Research And Application On Power System Intelligent Restoration Control Based On FCB Technology Of Large Thermal Units

With the power grid continues to expand and its structure becomes more and morecomplex, there is an upward trend of the occurrence of the large-scale blackouts, which causehuge economic loses and serious social impact. Basically, what the current power grid musttackle with are how to minimize the blackout scale and blackout load when there is a gridfailure, and how to expedite the power system restoration process as quick as possible after alarge-scale blackout. Currently, the control of power grid restoration after a blackout stillremains in a stage of offline-plan makeup and next, power system restoration according todispatcher’s experience. Researches about the automation of the power system restoration andthe application of advanced theory and technology to accelerate the restoration process have asignificant engineering and theoretical value.Black start is the first and most important stage in a power system restoration, and a largenumber of non-black start units need to be restored as soon as possible in this stage. The mostimportant parameter of the stage is restoration time. Traditional black start units are lowcapacity hydroelectric units and gas turbines, which cannot meet the requirements of a fastrestoration after a large-scale blackout due to the remote location, low capacity, and lowvoltage level. Fast Cut Back (FCB) technology can keeps thermal units continuing islandoperation to generate auxiliary power even after the units are split from the power grid, whichfinally makes thermal units an ideal black start power because thermal power can reconnectinto grid after the elimination of the grid failure. In this paper, the critical technologies forthermal units to acquire FCB function are discussed, and both the static and dynamic modelsof FCB units are established, which lays a modeling foundation to investigate the keyfunctions of FCB units in a power restoration process. The abilities of the FCB units tomaintain island operation and to start high voltage power grid are verified through the FCBtest of1000MW thermal unit in Taishan power plant and the test of charging unloaded500kVline. These also proceed to verify the significant role performed by the FCB units in therestoration control.Generally, it is hard to figure out a universal failure restoration strategy because the restoration control method has a strong relationship with the system’s characteristics.However, considering that the stage targets of different systems are the same, and the methodsto fulfill these targets are similar, it is possible to establish a compatible universal controlmethod for the power system restoration based on the decoupling of stage targets. Followingthis idea, issues of common concern and special requirements for power system restorationcontrol are analyzed. According to the idea of decoupling, the physical processes and the maincommon issues are investigated, and the restoration process is decoupled into severalindependent problems, and finally the target-based control method frame is established forpower system restoration. Considering that FCB units play a key role in power systemrestoration, an optimal control model is developed for power system with FCB units based onthe control frame method mentioned above. The model takes several operating constrains intoaccount and finds out the optimal unit starting sequence and the corresponding systemrestoration time. However, there are some integration terms in the objective function of thisnonlinear model, which cannot be solved directly using the current optimal method. Apractical computational method is proposed in this paper to avoid the onerous integrationcalculation, therefore it can be applied in finding out the optimal starting sequence of units ina much quicker way.The paper proceeds to investigate the influences of different FCB unit capacities andlocations on system restoration time. Basically, two main problems should be settled to findout the optimal layout of FCB units. The first one is how many units need to be transformedinto FCB units, the second one is to determine which thermal generators should betransformed. Computing the layout of FCB units by enumeration method exists a combinationexplosion problem, and the computation requirement is too heavy for the engineeringapplication. This paper introduces the Ordinal Optimization Theory to find out the optimallayout. The minimum system restoration time is regarded as the optimization goal, theconstraint conditions are considered, and the corresponding optimal model are developed. Thesolution to the model is also presented.Finally, based on the comprehensive consideration of both risk and efficiency, for a specific given layout, all of the optimal black start schemes are obtained through traverse. Theassessment indexes of these schemes are synthesized, and a quantized assessment resultreflecting the risk and efficiency level of the black start schemes is obtained. The assessmentmethod has some guiding significance on the layout of the FCB units since it can evaluate theefficiency and response capacity for risk of the corresponding black start process.This work was supported by Special Fund of Key Science and Technology Projects ofGruangdong Power Grid Corporation, China,(K-GD2011-553). Some of the research resultsare successfully applied in Gruangdong Power Grid Corporation, which has yielded somesatisfactory results through effectively solving the technical problem of a lack of hydroelectricunits in the power grid with a demand of high reliability of the grid operation.