| As the traditional fossil energy gradually drys up, Distributed Generators technology represented by photovoltaic power and wind power is more and more widely used, becoming the main direction of electric power industry in the 21 st century. The access of DGs, however, will change the single-power and centralized power supply structure of traditional distribution network, transforming it from the traditional one-way-flow-radiant power network to bi-direction-multi-source network. The changes in the structure will affect not only the reactive voltage characteristics of power distribution network, but also the traditional relay protection. Therefore, an system analysis of the effect of DGs' access on distribution network's fault characteristics has very important significance on the improvement of original relay principles as well as on putting forward new principlesOn the basis of consulting a large number of material and investigating IIDG manufacturers, this paper establishes a IIDG model with LVRT characteristics which is in line with the actural situation. Then, a method used to calculate control parameters and filter parameters inside IIDG is given. After that, a simulation of fault in a distribution network with IIDGs is carried out in PSCAD simulation platform. Based on the result of the simulation, the paper has analysised the effect of IIDG's access on the transient and steady-state fault characteristics.Later, in order to offer more specific theoretical basis for the improvement of the protection theory of distribution network with IIDGs, this paper puts forward a short-circuit current calculation method for distribution networks with IIDGs of different numbers and control strategies. Further more, based on the method, this paper summarises the general rule of short-circuit current changed with fault types, fault point location, PCC location, capacity of IIDG, running state of IIDG and so on. |
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