Power balance modulation strategy for hybrid cascaded H-bridge multi-level inverter

Under the traditional hybrid modulation strategy, the output powers of the hybrid cascaded H-bridge inverter are not balanced between the cascaded units. With a hybrid cascaded H-bridge 13-level inverter with a DC side voltage ratio of 1:1:1:3 (referred to as III-inverter in the paper) as the research object, a hybrid modulation power equalization strategy based on carrier rotation is proposed. Under the control of which, the output voltage of inverters is formed by superposition of multiple basic voltage waveforms. Firstly, the hybrid modulation strategy is adopted to modulate the inverter so that the high- and low-voltage units, respectively, operate in the low-frequency and high-frequency states. Then, the pulse sequence within the 3/2 output voltage cycle is made to circulate among all the cascaded units by carrier rotation. Finally, the output voltage of each cascaded units is made to contain all the basic voltage waveforms, thus implementing the output power balance between all the cascaded units. Based on simulation and experiment, the effectiveness of the strategy is verified, and it is shown that under the control of this power balance modulation strategy, the output voltage waveform quality of the inverter is high, there is no current backflow, and the output power can be balanced within 3/2 cycles.