Research On Distributed State Estimation In Interconnected Power Grid And Hybrid Measurement State Estimation

With the growing size and enhanced interconnection of modern power system and the increasingly complicated structure and operation mode, a better state estimation (SE) approach is required. The conventional integrated state estimation (ISE) has its limitations in the reliability and real time of estimation calculation for large-scale interconnected power grid. On one hand, the smooth operation of SE in integral system will be affected by the unobservable situation and bad data in partial system. On the other hand, in the system computation center a large number of measurements must be processed and the large-scale SE problem has to be solved as a result of the system's oversize dimension. It is very difficult for SE to meet the real-time demand of system analysis and control. The phasor measurement unit (PMU) has been placed in power system expansively, and provides another important data source. The PMU measurements have many advantages such as high precision, synchronous sampling and short updating cycle, and can measure phase angle directly. The problem about how to utilize the PMU measurements in the SE efficiently at shorter calculation cycle must be faced and solved.Aimed at the above two types of problems, the problem about distributed SE and hybrid measurement SE is studied in this paper. To improve the performance about reliability and real time of estimation calculation and to utilize hybrid measurements in hybrid measurement SE efficiently are the intention of the study, which makes SE work better for power system analysis.The concept of changed measurement is applied to SE in space, and a distributed SE based on measurement sensitivity analysis method is put forward. The topological decomposition of interconnected system is realized by the area division which a tie line belongs to two subsystems. The state estimators of subsystems at both ends of tie lines carry out individual calculation. And the mismatch power obtained is taken as the virtual changed measurements. According to the sensitivity relationship among state variables, measurements and power estimates, the unified solutions of subsystems are obtained by iteration. The problem of phase angle shifting for subsystems is analyzed, and several important factors that affect the estimation precision of this method are pointed out. The basic principle of spatial recursive algorithm is obtained by topologic decomposition and partitioned matrix computation. And the basic spatial recursive algorithm and the spatial recursive algorithm layer by layer are put forward which are all composed of forward and backward calculation processes. The spatial recursive algorithm layer by layer divides an interconnected power grid into subsystems and boundary system, and the forward and backward calculation is carried out between the two layers. The formula of sequential linear recursive calculation is deduced. Utilizing the formula, the backward calculation is finished after all additional border measurements are processed sequentially based on the results of forward calculation. The method quickens the calculation of the spatial recursive algorithm layer by layer effectively.A distributed SE method based on network sensitivity analysis is proposed in this paper. The method divides a large-scale interconnected power grid into some subsystems by setting a virtual bus on the tie lines among subsystems. The weighted residual mean of the power estimates flowing through the virtual bus can be calculated by the subsystem estimators at both sides of virtual bus. The mean is used to correct the estimates based on the network sensitivity and to coordinate the estimates obtained by individual SE calculation of each subsystem. No calculation center of entire system for coordination is needed, and the single-layer organization structure in which the relationships among calculation centers of subsystems are peer to peer can be realized.Combining the distributed SE with multi-agent technology, a design scheme of distributed SE multi-agent system (DSEMAS) is proposed. The three-layer architecture of DSEMAS and the organization structure of agent in each layer are built for the distributed SE algorithm based on network sensitivity, and the communication and operation mechanism of this MAS are also introduced in detail. The agents achieve the distributed SE in the interconnected grid together by cooperation.A real-time model for hybrid measurement SE based on Ward equivalence is put forward for the hybrid measurement system consisting of SCADA and PMU. PMU are placed according to the practical principle for the partial key plants, stations and lines in power system which can be monitored dynamically by WAMS. And the buses are divided into the internal and border buses observable to PMU and external buses unobservable to PMU. In the SCADA section, the enhanced measurement and nonlinear estimation model is adopted for improving estimation precision, and equivalent WAMS is built according to the Ward equivalence. In the PMU section, the linear SE is carried out in the equivalent WAMS utilizing all the real-time PMU measurements, and then the PMU measurements can be utilized at a shorter cycle.IEEE 30-bus and IEEE 118-bus systems are used to simulate the algorithms proposed in this paper. The results of simulation computation and analysis show that the algorithms are correct and effective, and are also valuable in both theory and practice.