| With the continuous development of the society,the photovoltaic grid-connected power generation technology has gradually matured,and at the same time,it has brought many problems to the power system.For example,the current of the original network will be changed,affecting the safe and reliable operation of the power grid.The existing relay protection scheme cannot be applied to the network containing photovoltaic systems.In this paper,it studies the relay protection of the photovoltaic distribution network with low voltage traversal(LVRT)capability.The research contents of this paper are described as follows:First of all,the photovoltaic grid-connected photovoltaic power generation system was summarized.For the unipolar photovoltaic power generation system,the photovoltaic inverter model was established,the double closed-loop control strategy was adopted to control the network parameters,and the disturbance observation method was introduced to complete the tracking and control of the maximum power point of the photovoltaic system.Secondly,in view of the existing DQ-PLL phase-locked ring technology defects,design a voltage sag detection method based on SOGI-PLL phase-locked ring technology,according to the domestic and foreign photovoltaic power station LVRT technical requirements,respectively in the symmetrical failure and asymmetric failure in the power grid,complete the power grid fault inverter LVRT control.Then,according to the LVRT control strategy of the photovoltaic grid-connected system,the calculation method of the short-circuit current of the traditional distribution network and the fault iterative correction method of the distribution network including the photovoltaic system were introduced.The three-phase short circuit simulation was conducted on the end of the distribution network and the different access points of the distribution network including the photovoltaic power supply.At the same time,the short circuit current of the traditional distribution network and the fault current of the photovoltaic distribution network with the LVRT ability are compared and analyzed.Finally,the influence of different fault positions on relay protection after photovoltaic access to the distribution network was analyzed,and an improved adaptive current protection was proposed for the photovoltaic power station distribution network with LVRT capability.Zhaodong region distribution network,for example,through the PSCAD software experiment simulation,build 10 k V distribution network model,the photovoltaic power generation system after grid distribution network current simulation analysis,simulation results show that the proposed setting principle can meet the requirements of relay protection,protection device can accurately action,compared with the traditional current rate protection,increased sensitivity,protection scope,the distribution system security is improved. |
