Research On SNOP And Its Application In Distribution Network

A high degree of penetration of distributed generation brings a widespread and profound impact on power transmission and system stability of distribution network. While it has put forward higher requirements to transform the network structure and power flow management. Advanced power electronics technology is an important basic and key mean to build a flexible, reliable and efficient active distribution network. Traditional distribution network is generally closed loop design and open-loop operation. SNOP (Soft Normally Open Points) is a power electronic device installed in place of a normally open switch that can control real and reactive power flow through each of its end-nodes and can be controlled at the local or central. SNOP also allow the distribution network combines the main advantages of radial and meshed networks, which means improving the reliability of power supply of distribution network and also to simplifying system protection strategy.Based on the back to back voltage source converter for SNOP implementation object, this paper analyzes the back to back VSC’s dynamic mathematical model in synchronous rotating dq coordinate system, and gives its dual closed loop coordinate control structure to achieve multiple control objectives, which based on its power exchange principles. On this basis, SNOP model is built on the DIgSILENT software. By control the power flow between SNOP and AC system, the study verified the correctness of the model as well as the feasibility of control strategies.At different load rate of IEEE-33bus distribution network, with SNOP replace normally open switch in different locations, the paper makes multiple optimization objectives and constraints by weight and the penalty function to form a comprehensive objective. By using simulated annealing algorithm to optimize and making SNOP’s control variables P、Q1and Q2as optimization variables, the study analyzed the effect of SNOP at different locations in the distribution network to reduce power losses and increase bus voltages, and obtain the optimal location of SNOP access distribution network in different cases.Fluctuation loads and distributed generation output are randomly. As the bus data change can not be accurately predicted, this paper established and verified the load and DG probability model and took probabilistic power flow calculation of the distribution network with DG using Monte Carlo sampling. On this basis, combined with simulated annealing algorithm, the paper made the average value of the objective function in multi-power flow section as optimization objective of SA’s "energy function", and finally got the best control variables P、Q1and Q2make best effect in average. The study simulated the IEEE-33bus distribution network as an example, and analyzed the effect of the SNOP in the distribution network.