Design of random pulse-width modulated inverter with lower-order harmonic elimination

A random pulse-width modulated inverter based on programmed PWM with lower-order harmonics elimination is presented in this paper. In motor drive applications, the high switching frequencies often results in acoustic noises, which make operator feel uncomfortable. The programmed PWM are used to solve nonlinear equation eliminating harmonics with initial value obtained by equal area PWM to obtain the switching angle. More than 50 sets of switching patterns are solved by the proposed method to randomly sample at every period to generate PWM waveform. Random probability function is used to obtain the harmonic spectrum distribution by random sampling method to determine the output voltage waveforms. The harmonic spectrum is spread out to normalize the side-band harmonics and lower-order harmonics are eliminated significantly as well so that the EMI problems can be alleviated efficiently. In practical circuit implementation, the random selection of the solved PWM switching patterns results in different switching pattern and harmonic spectra at every period so that the concentrated sideband harmonic energy can be spread out.