| The hydropower units,thanks to their flexibility in operation,play a key role in hourly optimizing the peak shaving in power systems.At the same time,the constraints and goals of the hydropower system are usually very complex,making the short-term hydro scheduling really challenging.This work presents a new peak-shaving model based on the mixed integer linear programming(MILP)without prearranging the hydro plants in order.With the complex hydraulic and electric connections between the cascaded reservoirs involved,a short-term hierarchical scheduling model of the cascaded reservoirs was formulated and then simulated to investigate the impacts on the hydropower scheduling of merging wind and solar powers into the power grid in top priority.The main works and contributions are summarized as follows.(1)Without prearranging hydro plants in order,this work presents a new power and energy balance model and procedure that achieve the peak-shaving task in an optimization way.The work employs an easy way to determine the plant-based operating zones by merging unit operating zones,and introduces a new constraint mathematically expressed to enforce the power output consistency with the trend of system load.The case studies on 6 cascaded hydropower reservoirs on the Lancang River verify the flexibility and scalability of the model.(2)A hierarchical model for short-term scheduling of cascaded reservoirs is proposed. With the system load,energy production and reservoir storage targets all known, the quarter-hourly hydropower generations during a day are scheduled while taking into account the hydraulic connections and after updating the water head to eliminate linearity errors.At the same time,the optimal unit commitments are obtained under the optimal releases determined by the cascade operation.In the case studies on 11 cascaded reservoirs on the Lancang River,the model and procedure can derive a satisfactory solution in less than 4 seconds,demonstrating the engineering practicability of the model and the efficiency of the method.(3)The impacts on hydropower scheduling from merging wind and solar powers into the power grid is analyzed.Assuming a full consumption of wind and photovoltaic powers,the complementary operation of hydropower,wind and photovoltaic is simulated in both dry and flood periods respectively based on the short-term hierarchical model.The case studies in the Lancang hydropower cascade reveal that in the dry season,the merging of wind and solar powers into the power load makes the whole hydro plants of the cascade more likely to generate with larger fluctuations and the upstream plants to put in greater working capacities.During the flood season,however,the impact from the wind and solar powers is quite different from day to day while Nuozhadu and Xiaowan are the main hydro plants affected. |
