Novel random pulse position modulation for three-phase four-leg inverters

Aiming at improving the harmonic spectra spreading effect, two randomized pulse position modulation strategies are proposed for three-phase four-leg inverters. Based on the volt-second balance law and the fixed switching frequency, the first proposed strategy places the center randomly during one carrier cycle with a limited degree of freedom, and the second proposed strategy randomly changes the carrier slope in each carrier cycle. To get better randomization effect of the proposed strategies, Well Equidistributed Long-period Linear algorithm was introduced to generate random numbers. In order to verify the validity of the proposed strategies, the modulation strategies are implemented with dSPACE DS1007-based real-time operating system. The experimental results show that the proposed strategies have dispersed the discrete harmonics to a wider sideband. Compared with the first strategy, a larger degree of freedom can be achieved in the second proposed strategy with lower harmonic spikes.