Performance Analysis of T-Type Three- Level Inverter under Different Modulation Indices

Abstract

In recent years, multi-level converters have emerged as a potentially useful solution for medium- and high-power applications. This is primarily owing to their capacity to create output voltages of superior quality, while simultaneously minimizing harmonic distortion and switching stress. Recently developed T-type converters, have been subjected to extensive research for the purpose of application in renewable energy systems, electric vehicles, motor drives, and grid-connected applications. In this work, a complete comparative performance analysis is presented. The analysis is based on important a performance indicator such as total harmonic distortion (THD) is presented.

Introduction

The text presents a comparative study of three-level multilevel converters, focusing mainly on Neutral Point Clamped (NPC) and T-Type converters for high-efficiency power conversion applications. The increasing demand for renewable energy systems, electric vehicle charging, industrial drives, and smart grids has encouraged the development of advanced converter topologies with improved efficiency, lower losses, and better power quality.

Multilevel converters provide several advantages over conventional two-level converters, including:

• Improved output voltage waveform quality
• Reduced harmonic distortion
• Lower electromagnetic interference (EMI)
• Reduced switching losses
• Lower voltage stress on semiconductor devices

Among various multilevel converter types, three-level converters are widely preferred because they provide a good balance between circuit complexity and performance. They generate multiple voltage levels, reducing harmonic content and improving efficiency.

The text reviews previous research on multilevel inverter technologies, including:

• Advanced control methods for improving converter efficiency and dynamic response.
• PWM techniques for reducing harmonics and improving voltage regulation.
• Applications of cascaded H-bridge, flying capacitor, NPC, and T-Type converters.
• Use of artificial intelligence and smart energy management in power systems.

The study identifies a research gap in the lack of a direct comparison between three-level NPC and T-Type converters under identical operating conditions. Therefore, the work aims to compare their performance based on output voltage quality, total harmonic distortion (THD), efficiency, and suitability for medium-voltage applications.

Methodology

A simulation model is developed in MATLAB/Simulink using a three-level converter connected to an RL load. The system consists of:

• A DC source and DC-link capacitors
• Three-level converter (NPC or T-Type)
• PWM controller using Phase Disposition PWM (PD-PWM)
• RL load representing practical industrial applications

Three-Level NPC Converter

The NPC converter uses:

• Series-connected DC-link capacitors
• Clamping diodes
• Semiconductor switches with anti-parallel diodes

The clamping structure allows the converter to produce three voltage levels:

• +Vdc
• 0
• −Vdc

This reduces device voltage stress and improves waveform quality compared with two-level converters.

Three-Level T-Type Converter

The T-Type converter eliminates clamping diodes and uses controlled switches to generate multilevel output voltage. It offers:

• Lower conduction losses
• Reduced switching losses
• Higher efficiency
• Improved output voltage quality

PD-PWM control is applied to generate switching signals and regulate output voltage.

Simulation and Results

The converters are tested under different modulation indices:

• M = 1.0
• M = 0.9
• M = 0.8

The performance is evaluated using:

• Line-to-line output voltage waveform
• Fundamental voltage magnitude
• FFT analysis
• Total Harmonic Distortion (THD)

For M = 1.0:

• NPC converter produced approximately 300.1 V fundamental voltage with 45.64% THD.
• T-Type converter produced approximately 301.4 V fundamental voltage with a lower 41.94% THD.

For M = 0.9:

• NPC converter achieved about 293 V output voltage with 44.01% THD.
• T-Type converter achieved about 293 V output voltage with improved 40.13% THD.

Conclusion

This research conducted a comparative performance analysis of the Three-Level Neutral Point Clamped (NPC) converter and the Three-Level T-Type converter across various modulation indices. The converters were assessed according to their line-to-line output voltage waveforms and harmonic performance by FFT analysis. Simulation results indicated that both topologies may produce multilayer output voltages while minimizing voltage stress on the power semiconductor devices. However, their harmonic properties exhibited considerable variation in response to alterations in the modulation index. Future research may concentrate on experimental validation, loss assessment, thermal performance evaluation, and sophisticated modulation approaches to further improve converter performance in dynamic operating settings

References

[1] Sharma, B., Kose, U., Singh, V.P., & Kumar, A. (Eds.). (2025). Computational Intelligence, and Smart Technologies in Solar Thermal Systems: Principles and Applications (1st ed.). CRC Press. https://doi.org/10.1201/9781003634737. [2] Haitham Abu?Rub, Atif Iqbal, JaroslawGuzinski. \"High Performance Control of AC Drives with MATLAB®/Simulink\", Wiley, 2021. [3] V. Narasimhulu, G. J. Rani and N. Jyothi, \"Comparative Exploration of a Seven-Level Cascaded H-Bridge Shunt Active Power Filter using Diverse DC-Link Voltage Controllers,\" 2026 International Conference on Electronics and Renewable Systems (ICEARS), Tuticorin, India, 2026, pp. 689-694, doi: 10.1109/ICEARS67481.2026.11416801. [4] Dae-Wook Kang, Byoung-Kuk Lee, Jae-Hyun Jeon, Tae-Jin Kim and Dong-Seok Hyun, \"A symmetric carrier technique of CRPWM for voltage balance method of flying-capacitor multilevel inverter,\" in IEEE Transactions on Industrial Electronics, vol. 52, no. 3, pp. 879-888, June 2005, doi: 10.1109/TIE.2005.847574. [5] V. Narasimhulu, D. V. Ashok Kumar, and Ch. Sai Babu, \"Comparative Simulation Analysis of Harmonics in Line-Line Output Voltage of Multilevel Inverters for Different Modulation Indices,\" International Journal of Control Theory and Applications, vol. 10, no. 5, pp. 289–296, Jan. 2017. [6] V. Narasimhulu, et al., “State of Art Review of Various Control Methods for Cascade H-Bridge 5-Level Inverter to Mitigate Harmonics,” International Journal of Control Theory and Applications, vol. 9, no. 49, pp. 1–9, 2016. [7] A. El-Hosainy, H. A. Hamed, H. Z. Azazi and E. E. El-Kholy, \"A review of multilevel inverter topologies, control techniques, and applications,\" 2017 Nineteenth International Middle East Power Systems Conference (MEPCON), Cairo, Egypt, 2017, pp. 1265-1275, doi: 10.1109/MEPCON.2017.8301344. [8] J. G. K and N. V, “Performance Analysis Of T-Type 3-Level Inverter In PV-Fuel Cell Hybrid Generation System,” 2023 International Conference on Ambient Intelligence, Knowledge Informatics and Industrial Electronics (AIKIIE), Ballari, India, 2023, pp. 1–6, doi: 10.1109/AIKIIE60097.2023.10390403. [9] R. Rojas, T. Ohnishi and T. Suzuki, \"Neutral-point-clamped inverter with improved voltage waveform and control range,\" in IEEE Transactions on Industrial Electronics, vol. 42, no. 6, pp. 587-594, Dec. 1995, doi: 10.1109/41.475499. [10] Narasimhulu, V., Jithendra Gowd, K. (2021). Performance Analysis of Single-Stage PV Connected Three-Phase Grid System Under Steady State and Dynamic Conditions. In: Gunjan, V.K., Suganthan, P.N., Haase, J., Kumar, A. (eds) Cybernetics, Cognition and Machine Learning Applications. Algorithms for Intelligent Systems. Springer, Singapore. https://doi.org/10.1007/978-981-33-6691-6_5. [11] A. De and M. Barai, \"An improved zero voltage switching SVPWM for three phase inverter,\" 2017 11th IEEE International Conference on Compatibility, Power Electronics and Power Engineering (CPE-POWERENG), Cadiz, Spain, 2017, pp. 169-174, doi: 10.1109/CPE.2017.7915164. [12] P. N. Enjeti, P. D. Ziogas and J. F. Lindsay, \"Programmed PWM techniques to eliminate harmonics: a critical evaluation,\" in IEEE Transactions on Industry Applications, vol. 26, no. 2, pp. 302-316, March-April 1990, doi: 10.1109/28.54257. [13] V. Narasimhulu, D. V. Ashok Kumar, and Ch. Sai Babu, \"Recital Analysis of Modular Multilevel Converter Based Shunt Active Power Filter,\" Journal of Mechanics of Continua and Mathematical Sciences, Special Issue 5, pp. 181–192, Jan. 2020. DOI: https://doi.org/10.26782/jmcms.spl.5/2020.01.00016 [14] A. Kumar, M. V. Aware, B. S. Umre and M. A. Waghmare, \"Grid Connected Multilevel Single to Three Phase Power Converter with Improved Performance,\" TENCON 2019 - 2019 IEEE Region 10 Conference (TENCON), Kochi, India, 2019, pp. 1535-1540, doi: 10.1109/TENCON.2019.8929411. [15] Stala, R.; Folmer, S.; Penczek, A.; Hachlowski, J.; Miko?, Z. Efficiency and Power Loss Distribution in a High-Frequency, Seven-Level Diode-Clamped Inverter. Energies 2023, 16, 7866. https://doi.org/10.3390/en16237866. [16] V. Narasimhulu et al., \"Maximum Power Extraction of PV Panel Adopting AI-MPPT Scheme in Standalone System,\" 2024 International Conference on Smart Systems for applications in Electrical Sciences (ICSSES), Tumakuru, India, 2024, pp. 1-4, doi: 10.1109/ICSSES62373.2024.10561358. [17] G. P. Rao et al., \"Smart Home Management System utilizing ESP32 Controller and Solar Power,\" 2026 IEEE International Conference on Emerging Computing and Intelligent Technologies (ICoECIT), Hyderabad, India, 2026, pp. 1-6, doi: 10.1109/ICoECIT68303.2026.11497927. [18] P. Voleti, Vandna, B. P. Reddy, G. J. Rani, B. R. S. Reddy and N. Jyothi, \"A Hybrid Neuro-Fuzzy Model for Power Quality and Stability Enhancement in EV Charging with Grid-PV Integration,\" 2025 International Conference on Information, Implementation, and Innovation in Technology (I2ITCON), Pune, India, 2025, pp. 1-7, doi: 10.1109/I2ITCON65200.2025.11210743.

Copyright

Copyright © 2026 G. Jhansi Rani, V. Narasimhulu. 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.