| The safe and economical operation of power grid has always been the focus of grid dispatching agency,while automatic voltage and reactive power control system has also been applied more and more widely all over the world.The main issues that impair the practicability of voltage reactive power control function are as follows: Firstly,the accuracy of the basic data,which is the basis for all subsequent analysis and optimization;Secondly,the deviation(caused by power grid runtime uncertainty)from power flow snapshot on which the optimization calculation is performed,without handling this,the optimal results may not be suitable for the actual control execution;Thirdly,the challenges for the operation and control of power grid as the growing renewable energy sources are connected to our grid,on the one hand,it has an impact on the original reactive power partition.on the other hand,the original adjustment method of the regional power grid is mainly based on discrete control such as transformer tap-changer and compensator or reactor switching,but now,their coordination with the reactive power regulation in new energy stations needs to be considered.Fourthly,in engineering practice,we must ensure that the system model can persistently be consistent with the actual physical grid,furthermore,computer processes must not be interrupted due to maintenance errors or the updating of new power grid models.Only by solving the above problems can the voltage and reactive power control system truly convert the research theory to a reliable system,which can provide safe and economical operation service for the power grid and make itself a trustworthy tool for grid dispatching.In view of the above key issues that affect the practical application of voltage and reactive power optimization control,this paper analyzes the data accuracy,the method of optimization considering the uncertain factors,reactive power partitioning,coordination method for new-energy plant station in regional automatic voltage control system,plug and play of new power grid model and uninterrupted software operation method:Methods of improving the accuracy of power flow snapshot data are proposed.Based on the WAMS data correlation recognition algorithm and AGC mirror system,the mixed-measurements state estimation method considering time lag effects and a new power flow calculation skill are designed to obtain the more accurate basic power flow snapshot data.The correlation indexes between SCADA and WAMS measurements in the same acquisition cycle are calculated,and the WAMS measurement timestamp with the best relevant correlation index is taken as the grid snapshot time,so the SCADA measurements are partitioned according to their correlation with the PMU measurements.For the datum in the same partition,they will be compensated the same time lag in state estimation calculation,and the method can effectively deal with the simultaneity problem of mixed measurement state estimation.In addition,considering the effect of frequency adjustment of the system in power flow calculation,especially the influence of AGC secondary frequency regulation effects on active-power flow,we can get a more accurate power flow snapshot matching the reality of power grid,especially when a disturbance occurs.The above two methods lay a solid foundation for voltage and reactive power control to get an accurate calculation case.The three-level voltage optimization control algorithm based on uncertainty theory is studied.Because the power grid is always in a dynamic state,the optimal results may not be suitable for the actual control execution even if the calculation is based on the above relatively accurate power flow snapshot,since the deviation cannot be avoided.Therefore,in this paper,the uncertainty is modeled by reactive power of energy consumers and the voltage amplitude of PV buses,and the scene analysis method is used to describe the randomness of the actual state of the power grid relative to the basic snapshot case.The normal distribution is used to calculate the probability of occurrence of each typical scene,after that,the reactive power optimization model used to minimize the network loss and the voltage deviation is built.First,the deterministic problem is fuzzified according to the fuzzy set theory;then the multi-objective model is transformed into a single-objective model by using the maximum satisfaction method;finally the improved particle swarm optimization algorithm is used to solve the problem.Grid partition method for voltage and reactive power control is also studied.According to the actual system operation requirements,the research is based on the shortest path algorithm.A real-time dynamic partitioning algorithm based on graph theory is proposed and the equivalent external characteristics of the renewable energy source are analyzed.Considering them as routine regulation source of reactive power can match the engineering practice,moreover,relevant algorithms of electric distance can still work.In grid dispatching,their influence on voltage and reactive power is calculated during real-time analysis,which can better reflect the effect of reactive power source on the zoning.The breadth-first search algorithm in this paper has a time complexity of O(n)and successfully reduces the shortest path time complexity of search single source node from O(n2)to O(n),which improves the computational efficiency significantly.In addition,checking and adjusting the sensitivity of the boundary nodes in a grid can avoid the defect that pure graph theory does not consider the impact of power flow distribution,making the partitioning result more comparable and more reasonable than the traditional theory.How to coordinate renewable energy plants in a regional voltage-reactive power control system is studied.Based on the prediction of active power output of load and solar energy,a method for regional grid voltage and reactive power coordination control,based on fuzzy logic algorithm,is proposed.It designs fuzzy rules for both discrete and continuous control facilities respectively,and it converts the control strategy of comprehensive grid operation experience into a hierarchical fuzzy inference,and can deal with not only the discrete control facilities but also the continuous control facilities of renewable-energy plants.At the same time,the discrete and continuous coordination layer is designed,which is effectively put into practice.The control system can handle discrete quantities such as power transformer tap-changer,compensator or reactor,etc.,and can also adjust the continuous output of reactive power of new energy stations,which has good practical value.From the two dimensions of computer memory management and model maintenance,the problem of uninterrupted operation of control software is studied.Large-scale control software needs to solve the online update problem of the power grid model in actual operation,and the important control process must not be interrupted when the power grid model is changed.This paper proposes the source-based maintenance technology to solve the "plug-and-play" problem of the new model after the change of it.By importing the panoramic model of the secondary device,the unique conversion of the IEC61850 model to the CIM model can be realized.The complete process of source-based maintenance between the substation and master control center is designed,and the IEC60870-5-104 protocol is extended to transmit the exchange file,making the technology useful.This paper also gives the principle of model publishing based on the computer memory management technology,accessing the new grid model by the pointer switching of the computer process,to achieve the purpose of uninterrupted operation.“Offline-maintenance,online-publish” technique solves the uninterrupted problem,while the source-side maintenance technology solves the new model " plug-and-play " problem.Through these two aspects of work,we can make the reactive power voltage control process in the actual system truly uninterrupted.It has important engineering value. |
