Improved switched-capacitor-based modular t-type inverter topology

Abstract

Switched-capacitor (SC) based multilevel inverters (MLIs) have gained great attention in renewable energy applications owing to their self-balancing of the capacitor’s voltage and ac voltage boosting. In most existing SCMLIs, the unequal charging and discharging duration of the SCs increase the capacitor’s voltage ripple problem. Recently, the switched-capacitor-based modular t-type inverter (SCMTI) topology resolved the problem by extending the charging period of all SCs to at least half of the fundamental switching period. However, the SCMTI topology suffers from two main drawbacks: a significantly high number of active switches and the number of switches in the charging loop Npath, C, which increases the power loss and distorts the quality of the voltage waveform. Hence, this work proposes a new SCMLI topology that retains the good traits of the SCMTI with device count reduction. The proposed inverter possesses a low Npath, C, significantly reducing the power loss for higher voltage levels. The proposed inverter is compared with other recent SC topologies to show its superiority. The number of active switches is the lowest compared to the SCMTI at each voltage level of the proposed inverter topology. For the proposed 7-level inverter, the requirement of active switches is only 12, which is 25% less than the SCMTI topology. This will reduce the overall cost and size significantly. The merits and feasibility of the proposed SCMLI are verified through simulation. Then a laboratory prototype is developed and tested for the 7-level module under steady-state and dynamic conditions to validate the simulation model. Finally, PLECs power-loss modelling and conversion efficiency evaluations are provided for the proposed topology, and a comparison is made with the SCMTI topology. The proposed inverter’s maximum experimental efficiency is 97.5% at 1.2 kW rated power. The proposed topology’s thermal analysis and loss estimation show better efficiency over the SCMTI topology. Further, the results show that the proposed inverter has 1% higher efficiency at a switching frequency of 10 kHz and 3% higher at a switching frequency of 20 kHz. This comparison confirms that the proposed topology has a significant loss reduction than the SCMTI, proving its potential merits.