Novel active nested neutral-point piloted nine-level converter

Abstract

This paper presents a new nine-level converter and its modulation for the medium- and high-voltage applications. The converter's topology is based on the combination of the five-level active neutral-point-clamped (ANPC) and the neutral-point piloted (NPP) converters and is called the Nine-Level Active Nested Neutral-Point Piloted converter. The converter consist of three flying capacitors (FCs) per phase, which can be maintained at a nominal reference voltage using the converter's redundant switching states. The proposed modulation is based on a phase-disposition pulse width modulation (PD-PWM) that incorporates a minimum energy property cost function along with a dynamic reference generation technique to improve the FCs voltage and the converter's performance. Both the steady-state and transient performance of the converter have been investigated. The results indicate a high-quality output waveform and a sufficient capacitor voltage balancing control that guarantees a safe operation of the proposed converter. Additionally, the dc-link capacitor voltage ripple has been analyzed for all modulation indices and load power factors. The analysis shows a significant increase in the voltage ripple at high modulation indices.