Analysis Of Voltage Stability In Semi-autonomous Distributed Compact Power Supply System

With the advent of global energy crisis, distributed generation has got more and more attention in power industry and become a research hotspot. The western and part of eastern of our country have abundant wind, solar and other renewable primary energy, so one type of distributed network (sub-network) with various and a large number of DGs is studied mainly, which takes supplying power for its own area for the task, connects with transmission network (major network) dynamically, has a certain ability of autonomy meanwhile is influenced by the major network. Generally, one major network and several sub-networks together form a semi-autonomous distributed compact power supplying system, for short SADC power supply system. Undoubtedly, stability is the most important problem when SADC power supply system runs reliably, where voltage stability is particularly difficult, considering the structural characteristics of the network, based on the power flow calculation, the voltage stability of SADC power supply system is mainly studied.Firstly, based on the traditional power flow calculation method for distribution network and transmission network, a two-story method of both alternative and iterative algorithm is proposed to simulate the typical SADC power supply system in Tongliao area. The simulated results prove the availability of the method for the power flow calculation of SADC power supply system.Secondly, in order to analyze the influence of DGs on voltage stability, a distributed load model in the subnet is established, an expression for voltage distribution considering the horizontal component of the voltage drop is derived and the influence of the access number, access position and injection capacity of DG on the voltage distribution is analyzed based on the simulated results.According to analyzing the relationship between reactive power and voltage level, a sensitivity index dQij/dQk, that is, the susceptibility of reactive power flow in the line resulted by the reactive power injected from the node to the system, is defined, calculated and used to keep the voltage stability. Then, three important factors influenced on the sensitivity index:power flow calculation method, line impedance parameters and selecting balancing bus are analyzed. Lots of simulations have been done aim at the 39-node transmission network in Tongliao area to prove the effectiveness of the sensitivity index.Finally, according to the similar process to major network, analyze the voltage stability of sub-network based on a sensitivity index dPij/dPk and the followed simulated results prove the validity.