A Novel Control Method to Improve the Performance of Single-Phase Cascaded H-Bridge Multilevel Converter Under Variable DC Voltages

Improvement of the performance of cascaded H-Bridge multilevel converters is considered as an important factor in the conditions of input DC voltages change. In this paper, using a novel control algorithm, the improvement of the performance of a seven-level converter under variable DC voltages has been examined. Since changing the input DC voltages changes the output phase voltage, the proposed controller has been used to control the modulation index to compensate for the effect of the phase voltage reduction. One of the challenges of presenting the control algorithm is the nonlinear variation of modulation index per input DC voltages change, which has been improved by presenting a suitable method by which phase voltage control is done instantly and online. In this paper, the phase voltage range has also been controlled without measuring DC voltages and only with the phase voltage measurement. This causes the lowest sensor to be employed to control the output voltage. The switching method used in this paper is the phase disposition pulse width modulation (PD-PWM). Finally, the simulation results in MATLAB software confirm the proposed algorithm.