Research On The Peak Regulation Of Power Grids With Large-scale Clean Energy Integrated

In recent years,China has made great efforts to develop clean energy,such as hydropower and wind power,to promote the transformation of energy structure and respond to the environment and climate change.China's clean energy and load demand generally show a reverse distribution pattern,so large-scale hydro energy produced in southwest and central China is transmitted to the eastern load centers via multiple high voltage direct current(HVDC)tie-lines to promote the utilization of clean energy sources.At the same time,the local offshore wind power and other new energy sources in the eastern region are continuously integrating into the power grids to promote the clean energy replacement work on the power-generation side.However,the current transmission mode of HVDC hydropower does not take into account the load characteristics of the eastern receiving-end power grids,which often results in the latter consuming a large amount of trans-regional hydro energy in the off-peak periods.Moreover,wind power has the characteristics of randomness,fluctuation and anti-peak regulation.Thus the power grids in the eastern region,which is' mainly installed with thermal power,are faced with great challenges in clean energy consumption due to their insufficient peak shaving capacity.Aiming at this problem,this paper focuses on the peak regulation of power grids with large-scale clean energy integrated,and conducts in-depth research from two aspects,i.e.,peak regulation scheduling of trans-regional hydropower and power plants directly operated by regional power grids,and coordinated scheduling of multi-type power sources.The former is to make full use of the advantages of grid interconnection to excavate the peak regulation capacity of the power grid,in order to reduce the peak and valley difference of the power grid as far as possible,and improve the consumption capacity of clean energy.And the latter aims at complementing the random fluctuations of wind power through the coordination of pumped storage,hydropower,natural gas and other conventional power sources,thereby enhancing the dynamic peak response capability of power system and addressing the problems of large-scale wind power interconnection and active power balance of the power grid.The specific research contents are as follows.(1)For the non-peak regulation or even anti-peak regulation transmission mode of the trans-regional hydropower,this paper develops an optimization model for detennining the short-term generation scheduling of the hydropower plants transmitting electric power across regions via high voltage direct current(HVDC)transmission lines.In this model,minimizing the peak-valley differences of receiving-end power grids is adopted as the objective,so as to alleviate the peak shaving pressure of the receiving-end power grids with the aid of large hydropower plants' capability to quickly respond to load changes.In addition to the hydraulic constraints,the operation constraints of individual units and HVDC power transmission limits are well considered.The nonlinearities in the model,including the nonlinear objective function,constraints related to water head,constraint on restricted operating zones,unit performance curves and the stair-like power transmission curve constraint,is linearized using linear approximation techniques.The original model is then converted into an MILP formulation.The formulated model is solved by Gurobi,an efficient commercial solver.Case studies demonstrate that the proposed model performed well at simultaneously flattening out load variations at the two receiving-end power grids,whilst meeting the specified quantity of the transmitted hydro energy and ensuring the stable operation of the sending-end hydropower plant.Moreover,frequent conversion of HVDC converter equipment can also be avoided,which makes the obtained generation schedule more executable.(2)Pumped-storage hydropower plants(PSHPs)directly operated by the regional power grids are usually required to shave the peak load and fill the valley load simultaneously for multiple power grids,which is an important way to relieve the growing peaking regulation pressure on power girds in eastern China.Hence,this paper develops a short-term peak shaving model for PSHPs in regional power grids,aiming to minimize the peak-valley difference of each provincial power grid.To increase the accuracy of the model,the performance of individual units and the head effect for units in generating mode and pumping mode are taken into account.The study mainly focuses on dealing with two nonlinearities,namely the constraints on the operation status of units and turbine performance curves.In particular,a novel meshing and triangulation technique is proposed to approximate the turbine performance curves.The short-term optimal scheduling problem which is highly nonlinear and non-convex is then converted into an MILP formulation.The compact MILP model is applied to the short-term operation of four PSHPs directly operated by the dispatch center of the ECPG.The optimization results demonstrate that the proposed model shows good performance in relieving the peak regulation pressure of each provincial power grid and could effectively facilitate the consumption of large-scale clean energy integrated into these girds.(3)The randomness and fluctuation of large-scale wind power have extremely adverse effects on the safe and economic operation of the power grid.Hence this paper proposes a novel strategy for joint operation of a wind farm and a PSHP,aiming to balance the random fluctuation of wind power and effectively promote wind power consumption through the peak shaving and valley filling of the PSHP.Firstly,a practical joint dispatching mode for a WF and a PSHP is proposed,which could take into account both the demand of stable operation of power grid and the demand of power company increasing its operational profit.Then,a stochastic MILP optimization formulation is developed to maximize the profit of the WF-PHSP union.In this model,a scenario analysis technique is used to deal with the forecast errors for wind power generation.The hydraulic constraints of the PSHP and the head effect on the performance of each unit are also considered to increase the accuracy of the model.Case studies demonstrate that the joint operation of the WF and PHSP can efficiently alleviate the negative effect of wind power fluctuations and significantly increase profit.Sensitivity analyses have been carried out to evaluate the effect of the penalty factor for energy imbalance and the electricity price mechanism in the power grid on the overall performance of the WF-PSHP union,which could provide an effective reference for both the owners of WFs and policy makers setting electricity and energy imbalance prices.(4)Regarding the issue of insufficient peak regulation capacity and difficulties in absorption of large-scale wind power,a coordinated scheduling method for wind-hydro-gas-thermal power system based on the dynamic peak regulation capacity margin is proposed.Firstly,considering the operation characteristics of various power sources,as well as the fluctuation and randomness of load and wind power,an index called dynamic peak regulation margin is proposed to optimize the allocation of limited peak shaving resources.On this basis,we formulate a wind-hydro-gas-thermal coordinated optimal dispatching model,in which the minimized total pollutant emission is taken as the objective.Based on hierarchic optimization strategy,this model is decomposed into four operation layers according to the type of power sources to reduce the complexity of the large-scale optimization problem.Then a solving framework,integrating mutative-scale optimization method,improved peak regulation method and improved particle swarm optimization algorithm coupled with a heuristic unit commitment method,is proposed to implement the optimal coordination between multi-type power sources.Simulation based on actual data of short-term optimal dispatching in a provincial power grid is performed to validate the proposed method.The results show that this method can ensure the full consumption of the wind power,and can reduce system reserve redundancy and pollutant emission at the same time.