Multilevel random pulse width modulation strategy based on Markov chain

The pulse width modulation (PWM) strategy is the main power electronic modulation method. It uses a fixed-frequency triangular carrier modulation, but the fixed-frequency carrier causes the harmonics in the output voltage to be highly concentrated at integer multiples of the carrier frequency, which generates electromagnetic interference. The multilevel PWM strategy effectively reduces the harmonic content of the inverter output voltage by increasing the number of levels, but it is unable to change the distribution location of harmonics. To address this issue, a multi-level random PWM (RPWM) strategy based on Markov chains is proposed. This approach randomizes the fixed carrier frequency using RPWM, dispersing harmonics concentrated at carrier frequency multiples across a broader frequency domain to reduce harmonic peaks. The introduced Markov chain effectively improves the random distribution probability of the random numbers and prevents the increase of voltage pulses due to excessive variations of random frequencies. The dispersion location of the harmonic content is analyzed using variance for a more intuitive comparison of the degree of dispersion of the harmonics. Finally, the effectiveness and feasibility of the proposed Markov chain multilevel stochastic PWM strategy is verified using simulation models and experimental studies with a CHB-type five-level inverter as an example.