Harmonic Optimization Vs. Component Complexity: A Comparative Study of Cascaded H-Bridge Multilevel Inverters Across 3,5, and 7-Level Configurations

Abstract

Multilevel inverters (MLIs) have emerged as a critical solution for high-power and medium-voltage applications, addressing limitations of conventional inverters such as high switching losses, harmonic distortion, and voltage stress. This study focuses on cascaded H-bridge multilevel inverters (CHB-MLIs), evaluating their performance across three-, five-, and seven-level configurations. Through MATLAB/Simulink simulations, the relationship between output voltage levels and total harmonic distortion (THD) is analyzed, demonstrating a significant reduction in THD as levels increase—from 34.16% in a three-level design to 16.83% in a seven-level system. The comparison highlights trade-offs between component count, complexity, and harmonic performance, emphasizing the cascaded H-bridge topology’s modularity and scalability. Key advantages include reduced voltage stress on switches, lower electromagnetic interference (EMI), and improved waveform quality. The findings underscore the suitability of CHB-MLIs for renewable energy integration, grid-tied systems, and industrial drives, where precise voltage control and efficiency are paramount.

Introduction

1. Introduction

An inverter converts DC (direct current) to AC (alternating current). Among inverter types, Multilevel Inverters (MLIs) are increasingly used in modern power systems due to their:

• High efficiency

• Lower harmonic distortion

• Suitability for high-voltage/high-power applications

Originally introduced in 1975, common MLI topologies include:

• Diode-Clamped

• Flying Capacitor

• Cascaded H-Bridge (CHB)

?? Topologies of MLIs

A. Diode-Clamped MLI

• Uses clamping diodes and capacitors.

• Pros: High efficiency, simple back-to-back system design.

• Cons: More components needed at higher levels; capacitor imbalance limits scalability.

B. Flying Capacitor MLI

• Replaces diodes with capacitors in switching cells.

• Pros: Capable of reactive power control; allows voltage balancing.

• Cons: High switching losses, bulky design, expensive.

C. Cascaded H-Bridge MLI (CHBI)

• Consists of series-connected H-bridge units, each powered by a separate DC source.

• Pros: Modular, low component stress, scalable, low THD.

• Applications: Ideal for industrial drives, renewable energy systems, and grid-tied inverters.

???? Simulation & Performance Analysis

Key Observations:

• THD Reduction: More levels → lower THD (better waveform quality).

• Scalability: Higher levels provide near-sinusoidal output.

• Complexity: Increases with more H-bridges (switches, DC sources).

• Waveform Quality: 7-level CHBI gives the best output but at a higher cost and complexity.

???? Related Work

• Various studies have improved MLI designs through hybrid topologies, selective harmonic elimination PWM (SHE-PWM), and space vector modulation to improve performance and reduce switching frequency.

?? Trade-Offs in Practical Applications

• 3-Level CHBI: Cost-effective, acceptable THD for simple applications.

• 5-Level CHBI: Balanced choice between performance and complexity.

• 7-Level CHBI: Best for high-precision, low-THD environments, but requires more hardware and cost.

Conclusion

Higher-level CHB-MLIs achieve superior harmonic performance (e.g., 16.83% THD for 7-level) but require increased components [6, 16]. Future work could explore hybrid topologies combining diode-clamped or flying capacitor features [14, 15].

References

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Copyright

Copyright © 2025 Somnath Sharma, K. P. Yadav. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.