Study on an improved DC voltage slope control strategy for VSC-MTDC

摘要

For the allocation of unbalanced power when the loads change in the Multi-terminal HVDC transmission system, a DC voltage slope control strategy considering the Optimal Unbalanced Power Allocation (OUPA) is proposed. The control strategy using hierarchical control includes processing layer and implementation layer. In the processing layer, a mathematical model of unbalanced power allocation is established, namely the OUPA mathematical model. The minimum of the extra generation cost is set as the objective function, and the constraints include the line capacity, generator capacity, converter station capacity and power balance. The optimal solution of the model is obtained by applying the Lagrange multiplier method. And then the unbalanced power is optimally allocated by the implementation layer. A five-terminal VSC-MTDC simulation model in the Matlab/Simulink platform is built in the article. The simulation results show that the proposed control strategy can greatly reduce the extra generation cost. The DC voltage can be stabilized and the system power can maintain balanced when faults occur. Besides, the control strategy has the advantages of simple structure, strong robustness and easy implementation.