Adaptive switching-loss-optimized space-vector modulation for three-level neutral-point-clamped converters

Abstract

With ever-increasing integration of intermittent renewable energy resources in the current ac grid, the grid stability is decreasing. A potential solution to this problem is integration of large battery energy storage systems that would act as buffers for short-term grid dynamics. Since the batteries store energy in dc, a power electronic interface in the form of an inverter is inevitable for coupling with the existing ac grid. A promising converter for medium-to-high power levels at low voltage is the so-called T-type Neutral-Point-Clamped (TNPC) converter. Such a converter is operated with Pulse Width Modulation (PWM) in order to comply with the Total Harmonic Distortion (THD) requirements in the grid codes. A generalized implementation of a variant of the well-known space-vector modulation featuring lower losses is proposed in this work. The highlight of this work is a set of relations to select a switching sequence that optimizes the switching loss and the output THD. The derived relations are based on the binary logic and symmetry of the possible states of the converter. The algorithm enables the dynamic adjustment of the clamping width and the position and hence, the switching sequences to accommodate the capacitive as well as inductive behavior of the converter.