Assessment of operation performance of power converters with low frequency PWM drive issues and field weakening

This paper addresses a study of a low frequency modulation technique performance, applied on frequency inverters and electric drive systems of medium to high power induction motors such as in the mining and steel industries. The main goal of using this technique is to minimize maintenance in applications with reliability and accessibility concerns. This paper focuses on modulation techniques with reduced dv/dt, and harmonics mitigation in energy conversion process, mainly those of higher amplitude which impose higher losses to the drives, being the 5th and 7th harmonics. The dv/dt reduction contributes to minimizing problems on motors windings, damaged insulation and electrostatic currents on the viscous fluid of bearings that cause motors degradation. Another concern is the need to avoid currents asymmetries that can induce pulsating torques in the machine, undesired DC voltages per phase and displacement of neutral voltage on three-phase loads, which in turn can influence common-mode current flows. The PD-PWM, POD-PWM modulation techniques and the selective harmonic elimination, SHE-PWM, are presented and evaluated, then compared through simulations and experimental results.