Topology and Modulation Strategy of Asymmetric Three-unit Thirteen-level Inverter
Compared with symmetrical cascade H-bridge multilevel inverters,hybrid cascade H-bridge multilevel in-verters can use fewer H-bridge units to obtain higher output voltage.However,the traditional hybrid cascade H-bridge multilevel inverters have the phenomenon of current inversion during the unit time.In order to solve the above problems,this paper improves the type Ⅲ inverters with 1:3 voltage ratio,and puts forward a kind of asymmetric three-unit 13-level inverters with 3:2:1 voltage ratio.At the same time,a hybrid modulation strategy is proposed for the inverter,which combines the advantages of ladder wave and PWM wave.The partial pulses obtained under this modulation strat-egy are logically calculated and distributed,which solves the problem of current inversion in traditional type Ⅲ inverters and improves the power quality of output voltage.With this hybrid modulation strategy,the high-voltage unit works at a lower frequency and the low-voltage unit works at a higher frequency to ensure the output voltage quality of the inverter.Finally,the validity and feasibility of the proposed inverter topology and the hybrid modulation strategy are verified by simulation and experiment.
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