Modeling and Simulation of New PWM Techniques for Hybrid 7-Level Inverters Using Simplified Switching Table

Abstract

Nowadays, Cascade H-bridge (CHB) multi-level inverters (MLI) have many applications in the fields of electric drive control, high-power energy control, medium-voltage power grids, and popularization in the conversion of renewable energy power. In order to improve the quality of MLI to meet today's needs while reducing costs, it is necessary to have new methods to improve the working efficiency of the converter. Therefore, this paper presents a novel PWM control for single-phase cascaded hybrid 7-level inverter using simplified switching table (SST). The SST table converts switching states of the traditional multi-level inverter to the switching state of the hybrid cascaded inverter. The SST table is effectively designed to reduce the number of switching when performing output voltage control, thus improving the converter's working efficiency. The PWM method using proposed SST has the advantage of simple implementation, utilizing the traditional Sin-PWM techniques without re-calculating the control function or changing the carrier waveforms. The effectiveness of the proposed method will be evaluated through the voltage and current harmonic distortion factors when applying level shift carrier arrangements (LS-PWM) and speed control application of 3-phase asynchronous motor. Furthermore, in order to prove the advantage of the PWM technique using the proposed SST, the power loss of the 7-level hybrid cascaded inverter is also calculated and compared with traditional seven-level inverter and 3-level inverter. The analysis and modeling results of the 7-level hybrid inverter control are verified and evaluated using MATLAB SIMILINK and PLECS software.