Cascaded H-Bridge and T-Type Seven-Level Inverter Fed by the Inductive DC-Link with Embedded Voltage Boosting

Abstract

Multilevel inverters (MLIs) for renewable energy applications usually require a certain form of voltage boosting. To achieve an embedded voltage-boost capability, this paper proposes a novel seven-level inverter based on the H-bridge (HB) inverter, whose two half-bridge legs are cascaded with a three-level T-type (3LTT) inverter, respectively. The proposed inverter is supplied by a single dc source in series with an inductor. The inductor is charged by the dc source when shooting through the HB switches. Voltage boosting is therefore embedded into the proposed inverter without extra switches. Auxiliary circuits for balancing the voltages of capacitors are not required either, since each capacitor can be charged by the inductive dc-link with the same step-up average voltage. The carrier-based phase-shift pulse-width modulation (PWM) scheme is applied to the HB inverter to produce two inductive-charge states within a switching period. The operating frequency of the inductor is thus doubled, reducing the high-frequency input current ripple. Operating principles and theoretical analysis of the proposed inverter are given. Simulation and experimental results agree well with each other, verifying the feasibility of the proposed inverter in achieving a boosted seven-level output voltage.