Power systems are complex systems that have great importance to socio-economic development due to the fact that the entire world relies on the electric network power supply for day-to-day life. Therefore, for the stable operation of power systems, several protection and control techniques are necessary. The power system controllers should have the ability to maintain power system stability. Three important quantities that should be effectively controlled to maintain the stability of power systems are frequency, rotor angle, and voltage. The voltage control in power systems maintains the voltage and reactive power within the required limits and the power factor control enhances the efficiency of power distribution systems by improving load power factors. Among various controls, the frequency control is the most time-consuming control mechanism of power systems due to the involvement of mechanical parts. As the control algorithms of frequency stabilization deliver control signals in the timescale of seconds, load frequency control (LFC) systems cannot handle complicated data validation algorithms, making them more vulnerable to disturbances and cyber-attacks. In addition, the LFC system has extended digital layers with open communication networks and is designed to operate with less human intervention. Moreover, the frequency fluctuation due to load change or cyber-attack in one area affects all other interconnected areas, and thus threatens the stability of the entire network. Due to these circumstances, research activities are still carried out in the field of frequency control and cyber-security. In this paper, a comprehensive review of the cyber-security of the LFC mechanism in the power system is presented. The highlights of the paper include the identification of attack points of different configurations of the LFC system, discussion of the attack strategies, formulation of various attack models, and a brief review of the existing detection and defense mechanisms against cyber-attacks on LFC.

The load frequency control (LFC) in modern power system like microgrid has turned out to be significantly challenging due to the high penetration of renewable energy sources (RESs) and the consequent reduction of overall system inertia. The inverter-equipped RESs like solar and wind power generation units, besides the load variations can prompt sustained frequency fluctuations in microgrid and further lead to system instability, power outages, and even complete system blackout in the worst case. As a solution to the concerns of intermittent power source integration and resulting microgrid frequency instability, in this work, two robust LFC schemes using conventional linear quadratic gaussian (LQG) and modified LQG with linear quadratic integral (LQI) control schemes are proposed for secondary/battery energy storage system (BESS)-based auxiliary (virtual inertia (VI)) control of islanded/non-linear microgrid. The efficacy of the suggested control strategy is confirmed through MATLAB/SIMULINK simulations and by comparing with other different control schemes under various scenarios of distinct load and RES disturbance input profiles. The simulation results exhibited superior frequency regulation performance for the proposed control mechanisms over other types of control schemes. The proposed control schemes also ensure fast settling of frequency transients and help improve frequency stability under stochastic loads and random RES output power. In addition to the development of an effective robust controller, the vulnerability of the microgrid LFC system towards the denial of service (DoS) attack is analyzed for different control schemes. The vulnerability analysis is performed in the presence and absence of local auxiliary control loop and the remote secondary measurement communication channel is considered as the DoS attack point. The simulation results indicate that the local auxiliary control mechanism can not only help to improve frequency stability but also helps to add cyber-attack resilience to an extent when the secondary control loop is under attack.

This study develops a secondary attack resilient observer-based event-triggered control (AROETC) strategy to counter false data injection (FDI) attack at the secondary measurement channel of an islanded microgrid load frequency control (LFC) system with auxiliary/virtual inertia (VI) control loop. The considered microgrid LFC system configuration consists of a local uncompromised VI control loop and a remotely located observer-based secondary controller that ensures FDI attack resilience and communication efficiency. The VI control loop employs a proposed regional pole placement (RPP)-based state feedback auxiliary controller for attaining desired VI performance. The RPP technique of the VI control strategy allows auxiliary control gain tuning by positioning the closed-loop auxiliary poles at the locations described by RPP parameters and thus ensures required auxiliary frequency regulation. Further, the secondary observer and controller gains, ensuring FDI attack resilience and prescribed H_∞ performance, are derived using Lyapunov-Krasovskii functional stability analysis, considering secondary measurement channel communication delay, output-based event-triggering condition, remote secondary observer location, and deceptive frequency measurement signal model. Additionally, the impact of FDI attack and the efficacy of the proposed FDI AROETC method are validated through simulation analysis under various disturbance input profiles.

The purpose of this work is to design a covert agent structure that can create a non-zero frequency deviation in the load frequency control (LFC) system and illustrate the necessity of a secure communication network for the load frequency control. LFC systems are one of the most time-consuming control loops of power systems that are vulnerable to cyber-attacks and disturbances. Cyber-attacks like covert attacks can affect the frequency performance of the LFC system without being detected, as the covert adversaries cancel out the influence of the deceptively added actuation signal by deducting the corresponding effect from the measurement signal. In this paper, a covert agent with feedback structure is formulated and it is shown that the covert adversary can take control of LFC system through the covert reference signal and can keep the relative offset between actual frequency deviation of LFC system and the measurement signal received by the integral controller within safe limits, such that the attacker remains undetected.

Varicella gangrenosa is a rare but life-threatening dermatological complication of infection with varicella-zoster virus. A healthy 37-year-old male who had been diagnosed with varicella 20 days back was admitted to our hospital with complaints of fever and painful necrotic skin lesions. Physical examination revealed multiple round to oval ulcers covered with eschar predominantly over arms, lower limbs, back of trunk and flanks. Streptococcus pyogenes and Staphylococcus aureus grew in wound culture. Biopsy revealed ulceration and necrosis of epidermis, and edema, hemorrhage and granulation tissue formation involving the dermis and subcutaneous tissue. The patient was treated with acyclovir - parenteral followed by oral, antibiotics and supportive measures. The lesions healed and he was discharged after 20 days. We report this case to draw attention to the fact that varicella gangrenosum, even though a rare complication, may occur in the lesions of chicken pox and that the survival of patient depends on early diagnosis and aggressive treatment.