With the urgent requirement of energy transformation and widespread deployment of information network represented by 5th generation mobile technology,the distributed resources are gradually merging from individual components to a uniform electricity-information system（EIS）.Since the distributed energy renewablization,conversion,storage,and mobility can not be achieved without the information flow,the component coupling inside EIS dominates the degree of evolution.With numerous dynamic components,topologies,demands and management strategies,the whole EIS formulates a complex time-varying system.Despite the bonding benefits of energy and information,challenges also arise in EISs,such as the heterogeneous participants,diversified management strategies,multiple communication targets,and stationary/mobile switching.All of these uncertainties may contribute to stability risks of dynamic system in the manner of the butterfly effect.The tighter of EIS integration,the more vulnerable of defect exposure.However challenging burden may seem,motivated by the lack of EIS model,stability assessment method,margin determination approach,quantified risk,and enhancement strategy,this thesis aims to seek a concise and unified approach to understand this complex time-varying system.This thesis focuses on the stability assessment and enhancement of EIS from the perspectives of modelling,analysis framework,and risk suppression.For each part,various systems and algorithms are demonstrated to check the possibility of unification.The main contributions of this thesis are summarized as follows:1)Modelling establishment.The modelling of electricity-information for electrical system is described in the transmission and microgrid levels as the example.First,unified modelling of direct current（DC）energy,hybrid energy storage（HESS）,alternating current（AC）energy,electric mobility,and AC-DC interconnected system are analyzed in the state space.Then,the information network is considered during the operation of the electricity-information system.Due to the uncertainties imposed by the information system,an interface variable,i.e.,information delay,is introduced to reflect the coupling of energy and information systems.By virtue of the proposed interface variable,the temporal relationship of information and energy parts is described.The communication delay,asynchronization of information system,the response speed,aggregation process of energy system,and the integration level of electricity-information system can be concisely reflected through a unified form,which provides the prerequisite for the stability assessment of power states.2)Margin determination.For the determination of the stability region,the searching technique and resultant conditions are developed.First,a critical searching technique is proposed utilizing the transcendental feature in the critical scenario.The time-delay stability switching boundary（TDSSB）is then defined and provided to elaborate the boundary dividing the stable area and unstable area.For the acceleration of the boundary calculation,Dixon resultant condition is established,in which the quasi-polynomial is built for the EIS model.The results in case studies indicate the TDSSB existence and the complete stability map during the evolution of power distribution-utilization system.3)Risk quantification.Although the stability margin and boundary are determined,the intrinsic process for the instability occurrence remains to be revealed,which formulates the stability risk inside EIS systems.To resolve this issue,a delay distorted matrix is formulated to represent the component coupling inside EISs,in which the transcendental impact on the interface is transferred to a polynomial approximation.On the basis of the delay distorted matrix,the damping ratio and parameter sensitivities are extracted to reveal the system oscillation factor.Then,the Newton correction and Krylov subspace are further introduced to accurately locate the oscillation centre and narrow the calculation space.Case studies demonstrate the effectiveness of the critical spectrum extraction.The computation efficiency is also boosted with the Newton iteration and subspace mapping.4)Stability enhancement.According to the oscillation risks induced by the energy and information connection,a multilayer strategy is developed for the stability enhancement covering the design,dynamic,and advanced stages.In the design layer,the whole stability area is separated based on the resultant analysis and two types of boundaries.In the kernel strategy,the EIS is designed to guarantee the good condition of one communication channel.Facing a large information delay,the offspring strategy is proposed to avoid the identical delay value in two channels.In the dynamic layer,a feedback strategy is proposed to enlarge the stability margin of EIS.The necessity and feedback objective are both investigated to build an effective feedback loop.Besides the strategies in the design and dynamic layers,an advanced enhancement approach is established by the proposed indexes of critical angle（CA）and critical impact（CI）.It is revealed that the information delay could cause the acceleration process entering the unstable area,which formulates an early-warning structure for the stability enhancement.The proposed model,assessment structure,region,risk,and enhancement strategy of EIS have also been applied and validated mathematically.The simulations and experimental results are both provided to support the investigation.By providing the technical solutions for stability modelling,analysing,and improvement of EIS,this thesis will boost the deeper integration of electricity and information systems for the evolution identifying the interlinking vulnerability.