Abstract
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.
Highlights
In the electric power industry, the demand of medium and high voltages and high power inverter is increasing
Compared with the traditional cascaded H-bridges, the hybrid cascaded H-bridges can greatly reduce the number of DC power supplies and switching transistors under the condition of the same output levels [4,5,6]
By performing a certain regular rotation cycle on the carrier, the output voltage of the cascaded unit is made to contain all the basic voltage waveforms, and the output power balance of the low-voltage unit is realized on the premise of maintaining the advantages of the modulation for the nearest level control and the in-phase disposition PWM to the III-inverter
Summary
In the electric power industry, the demand of medium and high voltages and high power inverter is increasing. In [16,17,18,19,20,21], the power balance between the cascaded H-bridge units is implemented by employing PD and carrier cycle, carrier reconstruction, pulse rotation and other power balance strategies, but the above research objects are all symmetrical cascaded H-bridge inverters. By performing a certain regular rotation cycle on the carrier, the output voltage of the cascaded unit is made to contain all the basic voltage waveforms, and the output power balance of the low-voltage unit is realized on the premise of maintaining the advantages of the modulation for the nearest level control and the in-phase disposition PWM to the III-inverter. Simulation and experiment verify the effectiveness of the proposed power balance strategy in this paper
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