This paper presents nonlinear pulse propagation characteristics for different input optical pulse shapes with various input pulse energy levels in semiconductor optical amplifiers. For simulation of nonlinear pulse propagation, finite-difference beam propagation method is used to solve the nonlinear Schrödinger equation. In this equation, gain spectrum dynamics, gain saturation are taken into account which depends on carrier depletion, carrier heating, spectral-hole burning, group velocity dispersion, self-phase modulation and two photon absorption. From Vanalysis, we obtained the output waveforms and spectra for different input pulse shapes as well as for different input energies. It shows clearly that the peak position of the output waveforms are shifted toward the leading edge which due to the gain saturation of the SOA for higher input pulse energies. We also analyzed and compared the normalized difference of full-width at half maximum for different input pulse shapes in the SOA.

This paper presents performance of intelligent fuzzy-based coordinated control for Automatic Voltage Regulator (AVR) and Power System Stabilizer (PSS), to prevent losing synchronism after major sudden faults and to achieve appropriate post-fault voltage level in multi-machine power systems. The AVR and PSS gains can adaptively change to guarantee the power system stability after faults. For change in AVR and PSS gains, at least one significant generator in each area of a multi-area power system is equipped with fuzzy logic unit. The fuzzy logic unit accepts normalized deviations of terminal voltage and phase difference of synchronous generators as inputs and generates the desirable gains for AVR and PSS. The construction of appropriate fuzzy membership functions and rules for best tuning of gains is described. The proposed fuzzy control methodology is applied to 11-bus 4-generator power system test case. Simulation results illustrate the effectiveness and robustness of the proposed fuzzy-based coordinated control strategy.

Microgrids (MGs)–the building blocks of the smart grid– are local grids comprise different technologies such as power electronics converters, distributed renewable and non-renewable energy sources, energy storage systems, and telecommunications which can operate either in islanded mode or connected to the main grid. Apart from the obvious benefits of MGs, their introduction into the traditional distribution network raises many new challenges, thus, a hierarchical control concept has been introduced for these systems. While the decentralized primary control of this hierarchy ensures the system stability and adjusts the frequency and voltage according to the active and reactive powers, the secondary control level is often used to regulate the system frequency and voltage to the rated values, eliminating deviations produced by primary level. The tertiary control is in charge of regulating power exchange with external grid or/and with other MGs and includes functions related to efficiency and economic enhancement.This thesis is focused on development of distributed control strategies for secondary control of autonomous ac and dc MGs to avoid a central controller and complex communication network, thus offering improved reliability and expandability. The special emphasis has been given to consensus-based protocols where the mathematical analysis has been also studied and presented. The proposed methodologies based on this approach are fully distributed meaning that each MG source requires exchanging information with only its direct neighbors through a sparse communication network. Loss of sources and communication links do not affect system operation as long as the communication graph remains connected. Moreover, they are scalable, for that prior knowledge of the system is not required, as a new component enters the MG. The proposed control frameworks for ac MGs include three modules, namely, frequency and active power sharing regulator, voltage regulator, and reactive power regulator. The first module addresses frequency synchronization without using any frequency measurement, which improves the system dynamic. The voltage regulator boosts the voltage across the MG to satisfy the global voltage regulation, while the reactive power regulator handles the proportional reactive power sharing considering transmission line impedances. Moreover, the proposed controllers are able to proportionally share the load power even at the presence of different control parameters and initial values.This thesis also proposes a distributed hierarchical control framework for dc MG clusters to ensure smooth connection and reliable operation of these systems. A decentralize adaptive droop method is introduced for primary control level which determines droop coefficients according to the state-of-charge (SOC) of batteries automatically. Then a small signal model is developed to investigate effects of the proposed method parameters and the system parameters on the stability of these systems, as well as to tune the control parameters. Finally, a consensus-based distributed control framework is proposed which provides all features of distributed control methods. It eliminates the average voltage deviation over the MGs while regulating the power flow control between the MGs according to their local SOCs at the same time. The proposed approach only needs neighbor-to-neighbor communication through a spars communication infrastructure.

Modern power systems require increased intelligence and flexibility in control and optimization. This issue is becoming more significant today due to the increasing size, changing structure, emerging renewable energy sources and Microgrids, environmental constraints, and the complexity of power systems. The control units and their associated tuning methods for modern power systems surely must be intelligent (based in flexible intelligent algorithms). This chapter addresses a new intelligent approach using a combination of fuzzy logic and Particle Swarm Optimization (PSO) techniques for optimal tuning of the existing most popular Proportional-Integral (PI) or Proportional-Integral-Derivative (PID) controllers in the power electric industry. In the proposed control strategy, the PI (PID) parameters are automatically tuned using fuzzy rules, according to the on-line measurements. In order to obtain an optimal performance, the PSO technique is used to determine the membership functions’ parameters. The proposed optimal tuning scheme offers many benefits for a new power system with numerous distributed generators and Renewable Energy Sources (RESs).In the developed tuning algorithm, the physical and engineering aspects have been fully considered. To demonstrate the effectiveness of the proposed control scheme, secondary frequency control problem in an islanded Microgrid (MG) system is considered a case study. The main source of power for a Microgrid is small generating units of tens of kW that are placed at the customer site. Simulation studies are performed to illustrate the capability of the proposed intelligent/optimal control approach.

Modern power systems require increased intelligence and flexibility in control and optimization. This issue is becoming more significant today due to the increasing size, changing structure, emerging renewable energy sources and Microgrids, environmental constraints, and the complexity of power systems. The control units and their associated tuning methods for modern power systems surely must be intelligent (based in flexible intelligent algorithms). This chapter addresses a new intelligent approach using a combination of fuzzy logic and Particle Swarm Optimization (PSO) techniques for optimal tuning of the existing most popular Proportional-Integral (PI) or Proportional-Integral-Derivative (PID) controllers in the power electric industry. In the proposed control strategy, the PI (PID) parameters are automatically tuned using fuzzy rules, according to the on-line measurements. In order to obtain an optimal performance, the PSO technique is used to determine the membership functions’ parameters. The proposed optimal tuning scheme offers many benefits for a new power system with numerous distributed generators and Renewable Energy Sources (RESs).In the developed tuning algorithm, the physical and engineering aspects have been fully considered. To demonstrate the effectiveness of the proposed control scheme, secondary frequency control problem in an islanded Microgrid (MG) system is considered a case study. The main source of power for a Microgrid is small generating units of tens of kW that are placed at the customer site. Simulation studies are performed to illustrate the capability of the proposed intelligent/optimal control approach.

In comparison of the conventional bulk power plants, in which the synchronous machines dominate, the distributed generator (DG) units have either very small or no rotating mass and damping property. With growing the penetration level of DGs, the impact of low inertia and damping effect on the grid stability and dynamic performance increases. A solution towards stability improvement of such a grid is to provide virtual inertia by virtual synchronous generators (VSGs) that can be established by using short term energy storage together with a power inverter and a proper control mechanism.The present paper reviews the fundamentals and main concept of VSGs, and their role to support the power grid control. Then, a VSG-based frequency control scheme is addressed, and the paper is focused on the poetical role of VSGs in the grid frequency regulation task. The most important VSG topologies with a survey on the recent works/achievements are presented. Finally, the relevant key issues, main technical challenges, further research needs and new perspectives are emphasized.

With high wind power penetration, imbalance between generation and consumption is increased, and as a consequence the frequency deviation from the nominal value will be magnified. For frequency control purpose in conventional power systems, the synchronous generators are only responsible. However, it is expected that the renewable energy sources (RESs) are also needed to contribute in frequency control issue in near future. In this paper, impacts of high wind penetration on the frequency control are studied, and an approach is introduced for creating the secondary reserve for doubly fed induction generator (DFIG) wind turbines. This reserve can contribute to load frequency control (LFC) task. Simulation results on updated standard IEEE 39-bus system are presented and it is shown that the wind turbines can contribute in LFC service, successfully.

The author addresses the problem of subcarrier sharing with discrete rate allocation in the downlink of multicell and multihop orthogonal frequency division multiple access networks. The co-channel interference makes the problem computationally intractable. The author therefore models the problem as a non-cooperative game among the transmitting nodes with smaller scale problems. Each problem is solved using dual decomposition. Moreover, to mitigate the degradation effect of co-channel interference in this game, the author additionally proposes a price-based game. This game charges the nodes for their transmit power on subcarriers. Numerical results demonstrate that price-based game outperforms the non-cooperative game as a result of distributed interference avoidance. In addition, both the games with subcarrier sharing achieve higher sum-rate in comparison with resource allocation schemes with no subcarrier sharing.

A power system must be capable to regain its stability and desired performance following any change of operating point. To meet satisfactory voltage regulation and damping performance on a wide range of operating conditions, the designed automatic voltage regulators (AVR) and power system stabilizers (PSS) must be enough robust, by working in a coordinated manner. This paper presents an overview of the key issues and new challenges on coordinated AVR-PSS design in interconnected power systems.

Economical harvesting of electrical energy on a large scale considering the environmental issues is a challenge. As a solution, Microgrids (MGs) promise to facilitate the widely penetration of renewable energy sources (RESs) and energy storage devices into the power systems, reduce system losses and greenhouse gas emissions, and increase the reliability of the electricity supply to the customers. Although the concept of MG is already established, the control strategies and energy management systems for MGs which cover power interchange, system stability, frequency and voltage regulation, active and reactive power control, islanding detection, grid synchronization, following contingencies and emergency conditions are still under development. Like a conventional power system, a Micro-grid (MG) needs emergency control and protection schemes to have secure and stable operation. Since MG can operate in both grid-connected and islanded mode, in addition to the control loops and protection schemes, extra issues must be considered. Transition between two operation modes requires an extra control plan to eliminate and stabilize transients due to mode changing. This paper presents an overview of the key issues and new challenges on emergency control and protection plans in the MG systems. The most important emergency control and protection schemes such as load shedding methods that have been presented over the past years are summarized.