Samer Saleh Hakami and Kyo-Beum Lee, "Proper Flying Capacitor Selection for Performance Enhancement of Five-Level Hybrid Active Neutral-Point-Clamped Inverters," Journal of Power Electronics, vol. 22, pp. 1687–1698, Oct. 2022. -SCIE > Paper

Flying capacitors (FCs) are considerably important in multilevel inverter systems to synthesize additional voltage levels for various medium-voltage

industrial applications, including renewable energy, motor drives, and power transmission. In particular, they are responsible for forming the five-level

output pole voltage in five-level hybrid active neutral-point-clamped (ANPC) topologies. This is only possible when FCs reach their reference values (i.e., 25% of the DC-link value). When the five-level hybrid ANPC inverter operates in the high-frequency (HF) range, the output three-phase current

waveforms are less distorted compared to the low-frequency (LF) performance. Instantaneously achieving a five-level output pole voltage during HF

operation is a challenging task. This is because of the large capacitance of some existing types of FCs. In this study, a novel analysis of the effect of FC on the performance of a five-level hybrid ANPC inverter is presented with simulation and experimental validations. Film capacitors significantly

enhanced the system performance compared to electrolytic capacitors owing to many features, including the capability of charging and discharging

quickly during HF operation. In addition, the total harmonic distortion of the output pole voltage is significantly suppressed. Consequently, the size of

the required filter can be reduced. Therefore, the proposed system is highly desirable for various industrial applications.