| With the development of energy Internet technology,ultra high-voltage direct current(UHVDC)technology has become an important part of the long distance and huge capacity power transmission for large-scale energy base,because of its large transmission capacity,low power loss and small install ed area of the converter station.However,the special commutation failure can restrict its developments and applications seriously.Supported by the opening foundation,"The study on the mechanism and prevention measures for the commutation failures of ±8 00 kV UHVDC transmission system" and the key project led by State Grid Hunan electric power limited company,"the construction of the physical simulation platform for the UHVDC power transmission and the study on failure mechanism and its suppression measures" for the Jiu-Hu Project.In the paper,a control strategy is proposed by adjusting the extinction angle of power switches to prevent commutation failures in the control system.The control strategy is tested in the simulation,and a low-voltage platform is built for a deep study.The main research works in this paper are as follows:(1)The switching characteristics of the thyristors are analyzed in detail,and the equivalent ideal model of the inverter station of UHVDC transmission system is established.The relationship between the extinction angle and its related electrical parameters is obtained according to the running characteristics of the commutation process.And the effect of the influence factors on the extinction angle of thyristors is analyzed in detail,and the mechanism of the commutation failure is analyzed from the view of the extinction angle.(2)According to the influence factors of the commutation failure and the characteristics of the common short-circuit fault,the resistance ability of the inverter system to the commutation failure under the fixed extinction angle mode is analyzed in detail,and a control strategy is proposed based on the adjustment of the extinction angle to suppress the continuous commutation failures.It can be div ided into two parts: the extinction angle regulator and the current suppressor,in which the former can judge whether the commutation failure occurs according to the voltage-droping level of the AC-Bus.In the case of commutation failure,it can be suppres sed by adjusting the value of extinction angle.The latter can increase the trigger angle of the rectifying side in a short time to suppress the sudden increase of the current when the former actions happen.The interaction and cooperation between them can suppress commutation failure effectively.(3)In this paper,PSCAD/EMTDC is used as a simulation platform,based on the standard model of Conference International des Grands Reseaux Electriques,CIGRE,the simulation of the suppression strategy is carried out.The characteristics of the extinction angle regulator and current suppressor are verified respectively,and then the whole suppression strategy is tested.The simulation results show that the suppression strategy for commutation failure proposed in t his paper is feasible.(4)The significance of the simulation platform for HVDC transmission is demonstrated,the designs of the hardware topology and the control system are introduced.The running state of the simulated platform is tested in the experimen t,and some works of simulated platform is completed preliminarily. |
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