Research On Optimization And Evaluation Approaches For Low Carbon Urban Energy Systems

Urban energy systems are novel integrated energy systems that satisfy the diversified energy demands of end-users in specific areas of the town or city through the integration of various energy technologies and complementary utilization of multiple energy resources.In the context of globalized sustainable urbanization and the low-carbon transition of the energy structure,urban energy systems are undergoing continuous transformation.Urban energy systems,which integrate renewable energy,distributed energy technologies and demand-side flexible resources,are low-carbon,efficient,reliable,flexible and economic due to the cross-sectoral collaboration,multienergy coupling,multi-technology complementarity and cascade utilization of energy.Therefore,iurban energy systems represent one of the inevitable choices for sustainable urban energy transformation.At the same time,low-carbon-oriented urban energy systems have higher digital and intelligent requirements.In the future smart city applications,the integrated planning and operation optimization of urban energy systems can realize the integration of different energy technologies,promote the complementary coupling of multiple energy sources and subsystems,as well as achieve the trade-off among different optimization objectives,so as to address the environmental challenges and improve the comprehensive benefits.Hence,it is one of the powerful measures to match the strategy of "peak carbon emissions" and "carbon neutrality",as well as to realize the sustainable development of urban energy.Based on China’s "30·60" decarbonization goal,lowcarbon urban energy systems require more diverse,flexible and complete planning theories,optimization methods and technical measures to match ever-enriching urban energy planning scenarios and the rapidly growing demand for engineering applications.In the above context,according to the planning and application scenarios of urban energy systems under the new situation of China’s "30·60" low-carbon transition,this dissertation determines the key issues of mathematical planning and modeling,carbon emission evaluation and multi-objective optimization that are involved in the optimization and evaluation research of low-carbon urban energy systems,focusing on the low-carbon development modes,integrated optimization schemes and synergistic emission reduction mechanisms of urban energy systems under different scenarios,and proposes innovative methods and comprehensive solutions to address the key challenges.The main contents and innovations of the dissertation are as follows:In Chapter 1,the research background and significance are addressed,and the connotation and definition of the low-carbon urban energy systems are clarified.In view of the mathematical planning and modeling,carbon emission evaluation and multi-objective optimization issues,the current status and problems of domestic and overseas research are reviewed and analyzed.The research ideas are sorted out,and the overall framework of the dissertation is constructed,whereas its innovation are clarified.In Chapter 2,based on the mathematical planning methods,a bottom-up modeling approach is adopted to establish the modular planning model of urban energy systems according to the coupling and interaction mechanism of energy,material,capital and information flows among the subsystems.The modular model architecture based on the coupling structure of "directed branch network" and "energy hub",the modular constraints based on the coupling form of multiple "generalized flow",as well as the modular hierarchical modeling method based on the "hierarchical network" form of coupling "spatial multi-layer network" and "multi-time domain network" at multiple spatial and temporal scales are elaborated.In Chapter 3,based on the carbon neutral perspective,the potential impact of carbon accounting approach on urban energy systems planning is analyzed,and a new"net carbon emission" evaluation approach is proposed to adapt the bi-directional power and carbon interaction characteristics of grid-connected urban energy systems and to take into account the "carbon offset".In addition,two novel multi-objective optimization methods are proposed to address the multi-objective trade-off problem of low-carbon urban energy systems that need to consider environmental,economic and technical indicators which have different subjective and objective decision-making requires.The approaches proposed combine new multi-objective trade-off perspectives and decision-making approaches,simplified solution algorithms,result evaluation methods and synergy of multiple methods.In Chapter 4,the multi-scenario planning problems of various types of urban energy systems under different planning conditions are investigated.The proposed modular modeling methods,low-carbon evaluation measures,multi-objective optimization and evaluation approaches are integrated to match the differentiated needs of specific planning cases and scenarios.Five comprehensive adaptation schemes for low-carbon urban energy systems planning are explored,and the proposed methods are validated with specific case studies.In Chapter 5,the results of the new methods proposed in this dissertation within multiple planning scenarios are summarized,and the subsequent research directions are prospected.