Studies On Iterative Infinitesimal Generator Discretization-based Eigen-analysis Method For Power System With Inclusion Of Time Delays

The influence of communication systems on the control of power systems has in-creased.For large-scale power systems,the Wide-Area Measurement System(WAMS)based on the Phasor Measurement Unit(PMU)can capture the operating parameters from remote locations in real-time and builds a new information platform for power sys-tem.The WAMS also provides a new method for the control of power system.What's more,the small-scale microgrid also relies on the reliable communication systems.However,in the transmitting and processing of wide-area measurements on the low-cost wireless communication network,such as WiFi,Zigbee etc.,and satellite commu-nication,time delays in the range of tens to several hundred milliseconds are inevitably introduced into power system.Therefore,the power systems is essentially a delayed cyber-physical power system(DCPPS).Time delays have significant effects on small signal stability of the system.It may be lost when time delay effects are taken into con-sideration.Therefore,it is necessary to intensively analyze the small signal stability of DCPPS.For DCPPS,the iterative infinitesimal generator discretization based eigen-analysis method and its application on microgrid are studied.Meanwhile,some stability analy-sis methods for DCPPS including IIGD are compared.The main work and some results of this thesis are addressed as follows:(1)The physical nature of DCPPS is introduced and the linearized small signal sta-bility model is established.Iterative infinitesimal generator discretization based eigen-analysis method is proposed for the computation of critical eigenvalues of DCPPS.First,the sparsity of the infinitesimal generator's discretized matrix,which possesses identical spectrum to DCPPS,is explored by reformulating its dominant blocks as sum of Kronecker products of constant Lagrange vectors and system state matrices,which lays the basis of further utilizing the sparsities in the augmented state matrices of DCPPS.Second,the shift-invert preconditioning technique is applied to transform the required eigenvalues into those dominated in moduli.Third,a novel subspace-based IDR(induced dimension reduction)method is adopted to efficiently and iteratively cal-culate the matrix-inversion and vector product.Forth,the Newton correction method is applied to obtain the accurate eigenvalues.Lastly,the effectiveness of IIGD are ex-tensively studied and thoroughly validated on the two-area four-machine test system and Shandong grid.(2)The small signal stability of microgrid with time delay is studied by IIGD based method.First,two microgrids are built.The generators in one of them are synchronous generators and inverter-based distributed generators.The other one only contains in-verter based distributed generators.An improved droop control strategy is adopted which redistributes the active power and reactive power of all inverters.Therefore,time delays are introduced into the microgrids.Subsequently,the complete linearized math-ematical models of two microgrid are established.Second,IIGD based eigen-analysis method is used to compute critical eigenvalues of the two microgrids in islanded mode.The effectiveness of IIGD for microgrid is verified and the distribution of eigenvalues for the two microgrids are compared.Lastly,the impact of control parameters of in-verters and time delays on the stability of DCPPS are investigated.(3)Delay-dependent stability criterion,Pade approximation based method as well as iterative infinitesimal generator discretization-based method(IIGD)are extensively compared from both theoretical and numerical analysis.First,the theories of a delay-dependent stability criterion with single time delay and Pade approximation based method are introduced in detail.Second,the theoretical comparison of the three meth-ods for stability analysis of DCPPS is given and the schemes of numerical comparisons are presented.Lastly,the conclusions of theoretical analysis are verified on the two-area four-machine test system and Shandong grid.In this paper,IIGD based eigen-analysis method is proposed which is suitable for the stability analysis of large-scale DCPPS and microgrids.This method has the ad-vantages of high accuracy and dealing with multi-time delays.