A Novel and Simple Single-Phase Modulator for the Nested Neutral-Point Clamped (NNPC) Converter

The nested neutral-point clamped (NNPC) converter is a four-level converter topology for medium-voltage applications with interesting properties such as operating over a wide range of voltages (2.4-7.2 KV) without the need for connecting the power semiconductor in series, high quality output voltage, and less number of components in compare to other classical four-level topologies. The control and balance of the flying capacitors (FCs) of the NNPC converter can be done by different control techniques taking advantage of the large number of redundant switching states. This paper presents a simple single-phase modulator for the NNPC converter, which can be applied to each phase of a three-phase NNPC converter. The proposed simple technique can control and balance the FCs to their desired values. Performance of the proposed technique under different operating conditions is investigated in the MATLAB/Simulink environment. The feasibility of the proposed converter is evaluated experimentally.