Research On Coordination Method For Giant Hydropower Station And Two Dispatching Power Grids

With the advancement of West-East electricity transmission project,hydropower in China has developed rapidly and inter-provincial UHV transmission scale expands gradually.Accordingly,hydropower dispatching operation mode has changed greatly,from operating a single cascade hydropower station to the inter-basin cross-regional coordination,from responding a single power grid load demand to multi power grid load demand,expanding small scale units to huge capacity and large scale.These changes have resulted in new challenges such as large-scale hydropower consumption,one reservoir with two dispatching power grids and multi-grid peaking shaving,etc.,which makes it more difficult for hydropower dispatching.Aiming at the problem of coordination method for giant hydropower stations and two dispatching power grids,this dissertation sets Xiluodu hydropower station and the dispatching Zhejiang and Guangdong power grids as the engineering background,and focuses on the source-grid coordination about inter-province hydropower system,multi-grid peaking shaving and large-scale unit commitment from the long-term and short-term scales.The following innovations have been achieved:(1)The paper puts forward the long term source-grid coordination method of hydropower plants connected by Direct Current(DC).Considering the difference of the distribution ratio in flood and dry season and complex operation requirements of Xiluodu hydropower plant,the optimal model of multi-objective minimax generation is established to improve guaranteed output in dry season by using the differences of hydrological characteristics,regulation capacity and installed capacity of inter-basin hydropower plants.The complicated multi-objective model is converted to a single objective model by using single objective optimal solution to construct the ideal points.A polynomial technique is employed to deal with complicated nonlinear relationship and the nonlinear programming method is finally used to address the optimization model.The case study shows that the electricity is effectively transferred from flood season to dry period through source-grid coordination.As a result,the guaranteed outputs in dry period of Zhejiang and Guangdong Power Grids are improved significantly.(2)The paper proposes the multi-grid peak model based on the peak shaving index.The model considers the difference between dispatching grids about load characteristics and the structure of the power source,and qualitative analytics the relationship between peak shaving demand and peak shaving performance.Then,the regulating-pressure index system is built based on the capacity,load tracking,load fluctuation.And the multi-grid peaking shaving function is established and solved by integer nonlinear programming method.The example analysis shows that the proposed model can not only reduce the difference between peak and valley and load fluctuation,but also better respond to the demand of load climbing than traditional model.(3)Considering complex nonlinear relationships of hydropower operations,this paper proposes a mixed integer nonlinear programming model(MINLP)for optimizing load distribution of hydropower plant.A polynomial fitting technology is used to deal with nonlinear functions involving at least two variables of water level,discharge,and generation in the MINLP.The order and formulation of each function is analyzed and determined.Considering the effect of water head on power generation,a quadratic function of water head and turbine discharge is proposed to accurately describe the power generation of the unit.Thus,a three-dimensional surface which can represent the relationship among water head,discharge,and generation is obtained,which can satisfy the requirement of calculating power generation under different net heads.Finally,The MINLP model is solved by a mathematical solver and verified by solving the actual load distribution problem of Xiluodu hydropower plant with 18 generating units.A comparison between MINLP and MILP is presented in terms of application complexity and result accuracy.The results show that the MINLP is easy to use and capable of producing higher-accuracy optimization results.Furthermore,the error of total turbine water consumption through the actual curve reverse interpolation is 91% less than that from MILP,better representing the actual unit operations.