Single-Source Cascaded Multilevel Inverter With Voltage-Boost Submodule and Continuous Input Current for Photovoltaic Applications

Abstract

Cascaded multilevel inverter (CMI) produces a step-up output voltage by series-connection of several submodules (SMs) supplied by isolated dc sources, which can be implemented by photovoltaic (PV) sources. The unbalanced power provided by different PV sources may however distort the output voltage. To use a single dc source while retaining the voltage boosting, this article proposes a novel CMI based on a four-switch SM. It is conditioned by an input inductor, which discharges with boosted voltages across the SMs. Furthermore, a continuous input current is achieved by the inductor. The proposed inverter can be extended to higher voltage-level operations using capacitors to supply its extended SMs. To avoid switched-capacitive charging, a two-phase configuration where capacitors are directly charged by the inductive input current is presented. The voltages of capacitors are well balanced at the same average value and feature a similar ripple. The operating principles and pulsewidth modulation scheme of the two-phase inverter are described. Theoretical analysis, calculations, and comparisons with the prior-art CMIs illustrate the superiorities of the proposed inverter. Simulation and experimental results agree well with each other and verify the feasibility of the proposed inverter for PV power applications.