Study Of The Short-Curcuit Current With A Short-Circuit Fault On The AC Side Of An Inverter

As the energy distribution of China shows to be reverse distribution, it is an inevitable choice to cooperate DC transmission system, especially HVDC transmission system, with AC transmission system to optimize the allocation of resources, save the transmission corridor and reduce power loss. Due to the high controllability of HVDC systems, the short circuit current contributed by DC systems with an AC-side fault is usually ignored. According to the plan, by 2020 there will be twelve HVDC transmission systems connected into the East China power grid, with a total capacity of 79.8GW. However, as the electricity load center, with the increasing of installed capacity and the more closer ties between power grid. East China power grid faces an increasingly prominent problem of the excessive short-circuit current. Against this background, the study of the short circuit current contributed by a DC system with a short circuit fault on the AC side of an inverter, is the basis to configure network equipment reasonably, to optimize grid operation mode and limit the short circuit current level of the grid.Firstly, this paper builds a detailed electromagnetic transient model of HVDC system based on an actual HVDC project, and in order to make the model to reflect the actual response of the DC system, the model parameters are set in accordance with the actual project. In the third chapter, for the three-phase fault on the AC side of an inverter, this paper presents the transient process of inverter commutation failure, studies the mechanism and characteristic of the short-circuit current contributed by a DC system, analyses the impact of the control system of DC systems, proposes a practical method for calculating the short-circuit current, and draws the conclusion that the DC system only affects the peak short-circuit current when a three-phase short-circuit fault occurs on the AC side of an inverter. In the fourth chapter,, this paper analyses the characteristic of the short-circuit current contributed by a DC system when a single-phase short-circuit fault occurs on the AC side of an inverter, and proposes the use of an improved full-wave Fourier transform method to eliminate the errors introduced by the decaying DC component. In the fifth chapter,, based on a large number of fault simulation data, this paper analyses the impact of those factors, which are fault time, short-circuit ratio, DC transmission power and control system, on the the short-circuit current contributed by a DC system, and draws the conclusion that when a single-phase short-circuit fault occurs on the AC side of an inverter, the existence of a DC system will decreases the initial symmetrical short-circuit current and increases the peak short-circuit current. Finally, the conclusions proposed in this paper is verified by the calculation of short-circuit current with short-circuit faults on the AC side of an HVDC system inverter, based on the actual power grid data of East China.