As the number of dc systems increases, it is natural to ask what other roles, aside that of bulk power transfer, that these systems could play in the operation of modern power systems. The objective of this research is to develop formulations and methods of solution to coordinate the dispatch of powers in an integrated ac-dc power system for purposes of minimizing transmission losses and production costs. In Section I we present an LP formulation and method of solution to minimize the ac and dc network transmission losses by coordinating the traditional reactive sources with the dispatch of the dc power transfers, taking into consideration the usual constraints on equipment ratings, line flows and bus voltage magnitudes. Results on sample test systems indicate that substantial reduction in network losses can be achieved by a coordinated dispatch involving the dc power transfers. Section II describes the mathematical formulation and method of solution for the optimal power flow problem of an integrated ac-dc power system. The method is capable of handling the network, converter tap, and control constraints of more than one multiterminal dc systems. The method uses a sequence of quadratic programming subproblems to determine the search directions. Also discussed are ways for determining the initial estimates of the Lagrange multiplier. Tests performed on modified IEEE 30 and 118 bus systems gave reasonable solution time and rate of convergence. The results obtained on the sample systems also indicate that there could be further economic advantage when the dispatch of dc powers is coordinated with the conventional controllable sources using the optimal power flow program. Section III reports on the findings from a comparative study of three methods to screen and rank severe contingencies for preventive dispatch.
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