An Intelligent Droop Control for Simultaneous Voltage and Frequency Regulation in Islanded Microgrids
TL;DR: A generalized droop control (GDC) scheme for a wide range of load change scenarios is developed and a new framework based on adaptive neuro-fuzzy inference system (ANFIS) is developed to remove its dependency to the line parameters and to propose a model-free based GDC.
Abstract: Voltage and frequency of microgrids (MGs) are strongly impressionable from the active and reactive load fluctuations. Often, there are several voltage source inverters (VSIs) based distributed generations (DGs) with a specific local droop characteristic for each DG in a MG. A load change in a MG may lead to imbalance between generation and consumption and it changes the output voltage and frequency of the VSIs according to the droop characteristics. If the load change is adequately large, the DGs may be unable to stabilize the MG. In the present paper, following a brief survey on the conventional voltage/frequency droop control, a generalized droop control (GDC) scheme for a wide range of load change scenarios is developed. Then to remove its dependency to the line parameters and to propose a model-free based GDC, a new framework based on adaptive neuro-fuzzy inference system (ANFIS) is developed. It is shown that the proposed intelligent control structure carefully tracks the GDC dynamic behavior, and exhibits high performance and desirable response for different load change scenarios. It is also shown that the ANFIS controller can be effectively used instead of the GDC. The proposed methodology is examined on several MG test systems.
Citations
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TL;DR: An enhanced VSG control is proposed, with which oscillation damping and proper transient active power sharing are achieved by adjusting the virtual stator reactance based on state-space analyses and communication-less accurate reactive power sharing is achieved based on inversed voltage droop control feature and common ac bus voltage estimation.
Abstract: Virtual synchronous generator (VSG) control is a promising communication-less control method in a microgrid for its inertia support feature. However, active power oscillation and improper transient active power sharing are observed when basic VSG control is applied. Moreover, the problem of reactive power sharing error, inherited from conventional droop control, should also be addressed to obtain desirable stable state performance. In this paper, an enhanced VSG control is proposed, with which oscillation damping and proper transient active power sharing are achieved by adjusting the virtual stator reactance based on state-space analyses. Furthermore, communication-less accurate reactive power sharing is achieved based on inversed voltage droop control feature ( V–Q droop control) and common ac bus voltage estimation. Simulation and experimental results verify the improvement introduced by the proposed enhanced VSG control strategy.
369 citations
Cites background from "An Intelligent Droop Control for Si..."
...This assumption is less valid if Xi is small, especially in a LV microgrid in which the line impedances are mainly resistive [42]....
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...Even if it is not the case, several online measurement or intelligent tuning methods for Zline i are available in [42] and [43]....
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TL;DR: An approach of coordinated and integrated control of solar PV generators with the maximum power point tracking (MPPT) control and battery storage control to provide voltage and frequency support to an islanded microgrid is proposed.
Abstract: The microgrid concept allows small distributed energy resources (DERs) to act in a coordinated manner to provide a necessary amount of active power and ancillary service when required. This paper proposes an approach of coordinated and integrated control of solar PV generators with the maximum power point tracking (MPPT) control and battery storage control to provide voltage and frequency (V-f) support to an islanded microgrid. Also, active and nonactive/reactive power (P-Q) control with solar PV, MPPT and battery storage is proposed for the grid connected mode. The control strategies show effective coordination between inverter V-f (or P-Q) control, MPPT control, and energy storage charging and discharging control. The paper also shows an effective coordination among participating microresources while considering the case of changing irradiance and battery state of charge (SOC) constraint. The simulation studies are carried out with the IEEE 13-bus feeder test system in grid connected and islanded microgrid modes. The results clearly verify the effectiveness of proposed control methods. The simulations are carried out in Matlab and Simpowersystems.
326 citations
TL;DR: A review of the primary and secondary control strategies for the ac, dc, and hybrid ac–dc microgrid is addressed and includes the highlights of the state-of-the-art control techniques and evolving trends in the microgrid research.
Abstract: The microgrid concept is gaining popularity with the proliferation of distributed generation. Control techniques in the microgrid are an evolving research topic in the area of microgrids. A large volume of survey articles focuses on the control techniques of the microgrid; however, a systematic survey of the hierarchical control techniques based on different microgrid architectures is addressed very little. The hierarchy of control in microgrid comprises three layers, which are primary, secondary, and tertiary control layers. A review of the primary and secondary control strategies for the ac, dc, and hybrid ac–dc microgrid is addressed in this paper. Furthermore, it includes the highlights of the state-of-the-art control techniques and evolving trends in the microgrid research.
303 citations
TL;DR: It is shown that transient instability can occur to the droop-controlled VSC when its current is saturated under large disturbances and a stability enhanced P-f droop control is proposed to deal with this instability problem.
Abstract: In the modern power grid, distributed generators are widely connected to the grid via voltage source converters (VSCs). Analyzing the transient stability of VSCs under large disturbances is useful for maintaining the security of the grid. However, this topic is very little studied. In this paper, the transient stability behavior of the droop-controlled VSC is theoretically explained. In particular, it is shown that transient instability can occur to the droop-controlled VSC when its current is saturated under large disturbances. In addition, the dynamics of the VSC under voltage sags that could incur instability problem is elaborately studied to consider special non-fault disturbances. To deal with this instability problem, a stability enhanced P-f droop control is proposed. Simulations and hardware-in-the-loop experiments verify the validity of the transient stability analysis and the effectiveness of the proposed control scheme.
254 citations
TL;DR: The voltage of the microgrid is controlled by using different controllers and their results are investigated, and the performance of controllers is investigated using MATLAB/Simulink SimPowerSystems.
Abstract: This paper describes the usefulness of renewable energy throughout the world to generate power. Renewable energy adds a remarkable scope in power system. Renewable energy sources act as the prime mover of a microgrid. The Microgrid is a small network of power system with distributed generation (DG) units connected in parallel. The integration challenges of renewable energy sources and the control of microgrid are described in this paper. The varied nature of DG system produces voltage and frequency deviation. The unknown nature of the load produces un-modeled dynamics. This un-modeled dynamic introduces measurable effects on the performance of the microgrid. This paper investigates the performance of the microgrid against different scenarios. The voltage of the microgrid is controlled by using different controllers and their results are also investigated. The performance of controllers is investigated using MATLAB/Simulink SimPowerSystems.
220 citations
References
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01 May 1993
TL;DR: The architecture and learning procedure underlying ANFIS (adaptive-network-based fuzzy inference system) is presented, which is a fuzzy inference System implemented in the framework of adaptive networks.
Abstract: The architecture and learning procedure underlying ANFIS (adaptive-network-based fuzzy inference system) is presented, which is a fuzzy inference system implemented in the framework of adaptive networks. By using a hybrid learning procedure, the proposed ANFIS can construct an input-output mapping based on both human knowledge (in the form of fuzzy if-then rules) and stipulated input-output data pairs. In the simulation, the ANFIS architecture is employed to model nonlinear functions, identify nonlinear components on-line in a control system, and predict a chaotic time series, all yielding remarkable results. Comparisons with artificial neural networks and earlier work on fuzzy modeling are listed and discussed. Other extensions of the proposed ANFIS and promising applications to automatic control and signal processing are also suggested. >
15,085 citations
"An Intelligent Droop Control for Si..." refers methods in this paper
...Adding the training ability of the ANN to the FL creates a new hybrid technique, known as ANFIS [29]....
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01 Nov 2009
TL;DR: The hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to MGs is presented and results are provided to show the feasibility of the proposed approach.
Abstract: DC and AC Microgrids are key elements to integrate renewable and distributed energy resources as well as distributed energy storage systems. In the last years, efforts toward the standardization of these Microgrids have been made. In this sense, this paper present the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to microgrids. The hierarchical control proposed consist of three levels: i) the primary control is based on the droop method, including an output impedance virtual loop; ii) the secondary control allows restoring the deviations produced by the primary control; and iii) the tertiary control manage the power flow between the microgrid and the external electrical distribution system. Results from a hierarchical-controlled microgrid are provided to show the feasibility of the proposed approach.
4,145 citations
"An Intelligent Droop Control for Si..." refers background or methods in this paper
...In the previous published works [19]–[25], MGs are usually considered as resistive or inductive systems....
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...To avoid circulating currents between parallel inverters connected to MG, usually control strategies based on droop characteristics are applied [19]....
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TL;DR: In this paper, the authors developed a model for autonomous operation of inverter-based micro-grids, where each sub-module is modeled in state-space form and all are combined together on a common reference frame.
Abstract: The analysis of the small-signal stability of conventional power systems is well established, but for inverter based microgrids there is a need to establish how circuit and control features give rise to particular oscillatory modes and which of these have poor damping. This paper develops the modeling and analysis of autonomous operation of inverter-based microgrids. Each sub-module is modeled in state-space form and all are combined together on a common reference frame. The model captures the detail of the control loops of the inverter but not the switching action. Some inverter modes are found at relatively high frequency and so a full dynamic model of the network (rather than an algebraic impedance model) is used. The complete model is linearized around an operating point and the resulting system matrix is used to derive the eigenvalues. The eigenvalues (termed "modes") indicate the frequency and damping of oscillatory components in the transient response. A sensitivity analysis is also presented which helps identifying the origin of each of the modes and identify possible feedback signals for design of controllers to improve the system stability. With experience it is possible to simplify the model (reduce the order) if particular modes are not of interest as is the case with synchronous machine models. Experimental results from a microgrid of three 10-kW inverters are used to verify the results obtained from the model
2,482 citations
"An Intelligent Droop Control for Si..." refers background in this paper
...The instantaneous active and reactive powers are passed through low-pass filters, as follows [28]....
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...Hz) are connected to two local load banks, at bus 1 and bus 3 [28]....
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TL;DR: In this article, the feasibility of control strategies to be adopted for the operation of a microgrid when it becomes isolated is evaluated and the need of storage devices and load shedding strategies is evaluated.
Abstract: This paper describes and evaluates the feasibility of control strategies to be adopted for the operation of a microgrid when it becomes isolated. Normally, the microgrid operates in interconnected mode with the medium voltage network; however, scheduled or forced isolation can take place. In such conditions, the microgrid must have the ability to operate stably and autonomously. An evaluation of the need of storage devices and load shedding strategies is included in this paper.
2,276 citations
TL;DR: In this paper, a new control method for the parallel operation of inverters operating in an island grid or connected to an infinite bus is described, where each inverter supplies a current that is the result of the voltage difference between a reference ac voltage source and the grid voltage across a virtual complex impedance.
Abstract: In this paper, a new control method for the parallel operation of inverters operating in an island grid or connected to an infinite bus is described. Frequency and voltage control, including mitigation of voltage harmonics, are achieved without the need for any common control circuitry or communication between inverters. Each inverter supplies a current that is the result of the voltage difference between a reference ac voltage source and the grid voltage across a virtual complex impedance. The reference ac voltage source is synchronized with the grid, with a phase shift, depending on the difference between rated and actual grid frequency. A detailed analysis shows that this approach has a superior behavior compared to existing methods, regarding the mitigation of voltage harmonics, short-circuit behavior and the effectiveness of the frequency and voltage control, as it takes the R to X line impedance ratio into account. Experiments show the behavior of the method for an inverter feeding a highly nonlinear load and during the connection of two parallel inverters in operation.
1,528 citations