Studies On Load Resilience Based Flexible And Effective Locally-Accommodating Strategies Of Renewable Energy Generation

The penetration rate of renewable energies such as wind power and PV is continuously increasing due to their advantages in the aspects of cost,efficiency and reliability.However,the renewable energy accommodating problem faced by the power grid is also becoming more and more serious with the rapid growth of the installed capacity.It is because that the renewable energy generation have undesirable natures like anti-peaking and output fluctuating.The accommodating problem is particularly severe in the power grids with a high penetration rate of renewable energy or adopting renewable energy as the main power source,including metropolitan microgrids connected with renewable energy,the regional power grids located the "Three North" area with huge renewable energy generation bases,and the isolated island microgrids.In recent years,the renewable energy accommodating problem has attracted the attention of many scholars,and a series of local consumption strategies and schemes based on load resilience,including the thermal energy storage,hydrogen production and sea water desalinization,have been put forward.However,taking into account the differentiation in terms of geography,economic and life features among the grid-connected microgrid,the regional power grid and the isolated microgrid,the existing work has not highlighted the potential and advantage of various accommodating apparatuses.It is still worth advancing on the aspect of thermal energy storage apparatus design,hydrogen/ desalination apparatus scheduling and the multi-time scale accommodating objective coordination.As a consequence,for the purpose of enhancing the flexibility and economy of local accommodation of renewable energy,the researches on the resilient accommodating apparatus of thermal energy storage,hydrogen production and desalination are carried out,the corresponding design schemes and flexible scheduling strategies are put forward,and the feasibility and superiority of the proposed schemes and strategies with theoretical derivation and extensive simulation tests are proven in this thesis.In the aspect of thermal energy storage apparatus scheme design,the following work has been accomplished in this thesis: Aiming at lacking of thermal energy storage apparatus with large capacity and low self-discharge rate in the residential side of gird-connected microgird,a thermal energy storage based renewable energy accommodating strategy by means of building phase change energy storage system is proposed.According to the analysis of thermal performance of phase change material,a building phase change material based thermal energy storage accommodating model is designed with a large capacity and low self-discharge rate.Subsequently,the electrical-thermal combined scheduling optimization model is established for the purpose of analyzing the performance of thermal energy storage,indoor temperature comfort degree and the economic indexes of the proposed renewable energy accommodating system.The effectiveness and superiority of the proposed thermal energy storage based accommodating strategy are demonstrated through extensive simulation studies.In the aspect of hydrogen/desalination apparatuses scheduling,flexible renewable energy local accommodating scheduling algorithms,which can fully utilize the flexible power-adjusting ability of accommodating apparatus,are proposed.Presently,the hydrogen production apparatus in the existing accommodating scheduling strategy only works in the condition of wind power curtailment,which greatly reduces the utilization rate of accommodating apparatus.To solve this problem,a day-ahead accommodation scheduling strategy for energy grid consisting of conventional thermal generating units,wind farms and large-scale hydrogen production apparatus is proposed.Firstly,an accurate power-efficiency characteristic analyzing model of hydrogen production apparatus is established to evaluate the marginal cost of hydrogen production.Subsequently,with consideration of the fuel cost and hydrogen yield,a renewable energy accommodating strategy capable of balancing the hydrogen output gains and fossil energy consumption expenses is presented,which maximizes the utilization of the hydrogen production apparatus and the total benefit of energy grid.Then an improved group-searching optimization algorithm is proposed to solve the complex non-linear optimization problem.The flexibility and economy of the accommodating strategy are verified by the simulation tests on a benchmark energy grid.In view of the relatively high expense of the existing scheduling strategy of isolated island microgrid due to ignoring of the power-adjusting capability of desalination apparatus,a series work has been accomplished.Firstly,an efficiency analyzing model considering the material balance and energy balance of desalination apparatus is established to analyze of the power-efficiency characteristics of this type of apparatus.Afterwards,a renewable energy accommodating scheduling strategy suitable for a wind/photovoltaic/ diesel/battery isolated island microgrid is proposed,of which,the objective is designed as minimum fuel cost and battery consumption cost.The rationality and the advantage in term of economy of the proposed strategy are verified by extensive simulation tests a benchmark isolated island microgrid.In the aspect of the multi-time scale accommodating objective coordination,the following work is accomplished: Aiming at the problem that the accommodating apparatus with power-efficiency characteristics cannot be utilized for peak load shifting and fluctuation balancing objectives in the meantime,a multi-time scale coordinated renewable energy accommodating strategy for isolated island microgrid is put forward.Firstly,the concept of flexible power load is defined for the universal description of such a type of load that is insensitive to working time but sensitive to the working power.Subsequently,with the scene of an isolated island microgrid,the index of cut-off power and objective-power capable for the flexible power load is proposed,and a micro-grid coordinative accommodating scheduling strategy is invented.In order to effectively solve this complex optimization problem,a fast solving algorithm referring to Benders decomposition is designed.The results of case study show that the proposed strategy can harmonize the objectives of peak load shifting and fluctuation balancing simultaneously by means of day-ahead assessment of the efficiency loss due to smoothing real-time power fluctuations.