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Power systems are naturally prone to numerous uncertainties. Power system functioning is inherently unpredictable, which makes the networks susceptible to instability. Rotor-angle instability is a critical problem that, if not effectively resolved, may result in a series of failures and perhaps cause blackouts (collapse). The issue of state feedback sliding mode control (SMC) for the excitation system is addressed in this work. Control is decentralized by splitting the global system into several subsystems. The effect of the rest of the system on a particular subsystem is considered a disturbance. The next step is to build the state feedback controller with the disturbance attenuation level in mind to guarantee the asymptotic stability of the closed-loop system. The algorithm for SMC design is introduced. It is predicated on choosing the sliding surface correctly using the invariant ellipsoid approach. According to the control architecture, the system motion in the sliding mode is guaranteed to only be minorly affected by mismatched disturbances in power systems. Furthermore, the proposed controllers are expressed in terms of Linear Matrix Inequalities (LMIs) using the Lyapunov theory. Lastly, an IEEE test system is used to illustrate how successful the suggested approach is. [ABSTRACT FROM AUTHOR]

A new passivity-based voltage tracker for islanded Direct Current (DC) microgrids is presented in this paper. The proposed design develops a new sufficient condition for passivity-based state feedback with proportional and integral control using the attracting ellipsoid method. In this paper, we consider the time behavior of the extended vector, which completely describes the principle properties of the closed-loop system such as the boundedness of the trajectories within some ellipsoid and the dependence of its "size" on the feedback gains. The next step, which we are realizing in this paper, is the minimization of the attractive ellipsoid by selecting the "best" admissible feedback parameters. Here, it is important to note that the applied feedback is of PD-type (proportional differential) on the system state and I-type (integral) on the output. This is a new construction of the suggested feedback which gives several advantages for a designer. The suggested control is decentralized and uses only the local states; it is cost-effective and avoids the time delays in the communication networks which are needed if centralized control is used. The suggested control is carried out in the bilinear matrix inequality (BMI) framework. Extensive simulation is performed on a test system composed of renewable energy sources, under plug and play (PnP) operations, and uncertainties in distribution lines and loads. The performance of the proposed decentralized voltage controller is compared with that of a voltage tracker present in the literature. The comparison shows the improvements introduced by the proposed control ensure the stability of the dc bus voltage and a quick response under different scenarios of operating conditions. [ABSTRACT FROM AUTHOR]

Background: Press fit ACL reconstruction is a surgical procedure used to repair a torn anterior cruciate ligament (ACL) in the knee. During press fit ACL reconstruction, a graft is used to replace the torn ACL. The graft can be harvested from various sources, such as the patient's own hamstring tendons or patellar tendon, or from a donor. The graft is then inserted into tunnels created in the femur and tibia bone. The term "press fit" refers to the technique used to secure the graft within these bone tunnels. Instead of using screws or other fixation devices, press fit ACL reconstruction relies on tight fitting of the graft within the tunnels. Objective: This study aimed to compare the subjective, objective, and radiological results of press fit anterior cruciate ligament (ACL) reconstruction using hamstring tendon graft versus quadriceps tendon graft. Methods: A total of 50 patients with complete ACL tears underwent press fit ACL reconstruction between March 2016 and June 2019. Among them, 25 patients received a hamstring tendon graft, and another 25 patients received a quadriceps tendon graft. Results: The study demonstrated favorable outcomes of press fit ACL reconstruction, with improvements observed in all 50 patients when comparing postoperative to preoperative parameters. The results also showed comparable outcomes between the quadriceps and hamstring groups in terms of subjective, objective, and radiological measures. Conclusion: The press fit technique for ACL reconstruction is a successful method of graft fixation that offers advantages such as fewer complications, lower cost, and easier revision compared to other commonly used techniques. [ABSTRACT FROM AUTHOR]

Background: The anterior cruciate ligament (ACL) is one of the most important stabilizing factors of the knee joint. The ACL is made up of two bundles: the anteromedial bundle and the posterolateral bundle. The increase in the incidence of ACL injury is attributed to the higher participation in sports activity by the general population. A popular orthopaedic surgical procedure involves reconstructing the anterior cruciate ligament with entire tibial tunnels. Aim: the clinical outcome of the reconstruction of the ACL using the All-Inside technique through retrograde drilling of both femur and tibia sockets, with the graft fixated by tight ropes on both tibial and femoral sides. Methods: We included forty patients with an ACL tear, who underwent ACL reconstruction using a single semitendinosus tendon graft, through an all-inside technique (retrograde femoral and tibial drilling). Results: The data from the forty cases were analyzed. The Lysholm score was improved to 92.78 ±4.24, postoperatively. There was a statistically highly significant difference in comparing preoperative and postoperative results in favour of postoperative results (p<0.001). Besides, the IKDC improved to 91.12 ±4.85, postoperatively. There was a statistically highly significant difference in comparing preoperative and postoperative results in favour of postoperative results (p<0.001). Conclusion: Based on our analysis, we found that the short-term outcomes of the all-inside approach for ACL restoration are good to exceptional. With specially created instrumentation, it has many benefits. However, the increased usage of flipcutters drives up the overall cost of surgery. [ABSTRACT FROM AUTHOR]

Power system stability is greatly affected by two types of stochastic or random disturbances: (1) topological and (2) parametric. The topological stochastic disturbances due to line faults caused by a series of lightning strikes (associated with circuit breaker, C.B., opening, and auto-reclosing) are modeled in this paper as continuous-time Markov jumps. Additionally, the stochastic parameter changes e.g., the line reactance, are influenced by the phase separation, which in turn depends on the stochastic wind speed. This is modeled as a stochastic disturbance. In this manuscript, the impact of the above stochastic disturbance on power system small-disturbance stability is studied based on stochastic differential equations (SDEs). The mean-square stabilization of such a system is conducted through a novel excitation control. The invariant ellipsoid and linear matrix inequality (LMI) optimization are used to construct the control system. The numerical simulations are presented on a multi-machine test system. [ABSTRACT FROM AUTHOR]