Study Of The Dynamic Process Of Induction Motors Caused By Voltage Sags

Voltage sag and short interruption are important issues facing our country, which accountedfor more than92%of all industrial power quality problems. The transmission of voltage sagstook place in transmission and distribution lines through transformers to low tension bus areanalyzed. According to its simplified first-order model, the low-voltage ride through capability(LRTC) of induction motor (IM) after voltage short interruption is studied. The analyticexpressions of IM slip and critical time under three-phase asymmetrical voltage sag (TAVS) arededuced by applying symmetrical component. The voltage sag detection is an essentialprerequisite for its compensation in order to reduce its impact on IM and other sensitiveequipments. The single-phase voltage sag (SVS) detection based on differential eguation is putforward. The synchronous coordinate transformation is used for the dectection of TAVS. And thedetection method using improved instantaneous symmetrical component (IISC) based on αβstationary frame is proposed to get the DC voltage of dq rotating frame directly. Thecomplex-domain instantaneous symmetrical component (CISC) is introduced to the voltage sagdetection filed, and two complex-domain detection methods which are abc/dq transformationand120/dq transformation are put forward. Simulation results demonstrate the effectiveness ofthe proposed detection method. Finally, the overall structure and software configuration of thedistributed voltage sag monitoring system is introduced.