Uncertainties Consideration In Power System State Estimation And PMU Sequential Deployment

The safe and stable operation of the power grid is of great significance to the national security and economic growth.With the continuous expansion and interconnection of the power grid,its operating condition is also increasingly complicated,and the requirement for the safe and stable operation is getting higher and higher.Once the grid operation fails,it is possible to cause a large-scale power outage,which will cause a negative impact on social production and daily life.In addition,the continuous increase of power load also brings power system closer and closer to its stability limit.Therefore,the accurate and rapid state estimation of the power grid can effectively improve the ability to resist risks.As a basic function of energy management system(EMS),state estimation(SE)can filter the raw data uploaded by the terminal,identify the bad data and calculate the complete and accurate electrical quantity.It has been widely used in the real-time scheduling of power system.SE is one of the most basic applications of EMS.Other online applications require SE to provide accurate and real-time power flow data,thus the accuracy of the SE results must be guaranteed.The main factors affecting the SE accuracy include the accuracy of the measuring device and the grid parameters.Affected by the measuring device and environmental conditions,the measured values and the line parameters are all with uncertainty,which makes the SE results also distributed probably.Therefore,it is capable of accurately characterizing the operating status of power system,when given the distribution range and confidence probability of the estimated states on the basis of traditional 'point' estimation.In addition,the development of synchronous phasor measurement unit(PMU)provides important technical support for power grid real-time wide-area measurement and monitoring.However,due to the economic conditions and communication conditions and other factors,it is still unable to configure the PMU in all buses in real grid.Therefore,it is necessary to study the optimal configuration of PMU according to the various performance requirements.It is the key issues to configure PMU under multiple objectives and constraints.The key issues in SE and PMU configuration are discussed detailedly in this paper.An approach for interval SE considering uncertainties is put forward in this paper.An approach for SE considering ETC and multi-objective PMU configuration is also proposed.The specific contents and research results are as follows:(1)Research on interval SE considering uncertainties.The source of uncertainty in power grid is divided into two categories:measurement uncertainty and line parameter uncertainty.An algorithm based on Latin hypercube sampling Monte Carlo simulation is proposed to estimate interval states of power grid.The detailed flow chart and simulation steps are given,with error evaluation index and unbiased test;furthermore,this paper proposes an interval SE algorithm based on semi-invariants and Gram-Charlier series expansion,and compares the two methods from the principle,the simulation results,computational efficiency and applicability.On the basis of above research,continue to consider the influence of different distribution forms of measurement uncertainty(such as Gaussian distribution,uniform distribution,etc.)on estimation results and unbiasedness.Finally,based on the measurement uncertainty,the uncertainty of line parameters R and X is considered,and the significant factors affecting the uncertainty of state variables are summarized.(2)Research on power system SE considering ETC.Based on the theory of ETC,the heat balance equation of transmission line is combined with the power flow(PF)equation in this paper to propose an ETC-PF model.The similarity between SE and PF calculation in terms of the model and algorithm is compared,and a two-step ETC-SE model and algorithm is put forward.Flow chart and its relevant modular design are given.Based on the traditional SE model,the algorithm adds the outer temperature correction cycle and updates the line temperature and resistance,so as to ensure the reliable convergence of the electric quantity and the line temperature.Furthermore,with the HBE taken as the measurement and line temperature taken as the state variable,a joint ETC-SE model and algorithm is proposed.Formula to calculate the related elements in Jacobian matrix H is deduced in detail.Finally,IEEE 39-bus and 118-bus cases are utilized to verify the validity,accuracy,computational efficiency and convergence of two ETC-SE algorithms.(3)Research on multi-objective PMU sequential configuration considering uncertainty.Based on the results of the state uncertainty obtained above,the multi-objective PMU configuration scheme is studied to reduce the uncertainty of the state quantity and increase measurement redundancy.Several objective functions of PMU are proposed,such as the least PMU numbers,the lowest economic cost,the highest measurement redundancy and the lowest uncertainty of state variables.To solve the problem of the optimization of multiple objective functions,this paper constructs a unified objective function by the least deviation method,which transforms the above multi-objective optimization problem into the single-objective optimization problem.In addition,this paper also introduces an effective method for the values of weight coefficients in the objective function.On this basis,the multiple constraints in PMU optimization configuration is discussed in this paper,including normal operation,accidental situation,depth of system unobservability,fault observability and so on.A simple 9-bus case is utilized as an example to compare different constraints,and a general representation of the mathematical model for multiple constraints is presented in this paper.Moreover,this paper also proposes a novel constraint for zero-injection bus,whose principle is easily understood and easy to programme.The IEEE 14,39,and 118-bus cases are used to simulate the PMU configurations.Compared with the existing literature,the PMU configuration scheme of this study enables to reduce the number of PMUs,decrease the uncertainty of all buses in the whole network,and reduce the probability of gross error.