Finite-time Secondary Control Research Articles

Event-Based Distributed Finite-Time Secondary Control for Multiterminal DC Transmission Systems: Restores Average Voltage and Achieves Power Sharing

Event-Based Distributed Finite-Time Secondary Control for Multiterminal DC Transmission Systems: Restores Average Voltage and Achieves Power Sharing

Distributed fast finite-time secondary control of islanded microgrids: A disturbance observer-based approach

For islanded microgrids with inverter-based distributed generators (DGs), this article focuses on the fast finite-time secondary voltage and frequency control problem considering system uncertainties. The distributed controller is designed based on the command filtered backstepping procedure, and a disturbance observer is constructed to estimate the lumped system uncertainties (including parameter perturbations, unmeasurable variables, etc.). In addition, the singularity issue derived from differentiating the virtual control law is avoided by using a smooth switch function. The proposed controller guarantees that the tracking errors of voltage and frequency converge to a small region around the origin in a finite time, while achieving desired active power sharing ratio. Case studies are conducted on a microgrid system to demonstrate the effectiveness of the proposed strategy in the presence of load changes and parameter perturbations.

Distributed Finite-Time Secondary Frequency and Voltage Restoration Control Scheme of an Islanded AC Microgrid

To solve the problems of frequency and voltage deviation caused by the droop control while meeting the requirements of rapid response, a distributed finite-time secondary control scheme is presented. Unlike the traditional cooperative controllers, this scheme is fully distributed; each unit only needs to communicate with its immediate neighbors. A control protocol for frequency restoration and active power sharing is proposed to synchronize the frequency of each unit to the reference value, and achieve accurate active power distribution in a finite-time manner as well. The mismatch of the line impedance is considered, and a consensus-based adaptive virtual impedance control is proposed. The associated voltage drop is considered to be the compensator for the voltage regulation. Then, a distributed finite-time protocol for voltage restoration is designed. The finite-time convergence property and the upper bound of convergence times are guaranteed with rigorous Lyapunov proofs. Case studies in MATLAB are carried out, and the results demonstrate the effectiveness, the robustness to load changes, plug-and play capacity, and better convergence performance of the proposed control scheme.

Distributed Robust Finite-Time Secondary Control for Stand-Alone Microgrids With Time-Varying Communication Delays

In this paper we consider the problem of restoring the voltage for stand-alone inverter-based Microgrids despite the effects of the time-delays arising with the information exchange among the electrical busses. To guarantee that all Distributed Generators (DGs) reach in a finite-time and maintain the voltage set-point, as imposed by a virtual DG acting as a leader, we suggest a novel robust networked-based control protocol that is also able to counteract both the time-varying communication delays and natural fluctuations caused by the primary controllers. The finite-time stability of the whole Microgrid is analytically proven by exploiting Lyapunov-Krasovskii theory and finite-time stability mathematical tools. In so doing, delay-dependent stability conditions are derived as a set of Linear Matrix Inequalities (LMIs), whose solution allows the proper tuning of the control gains such that the control objective is achieved with required transient and steady-state performances. A thorough numerical analysis is carried out on the IEEE 14-bus test system. Simulation results corroborate the analytical derivation and reveal both the effectiveness and the robustness of the suggested controller in ensuring the voltage restoration in finite-time in spite of the effects of time-varying communication delays.

Improved Distributed Prescribed Finite-Time Secondary Control of Inverter-Based Microgrids: Design and Real-Time Implementation

The aim of this study is to develop a novel distributed robust prescribed finite-time secondary control for both frequency and voltage restoration along with accurate active power sharing in islanded microgrids (MGs). The prescribed finite-time convergence property irrespective of the values of initial conditions helps to design an offline settling time that leads to power loss reduction. Moreover, thanks to the use of a piecewise-function based approach the upper bound of convergence time is reduced. The fixed-time stability of the proposed scheme is rigorously confirmed by applying the Lyapunov theory, which results in a set of tuning rules. The main challenge is to establish the stability conditions through asymmetrical connections under a directed graph. Finally, the architecture of the experimental setup is constructed for an inverter-based microgrid consisting of six distributed generators (DGs). The OPAL-RT real-time simulator is exploited to verify the applicability of the proposed distributed fixed-time controller.

Distributed Resilient Finite-Time Secondary Control for Heterogeneous Battery Energy Storage Systems Under Denial-of-Service Attacks

This article addresses the problem of distributed resilient finite-time control of multiple heterogeneous battery energy storage systems (BESSs) in a microgrid subject to denial-of-service (DoS) attacks. Note that DoS attacks may block information transmission among BESSs by preventing the BESS from sending data, compromising the devices and jamming a communication network. A distributed secure control framework is presented, where an acknowledgment (ACK)-based attack detection strategy and a communication recovery mechanism are introduced to mitigate the impact of DoS attacks by repairing the paralyzed topology graphs caused by DoS attacks back into the initial connected graph. Under this framework, a distributed resilient finite-time secondary control scheme is proposed such that frequency regulation, active power sharing, and energy level balancing of BESSs can be achieved simultaneously in a finite time; meanwhile, operational constraints can be satisfied at any control transient time. Moreover, based on theoretical analysis, the impact of the duration time of DoS attacks on the convergence time of the control algorithm can be explicitly revealed. Finally, validity and effectiveness of the proposed control scheme are demonstrated by case studies on a modified IEEE 57-bus testing system.

Distributed Finite-Time Secondary Control for DC Microgrids With Virtual Impedance Arrangement

In direct current (DC) microgrids, the accurate current sharing could be achieved by regulating the virtual impedance (droop coefficient) and the output voltage average value of each distributed generator (DG) could be restored by regulating the voltage reference value with a secondary controller. However, there is a coupling relationship between the current sharing and the voltage restoration process. In this paper, a distributed finite-time secondary control strategy is proposed aiming at overcoming the coupling effect. The proposed controller consists of four control loops, which are the current sharing controller (CSC), the virtual impedance average value restoration controller (AIRC), the reference voltage consensus controller (RVCC), and the voltage average value restoration controller (AVRC). With the proposed controller, the coupling effect is eliminated and the virtual impedance of each DG is only determined by the system load distribution. Besides, a simplified control strategy is also proposed which only contains the CSC and AIRC, and the reference voltage value can be calculated using the local information. The stability of the proposed controller is analyzed using the Lyapunov method. At last, the proposed controller is simulated in MATLAB/Simulink to verify its effectiveness.

Distributed Robust Finite-Time Secondary Voltage and Frequency Control of Islanded Microgrids

This paper presents a distributed, robust, finite-time secondary control for both voltage and frequency restoration of an islanded microgrid with droop-controlled inverter-based distributed generators (DGs). The distributed cooperative secondary control is fully distributed (i.e., uses only the information of neighboring DGs that can communicate with one another through a sparse communication network). In contrast to existing distributed methods that require a detailed model of the system (such as line impedances, loads, other DG units parameters, and even the microgrid configuration, which are practically unknown), the proposed protocols are synthesized by considering the unmodeled dynamics, unknown disturbances, and uncertainties in their models. The other novel idea in this paper is that the consensus-based distributed controllers restore the islanded microgrid's voltage magnitudes and frequency to their reference values for all DGs within finite time, irrespective of parametric uncertainties, unmodeled dynamics, and disturbances, while providing accurate real-power sharing. Moreover, the proposed method considers the coupling between the frequency and voltage of the islanded microgrid. Unlike conventional distributed controllers, the proposed approach quickly reaches consensus and exhibits a more accurate robust performance. Finally, we verify the proposed control strategy's performance using the MATLAB/SimPowerSystems toolbox.