EFFECT OF HVDC POWER MODULATION ON STABILITY OF AC/DC PARALLEL POWER SYSTEMS
Date
1978-08
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Degree Level
Doctoral
Abstract
Stability of power systems remains an area of concern mainly because of the extensive use of large interconnected power systems and large synchronous machines. Investigations reported in the last two decades have shown that HVDC transmission can improve system stability. This stems from the fact that the DC power can be modulated by fast acting controllers to provide additional damping to the associated AC networks. It is the main objective of this thesis to examine the dynamic (small perturbations) and transient (large disturbances) stability of AC/DC power systems.
A mathematical treatment of a parallel AC/DC system with sending- and receiving-end systems has been developed. Such an analysis has involved a series of rigorous analytical and digital simulations for the system under small and large disturbances. In this respect, a detailed model of synchronous machines based on using their frequency response data has been developed. This model is used to represent the machines which are elec—trically near to the locations of the disturbances during the transient stability studies. Experimental studies have also been conducted to verify the validity and accuracy of this model.
A good deal of the work of this thesis is devoted to:
(i) investigating the effect of the various system parameters on its dynamic and transient stability, and comparing the stability results obtained by the finite-machine and the infinite-bus representations of the receiving-end system.
(ii) investigating and comparing the effect of various HVDC control signals on the damping and the frequency of the critical mode of oscilla—tions, on the dynamic and transient stability limits and on the maximum transmission capacity of the AC line for stable operation.
(iii) investigating the dynamic and transient stability of the AC/DC parallel system under the abnormal mode of control, and conducting a comparative study between the normal and the abnormal modes from the stability point of view, with and without DC power modulation.
(iv) conducting a comparative study on the stability and the maximum transmission capability obtained by a purely AC or AC/DC transmission systems, with and without DC power modulation.
(v) investigating the effect of the time delay in applying the HVDC control signals on the system transient stability.
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Degree
Doctor of Philosophy (Ph.D.)
Department
Electrical Engineering