Reliability Assessment of Hybrid Capacitor Bank Using Electrolytic- and Film-Capacitors in Three-Level Neutral-Point-Clamped Inverters

Hybrid capacitor banks using electrolytic capacitors (E-Caps) and film capacitors (F-Caps) provide a cost-effective solution for DC links. However, the hybrid ratio between two types of capacitors is mostly experience based. This paper studies the quantitative solution to size the hybrid ratio for capacitor banks from a reliability point of view. Considering the parasitic parameters and thermal inertia of individual capacitors in a bank, an analytical model to obtain the electro-thermal performance for the individual type of capacitor is proposed. The quantitative relationship between the hybrid ratio and capacitor-bank reliability is acquired by applying a mission profile based reliability analysis. In addition, a DC-link capacitor bank in three-level neutral-point-clamped inverter is designed and implemented to validate the accuracy of the proposed method.