in the electrical grid. Microgrids are able to operate either connected to the distribution grid or in islanded mode. In this paper, the influence of different power control strategies of DER is studied with respect to the voltage profile in an islanded microgrid. A description of the control strategies is presented, as well as some simulation results for a basic microgrid.
Microgrid During Grid-Connected Mode and Islanded Mode - a Review
International Journal of Advance Engineering and Research Development
Future active distribution grids (ADGs) will incorporate a plethora of Distributed Generators (DGs) and other Distributed Energy Resources (DERs), allowing them to provide ancillary services in grid-connected mode and, if necessary, operate in an islanded mode to increase reliability and resilience. In this paper, we investigate the ability of an ADG to provide frequency control (FC) in grid-connected mode and ensure reliable islanded operation for a pre-specified time period. First, we formulate the operation of the grid participating in Europeantype FC markets as a centralized multi-period optimal power flow problem with a rolling horizon of 24 hours. Then, we include constraints to the grid-connected operational problem to guarantee the ability to switch to islanded operation at every time instant. Finally, we explore the technical and economic feasibility of offering these services on a balanced low-voltage distribution network. The results show that the proposed scheme is able to offer and respond to different FC products, while ensuring that there is adequate energy capacity at every time step to satisfy critical load in the islanded mode.
Stable operation of distributed generation units in microgrid networks
2015 Australasian Universities Power Engineering Conference (AUPEC), 2015
This paper presents a control technique for enhancing the stable operation of distributed generation (DG) units during islanding and grid-connected modes. The compensation of instantaneous variations in the reference current components of DG units in ac-side, and dc-link voltage variations in dc-side of interfaced converters, are considered properly in the control loop of DG units, which is the main contribution and novelty of this control technique over other control techniques. By using the proposed control technique, DG units can provide the continuous injection of active power from DG sources to the local loads and/or utility grid. Moreover, by setting appropriate reference current components in the control loop of DG units, reactive power and harmonic current components of loads can be supplied with a fast dynamic response. The performance of the developed control is assessed through simulation results during dynamic and steady-state operating conditions. Keywords-Microgrid (MG); distributed generation (DG); droop control; grid-connected mode; islanding mode. I. NOMENCLATURE A. Indices i 1,2 w d,q B. Abbreviations DG Distributed Generation PI Proportional-Integral LPF Low Pass Filter VSC Voltage Source Converter PCC Point of Power Coupling STSs Static Transfer Switches BESS Battery Energy Storage System CC Capacity Curve C. Variables i cwi DG current components Instantaneous variations of DG currents Instantaneous variations of reference current cwi i Δ Deviation of DG currents i fwi Currents of capacitor filters R Radius of i cdi-i cqi curve (α,β) Centre of i cdi-i cqi curve v dci dc-link voltage v wi Voltage at the PCC Instantaneous variations of dc-link voltage u eqwi Equivalent switching state functions
Journal of Control Engineering and Applied Informatics, 2016
The control of distributed generations (DGs) with renewable resources is an important endeavor in modern power systems due to the fact that the system frequency and voltages are highly variable in these kinds of networks especially in the island mode. This paper introduces a new combination of conventional controllers for solving the critical problems in islanded microgrid systems. With considering the -phase operation of power networks and comfort controllability of the system, the general controller is designed based on two mentioned techniques. The indicator of proper performance of studied microgrid controller is to provide reliable electric power in the presence of the transmission line impact and abnormal conditions. The control system parameters are optimized by Imperialist competitive algorithm (ICA) for enhancing the power quality. The effectiveness of recommended method is contrasted with other controllers and studies. The simulation results show the truth behavior of sug...
Advanced Islanded-Mode Control of Microgrids
2011
This thesis is focused on modeling, control, stability, and power management of electronically interfaced Distributed Energy Resource (DER) units for microgrids. Voltage amplitude and frequency regulation in an islanded microgrid is one of the main control requirements. To that end, first a mathematical model is developed for an islanded DER system and then, based on the developed model, amplitude and frequency control schemes are proposed for (i) balanced and linear loads and (ii) unbalanced and nonlinear loads. The proposed control strategy for unbalanced and nonlinear loads, utilizes repetitive control scheme to reject the effects of unbalanced and/or distorted load currents. Moreover, a new approach is proposed to maintain the effectiveness of the repetitive control under variable-frequency operational scenarios. The thesis also presents an adaptive feedforward compensation strategy to enhance the stability and robustness of the droop-controlled microgrids to droop coefficients and network uncertainties. The proposed feedforward strategy preserves the steady-state characteristics that the conventional droop control strategy exhibits and, therefore, does not compromise the steadystate power shares of the DER systems or the voltage/frequency regulation of the microgrid. Finally, a unified control strategy is proposed to enable islanded and grid-connected operation of DER systems, with no need to detect the microgrid mode of operation or to switch between different controllers, simplifying the control of the host microgrid. The effectiveness of the proposed control strategies are demonstrated through time-domain simulation studies conducted in the PSCAD/EMTDC software environment.
Control and stability of microgrid during transient states
Elsevier
Modern Microgrid can operate either in grid or islanded mode. In general the Microgrid is in synchronism with the main grid or utility grid with all its Distributed Generators (DGs), Battery Energy Storage Systems (BESS) and loads via Static Transfer Switch (STS), thorough Point of Common Coupling (PCC). This is normal condition. In grid connected mode the controller allows the DGs, to share the load proportionally. In this condition the DGs and the storage system must supply power to the loads and the excess power is to be exported to Grid on a pre-determined tariff. When everything is in steady state condition for any disturbance like a fault on the grid, the Microgrid is to be transferred seamlessly to islanding mode with an islanding detection method. To achieve this, a Phase Locked Loop (PLL) controller has to monitor the magnitude of frequency, voltage and phase of the main grid at PCC and give open command to the Static Transfer Switch within a preset time, before voltage transients are introduced into the Microgrid. And again in this islanding mode, inverter controlller should adopt P-Q control for load sharing and also V-f control as the main grid is not available. But re-synchronization back to grid is a planned program. It has to monitor all the parameters like voltage, frequency and phase angle at PCC, and then it should be connected back to main grid seamlessly via Synchronizing Controller, through static transfer switch. In this paper two DGs are used to test the stability criterion, one is PV and the other is Battery. Rate Of Change Of Frequency (ROCOF) method of Islanding Detection is used in this paper. An automatic load shedding technique also used to maintain PCC frequency with segregation of essential and non esssential loads as a first step in islanded mode to achieve stability. Battery system will be in discharge mode to maintain voltage of Microgrid in islanding but during grid mode it changes to charging mode (SOC).
Modeling and Control of a Microgrid in Islanding Mode
Renewable Energy and Power Quality Journal, 2017
Recent researches show the importance of modeling and control the DC/DC and DC/AC power converters in order to obtain proper-islanded microgrids or safe connection of different generation sources to the utility grid. The control needs arise because the high penetration of the low scale generation may produce frequency and voltage deviations from desired levels. In this context, this paper develops a model of distinct power converters and proposes a decentralized control strategy to regulate the frequency and voltage in a microgrid with different generators and loads. Simulations show the application of the control strategy in a simple microgrid model with the evaluation of every control stage in the grid.
2021
The voltage deviation challenge associated with Islanded microgrid system terminal voltage usually impacts negatively on the stability of the Islanded microgrid. This occurs as a result of load variation conditions and the intermittency nature of distributed generation (DG) in the Islanded MG. To curtail this effect and ensure the stability of the system for power quality improvement, an optimal voltage control technique can be employed to minimize this drawback on Islanded microgrid operations. This study utilized the Sine Cosine algorithm (SCA) to optimize the control gains of the PI controller for voltage deviation minimization in an Islanded microgrid. The SCA technique was implemented on modelled Islanded microgrid with two parallelconnected inverters. Stability analysis was carried out on the Islanded microgrid and voltage deviation, overshoot, settling time, and rise time was used as performance metrics. The simulation results that emerged from the MATLAB/Simulink are compared to the PSO technique established in the literature. The results reveal that the SCA optimized PI controller has achieved a voltage overshoot improvement of 21.6%. The results indicate that SCA optimized PI controller outperformed the PSO reported in the literature.
Robust AC Voltage Regulation of Microgrids in Islanded Mode with Sinusoidal Internal Model
SICE Journal of Control, Measurement, and System Integration, 2017
This paper shows that the H ∞ control is an effective tool for electric voltage regulation. We here consider robust AC voltage regulation of microgrids in an islanded mode. When a microgrid is disconnected from a utility grid, it automatically switches to an islanded mode to provide necessary power using a battery system until the grid is recovered. In the islanded mode, it is important to regulate the electric voltage generated in the grid to track a predetermined AC voltage reference. A difficulty is that there exits unmodeled dynamics in the grid that may cause large power fluctuations. To resolve this problem, we adapt the H ∞ control with a sinusoidal internal model to robust AC voltage regulation in microgrids. Simulation and experimental results confirm that the proposed H ∞ control can achieve robust tracking performance.
Voltage control in islanded microgrids by means of a linear-quadratic regulator
5th IEEE Joint IAS, PELS & PES Benelux Chapter Young Researchers Symposium (YRS 2010), 2010
The increased public interest in renewables and the development of the distributed generation (DG) technology are leading to an increasing amount of generators connected to the distribution network. New opportunities for the coordinated operation of these DGs rise with the development of the microgrid, a cluster of DGs, loads and power storage devices. The grid elements are mainly connected to the microgrid via a voltagesource inverter with dc-bus. In order to exploit the DGs in an islanded microgrid effectively, new control methods for these inverters have to be developed. Usually, an islanded microgrid is controlled by two control loops with different bandwidths. The grid voltage is controlled in the inner voltage control loop and its set value of amplitude and frequency is determined by an outer control loop. In this paper, the inner voltage control loop is studied. For the voltage control, a linear-quadratic regulator is proposed and the performance of this control method is studied.