Elasticity Mechanics Analogy Based Power System Energy Structure And Its Application In Analysis Of Low Frequency Oscillation

Low frequency oscillation(LFO)is one of the severe threats to the stability of power systems.With the expansion of interconnected power grid and the injection of large-scale renewable energy,the system scale becomes larger,the operating points change more flexibly,and the system models get more complicated,which increases the difficulty of the analysis of LFO.Furthermore,comprehensive decision assistant information is quite useful for system operators to take appropriate measures to suppress LFO.Meanwhile,the development of wide-area measurement technology creates advantageous conditions for the dynamic monitoring and analysis of LOF.In face of these challenges and opportunities,the dissertation introduces the energy theory of elasticity mechanics into LFO study of power system,and reveals the damping mechanism of LFO from the perspective of energy characteristic analysis.It also studies the quantitative analysis method of LFO based on power system energy structure,and explore application of the method in the detailed evaluation of generator damping property,identification of main oscillation path,and damping tracking of power system with wind power penetration.The dissertation provides practical and feasible new ideas for effectively identifying pivotal links in the network,researching the whole damping property of power system on basis of local property,and enriching decision assistant information of LFO.The main contributions of this thesis are as follows:(1)According to the similarity analysis between power system and elastic network,the model of an analogous elastic network mapping for power systems is presented.Based on the energy conversion of the disturbed analogous network,the energy functions of generators,networks and loads in multi-machine power system are derived.The above energy functions agree the law of energy conservation.It provides model foundation for studying of LFO in power system from the perspective of energy.(2)The composition of energy functions obtained from the elastic mapping is analyzed,which reveals the physical significance of dissipation energy for each components,and remodeling the notions of power system energy functions;The conservative power system energy structure is built.In the energy structure framework,the relationship between dissipation energy and damping is studied based on the concept of damping loss factor in mechanics,to understand the damping mechanism from the view of energy and to realize the representation of damping of power system in a dispersed manner;According to the above relationship,the negative damping mechanism of excitation and governor control system during LFO is revealed from the perspective of generation of dissipation energy,which lays a solid foundation for evaluating generator damping based on the generator dissipation energy.(3)The generator damping loss factor(GDLF)is defined to quantitatively evaluate the generator damping contribution during LFO.In the situation of only generators providing damping,the quantitative relationship between GDLF and damping ratio from the modal analysis is analyzed;In order to calculate GDLF for multi-modes oscillations,the modal composition of the generator dissipation energy is studied,and a signal decomposition method based on multi-scale chirplet sparse signal decomposition(MCSSD)is proposed for measurement data processing;On the basis of GDLF,a method for the detailed evaluation of the generator damping contribution during oscillation periods is proposed,and its online application potential is also discussed.(4)The time domain feature of dissipation energy in power system energy structure is studied.Driven by the feasibility of extraction of dissipation energy from the measurement data,the branch-form energy structure and the port form energy structure with wind generation are derived.Considering the dominated oscillation paths are the basis of suppression and control of poorly damped LFO,a method for online identification of dominated oscillation paths is proposed;Considering the model complexity of wind farm,a port-form damping loss factor based on the measurement of generator port is defined.Based on the port form energy structure,a method for online tracking the generator damping contribution during LFO is proposed.