Comparison between back-to-back and matrix converter drives under faulty conditions

This paper presents a comparison study between the operation of a back-to-back and a matrix converter induction motor drive under the presence of faults in the power switches of these converters. These two topologies are functionally equivalent in terms of input power quality and energy regeneration capabilities but need to be compared in terms of performance under faulty conditions as well due to the high number of switches involved in these two converters. In particular, the total waveform distortion of the input/output currents of the two converters and the motor torque oscillations were measured with the aim to determine which converter performs better under faulty conditions. Based on simulation results obtained with a detailed model of the two drive systems, it is shown that the distortions of the input/output currents caused by a single-fault in a matrix converter are approximately identical to the ones that appear in a back-to-back converter with two faults, one in the rectifier stage and the other one in the inverter stage. On the other hand, the back-to-back converter is perfectly capable of operating with an open-circuit fault provided that it is located in the rectifier stage, being the operation of the motor practically unaffected in that case. In general terms it can be said that due to the absence of an energy storage element, the matrix converter is particular sensitive to the appearance of faults. The back-to-back converter, on the other hand, is capable of maintaining a better quality of operation of the motor under faulty conditions, provided that the faults are not located in the inverter stage.