Flexibility-oriented Unit Commitment And Its Application To Generation Expansion Planning In Wind-CSP Power Systems

Up to now,China has become the country with the highest installed wind power capacity in the world.However,due to the unreasonable power supply structure,weak power grid planning and limited load scale in the grid-connected regions,wind curtailment and threats to system security caused by large-scale centralized grid-connected wind power occur from time to time.By virtue of its green,flexible and controllable characteristics,concentrating solar power(CSP)is expected to be complementary with wind power and connected to the grid,so as to improve the consumption level of wind power.Combining the time-sharing complementary operation characteristics of wind power and CSP,it is of great significance to construct a wind-CSP power system and study the unit commitment to guide the optimization of system operation and power expansion planning.Supported by National Key R&D Program of China(No.2017YFB0902200),Science and Technology Project of State Grid Corporation of China(No.5228001700CW),this paper conducts the esearch on the unit commitment of wind-CSP power systems,focusing on the improvement of unit commitment solution algorithm considering security constraints,the sampling method of typical wind power output scenarios taking into account the temporal correlation of prediction errors,and the flexibility modeling of CSP stations.In order to simulate the operation scenario of wind-CSP power systems,a unit commitment model of wind-CSP power systems with grid and flexibility constraints is established,and a modified Benders decomposition algorithm which the convergence of the algorithm is improved by incremental selection of active constraints was proposed to solve the model.Firstly,based on the static energy flow model of CSP station,a security constrainted unit commitment model of wind-CSP power systems is established.The model takes the minimum operating cost of the system with wind/light abandoning punishment cost as the objective function,and considers the operating constraints of units and the static energy flow constraints of CSP station.Secondly,the original problem is decomposed into the main problem of unit combination and the subproblem of power flow correction by using Benders decomposition algorithm and iterativly solved.The proposed method is verified effective by a modified IEEE RTS-79 and a IEEE RTS-96 test system.The results show that the flexible and controllable CSP has a positive impact on the system cost efficiency,peak load regulation efficiency and transmission efficiency,and the thermal energy storage system is the key part affecting the flexible and controllable characteristics of CSP.Compared with the traditional Benders decomposition algorithm,the modified Benders decomposition algorithm reduces the overall solution time by improving the convergence.Wind power prediction error and unit start-stop peak regulation are two potential factors affecting system flexibility.In this paper,a unit commitment model of wind-CSP power systems is established,which takes into account the temporal correlation of wind power prediction error and unit start-stop peak regulation.This model considers that the wind power prediction error will bring additional ramp demands to the system,and the temporary start and stop which is not planned in the day-ahead schedule can provide climbing resources.Firstly,a sampling method of typical output scenes of multiple wind farms was put forward based on Cholesky decomposition and Latin hypercube sampling generation,taking into account the temporal correlation of wind power prediction errors.The generated scenes were applied to the unit combination to describe the spinning reserve requirements.Secondly,the operating conditions that limit the start-stop peak regulation ability of units are analyzed.Based on this,the flexibility model of units is established and embedded into the unit commitment.The results show that taking into account the temporal correlation of wind power prediction errors can make the unit commitment result more accurate,and the stronger the temporal correlation of the prediction error is,the more conservative the system operation cost will be.Power systems are more flexible and the unit commitment result is better taking into account of unit start-stop peak regulation.Optimizing the power supply structure of wind-CSP power systems is the fundamental measure to improve the consumption level of wind power.In this paper,a coordinated generation expansion planning model of wind-CSP power systems based on unit commitment is established to plan the installed capacity of wind power and CSP,and to optimize the parameters that affect the capacity configuration of the subsystem of CSP station-the ratio of photovoltaic capacity and the time of heat storage.In order to accurately describe the operation ability of CSP stations,the unit commiment based on the influence analysis of factors such as ramp rate,maximum/minimum output,start-stop ability and performance of thermal storage system on the flexibility of CSP station is proposed in low layer.The results show that the comprehensive benefit of the wind-CSP complementary planning is better than that of the single wind planning and wind-photovoltaic complementary planning.Different system parameter combinations of CSP station will affect the allocation of wind power and CSP planning capacity,and the primary investment cost of CSP is the main factor affecting the development prospect of wind power and CSP complementary planning at present.The performance of thermal energy storage system will have a significant impact on the operation flexibility of CSP stations with small heat storage capacity.