Optimized selection of the random PWM switching frequencies in a limited pool

Abstract

A new and simple idea is presented to optimize the selection of the switching frequencies in a limited-pool random pulse width modulation (RPWM) technique. This idea makes use of a novel formula to: (a) select the small number of switching frequencies in the pool; and (b) provide a numerical value that serves as a "figure of merit" of the line-to-line voltage spectrum for comparing different PWM and RPWM techniques. The limited-pool RPWM is implemented in a Texas Instruments (TI) TMS320C240 Digital Signal Processor (DSP) controlling an inverter-driven three-phase induction motor (IM). The advantages of the proposed ideas are illustrated through an analysis of measurements of the line-to-line voltage and acoustic noise spectra.