Yakup Hames

In the present study, a novel sliding mode controller (SMC) is proposed for robust and reliable voltage regulation in modern power systems. The proposed SMC is designed for a nonlinear model of an automatic voltage regulator (AVR) system having limiters in line with IEEE recommendations. The mathematical derivation of the control input is described in detail, and the asymptotic stability is guaranteed by Lyapunov stability theorem. The number of the controller parameters is reduced from four to two, and the control input is simplified without sacrificing the performance of the controller. This feature simplifies the control signal and makes the controller easy to optimize. It has been revealed that the number of controller parameters in the proposed study is less than the number ranging from three to seven in other AVR controller studies in the literature. The SMC algorithm differs from design-oriented studies in the literature in that it simplifies the control signal without affecting the controller’s performance. In the optimization stage of the study, the Sine Cosine Optimization Algorithm is conducted and its performance is evaluated with respect to a different number of agents and iterations. The results showed that the proposed controller parameters need very few simulations to find their optimum values. It can be easily seen that ten iterations with five agents are sufficient for the optimization of the proposed controller. It was clearly seen that the total number of simulations with 50 simulations in the proposed study was significantly less than the number of simulations in other related studies in the literature. The resulting optimum controller parameters were obtained as ksw = 744.5885 and k3 = 0.0711. A 0.5% overshoot at the output of the generator is allowed in the objective function of the optimization. Simulation results show that the proposed controller is robust and reliable against parameter uncertainties and various types of output disturbances.

The downscaling of optical devices into nanometer scale has the potential to enable exciting technologies such as all-optical computing and ultra-fast optical communications. With the advancements in nanofabrication techniques, confinement and manipulation of light below the diffraction limit have been achieved. However, the realization of ultra-fast and efficient nano light-sources is still a challenge. Utilizing Purcell effect with all-dielectric nanophotonics can be a promising solution to address the limitations. In this context, we offer an all-dielectric silicon hollow nanocuboid structure that can be employed to obtain enhanced magnetic dipole emission. According to the simulation results, silicon hollow nanocuboid provides a strong magnetic resonance and enhances magnetic dipole emission of a source in visible range. In this design, the hollow in the middle of structure supports accessible magnetic hotspots which can interact with magnetic dipole sources to force them emit with a higher decay rate. According to the results, the hollow nanocuboid design has a higher potential to increase the magnetic dipole decay rate enhancement in comparison to the previously reported structures and it can be used as a nano light-source in photonic integrated circuits, all-optical processors, and wideband optical communication networks.

This paper deals with the computation of all proportional-integral (PI)-based pitch controllers which achieve the desired frequency-domain specifications, namely, gain and phase margins (GPMs) of a large wind turbine (LWT) with communication delays. An efficient graphical method based on extracting the boundaries of stability regions in PI controller parameter space having user-defined GPMs has been employed to determine GPM-based stability regions for a wide range of time delays. The theoretical region boundaries are validated by using a powerful numerical method known as the quasi-polynomial mapping-based root finder (QPmR) and time-domain simulations. Results indicate that the proposed scheme gives an improved dynamic response compared to the recently developed scheme based on stability only for the pitch control of LWTs with communication delays.

This study includes the design of quadratic cascade DC/DC boost converter with PI controller. Two or more cascade boost converters have been used to increase system efficiency. Advantages of the proposed converter compared to the conventional boost converter are less current fluctuations and output voltage, the prolongation of system life by dividing the input current, and the less number of semiconductor elements used. What makes this converter more advantageous than others is that it only works with a single controller circuit by adding a diode, capacitor and inductor. The mathematical equations of the system have been obtained by the equivalent circuit analysis and thus the control circuit has been designed. The purpose of the generated control circuit is to keep the output voltage of the system constant due to the power sources that produce different voltages. The controller realizes this by applying to the power switches after generating different pulse widths at variable loads. The proposed quadratic cascade DC/DC boost converter has not caused any change in the output voltage despite the variable load and input voltage values. As a result, the proposed system is longer lasting compared to the conventional boost converters.

This paper investigates the effect of gain and phase margins (GPMs) on the delay-dependent stability analysis of the pitch control system (PCS) of large wind turbines (LWTs) with time delays. A frequency-domain based exact method that takes into account both GPMs is utilized to determine stability delay margins in terms of system and controller parameters. A gain-phase margin tester (GPMT) is introduced to the PCS to take into GPMs in delay margin computation. For a wide range of proportional–integral controller gains, time delay values at which the PCS is both stable and have desired stability margin measured by GPMs are computed. The accuracy of stability delay margins is verified by an independent algorithm, Quasi-Polynomial Mapping Based Rootfinder (QPmR) and time-domain simulations. The time-domain simulation studies also indicate that delay margins must be determined considering GPMs to have a better dynamic performance in term of fast damping of oscillations, less overshoot and settling time.

We suggest a practical method for obtaining the particular solution of non-homogeneous higher order linear differential equations with constant coefficients. The proposed method can be applied directly and simply to such problems. We revealed that is valid for the different type of problem by using sample solutions. This simple analytical solution that we have introduced will help to create a fast numerical algorithm for computers and thus simplify the numerical solutions of higher order physical problems.