Phase-Shifted Carrier Pulse Width Modulation Based on Particle Swarm Optimization for Cascaded H-bridge Multilevel Inverters with Unequal DC Voltages

Xin-Jian Cai,Shu-Xiu Wang,Zhen-Xing Wu,Quan-Feng Li

doi:10.3390/en8099670

Abstract

High-voltage cascaded H-bridge multilevel (CHBML) inverters usually include many isolated dc voltage sources. Some dc source faults result in a drop in the dc voltage, thereby leading to unequal cell dc voltages. On the other hand, the differences in cell dc source parameters result in unequal dc voltages too. At present, riding through the faults of dc sources and operating under the condition of unequal dc voltages are required to improve the reliability of CHBML inverters. Unfortunately, the conventional phase-shifted carrier pulse width modulation (PSCPWM), which is widely used for CHBML inverters, cannot eliminate low-frequency sideband harmonics when cell dc voltages are not equal. This paper analyzes the principle of sideband harmonic elimination, and proposes an improved PSCPWM based on the particle swarm optimization algorithm. This modulation technique eliminates low-frequency sideband harmonics by calculating and regulating the carrier phases according to different cell dc voltages. The proposed PSCPWM enhances the reliability of the CHBML inverter and extends the range of its application. Simulation and experimental results obtained from the prototype of the CHBML inverter verify the theoretical analysis and the achievements made in this paper.

Highlights

At present, cascaded H-bridge multilevel (CHBML) inverters are widely used for motor drives, static synchronous compensator (STATCOM) and photovoltaic power conversion, because of their high-voltage output, improved electromagnetic compatibility, extreme modularity, and lesser number of components for synthesizing the same number of voltage levels [1,2,3,4,5,6,7,8]
The cell dc source faults that lead to a drop in the dc voltage result in unequal cell dc voltages, and some differences in cell dc source parameters result in unequal cell dc voltages too
Based on the principle of sideband harmonic elimination, an improved phase-shifted carrier pulse width modulation (PSCPWM) is proposed to cancel the low-frequency sideband harmonics by regulating the carrier phases according to different cell dc voltages

Summary

Introduction

At present, cascaded H-bridge multilevel (CHBML) inverters are widely used for motor drives, static synchronous compensator (STATCOM) and photovoltaic power conversion, because of their high-voltage output, improved electromagnetic compatibility, extreme modularity, and lesser number of components for synthesizing the same number of voltage levels [1,2,3,4,5,6,7,8]. Another example is the inverter in which each phase leg includes five cascaded H-bridge cells.

Simulation

Conclusions