Intelligent Approach for Control Techniques Based on Complex Converter Structures

Hybrid frequency control strategies are used to eliminate the problem of current inversion in multilevel cascaded asymmetrical H-bridge inverters. Unfortunately, this technique results in unbalanced power at the inverter output. The improved hybrid PWM modulation strategy helps to regulate power balances within a reasonable range at high and low voltages, by adjusting the conduction angle of the cells in high frequencies. However, as the conduction angle of a high-voltage cell increases, the fundamental amplitude of the inverter output voltage decreases, since waveforms with absolute values greater than 2E cannot be perfectly modulated. Based on mathematical models of the conduction time for each level synthesis method, a new modulation strategy is proposed to solve the problems associated with the two strategies mentioned above. This new high-frequency modulation strategy adopts a combination of pulse-width modulation (PWM) and step modulation to combine control of the high-voltage and low-voltage units. At given intervals, the control voltage signals of the low-voltage unit are exchanged. Finally, the power of each unit is balanced and the basic amplitude of the inverter output voltage is not affected. Finally, the MATLAB/Simulink simulation model and experimental platform verify the feasibility of this strategy.