Communication-based distributed secondary control is deemed necessary to restore the state of islanding AC microgrids to set points. As its limited global information, the microgrids become vulnerable to cyber-attacks, which by falsifying the communicating singles, like the angular frequency, can disturb the power dispatch in the microgrids or even induce blackout by pushing the microgrids beyond the safe operation area and triggering the protection. To make the microgrids more cyber secure, adaptive resilient control for the secondary frequency regulation is proposed. It assumes that each converter is communicating with its adjacent converters. With the proposed control, the weight of the communication channel being attacked is automatically reduced, and the more the communicating signals are falsified, the further the weight of that communication channel is weakened. The proposed approach does not rely on attack detection and thereby is easy to implement; Besides, it still works when challenged by a combination of multi-attack signals; Moreover, it applies to multiple communication lines getting attacked cases. Finally, the effectiveness and feasibility of the proposed resilient control scheme are validated by both simulations and experimental results.

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This article proposes an analytic approach to design the typical power factor correction (PFC) control of an electric vehicle (EV) charger to ensure small signal stability in weak grid conditions. Compared to the previous works, the proposed method considers the dynamics of all the control loops, i.e., phase-locked loop (PLL), voltage loop (VL), and current loop (CL). The impacts of key influential parameters on stability are analyzed. Furthermore, the upper limits of the PLL and VL bandwidth to ensure small signal stability are derived. Accordingly, the influences of the CL bandwidth, short circuit ratio (SCR), and the filter inductance on the upper limit of the PLL bandwidth and the VL bandwidth are quantified. Consequently, a design procedure that eliminates the need to model the input impedance for tuning the controller to prevent small signal instability is proposed. Simulations and experiments validate the analysis.@en

This paper concerns the control problem of the active caused by the mismatched impedance in resistive feeders-dominated microgrids. A distributed model predictive control (DMPC) scheme is suggested to regulate the virtual impedance of each involved unit. Moreover, the proposed method benefits resilience to communication failure by designing the communication matrix. Furthermore, it involves propagating information among units in a short period, significantly reducing the communication and computation burden. Finally, the performance of the proposed control scheme is evaluated in terms of its convergence, robustness to communication delay and load variations, resilience to communication failure, and plug-and-play functionality without communication in an inverter-connected system.

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The communication network used in distributed sec-ondary control (DSC) for microgrid power and voltage regulation is vulnerable to cyber-attacks. Unlike the predominantly resilient research on secondary control, which tends to employ passive defense strategies, this paper presents a proactive defense mecha-nism to design a resilient network for microgrid secure operation. This proposed method involves preparing the resilient scheme before attacks occur and facilitates timely resilience during an attack. First, novel metrics are introduced to effectively quantify the impact of various cyber attacks. Then, a multiobjective optimization method is applied to design the communication graph considering the quantified attacks, convergence, time-delay robustness, and communication cost. Simulations are performed on a microgrid consisting of 10 inverter units under different scenarios to validate the effectiveness of the proposed methodology.

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This paper concerns the control problem of the active and harmonic power sharing caused by the mismatched impedance in resistive feeders-dominated microgrids. A distributed model predictive control (DMPC) scheme is suggested to regulate the virtual impedance of each involved unit for power sharing based on the neighbor's state. With the distributed philosophy, the central controller is not required. Moreover, the proposed method benefits resilience to communication failure by designing the communication matrix. Furthermore, it involves propagating information among units in a short period, significantly reducing the communication and computation burden. Finally, the performance of the proposed control scheme is evaluated in terms of its convergence, robustness to communication delay and load variations, resilience to communication failure, and plug-and-play functionality without communication in an inverter-connected system.

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This paper proposes a virtual impedance reshaping strategy to share active and harmonic power while promoting the PCC voltage quality. Moreover, the suggested method is resilient to cyber-attacks and immune to communication interruption and delay. Furthermore, it significantly reduces the communication burden. Experiments verify the effectiveness.

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Due to the mismatched feeder impedances in a resistive feeder AC microgrid, it's challenging to accurately share harmonic and active power while promising a low bus voltage distortion rate. To address this issue, this paper proposes a distributed philosophy-based virtual impedance modulation strategy. The proposed method regulates the fundamental and harmonic impedance at the desired value by exchanging information with its adjacent inverters. Notably, the proposed method benefits from resilience against communication delay, failure, and cyber-attacks. Moreover, it significantly reduces the communication burden. The proposed method's effectiveness is validated through experiments conducted in various cases, including different communication scenarios and plug-and-play operations.

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In multi-inverter parallel connected islanded micro-grids, reactive power sharing is challenged by the differences in feeder impedance and various controller parameters. In order to address this issue, a virtual impedance reshaping strategy based on the consensus algorithm is proposed in this paper. The proposed method facilitates adaptive modulation of virtual impedance to ensure that it is consistent with the desired value. Notably, the method has the advantage of accurate reactive power sharing even in the presence of communication delays and interruptions. Furthermore, the proposed strategy exhibits resistance to malicious cyber-attacks by integrating an auxiliary controller that reconstructs the propagated information in the face of cyber threats that challenge the integrity of the original signal. Furthermore, this paper introduces an exit strategy that enables data exchange during the system construction phase and subsequently fixes the virtual impedance proportionally. This feature significantly reduces the communication burden. The effectiveness of the proposed control strategy is evaluated through several experimental cases, including accurate reactive power sharing and plug-and-play capability.

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The critical short circuit ratio (CSCR), as an important metric for grid stability evaluation, is not clearly defined in the literature. Aimed at clarifying the misunderstandings, the paper compares the different CSCR definitions. Moreover, CSCR reduction-oriented design is studied for electric vehicle chargers. Simulations verify the analysis.@en

Distributed secondary control is deemed necessary to restore the state of AC micro-grids to set points. However, for its limited global information, the power electronic system is vulnerable to cyber-attacks that aim to desynchronize converters or even cause a shutdown of micro-grids by unnecessarily triggering the protection schemes. To this end, an adaptive communication weight update for the secondary control layer is proposed. It guarantees frequency synchronization and active power sharing despite the presence of these attacks. Moreover, it automatically dispatches optimal communication lines when all its neighboring data are corrupted to different levels. Finally, the efficacy of the proposed resilient control method is demonstrated using simulations.

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Smart grid steady control relies heavily on the communication infrastructure among sensors, actuators, and control systems, which makes it vulnerable to cyber-attacks. Accurate acquisition of dynamic state information is deemed vital for efficient detection of these cyber-attacks on a smart grid. However, several popular state estimation methods at the present stage are restricted in practical use and require some assumptions. In this paper, we investigate the security of smart grid systems. We (1) identify and define the security problem in the smart grid, (2) compare the performance of several state estimate methods including Least Square, Kalman filter, Extend Kalman filter, in identifying smart grid dynamic information using measurements, and (3) investigate the Chi-square detector, Euclidean Distance, and Cosine similarity matching approaches for attack detection.

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