A Method for Calculating Current Harmonics and RMS of DC-Link Capacitor Considering AC Output Current Harmonics

DC-link capacitor current is a decisive factor for capacitor design and lifetime predictions. However, the conventional ripple current calculation method assumes that the inverter’s output current is an ideal sinusoidal wave modulated by naturally sampled. It results in an underestimation of the capacitor current RMS against the actual value. This article proposes a method to accurately quantity the spectrum and RMS of the DC-link capacitor current, and compares the results with and without considering the carrier sideband harmonics in two-level inverter and Neutral Point Clamped (NPC) three-level inverter. This method enables accurate calculation of the spectrum of DC-link capacitor ripple current and provides more reliable results for capacitor design.