Hyo-Chul In, Seok-Min Kim, Seong-Soo Park, and Kyo-Beum Lee, "A Control Scheme for Quality Improvement of Input-Output Current of Small DC-Link Capacitor Based Three-Level NPC Inverters," The Transactions of the Korean Institute of Power Electronics, vol. > Paper

This paper presents a control scheme for three-level NPC inverters using small DC-link capacitors. To reduce the inverter system 

volume, the film capacitor with small capacitance is a promising candidate for the DC-link. When small capacitors are applied in a 

three level inverter, however, the AC ripple component increases in the DC-link NPV (neutral point voltage). In addition, the three-

phase input grid currents are distorted when the DC-link capacitors are fed by diode rectifier. In this paper, the additional circuit 

is applied to compensate for small capacitor systems defect, and the offset voltage injection method is presented for the stabilization 

in NPV. These two proposed processes evidently ensure the quality improvement of the input grid currents and output load currents. 

The feasibility of the proposed method is verified by experimental results.