Investigations on ride-through capabilities of ASD's during three-phase unsymmetrical faults

Sensitivity of adjustable speed drives (ASD's) to voltage sags is a subject of various studies and experimental researches. The main criteria for determining the threshold sensitivity is the input voltage value that causes the disconnection/tripping of frequency converter. It is a known fact that the voltage sags, especially unsymmetrical, can cause ASD's performance degradation, primarily reduction of available motor torque and the occurrence of significant DC-Link voltage ripple. The objective of this paper is to investigate the performance of an ASD's under unsymmetrical fault. Only the single line to ground fault has been considered. The performance of the proposed topology is identical for the remaining types of unsymmetrical faults. The application of capacitor bank, battery bank or supercapacitors bank with boost converter to inject energy at DC-Link under unsymmetrical fault i.e. unbalanced voltage sag as ride-through alternative is given in this paper. The observations are made on the basis of simulation and experimental work.