Description of processes in an active front-end with a fourth branch

Abstract

Neutral wire is used in multiple active front-end application. Some of these applications are single phase loads and maintaining system stability in case of emerging unsymmetrical components, which can lead to malfunction and device failure. In such cases neutral wire potential can be middle point of DC-link, what leads to capacitor separation, but also can be implemented as additional arm, leading to full DC-link voltage utilization and additional control channel for zero symmetrical component in case of unsymmetrical load. In order to perform control system synthesis for such a complicated object, knowledge of its complex mathematical model is required. Four arms active front-end mathematical model is developed for analysis and control system development, featuring phase-coordinates usage and taking into account multiple peculiarities of this converter. Diagrams of main voltages and currents components are derived from model research.