Research On Parameter Optimization And Coordination Control Method For Mitigating The Transient Overvoltage On The HVDC Sending System

In recent years,with the increasing demand for electricity in China and the large-scale access of renewable energy,new energy generation represented by wind power and HVDC transmission technology have been rapidly developed.However,when large-scale wind power is transmitted via HVDC,if the fault of the AC system on the inverter side leads to DC commutation failure,it will lead to transient overvoltage of HVDC sending-side system and cause wind turbine off-grid problem and its chain reactions.In order to mitigate the transient overvoltage of HVDC sending-side system,this article analyzes from the aspects of how to optimize power grid component parameters and how to coordinate and control.The main research contents are as follows:In terms of parameter optimization method,a coordinated optimization method for HVDC and wind power control parameters is proposed.Firstly,it analyzes the generation mechanism of the transient overvoltage of HVDC sending-side system from the perspective of reactive conversion of rectifier station and wind power plant,and then studies on the influence mechanism of the control parameters of HVDC rectifier side and wind power rotor-side converter on the transient overvoltage in terms of the reactive characteristics of system,thus providing theoretical basis for coordinated optimization of control parameters of transient overvoltage.Then,an optimization model targeting to maximize the peak value of transient overvoltage of HVDC sending-side system is established.Through combined invocation,based on the accurate simulation of electromagnetic transient process of AC/DC system by using electromagnetic transient model,the improved particle swarm optimization algorithm is further used to coordinatively optimize the HVDC and wind power control parameters and effectively mitigate the transient overvoltage of HVDC sending-side system.Finally,the validity and accuracy of the proposed method is verified by conducting the simulation analysis on the modified four-machine eleven-bus system and IEEE-39 bus system.In terms of coordinated control method,a two-stage optimization control strategy to mitigate the transient overvoltage by using the trajectory sensitivity is proposed.At first,building an objective function with cost of control and voltage prediction bias as transient overvoltage control model.To remedy the deficiency of poor efficiency of the nonlinear control model of transient overvoltage,we transformed the nonlinear model into a quadratic programming model with the controlled quantity increment as an independent control variable depending on the trajectory sensitivity of transient overvoltage and voltage in the recovery phase towards controlled quantity,thus enhancing transient overvoltage control efficiency.Then,addressing circumstances of transient overvoltage instability,we solved the variation of the controlled quantity of transient overvoltage preventive control prior to the failure,and took transient overvoltage preventive control to avoid serious transient overvoltage hazards.In the event that the controlled voltage in the recovery phase was not safe,we should work out variation of the quantity of voltage control during the recovery phase,and adjust the controlled quantity by means of voltage control in the recovery phase till the voltage in the recovery phase fell back to a safe level.The proposed method of control can both clamp transient overvoltage and ensure the security of transient overvoltage recovery,which provides a reference for the dispatching personnel to control transient overvoltage stability.Finally,the simulation results of the modified IEEE-39 bus system verifies validity of proposed control measure.