Research On Protection Setting For Distribution Network With Photovoltaic Generation

In recent years,with the government's new energy development policy as an opportunity,photovoltaic power generation technology has been rapidly developed,the manufacturing technology of photovoltaic cells has been continuously improved,the cost per unit of power generation has been rapidly reduced,and the proportion of photovoltaic output in power generation has been rising.However,unlike centralized generation and one-way transmission in traditional power system,photovoltaic power is mostly connected to distribution network in the form of photovoltaic power station(PG)or distributed energy(DG)to realize the self-absorption of distribution network energy.Under such a distributed,multi-source power system model,the electrical characteristics and power flow distribution of the distribution network will also change,greatly different from the previous.In addition,the photovoltaic power generation principle,fault characteristics and the traditional synchronous machine are different,will lead to the distribution network transient mechanism and fault characteristics change,the original distribution network protection principle is not applicable.In order to ensure the normal operation of the protection of the complex distribution network with PV integration,it is necessary to study the impact of PV integration on the distribution network to propose a new adaptive protection principle.In this paper,the effect of photovoltaic power supply access to distribution network on relay protection behavior is investigated,and then a set-point algorithm is summarized.Finally,an example is given to demonstrate the effectiveness of the proposed scheme.The main contents are as follows:Chapter I first introduces the background and engineering significance of the research topic,and systematically expounds the exploration process of the subject so far.Including the evolution of the theoretical model of PV power integration into distribution network and its impact on traditional relay protection,this paper summarizes the research achievements of new relay protection.Chapter ? and ? reveal the basic principle of photovoltaic electricity generation from the point of view of physical essence,simplify and put forward its volt-ampere equation,draw its volt-ampere and power characteristics,and further investigate the physical factors(temperature,light intensity,etc.)on the basis of this disturbance to its external characteristics.At the same time,the photovoltaic power generation system is classified according to inverter and topology.The principle,advantages and disadvantages of MPPT and inverter control strategy are introduced.Chapter IV and V convert the calculation of equivalent impedance of power supply into the calculation of the maximum short-circuit current output by power supply from the point of engineering practicability according to the analysis of over-current characteristics of inverter equipment.On the basis of systematically explaining the impact of photovoltaic power supply merging into distribution network,a new type of distribution system is proposed.Net relay protection is set and improved.Finally,in order to verify the performance of the proposed method,the fifth chapter takes the actual current protection setting of a photovoltaic power supply in Weifang as an example.This practical example confirms the effectiveness of the proposed method.