I. Introduction
Power quality (PQ) monitoring has become an important part of utility services in recent years. The PQ study involves a critical step: the monitoring of the actual voltage and current waveforms and the detection of the PQ disturbances that occur during the monitoring. Detected disturbances are subsequently classified, and the information describing their localization, duration, and types, is stored and/or displayed. According to the IEEE 1159–1995 standard [1], the PQ disturbances can be divided into the following main categories: sags, swells, interruptions, transients, and waveform distortions (e.g., harmonics and noise). At the present time, the quality of electricity supplies has become an important concern to electronic product manufacturers and end-users. Poor electric power quality might lead to equipment and small electronic devices malfunctioning or instability. The lifetime of electronic devices might also be shortened due to the resonance effect caused by harmonics or voltage flicker. Moreover, the disturbances caused by an end user's device will affect the power supply system, and further influence all of the connected devices. Poor PQ can be attributed to power line disturbances, such as wave shape faults. Thus, the solutions to PQ problems must be found.