Virtual Impedance Sliding Mode Control-Based MMC Circulating Current Suppressing Strategy

Abstract

The device rated capacity, system loss, and cost of a modular multilevel converter are proportional to the circulating current value. In order to enhance suppressing the second order harmonic component of circulating current and improve the dynamic response of the system, a novel circulating current suppressing strategy based on virtual impedance sliding mode control (VI-SMC-CCS) is proposed. This paper first analyzes the essential CCS mechanism, then presents a circulating current decoupling model using a state feedback linearization method, improving the system accuracy. Moreover, the sliding mode control and virtual impedance loop are introduced to strengthen system robustness. Different circulating current suppressing strategies are compared by simulation, the results demonstrate the correctness of the VI-SMC-CCS, which not only effectively reduces the second order harmonic component of the circulating current, but also improves the stability, reliability, and rapidity of the system.

Keywords

• Modular multilevel converter (MMC)
• virtual impedance
• sliding mode control (SMC)
• circulating current suppressing
• state feedback decoupling control