Research On ODE Modeling Method And Application Of Uhvdc Converter Station

With the large-scale application of UHVDC transmission in China,design and operation problems related to it have become increasingly prominent.Due to the huge scale and complex structure of the UHVDC transmission system,parameter design and fault analysis often rely on modeling and simulation.Online real-time simulation represented by RTDS has a high threshold for use and is expensive,and the existing simplified model is difficult to guarantee the fault state.Therefore,it is urgent to propose a new modeling method that has higher operating efficiency while ensuring higher accuracy,thereby reducing the simulation difficulty and investment cost of the DC transmission system.In addition,the operational reliability of the UHVDC converter station still needs to be improved.A deeper understanding of the system operation mechanism can better guide the system parameter design and control and protection system setting,thereby reducing the system failure rate,which requires more in-depth theory.support.Taking a domestic UHVDC transmission system as an engineering reference,the paper introduces the primary system overview of the DC transmission system,including the main wiring of the system,the parameters and operating principles and characteristics of the primary equipment,and a detailed introduction to the secondary system including the control system and protection.Based on the structure and control principle of the system,a detailed model of the UHVDC transmission system was established in MATLAB/Simulink,and the accuracy of the detailed model was proved by reproducing the fault case of the converter station at the receiving end of the system.And reference value.Then,the paper proposed an ordinary differential equation(ODE)model of the UHVDC transmission system based on the switching function theory.After analyzing the influence of the natural commutation point offset and commutation failure on the switching function,a new method considering the fault state was proposed.Switch function modulation strategy;combined with simulation examples,the operating characteristics of the ODE model under various fault conditions are studied,and the detailed model is used as a reference to compare the simulation error and operating efficiency of the ODE model.The simulation results show that the ODE model proposed in the thesis can accurately reflect the various fault states of the converter valve,and has the advantages of small error and high efficiency.Finally,the harmonic function of the ODE model is analyzed based on the frequency domain components of the switching function,and the harmonic function expression of the instantaneous power of the AC and DC system is derived.According to the instantaneous power component,the quantitative relationship of each instantaneous power component is analyzed,and the AC-DC system energy coupling channel including the main power channel,active power loss channel and oscillating power channel is established.Through the simulation comparison with the detailed model,the error and AC/DC coupling characteristics of the energy coupling channel are analyzed.The simulation results show that the energy coupling channel proposed in the thesis can accurately reflect the transfer relationship of the active power channel and the low-frequency harmonic characteristics of the oscillating power,which has guiding significance for the study of the operation mechanism of the UHVDC transmission system and the design of the control and protection system.In addition,the thesis puts forward an active power control strategy for UHVDC converter stations based on the coupling channel theory,and verifies the effectiveness and accuracy of the active power control strategy through simulation examples.