Restoration Optimization Decision In Muti-infeed HVDC Receiving Power System

With the continuous expansion of the power system and the rapid development of the power industry,the modern power system operates closely to their limits and blackouts often occur especially in recent years.With large-scale HVDC projects being built,new power equipments participating in system operation and high proportion of renewable energy distributed throughout the power grid make the risk of blackouts high.The rapid and safe recovery of power systems has become a major concern all over the world.Starting from the basic national conditions of China's electric power construction,this dissertation focusing on the multi-infeed HVDC receiving system considers the uncertainty in the recovery process caused by high proportion of renewable energy and has a detailed study on the optimization of unit startup sequence with multiple HVDCs participation during early stage of network reconstruction,the path recovery optimization strategy to enhance the strength of the receiving system,the load restoration considering wind power and unit output optimization during last stage of network reconfiguration.The main contributions and innovations are described as following:1)With the consideration of interaction between AC and HVDC during the initial stage of network reconstruction,the multi-infeed integrated short circuit ratio(MISCR)is applied to describe the voltage stability in restoration where the HVDC system control mode and transmission capacity is different from the normal status.The recovery path optimization strategy to increase the busbar shortcircuit capacity and the HVDC bus voltage support capability is proposed.The mixed-integer nonlinear programming(MINLP)with the goal of maximizing power generation and the constraints of DC system safe operation during the network reconstructionis is established,which can be resolved by efficient solution method based on Benders decomposition.The IEEE-39 node system simulation verifies the effectiveness of the proposed strategy and solution method.2)A source-load coordination optimization model which takes into account the uncertainty of wind power and load is established.The load and output of wind farms are expressed as fuzzy parameters.Frequencyconstraints and spinning reserve constraints are introduced to deal with the influence of power prediction error on the recovery process.From an economic point of view,minimizing the total interuption cost is more important than maximizing the number of lost load during load restoration because of different interuption cost functions of different customers.Furthermore,a linear method is proposed,by which can simplify the non-linear programming model to bi-level linear programming model and dramatically improve the computation efficiency.The effectiveness and validity of the proposed model and method are verified by IEEE-30 bus system and IEEE-118 bus system with wind forms.3)For the unit output optimizationproblem in the multi-infeed HVDC receiving system,HVDC transmission capacity adjustment model is proposed,which considers the operating characteristics such as the coordination of sending and receiving system,equipment adjustment frequency in converter station and so on.The unit output optimization model in the multi-infeed HVDC receiving system takes into account power balance,the safety of voltage and frequency,unit ramp rate limit.Furthermore,it is converted to mixed-integer linear model by LPAC.The unit output and HVDC transmission powerare obtained after every restoration time step.The validity of the model is verified by IEEE-30 nodes and IEEE-118 nodes.