Multilevel current source inverter topology based on dual structure associations

A multilevel power converter topology based on dual current source inverter for large induction motor drives has been proposed. The topology utilizes the combination of the load commutated inverter (LCI) using thyristors and the current source inverter (CSI) using gate turn-off thyristors (GTO). As a result, the multilevel inverter operation takes advantages of soft switching by the LCI and hard switching by the CSI. The output capacitor is required to generate the leading power factor for load commutation of the LCI. It is shown that the proposed multilevel operation contributes to the leading power factor generation by providing the effective phase shift. Thus, the leading power factor required for the load commutation of the LCI is obtained with significantly smaller capacitors at the inverter´s output terminals. As a result, the proposed approach can employ the LCI and utilize its soft switching operation, yielding cost-effective solution compared with the conventional multilevel CSI using two GTO CSIs. The switching losses are curtailed due to the natural commutation of the LCI and the six-step operation of the GTO CSI. Therefore, the proposed multilevel inverter can both increase the output power level and decrease the output capacitor size for LCI. The simulation and experimental results have been shown to verify the feasibility of the proposed multilevel topology and its operation.