Real-Time Lifetime Estimation and Supervised Voltage Regulation of Flying Capacitors in a Three-Phase Four-Level Three-Capacitor Converter

Three-phase four-level three-capacitor converter (3P4L3C) employs a single flying capacitor per phase, eliminating redundant switching states. However, this topology presents a significant challenge in capacitor voltage regulation, as conventional modulation techniques, including carrier-based SPWM and SVM, fail to maintain voltage balance. This paper proposes a supervised voltage regulation method that dynamically adjusts duty ratios to compensate for capacitor voltage deviations, ensuring stable operation. Beyond regulation, a unified electrothermal lifetime evaluation framework is introduced to quantify how improved regulation impacts capacitor reliability. The framework integrates ripple-spectrum-based ESR loss calculation, hotspot temperature estimation, nonlinear damage accumulation, and Monte Carlo simulation under realistic mission profiles. Simulation and experimental results confirm that the proposed SVR achieves stable capacitor voltage regulation while reducing ripple current and thermal stress. As a result, the 3P4L3C converter demonstrates approximately 20% longer capacitor lifetime compared to the conventional 3P4L6C topology, highlighting the benefit of integrating control and reliability assessment within a single design framework.