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This paper proposes a fuzzy-logic-controlled super-conducting magnetic energy storage (SMES) scheme for the stabilization of grid-connected wind-generator systems. The control scheme of SMES is based on a sinusoidal pulsewidth-modulation voltage-source converter and a two-quadrant dc-dc chopper using an insulated-gate bipolar transistor. A comparative study is carried out between the proposed fuzzy-logic-controlled SMES and the fuzzy-logic-based pitch controller to improve the wind-generator stability. Simulation results demonstrate that the performance of the proposed fuzzy-logic-controlled SMES is better than that of the fuzzy-logic-based pitch controller in order to stabilize the wind generator. Index Terms--Fuzzy-logic controller, pitch controller, super-conducting magnetic energy storage (SMES), unsuccessful reclosing, voltage-source converter (VSC), wind-generator stability.

This paper presents a new method to enhance the transient stability of multimachine power system including wind farms, when a severe network disturbance occurs in the power system. For this purpose, the energy capacitor system (ECS) composed of power electronic devices and electric double layer capacitor (EDLC) is proposed. The control scheme of ECS is based on a sinusoidal PWM voltage source converter (VSC) and fuzzy logic controlled dc--dc buck/boost converter using insulated gate bipolar transistors (IGBT). Two wind farms are considered to be connected to the power system. Two-mass drive train model of wind turbine generator system (WTGS) is used in the analyses as the drive train modeling has great influence on the dynamic characteristics of WTGS. Real wind speed data are used in the analyses to obtain realistic responses. Different types of symmetrical and unsymmetrical faults are considered as the network disturbance. Simulation results clearly show that the proposed ECS can enhance the transient stability of wind generators in muitimachine power system as well as their low voltage ride through (LVRT) capability. Index Terms--Dc--dc buck/boost converter, electric double layer capacitor (EDLC), energy capacitor system (ECS), pitch controller, transient stability, voltage source converter (VSC), wind energy.

This paper aims at investigating the effect of the coordination of fuzzy logic-controlled superconducting magnetic energy storage (SMES) and optimal reclosing on the transient stability in a simulated multi-machine power system during unsuccessful reclosing of circuit breakers. The performance of the coordinated operation of fuzzy logic-controlled SMES and optimal reclosing is compared to that of the coordinated operation of fuzzy logic-controlled SMES and conventional auto-reclosing. Also, the performance of the fuzzy logic-controlled SMES is compared to that of an alternative static nonlinear controlled SMES. The control scheme of SMES is based on a pulse width modulation (PWM) voltage source converter (VSC) and a two-quadrant dc-dc chopper using gate-turn-off (GTO) thyristor. The parameters of the proposed fuzzy logic controller are optimally tuned by the genetic algorithm (GA) method. Simulation results of both balanced and unbalanced faults at different points in a multi-machine power system show that the coordinated operation of fuzzy controlled SMES and optimal reclosing is able to stabilize the system well in case of an unsuccessful reclosing. Moreover, the transient stability performance of the coordinated operation of fuzzy controlled SMES and optimal reclosing is better than that of the coordinated operation of fuzzy controlled SMES and conventional auto-reclosing. Also, the performance of the fuzzy logic-controlled SMES is better than that of the static nonlinear controlled SMES. Index Terms--Dc-dc chopper, fuzzy controller, global positioning system (GPS), optimal reclosing, power system transient stability, static nonlinear controller, superconducting magnetic energy storage (SMES), unsuccessful reclosing, voltage source converter (VSC).

This paper analyzes the effect of the coordination of optimal reclosing and fuzzy logic-controlled braking resistor on the transient stability of a multimachine power system in case of an unsuccessful reclosing of circuit breakers. The transient stability performance of the coordinated operation of optimal reclosing and fuzzy controlled braking resistor is compared to that of the coordinated operation of conventional auto-reclosing and fuzzy controlled braking resistor. The effectiveness of the proposed method is confirmed by simulations in case of a nine-bus power system model as well as a ten-machine system. Simulation results of both balanced and unbalanced faults at different points in the power systems show that the coordinated operation of optimal reclosing and fuzzy controlled braking resistor is able to stabilize the systems well in case of an unsuccessful reclosing. Moreover, the transient stability performance of the coordinated operation of optimal reclosing and fuzzy controlled braking resistor is better than that of the coordinated operation of conventional auto-reclosing and fuzzy controlled braking resistor. Index Terms--Balanced fault, braking resistor (BR), fuzzy controller, global positioning system (GPS), optimal reclosing, power system transient stability, unbalanced faults, unsuccessful reclosing.

Braking resistor is a very powerful tool to improve transient stability in a power system. Usually, a fixed value of the braking resistor is considered for the transient stability analysis. However, when the braking resistor is in operation, temperature of the resistor material rises above ambient temperature which ultimately causes the resistance value to increase. This paper analyzes the effect of the temperature rise of the fuzzy logic-controlled braking resistor on the transient stability in a multimachine power system. The performance of the braking resistor scheme with fuzzy controller is compared to that of with conventional proportional-integral-derivative (PID) controller. Simulation results of both balanced and unbalanced faults at different points in the system indicate that the temperature rise of the fuzzy logic-controlled braking resistors has little or almost no effect on the transient stability of the multimachine power system. Moreover, it is found that the performance of fuzzy logic controller is better than that of conventional PID controller. Thus, the proposed fuzzy control strategy provides a simple and effective method of transient stability enhancement. Index Terms--Balanced and unbalanced faults, braking resistor, EMTP, fuzzy logic controller, genetic algorithm, PID controller, temperature rise effect, transient stability.

It has been observed that the values of the magnetizing reactances in both d- and q-axis are reduced significantly from their corresponding unsaturated values as a result of nonlinearities introduced by saturation under both steady-state and transient operations. In the round rotor synchronous machine, q-axis magnetic circuit saturates appreciably more than that along the d-axis because of the presence of the rotor teeth. In the second section, a new method to calculate the q-axis saturation characteristic from the existing d-axis saturation characteristic has been presented. We have next calculated the saturated values of the d- and q-axis self magnetizing reactances and mutual cross magnetizing reactances between the two orthogonal axes under the steady-state operation. Finally, the effect of saturation, particularly the effect of q-axis saturation, on the power system transient stability has been presented. Index Terms--Cross-Saturation, q-axis saturation, saturated reactances, saturation, synchronous machine, transient stability.