A VOLTAGE SAG SUPPORTER UTILIZING A PWM-SWITCHED AUTOTRANSFORMER-Thesis(doctoral)-- Georgia Institute of Technology : Electrical & Computer Engineering 2004-Dong-Myung Lee

 1.1 Background 

A power distribution system is similar to a vast network of rivers. It is important to remove any system faults so that the rest of the power distribution service is not interrupted or damaged. When a fault occurs somewhere in a power distribution system, the voltage is affected throughout the power system. Among various power quality problems, the majority of events are associated with either a voltage sag or a voltage swell, and they often cause serious power interruptions. A voltage sag condition implies that the voltage on one or more phases drops below the specified tolerance for a short period of time. A voltage swell condition occurs when the voltage of one or more phases rises above the specified tolerance for a short period of time. The causes of voltage sags and swells are associated with faults within the power distribution system. Users located a close distance to the fault experience voltage sags much greater in magnitude and duration than users located farther away, and as the electrical system recovers after removing the fault, voltage swells are produced throughout the system for short periods of time. Often all users who are served by the power distribution system have power interruptions during a fault because of the effects of a voltage sag or voltage swell produced in the system by the fault. The objective of this research is to develop a novel voltage control scheme that can compensate for voltage sag and swell conditions in three-phase power systems. Power systems supply power for a wide variety of different user applications, and sensitivity to voltage sags and swells varies widely for different applications. Some applications such as automated manufacturing processes are more sensitive to voltage sags and swells than other applications. For sensitive loads, even a voltage sag of short duration can cause serious problems in the manufacturing process. Normally, a voltage interruption triggers a protection device, which causes the entire branch of the system to shut down.

LINK PART OF THE THESIS:
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LINKS PAPERS IEEE

A voltage sag supporter utilizing a PWM-switched autotransformer
Dong-Myung Lee ; Habetler, T.G. ; Harley, R.G. ; Rostron, J. ; Keister, T. Power Electronics Specialists Conference, 2004. PESC 04. 2004 IEEE 35th Annual Volume: 6 DOI: 10.1109/PESC.2004.1354751 Publication Year: 2004 , Page(s): 4244 - 4250 Vol.6 Cited by: Papers (5) IEEE Conference Publications

A Voltage Sag Supporter Utilizing a PWM-Switched Autotransformer
Dong-Myung Lee ; Habetler, T.G. ; Harley, R.G. ; Keister, T.L. ; Rostron, J.R. Power Electronics, IEEE Transactions on
Volume: 22 , Issue: 2
DOI: 10.1109/TPEL.2006.890004
Publication Year: 2007 , Page(s): 626 - 635
Cited by:  Papers (28)
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Design and control of unified power conversion system for EV
ABSTRACT
Most developed countries that produce vehicles and automobile companies invest in lots of budgets for developing electric vehicle to reduce the use of fossil fuel. Particularly, as the battery technology has been made rapid progress, electric vehicles are able to operate with only battery system. In this context, battery charger connected with grid is required to charge the batteries attached with vehicles. Battery charger charges the battery bank through using the electrical energy of grid, and the operation is similar with that fossil fuel is injected into the gas tank of an internal-combustion engine. This system requires input power factor controller and energy conversion system for charging the battery bank, and the system generally consists of diode rectifier and DC/DC converter or single stage AC/DC PWM converter. In the case of the charger that consists of diode rectifier and DC/DC converter, based on the voltage level of battery, the battery is charged through using buck type or boost type DC/DC converter, and the input power factor is controlled as well. On the other hand, AC/DC PWM converter contains single stage circuit that consists of power semi-conductor switching devices instead of diode rectifier, and the converter charges battery and controls input power factor. Moreover, the structures of energy conversion system to control motor are classified into two types. The first type is that the voltage and capacity of battery bank is bulky. In this case, the battery bank is employed as the input of inverter. The inverter supplies energy for operating to motor and transports free-wheeling energy generated when vehicle brakes suddenly to the battery bank through simple rectifying operation. The second type is that the voltage and capacity of the battery bank is comparably low. When the vehicle is operating, the Bi-directional DC/DC converter boosts the battery energy until the voltage is same as that of inverter DC-link. On the other hand, when the vehicle is braking, the free-wheeling energy is charged into the battery bank through the Bi-directional DC/DC converter.

In this paper, battery charger used for electric vehicle as an energy conversion system, Bi-directional DC/DC converter, and three-phase voltage source inverter were designed. The inverter performs the vector control of interior synchronous permanent magnet motor for electric vehicle. Also, depending on the driving mode, simulation was performed through using the designed energy conversion system. The battery charger charges four 12[V] series connected lead battery bank with single commercial power, and the charger was designed based on AC/DC PWM buck converter. The capacity of the employed battery bank is 48[V]/100[Ah], and the battery bank was charged in constant current control condition with 0.2[C-rate], 20[A]. The Bi-directional DC/DC converter was designed based on three-phase interleaved type buck-boost DC/DC converter. The designed converter controls the output voltage constantly as 250[V] in operating condition, and the inductor current of each phase was controlled by the designed converter to have same average current value.


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LINK
https://copy.com/8KlrtiJczM6sz0lm