Real-time Optimal Operation And Economic Load Scheduling For Cascade Hydropower Plants

The study of hydropower plant real-time operation and inter-plant economic load dispatch has a significant importance not only for improving power supply reliability to power grid, but also reducing electricity generation costs and providing reference frame for hydropower plant operating safely and stably. It plays a key role in lowering unit service life consumption, tapping power generation potential, enhancing economic benefits of power enterprises, alleviating shortages of energy supply and so on. Several cascade hydropower plants real-time optimal operation models and solution strategy were proposed from single plant operation to cascade hydropower plants of the Qingjiang basin. According to simulation calculation of short-term operation, a mixed pumped-storage plant optimization model was applied to the Baishan hydropower plant and the impact of hydropower plant long-term operation was discussed after increasing pumped-storage sets. The main contents and innovations of this thesis were summarized as following:(1) The hydropower plant economic operation theory and methodology were summarized extensively both in home and abroad, several concerned topics of real-time operation were analyzed and research ideas were provided. The development course and research advancement of pumped-storage plant were reviewed, of which operation mode and benefit analysis were also investigated.(2) The cascade hydropower plants operating mode and optimal scheduling rules were conducted. Two kinds of results were summarized in comparison with different short-term optimal operation models for the Qingjiang cascade hydropower plants. Four types of inner-plant economic operating mathematical programming were introduced and several approaches to solving given units load distribution were analyzed qualitatively. The Geheyan and Gaobazhou hydropower plants were selected as case study for spatial and temporal inner-plant economic operation analysis and calculation.(3) Real-time load distribution strategy in the mode of unit automatic control for the Geheyan hydropower plant was developed based on double object functions according to spatial and temporal aspects, and the identifiable method and operation strategy of power uncontrolled range were proposed. Temporally, unit commitment scheme of real-time operation was setting by combining unit priority list with unit open-down rules. A set of optimal solutions can be obtained by using dynamic programming to resolve spatial object function and as sort with temporal object, from which the load distribution scheme rules were chosen in accordance with real-time control demand. Under the condition of given different reserve load modes, the proposed model had been successfully used in saving water, reducing units open-down numbers and reducing frequency number of unit crossing oscillation range.(4) Based on inter-plant jointly avoiding unit oscillation range, unit open-down strategy and neglecting flow lag time of real-time operation between cascade reservoirs, two real-time load distribution models for the Qingjiang cascade hydropower plants were proposed and discussed, which took energy consumption minimization as the objective. According to inter-plant to inner-plant water and power balance, the modelⅠdistributed initial load to each power plant. If it satisfied constraint conditions of inter-plant combined avoiding power non-operation area and large range load transfer also made unit startup-shutdown strategy, then economical operation of inner-plant was obtained based on the objective function of minimum hydropower consumption for cascade hydropower plants. ModelⅡdivided cascade plants into several dual subsystems according to aggregation and decomposition methods. The subsystem was composed of two dual hydropower plants, one used power load as input and water consumption as output, the other took water consumption as input and power load as output. Each dual subsystem can be aggregated as a virtual power plant to optimize object function considering generating set as basic unit. The results of real-time simulation operation shows that modelⅠand modelⅡcould save water 1.35% and1.45%,0.95% and1.6% for the Geheyan and Gaobazhou hydropower plants, respectively, and reduced frequency number of units crossing non-operation area 9.83% and 17.3% for the Geheyan hydropower plant. It is also shown that the economic benefit and operating security of hydropower plants are significantly increased by the two proposed models.(5) According to the complementarities between the Shubuya and Geheyan hydropower plant unit oscillation range, a real-time combined economic and optimal operation model for the Qingjiang cascade hydropower plants was investigated. The whole cascade power plants were regarded as a virtual plant which was divided into four basic elements composed with only one unit in the Shuibuya, Geheyan and Gaobazhou hydropower plants, respectively. The load distribution between fixed units concept was adopted for load scheduling of each basic element. Hydraulic connection for cascade plants was coordinated by energy consumption minimization objective. It simplified inter-plant load adjustment in the distribution process. The comparative results between optimal simulation operation and practical operation have shown that the model is able to save more cascade reservoirs water potential.(6) Daily operation model for the Baishan mixed pumped-storage plant was analyzed and discussed. Water consumption and water level fluctuation were compared under the condition of three different pump discharge forms. The derived incremental benefit would be described after increasing pumped-storage units, the relationship between power generation and power consumption of pump water was developed in accordance with maximum pumping capacity. Based on pumping and generating cycle operation mode, an optimal operation model of the Baishan pumped-storage plant was developed, its objective function was minimization of power generation costs. Finally, the long-term operation difference of conventional power plant and mixed pumped-storage plant was analyzed, and kinds of hydropower plant economic indicators were compared in the condition of identical pump discharge monthly.