Study Of Impacts Of Grid-connected PV On Distribution System

Under the dual pressure of environmental pollution and shortage of resources, the utilization of new energy has been increased in countries around the world. In the electric power industry, distributed generation based on new energy has been the focus of current research. There is much solar energy resource in China, and photovoltaic power generation has many advantages as following. It does not consume fuel, has no pollution to the environment, It is flexible in site selection. As so, people have paid more attention to photovoltaic generation. As a kind of distributed generation, it is mainly used in connection to distribution network, so all kinds of impacts will be occurred on distribution network. In order to make better use of solar energy, it is necessary to study the impacts of grid-connected PV on distribution network. In this paper, the uncertainty of the photovoltaic output power is simulated using software. Also the impacts of grid-connected PV on distribution network’s voltage, power loss and relay protection are studied in this paper. The detailed researches are as follows:(1) The advantages of grid-connected PV systems are described, and the output characteristic of solar cell is simulated. The principle of the photovoltaic effect is used in solar cells. Solar energy is converted into electrical energy directly in this system. The output power of photovoltaic is uncertain and affected by the ambient temperature, irradiance and other factors. Photovoltaic cell is simulated in Matlab/Simulink, so its output characteristics can be seen and analyzed. A maximum power point is seen from the curve of output characteristics, so it is needed to adopt a reasonable technology to track this maximum power point. On this basis, several maximum power point tracking algorithm were introduced.(2) OpenDSS has been introduced and the power flow calculation of grid-connected PV system has been made on the platform of OpenDSS. The complexity of the power flow calculation will increase greatly when photovoltaic generator is combined into the distribution network. The simulation software OpenDSS is developed as a system analysis tool primarily for distribution network. Based on the platform of OpenDSS, the photovoltaic power model is established. Power flow of grid-connected PV system is calculated through fixed-point iteration algorithm. The external conditions such as ambient temperature and irradiance are considered fully, the output power of the photovoltaic is simulated with the changes of time. Studies have shown that the sudden drop of large, centralized grid-connected photovoltaic power generation system installed at the end of the system will cause the system voltage deviate from the normal value and cause impacts to the stability of the system. Photovoltaic/battery hybrid generation system uses the storage battery to supplement the decline of the output of PV system, so that the system voltage remains stable. Finally, the correctness is verified combined with specific examples.(3) The different impacts on distribution network voltage and losses are caused by different capacity of accessed photovoltaic power. Different capacity of PV is connected in the distribution network, according to the results of power flow calculation, the network voltage and losses are compared. System voltage improvement and network losses improvement are used to measure the impact of PV on distribution network voltage and losses. The relevant conclusions are obtained combined with specific examples.(4) The operating reliability of the original system protection devices would be threatened by the access of photovoltaic First the impact of PV connected to the grid three-current protection and automatic reclosing is analyzed from theoretical. The system stability and power quality are affected by the emergence of the island, so the effective island monitoring technology is needed, several commonly used islanding detection technology are introduced, the pros and cons of various methods are analyzed. Then specific example is used to verify the impacts of PV connected based on the platform of OpenDSS. Finally, several existing protection scheme are concluded and introduced briefly.