Introducing the elliptical carrier for PWM inverters: Derivation and properties for phase-shift compensation

Carrier-based Sinusoidal PWM schemes have been developed in order to improve the output spectrum of power inverters, disregarding its phase characteristic. Additionally, the carriers analyzed in the literature have always consisted in triangular or sawtooth waveforms. This paper introduces a modified carrier able to manipulate the phase of the reference signal in Sinusoidal PWM while maintaining the characteristics of its frequency spectrum. The paper presents a method that can be applied to find the modified carrier for a given phase-shift by calculating the PWM pulse widths. Initially, the pulse widths are approximated to a sinusoidal function by assuming a high switching frequency, and then a recursive numerical method is proposed for moderate to low frequencies. The phase control characteristics and the nature of the elliptical carrier are studied, and finally an FFT analysis is performed to evaluate the resulting signals. The elliptical carrier is a significant contribution towards the extension of properties in carrier-based PWM modulation.