Modeling and simulation of dv/dt filters for AC drives with fast switching transients

Many of today's induction machines are operated using variable speed drives (VSD). VSDs are used for controlling the speed of induction machine by adjusting the amplitude and frequency of the AC voltage. These adjustments are made by advanced technology in semiconductors, which are faster switching devices. Faster switching reduces the switching power loss, requiring less heat sink, thus enabling drives to become more efficient and smaller, and this also helps to reduce cost. Along with the better performance enabled by the high switching speed and increased switching frequency, they have also raised several concerns related to the consequences of high speed switching. One of these concerns is the over-voltage that appears at the motor terminals due to the impedance mismatch between the power cable and the motor. In this paper, overvoltages at the motor terminal are analyzed and accurate simulation models of different filters are designed to reduce the overvoltage problems. The models can be readily implemented using computational tools like Matlab, thereby providing a convenient method to develop the best dv/dt filter solution for a particular drive to reduce the over voltage & hence increases the life of the motor.