DC-Link Capacitor Current Modeling and Analysis for Three-Level Voltage Source Inverters

As a critical specification for the dc-link design of a voltage source inverter (VSI), the root-mean-square (RMS) value of the capacitor current should be accurately determined. Various work has been done on the modeling and analysis for the dc-link current, however an accurate model for the dc-link capacitor current still needs to be developed, especially for multilevel inverters. In this work, a detailed model for the dc-link capacitor current of a three-level VSI is proposed, and based on the model, the closed-form expression of dc-link capacitor RMS current is derived from the switching states of space vector pulse width modulation (SVPWM). The expression is a function of the modulation index and power factor, and can be used to estimate the maximum dc-link capacitor RMS current. Both simulation and experimental results are presented to validate the accuracy of the proposed model and the derived expression of the dc-link capacitor RMS current.