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In order to enhance the operating performance of the multi-terminal HVDC system. A model predictive direct power control suitable for multi-terminal HVDC system is designed. Model predictive control (MPC) algorithm is used to replace the traditional PI controller in the inner power loop, the error of active power and reactive power is taken as the input of model predictive controller , at the same time, the internal model feedback correction link is introduced to correct the predicted set value of the power in each sampling period , so the high-precision tracking of instantaneous power is realized .This method does not need AC voltage sensor, cost savings, improved reliability,the active power and reactive power are compensated, the voltage fluctuation is reduced. Finally, the effectiveness of the proposed strategy is verified by establishing a three terminal HVDC flexible DC system in MATLAB/ SIMULINK.

In order to improve the support capacity of the grid frequency for maximum power point tracking of wind turbines, a virtual synchronous generator is usually used to increase the rotational inertia of the system. However, when the parameters change and the load changes abruptly, it would cause the power oscillation problem. For suppressing the power oscillation problem, firstly, the influence of damping coefficient on power oscillation is analyzed by second-order virtual synchronous motor model. Secondly, a virtual synchronous machine control strategy with parameter adaptive ability is designed by using lead-lag link and fuzzy logic control algorithms. In addition, the introduction of lead-lag link improves the response speed of virtual synchronous machine. The simulation results of MATLAB/Simulink verify the effectiveness and feasibility of the designed control method.