A Voltage Sag Supporter Utilizing A PWM-Switched Autotransformer
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This research suggests a novel voltage control scheme that can compensate for voltage sag and swell conditions in three-phase power systems. Faults occurring in power distribution systems or facilities in plants cause the voltage sag or swell. For sensitive loads, even voltage sags of short duration can cause serious problems in the entire system. In order to mitigate power interruptions, this research proposes a scheme called Voltage Sag Supporter utilizing a PWM (Pulse Width Modulation)-Switched Autotransformer. The proposed scheme is able to quickly recognize the voltage sag or swell condition, and it can correct the voltage by either boosting the input voltage during voltage sag events or reducing the input voltage during voltage swell events. Among existing methods, the scheme based on the inverter system such as dynamic voltage restorers (DVR) require an inverter, a rectifier, and a step-up down transformer, which makes the system expensive. AC converters can be used for the purpose of the research. However, they consist of two solid-state switches per one phase and include energy storage devices such as reactors and capacitors. The switching device for the high voltage application is relatively expensive so that this research suggests a scheme utilizing only one switch for the output voltage control, which makes the system more stable and cost effective. The proposed scheme can be applied at any voltage and provides cost and size advantages over existing methods due to the reduced number of switching components and no need of energy storage devices. Simulations and experiments have been carried out to verify the validity of the proposed scheme, and prototype experiments are being done to confirm the control scheme.