Direct Arm Energy Control in Modular Multilevel Converter Under Unbalanced Grid Conditions

Abstract

This paper studies the behaviour of the gridconnected modular multilevel converter under unbalanced grid conditions in terms of the energy imbalances within the converter, and proposes a novel approach for dealing with imbalances. Since the energy content within the arms of modular multilevel converter depends on the interaction between the terminal and internal voltages and currents, standard energy control methods, designed mainly for balanced grid conditions require improvement. This paper proposes a novel approach for the direct arm energy control, valid for both balanced and unbalanced grid conditions. The approach is characterized with its simple implementation, minimization of the current stress imposed on the converter, as well as with minimization of the risk of overmodulation. Theoretical foundation for mitigating the problem are supported with the simulation results, thus verifying the validity and performance of the proposed control concepts.

Direct Arm Energy Control of the Modular Multilevel Matrix Converter

“…Similar issue occurs in a standard MMC, and has already been analysed in [10], [11], [27], [28], and [29]. Reference [28] shows two possible approaches in modifying the original current references, illustrated in Fig.…”

“…3.c is obtained under the zero-sum constraint and minimizing the function A 2 . Although the solution does not fully preserve the power references, it is characterized by a simpler implementation with respect to the first one, as well as validity under both balanced and unbalanced grid conditions, as demonstrated in [27].…”

“…This paper presents an extension of the direct arm energy control methods, firstly derived for a standard MMC [27], [28], to the M3C. The methods presented within this paper are characterized by an intuitive and simple implementation, which might be of great value to the control engineers and researchers entering the field.…”