DC‐link capacitor current observation based stability enhancement control for back‐to‐back converter

Abstract

This article presents a stability enhancement control scheme applied in the three-phase back-to-back (BTB) converters with L filter. The stability enhancement control scheme is concocted using the feedback of DC-link capacitor current without additional sensors. Both grid-side converters are equipped with this control scheme, which can also be called the coordinated compensation control scheme. In this article, DC terminal impedance models of two converters before and after optimization and stability criterion are introduced. Furthermore, means of impedance analysis, including Bode plot and Nyquist curve, are discussed to categorize the causes of BTB converter instability caused by the increased power. The coordinated scheme is compared with the conventional scheme for revealing the theoretical basis. The proposed method is capable of optimizing the disturbance suppression capability of DC-link voltage, which would potentially reduce capacitor volume and physical size of the DC-link. The impedance-based stability analysis indicates that the controllability and stability of the BTB converter is enhanced with the proposed DC-link capacitor current coordinated control. Furthermore, the proposed control scheme is implemented in the MATLAB/Simulink environment. Moreover, for further validation, the feasibility of the coordinated control scheme is verified with the experimental results.