Multi-harmonic Linearization Based Small-Signal Impedance Modeling of a Modular Multilevel Converter With DSOGI-PLL

In recent years, the grid-connected stability of modular multilevel converter (MMC) has attracted widespread attention. The performance of MMC control has a significant impact on its stability, among which the phase-locked loop (PLL) plays an important role in maintaining system stability. Compared with the traditional single-synchronous coordinate system PLL, the PLL using a dual second-order generalized integrator (DSOGI-PLL) is more capable of accurately locking the phase in situations of three-phase imbalance and complex system harmonics, providing accurate phase information for the design of subsequent control systems. However, the traditional single synchronous coordinate system PLL is widely used in most of the current research, while the MMC impedance model using DSOGIPLL has not been established. Therefore, this article is intended to fill a gap in this aspect of MMC modeling. In this paper, the small-signal impedance models of the MMC using DSOGI-PLL are first developed based on the multi-harmonic linearization approach. Then analyze the effects of DSOGI-PLL parameters, current controller bandwidth and circulation suppression bandwidth on the impedance characteristics of MMC. Finally, the correctness of the established multi-harmonic linearization impedance models and theoretical analysis using DSOGI-PLL are proved based on MATLAB/Simulink.