Estimation of Equivalent Capacitance in Three-Level NPC Inverter SiC-Based

This paper presents an algorithm to estimate the equivalent capacitance of the DC bus in a three-phase, three-level neutral point-clamped inverter. The proposed method involves the injection of a low-frequency current through the midpoint of the converter, inducing a low-frequency oscillation in the DC bus. This technique enables the estimation of the equivalent capacitance of the capacitors without the need for external equipment. The algorithm demonstrates effectiveness under different operating conditions. The analysis incorporates considerations of the limitations of the injected current. The efficacy of the proposed method is supported by experimental and simulation tests conducted using a three-phase synchronous reluctance motor driven by a three-phase, three-level inverter.