Studies On Risk Assessment And Control Of Multi-infeed HVDC System

China's energy resources and load centers are inversely distributed.In order to meet the large-scale optimization of energy resources,the scale of multi-feed DC systems has increased.With the increase of HVDC system transmission power,once a severe AC failure occurs,the power flow caused by multiple HVDC transmission power interruption will cause a large-scale grid load loss,splitting and other chain failures that seriously threaten the safe operation of the power system.Existing quantitatively evaluating methods of commutation failure risk have oversimplified the dynamic characteristics of each component and the operation mode of the receiving end system,while the digital simulation analysis method is too time-consuming.Existing suppressing commutation failures methods have been studied from two aspects:reactive power compensation and DC control protection strategies,lacking a coordinated control method that combines their respective advantages.Aiming the seriousness security situation of multi-infeed DC systems and the limitations of current commutation failure evaluation and suppression methods,the reactive power voltage characteristics and commutation failure mechanism of multi-infeed HVDC receiving power systems were studied,and the method for evaluating commutation failure of multi-feed DC system considering multi-device reactive power voltage characteristics and operation mode is designed,and the continuous commutation failure suppression strategy considering multi-resource coordination is proposed,which has important theoretical reference and engineering practical significance for the rational planning and stability control of a multi-feed HVDC system.The main research results of the thesis are as follows:1)Simultaneous commutation failure risk evaluation method considering multi-infeed HVDC system reactive power voltage characteristics is proposed.Starting from the commutation failure mechanism,considering the reactive power voltage characteristics of two types of reactive power compensation devices in converter stations,including synchronous condenser and static reactive power compensation devices,and reactive power voltage interaction under different DC control modes,the Multi-infeed interaction factor is derived.According to the essence of commutation failure are extinction angle,the commutation failure evaluation factor was defined.Based on the Multi-infeed interaction factor and commutation failure evaluation factor,the simultaneous commutation failure risk of the multi-infeed HVDC system with synchronous condenser was evaluated.The Shandong power grid was taken as an example to verify the results that the proposed method could effectively evaluate the multi-infeed HVDC simultaneous commutation failure.2)This paper proposes Multi-infeed HVDC receiving power system commutation failure boundary division method based on the extended Jacobian matrix.Aiming at the risk assessment of HVDC system commutation failure,a definition of AC-DC interaction factor is proposed based on the multi-feed interaction factor is proposed.And based on the extended Jacobian matrix calculation method is proposed.Comparison and analysis of the characteristics and applicable scenarios of the AC-DC interaction factor calculation method based on the extended Jacobian matrix and the based on the impedance ratio is proposed in this paper.According to the commutation failure estimate factor,a graded commutation failure estimate factor is proposed to realize the commutation failure risk classification.Taking Shandong power system under different operation modes as examples,the effectiveness of the AC-DC interaction factor calculation method based on the extended Jacobian matrix and the accuracy of Multi-infeed HVDC receiving power system commutation failure boundary division method based on the extended Jacobian matrix are simulated and analyzed.3)A HVDC continuous commutation failure emergency control method considering multi-resource collaboration is proposed.Aiming at the HVDC system continuous commutation failure problem,based on the analysis of the continuous commutation failure process,mechanism and influencing factors,this paper proposes a continuous commutation failure emergency control method with synchronous condenser strong excitation and DC power fast decrease.And based on the characteristics of synchronous condenser,the spontaneous reactive response and strong excitation control are used to suppress continuous commutation failure.The DC power fast decrease control method is used to compensate for the lack of synchronous condenser action time.And the two-part coordinated continuous commutation failure emergency control method is proposed.According to the simulation of the Shandong UHVDC transmission system,the proposed emergency control method can effectively reduce voltage fluctuations,suppress continuous commutation failure.