Double-Frame Current Control with a Multivariable PI Controller and Power Compensation forWeak Unbalanced Networks

TL;DR

This paper introduces a double-frame current control method with a multivariable PI controller and power compensation to improve the handling of weak, unbalanced networks with asymmetric loads and disturbances.

Contribution

It proposes a novel control approach combining double-frame control and power compensation for better management of unbalanced weak networks.

Findings

Effective suppression of power oscillations in unbalanced networks

Enhanced decoupling capabilities of the PI-based controller

Guidelines for network synchronization and dimensioning

Abstract

The handling of weak networks with asymmetric loads and disturbances implies the accurate handling of the second-harmonic component that appears in an unbalanced network. This paper proposes a classic vector control approach using a PI-based controller with superior decoupling capabilities for operation in weak networks with unbalanced phase voltages. A synchronization method for weak unbalanced networks is detailed, with dedicated dimensioning rules. The use of a double-frame controller allows a current symmetry or controlled imbalance to be forced for compensation of power oscillations by controlling the negative current sequence. This paper also serves as a useful reminder of the proper way to cancel the inherent coupling effect due to the transformation to the synchronous rotating reference frame, and of basic considerations of the relationship between switching frequency and control bandwidth.