Development of a Novel Single-Source Three-Phase Step-Up Multilevel Inverter Topology

Abstract

DC to AC power conversion is required for numerous applications including electric drives, utilization of renewable energy sources and dc sources, flexible ac transmission systems (FACTS), etc. The use of Multilevel Inverters (MLI) have seen active development in these areas due to their various advantages such as reduced harmonics, voltage stress, etc. The classical topologies such as Cascaded H-bridge (CHB), Neutral-point clamped (NPC) and Flying Capacitor (FC) were the initial structures to be developed. But there are various issues which limited their use in some applications such as requirement of isolated DC sources and lack of voltage boosting capability among others. Switched Capacitor (SC) based topologies have the capability to boost the output voltage greater than input voltage, thus, giving a voltage gain greater than unity. In this regard, this work proposes a novel SC based MLI (SCMLI) three-phase (3-φ) topology having a voltage boosting capability using a single DC input voltage source. The converter structure is able to provide voltage gain which is twice the applied input source voltage. Theoretical study and analysis are done to show the proper working of the proposed converter structure. The multicarrier based Level-Shifted Pulsewidth Modulation (LSPWM) strategy is used for the modulation of power semicondutor switches. The proposed MLI is able to provide bootsted line-to-line (l-l) pwm voltage output giving a five-level waveform. Further, soft charging of the switched capacitor strucutre is achieved by employing an inductor of a small value which is connected in series with input source. Finally, the simulations are performed and the obtained results are shown for a 100 KW inverter having an input voltage of 285V to validate the working of the topology. Here, LSPWM strategy using both Phase Opposition Disposition (POD-LSPWM) and Phase Disposition (PD-LSPWM) techniques is used for the modulation of power semicondutor switches during simulation. And comparison between these two modulation schemes is done and results are presented which show that PD type LSPWM scheme gives better results.