An Evaluation Method Of Wind Power Integration In Power System With Flexible Combined Heat And Power Plant

In recent years,in order to solve the problem of a large amount of wind abandonmentduring heating period in the "Three North" areas,China is improving the operation flexibility of combined heat and power(CHP)plants.However,the effectiveness of flexibility transformation on the curtailment of wind power has still not been well evaluated.In the existing evaluation methods,the method of establishing a simulation scheduling model requires more data,and the deviation of the model and the boundary condition data is likely to make the advantages of accurate modeling difficult to reflect.The principle based on the down-regulation balance is simple and the calculation complexity is low.Since the model of the CHP unit is more complicated than the previous output range model after transformation,the method based on down-regulation balance may be more applicable.However,the current method based on down-regulation balance aggregates the CHP units into a single unit during the evaluation,which is impossible to consider the differences of unit parameters and the thermal load in each CHP plant.Moreover,no consideration was given to cutting off the low-pressure cylinder by the CHP unit.Therefore,based on the principle of down-regulation balance,this paper proposes a wind power integration evaluation method for power systems with flexible CHP plants.The main work and conclusions are as follows:The core of the down-regulation balance evaluation method is to calculate the minimum electricity output of the CHP unit after flexibility transformation.Therefore,on the basis of the traditional CHP unit boundary model,an operation boundary model for each flexible CHP unit under the ability of flexible cutting off low-pressure cylinder with heat storge(HS)and electric boiler(EB)is established.Aiming at the problem of period coupling in the operation boundary model of the CHP unit after transformation,a wind power evaluation process considering the period coupling characteristics is proposed.According to the evaluation process,combined with the wind abandonment situation before transformation and the adjustment ability of the electricity output of the CHP unit after transformation,the power generation space allocation model during the non-abandonment period and the wind abandonment electricity allocation model during the abandonment period are established.Using the model for calculation,the adjustment amount of the electricity output of the CHP unit in the current period can be obtained.Finally,based on the adjustment amount of the electricity output of the CHP unit,by establishing the internal coordinated operation model of the flexible CHP plant,the remaining heat of the HS at the end of the current period iscalculated,and then the minimum electricity output of the CHP unit after flexibility transformation in the next period is determined.Through hour-by-hour calculation,the amount of wind which can’t be absorbed and the down-regulation depth of the CHP unit can be calculated.By calculating the wind abandonment and down-regulation subsidy of the transformed system,the purpose of evaluating the wind power integration of the system with flexible CHP plants and the deep down-regulation subsidy can be achieved.Based on the above evaluation method,the wind power integration of the system after the transformation of a CHP plant during the heating period of a province in Northeast China is evaluated.The calculation results are consistent with the theoretical analysis to verify the effectiveness of the proposed method.The evaluation results show that the effect of the EB on wind power integration is better,but the change of its capacity has a greater impact on the down-regulation subsidy than the HS.In areas where the installed capacity of wind power is large,the installation of the EB has good applicability if not cutting off the cylinder of the CHP unit,if the unit undergoes a variety of flexible transformations,cutting off the low-pressure cylinder of the CHP unit has a good applicability.The flexibility transformation of CHP plant can effectively improve the wind power integration potential of the systemAccording to the evaluation results,it can be known that the plan to cut off the low-pressure cylinders of the CHP units and install HS and EB will maximize the amount of wind curtailment.The capacity of the system’s down-regulation subsidy increases with the increase of the capacity of the HS and the EB,but it is mainly affected by the change of the capacity of the EB.In areas with large installed wind power capacity,the low-pressure cylinder removal scheme has better applicability.After all the CHP plants in the region have improved their operating flexibility,the system’s wind power can reach about 50% under the condition of 5% wind curtailment.The evaluation method and results in this paper can provide a reference for the selection and planning of flexible transformation plans for CHP plants in China.