Maximum Entropy Based Probabilistic Load Flow For Power System With Wind Power And Electric Vehicles

Power system planning,design and operation analysis always involve the power flow calculation.The rationality of the theoretical method for power flow calculation has a direct impact on the safety and reliability of power grid.In recent years,with the increasing concern on the concept of energy saving and sustainable development,the intermittent renewable energy generations and probabilistic loads such as electric vehicles are developing rapidly.As a result,the uncertainty in the grid has greatly increased,which brings new challenges to the operation and planning of the traditional power system.Different charging modes of electric vehicles and wind turbine integration will lead the grid operating in various conditions.Therefore,much more attentions have been paid to the concept of probabilistic load flow(PLF)in order to deal with current problems in current power systems.As a most widely used PLF approach,combined cumulant and Gram-Charlier approach greatly enhance the efficiency of PLF calculation.However,active and reactive powers will become dependent in a system integrated with wind power and electric vehicles(EV).This dependences have not been considered properly in traditional cumulant calculation framework.Besides,Gram-Charlier series sometimes obtain negative probability density functions,and has great truncation errors.Also,its accuracy can be easily influenced by calculation situations.In order to solve the problems in traditional PLF calculations,a PLF approach based on cumulant framework and the principle of maximum entropy is proposed in this paper,aiming at calculating the PLF for power systems integrated with wind turbine and EV in different hours and parameters conditions.Firstly,the short term probability models of basic load,wind power and EV charging load are set up.Then,a cumulant computation framework considering the linear dependence between active and reactive power of wind power or EV charging load is developed.Finally,the probability density functions and confidential intervals of bus voltages and branch flows are obtained by the principle of maximum entropy.IEEE 118 bus test system and Polish power system are used to validate the proposed approach.It is indicated that the approach can solve the PLF of power system integrated with wind turbine and EV charging load accurately and efficiently.Besides,its accuracy is not influenced by the changes of parameters and conditions.It can keep high accuracy without sacrificing calculation efficiency,the output results of which can offer some probability information about power system operations.In conclusion,the proposed approach is useful and helpful.