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A flowchart summarising the steps of the proposed controller design, where, C k is C in for inner loop and Cout for outer loop
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![Fig. 5. Single line diagram of benchmark LVAC microgrid [34]](profile/Saikat-Chakrabarti-3/publication/349149646/figure/fig3/AS:1063811184353282@1630643759832/Single-line-diagram-of-benchmark-LVAC-microgrid-34_Q320.jpg)
A battery energy storage system (BESS) can play a critical role in regulating system frequency and voltage in an islanded microgrid. A
$\mu$
-synthesis-based robust control has been proposed for dc link voltage regulation of BESS for achieving frequency regulation and voltage quality enhancement of islanded microgrid. Variation in the operating c...
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... gain. Therefore, a frequency-loop shaping technique is adopted for adjusting controller parameters, in order to check numerically the associated Wg, until the desired performance is achieved for the step response of the worst case plant. Steps involved in the design of the proposed robust controller have been summarised through the flowchart in Fig. 4. [34], as shown in Fig. 5, has been simulated on a Simulink-MATLAB platform. The test microgrid network is a 400 V, 50 Hz distribution system connected to the utility through a 20 kV/400 V, 400 kVA transformer at the point of common coupling (PCC) bus. For this test system, the PCC switch is in an open condition and forms a standalone ...
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... robust controller performance has been validated for 40% load switching event for 3 − 7 s duration. SCADA panel results for V DC and duty ratio of dc/dc converter (DR) are shown in Fig. 14. It could be seen that V DC has similar response to Section VI.B with desired Mp and Tss. Hardwarein-loop implementation would be carried out as future work for coordinated power exchange among all generation sources. ...
Citations
... W ITH high penetrations of distributed energy resources (DERs), microgrids exhibit superior operating efficiencies, dynamic tracking, and stability performance than the traditional power systems. The DERs generally refer to the power-electronics-based dispatchable units that require hierarchical control strategies to ensure stability of multiple penetrations [1]. Peer-to-peer distributed control is proved to be a cost-effective method to ensure the voltage stabilization and efficiency power flow regulations under various types of disturbance, including cyber-attacks [2]. ...
Distributed hierarchical control with first-order observers has been widely adopted to mitigate the false data injection (FDI) attacks on distributed energy resources (DERs) in ac microgrids. However, the conventional direct feedback control requires neighboring data feedback to ensure the robustness of distributed observers and suffers from inaccurate detections of high-order FDI attacks. To address those issues, a distributed proportional-integral observer (DPIO)-based hierarchical control is proposed. The proposed control is designed by adopting the generalized proportional-integral observers (GPIOs) which have been successively adopted in robotics, motor drives and dc/dc converters. It comprises a consensus-based secondary control, a droop control, and a local dual-loop control. Compared to the conventional control schemes, the proposed control scheme exhibits superior dynamic tracking performance, higher robustness against disturbance, and simpler algorithms and implementations. Both simulation and OPAL-RT-based hardware-in-loop experiments validate the effectiveness and enhanced performance of the proposed control to detect and eliminate FDI attacks in various cases.
... Microgrids are categorized into three types, based on the type of current flowing on the system: alternating current (AC), direct current (DC), and AC/DC hybrid microgrids [10,11]. DC microgrids have become attractive in the new generation of power grids due to their techno-economic features for integrating renewable energy and energy storage systems and the increasing demand for DC loads and sources [12,13]. ...
The rising interest in hybrid alternating current (AC)/ direct current (DC) microgrids among the global research community can be attributed to the widespread adoption of distributed generation systems (DGs). Therefore, this study applies the modular multilevel converter (MMC) in interconnected microgrids to serve as an interlinking converter involving the AC and DC systems. In this topology, the MMC consists of several submodules (SMs) where a low-voltage direct current (LVDC) microgrid is connected to the output of each SM through a dual active bridge (DAB) converter. As a result of using this topology, more LVDC microgrids can be linked, thus enhancing power transition feasibility. However, during unequal power distribution across LVDC microgrids, the arm capacitor voltage balancing becomes a challenging task and if left unsolved, it will result in unbalanced output voltage at the MMC terminal, thereby affecting the overall system. Therefore, this paper proposes the use of the direct modulation method that is capable of naturally producing fundamental and DC components of the circulating current within the MMC. These circulating current components are responsible for uniformly distributing the energy between the arms of the MMC and balancing the arm capacitor voltage. The effectiveness of the proposed method is further assessed through real-time simulation in the OPAL-RT (OP5700) environment. The findings of this study validate that direct modulation can maintain the optimal performance of a multiterminal hybrid microgrid based on MMC under unbalanced power conditions without applying additional controllers, thus simplifying the system design, and improving the overall efficiency.
... As a result, numerous issues arise, such as frequency deviation, system instability, voltage fluctuations, supply-demand imbalances, etc. [1]. Due to these uncertainties, an MG is operated under highly stressed conditions; thus, a robust control strategy is required to guarantee an efficient and reliable operation [2]. ...
A distributed control of a Microgrid (MG) depends on the communication network for the exchange of information among the Distributed Generators (DGs). Most of the control schemes consider ideal communication among the DGs; however, in practical systems, delays are inherited in a system that can affect the dynamic performance and even destabilize an MG. Therefore, in this research work, a distributed Secondary Controller (SC) for an islanded MG is designed considering Communication Time Delays (CTDs). Sufficient delay-independent conditions for the robust stability of a buffer-free distributed averaging proportional integral control scheme are proposed. The CTDs are analyzed using the Lyapunov Krasovskii approach. A proposed method synchronizes the frequencies and voltages of the DGs to their respective references while confirming proportionate power sharing in the presence of CTDs. Moreover, different adaptive controllers are designed to update the fixed SC gain parameters to enhance the system’s performance. Finally, the efficacy of the controller is demonstrated through simulation studies that validate its performance against load variation and plug-and-play functionality.
... Microgrid is one of the most popular solutions for problems caused by renewable energy sources (RESs) integration and electrical loads increase. Microgrid can operate in parallel with the grid, as an autonomous power island or in transition between grid-connected mode and island mode of operation [1]- [3]. A microgrid is formed by distributed loads, distributed RESs, and distributed energy storage system (DESS) [4]. ...
This paper develops a Decentralized Multi-Agent Reinforcement Learning (Dec-MARL) method to solve the SoC balancing problem in the distributed energy storage system (DESS). First, the SoC balancing problem is formulated into a finite Markov decision process with action constraints derived from demand balance, which can be solved by Dec-MARL. Specifically, the first-order average consensus algorithm is utilized to expand the observations of the DESS state in a fully-decentralized way, and the initial actions (i.e., output power) are decided by the agents (i.e., energy storage units) according to these observations. In order to get the final actions in the allowable range, a counterfactual demand balance algorithm is proposed to balance the total demand and the initial actions. Next, the agents execute the final actions and get local rewards from the environment, and the DESS steps into the next state. Finally, through the first-order average consensus algorithm, the agents get the average reward and the expended observation of the next state for later training. By the above procedure, Dec-MARL reveals outstanding performance in a fully-decentralized system without any expert experience or constructing any complicated model. Besides, it is flexible and can be extended to other decentralized multi-agent systems straightforwardly. Extensive simulations have validated the effectiveness and efficiency of Dec-MARL.
... This ensures some energy can be saved for later restart of the BESS unit. Moreover, the dc link voltage must be regulated within userspecified bounds for converter safety, better ac-side voltage quality, and to avoid inter-mode oscillations among parallelconnected BESS units in an IRM [24], [25]. Thus, a robust controller is adopted from our previous work [25] to regulate the dc link voltage with guaranteed performance specifications under varying operating conditions. ...
... Moreover, the dc link voltage must be regulated within userspecified bounds for converter safety, better ac-side voltage quality, and to avoid inter-mode oscillations among parallelconnected BESS units in an IRM [24], [25]. Thus, a robust controller is adopted from our previous work [25] to regulate the dc link voltage with guaranteed performance specifications under varying operating conditions. ...
Due to limited reserves and 100% inverter-based resources in an islanded residential microgrid (IRM), largefrequency oscillations may arise during load/generation fluctuations. As an independent grid-forming unit, a battery energy storage system (BESS) can participate in load-frequency control (LFC) to achieve environment-friendly and reliable supply in IRMs. The formation of an interconnected islanded residential microgrid (IIRM) system and coordinated active power interchange among IRMs can help overcome BESS units limited reserve constraints. In this work, a reserve control (RC) level is proposed to be added in the conventional LFC architecture to provide frequency support to disturbance-affected areas with the help of a set of BESS units available reserve capacity. Following a significant disturbance detected, the RC level is activated based on their pre-defined contracted demands and net generation change information. The RC level also considers real-time monitoring of each microgrid's active power reserve to avoid frequency instability during emergency conditions. System performance with the proposed LFC model is analyzed with extensive tests conducted on a CIGRE TF C6:04:02 benchmark IIRM system. The proposed algorithms are also validated using a real-time digital simulator with hardware-in-the-loop setup.
... MG can be divided into three types: DC MG, AC MG, and AC/DC MG (hybrid MG) [14]. In low-voltage systems such as smart buildings, military locations, and rural regions, AC microgrids are often used in which distributed generation units and loads are all connected to an AC bus [15], [16]. DC microgrids, on the other hand, have grown in popularity in recent years. ...
Recently, the Modular Multilevel Converter (MMC) has drawn significant attention due to its diverse merits and its applicability to a wide range of medium to high-power applications. The growing interest in the MMC can be attributed to its attractive features such as modularity, reliability, and high voltage capability. Significant research has been conducted on the MMC over the last few years to develop its operation and control in various applications. However, the application of MMCs in microgrids remains a largely unexplored topic. Therefore, this paper aims to address this research gap by offering an in-depth review of the latest developments concerning circuit topologies, control schemes, and fault-tolerance strategies of MMC within microgrid applications. This comprehensive review not only provides a synthesized overview of the current state of the art but also paves the way for future investigations in this promising field. The outcomes from this study are expected to stimulate further advancements in MMC applications in microgrid systems, thus contributing to the continuous improvement and evolution of microgrids.
... [22][23][24] l-synthesis control has been adopted in many 105 research fields. [25][26][27][28][29][30] In Refs. 10,31, robust l-synthesis was 106 adopted for the multivariable control of ASTF. ...
Due to the dynamic coupling and multi-source uncertainties, it is difficult to accurately control the pressure and temperature of the Aeropropulsion System Test Facility (ASTF) in the presence of rapid command and large disturbance. This paper presents the design of μ-synthesis control to solve the problem. By incorporating the pressure ratio into the linear equation of the control valve, the modeling error of ASTF in the low frequency range is effectively reduced. Then, an uncertain model is established by considering various factors, including parameter variations, modeling error in the low frequency range, unmodeled dynamics, and changes in the working point. To address the dynamic coupling, a diagonal reference model with desired performance is incorporated into μ-synthesis. Furthermore, all weighting functions are designed according to the performance requirements. Finally, the μ-controller is obtained by using the standard μ-synthesis method. Simulation results indicate that the μ-controller decouples the pressure and temperature dynamics of ASTF. Compared with the multivariable PI controller, integral-μ controller, and double integral-μ controller, the proposed μ-controller can achieve higher transient accuracy and better disturbance rejection. Moreover, the robustness of the μ-controller is demonstrated by Monte Carlo simulations.
... From the perspective of energy production, the thermal power that formerly predominated will eventually decline and the part of RESs will increasingly rise. Furthermore, due to its high absorption capacity and potential impact on the microgrid, it is vital to research the frequency control of the microgrid (μG) [5,6]. ...
The operation of the system’s frequency can be strongly impacted by load change, solar irradiation, wind disturbance, and system parametric uncertainty. In this paper, the application of an adaptive controller based on a hybrid Jaya-Balloon optimizer (JBO) for frequency oscillation mitigation in a single area smart μG system is studied. The proposed adaptive control approach is applied to control the flexible loads such as HPs and EVs by using the JBO which efficiently controls the system frequency. The suggested technique uses the power balance equation to provide a dynamic output feedback controller. The main target is to regulate the frequency and power of an islanded single area μG powered by a PV and a diesel generator with integrations of smart bidirectional loads (HPs and EVs) that are controlled by the proposed adaptive controller in presence of electrical random loads. Moreover, the JBO is designed to minimize the effect of the system load disturbance and parameter variations. For a better assessment, the proposed controller using JBO technique is compared with two other methods which are the coefficient diagram method (CDM) and adaptive one using classical the Jaya technique. In the obtained results, the frequency deviation is found as 0.0015 Hz, which is fully acceptable and in the range of the IEEE standards. The MATLAB simulation results reveal that the suggested technique has a substantial advantage over other techniques in terms of frequency stability in the face of concurrent disturbances and parameter uncertainties. The real-time simulation tests are presented using a dSPACE DS1103 connected to another PC via QUARC pid_e data acquisition card and confirmed the MATLAB simulation results.
... In order to accomplish this purpose, an ESS must be linked to a bidirectional DC-DC converter. Depending on its level of charge and DC-bus voltage status, it operates in buck or boost mode [26,27]. ...
... All the works in [9]- [18] dealt with the instability issues due to ac-side dynamics. In contrast, dc-side dynamics also impact the stability by introducing new dominant eigenvalues in the system [19]. In this regard, the authors in [20] included dc link dynamics in the small-signal model, while in [5], [21], the authors studied the impact of the dc-side current limitation on stability. ...
... In this regard, the authors in [20] included dc link dynamics in the small-signal model, while in [5], [21], the authors studied the impact of the dc-side current limitation on stability. Since, the dc-source dynamics also impact stability [19], it needs to be included in small-signal analysis. The work in [22] modeled the configuration of the dc energy source with an ideal voltage source behind a resistance. ...
... In this work, robust PI controllers are adopted for G ink (s) and G outk (s) in order to handle variation in system operating conditions. The details for the robust controller synthesis can be found in the authors' previous work [19], which ensures fast frequency response and quick recovery for bounded variations in system operating conditions, such as, battery output current, dc link voltage, state of charge, etc. ...
Battery energy storage system (BESS), as grid forming unit, can quickly regulate voltage and frequency for a 100% inverter-based islanded low voltage microgrid. However, due to some inherent characteristics of this network, such as: (a) coupling among voltage and frequency dynamics, (b) dynamics of dc source, and (c) timescale coupling among converter and network, small-signal stability is a major concern. This paper proposes an adaptive feed-forward compensation scheme for each BESS unit to reduce dynamic interactions among converters and network/load parameters. Additionally, the proposed scheme can enhance system damping capability for a wide range of operating conditions without the need for any prior/ continuous generation/network information or additional sensors. This technique can preserve the voltage/frequency regulation capability of the traditional (ω − P/V − Q) droop control scheme for any low voltage networks. The existing small-signal model is modified to include dc-source, dc link, and proposed feed-forward dynamics, which assists in analyzing the impact of dc-side, acside, and network parameters on system small-signal stability. The system performance is analyzed with extensive case studies conducted on a CIGRE TF C6 : 04 : 02 benchmark system. The proposed model is validated using a real-time digital simulator with hardware-in-loop setup
