DC Transformation Of Contact Line And Operation Strategy In High Permeability Photovoltaic Distribution Network

In the background of the “Emission Peak” and “Carbon Neutrality” goals,renewable energy access has been increasing in recent years,and PV has become the first choice in urban areas due to its characteristics of low noise,convenient installation and convenient utilization.At present,photovoltaic is mainly transmitted to the main network by centralized access,and distributed photovoltaic has great development potential in the distribution network.In order to achieve the certain proportion of renewable energy in the total energy consumption,the installation of renewable energy is often assigned by consumption index,resulting in the connection of a large number of PV power into distribution network in a short period of time,which makes it difficult for the existing distribution network to meet the high permeability PV access.In view of this problem,this paper focuses on the reconstruction of the existing distribution network to absorb photovoltaic access to meet the certain permeability index.Firstly,the spatial and temporal distribution model of PV output is established.Different from the traditional correlation analyzing method that regard PV output as a whole,after analyzing the factors affecting photovoltaic output,this paper decomposes photovoltaic output into basic value and fluctuation value,and thinks that the correlation only exists between fluctuation value due to the similarity of the external environment in a small range.Subsequently,adding Lilliefors test step before sampling space transformation can avoid complex calculation brought by Nataf transformation and build multi-variable joint distribution quickly under the condition that the distribution of fluctuation values meets normal distribution.Through the photovoltaic output simulation model,the photovoltaic output simulation value satisfies both the probability distribution of a single photovoltaic output in time sequence and the correlation coefficient matrix in space.Then,the K-means method is used to cluster the load characteristics,and then the features of the "Duck Curve" of net load and its influence on distribution network operation in the case of high permeability PV is analyzed.The probability risk assessment method is used to evaluate the voltage violation risk to the distribution network.The idea of “reactive power first and active power later” is adopted for the voltage violation period while the structure of the power grid is not changed.Considering the means of on-load voltage regulation and energy storage regulation,a two-stage adjustment strategy is proposed to adjust the over-limit voltage.When the voltage does not cross the line,the PSO algorithm is used to reduce the network loss through reactive power optimization.An example of petal-shaped distribution network is used to verify the proposed strategy.Finally,a DC reconstruction project of connecting line is proposed in this paper,in view of the shortcomings of the AC scheme that is not flexible and need to add much energy storage.A three-stage off-limit voltage adjustment strategy based on multi-VSC power coordination is proposed using the flexibility of VSC.The results of the example show that the strategy has a strong ability to regulate the voltage over the limit,and the adjustment cost is low.Under the condition of the example,there is no need to add additional energy storage.From the overall economic perspective,the difference between the AC-DC scheme and the AC scheme is not significant,which provides a new idea for the transformation project of distribution network.