Impact of Orientation and Phase-shift in Carrier Signals on Line-Current Harmonics for an OWIM Drive Operated with Synchronous PWM

High-power, medium-voltage squirrel cage induction motor (SCIM) drives used for railway traction application are invariably operated with low inverter switching frequency in order to curb the switching energy losses. Carrier-based synchronous PWM techniques are very popular in such cases. Here, the carrier frequency (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf>) is continuously varied such that its ratio with the frequency of the modulating signal (f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf>) remains constant. This ratio is defined as the Pulse number (P). Open-end winding induction motor (OWIM) has been recently established as suitable replacement for the conventional Y-connected SCIM drives specially for railway traction application. It has been established that OWIM drive offers more flexibilities in the choice of P. In this paper, the impact of orientation of the triangular carrier with respect to the modulating signal on the machine line-currents harmonics in analysed using double-fourier series. Double fourier series is used to calculate an appropriate phase-shift between the carrier signals of the two inverters of OWIM drive to improve the line-current THD further. The analytical findings are validated both through simulations as well as experimentally.