Research On The Optimal Dispatch In Power Systems With High Proportional Renewable Power Sources

Power systems that connected with high proportional renewable power sources are called power systems with high proportional renewable power sources.Power systems with high proportional renewable power sources have already appeared with an increasing number,which has become a necessary trending for the future of power systems.Intermittent power sources such as wind power and solar power have their intrinsic uncertainties.The influence of power uncertainty towards power balancing has become a global top research area.Different from traditional or low penetrational power networks,to fully accommodate the renewable power sources,not only the power systems with high proportional renewable power sources should have enough ability for power accommodation,but also the structure function of its dispatch control system is required to adjust practical situations of high proportional intermittent power sources.Moreover,a period optimal power flow method about power balancing should be proposed.Therefore,the topic of this paper is “research on the period optimal power flow in power systems with high proportional renewable power sources”.This paper first proposes the statistical regularity of power uncertainty,then adjusts the corresponding dispatch control system,then propose a period optimal power flow method and finally apply the above into dispatching systems.The detailed research topics of this paper are shown as follows.First,an uncertain function is proposed based on the statistical regularity of uncertain power forecasting error.For the power forecasting error of intermittent power sources such as wind power and solar power,although the samples are individual cases yet there is statistical regularity.The paper defines the forecasting root mean square error as the uncertainty,and proposes an uncertain function(? function)that is based on two numerical characteristics of magnit ude and time constant to describe the power uncertainty with respect to advanced forecasting time.It has not only established a system consists of ? functions of wind power source,solar power source,intermittent power source and all power sources;but also established a calculation system consists of sum calculation,contour calculation and proportion calculation.The uncertain function has provided a simple and clear mathematical tool to characterize the power uncertainty genera lly.4 propositions have guaranteed the rigor of the proposed uncertain function system.Second,this paper proposes an equation of critical timescale for real-time dispatch and established a strategy to adjust the dispatch control system for power systems with high proportional renewable power sources.The two basic keys to adjust the dispatching system are the scientific real-time dispatch timescale and the reasonable power balancing function,respectively.The equation of critical timescale for real-time dispatch can be obtained by first employing ? function to represent the power uncertainty and then considering the power adjustment capability of automatic generation control(AGC).Based on the fact that the power uncertainty gets clearer when advanced forecasting time gets shorter,short-term(day-ahead)scheduling arranges the generation plans for short-term forecasting power,and store the controllable power reserve including power accommodation reserve;real-time dispatch accommodates the uncertain power from forecasting power difference between the real-time dispatch and short-term scheduling;AGC balances the unbalanced power from real-time dispatch forecasting power.Three dispatch control levels have built a coherent dispatch control mechanism,and have provided the dispatch control guarantee to fully accommodate uncertain power.Third,this paper investigates the property of linear time period in a steadystate power grid.Besides that,it proposes a time-varying power flow of linear time period algorithm,and it also defines the conception of linear time period in load power space.According to linear time period,this paper analyzes the norms of voltage derivatives in rectangular coordinate system,it also proves that the norms of voltage derivatives change in shape of ‘U',it constructs the combined timevarying voltage function of linear time period,and it establishes the high-accuracy linear time period algorithm of time-varying power flow.The algorithm can significantly simplifie the complexity of non-linear time-varying functions.It is a reliable,accurate and fast time-varying power flow algorithm.Fourth,on behalf of satisfying the constraints for whole time period,this paper proposes the conception of period optimal power flow(POPF)and the corresponding model and algorithm.Traditional optimal power flow(TOPF)is focused on a single time scan,however it should be oriented to the whole time period,and the optimized result of a single time scan cannot guarante e that the whole time period's power constraints as well as voltage constraints.The optimal power flow that can guarantee the whole time period is POPF.On each linear time period,the discretization has been employed when the average time scan is taken a s optimized function and the two boundary time scans are considered to check security constraints,which simplifies the nonlinear time-varying optimization problem into a three-time-scan optimization problem.Different optimal power flow for different time periods connects by sequence and then establishes the POPF,which can achieve the optimization by satisfying the security constraints in the whole time period.Simulation results have illustrated the effectiveness and simplicity of the proposed POPF.Finally,oriented to power systems with high proportional renewable power sources,this paper proposes a coherent POPF algorithm.According to short-term forecasting power,short-term POPF arranges short-term generation plans;it considers the line power adequacy based on the locally accommodation principle,and it stores the controllable power accommodation reserve according to uncertain functions.Based on the results from short-term POPF and the accommodation reserve,the real-time dispatch arranges real-time generation plans in accordance with real-time forecasting power.This paper has established a coherent POPF algorithm on function and timescale.The simulation results from a certain city of north China power grid as well as a modified IEEE 118-bus system have shown that,by satisfying the constraints for the whole time period,the coherent POPF algorithm can not only achieve the power balancing function,but also carry its reliability and effectiveness.