Date of Award

3-26-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Systems Engineering

First Advisor

Jing Zhang

Abstract

This work is the study of potential applications of battery-based energy storages in the power system so that the performance can be improved. The research is focused on the case where batteries are installed at the load side. Such a battery works like an energy buffer between power system and a load. It is possible to control the battery charging time based on the status of the power system operation and the state of charger of the battery so that the power flow in the power system can become more stable. The strategy of load frequency control (LFC) was investigated for the control of battery charging. LFC is a common control strategy in the current power system which controls the power generation to keep the steady-state line frequency and tie-line power flow equal to the scheduled values. The deviation of line frequency is a measure for the balance between the power generation and power consumption. When the measured line frequency is higher than the scheduled value, the power generation is more than the power consumption. When the measured line frequency is lower than the scheduled value, the power generation is less than the power consumption. The measured line frequency can be used to control the battery charging time of a load so that the battery is charged only when the power generation is more than the power consumption. Such a battery-buffered load will play a positive role for the power system stabilization. The investigation began with the study of the practical measured line-frequency for a whole year 2013. The data was provided by Southwest Power Pool (SPP) in Little Rock. The sampling rate of the line frequency is one sample per 10 seconds. The data was evaluated to find out how the practical line frequency of the power system changed on daily base and season base during the whole year. The study also resulted in the reasonable threshold of frequency deviation in the range of 0.01 Hz to 0.02 Hz which can be used for the control of the battery charging time. To confirm the effectiveness of the LFC-controlled batteries for the power system stabilization, system simulation was performed for power network with single-area and multi-interconnected areas. The simulation was done with Matlab/Simulink. Although the simulation models used in this work were quite simple compared to a practical power system, the results are significant in principle for the confirmation of the effectiveness of the LFC-controlled batteries for the power system stabilization. This work is significant for the practice. In the power system, more and more loads are connected with batteries, for examples, laptop computers and mobile communication devices. Although the energy capacity of each battery in such an application is very small, the effect may be significant by considering the large amount of such devices in the applications. Battery-buffered loads will also provide many other advantages instead of the power system stabilization. They will improve the quality of electrical power supply. They are also helpful for the operation of smart grid and usage of renewable energy. We may expect that not only laptop computers and mobile communication devices, but also other appliances such as refrigerators, home entertainment equipment use battery for the power supply. Of course the biggest ones should be electrical vehicles in the future.

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