Theoretical harmonic analysis of cascaded H-bridge inverter under hybrid pulse width multilevel modulation

This study investigates the analytical approach for determining the spectral components of a hybrid pulse width modulation (HPWM) strategy for cascaded H-bridge (CHB) multilevel inverters. By decomposing the HPWM voltage into a staircase waveform and a non-sinusoidal pulse width modulation waveform and applying the one-dimensional Fourier series as well as double Fourier series methods, the closed-form solution for arbitrary level HPWM voltage is derived. Based on the derived solution, analysis of HPWM output with a changed modulation index is also performed, with good stability and control dynamic demonstrated. The spectral analytical expression is verified extensively by comparison of theoretical calculation results with those of the simulation and laboratory experiment, which coincide with each other very well. Furthermore, a brief switch function rotation balancing method for HPWM-based CHB inverter is utilised, and is also validated by experimental results.