| When a sending end and a receiving end are linked only by DC lines, an asynchronous networking is formed. When a large capacity direct current system is blocked, frequencies in both sending end grid and receiving end grid have the risk of exceeding the limit. Factors which can affect the stability of an asynchronous system include primary frequency control, load frequency properties and direct current power support. Based on these three aspects, the following work has been done in this thesis.The modeling method of main elements in power grids with PSS/E is introduced. The step responses of several prime mover-speed regulator models are compared. The analysis of certain parameters which have significant effect on frequency stability is carried out. A four-generators asynchronous system including two DC lines is built. Based on this system, when there is a DC pole blocking fault, the effects on frequency stability with different load frequency characteristics are simulated and compared. After a brief introduction of two main DC power modulation methods, which are the emergency DC power support and the auxiliary frequency control, the effects on frequency stability with different DC power support methods are simulated and compared.Taking Yunnan Power Grid which will be asynchronously linked to the main grid of China Southern Power Grid in2016for an example, the stable frequencies of different DC block faults are calculated and compared with the simulation values. The effect of a different number of hydroelectric generating sets engaged in speed regulating is simulated and analyzed. Besides this, the peak frequencies under different amount of power capacity and load are computed and compared to figure out the effect of each factor. For the DC faults which lead to the frequency out of limit, tripping generators, DC auxiliary frequency control are taken as treatment measures to deal with the frequency problems. |
PDF Full Text Request