Abstract
The stability of Modular multilevel converter (MMC) itself is the premise of analyzing the stability of MMC cascading with other cells, so this paper addressed the small-signal stability of MMC with dc voltage control mode which is the common operation mode of grid-side MMC in high-voltage direct current (HVDC) systems. First, the small signal model of MMC with open-loop control mode and dc voltage control mode while considering the dc voltage controller and current controller are established with the harmonic state-space (HSS) modeling method. Subsequently, eigenvalues and participation factors are analyzed to estimate the stability of MMC system and the influence of controller parameters, especially the proportional coefficients of dual-loop controllers, which can improve the design efficiency of control system. Finally, time-domain simulations in MATLAB/Simulink are provided to verify the accuracy of HSS small signal model and the effectiveness of the theoretical stability analysis.
Highlights
Modular multilevel converter (MMC) topology was first introduced in 2003 [1,2] and it has been widely used in high voltage and high power applications, due to its advantages of modularity, scalability, and power controllability
MMC is characterized by the obvious internal dynamics in sub-module capacitor voltages and arm currents [3,4], which makes its modeling considerably more complicated than the conventional two/three-level voltage source converters (VSCs)
Changes of ic (t), which proves that the small-signal model that is presented in this paper could reflect the internal harmonic interactions of MMC
Summary
Modular multilevel converter (MMC) topology was first introduced in 2003 [1,2] and it has been widely used in high voltage and high power applications, due to its advantages of modularity, scalability, and power controllability. Only the second harmonic components of submodule capacitor voltages were considered and harmonics of other variables, e.g., arm currents, were neglected Another state-space model of MMC that was based on dynamic phasors was built in dq coordinate frame [14,15], but this modeling method needs to take park transformations at different frequencies which makes the modeling process complicated. This paper develops a precise small signal model of MMC under dc voltage control mode based on the HSS method in frequency domain, while considering both internal and external harmonic dynamics, as well as the interactions.
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