| Presently, the electric power industry has entered into a new era which can becharacterized as very large grid, generator units with huge capacity, ultra high voltage level,heavy loading condition and very long transmission line. Meanwhile, with the establishmentand development of electric market, utilities are increasingly pursuing economics of powersystem. As a result, modern electric power systems have constantly been forced to operatemuch closer to their stability limits, and power system transient instability happens from timeto time. All kinds of control methods can be utilized to optimize power system's economicsand enhance system's stability level, balancing system's economics and security, which canproduce significant econimics and social benefits. At present, transient stability constrainedoptimal power flow (TSCOPF) is the most concerned hot topic in this studying area, andmakes important sense in both theoretical and pratical aspects. Starting from TSCOPF, i.e.one preventive control method, several novel transient stability control algorithms areproposed in this paper.TSCOPF is studied firstly, in which generation active power and reactive power areredispatched in order to search system's economic operating point while maintaining transientstability under multi-contingency condition at the same time. Two theoretical points areparticularly studied in this paper: stability margin control and TSCOPF global optimalsolution.On the basis of analyzing the existing problems in trajectory sensitivity method fortransient stability constrained optimal power flow (TSCOPF) under multi-contingencycondition, a computational method for TSCOPF is proposed based on one-machine infinitebus equivalent and trajectory sensitivity in order to control system's transient stability marginand enhance TSCOPF's computational efficiency. The following merits are produced fromthe algorithm.â‘ According to one-machine infinite bus equivalent, the strict transientstability criterion could be introduced in TSCOPF model, while trajectory sensitivity methodis used to enhance computational efficiency.â‘¡One transient stability constraint correspondsto one fault, highly reducing transient stability constraints number in the proposed algorithm.Furthermore, all contingencies are classified into stable, extreme stable, generally unstable,and very unstable ones, which could be handled in transient stability constraints respectivelyand filtered rapidly, saving the corresponding sensitivity computation, deleting the ineffectiveconstraints and improving computational efficiency. Meantime, the search of critical stabletrajectories could be avoided for unstable faults and hence simulation time is saved greatly.â‘¢ Transient stability margin is properly controlled, meeting with the utilities' stabilityrequirements. The effectiveness of the proposed method is verified on3-machine,10-machineand20-machine systems.In order to search TSCOPF global optimization solution, prediction-correction method isfirstly proposed to enhance the single-contingency TSCOPF optimization correctness.Furthermore, in order to pursue fast convergence features of the improved trajectorysensitivity method and global search ability of the differential evolution (DE) method, ahybrid algorithm for TSCOPF under multi-contingency condition is formed by thecombination of these two methods. Population size and computation burden are greatlydecreased in the proposed DE method. The DE fitness value considering normalized stablemargin for unstable faults better evaluates the individual's stability and economiccharacteristics. The proposed algorithm shows strong global searching ability and thecomputation speed is highly improved. Efficiency and practicality of the proposed method arevalidated on a3-machine system and a10-machine test system.However, power system transient stability is improved on the cost of system operatingeconomics decrease, which does harm to the benefits of utilities and increase the energyconsumption, betraying the nowadays' energy-saving and environmental protection socialdevelopment trends. Furthermore if considering power system disturbance probability, it isextremely unreasonable to prevent small probability event by the high cost increase of powersystem operation. So fast acting dynamic controllers, e.g. generator automatic voltageregulators (AVRs), are creatively used to perform transient stability control. An optimaltransient stability excitation control (OTSEC) based on a one-machine-infinite-bus (OMIB)equivalent and a trajectory sensitivity method is proposed in this paper to maintain powersystem stability, which is used to determine the generator voltage regulator reference setpoints to improve system's transient stability,and is easier to implement than previouslyproposed techniques based on generation rescheduling, and does no harm to systemoperation economics.
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