Research On Optimal Power Flow For Hybrid Ac/dc System With VSC-HVDC Considering Security Constraints

VSC-HVDC technology is a new generation of HVDC technology based on VSC and PWM.It not only has the advantages of low manufacturing cost,low loss and low operation cost,but also it is not affected by the short-circuit capacity of the terminal system and commutation failure.And now,it is being vigorously studied and promoted by all countries in the world.With the application of VSC-HVDC,the traditional AC network contains DC part,which brings new challenges to the operation and analysis of power system.Especially in today's economy,more and more attention has been paid to the economic benefits,how to make the hybrid AC/DC system with VSC-HVDC run in the most economical way under the safe conditions,which is a problem that needs our electric workers and researchers to solve.Security constrained optimal power flow(SCOPF),which not only needs to consider the minimum operating cost of the system,but also needs to consider that the system can meet the safety constraints after failures.In this paper bases on the classical optimal power flow model,adds the safety constraints to construct the SCOPF model,and VSC-HVDC is introduced to solve the hybrid AC / DC system.When solving the model,this paper improves the fault sequencing index,considers the probability of line outage caused by weather factors,and uses the prediction correction interior point method to solve the problem.Compared with the traditional method,the method in this paper can effectively improve the calculation efficiency.The main work of this paper is as follows:First of all,this paper analyzes the model of VSC-HVDC,deduces the steady-state power flow model of VSC-HVDC,and connects it into the AC system,realizes the power flow calculation of hybrid AC/ DC power grid,and verifies it on the two areas four machines system and IEEE 39 buses test system.Secondly,this paper establishes the SCOPF model of AC power grid.In the model,contingency selection and ranking is used to reduce the calculation scale.The fault severity ranking index of line outage caused by weather factors has been used in contingency selection and ranking which makes it closer to the actual production.The primal dual interior point method is used to solve the model which gives full play to the advantages of interior point method,such as fast speed,good robustness and insensitivity to initial value.Through IEEE 9buses test system,the whole calculation process is explained in detail,and the validity of the method is verified.Finally,the VSC-HVDC model is introduced into the AC system,and the improved prediction-correction interior point method is used to solve the problem.This method isimplemented in IEEE 14 buses system,in addition,compared with the conditions that whether or not to adopt the prediction correction interior point method and whether or not to adopt the contingency ranking on considering of weather factors leading to line outage in the New England 39 buses system.It can be found that the prediction correction interior point method can reduce the number of iterations and improve the calculation efficiency;after considering the overload severity index of line outage probability under different weather conditions,it can reduce the number of calculation of optimal power flow and improve the convergence speed.The addition of VSC-HVDC will not significantly increase the calculation amount,but also reduce the operating cost of the system.