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The modular multilevel converter (MMC) represents the important technological innovation that emerged among the diverse available topologies of voltage source converter and is avowedly the most suitable solution for converters in high voltage direct current (HVDC) transmission and multiterminal direct current grids. Special focus is given through this paper to the dynamic performance of an MMC-based, point-to-point HVDC system. Using an optimal guaranteed cost control theory, a robust control approach is designed in order to reject the impact of the unmodeled uncertainty, mainly in the ac side of the MMC. For this aim, a small-signal state-space linear model is derived for the control design of an advanced local controller of each MMC station. Furthermore, a new optimal guaranteed cost controller is proposed based on the convex optimization problem using linear matrix inequality optimization approach. The proposed strategy leads to regulate simultaneously the ac grid and differential currents as well as total stored energy per phase in abc frame. To ensure the energy balancing between upper and lower arm per phase, an outer control loop is used in order to control the energy difference per phase between upper and lower arms of MMC. For the MMC linked to HVDC system, the active power reference is generated through an outer classical dc voltage controller. This combined control strategy between classic and advanced robust regulation methods allows exploiting the advantages of both control methods. Effectiveness of the proposed optimal robust control strategy for point-to-point MMC-HVDC system is evaluated across accurate and skillful simulation study under MATLAB/SimPowerSystem environment. The simulation results convince satisfactory dynamics responses of a two-terminal MMC-HVDC system based on the robust control approach under various operating conditions, even under unbalanced ac grid conditions (e.g., asymmetrical fault). [ABSTRACT FROM AUTHOR]

This paper presents the finite time stabilisation strategy of two problems: the first one is the control of the high voltage direct current based on voltage source converter, while the second is the control of the multi-terminal direct current transmission systems. Subject to finite-time control design strategy, a linear and nonlinear dynamic model are derived based on the state-space description. Furthermore, continuous or discontinuous finite-time feedbacks are proposed to ensure the tracking of the output variables and to enhance the stability of the studied high voltage direct current system. In addition, the proposed control strategy is extended for the multi-terminal direct current system. A comparative study between various approaches (Proportional-Integral control, continuous or discontinuous stabilising finite-time controllers and control by backstepping) is presented and shows that the finite-time continuous feedback gives an excellent transient response. [ABSTRACT FROM AUTHOR]