Research on coordinated control strategy based on hybrid multi-terminal HVDC transmission network

Most of the control strategies of hybrid multi-terminal HVDC transmission technology consider frequency support, voltage control and power control, which ignore the influence of external parameter disturbance and power change. Aiming at the deficiencies of the above control strategies, this paper proposes a coordinated control strategy that can resist the external parameters to be disturbed and suppress the bus voltage to be fluctuated caused by the power mutation. Firstly, the control law function with passive characteristics is derived by using the system topology, and the optimal injection damping parameters can be selected by the bode diagram of the transfer function of the state variable, which proves that the traditional passivity-based control (PBC) strategy has certain anti-parameter disturbance ability. Secondly, considering that the traditional PBC strategy does not eliminate the influence of sudden external power changes on the AC bus voltage, the nonlinear disturbance observer (NDO) is applied to the PBC strategy to realize real-time monitoring of disturbance variables. Meanwhile, the selection of appropriate observer gain can shorten the time of voltage fluctuation and improve its stability. Finally, simulation results based on Matlab/Simulink verify the practicability and effectiveness of the control method proposed in the hybrid multi-terminal HVDC grid.