Study On Photovoltaic Penetration Improvement Based On Soft Normally-Open Points(SNOPs) In Distribution Network

The gradual depletion of traditional energy and the environmental pollution caused by the traditional energy consumption have influenced the sustainable development of human society. Using new energy to replace traditional energy gradually is the future trend of development. And solar energy with its rich resources, cheap, no pollution and other characteristics, has broad prospects for development.With the rapid development of photovoltaic (PV) generation industry, the proportion of PV generation in power network is increasing. However, with a large number of PV generation connected to the distribution network, there come a series of power quality problems. And the more PV generation, the more serious of power quality problems. Particularly, the key limiting factor in large scale PV integration remains the voltage violations on network buses. How to solve this issue has become a key research direction of domestic and international power researchers. The soft normally-open point (SNOP) can control the power flow of the distribution network, so it is an effective way to solve the voltage violation issues and increase PV penetration of the distribution network. Therefore, for the construction and reconstruction of the distribution network, it is very important to study the use of SNOP to increase PV penetration. The main work of this thesis includes the following aspects.Firstly, this thesis introduces the device SNOP which is based on voltage source converters, including its circuit structure, working principle, mathematical model, control strategy, etc. Then two ways are presented to install the SNOP in the distribution network. And on the basis of the analysis of the constraints that the SNOP must satisfy, two control modes of the SNOP are defined.Secondly, this thesis analyzes the influence of PV generation on distribution network voltage. The SNOP is used to solve the voltage violation issues, and increase the PV penetration. An objective function is proposed to measure the PV penetration of the distribution network. Then an algorithm of calculating the objective function is given. The simulation results of 33 nodes and 102 nodes distribution network cases indicate that, the SNOP can increase the PV penetration effectively. What’s more, the PV penetration and the SNOP capacity are closely related.Finally, in view of the real time variation of distribution network voltage due to the variation of parameters such as load and PV output, a new optimal operation control strategy of the SNOP based on Perturbation and Observation is proposed. This strategy can obtain the real-time control parameters of the SNOP by applying power disturbance to the distribution network, and then realize the real-time control of the distribution network voltage. The simulation results of 33 nodes and 102 nodes distribution network cases indicate that, by adopting the proposed control strategy, the SNOP can keep the voltage of distribution network in normal level, and suppress the sharp fluctuation of the voltage at the end of the feeders. Therefore, the voltage quality of distribution network is improved significantly.