Citation: Iglesias-Rojas, J.C.; Velázquez-Lozada, E.; Baca-Arroyo, R. Online Failure Diagnostic in Full-Bridge Module for Optimum Setup of an IGBT-Based Multilevel Inverter. Energies 2022, 15, 5203. https://doi.org/10.3390/ en15145203 Academic Editors: Seleme Isaac Seleme, Jr., Heverton Augusto Pereira and Allan Fagner Cupertino Received: 19 June 2022 Accepted: 14 July 2022 Published: 18 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Online Failure Diagnostic in Full-Bridge Module for Optimum Setup of an IGBT-Based Multilevel Inverter Juan Carlos Iglesias-Rojas * , Erick Velázquez-Lozada and Roberto Baca-Arroyo Instituto Politécnico Nacional—ESIME Zacatenco, Unidad Profesional Adolfo López Mateos, Alcaldía Gustavo A. Madero, Mexico City 07738, Mexico; evelazquezl@ipn.mx (E.V.-L.); rbaca02006@yahoo.com.mx (R.B.-A.) * Correspondence: jiglesias@ipn.mx; Tel.: +52-01-5729-6000 Abstract: An online failure diagnostic test is essential to ensure the robustness and reliability of high-powered systems. Furthermore, the overall design must comprise diagnostic strategies to detect in-service and high-powered module defects. This paper describes the critical failure mechanisms—- cross-conduction, inductive avalanche, second turn-on, VS-undershoot, inrush current, and thermal runaway—-that directly affect insulated gate bipolar transistor (IGBT) operation. The constructed inverter contains 18 transformer-based taps (six per phase); however, this work studied a single tap (IGBT-based full-bridge module) to understand the reasons for failure and the routes to mitigate them. Moreover, a cost-effective solution using the IR2127STRPBF driver circuit was implemented to reduce the probability of thermal runaway in case of overcurrent, short-circuit, or avalanche events. For this reason, the electrical current state was adjusted using an FPGA digital resource to perform dynamic PWM control signals. The obtained correlation waveforms are valuable for verifying diagnostic data at the design stage to emphasize the significance of evading premature failure events. The comprehensive study on failure diagnosis enabled successful design strategies to construct a robust 45 kVA three-phase multilevel inverter for a 22 kW eolic-photovoltaic generation plant. Keywords: critical failures mechanisms; low-frequency transformers; IGBT devices; on-line diagnostic method; isolated multilevel inverter 1. Introduction Multilevel inverters (MLIs) have become more popular than conventional DC/AC inverters for some application fields because they operate with many voltage steps that im- prove the output waveform. They are categorized into non-isolated and isolated multilevel inverters, which are widely used in renewable energy systems and industrial applications, among others. Isolated MLIs exploit low-frequency transformers to improve robustness and reliability and are subcategorized into DC-side and AC-side. The MLIs feature several advantages over conventional topologies. MLIs operate at both high and low frequencies, reducing the device-switching rate; feature low-output harmonic distortion; achieve a high- power capability by dividing the total power into several switching devices; and extend the switching device’s lifetime and reliability due to low switching rates. Low-frequency MLIs reduce switching losses considerably, thereby enhancing overall efficiency. An extensive comparison among multilevel topologies (state of the art) elaborates on [1]. In this work, the low-frequency transformer plays a critical role at the design stage. Its electrical properties, such as high inductance, high inrush current, reduced di/dt, and high efficiency at heavy loads, determine several design techniques to prevent failure [2–4]. In addition, the full-bridge module sets up two arms that contain two isolated gate bipolar transistor (IGBT) devices. In any situation, one IGBT within an arm is solely on-state. However, when both IGBTs are on-state in a failure scenario, the current through the IGBT devices abruptly increases. This current is, in most cases, high enough to instantly damage the switching devices. In addition, the enormous di/dt may damage the IGBT and driver Energies 2022, 15, 5203. https://doi.org/10.3390/en15145203 https://www.mdpi.com/journal/energies