A novel PWM scheme for harmonic reduction in power converters

The harmonic content in the output of the rectifier can be reduced by employing pulse-width modulation. Sinusoidal pulse-width modulation (SPWM) is commonly used to reduce the harmonic content in the output and to vary the average voltage. However, the SPWM technique gives a large second harmonic component in the output and a low fundamental output voltage. The paper describes a novel PWM scheme called inverted-sine PWM (ISPWM) which uses a sinusoidal reference signal and an inverted-sine carrier. The ISPWM has a better spectral quality and a higher average voltage compared to the SPWM. The paper computes the harmonic content of the ISPWM output for different values of modulation index and compares them with the results obtained for a conventional SPWM. The complete control circuit for generating the ISPWM control signal for a PWM rectifier is developed. Experimental waveforms of voltages and currents and their frequency spectra are presented