Minimization of Negative Effects of Time Delay in Smart Grid System

Previous studies found that using remote signals can stabilize inner oscillation, so the research on wide area control in power fields has been taken seriously. However, communication delay is one of the inevitable problems when using wide area measurement system (WAMS) and it has adverse effects on control systems. This paper aims at explaining current research on communication delay in power systems and providing a new method to minimize negative effects brought by time delay. Simulation takes place on an IEEE nine-bus system using Matlab/Simulink software. Circuit breakers in the system are controlled by the optimal reclosing time (OPRT) method. Different types of faults and different time delays had been considered. The performance of the system considering time delays with and without the proposed predictor has been compared. From the simulation results, it is shown that the proposed predictor performs well in minimizing the negative effects of time delays

Influence of communication delay on the performance of fuzzy logic-controlled braking resistor against transient stability

This paper analyzes the influence of communication delays introduced in online calculation of the global input variable of the fuzzy logic controller for braking resistor (BR) switching on the transient stability of a multi-machine power system. The time derivative of the total kinetic energy deviation (D) of the synchronous generators is used as the global input of the fuzzy logic controller in this work. The Global Positioning System (GPS) is proposed for the practical implementation of the calculation of the global input of the fuzzy controller. Communication delays may affect the control system, and consequently, the transient stability of the power system also. A prediction function is proposed to minimize the negative effect caused by the communication delay on the transient stability. Also, the performance of the fuzzy logic-controlled BR is compared to that of the conventional proportional-integral (PI) controlled BR. Simulation results of both balanced and unbalanced faults at different points in the system show that the communication delay associated with the fuzzy controller input calculation has an influence on the transient stability. Moreover, the negative effect caused by the communication delay on the transient stability enhancement using fuzzy-controlled BR can be minimized by the prediction method. Also, the performance of the fuzzy logic-controlled BR is better than that of the PI-controlled BR. © 2008 IEEE

Transient Stability Enhancement of Electric Power Grid by Novel Braking Resistor Models

The dynamic braking resistor is one of the effective methods to enhance the transient stability of power grid system. In this work, two new braking resistor models, namely, rectifier controlled braking resistor and chopper rectifier controlled braking resistor mod-els, using a single unit of braking resistor are proposed, and their performance is compared with the existing thyristor controlled braking resistor model. Comparison is made in terms of the speed indices, number of components used, heat loss, harmonics, and cost. The effectiveness of the proposed methodology is tested through Matlab/ Simulink simu-lations considering both temporary and permanent faults in power system. Simulation results for all braking resistor models are compared and analyzed. The performance of the proposed models is comparable to the existing braking resistor model. Therefore, the proposed braking resistor models can be considered as an alternative to the existing BR model for improving the transient stability of power systems