An analytical technique for the determination of spectral components of multilevel carrier-based PWM methods

This paper presents an analytical approach for determining the spectral components of multilevel pulsewidth modulation (PWM) strategies, which avoids the problems of spectral leakage, roundoff, and subtle programming errors associated with the more usual approach of using discrete Fourier transforms of simulated switched waveforms. The approach uses a double Fourier integral formulation to analyze the inverter switched output, establishing the inner and outer integral limits of this formulation under conditions of natural sampling, regular sampling, and overmodulation. Closed-form and numerical integration solutions are presented for phase disposition PWM of a diode-clamped inverter to illustrate the technique, together with a comparison of theoretical and experimental spectral results for the naturally and asymmetric regularly sampled cases to confirm the validity of the approach.