Research On Multi-Objective Control Technology For VSC-MTDC With Multi-Scenario

Flexible direct current transmission technology(VSC-HVDC)has many advantages such as various controllable methods,independent adjustment and control of active and reactive power,and easy formation of multi-terminal flexible direct transmission(VSC-MTDC),etc.,thus,it is widely used in many scenarios such as building a high-proportion renewable energy consumption core hub,efficiently improving the optimal allocation of resources and regulating mutual aid capabilities.On one hand,the diversified development of flexible DC power grids in terms of topology,wiring modes,and commuation technology can effectively improve the flexible collection and consumption of various energy sources including large-scale renewable energy sources and energy storage with different characteristics,to realize power exchange between different forms of AC power grids,and to further improve the transmission capacity and security and stability level of AC and DC power electronic system,providing certain technical support for China’s newly proposed "double carbon" energy strategic goal.On the other hand,with the expansion of the scale of the DC power grid and the improvement of its structural complexity,it will inevitably bring about problems in the operation and control of the DC power grid.It is a scientific and technological problem to be solved urgently at present to realize the coordinated operation and control of the VSC-MTDC system under multiple operating conditions.This paper studies the multi-objective control technology of VSC-MTDC with multiple scenarios.The main research and achievements are as follows:(1)Combined with the universal DC power flow calculation method,the fast and accurate acquisition of the grid state of the true bipolar VSC-MTDC is realized.When the positive and negative DC networks of the bipolar VSC-MTDC operates independently,the proposed universal DC power flow algorithm can accurately obtain the independent power flow of the bipolar DC grid.A universal VSC-MTDC system optimization model for different DC grid topology,wiring modes and operating conditions is further constructed and proposed,which is suitable for various types of DC operation and control strategies.(2)On the basis of the universal VSC-MTDC system optimization model,the control characteristics and regulation requirements of multi-type AC systems and multi-type power sources connected to the flexible DC grid are studied,and optimizations are proposed for the flexible DC grid under multiple scenarios.The operation and control scheme realizes the full utilization of the capacity margin of each converter station and the transmission power margin of each line through the global optimization design of the active power distribution strategy of each converter station and converter,and effectively improves the flexible DC power grid.Under normal and fault conditions,the ability to consume large-scale renewable energy and the ability to transmit power between the interconnected power grid.(3)A real-time regulation technology framework based on time-driven and event-driven VSC-MTDC system safety monitoring,optimization and recovery control is proposed.For time-driven optimization technology,the expected recovery plan is firstly generated according to the expected accident set,and when the system fault happens,according to the type of failure,the corresponding solutions in the set of recovery solutions are quickly matched to realize the preliminary optimization and recovery of the system;for the event-driven optimization technology,according to the latest operating state of the system at the moment before the failure occurs,a new round of optimization is initiated after the system failure.The recovery plan is calculated,and the preliminary optimized recovery plan obtained by the time-driven is updated to the precise optimal recovery plan obtained by the event-driven optimization.Through the cooperation of time-driven and event-driven optimization technologies,the requirements for rapidity and accuracy of the optimal regulation of flexible DC grids are satisfied at the same time.The adaptive switching methods for different optimization objectives are further proposed,and the corresponding optimal restoration schemes are calculated according to different scenarios of the DC power grid,and the automatic matching method of the operation control strategy of the DC power grid at each level is proposed according to the optimal restoration schemes.Finally,the scheme calculation and timely and accurate execution of the adaptive optimal operation and control of the flexible DC grid are realized.