| Voltage source converter based multi-terminal direct current（VSC-MTDC）has the characteristics of multi-power supply,multi-point receiving and various operation modes,and has good scalability and reliability.It can be used in large-scale new energy grid connection,island power supply and multiple asynchronous grid interconnection projects have broad application prospects.With the adjustment of the energy structure of various countries and the continuous development of DC transmission technology,VSC-MTDC technology has become a powerful means to solve the problem of new energy delivery.As a typical high-end system,there are complex coupling relationships in the VSC-MTDC system.The new energy power generation has the characteristics of random and intermittent,which is easy to have adverse effects on the entire system,which brings challenges to the safe and stable operation of the system.To a certain extent,the coupling in the VSC-MTDC system has limited the engineering application of wind power grid connection.Therefore,studying the decoupling control strategy of the VSC-MTDC system with new energy access is of great significance to the safety,stability and economic operation of the system.Firstly,according to the structure of voltage source converter（VSC）,the mathematical model of VSC in dq rotating coordinate system is obtained,according to the system topology,the VSC-MTDC system with new energy access is divided into two parts:the VSC-MTDC connecting AC system and the VSC-MTDC system,to establish a global small signal model of the entire system,analyze and derive the coupling mechanism existing in the system,and use the PI double closed-loop controller for simulation analysis to verify the accuracy of the established small-signal model.Aiming at the coupling problem in the system,a neural network internal model decoupling control strategy（NNIMC）is proposed based on the small signal model and coupling mechanism of the VSC-MTDC system with new energy access.The internal model and internal model controller in internal model control are constructed by neural network,and the feedback controller is added to the control system to deal with the problem that the internal model of neural network and the internal model controller of neural network are not trained enough times at the initial stage of the control system,resulting in poor control effect.The decoupling effect of the designed controller is verified in MATLAB/SIMULINK,which greatly weakens the coupling existing in the system and improves the stability of the whole system on the basis of improving the performance of the control system.Aiming at the shortcomings of NNIMC,a hybrid H2/H∞robust decoupling control is proposed,which takes the decoupling performance of control system as the controller design objective.The decoupling control problem of VSC-MTDC with new energy access is transformed into a hybrid H2/H∞robust control problem,and the hybrid H2/H∞robust control problem is solved by optimizing the H2 performance and H∞performance of control system and pole assignment in LMI region.The hybrid H2/H∞robust decoupling controller is simulated and compared with PI controller and NNIMC in MATLAB/SIMULINK,which proves that the designed controller has better decoupling performance and makes the control system have better post fault recovery performance. |
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