| Distributed generation(DG),using renewable energy and new energy, providing clean and efficient energy, being introduced to distribution network will be the future trend. The voltage stability of distribution network with DGs is studied. First of all, according to different network interfaces and operating modes, DGs are classified into four different node types. Their processing methods in power flow calculation are analysed, especially focusing on PV node beyond reactive power limit, on PI node conversion calculation, and on wind turbine reactive power compensation. Through programming in the Newton-Raphson power flow calculation, methods are implemented. Secondly, through formula derivation of the distribution of power and voltage of a simple system, the node voltage is elevated by PQ-type DGs.The more back location and the larger capacity, the higher voltage, and the end node increases the most. The conclusion is verified by simulation. For estimation of impact of DGs on system voltage stability, two types of voltage stability index are discussed and improved. One type is based on the existence of powe flow solution, reflecting system ability to withstand load growth. The other type is based on the load-voltage property, reflecting system ability to withstand voltage disturbance. The feasibility and effectivity is proved by judgement in distribution system. With four types of DGs, simulations and analysis of the impact on the two voltage stability indexes are studied. Results show that the two types of voltage stability have been reduced by PV-type DGs, which should not be installed too much. But the stability has been improved by PQ-type DGs. Finally, after the study on different location and different capacity, the method of choice of DGs configuration is given. PV-type DGs, with small capacity, are not suitable to be installed on the end of feeder. And two types of DGs are not suitable to be installed on the originally unstable nodes. |
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