Virtual-Flux-Based DPC of Grid Connected Converters with Fast Dynamic and High Power Quality

Abstract

Grid connected voltage source converters (VSCs) are unavoidable means for developing and supporting power systems. Nevertheless, their harmonic injection may cause deterioration of power quality and current THD. Therefore, injected harmonics through VSCs must observe the corresponding standards, while lower switching frequencies and rapid transient responses are required. This paper, presents a sensorless virtual flux direct power control of VSCs based on a novel modified switching table for fast dynamic response, high power quality and low current THD. An analysis is carried out to determine the best voltage vector for virtual flux direct power control of VSCs at transient and steady states. It mathematically proves that the vector is oriented along the grid voltage vector, which is perpendicular to the grid virtual flux vector, at transient state. Moreover, the modified switching table uses a new logic for selecting the voltage vectors under steady to provide smooth performance. In comparison with the conventional direct power control, the proposed method enjoys faster transient response and lower power ripples and current THD due to utilization of the modified switching table, without requiring grid voltage sensors.